publications

conference & journal articles

2023

1. CPC

   Search for the rare decays \(W^+ \to D^+_s\gamma\) and \(Z \to D^0\gamma\) at LHCb

   LHCb Collaboration: R. Aaij, and  others

   Chinese Phys. C 47 (2023) 093002 – Published on 1 Sep 2023

   Abs arXiv DOICDS

   TBA

2. CPC

   Search for the doubly heavy baryon \(\Xi_{bc}^{+}\) decaying to \(J/\psi \Xi_{c}^{+}\)

   LHCb Collaboration: R. Aaij, and  others

   Chinese Phys. C 47 (2023) 093001 – Published on 1 Sep 2023

   Abs arXiv DOICDS

   A first search for the \(\Xi_{bc}^{+} \to J/\psi \Xi_{c}^{+}\) decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\) recorded at centre-of-mass energies of \(7\), \(8\), and \(13~\rm{TeV}\). Two peaking structures are seen with a local (global) significance of \(4.3 \, (2.8)\) and \(4.1 \, (2.4)\) standard deviations at masses of \(6571~\rm{MeV}/c^{2}\) and \(6694~\rm{MeV}/c^{2}\), respectively. Upper limits are set on the \(\Xi_{bc}^{+}\) baryon production cross-section times the branching fraction relative to that of the \(B_{c}^{+} \to J/\psi D_{s}^{+}\) decay at centre-of-mass energies of \(8\) and \(13~\rm{TeV}\), in the \(\Xi_{bc}^{+}\) and in the \(B_{c}^{+}\) rapidity and transverse-momentum ranges from \(2.0\) to \(4.5\) and \(0\) to \(20~\rm{GeV}/c\), respectively. Upper limits are presented as a function of the \(\Xi_{bc}^{+}\) mass and lifetime.

3. PRL

   Observation of a resonant structure near the \(D_s^+ D_s^-\) threshold in the \(B^+\to D_s^+ D_s^- K^+\) decay

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. Lett. 131 (2023) 071901 – Published on 14 Aug 2023

   Abs arXiv DOICDS

   An amplitude analysis of the \(B^+\to D_s^+ D_s^- K^+\) decay is carried out to study for the first time its intermediate resonant contributions, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\). A near-threshold peaking structure, referred to as \(X(3960)\), is observed in the \(D_s^+ D_s^-\) invariant-mass spectrum with significance greater than 12 standard deviations. The mass, width and the quantum numbers of the structure are measured to be \(3956 \pm 5 \pm 10~\rm{MeV}\), \(43 \pm 13 \pm 8~\rm{MeV}\) and \(J^{PC}=0^{++}\), respectively, where the first uncertainties are statistical and the second systematic. The properties of the new structure are consistent with recent theoretical predictions for a state composed of \(c\bar{c}s\bar{s}\) quarks. Evidence for an additional structure is found around \(4140~\rm{MeV}\) in the \(D_s^+ D_s^-\) invariant mass, which might be caused either by a new resonance with the \(0^{++}\) assignment or by a \(J/\psi \phi \leftrightarrow D^+_s D^-_s\) coupled-channel effect.

4. PRD

   Search for \(CP\) violation using \(\hat{T}\)-odd correlations in \(B^{0} \to p \bar p K^{+} \pi^{-}\) decays

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. D 108 (2023) 032007 – Published on 8 Aug 2023

   Abs arXiv DOICDS

   A search for \(CP\) and \(P\) violation in charmless four-body \(B^{0} \to p \bar p K^{+} \pi^{-}\) decays is performed using triple-product asymmetry observables. It is based on proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\), corresponding to a total integrated luminosity of \(8.4~\rm{fb}^{-1}\). The \(CP\)- and \(P\)-violating asymmetries are measured both in the integrated phase space and in specific regions. No evidence is seen for \(CP\) violation. \(P\)-parity violation is observed at a significance of \(5.8\) standard deviations

5. PRD

   Search for \(K^0_{\rm{S(L)}} \to \mu^+ \mu^- \mu^+ \mu^-\) decays at LHCb

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. D 108 (2023) L031102 – Published on 3 Aug 2023

   Abs arXiv DOICDS

   TBA

6. PRD

   Amplitude analysis of the \(\Lambda^+_c\to pK^-\pi^+\) decay and \(\Lambda^+_c\) baryon polarization measurement in semileptonic beauty hadron decays

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. D 108 (2023) 012023 – Published on 28 Jul 2023

   Abs arXiv DOICDS

   An amplitude analysis of \(\Lambda^+_c \to p K^- \pi^+\) decays together with a measurement of the \(\Lambda^+_c\) polarization vector in semileptonic beauty hadron decays is presented. A sample of \(400000\) candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of \(13~\rm{TeV}\). An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the \(\Lambda(2000)\) state are also determined. A significant \(\Lambda^+_c\) polarization is found. A large sensitivity of the \(\Lambda^+_c \to p K^- \pi^+\) decay to the polarization is seen, making the amplitude model suitable for \(\Lambda^+_c\) polarization measurements in other systems.

7. PRD

   Search for the baryon- and lepton-number violating decays \(B^0\to p\mu^-\) and \(B^0_s\to p\mu^-\)

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. D 108 (2023) 012021 – Published on 28 Jul 2023

   Abs arXiv DOICDS

   A search for the baryon- and lepton-number violating decays \(B^0\to p\mu^-\) and \(B^0_s\to p\mu^-\) is performed at the LHCb experiment using data collected in proton-proton collisions at \(\sqrt{s}=7\), \(8\) and \(13~\rm{TeV}\), corresponding to integrated luminosities of \(1\), \(2\) and \(6~\rm{fb}^{-1}\), respectively. No significant signal for \(B^0\to p\mu^-\) and \(B^0_s\to p\mu^-\) decays is found and the upper limits on the branching fractions are determined to be \(\mathcal{B}(B^0\to p\mu^-) < 2.6 (3.1) \times 10^{-9}\) and \(\mathcal{B}(B^0_s\to p\mu^-) < 12.1 (14.0) \times 10^{-9}\), respectively, at \(90\% \, (95\%)\) confidence level. These are the first limits on these decays to date.

8. PRD

   Test of lepton flavour universality using \(B^0 \to D^{*-}\tau^+\nu_{\tau}\) decays with hadronic \(\tau\) channels

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. D 108 (2023) 012018 – Published on 27 Jul 2023

   Abs arXiv DOICDS

   TBA

9. PRD

   Amplitude analysis of \(B^0 \to \bar{D}^0 D_s^+ \pi^-\) and \(B^+ \to D^- D_s^+ \pi^+\) decays

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. D 108 (2023) 012017 – Published on 27 Jul 2023

   Abs arXiv DOICDS

   TBA

10. PRD

    Observation of sizeable \(\omega\) contribution to \(\chi_{c1}(3872)\to\pi^+\pi^-J/\psi\) decays

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. D 108 (2023) L011103 – Published on 27 Jul 2023

    Abs arXiv DOICDS

    Resonant structures in the dipion mass spectrum from \(\chi_{c1}(3872) \to \pi^{+} \pi^{-} J/\psi\) decays, produced via \(B^{+} \to K^{+} \chi_{c1}(3872)\) decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). A sizeable contribution from the isospin conserving \(\chi_{c1}(3872) \to \omega J/\psi\) decay is established for the first time, \((21.4 \pm 2.3 \pm 2.0)\%\), with a significance of more than \(7.1\sigma\). The amplitude of isospin violating decay, \(\chi_{c1}(3872) \to \rho^{0} J/\psi\), relative to isospin conserving decay, \(\chi_{c1}(3872) \to \omega J/\psi\), is properly determined, and it is a factor of six larger than expected for a pure charmonium state.

11. EPJC

    Search for \(D^{*}(2007)^0\to\mu^+\mu^-\) in \(B^-\to\pi^-\mu^+\mu^-\) decays

    LHCb Collaboration: R. Aaij, and  others

    Eur. Phys. J. C 83 (2023) 666 – Published on 26 Jul 2023

    Abs arXiv DOICDS

    The very rare \(D^{*}(2007)^0\to\mu^+\mu^-\) decay is searched for by analysing \(B^-\to\pi^-\mu^+\mu^-\) decays. The analysis uses a sample of beauty mesons produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). The signal signature corresponds to simultaneous peaks in the \(\mu^+\mu^-\) and \(\pi^-\mu^+\mu^-\) invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at \(\mathcal{B} \left ( D^{*}(2007)^0\to\mu^+\mu^- \right ) < 2.6 \times 10^{-8}\) at \(90\%\) confidence level. This is the first limit on the branching fraction of \(D^{*}(2007)^0\to\mu^+\mu^-\) decays and the most stringent limit on \(D^{*}(2007)^0\) decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays.

12. JHEP

    Amplitude analysis of the \(D_s^+ \to \pi^- \pi^+ \pi^+\) decay

    LHCb Collaboration: R. Aaij, and  others

    JHEP 07 (2023) 204 – Published on 26 Jul 2023

    Abs arXiv DOICDS

    A Dalitz plot analysis of the \(D_s^+ \to \pi^- \pi^+ \pi^+\) decay is presented. The analysis is based on proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy \(\sqrt{s} = 8~\rm{TeV}\) and corresponding to an integrated luminosity of \(1.5~\rm{fb}^{-1}\). The resonant structure of the decay is obtained using a quasi-model-independent partial-wave analysis, in which the \(\pi^+ \pi^-\) S-wave amplitude is parameterised as a generic complex function determined by a fit to the data. The S-wave component is found to be dominant, followed by the contribution from spin-2 resonances and a small contribution from spin-1 resonances. The latter includes the first observation of the \(D_s^+ \to \omega(782) \pi^+\) channel in the \(D_s^+ \to \pi^- \pi^+ \pi^+\) decay. The resonant structures of the \(D_s^+ \to \pi^- \pi^+ \pi^+\) and \(D^+ \to \pi^- \pi^+ \pi^+\) decays are compared, providing information about the mechanisms for the hadron formation in these decays.

13. EPJC

    \(J/\psi\) and \(D^0\) production in \(\sqrt{s_{\rm{NN}}} = 68.5~\rm{GeV}\) \(\rm{PbNe}\) collisions

    LHCb Collaboration: R. Aaij, and  others

    Eur. Phys. J. C 83 (2023) 658 – Published on 25 Jul 2023

    Abs arXiv DOICDS

    The first measurement of \(J/\psi\) and \(D^0\) production in \(\rm{PbNe}\) collisions by the LHCb experiment in its fixed-target configuration is reported. The production of \(J/\psi\) and \(D^0\) mesons is studied with a beam of lead ions with an energy of \(2.5~\rm{TeV}\) per nucleon colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy of \(\sqrt{s_{\rm{NN}}} = 68.5~\rm{GeV}\). The \(J/\psi D^0\) production cross-section ratio is studied as a function of rapidity, transverse momentum and collision centrality. These data are compared with measurements from \(p\rm{Ne}\) collisions at the same energy. No anomalous \(J/\psi\) suppression that could indicate the formation of a deconfined medium is observed.

14. PRL

    Nuclear modification factor of neutral pions in the forward and backward regions in \(p\rm{Pb}\) collisions

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. Lett. 131 (2023) 042302 – Published on 24 Jul 2023

    Abs arXiv DOICDS

    The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of \(8.16~\rm{TeV}\) with the LHCb detector. The \(\pi^0\) production cross section is measured differentially in transverse momentum (\(p_T\)) for \(1.5 < p_T < 10.0~\rm{GeV}\) and in center-of-mass pseudorapidity (\(\eta_{CM}\)) regions \(2.5 < \eta_{CM} < 3.5\) (forward) and \(-4.0 < \eta_{CM} < -3.0\) (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of π0 production, while the backward measurement shows the first evidence of \(\pi^0\) enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.

15. PRD

    Search for direct \(CP\) violation in charged charmless \(B \to PV\) decays

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. D 108 (2023) 012013 – Published on 20 Jul 2023

    Abs arXiv DOICDS

    Measurements of \(CP\) asymmetry in charmless \(B \to PV\) decays are presented, where \(P\) and \(V\) denote a pseudoscalar and a vector meson, respectively. Five different \(B \to PV\) decays from four final states, \(B^{\pm} \to \pi^{\pm} \pi^{+} \pi^{-}\), \(B^{\pm} \to K^{\pm} \pi^{+} \pi^{-}\), \(B^{\pm} \to K^{\pm} K^{+} K^{-}\) and \(B^{\pm} \to \pi^{\pm} K^{+} K^{-}\) are analysed. The measurements are based on a method that does not require full amplitude analyses, and are performed using proton-proton collision data at a centre-of-mass energy of \(13~\rm{TeV}\) collected by LHCb between 2015 and 2018, corresponding to an integrated luminosity of \(5.9~\rm{fb}^{-1}\). In the \(B^{\pm} \to \rho(770)^{0} K^{\pm}\) decay, a \(CP\) asymmetry of \(A_{CP} = 0.150 \pm 0.019 \pm 0.011\) is measured, where the first uncertainty is statistical and the second is systematic. This is the first observation of \(CP\) violation in this decay. For the other four decay channels, \(B^{\pm} \to \rho(770)^{0} \pi^{\pm}\), \(B^± \to \overset{(-)}{K^{*}}(892)^{0} \pi^{\pm}\), \(B^± \to \overset{(-)}{K^{*}}(892)^{0} K^{\pm}\) and \(B^{\pm} \to \phi(1020) K^{\pm}\) decays, \(CP\) asymmetries compatible with zero are measured.

16. JHEP

    Measurement of the CKM angle \(\gamma\) with \(B^\pm \to D \left [ K^\mp \pi^\pm \pi^\pm \pi^\mp \right ] h^\pm\) decays using a binned phase-space approach

    LHCb Collaboration: R. Aaij, and  others

    JHEP 07 (2023) 138 – Published on 17 Jul 2023

    Abs arXiv DOICDS

    The CKM angle \(\gamma\) is determined from \(CP\)-violating observables measured in \(B^\pm \to D \left [ K^\mp \pi^\pm \pi^\pm \pi^\mp \right ] h^\pm\), \((h = K, \pi)\) decays, where the measurements are performed in bins of the decay phase-space of the \(D\) meson. Using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\), corresponding to a total integrated luminosity of \(9~\rm{fb}^{-1}\), \(\gamma\) is determined to be \(\gamma = \left ( \, 54.8^{\, + \, 6.0 \, + \, 0.6 \, + \, 6.7}_{\, - \, 5.8 \, - \, 0.6 \, - \, 4.3} \, \right )^{\rm{o}}\), where the first uncertainty is statistical, the second systematic and the third from the external inputs on the coherence factors and strong phases of the \(D\)-meson decays.

17. EPJC

    Measurement of \(\tau_{L}\) using the \(B_{s}^{0} \to J/\psi \eta\) decay mode

    LHCb Collaboration: R. Aaij, and  others

    Eur. Phys. J. C 83 (2023) 629 – Published on 17 Jul 2023

    Abs arXiv DOICDS

    Using a proton-proton collision data sample collected by the LHCb detector and corresponding to an integrated luminosity of \(5.7~\rm{fb}^{-1}\), the lifetime of the \(B_{s}^{0}\) mass eigenstate, \(\tau_{L}\), is measured using \(B_{s}^{0} \to J/\psi \eta\) decay mode to be \(\tau_{L} = 1.445 \pm 0.016~\rm{(stat)} \pm 0.008~\rm{(syst)}~\rm{ps}\). A combination of this result with a previous LHCb analysis using an independent dataset corresponding to \(3~\rm{fb}^{-1}\) of integrated luminosity gives \(\tau_{L} = 1.452 \pm 0.014 \pm 0.007 \pm 0.002~\rm{ps}\), where the first uncertainty is statistical, the second due to the uncorrelated part of the systematic uncertainty and the third due to the correlated part of the systematic uncertainty.

18. EPJC

    Charmonium production in \(p\rm{Ne}\) collisions at \(\sqrt{s_{\rm{NN}}} = 68.5~\rm{GeV}\)

    LHCb Collaboration: R. Aaij, and  others

    Eur. Phys. J. C 83 (2023) 625 – Published on 17 Jul 2023

    Abs arXiv DOICDS

    The measurement of charmonium states produced in proton-neon (\(p\rm{Ne}\)) collisions by the LHCb experiment in its fixed-target configuration is presented. The production of \(J/\psi\) and \(\psi(2S)\) mesons is studied with a beam of \(2.5~\rm{TeV}\) protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy \(\sqrt{s_{\rm{NN}}} = 68.5~\rm{GeV}\). The data sample corresponds to an integrated luminosity of \(21.7 \pm 1.4~\rm{nb}^{-1}\). The \(J/\psi\) and \(\psi(2S)\) hadrons are reconstructed in \(\mu^+ \mu^-\) final states. The \(J/\psi\) production cross-section per target nucleon in the centre-of-mass rapidity range \(y^* \in [-2.29, 0]\) is found to be \((506 \pm 8 \pm 25)~\rm{nb}/{nucleon}\). The \(\psi(2S)\) to \(J/\psi\) relative production rate is found to be \((1.67 \pm 0.27 \pm 0.10)\%\) in good agreement with other measurements involving beam and target nuclei of similar sizes.

19. PRL

    Observation of a \(J/\psi\Lambda\) resonance consistent with a strange pentaquark candidate in \(B^-\to J/\psi\Lambda\bar{p}\) decays

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. Lett. 131 (2023) 031901 – Published on 17 Jul 2023

    Abs arXiv DOICDS

    An amplitude analysis of \(B^-\to J/\psi\Lambda\bar{p}\) decays is performed using about \(4400\) signal candidates selected on a data sample of \(pp\) collisions recorded at center-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\) with the LHCb detector, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). A narrow resonance in the \(J/\psi\Lambda\) system, consistent with a pentaquark candidate with strangeness, is observed with high significance. The mass and the width of this new state are measured to be \(4338.2 \pm 0.7 \pm 0.4~\rm{MeV}\) and \(7.0 \pm 1.2 \pm 1.3~\rm{MeV}\), where the first uncertainty is statistical and the second systematic. The spin is determined to be \(1/2\) and negative parity is preferred. Due to the small Q-value of the reaction, the most precise single measurement of the \(B^-\) mass to date, \(5279.44 \pm 0.05 \pm 0.07~\rm{MeV}\), is obtained.

20. PRD

    Search for the rare hadronic decay \(B_s^0\to p \bar{p}\)

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. D 108 (2023) 012007 – Published on 14 Jul 2023

    Abs arXiv DOICDS

    A search for the rare hadronic decay \(B_s^0\to p \bar{p}\) is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of \(13~\rm{TeV}\), corresponding to an integrated luminosity of \(6~\rm{fb}^{-1}\). No evidence of the decay is found and an upper limit on its branching fraction is set at \(\mathcal{B} (B_s^0\to p \bar{p}) < 4.4 (5.1) \times 10^{-9}\) at \(90\% (95\%)\) confidence level; this is currently the world's best upper limit. The decay mode \(B^0\to p \bar{p}\) is measured with very large significance, confirming the first observation by the LHCb experiment in 2017. The branching fraction is determined to be \(\mathcal{B} (B^0\to p \bar{p}) = ( 1.27 \pm 0.15 \pm 0.05 \pm 0.04 ) \times 10^{-8}\), where the first uncertainty is statistical, the second is systematic and the third is due to the external branching fraction of the normalization channel \(B^0 \to K^+ \pi^-\). The combination of the two LHCb measurements of the \(B^0\to p \bar{p}\) branching fraction yields \(\mathcal{B} (B^0\to p \bar{p}) = ( 1.27 \pm 0.13 \pm 0.05 \pm 0.03 ) \times 10^{-8}\).

21. PRD

    Direct \(CP\) violation in charmless three-body decays of \(B^{\pm}\) mesons

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. D 108 (2023) 012008 – Published on 13 Jul 2023

    Abs arXiv DOICDS

    Measurements of \(CP\) asymmetries in charmless three-body decays of \(B^{\pm}\) mesons are reported using proton-proton collision data collected by the LHCb detector, corresponding to an integrated luminosity of \(5.9~\rm{fb}^{-1}\). The previously observed \(CP\) asymmetry in \(B^{\pm} \to \pi^{\pm} K^{+} K^{-}\) decays is confirmed, and \(CP\) asymmetries are observed with a significance of more than five standard deviations in the \(B^{\pm} \to \pi^{\pm} \pi^{+} \pi^{-}\) and \(B^{\pm} \to K^{\pm} K^{+} K^{-}\) decays, while the \(CP\) asymmetry of \(B^{\pm} \to K^{\pm} \pi^{+} \pi^{-}\) decays is confirmed to be compatible with zero. The distributions of these asymmetries are also studied as a function of the three-body phase space and suggest contributions from rescattering and resonance interference processes. An indication of the presence of the decays \(B^{\pm} \to \pi^{\pm} \chi_{c0}(1P)\) in both \(B^{\pm} \to \pi^{\pm} \pi^{+} \pi^{-}\) and \(B^{\pm} \to \pi^{\pm} K^{+} K^{-}\) decays is observed, as is \(CP\) violation involving these amplitudes.

22. JHEP

    Observation of the \(B^0_s \to D^{*+}D^{*-}\) decay

    LHCb Collaboration: R. Aaij, and  others

    JHEP 07 (2023) 119 – Published on 13 Jul 2023

    Abs arXiv DOICDS

    The first observation of the \(B^0_s \to D^{*+}D^{*-}\) decay and the measurement of its branching ratio relative to the \(B^0 \to D^{*+}D^{*-}\) decay are presented. The data sample used corresponds to an integrated luminosity of \(9~\rm{fb}^{-1}\) of proton-proton collisions recorded by the LHCb experiment at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\) between 2011 and 2018. The decay is observed with a very high significance and the ratio of branching fractions is determined to be \(\frac{\mathcal{B}(B^0_s \to D^{*+}D^{*-})}{\mathcal{B}(B^0 \to D^{*+}D^{*-})} = 0.269 \pm 0.032 \pm 0.011 \pm 0.008\), where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio \(f_s/f_d\). The \(B^0_s \to D^{*+}D^{*-}\) branching fraction is calculated to be \(\mathcal{B}(B^0_s \to D^{*+}D^{*-}) = (2.15 \pm 0.26 \pm 0.09 \pm 0.06 \pm 0.16) \times 10^{-4}\), where the fourth uncertainty is due to the B^0 \to D^{*+}D^{*-} branching fraction.

23. JHEP

    First observation and branching fraction measurement of the \({\Lambda}_b^0 \to {D}_s^{-} p\) decay

    LHCb Collaboration: R. Aaij, and  others

    JHEP 07 (2023) 075 – Published on 10 Jul 2023

    Abs arXiv DOICDS

    TBA

24. JHEP

    Measurement of \(\Upsilon\) production in \(pp\) collisions at \(\sqrt{s} = 5~\rm{TeV}\)

    LHCb Collaboration: R. Aaij, and  others

    JHEP 07 (2023) 069 – Published on 7 Jul 2023

    Abs arXiv DOICDS

    TBA

25. JHEP

    Search for \(CP\) violation in \(D_{(s)}^{+}\rightarrow K^{-}K^{+}K^{+}\) decays

    LHCb Collaboration: R. Aaij, and  others

    JHEP 07 (2023) 067 – Published on 7 Jul 2023

    Abs arXiv DOICDS

    TBA

26. JHEP

    Measurement of the ratio of branching fractions \(\mathcal{B}(B_c^+ \to B_s^0 \pi^+)/\mathcal{B}(B_c^+ \to J/\psi \pi^+)\)

    LHCb Collaboration: R. Aaij, and  others

    JHEP 07 (2023) 066 – Published on 7 Jul 2023

    Abs arXiv DOICDS

    The ratio of branching fractions of \(B_c^+ \to B_s^0 \pi^+\) and \(B_c^+ \to J/\psi \pi^+\) decays is measured with proton-proton collision data of a centre-of-mass energy of \(13~\rm{TeV}\). The data were collected with the LHCb experiment during 2016-2018, corresponding to an integrated luminosity of \(5.4~\rm{fb}^{-1}\). The \(B^0_s\) mesons are reconstructed via the decays \(B^0_s \to J/\psi \phi\) and \(B^0_s \to D^-_s \pi^+\). The ratio of branching fractions is measured to be \(\mathcal{B}(B_c^+ \to B_s^0 \pi^+)/\mathcal{B}(B_c^+ \to J/\psi \pi^+) = 91 \pm 10 \pm 8 \pm 3\) where the first uncertainty is statistical, the second is systematic and the third is due to the knowledge of the branching fractions of the intermediate state decays.

27. EPJC

    A study of \(CP\) violation in the decays \(B^\pm\to[K^+K^-\pi^+\pi^-]_D h^{\pm}\) \((h = K, \pi)\) and \(B^\pm\to[\pi^+\pi^-\pi^+\pi^-]_D h^{\pm}\)

    LHCb Collaboration: R. Aaij, and  others

    Eur. Phys. J. C 83 (2023) 547 – Published on 29 Jun 2023

    Abs arXiv DOICDS

    TBA

28. EPJC

    Measurement of antiproton production from antihyperon decays in \(p\rm{He}\) collisions at \(\sqrt{s_\rm{NN}}=110~\rm{GeV}\)

    LHCb Collaboration: R. Aaij, and  others

    Eur. Phys. J. C 83 (2023) 543 – Published on 27 Jun 2023

    Abs arXiv DOICDSData

    The interpretation of cosmic antiproton flux measurements from space-borne experiments is currently limited by the knowledge of the antiproton production cross-section in collisions between primary cosmic rays and the interstellar medium. Using collisions of protons with an energy of \(6.5~\rm{TeV}\) incident on helium nuclei at rest in the proximity of the interaction region of the LHCb experiment, the ratio of antiprotons originating from antihyperon decays to prompt production is measured for antiproton momenta between \(12\) and \(110~\rm{GeV}/c\). The dominant antihyperon contribution, namely \(\bar{\Lambda} \to p^- \pi^+\) decays from promptly produced \(\bar{\Lambda}\) particles, is also exclusively measured. The results complement the measurement of prompt antiproton production obtained from the same data sample. At the energy scale of this measurement, the antihyperon contributions to antiproton production are observed to be significantly larger than predictions of commonly used hadronic production models.

29. JHEP

    Search for the lepton-flavour violating decays \(B^0 \to K^{*0} \tau^\pm \mu^\mp\)

    LHCb Collaboration: R. Aaij, and  others

    JHEP 06 (2023) 143 – Published on 23 Jun 2023

    Abs arXiv DOICDS

    A first search for the lepton-flavour violating decays \(B^0 \to K^{*0} \tau^\pm \mu^\mp\) is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\) between 2011 and 2018, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). No significant signal is observed, and upper limits on the branching fractions are determined to be \(\mathcal{B} (B^0 \to K^{*0} \tau^+ \mu^-) < 1.0 \, (1.2) \times 10^{-5}\) and \(\mathcal{B} (B^0 \to K^{*0} \tau^- \mu^+) < 8.2 \, (9.8) \times 10^{-6}\) at the \(90\% \, (95\%)\) confidence level.

30. JHEP

    Measurement of the \(\Lambda_c^+\) to \(D^0\) production cross-section ratio in peripheral \(\rm{PbPb}\) collisions

    LHCb Collaboration: R. Aaij, and  others

    JHEP 06 (2023) 132 – Published on 22 Jun 2023

    Abs arXiv DOICDS

    We report on a measurement of the \(\Lambda_c^+/D^0\) production ratio in \(\rm{PbPb}\) collisions at \(\sqrt{s_\rm{NN}}=5.02~\rm{TeV}\) with the LHCb detector in the forward rapidity region \(2 < y < 4.5\). The \(\Lambda_c^+\) (\(D^0\)) hadrons are reconstructed via the decay channel \(\Lambda_c^+ \to p K^+ \pi^-\) (\(D^0 \to K^- \pi^+\)) for \(2 < p_T < 8 ~\rm{GeV}/c\) and in the centrality range of about \(65 - 90\%\). The results show no significant dependence on \(p_T\), \(y\) or the mean number of participating nucleons. They are also consistent with similar measurements obtained by the LHCb collaboration in \(\rm{pPb}\) and \(\rm{Pbp}\) collisions at \(\sqrt{s_\rm{NN}}=5.02~\rm{TeV}\). The data agree well with predictions from Pythia in \(\rm{pp}\) collisions at \(\sqrt{s}=5~\rm{TeV}\) but are in tension with predictions of the Statistical Hadronization model.

31. PoS
    Oral

    Lamarr: the ultra-fast simulation option for the LHCb experiment

    L. Anderlini, M. Barbetti, G. Corti, and 7 more authors

    in 41st International Conference on High Energy Physics (ICHEP 2022)

    PoS 414 (2023) 233 – Published on 15 Jun 2023

    Abs DOI Slides

    During Run 2 of the Large Hadron Collider at CERN, the LHCb experiment has spent more than 80% of the pledged CPU time to produce simulated data samples. The upcoming upgraded version of the experiment will be able to collect larger data samples, requiring many more simulated events to analyze the data to be collected in Run 3. Simulation is a key necessity of analysis to interpret signal vs background and measure efficiencies. The needed simulation will far exceed the pledged resources, requiring an evolution in technologies and techniques to produce these simulated samples. In this contribution, we discuss Lamarr, a Gaudi-based framework to deliver simulated samples parametrizing both the detector response and the reconstruction algorithms. Generative Models powered by several algorithms and strategies are employed to effectively parametrize the high-level response of the single components of the LHCb detector, encoding within neural networks the experimental errors and uncertainties introduced in the detection and reconstruction process. Where possible, models are trained directly on real data, resulting into a simulation process completely independent of the detailed simulation used to date.

32. JHEP

    Search for the lepton-flavour violating decays \(B^0 \to K^{*0} \mu^\pm e^\mp\) and \(B_s^0 \to \phi \mu^\pm e^\mp\)

    LHCb Collaboration: R. Aaij, and  others

    JHEP 06 (2023) 073 – Published on 14 Jun 2023

    Abs arXiv DOICDS

    A search for the lepton-flavour violating decays \(B^0 \to K^{*0} \mu^\pm e^\mp\) and \(B_s^0 \to \phi \mu^\pm e^\mp\) is presented, using proton-proton collision data collected by the LHCb detector at the LHC, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). No significant signals are observed and upper limits of \(\mathcal{B}(B^0 \to K^{*0} \mu^+ e^-) < 5.7 \times 10^{-9} (6.9 \times 10^{-9})\), \(\mathcal{B}(B^0 \to K^{*0} \mu^- e^+) < 6.8 \times 10^{-9} (7.9 \times 10^{-9})\), \(\mathcal{B}(B^0 \to K^{*0} \mu^\pm e^\mp) < 10.1 \times 10^{-9} (11.7 \times 10^{-9})\), \(\mathcal{B}(B_s^0 \to \phi \mu^\pm e^\mp) < 16.0 \times 10^{-9} (19.8 \times 10^{-9})\) are set at \(90\% (95\%)\) confidence level. These results constitute the world's most stringent limits to date, with the limit on the decay \(B_s^0 \to \phi \mu^\pm e^\mp\) the first being set. In addition, limits are reported for scalar and left-handed lepton-flavour violating New Physics scenarios.

33. JHEP

    Amplitude analysis of the \(D^+\to\pi^- \pi^+\pi^+\) decay and measurement of the \(\pi^-\pi^+\) S-wave amplitude

    LHCb Collaboration: R. Aaij, and  others

    JHEP 06 (2023) 044 – Published on 9 Jun 2023

    Abs arXiv DOICDS

    An amplitude analysis of the \(D^+ \to \pi^- \pi^+ \pi^+\) decay is performed with a sample corresponding to \(1.5~\rm{fb}^{-1}\) of integrated luminosity of \(pp\) collisions at a centre-of-mass energy \(\sqrt{s} = 8~\rm{TeV}\) collected by the LHCb detector in 2012. The sample contains approximately six hundred thousand candidates with a signal purity of \(95\%\). The resonant structure is studied through a fit to the Dalitz plot where the \(\pi^- \pi^+\) S-wave amplitude is extracted as a function of \(\pi^- \pi^+\) mass, and spin-1 and spin-2 resonances are included coherently through an isobar model. The S-wave component is found to be dominant, followed by the \(\rho(770)^0 \pi^+\) and \(f_2(1270) \pi^+\) components. A small contribution from the \(\omega(782) \to \pi^- \pi^+\) decay is seen for the first time in the \(D^+ \to \pi^- \pi^+ \pi^+\) decay.

34. JHEP

    Measurement of the \(Z\) boson production cross-section in proton-lead collisions at \(\sqrt{s_\rm{NN}}=8.16~\rm{TeV}\)

    LHCb Collaboration: R. Aaij, and  others

    JHEP 06 (2023) 022 – Published on 5 Jun 2023

    Abs arXiv DOICDS

    This article presents the first measurement of the differential \(Z\)-boson production cross-section in the forward region using proton-lead collisions with the LHCb detector. The dataset was collected at a nucleon-nucleon centre-of-mass energy of \(\sqrt{s_\rm{NN}}=8.16~\rm{TeV}\) in 2016, corresponding to an integrated luminosity of \(30.8~\rm{nb}^{-1}\). The forward-backward ratio and the nuclear modification factors are measured together with the differential cross-section as functions of the \(Z\) boson rapidity in the centre-of-mass frame, the transverse momentum of the \(Z\) boson and a geometric variable \(\phi^*\). The results are in good agreement with the predictions from nuclear parton distribution functions, providing strong constraining power at small Bjorken-\(x\).

35. JHEP

    Measurement of \(CP\) asymmetries in \({D}_{(s)}^{+}\to \eta {\pi}^{+}\) and \({D}_{(s)}^{+}\to {\eta}^{\prime}{\pi}^{+}\) decays

    LHCb Collaboration: R. Aaij, and  others

    JHEP 04 (2023) 081 – Published on 18 Apr 2023

    Abs arXiv DOICDS

    Searches for \(CP\) violation in the decays \({D}_{(s)}^{+} \to \eta {\pi}^{+}\) and \({D}_{(s)}^{+} \to {\eta}^{\prime }{\pi}^{+}\) are performed using pp collision data corresponding to \(6~\rm{fb}^{-1}\) of integrated luminosity collected by the LHCb experiment. The calibration channels \({D}_{(s)}^{+} \to \phi {\pi}^{+}\) are used to remove production and detection asymmetries. The resulting \(CP\)-violating asymmetries are \(A^{CP}({D}^{+} \to \eta {\pi}^{+}) = (0.34 \pm 0.66 \pm 0.16 \pm 0.05)\%\), \(A^{CP}({D}_{s}^{+} \to \eta {\pi}^{+}) = (0.32 \pm 0.51 \pm 0.12)\%\), \(A^{CP}({D}^{+} \to {\eta}^{\prime}{\pi}^{+}) = (0.49 \pm 0.18 \pm 0.06 \pm 0.05)\%\), \(A^{CP}({D}_{s}^{+} \to {\eta}^{\prime}{\pi}^{+}) = (0.01 \pm 0.12 \pm 0.08)\%\), where the first uncertainty is statistical, the second is systematic and the third, relevant for the \(D^+\) channels, is due to the uncertainty on \(A^{CP}(D^+ \to \phi \pi^+)\). These measurements, currently the most precise for three of the four channels considered, are consistent with the absence of \(CP\) violation. A combination of these results with previous LHCb measurements is presented.

36. Cancers

    Characterization of Mediastinal Bulky Lymphomas with FDG-PET-Based Radiomics and Machine Learning Techniques

    E. M. Abenavoli, M. Barbetti, F. Linguanti, and 12 more authors

    Cancers 15 (2023) 1931 – Published on 23 Mar 2023

    Abs DOI Code

    Background: This study tested the diagnostic value of 18F-FDG PET/CT (FDG-PET) volumetric and texture parameters in the histological differentiation of mediastinal bulky disease due to classical Hodgkin lymphoma (cHL), primary mediastinal B-cell lymphoma (PMBCL) and grey zone lymphoma (GZL), using machine learning techniques. Methods: We reviewed 80 cHL, 29 PMBCL and 8 GZL adult patients with mediastinal bulky disease and histopathological diagnoses who underwent FDG-PET pre-treatment. Volumetric and radiomic parameters were measured using FDG-PET both for bulky lesions (BL) and for all lesions (AL) using LIFEx software (threshold SUV ≥ 2.5). Binary and multiclass classifications were performed with various machine learning techniques fed by a relevant subset of radiomic features. Results: The analysis showed significant differences between the lymphoma groups in terms of SUVmax, SUVmean, MTV, TLG and several textural features of both first- and second-order grey level. Among machine learning classifiers, the tree-based ensembles achieved the best performance both for binary and multiclass classifications in histological differentiation. Conclusions: Our results support the value of metabolic heterogeneity as an imaging biomarker, and the use of radiomic features for early characterization of mediastinal bulky lymphoma.

37. JPCS
    Oral

    Towards Reliable Neural Generative Modeling of Detectors

    Lucio Anderlini, Matteo Barbetti, Denis Derkach, and 3 more authors

    in 20th International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT 2021)

    J. Phys.: Conf. Ser. 2438 (2023) 012130 – Published on 15 Feb 2023

    Abs arXiv DOICDS Slides

    The increasing luminosities of future data taking at Large Hadron Collider and next generation collider experiments require an unprecedented amount of simulated events to be produced. Such large scale productions demand a significant amount of valuable computing resources. This brings a demand to use new approaches to event generation and simulation of detector responses. In this paper, we discuss the application of generative adversarial networks (GANs) to the simulation of the LHCb experiment events. We emphasize main pitfalls in the application of GANs and study the systematic effects in detail. The presented results are based on the Geant4 simulation of the LHCb Cherenkov detector.

38. NIMA
    Poster

    A full detector description using neural network driven simulation

    F. Ratnikov, A. Rogachev, S. Mokhnenko, and 7 more authors

    in 15th Pisa Meeting on Advanced Detectors

    Nucl. Instrum. Meth. A 1046 (2023) 167591 – Published on 11 Jan 2023

    Abs DOI Poster

    The abundance of data arriving in the new runs of the Large Hadron Collider creates tough requirements for the amount of necessary simulated events and thus for the speed of generating such events. Current approaches can suffer from long generation time and lack of important storage resources to preserve the simulated datasets. The development of the new fast generation techniques is thus crucial for the proper functioning of experiments. We present a novel approach to simulate LHCb detector events using generative machine learning algorithms and other statistical tools. The approaches combine the speed and flexibility of neural networks and encapsulates knowledge about the detector in the form of statistical patterns. Whenever possible, the algorithms are trained using real data, which enhances their robustness against differences between real data and simulation. We discuss particularities of neural network detector simulation implementations and corresponding systematic uncertainties.

2022

1. EPJC

   Open charm production and asymmetry in \(p\rm{Ne}\) collisions at \(\sqrt{s_{\rm{NN}}} = 68.5~\rm{GeV}\)

   LHCb Collaboration: R. Aaij, and  others

   Eur. Phys. J. C 83 (2022) 541 – Published on 21 Nov 2022

   Abs arXiv DOICDS

   A measurement of D0 meson production by the LHCb experiment in its fixed-target configuration is presented. The production of \(D^0\) mesons is studied with a beam of \(2.5~\rm{TeV}\) protons colliding on a gaseous neon target at rest, corresponding to a nucleon-nucleon centre-of-mass energy of \(\sqrt{s_{\rm{NN}}} = 68.5~\rm{GeV}\). The \(D^0\) and \(\overline{D}^0\) production cross-section in \(p\rm{Ne}\) collisions in the centre-of-mass rapidity range \(y^* \in [-2.29, 0]\) is found to be \(\sigma^{y^* \in [-2.29, 0]}_{D^0} = (48.2 \pm 0.3 \pm 4.5)~\mu\rm{b}/\rm{nucleon}\) where the first uncertainty is statistical and the second is systematic. The \(D^0 - \overline{D}^0\) production asymmetry is also evaluated and suggests a negative trend at large negative \(y^*\). The considered models do not account precisely for all the features observed in the LHCb data, but theoretical predictions including \(1\%\) intrinsic charm and \(10\%\) recombination contributions better describe the data than the other models considered.

2. PRL

   First measurement of the \(Z \to \mu^+ \mu^-\) angular coefficients in the forward region of \(pp\) collisions at \(\sqrt{s}=13~\rm{TeV}\)

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. Lett. 129 (2022) 091801 – Published on 24 Aug 2022

   Abs arXiv DOICDS

   The first study of the angular distribution of \(\mu^+ \mu^-\) pairs produced in the forward rapidity region via the Drell-Yan reaction \(pp \to \gamma^* / Z + X \to \ell^+ \ell^- + X\) is presented, using data collected with the LHCb detector at a centre-of-mass energy of \(13~\rm{TeV}\), corresponding to an integrated luminosity of \(5.1~\rm{fb}^{-1}\). The coefficients of the five leading terms in the angular distribution are determined as a function of the dimuon transverse momentum and rapidity. The results are compared to various theoretical predictions of the \(Z\)-boson production mechanism and can also be used to probe transverse-momentum-dependent parton distributions within the proton.

3. JHEP

   Constraints on the CKM angle \(\gamma\) from \(B^\pm \to Dh^\pm\) decays using \(D \to h^\pm h^{\prime\mp}\pi^0\) final states

   LHCb Collaboration: R. Aaij, and  others

   JHEP 07 (2022) 099 – Published on 15 Jul 2022

   Abs arXiv DOICDS

   A data sample collected with the LHCb detector, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\), is used to measure \(CP\) observables in \(B^\pm \to Dh^\pm\) decays, where \(h^{(\prime)}\) is either a kaon or a pion, and the neutral \(D\) meson decay is reconstructed in the three-body final states \(K^\pm \pi^\mp \pi^0\), \(\pi^\pm \pi^\mp \pi^0\), and \(K^\pm K^\mp \pi^0\). The most suppressed of these modes, \(B^\pm \to \left [ \pi^\pm K^\mp \pi^0 \right ]_D K^\pm\), is observed with a significance greater than seven standard deviations and constraints on the CKM angle \(\gamma\) are calculated from the combination of the measurements.

4. PoS
   Oral

   \(\mathtt{scikinC}\): a tool for deploying machine learning as binaries

   Lucio Anderlini, and Matteo Barbetti

   in Computational Tools for High Energy Physics and Cosmology

   PoS 409 (2022) 034 – Published on 14 Jul 2022

   Abs DOI Code Slides

   Machine Learning plays a major role in Computational Physics providing arbitrarily good approximations of arbitrarily complex functions, for example with Artificial Neural Networks and Boosted Decision Trees. Unfortunately, the integration of Machine Learning models trained with Python frameworks in production code, often developed in C, C++, or FORTRAN, is notoriously a complicated task. We present scikinC, a transpiler for scikit-learn and Keras models into plain C functions, intended to be compiled into shared objects and linked to other applications. An example of application to the parametrization of a detector is discussed.

5. JHEP

   Precision measurement of forward \(Z\) boson production in proton-proton collisions at \(\sqrt{s} = 13~\rm{TeV}\)

   LHCb Collaboration: R. Aaij, and  others

   JHEP 07 (2022) 026 – Published on 5 Jul 2022

   Abs arXiv DOICDS

   A precision measurement of the \(Z\) boson production cross-section at \(\sqrt{s} = 13~\rm{TeV}\) in the forward region is presented, using \(pp\) collision data collected by the LHCb detector, corresponding to an integrated luminosity of \(5.1~\rm{fb}^{-1}\). The production cross-section is measured using \(Z \to \mu^+ \mu^-\) events within the fiducial region defined as pseudorapidity \(2.0 < \eta < 4.5\) and transverse momentum \(p_T > 20~\rm{GeV}/c\) for both muons and dimuon invariant mass \(60 < M_{\mu\mu} < 120~\rm{GeV}/c^2\). The integrated cross-section is determined to be \(\sigma (Z \to \mu^+ \mu^-) = 195.3 \pm 0.2 \pm 1.5 \pm 3.9~\rm{pb}\), where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions, including a prediction at next-to-next-to-leading order in perturbative quantum chromodynamics and a prediction with resummation.

6. Nat. Commun.

   Study of the doubly charmed tetraquark \(T_{cc}^+\)

   LHCb Collaboration: R. Aaij, and  others

   Nat. Commun. 13 (2022) 3351 – Published on 16 Jun 2022

   Abs arXiv DOICDSData

   An exotic narrow state in the \(D^0 D^0 \pi^+\) mass spectrum just below the \(D^{*+} D^0\) mass threshold is studied using a data set corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\) acquired with the LHCb detector in proton-proton collisions at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\). The state is consistent with the ground isoscalar \(T_{cc}^+\) tetraquark with a quark content of \(c c \bar{u} \bar{d}\) and spin-parity quantum numbers \(J^P = 1^+\). Study of the \(DD\) mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell \(D^{*+}\) mesons is confirmed by the \(D^0 \pi^+\) mass distribution. The mass of the resonance and its coupling to the \(D^* D\) system are analysed. Resonance parameters including the pole position, scattering length, effective range and compositeness are measured to reveal important information about the nature of the \(T_{cc}^+\) state. In addition, an unexpected dependence of the production rate on track multiplicity is observed.

7. Nat. Phys.

   Observation of an exotic narrow doubly charmed tetraquark

   LHCb Collaboration: R. Aaij, and  others

   Nat. Phys. (2022) – Published on 16 Jun 2022

   Abs arXiv DOICDSData

   Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. The observation of a new type of hadronic state, a doubly charmed tetraquark containing two charm quarks, an anti-\(u\) and an anti-\(d\) quark, is reported using data collected by the LHCb experiment at the Large Hadron Collider. This exotic state with a mass of about \(3875~\rm{MeV}/c^2\) manifests itself as a narrow peak in the mass spectrum of \(D^0 D^0 \pi^+\) mesons just below the \(D^{*+} D^0\) mass threshold. The near threshold mass together with a strikingly narrow width reveals the resonance nature of the state.

8. PRL

   Angular analysis of \(D^0 \to \pi^+\pi^-\mu^+\mu^-\) and \(D^0 \to K^+K^-\mu^+\mu^-\) decays and search for \(CP\) violation

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. Lett. 128 (2022) 221801 – Published on 3 Jun 2022

   Abs arXiv DOICDS

   The first full angular analysis and an updated measurement of the decay-rate \(CP\) asymmetry of the \(D^0 \to \pi^+\pi^-\mu^+\mu^-\) and \(D^0 \to K^+K^-\mu^+\mu^-\) decays are reported. The analysis uses proton-proton collision data collected with the LHCb detector at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\). The data set corresponds to an integrated luminosity of \(9~\rm{fb}^{-1}\). The full set of \(CP\)-averaged angular observables and their \(CP\) asymmetries are measured as a function of the dimuon invariant mass. The results are consistent with expectations from the Standard Model and with \(CP\) symmetry.

9. PRD

   Measurement of the charm mixing parameter \(y_{CP} - y_{CP}^{K\pi}\) using two-body \(D^0\) meson decays

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. D 105 (2022) 092013 – Published on 25 May 2022

   Abs arXiv DOICDS

   A measurement of the ratios of the effective decay widths of \(D^0 \to \pi^- \pi^+\) and \(D^0 \to K^- K^+\) decays over that of \(D^0 \to K^- \pi^+\) decays is performed with the LHCb experiment using proton-proton collisions at a centre-of-mass energy of \(13~\rm{TeV}\), corresponding to an integrated luminosity of \(6~\rm{fb}^{-1}\). These observables give access to the charm mixing parameters \(y_{CP}^{\pi\pi} - y_{CP}^{K\pi}\) and \(y_{CP}^{KK} - y_{CP}^{K\pi}\), and are measured as \(y_{CP}^{\pi\pi} - y_{CP}^{K\pi} = ( 6.57 \pm 0.53 \pm 0.16 ) \times 10^{-3}\), \(y_{CP}^{KK} - y_{CP}^{K\pi} = ( 7.08 \pm 0.30 \pm 0.14 ) \times 10^{-3}\), where the first uncertainties are statistical and the second systematic. The combination of the two measurements is \(y_{CP} - y_{CP}^{K\pi} = ( 6.96 \pm 0.26 \pm 0.13 ) \times 10^{-3}\), which is four times more precise than the previous world average.

10. PRL

    Observation of the decay \(\Lambda_b^0 \to \Lambda_c^+ \tau^- \overline{\nu}_{\tau}\)

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. Lett. 128 (2022) 191803 – Published on 13 May 2022

    Abs arXiv DOICDS

    The first observation of the semileptonic \(b\)-baryon decay \(\Lambda_b^0 \to \Lambda_c^+ \tau^- \overline{\nu}_{\tau}\), with a significance of \(6.1 \sigma\), is reported using a data sample corresponding to \(3~\rm{fb}^{-1}\) of integrated luminosity, collected by the LHCb experiment at centre-of-mass energies of \(7\) and \(8~\rm{TeV}\) at the LHC. The \(\tau^-\) lepton is reconstructed in the hadronic decay to three charged pions. The branching fraction \(\mathcal{B} (\Lambda_b^0 \to \Lambda_c^+ \tau^- \overline{\nu}_{\tau}) = (1.50 \pm 0.16 \pm 0.25 \pm 0.23) \%\) is obtained, where uncertainties are statistical, systematic and from the external branching fraction of the normalisation channel \(\Lambda_b^0 \to \Lambda_c^+ \pi^- \pi^+ \pi^-\). The ratio of semileptonic branching fractions \(\mathcal{R} (\Lambda_c^+) \equiv \mathcal{B} (\Lambda_b^0 \to \Lambda_c^+ \tau^- \overline{\nu}_{\tau}) / \mathcal{B} (\Lambda_b^0 \to \Lambda_c^+ \mu^- \overline{\nu}_{\mu})\) is derived to be \(0.242 \pm 0.026 \pm 0.040 \pm 0.059\), where the external branching fraction uncertainty from the channel \(\Lambda_b^0 \to \Lambda_c^+ \mu^- \overline{\nu}_{\mu}\) contributes to the last term. This result is in agreement with the Standard Model prediction.

11. PRL

    Tests of lepton universality using \(B^0\to K^0_S \ell^+ \ell^-\) and \(B^+\to K^{*+}\ell^+\ell^-\) decays

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. Lett. 128 (2022) 191802 – Published on 11 May 2022

    Abs arXiv DOICDS

    Tests of lepton universality in \(B^0\to K^0_S \ell^+ \ell^-\) and \(B^+\to K^{*+}\ell^+\ell^-\) decays where \(\ell\) is either an electron or a muon are presented. The differential branching fractions of \(B^0\to K^0_S e^+ e^-\) and \(B^+\to K^{*+} e^+ e^-\) decays are measured in intervals of the dilepton invariant mass squared. The measurements are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). The results are consistent with the Standard Model and previous tests of lepton universality in related decay modes. The first observation of \(B^0\to K^0_S e^+ e^-\) and \(B^+\to K^{*+} e^+ e^-\) decays is reported.

12. JHEP

    Search for the decay \(B^0 \to \phi \mu^+ \mu^-\)

    LHCb Collaboration: R. Aaij, and  others

    JHEP 05 (2022) 067 – Published on 11 May 2022

    Abs arXiv DOICDS

    A search for the decay \(B^0 \to \phi \mu^+ \mu^-\) is performed using proton-proton collisions at centre-of-mass energies of \(7\), \(8\), and \(13~\rm{TeV}\) collected by the LHCb experiment and corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). No evidence for the \(B^0 \to \phi \mu^+ \mu^-\) decay is found and an upper limit on the branching fraction of \(4.4 \times 10^{-3}\) at a \(90\%\) credibility level, relative to that of the \(B^0_s \to \phi \mu^+ \mu^-\) decay, is established. Using the measured \(B^0_s \to \phi \mu^+ \mu^-\) branching fraction and assuming a phase-space model, the absolute branching fraction of the decay \(B^0 \to \phi \mu^+ \mu^-\) is determined to be less than \(3.2 \times 10^{-9}\) at a \(90\%\) credibility level.

13. JHEP

    Observation of the doubly charmed baryon decay \(\Xi_{cc}^{++}\to \Xi_{c}^{'+}\pi^{+}\)

    LHCb Collaboration: R. Aaij, and  others

    JHEP 05 (2022) 038 – Published on 6 May 2022

    Abs arXiv DOICDS

    The \(\Xi_{cc}^{++}\to \Xi_{c}^{'+}\pi^{+}\) decay is observed using proton-proton collisions collected by the LHCb experiment at a centre-of-mass energy of \(13~\rm{TeV}\), corresponding to an integrated luminosity of \(5.4~\rm{fb}^{-1}\). The \(\Xi_{cc}^{++}\to \Xi_{c}^{'+}\pi^{+}\) decay is reconstructed partially, where the photon from the \(\Xi_{c}^{'+} \to \Xi_{c}^{+} \gamma\) decay is not reconstructed and the \(p K^{-} \pi^{+}\) final state of the \(\Xi_{c}^{+}\) baryon is employed. The \(\Xi_{cc}^{++}\to \Xi_{c}^{'+}\pi^{+}\) branching fraction relative to that of the \(\Xi_{cc}^{++}\to \Xi_{c}^{+}\pi^{+}\) decay is measured to be \(1.41 \pm 0.17 \pm 0.10\), where the first uncertainty is statistical and the second systematic.

14. EPJC

    Search for massive long-lived particles decaying semileptonically at \(\sqrt{s} = 13~\rm{TeV}\)

    LHCb Collaboration: R. Aaij, and  others

    Eur. Phys. J. C 82 (2022) 373 – Published on 28 Apr 2022

    Abs arXiv DOICDS

    A search is performed for massive long-lived particles (LLP) decaying semileptonically into a muon and two quarks. Two kinds of LLP production processes were considered. In the first a Higgs-like boson with mass from \(30\) to \(200~\rm{GeV}\) is produced by gluon fusion and decays into two LLPs. The analysis covers LLP mass values from \(10~\rm{GeV}\) up to about one half the Higgs-like boson mass. The second LLP production mode is directly from quark interactions, with LLP masses from \(10\) to \(90~\rm{GeV}\). The LLP lifetimes considered range from \(5\) to \(200~\rm{ps}\). This study uses LHCb data collected from proton-proton collisions at \(\sqrt{s} = 13~\rm{TeV}\), corresponding to an integrated luminosity of \(5.4~\rm{fb}^{-1}\). No evidence of these long-lived states has been observed, and upper limits on the production cross-section times branching ratio have been set for each model considered.

15. PRL

    Observation of two new excited \(\Xi_b^0\) states decaying to \(\Lambda_b^0 K^-\pi^+\)

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. Lett. 128 (2022) 162001 – Published on 21 Apr 2022

    Abs arXiv DOICDS

    Two narrow resonant states are observed in the \(\Lambda_b^0 K^-\pi^+\) mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of \(13~\rm{TeV}\), collected by the LHCb experiment and corresponding to an integrated luminosity of \(6~\rm{fb}^{-1}\). The minimal quark content of the \(\Lambda_b^0 K^-\pi^+\) system indicates that these are excited \(\Xi_b^0\) baryons. The masses of the \(\Xi_b(6327)^0\) and \(\Xi_b(6333)^0\) states are \(m ( \Xi_b(6327)^0 ) = 6327.28^{+0.23}_{-0.21} \pm ±0.08 \pm ±0.24~\rm{MeV}\) and \(m ( \Xi_b(6333)^0 ) = 6332.69^{+0.17}_{-0.18} \pm 0.03 \pm 0.22~\rm{MeV}\), respectively, with a mass splitting of \(\Delta m = 5.41^{+0.26}_{-0.27} \pm 0.06~\rm{MeV}\), where the uncertainties are statistical, systematic and due to the \(\Lambda_b^0\) mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of \(\Gamma ( \Xi_b(6327)^0 ) < 2.20 (2.56)~\rm{MeV}\) and \(\Gamma ( \Xi_b(6333)^0 ) < 1.55 (1.85)~\rm{MeV}\) at a \(90\% (95\%)\) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D \(\Xi_b^0\) resonances.

16. PRD

    Observation of the \(B^0 \to \overline{D}^{*0} K^{+} \pi^{-}\) and \(B_s^0 \to \overline{D}^{*0} K^{-} \pi^{+}\) decays

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. D 105 (2022) 072005 – Published on 20 Apr 2022

    Abs arXiv DOICDS

    The first observations of \(B^0 \to \overline{D}^{*} (2007)^{0} K^{+} \pi^{-}\) and \(B_s^0 \to \overline{D}^{*} (2007)^{0} K^{-} \pi^{+}\) decays are presented, and their branching fractions relative to that of the \(B^0 \to \overline{D}^{*0} (2007) \pi^{+} \pi^{-}\) decay are reported. These modes can potentially be used to investigate the spectroscopy of charm and charm-strange resonances and to determine the angle \(\gamma\) of the CKM unitarity triangle. It is also important to understand them as a source of potential background in determinations of \(\gamma\) from \(B^+ \to D K^+\) and \(B^0 \to D K^+ \pi^-\) decays. The analysis is based on a sample corresponding to an integrated luminosity of \(5.4~\rm{fb}^{-1}\) of proton-proton collision data at \(13~\rm{TeV}\) centre-of-mass energy recorded with the LHCb detector. The \(\overline{D}^{*} (2007)^{0}\) mesons are fully reconstructed in the \(\overline{D}^{0} \pi^0\) and \(\overline{D}^{0} \gamma\) channels, with the \(\overline{D}^{0} \to K^+ \pi^-\) decay. A novel weighting method is used to subtract background while simultaneously applying an event-by-event efficiency correction to account for resonant structures in the decays.

17. JHEP

    Study of charmonium and charmonium-like contributions in \(B^+ \rightarrow J/\psi \eta K^+\) decays

    LHCb Collaboration: R. Aaij, and  others

    JHEP 04 (2022) 046 – Published on 8 Apr 2022

    Abs arXiv DOICDS

    A study of \(B^+ \to J/\psi \eta K^+\) decays, followed by \(J/\psi \to \mu^+ \mu^-\) and \(\eta \to \gamma \gamma\), is performed using a dataset collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\), corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). The \(J/\psi \eta\) mass spectrum is investigated for contributions from charmonia and charmonium-like states. Evidence is found for the \(B^+ \to \left ( \psi_2 (3823) \to J/\psi \eta \right ) K^+\) and \(B^+ \to \left ( \psi (4040) \to J/\psi \eta \right ) K^+\) decays with significance of \(3.4\) and \(4.7~\sigma\), respectively. This constitutes the first evidence for the \(\psi_2 (3823) \to J/\psi \eta\) decay.

18. PRD

    Measurement of the photon polarization in \(\Lambda_b \to \Lambda \gamma\) decays

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. D 105 (2022) L051104 – Published on 23 Mar 2022

    Abs arXiv DOICDS

    The photon polarization in \(b \to s \gamma\) transitions is measured for the first time in radiative \(b\)-baryon decays exploiting the unique spin structure of \(\Lambda_b \to \Lambda \gamma\) decays. A data sample corresponding to an integrated luminosity of \(6~\rm{fb}^{-1}\) collected by the LHCb experiment in \(pp\) collisions at a center-of-mass energy of \(13~\rm{TeV}\) is used. The photon polarization is measured to be \(\alpha_\gamma = 0.82^{+0.17+0.04}_{-0.26-0.13}\), where the first uncertainty is statistical and the second systematic. This result is in agreement with the Standard Model prediction and previous measurements in \(b\)-meson decays. Charge-parity breaking effects are studied for the first time in this observable and found to be consistent with \(CP\) symmetry.

19. JHEP

    Observation of \(\Lambda_b^0 \to D^+ p \pi^-\pi^-\) and \(\Lambda_b^0 \to D^{*+} p \pi^-\pi^-\) decays

    LHCb Collaboration: R. Aaij, and  others

    JHEP 03 (2022) 153 – Published on 23 Mar 2022

    Abs arXiv DOICDS

    The multihadron decays \(\Lambda_b^0 \to D^+ p \pi^-\pi^-\) and \(\Lambda_b^0 \to D^{*+} p \pi^-\pi^-\) are observed in data corresponding to an integrated luminosity of \(3~\rm{fb}^{-1}\), collected in proton-proton collisions at centre-of-mass energies of \(7\) and \(8~\rm{TeV}\) by the LHCb detector. Using the decay \(\Lambda_b^0 \to \Lambda_c^+ \pi^+ \pi^-\pi^-\) as a normalisation channel, the ratio of branching fractions is measured to be \(\frac{\mathcal{B}(\Lambda_b^0 \to D^+ p \pi^-\pi^-)}{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+ \pi^+ \pi^-\pi^-)} \times \frac{\mathcal{B}(D^+ \to K^- \pi^+ \pi^+)}{\mathcal{B}(\Lambda_c^+ \to p K^- \pi^+)} = (5.35 \pm 0.21 \pm 0.16)\%\), where the first uncertainty is statistical and the second systematic. The ratio of branching fractions for \(\Lambda_b^0 \to D^{*+} p \pi^-\pi^-\) and \(\Lambda_b^0 \to D^+ p \pi^-\pi^-\) decays is found to be \(\frac{\mathcal{B}(\Lambda_b^0 \to D^{*+} p \pi^-\pi^-)}{\mathcal{B}(\Lambda_b^0 \to D^+ p \pi^-\pi^-)} \times (\mathcal{B}(D^{*+} \to \pi^0) + \mathcal{B}(D^{*+} \to \gamma)) = (61.3 \pm 4.3 \pm 4.0)\%\).

20. JHEP

    Searches for rare \(B_s^0\) and \(B^0\) decays into four muons

    LHCb Collaboration: R. Aaij, and  others

    JHEP 03 (2022) 109 – Published on 17 Mar 2022

    Abs arXiv DOICDS

    Searches for rare \(B_s^0\) and \(B^0\) decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\). Direct decays and decays via light scalar and \(J/\psi\) resonances are considered. No evidence for the six decays searched for is found and upper limits at the \(95\%\) confidence level on their branching fractions ranging between \(1.8 \times 10^{-10}\) and \(2.6 \times 10^{-9}\) are set.

21. Sci. Bull.

    Measurement of the lifetimes of promptly produced \(\Omega^{0}_{c}\) and \(\Xi^{0}_{c}\) baryons

    LHCb Collaboration: R. Aaij, and  others

    Sci. Bull. 67 (2022) 5 – Published on 15 Mar 2022

    Abs arXiv DOICDS

    A measurement of the lifetimes of the \(\Omega^{0}_{c}\) and \(\Xi^{0}_{c}\) baryons is reported using proton-proton collision data at a centre-of-mass energy of \(13~\rm{TeV}\), corresponding to an integrated luminosity of \(5.4~\rm{fb}^{-1}\) collected by the LHCb experiment. The \(\Omega^{0}_{c}\) and \(\Xi^{0}_{c}\) baryons are produced directly from proton interactions and reconstructed in the \(p K^- K^- \pi^+\) final state. The \(\Omega^{0}_{c}\) lifetime is measured to be \(276.5 \pm 13.4 \pm 4.4 \pm 0.7~\rm{fs}\), and the \(\Xi^{0}_{c}\) lifetime is measured to be \(148.0 \pm 2.3 \pm 2.2 \pm 0.2~\rm{fs}\), where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the \(D^0\) lifetime. These results confirm previous LHCb measurements based on semileptonic beauty-hadron decays, which disagree with earlier results of a four times shorter \(\Omega^{0}_{c}\) lifetime, and provide the single most precise measurement of the \(\Omega^{0}_{c}\) lifetime.

22. PRL

    Study of \(Z\) bosons produced in association with charm in the forward region

    LHCb Collaboration: R. Aaij, and  others

    Phys. Rev. Lett. 128 (2022) 082001 – Published on 24 Feb 2022

    Abs arXiv DOICDS

    The fraction of \(Z\)+jet events that contain a charm jet is measured for the first time in the forward region of proton-proton collisions. The data sample used corresponds to an integrated luminosity of \(6~\rm{fb}^{-1}\) collected at a center-of-mass energy of \(13~\rm{TeV}\) with the LHCb detector. The ratio of production cross sections \(\sigma(Zc) / \sigma(Zj)\) is determined in intervals of \(Z\)-boson rapidity in the range \(2.0 < y(Z) < 4.5\). A sizable enhancement is observed in the forward-most \(y(Z)\) interval, which could be indicative of a valence-like intrinsic-charm component in the proton wave function.

23. JINST

    Identification of charm jets at LHCb

    LHCb Collaboration: R. Aaij, and  others

    JINST 17 (2022) P02028 – Published on 22 Feb 2022

    Abs arXiv DOICDS

    The identification of charm jets is achieved at LHCb for data collected in 2015-2018 using a method based on the properties of displaced vertices reconstructed and matched with jets. The performance of this method is determined using a dijet calibration dataset recorded by the LHCb detector and selected such that the jets are unbiased in quantities used in the tagging algorithm. The charm-tagging efficiency is reported as a function of the transverse momentum of the jet. The measured efficiencies are compared to those obtained from simulation and found to be in good agreement.

24. JHEP

    Measurement of \(\chi_{c1}(3872)\) production in proton-proton collisions at \(\sqrt{s}=8\) and \(13~\rm{TeV}\)

    LHCb Collaboration: R. Aaij, and  others

    JHEP 01 (2022) 131 – Published on 24 Jan 2022

    Abs arXiv DOICDS

    The production cross-section of the \(\chi_{c1}(3872)\) state relative to the \(\psi(2S)\) meson is measured using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of \(\sqrt{s}=8\) and \(13~\rm{TeV}\), corresponding to integrated luminosities of \(2.0\) and \(5.4~\rm{fb}^{-1}\), respectively. The two mesons are reconstructed in the \(J/\psi \pi^+ \pi^-\) final state. The ratios of the prompt and nonprompt \(\chi_{c1}(3872)\) to \(\psi(2S)\) production cross-sections are measured as a function of transverse momentum, \(p_T\), and rapidity, \(y\), in the kinematic range \(4 < p_T < 20~\rm{GeV}/c\) and \(2.0 < y < 4.5\). The prompt ratio is found to increase with \(p_T\) independently of \(y\). The double-differential cross-section ratio of \(\chi_{c1}(3872)\) relative to \(\psi(2S)\) mesons between \(13\) and \(8~\rm{TeV}\) is also measured for the prompt component and observed to be consistent with unity, independent of \(p_T\) and centre-of-mass energy.

25. JHEP

    Study of the \(B_c^+\) decays into charmonia and three light hadrons

    LHCb Collaboration: R. Aaij, and  others

    JHEP 01 (2022) 065 – Published on 13 Jan 2022

    Abs arXiv DOICDS

    Using proton-proton collision data, corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\) collected with the LHCb detector, seven decay modes of the \(B_c^+\) meson into a \(J/\psi\) or \(\psi(2S)\) meson and three charged hadrons, kaons or pions, are studied. The decays \(B_c^+ \to \left ( \psi(2S) \to J/\psi \pi^+ \pi^- \right ) \pi^+\), \(B_c^+ \to \psi(2S) \pi^+ \pi^+ \pi^-\), \(B_c^+ \to J/\psi K^+ \pi^+ \pi^-\) and \(B_c^+ \to K^+ K^+ K^-\) are observed for the first time, and evidence for the \(B_c^+ \to \psi(2S) K^+ K^- \pi^+\) decay is found, where \(J/\psi\) and \(\psi(2S)\) mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different \(B_c^+\) decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.

26. JHEP

    Measurement of the \(W\) boson mass

    LHCb Collaboration: R. Aaij, and  others

    JHEP 01 (2022) 036 – Published on 10 Jan 2022

    Abs arXiv DOICDS

    The \(W\) boson mass is measured using proton-proton collision data at \(s = \sqrt{13}~\rm{TeV}\) corresponding to an integrated luminosity of \(1.7~\rm{fb}^{-1}\) recorded during 2016 by the LHCb experiment. With a simultaneous fit of the muon \(q / p_T\) distribution of a sample of \(W \to \mu \nu\) decays and the \(\phi^*\) distribution of a sample of \(Z \to \mu \mu\) decays the \(W\) boson mass is determined to be \(m_W = 80354 \pm 23_\rm{stat} \pm 10_\rm{exp} \pm 17_\rm{theory} \pm 9_\rm{PDF}~\rm{MeV}\), where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.

2021

1. PRD

   Observation of the suppressed \(\Lambda_b^0\to D p K^-\) decay with \(D\to K^+ \pi^-\) and measurement of its \(C\!P\) asymmetry

   LHCb Collaboration: R. Aaij, and  others

   Phys. Rev. D 104 (2021) 112008 – Published on 27 Dec 2021

   Abs arXiv DOICDS

   A study of \(\Lambda_b^0\) baryon decays to the \(D p K^-\) final state is presented based on a proton-proton collision data sample corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\) collected with the LHCb detector. Two \(\Lambda_b^0\) decays are considered, \(\Lambda_b^0\to D p K^-\) with \(D\to K^- \pi^+\) and \(D\to K^+ \pi^-\), where \(D\) represents a superposition of \(D^0\) and \(\overline{D}^0\) states. The latter process is expected to be suppressed relative to the former, and is observed for the first time. The ratio of branching fractions of the two decays is measured, and the \(C\!P\) asymmetry of the suppressed mode, which is sensitive to the CKM angle \(\gamma\), is also reported.

2. JHEP

   Simultaneous determination of CKM angle \(\gamma\) and charm mixing parameters

   LHCb Collaboration: R. Aaij, and  others

   JHEP 12 (2021) 141 – Published on 21 Dec 2021

   Abs arXiv DOICDS

   A combination of measurements sensitive to the \(CP\) violation angle \(\gamma\) of the Cabibbo-Kobayashi-Maskawa unitarity triangle and to the charm mixing parameters that describe oscillations between \(D^0\) and \(\overline{D}^0\) mesons is performed. Results from the charm and beauty sectors, based on data collected with the LHCb detector at CERN's Large Hadron Collider, are combined for the first time. This method provides an improvement on the precision of the charm mixing parameter \(y\) by a factor of two with respect to the current world average. The charm mixing parameters are determined to be \(x = (0.400^{+0.052}_{-0.053})\%\) and \(y = (0.630^{+0.033}_{-0.030})\%\). The angle \(\gamma\) is found to be \(\gamma = (65.4^{+3.8}_{-4.2})^\rm{o}\) and is the most precise determination from a single experiment.

3. JHEP

   Updated search for \(B_c^+\) decays to two charm mesons

   LHCb Collaboration: R. Aaij, and  others

   JHEP 12 (2021) 117 – Published on 17 Dec 2021

   Abs arXiv DOICDS

   A data set corresponding to an integrated luminosity of \(9~\rm{fb}^{-1}\) of proton-proton collisions collected by the LHCb experiment has been analysed to search for \(B^{+}_{c} \to D^{(*)+}_{(s)} \overset{(-)}{D}\)\(^{(*)0}\) decays. The decays are fully or partially reconstructed, where one or two missing neutral pions or photons from the decay of an excited charm meson are allowed. Upper limits for the branching fractions, normalised to \(B^+\) decays to final states with similar topologies, are obtained for fourteen \(B^+_c\) decay modes. For the decay \(B^+_c \to D^+_s \overline{D}^0\), an excess with a significance of \(3.4\) standard deviations is found.

4. JHEP

   Search for the doubly charmed baryon \(\it{\Xi}_{cc}^{+}\) in the \(\it{\Xi}_{c}^{+} \pi^{-} \pi^{+}\) final state

   LHCb Collaboration: R. Aaij, and  others

   JHEP 12 (2021) 107 – Published on 16 Dec 2021

   Abs arXiv DOICDS

   A search for the doubly charmed baryon \(\it{\Xi}_{cc}^{+}\) is performed in the \(\it{\Xi}_{c}^{+} \pi^{-} \pi^{+}\) decay mode, where the \(\it{\Xi}_{c}^{+}\) baryon is reconstructed in the \(p K^- \pi^+\) final state. The study uses proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of \(13~\rm{TeV}\), corresponding to a total integrated luminosity of \(5.4~\rm{fb}^{-1}\). No significant signal is observed in the invariant-mass range of \(3.4 - 3.8~\rm{GeV}/c^2\). Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the \(\it{\Xi}_{cc}^{+} \to \left ( \it{\Xi}_{c}^{+} \to p K^- \pi^+ \right ) \pi^+\) decay for different \(\it{\Xi}_{cc}^{+}\) mass and lifetime hypotheses in the rapidity range from \(2.0\) to \(4.5\) and the transverse momentum range from \(2.5\) to \(25~\rm{GeV}/c\). The results from this search are combined with a previously published search for the \(\it{\Xi}_{cc}^{+} \to \Lambda_c^+ K^- \pi^+\) decay mode, yielding a maximum local significance of \(4.0\) standard deviations around the mass of \(3620~\rm{MeV}/c^2\), including systematic uncertainties. Taking into account the look-elsewhere effect in the \(3.5 - 3.7~\rm{GeV}/c^2\) mass window, the combined global significance is \(2.9\) standard deviations including systematic uncertainties.

5. JHEP

   Measurement of \(J/\psi\) production cross-sections in \(pp\) collisions at \(\sqrt{s}=5~\rm{TeV}\)

   LHCb Collaboration: R. Aaij, and  others

   JHEP 11 (2021) 181 – Published on 24 Nov 2021

   Abs arXiv DOICDSData

   The production cross-sections of \(J/\psi\) mesons in proton-proton collisions at a centre-of-mass energy of \(\sqrt{s} = 5~\rm{TeV}\) are measured using a data sample corresponding to an integrated luminosity of \(9.13 \pm 0.18~\rm{pb}^{-1}\), collected by the LHCb experiment. The cross-sections are measured differentially as a function of transverse momentum, \(p_T\), and rapidity, \(y\), and separately for \(J/\psi\) mesons produced promptly and from beauty hadron decays (nonprompt). With the assumption of unpolarised \(J/\psi\) mesons, the production cross-sections integrated over the kinematic range \(0 < p_T < 20~\rm{GeV}/c\) and \(2.0 < y < 4.5\) are \(8.154 \pm 0.010 \pm 0.283~\mu\rm{b}\) for prompt \(J/\psi\) mesons and \(0.820 \pm 0.003 \pm 0.034~\mu\rm{b}\) for nonprompt \(J/\psi\) mesons, where the first uncertainties are statistical and the second systematic. These cross-sections are compared with those at \(\sqrt{s} = 8~\rm{TeV}\) and \(13~\rm{TeV}\), and are used to update the measurement of the nuclear modification factor in proton-lead collisions for \(J/\psi\) mesons at a centre-of-mass energy per nucleon pair of \(s_{NN} = \sqrt{5}~\rm{TeV}\). The results are compared with theoretical predictions.

6. JHEP

   Angular analysis of the rare decay \(B_s^0 \to \phi \mu^+ \mu^-\)

   LHCb Collaboration: R. Aaij, and  others

   JHEP 11 (2021) 043 – Published on 8 Nov 2021

   Abs arXiv DOICDS

   An angular analysis of the rare decay \(B_s^0 \to \phi \mu^+ \mu^-\) is presented, using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of \(7\), \(8\) and \(13~\rm{TeV}\), corresponding to an integrated luminosity of \(8.4~\rm{fb}^{-1}\). The observables describing the angular distributions of the decay \(B_s^0 \to \phi \mu^+ \mu^-\) are determined in regions of \(q^2\), the square of the dimuon invariant mass. The results are consistent with Standard Model predictions.