LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Measurement of the Z boson production cross-section in pp collisions at √s=5.02 TeV. J. High Energy Phys., 02(2), 070–38pp.
Abstract: The first measurement of the Z boson production cross-section at centre-of-mass energy v s = 5.02TeV in the forward region is reported, using pp collision data collected by the LHCb experiment in year 2017, corresponding to an integrated luminosity of 100 +/- 2 pb-1. The production cross-section is measured for final-state muons in the pseudorapidity range 2.0 <. < 4.5 with transverse momentum pT > 20 GeV/c. The integrated cross-section is determined to be sZ.mu+mu- = 39.6 +/- 0.7(stat) +/- 0.6(syst) +/- 0.8(lumi) pb for the di-muon invariant mass in the range 60 < M μμ< 120 GeV/c2. This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling constant. Based on a previous LHCb measurement of the Z boson production cross-section in pPb collisions at v sNN = 5.02TeV, the nuclear modification factor RpPb is measured for the first time at this energy. The measured values are 1.2+0.5 -0.3(stat) +/- 0.1(syst) in the forward region (1.53 < y* μ< 4.03) and 3.6+1.6 -0.9(stat)+/- 0.2(syst) in the backward region (-4.97 < y* μ< -2.47), where y* μrepresents the muon rapidity in the centre-of-mass frame.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). A search for rare B → D μ+ μ- decays. J. High Energy Phys., 02(2), 032–23pp.
Abstract: A search for rare B. D mu+ mu- decays is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb-1. No significant signals are observed in the non-resonant mu+ mu- modes, and upper limits of B -> B0. D0 mu+ mu- < 5.1 x 10-8, B B+. D+ s mu+ mu- -> < 3.2 x 10-8, B -> B0 s. D0 mu+ mu--> < 1.6 x 10-7 and fc/fu center dot B B+ c. D+ s mu+ mu--> < 9.6 x 10-8 are set at the 95% confidence level, where fc and fu are the fragmentation fractions of a B meson with a c and u quark respectively in proton-proton collisions. Each result is either the first such measurement or an improvement by three orders of magnitude on an existing limit. Separate upper limits are calculated when the muon pair originates from a J/.. mu+ mu- decay. The branching fraction of B+ c. D+ s J/. multiplied by the fragmentation-fraction ratio is measured to be fc fu center dot B -> B+ c. D+ s J/.-> = (1.63 +/- 0.15 +/- 0.13) x 10-5, where the first uncertainty is statistical and the second systematic.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2024). Measurement of the CKM angle γ in the B0 → D K*0 channel using self-conjugate D → KS0 h+ h- decays. Eur. Phys. J. C, 84(2), 206–18pp.
Abstract: A model-independent study of CP violation in B-0 -> DK (*0) decays is presented using data corresponding to an integrated luminosity of 9 fb(-1) collected by the LHCb experiment at centre-of-mass energies of v s = 7, 8 and 13TeV. The CKM angle. is determined by examining the distributions of signal decays in phase-space bins of the self-conjugate D. K(S)(0)h(+) h(-) decays, where h = p, K. Observables related to CP violation are measured and the angle. is determined to be = (49+22 -19). Measurements of the amplitude ratio and strong-phase difference between the favoured and suppressed B-0 decays are also presented.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Observation of CP Violation in Charm Decays. Phys. Rev. Lett., 122(21), 211803–12pp.
Abstract: A search for charge-parity (CP) violation in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb(-1) collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D* (2010)(+) -> D-0 pi(+) decays or from the charge of the muon in (B) over bar -> D-0 mu(-)(nu) over bar X-mu decays. The difference between the CP asymmetries in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is measured to be Delta A(CP) = [-18.2 +/- 3.2(stat) +/- 0.9(syst)] x 10(-4) for pi-tagged and Delta A(CP) = [-9 +/- 8(stat) +/- 5(syst)] x 10(-4) for mu-tagged D-0 mesons. Combining these with previous LHCb results leads to Delta A(CP) = (-15.4 +/- 2.9) x 10(-4), where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Search for the Lepton-Flavor-Violating Decays B-s(0) -> pi(+/-mu -/+) and B-0 -> tau(+/-mu -/+). Phys. Rev. Lett., 123(21), 211801–11pp.
Abstract: Results are reported from a search for the rare decays B-s(0) -> tau(+/-)mu(+/-) 1T and B -> tau(+/-)mu(+/-), where the r lepton is reconstructed in the channel r- irrg vr. These processes are effectively forbidden in the standard model, hut they can potentially occur at detectable rates in models of new physics that can induce lepton flavor-violating decays. The search is based on a data sample corresponding to 3 fb-1 of proton -proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected r neutrino, the 1.3 and B signal regions are highly overlapping. Assuming no contribution from B r1, r, the upper limit 8(B r 71) < 4.2 x 10-5 is obtained at 95% confidence level. If no contribution from tau(+/-)mu(+/-) is assumed, a limit of B(B r prn < 1.4 x 10-5 is obtained at 95% confidence level. These results represent the first limit on B(B? r5+) and the most stringent limit on B(B tau(+/-)mu(+/-).)
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Search for the Rare Decays B-s(0) -> e(+) e(-) and B-0 -> e(+) e(-). Phys. Rev. Lett., 124(21), 211802–11pp.
Abstract: A search for the decays B-s(0) -> e(+)e(-) and B-0 e(+)e(-) is performed using data collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to integrated luminosities of 1, 2, and 2 fb(-1), respectively. No signal is observed. Assuming no contribution from B-0 -> e(+)e(-) decays, an upper limit on the branching fraction B(B-s(0) -> e(+)e(-)) < 9.4(11.2) x 10(-9) is obtained at 90(95)% confidence level. If no B-s(0) -> e(+)e(-) contribution is assumed, a limit of B(B-0 -> e(+)e(-)) < 2.5(3.0) x 10(-9) is determined at 90(95)% confidence level. These upper limits are more than one order of magnitude lower than the previous values.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Observation of Enhanced Double Parton Scattering in Proton-Lead Collisions at root s(NN)=8.16 TeV. Phys. Rev. Lett., 125(21), 212001–13pp.
Abstract: A study of prompt charm-hadron pair production in proton-lead collisions at root s(NN) = 8.16 TeV is performed using data corresponding to an integrated luminosity of about 30 nb(-1), collected with the LHCb experiment. Production cross sections for different pairs of charm hadrons are measured and kinematic correlations between the two charm hadrons are investigated. This is the first measurement of associated production of two charm hadrons in proton-lead collisions. The results confirm the predicted enhancement of double parton scattering production in proton-lead collisions compared to the single parton scattering production.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2017). chi(c1) and chi(c2) Resonance Parameters with the Decays chi(c1,c2) -> J/psi mu(+)mu(-). Phys. Rev. Lett., 119(22), 221801–9pp.
Abstract: The decays chi(c1) -> J/psi mu(+)mu(-) and chi(c1) -> J/psi mu(+)mu(-) are observed and used to study the resonance parameters of the chi(c1) and chi(c2) mesons. The masses of these states are measured to be m(chi(c1)) = 3510.71 +/- 0.04(stat) +/- 0.09(syst) MeV and m(chi(c2)) = 3556.10 +/- 0.06(stat) +/- 0.11(syst) MeV, where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m(chi(c2)) – m(chi(c1)) = 45.39 +/- 0.07(stat) +/- 0.03(syst) MeV. The natural width of the chi(c2) meson is measured to be Gamma(chi(c2)) = 2.10 +/- 0.20(stat) +/- 0.02(syst) MeV. These results are in good agreement with and have comparable precision to the current world averages.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). Evidence for the Rare Decay Sigma(+) -> p mu(+)mu(-). Phys. Rev. Lett., 120(22), 221803–10pp.
Abstract: A search for the rare decay Sigma(+) -> p mu(+)mu(-) is performed using pp collision data recorded by the LHCb experiment at center-of-mass energies root s = 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb(-1). An excess of events is observed with respect to the background expectation, with a signal significance of 4.1 standard deviations. No significant structure is observed in the dimuon invariant mass distribution, in contrast with a previous result from the HyperCP experiment. The measured Sigma(+) -> p mu(+)mu(-) branching fraction is (2.2(-1.3)(+1.8)) x 10(-8), where statistical and systematic uncertainties are included, which is consistent with the standard model prediction.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). Measurement of Antiproton Production in p-He Collisions at root S-NN=110 GeV. Phys. Rev. Lett., 121(22), 222001–10pp.
Abstract: The cross section for prompt antiproton production in collisions of protons with an energy of 6.5 TeV incident on helium nuclei at rest is measured with the LHCb experiment from a data set corresponding to an integrated luminosity of 0.5 nb(-1). The target is provided by injecting helium gas into the LHC beam line at the LHCb interaction point. The reported results, covering antiproton momenta between 12 and 110 GeV/c, represent the first direct determination of the antiproton production cross section in p-He collisions, and impact the interpretation of recent results on antiproton cosmic rays from space-borne experiments.
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