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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Search for the rare decays B-0 -> J/psi gamma and B-s(0)-> J/psi gamma. Phys. Rev. D, 92(11), 112002–9pp.
Abstract: A search for the rare decay of a B-0 or B-s(0) meson into the final state J/psi gamma is performed, using data collected by the LHCb experiment in pp collisions at root s = 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb(-1). The observed number of signal candidates is consistent with a background-only hypothesis. Branching fraction values larger than 1.5 x 10(-6) for the B-0 -> J/psi gamma decay mode are excluded at 90% confidence level. For the B-s(0) -> J/psi gamma decay mode, branching fraction values larger than 7.3 x 10(-6) are excluded at 90% confidence level; this is the first branching fraction limit for this decay.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). First observation of the rare B+ -> D+K+pi(-) decay. Phys. Rev. D, 93(5), 051101–11pp.
Abstract: The B+ -> D+K+pi(-) decay is observed in a data sample corresponding to 3.0 fb(-1) of pp collision data recorded by the LHCb experiment during 2011 and 2012. The signal significance is 8 sigma and the branching fraction is measured to be B(B+ -> D+K+pi(-)) = (5.31 +/- 0.90 +/- 0.48 +/- 0.35) x 10(-6), where the uncertainties are statistical, systematic and due to the normalization mode B+ -> D-K+pi(+), respectively. The Dalitz plot appears to be dominated by broad structures. Angular distributions are exploited to search for quasi-two-body contributions from B+ -> D*(2)(2460)K-0(+) and B+ -> (D+K*)(892)(0) decays. No significant signals are observed and upper limits are set on their branching fractions.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of the B-s(0) -> D-s(()*D-)+(s)(*()-) branching fractions. Phys. Rev. D, 93(9), 092008–11pp.
Abstract: The branching fraction of the decay B-s(0) -> D-s(()*D-)+(s)(*()-) is measured using pp collision data corresponding to an integrated luminosity of 1.0 fb(-1), collected using the LHCb detector at a center-of-mass energy of 7 TeV. It is found to be B(B-s(0) -> D-s(()*D-)(s)(*()-)) = (3.05 +/- 0.10 +/- 0.20 +/- 0.34)%, where the uncertainties are statistical, systematic, and due to the normalization channel, respectively. The branching fractions of the individual decays corresponding to the presence of one or two D-s(*+/-) are also measured. The individual branching fractions are found to be B(B-s(0) -> D-s*D-+/-(s)-/+) = (1.35 +/- 0.06 +/- 0.09 +/- 0.15)%, B(B-s(0) -> D-s*D-+(s)*(-)) = (1.27 +/- 0.08 +/- 0.10 +/- 0.14)%. All three results are the most precise determinations to date.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Search for violations of Lorentz invariance and CPT symmetry in B-(s)(0) mixing. Phys. Rev. Lett., 116(24), 241601–10pp.
Abstract: Violations of CPT symmetry and Lorentz invariance are searched for by studying interference effects in B-0 mixing and in B-s(0) mixing. Samples of B-0 -> J/psi K-S(0) and B-0(s) -> J/psi K+K- decays are recorded by the LHCb detector in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb(-1). No periodic variations of the particle-antiparticle mass differences are found, consistent with Lorentz invariance and CPT symmetry. Results are expressed in terms of the standard model extension parameter Delta a(mu) with precisions of O(10(-15)) and O(10(-14)) GeV for the B-0 and B-s(0) systems, respectively. With no assumption on Lorentz (non) invariance, the CPT-violating parameter z in the B-s(0) system is measured for the first time and found to be Re(z) = -0.022 +/- 0.033 +/- 0.005 and Im(z) = 0.004 +/- 0.011 +/- 0.002, where the first uncertainties are statistical and the second systematic.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). A precise measurement of the B-0 meson oscillation frequency. Eur. Phys. J. C, 76(7), 412–14pp.
Abstract: The oscillation frequency, Delta m(d), of B-0 mesons is measured using semileptonic decays with a D- or D*(-) meson in the final state. The data sample corresponds to 3.0 fb(-1) of pp collisions, collected by the LHCb experiment at centre-of-mass energies root s = 7 and 8 TeV. A combination of the two decay modes gives Delta m(d) = (505.0 +/- 2.1 +/- 1.0) ns(-1), where the first uncertainty is statistical and the second is systematic. This is the most precise single measurement of this parameter. It is consistent with the current world average and has similar precision.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the B(s) (0) -> φφ branching fraction and search for the decay B(0) -> φφ. J. High Energy Phys., 10(10), 053–18pp.
Abstract: Using a dataset corresponding to an integrated luminosity of 3.0 fb(-1) collected in pp collisions at centre-of-mass energies of 7 and 8 TeV, the B (s) (0) -> aEuro parts per thousand I center dot I center dot branching fraction is measured to be B(B-0 -> phi phi) = (1.84 +/- 0.05(stat) +/- 0.07 (syst) +/- 0.11 (f(s)/f(d)) +/- 0.12 (norm)) x 10(-5) where f (s) /f (d) represents the ratio of the B (s) (0) to B (0) production cross-sections, and the B (0) -> I center dot K (*)(892)(0) decay mode is used for normalization. This is the most precise measurement of this branching fraction to date, representing a factor five reduction in the statistical uncertainty compared with the previous best measurement. A search for the decay B (0) -> I center dot I center dot is also made. No signal is observed, and an upper limit on the branching fraction is set as B(B-0 -> phi phi < 2.8 x 10(-8)) at 90% confidence level. This is a factor of seven improvement compared to the previous best limit.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Study of psi(2S) production and cold nuclear matter effects in pPb collisions at root s(NN)=5 TeV. J. High Energy Phys., 03(3), 133–21pp.
Abstract: The production of psi(2S) mesons is studied in dimuon final states using proton-lead (pPb) collision data collected by the LHCb detector. The data sample corresponds to an integrated luminosity of 1.6 nb(-1). The nucleon-nucleon centre-of-mass energy of the pPb collisions is root s(NN) = 5 TeV. The measurement is performed using psi(2S) mesons with transverse momentum less than 14 GeV/c and rapidity y in the ranges 1.5 < y < 4.0 and -5.0 < y < -2.5 in the nucleon-nucleon centre-of-mass system. The forward-backward production ratio and the nuclear modi fi cation factor are determined for psi(2S) mesons. Using the production cross-section results of psi(2S) and J/psi mesons from b-hadron decays, the b (b) over bar cross-section in pPb collisions at root s(NN) = 5 TeV is obtained.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). First observation of the decay D-0 -> K-pi(+)mu(+)mu(-) in the rho(0)-omega region of the dimuon mass spectrum. Phys. Lett. B, 757, 558–567.
Abstract: A study of the decay D-0 -> K-pi(+)mu(+)mu(-) is performed using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2.0 fb(-1). Decay candidates with muon pairs that have an invariant mass in the range 675-875 MeV/c(2) are considered. This region is dominated by the rho(0) and omega resonances. The branching fraction in this range is measured to be B(D-0 -> K-pi(+)mu(+)mu(-)) = (4.17 +/- 0.12 (stat) +/- 0.40 (syst)) x 10(-6). This is the first observation of the decay D-0 -> K-pi(+)mu(+)mu(-). Its branching fraction is consistent with the value expected in the Standard Model.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the Z plus b-jet cross-section in pp collisions at root s=7 TeV in the forward region. J. High Energy Phys., 01(1), 064–15pp.
Abstract: The associated production of a Z boson or an off-shell photon gamma* with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of 7TeV. The Z bosons are reconstructed in the Z/gamma* -> mu(+)mu(-) final state from muons with a transverse momentum larger than 20 GeV, while two transverse momentum thresholds are considered for jets (10 GeV and 20 GeV). Both muons and jets are reconstructed in the pseudorapidity range 2.0 < eta < 4.5. The results are based on data corresponding to 1.0 fb(-1) recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet cross-section is normalized to the Z+jet cross-section. The measured cross-sections are (Z/ (mu+ mu-) + b-jet) = 295 60 (stat) 51 (syst) 10 (lumi) fb (0.1) for p T(jet) > 10 GeV, and (Z/ (mu+ mu-) + b-jet) = 128 36 (stat) 22 (syst) 5 (lumi) fb (0.2) for p T(jet) > 20 GeV.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurements of long-range near-side angular correlations in root sNN=5TeV proton-lead collisions in the forward region. Phys. Lett. B, 762, 473–483.
Abstract: Two-particle angular correlations are studied in proton-lead collisions at a nucleon-nucleon centre-ofmass energy of root sNN= 5 TeV, collected with the LHCb detector at the LHC. The analysis is based on data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, Delta eta, and relative azimuthal angle, Delta phi, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, Delta phi approximate to 0, is observed in the pseudorapidity range 2.0 < eta < 4.9. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to eta= 4.9. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.
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