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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). First observation and measurement of the branching fraction for the decay B-s(0) -> D-s*K-/+(+/-). J. High Energy Phys., 06(6), 130–16pp.
Abstract: The first observation of the B-s(0) -> D-s*(-/+) K-+/- decay is reported using 3.0 fb(-1) of proton-proton collision data collected by the LHCb experiment. The D-s*(-/+) mesons are reconstructed through the decay chain D-s*(-/+) -> gamma D-s(-/+) ((KK +/-)-K--/+pi(-/+)). The branching fraction relative to that for B-s(0) -> D-s*(-)pi(+) decays is measured to be B (B-s(0) -> D-s*K--/+(+/-))/B(B-s(0) -> D-s*(-)pi(+)) = 0.068 +/- 0.005(-0.002)(+0.003), where the first uncertainty is statistical and the second is systematic. Using a recent measurement of B(B-s(0) -> D-s*(-)pi(+)), the absolute branching fraction of B-s(0) -> Ds*K--/+(+/-) is measured as B(B-s(0) -> D*K--/+(+/-)) = (16.3 +/- 1.2(stat)(-0.5)(+0.7)(syst) +/- 4.8(norm)) x 10(-5), where the third uncertainty is due to the uncertainty on the branching fraction of the normalisation channel.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Model-independent measurement of the CKM angle gamma using B-0 -> DK*0 decays with D -> K (S) (0) pi (+)pi (-) and K (S) (0) K+K-. J. High Energy Phys., 06(6), 131–31pp.
Abstract: A binned Dalitz plot analysis of the decays B (0) -> DK*(0), with D -> K (S) (0) pi(+)pi(-) and D -> K (S) (0) K+K-, is performed to measure the observables x(+/-) and y(+/-), which are related to the CKM angle gamma and the hadronic parameters of the decays. The D decay strong phase variation over the Dalitz plot is taken from measurements performed at the CLEO-c experiment, making the analysis independent of the D decay model. With a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), collected by the LHCb experiment, the values of the CP violation parameters are found to be x(+) = 0.05 +/- 0.35 +/- 0.02, x(-) = -0.31 +/- 0.20 +/- 0.04, y(+) = -0.81 +/- 0.28 +/- 0.06 and y(-) = 0.31 +/- 0.21 +/- 0.05, where the first uncertainties are statistical and the second systematic. These observables correspond to values gamma = (71 +/- 20)degrees, gamma(B0) = 0.56 +/- 0.17 and delta(B0) = (204(-20)(+21))degrees. The parameters gamma(B0) and delta(B0) are the magnitude ratio and strong phase difference between the suppressed and favoured B-0 decay amplitudes, and have been measured in a region of +/- 50 MeV/c(2) around the K*(892)(0) mass and with the magnitude of the cosine of the K*(892)(0) helicity angle larger than 0.4.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of the CP Asymmetry in B-s(0) – (B)over-bar(s)(0) Mixing. Phys. Rev. Lett., 117(6), 061803–9pp.
Abstract: The CP asymmetry in the mixing of B-s(0) and (B) over bar (0)(s) mesons is measured in proton-proton collision data corresponding to an integrated luminosity of 3.0 fb(-1), recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV. Semileptonic B-s(0) and (B) over bar (s) (0) decays are studied in the inclusive mode D-s(-/+)mu(+/-)nu((-)) X-mu with the D-s(-/+) mesons reconstructed in the K+K-pi(-/+) final state. Correcting the observed charge asymmetry for detection and background effects, the CP asymmetry is found to be a(sl)(s) = (0.39 +/- 0.26 +/- 0.20)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of a(sl)(s) to date. It is consistent with the prediction from the standard model and will constrain new models of particle physics.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Measurements of prompt charm production cross-sections in pp collisions at root s=5TeV. J. High Energy Phys., 06(6), 147–41pp.
Abstract: Production cross-sections of prompt charm mesons are measured using data from pp collisions at the LHC at a centre-of-mass energy of 5TeV. The data sample corresponds to an integrated luminosity of 8 : 60 +/- 0 : 33 pb(-1) collected by the LHCb experiment. The production cross-sections of D-0, D+, D-s(+), and D*(+) mesons are measured in bins of charm meson transverse momentum, p(T), and rapidity, y. They cover the rapidity range 2 : 0 < y < 4 : 5 and transverse momentum ranges 0 < p(T) < 10 GeV/c for D-0 and D+ and 1 < p(T) < 10 GeV/c for D-s(+) and D*(+) mesons. The inclusive cross- sections for the four mesons, including charge-conjugate states, within the range of 1 < p(T) < 8 GeV/c are determined to be sigma (pp -> D-0 X) – 1004 +/- 3 +/- 54 μb; sigma ( pp -> D+ X) = 402 +/- 2 +/- 30 μb; sigma ( pp -> Ds+X) = 170 +/- 4 +/- 16 μb; sigma ( pp -> D*(+) X) = 421 +/- 5 +/- 36 μb; where the uncertainties are statistical and systematic, respectively.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Observation of the decay Lambda(0)(b) -> pK(-)mu(+)mu(-) and a search for CP violation. J. High Energy Phys., 06(6), 108–17pp.
Abstract: A search for CP violation in the decay Lambda(0)(b) -> pK(-)mu(+)mu(-) is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb(-1). The Lambda(0)(b) -> pK(-)mu(+)mu(-) decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, Delta A(CP) equivalent to A(CP) (Lambda(0)(b) -> pK(-)mu(+)mu(-)) – A(CP) (Lambda(0)(b) -> pK(-)J/psi) and a(CP)((T) over cap -odd), where the latter is based on asymmetries in the angle between the mu(+)mu(-) and pK(-) decay planes. These are measured to be Delta A(CP) = (-3.5 +/- 5.0 (stat) +/- 0.2 (syst)) x 10(-2), a(CP)((T) over cap -odd) = (1.2 +/- 5.0 (stat) +/- 0.7 (syst)) x 10(-2), and no evidence for CP violation is found.
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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). Observation of the Decays Alpha(0)(b) -> chi(c1)pK(-) and Alpha(0)(b) ->chi(c2)pK(-). Phys. Rev. Lett., 119(6), 062001–11pp.
Abstract: The first observation of the decays Lambda(b)(0) -> chi(c1)pK(-) and Lambda(0)(b) -> chi(c2)pK(-) is reported using a data sample corresponding to an integrated luminosity of 3.0 fb(-1), collected by the LHCb experiment in pp collisions at center-of-mass energies of 7 and 8 TeV The following ratios of branching fractions are measured: B(Lambda(0)(b) -> chi(c1)pK(-))/B(Lambda(0)(b) -> J/psi pK(-)) = 0.242 +/- 0.014 +/- 0.013 +/- 0.009, B(Lambda(0)(b) -> chi(c2)pK(-))/B(Lambda(0)(b) -> J/psi pK(-)) = 0.248 +/- 0.020 +/- 0.014 +/- 0.009, B(Lambda(0)(b) -> chi(c2)pK(-))/B(Lambda(0)(b) -> chi(c1)pK(-)) = 1.02 +/- 0.010 +/- 0.02 +/- 0.05, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the x(c1) -> J/psi gamma and chi(c2) -> J/psi gamma decays. Using both decay modes, the mass of the Ab baryon is also measured to be m(Lambda b0) = 5619.44 +/- 0.28 +/- 0.26 MeV/c(2), where the first and second uncertainties are statistical and systematic, respectively.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Measurement of the J/psi pair production cross-section in pp collisions at root s=13 TeV. J. High Energy Phys., 06(6), 047–38pp.
Abstract: The production cross-section of J/psi pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of root s = 13TeV, corresponding to an integrated luminosity of 279 +/- 11 pb(-1). The measurement is performed for J/psi mesons with a transverse momentum of less than 10 GeV/c in the rapidity range 2.0 < y < 4.5. The production cross-section is measured to be 15.2 +/- 1.0 +/- 0.9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/psi pair are measured and compared to theoretical predictions.
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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). Search for Dark Photons Produced in 13 TeV pp Collisions. Phys. Rev. Lett., 120(6), 061801–11pp.
Abstract: Searches are performed for both promptlike and long-lived dark photons, A', produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using A' -> mu(+)mu(-) decays and a data sample corresponding to an integrated luminosity of 1.6 fb(-1) collected with the LHCb detector. The promptlike A' search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived A' search is restricted to the low-mass region 214 < mo(A') < 350 MeV. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the gamma-A' kinetic-mixing strength. The constraints placed on promptlike dark photons are the most stringent to date for the mass range 10.6 < m(A') < 70 GeV, and are comparable to the best existing limits for m(A') < 0.5 GeV. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature.
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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). Studies of the resonance structure in D-0 -> K-/+ pi(+/-) pi(+/-) pi(-/+) decays. Eur. Phys. J. C, 78(6), 443–31pp.
Abstract: Amplitude models are constructed to describe the resonance structure of D-0 -> K-pi(+) pi(+) pi(-) and D-0 -> K+ pi(-)pi(-)pi(+) decays using pp collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of 3.0 f b(-1). The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes D-0 -> a(1)(1260)(+) K- and D-0 -> K-1(1270/1400)(+)pi(-) being prominent in D-0 -> K-pi(+) pi(+) pi(-) and D-0 -> K+pi(-)pi(-)pi(+), respectively. Precise measurements of the lineshape parameters and couplings of the a(1)(1260)(+), K-1(1270)(-) and K(1460)(-) resonances are made, and a quasi model-independent study of the K(1460)(-) resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be R-K3 pi = 0.459 +/- 0.010 (stat) +/- 0.012 (syst) +/- 0.020 (model), which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle gamma and studies of charm mixing and CP violation.
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). Limits on neutral Higgs boson production in the forward region in pp collisions at root s=7 TeV. J. High Energy Phys., 05(5), 132–13pp.
Abstract: Limits on the cross-section times branching fraction for neutral Higgs bosons, produced in p p collisions at root s = 7 TeV, and decaying to two tau leptons with pseudorapidities between 2.0 and 4.5, are presented. The result is based on a dataset, corresponding to an integrated luminosity of 1.0 fb(-1), collected with the LHCb detector. Candidates are identified by reconstructing final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. A model independent upper limit at the 95% confidence level is set on a neutral Higgs boson cross-section times branching fraction. It varies from 8.6 pb for a Higgs boson mass of 90 GeV to 0.7 pb for a Higgs boson mass of 250 GeV, and is compared to the Standard Model expectation. An upper limit on tan beta in the Minimal Supersymmetric Model is set in the m(h0)(max) scenario. It ranges from 34 for a CP-odd Higgs boson mass of 90 GeV to 70 for a pseudo-scalar Higgs boson mass of 140 GeV.
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