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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 Doubly Charmed Baryon Xi(++)(cc). Phys. Rev. Lett., 119(11), 112001–10pp.
Abstract: A highly significant structure is observed in the Lambda K-+(c)-pi(+)pi(+) mass spectrum, where the Lambda(+)(c) baryon is reconstructed in the decay mode pK(-)pi(+). The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon Xi(++)(cc). The difference between the masses of the Xi(++)(cc) and Lambda(+)(c) states is measured to be 1334.94 +/- 0.72(stat.) +/- 0.27(syst.) MeV/c(2), and the Xi(++)(cc) mass is then determined to be 3621.40 +/- 0.72(stat.) +/- 0.27(syst.) +/- 0.14(Lambda(+)(c)) MeV/c(2), where the last uncertainty is due to the limited knowledge of the Lambda(+)(c) mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb(-1), and confirmed in an additional sample of data collected at 8 TeV.
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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). Measurement of B-s(0) and D-s(-) Meson Lifetimes. Phys. Rev. Lett., 119(10), 101801–10pp.
Abstract: We report on a measurement of the flavor-specific B-s(0) lifetime and of the D-s(-) lifetime using proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to 3.0 fb(-1) of integrated luminosity. Approximately 407 000 B-s(0) -> D-s(()*()) -> D-s(()*()-) mu+v(mu) decays are partially reconstructed in the K+K-pi(-)mu(+) final state. The B-s(0) and D-s(-) natural widths are determined using, as a reference, kinematically similar B-0 -> Dd(*)(-) mu+v(mu) decays reconstructed in the same final state. The resulting differences between widths of B-s(0) and B-0 mesons and of D-s(-) and D- mesons are Delta(Gamma)(B) = -0.0115 +/- 0.0053(stat) +/- 0.0041 (syst) ps(-1) and Delta(Gamma)(D) = 1.0131 +/- 0.0117(stat) +/- 0.0065(syst) ps(-1), respectively. Combined with the known B-0 and D- lifetimes, these yield the flavor-specific B-s(0) lifetime, tau(fs)(Bs0) = 1.547 +/- 0.013 (stat) +/- 0.010 (syst) +/- 0.004(tau(B)) ps and the D-s(-) lifetime, tau(Ds-) = 0.5064 +/- 0.0030(stat) +/- 0.0017(syst) +/- 0.0017(sys) +/- 0.0017(tau(D)). The last uncertainties originate from the limited knowledge of the B-0 and D- lifetimes. The results improve upon current determinations.
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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). Test of lepton universality with B-0 -> K*(0)l(+)l(-) decays. J. High Energy Phys., 08(8), 055–31pp.
Abstract: A test of lepton universality, performed by measuring the ratio of the branching fractions of the B-0 -> K*(0)mu(+) mu(-) and B-0 -> K*e(+)e(-) decays, R-K*0, is presented. The K*(0) meson is reconstructed in the final state K+pi(-), which is required to have an invariant mass within 100 MeV/c(2) of the known K*(892)(0) mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb(-1), collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q(2), to be R-K*0 – {0.66(-0.007)(+0.11)(stat) +/- 0.03(syst) for 0.045 < q(2) < GeV2/c(4), 0.69(-0.07)(+0.11)(stat) +/- 0.05(syst) for 1.1 < q(2) < 6.0 GeV2/c(4). The corresponding 95.4% confidence level intervals are [0.52, 0.89] and [0.53, 0.94]. The results, which represent the most precise measurements of R-K*0 to date, are compatible with the Standard Model expectations at the level of 2.1-2.3 and 2.4-2.5 standard deviations in the two q(2) regions, 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). Search for massive long-lived particles decaying semileptonically in the LHCb detector. Eur. Phys. J. C, 77(4), 224–16pp.
Abstract: A search is presented formassive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8TeV, corresponding to integrated luminosities of 1 and 2fb(-1), respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80GeV/c(2) and lifetimes from 5 to 100 ps are explored. Results are also interpreted in terms of neutralino production in different R-Parity violating supersymmetric models, with masses in the 23-198 GeV/c(2) range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.
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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 charmless baryonic decays B-(s)(0) -> p(p)over-barh plus h '(-). Phys. Rev. D, 96(5), 051103–10pp.
Abstract: Decays of B-0 and B-s(0) mesons to the charmless baryonic final states p (p) over barh(+)h'(-), where h and h' each denote a kaon or a pion, are searched for using the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb(-1). Four-body charmless baryonic B-s(0) decays are observed for the first time. The decays B-s(0) -> p (p) over barK(+) K-, B-s(0) -> p (p) over barK(+/-) pi(inverted perpendicular), B-0 -> p (p) over barK(+) pi(inverted perpendicular) and B-0 -> p (p) over bar pi(+) pi(-) are observed with a significance greater than 5 standard deviations; evidence at 4.1 standard deviations is found for the B-0 -> p (p) over barK(+) K- decay and an upper limit is set on the branching fraction for B-s(0) -> p (p) over bar pi(+) pi(-). Branching fractions in the kinematic region m(p (p) over bar) < 2850 MeV/c(2) are measured relative to the B-0 -> J/psi(-> p<(p)over bar>) K* (892)(0) channel.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2017). Evidence for CP violation in B+ -> K*(892)(+)pi(0) from a Dalitz plot analysis of B+ -> K-S(0) pi(+)pi(0) decays. Phys. Rev. D, 96(7), 072001–21pp.
Abstract: We report a Dalitz plot analysis of charmless hadronic decays of charged B mesons to the final state K-S(0)pi(1) pi(0) using the full BABAR data set of 470.9 +/- 2.8 million B (B) over bar events collected at the gamma (4S) resonance. We measure the overall branching fraction and CP asymmetry to be B(B+ -> K-0 pi(+)pi(0)) = (31.8 +/- 1.8 +/- 2.1(-0.0)(+6.0)) x 10(-6) and A(CP)(B+ -> K-0 pi(+)pi(0)) = 0.07 +/- 0.05 +/- 0.03(-0.03)(+0.02), where the uncertainties are statistical, systematic, and due to the signal model, respectively. This is the first measurement of the branching fraction for B+ -> K-0 pi(+)pi(0). We find first evidence of a CP asymmetry in B+ -> K*(892)(+) pi(0) decays: A(CP)(B+ -> K*(892)(+)pi(0)) = -0.52 +/- 0.14 +/- 0.04(-0.02)(+0.04). The significance of this asymmetry, including systematic and model uncertainties, is 3.4 standard deviations. We also measure the branching fractions and CP asymmetries for three other intermediate decay modes.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2017). Search for Invisible Decays of a Dark Photon Produced in e(+)e(-) Collisions at BABAR. Phys. Rev. Lett., 119(13), 131804–7pp.
Abstract: We search for single-photon events in 53 fb(-1) of e(+)e(-) collision data collected with the BABAR detector at the PEP-II B-Factory. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle A' through the process e(+)e(-) -> gamma A'; A' -> invisible. Such particles, referred to as “dark photons,” are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A' to e(+)e(-) in the mass range m(A') <= 8 GeV. In particular, our limits exclude the values of the A' coupling suggested by the dark-photon interpretation of the muon (g – 2)(mu) anomaly, as well as a broad range of parameters for the dark-sector models.
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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 Xi(-)(b) -> J/psi Lambda K- decay. Phys. Lett. B, 772, 265–273.
Abstract: The observation of the decay Xi(-)(b)-> J/psi Lambda K- is reported, using a data sample corresponding to an integrated luminosity of 3 fb(-1), collected by the LHCb detector in pp collisions at centre-of-mass energies of 7 and 8 TeV. The production rate of Xi(-)(b) baryons detected in the decay Xi(-)(b) -> J/psi Lambda K- is measured relative to that of Lambda(0)(b) baryons using the decay Lambda(0)(b) -> J/psi Lambda. Integrated over the b-baryon transverse momentum p(T) < 25 GeV/c and rapidity 2.0 < y < 4.5, the measured ratio is f Xi(-)(b/) f Lambda(0)(b) B(Xi(-)(b)-> J/psi Lambda K-) / B(Lambda(0)(b)-> J/psi Lambda) = (4.19 +/- 0.29 (stat) +/- 0.15 (syst)) x 10(-2), where f(Xi)(b)(-) band f(Lambda)(b)(0)are the fragmentation fractions of b ->Xi(-)(b)and b ->Lambda(0)(b)transitions, and ss represents the branching fraction of the corresponding b- baryon decay. The mass difference between Xi(-)(b) and Lambda(0)(b) baryons is measured to be M(Xi(-)(b))-M(Lambda(0)(b)) = 177.08 +/- 0.47 (stat) +/- 0.16 (syst) MeV/c(2).
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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). Study of prompt D-0 meson production in pPb collisions at root(NN)-N-s=5 TeV. J. High Energy Phys., 10(10), 090–28pp.
Abstract: Production of prompt D-0 mesons is studied in proton-lead and lead-proton collisions recorded at the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of 1.58 +/- 0.02 nb(-1) recorded at a nucleon-nucleon centre-of-mass energy of root(NN)-N-s = 5 TeV. Measurements of the differential cross-section, the forward-backward production ratio and the nuclear modification factor are reported using D-0 candidates with transverse momenta less than 10 GeV/c and rapidities in the ranges 1.5 < y* < 4.0 and -5.0 < y* < -2.5 in the nucleon-nucleon centre-of-mass system.
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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). Search for Baryon-Number Violating Xi(0)(b) Oscillations. Phys. Rev. Lett., 119(18), 181807–9pp.
Abstract: A search for baryon-number violating Xi(0)(b) oscillations is performed with a sample of pp collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb(-1). The baryon number at the moment of production is identified by requiring that the Xi(0)(b) come from the decay of a resonance Xi(b)*(-) -> Xi(0)(b)pi(-) or Xi(b)'(-) -> Xi(0)(b)pi(-) and the baryon number at the moment of decay is identified from the final state using the decays Xi(0)(b) -> Xi(0)(c)pi(-) , Xi(+-)(c) -> pK(-)pi(+). No evidence of baryon-number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of omega < 0.08 ps(-1), where. is the associated angular frequency.
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