108 research outputs found

    Apparatus to study crystal channeling and volume reflection phenomena at the SPS H8 beamline

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    A high performance apparatus has been designed and built by the H8-RD22 collaboration for the study of channeling and volume reflection phenomena in the interaction of 400 GeV/c protons with bent silicon crystals, during the 2006 data taking in the external beamline H8 of the CERN SPS. High-quality silicon short crystals were bent by either anticlastic or quasimosaic effects. Alignment with the highly parallel (8 mu rad divergence) proton beam was guaranteed through a submicroradian goniometric system equipped with both rotational and translational stages. Particle tracking was possible by a series of silicon microstrip detectors with high-resolution and a parallel plate gas chamber, triggered by various scintillating detectors located along the beamline. Experimental observation of volume reflection with 400 GeV/c protons proved true with a deflection angle of (10.4 +/- 0.5) mu rad with respect to the unperturbed beam, with a silicon crystal whose (111) planes were parallel to the beam

    Amplitude analysis of the B(s)0K0K0B^0_{(s)} \to K^{*0} \overline{K}^{*0} decays and measurement of the branching fraction of the B0K0K0B^0 \to K^{*0} \overline{K}^{*0} decay

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    International audienceThe B0K0K0 {B}^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} and Bs0K0K0 {B}_s^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} decays are studied using proton-proton collision data corresponding to an integrated luminosity of 3 fb1^{−1}. An untagged and timeintegrated amplitude analysis of B_{( s}_{)}^{0}  → (K+^{+}π^{−})(K^{−}π+^{+}) decays in two-body invariant mass regions of 150 MeV/c2^{2} around the K0^{∗0} mass is performed. A stronger longitudinal polarisation fraction in the B0K0K0 {B}^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} decay, fL_{L} = 0.724 ± 0.051 (stat) ± 0.016 (syst), is observed as compared to fL_{L} = 0.240 ± 0.031 (stat) ± 0.025 (syst) in the Bs0K0K0 {B}_s^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} decay. The ratio of branching fractions of the two decays is measured and used to determine B(B0K0K0)=(8.0±0.9(stat)±0.4(syst))×107 \mathrm{\mathcal{B}}\left({B}^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0}\right)=\left(8.0\pm 0.9\left(\mathrm{stat}\right)\pm 0.4\left(\mathrm{syst}\right)\right)\times {10}^{-7}

    Measurement of CPCP-violating and mixing-induced observables in Bs0ϕγB_s^0 \to \phi\gamma decays

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    International audienceA time-dependent analysis of the Bs0→ϕγ decay rate is performed to determine the CP -violating observables Sϕγ and Cϕγ and the mixing-induced observable AϕγΔ. The measurement is based on a sample of pp collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3  fb-1 at center-of-mass energies of 7 and 8 TeV. The measured values are Sϕγ=0.43±0.30±0.11, Cϕγ=0.11±0.29±0.11, and AϕγΔ=-0.67-0.41+0.37±0.17, where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables S and C in radiative Bs0 decays. The results are consistent with the standard model predictions

    Observation of an excited Bc+B_c^+ state

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    International audienceUsing pp collision data corresponding to an integrated luminosity of 8.5  fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+)  MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc*(2S31)+ state reconstructed without the low-energy photon from the Bc*(1S31)+→Bc+γ decay following Bc*(2S31)+→Bc*(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+)  MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date

    Measurement of bb hadron fractions in 13 TeV pppp collisions

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    International audienceThe production fractions of B¯s0 and Λb0 hadrons, normalized to the sum of B- and B¯0 fractions, are measured in 13 TeV pp collisions using data collected by the LHCb experiment, corresponding to an integrated luminosity of 1.67  fb-1. These ratios, averaged over the b hadron transverse momenta from 4 to 25 GeV and pseudorapidity from 2 to 5, are 0.122±0.006 for B¯s0, and 0.259±0.018 for Λb0, where the uncertainties arise from both statistical and systematic sources. The Λb0 ratio depends strongly on transverse momentum, while the B¯s0 ratio shows a mild dependence. Neither ratio shows variations with pseudorapidity. The measurements are made using semileptonic decays to minimize theoretical uncertainties. In addition, the ratio of D+ to D0 mesons produced in the sum of B¯0 and B- semileptonic decays is determined as 0.359±0.006±0.009, where the uncertainties are statistical and systematic
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