1,327 research outputs found
Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at âs=7 TeV
Bose-Einstein correlations of same-sign charged pions, produced in protonproton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected
by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the
form of an enhancement of pairs of like-sign charged pions with small four-momentum
difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source
is investigated, determining both the correlation radius and the chaoticity parameter. The
measured correlation radius is found to increase as a function of increasing charged-particle
multiplicity, while the chaoticity parameter is seen to decreas
Study of charmonium production in b -hadron decays and first evidence for the decay Bs0
Using decays to Ï-meson pairs, the inclusive production of charmonium states in b-hadron decays is studied with pp collision data corresponding to an integrated luminosity of 3.0 fbâ1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Denoting byBC ⥠B(b â C X) Ă B(C â ÏÏ) the inclusive branching fraction of a b hadron to a charmonium state C that decays into a pair of Ï mesons, ratios RC1C2 ⥠BC1 /BC2 are determined as RÏc0ηc(1S) = 0.147 ± 0.023 ± 0.011, RÏc1ηc(1S) =0.073 ± 0.016 ± 0.006, RÏc2ηc(1S) = 0.081 ± 0.013 ± 0.005,RÏc1 Ïc0 = 0.50 ± 0.11 ± 0.01, RÏc2 Ïc0 = 0.56 ± 0.10 ± 0.01and Rηc(2S)ηc(1S) = 0.040 ± 0.011 ± 0.004. Here and below the first uncertainties are statistical and the second systematic.Upper limits at 90% confidence level for the inclusive production of X(3872), X(3915) and Ïc2(2P) states are obtained as RX(3872)Ïc1 < 0.34, RX(3915)Ïc0 < 0.12 andRÏc2(2P)Ïc2 < 0.16. Differential cross-sections as a function of transverse momentum are measured for the ηc(1S) andÏc states. The branching fraction of the decay B0s â ÏÏÏ is measured for the first time, B(B0s â ÏÏÏ) = (2.15±0.54±0.28±0.21B)Ă10â6. Here the third uncertainty is due to the branching fraction of the decay B0s â ÏÏ, which is used for normalization. No evidence for intermediate resonances is seen. A preferentially transverse Ï polarization is observed.The measurements allow the determination of the ratio of the branching fractions for the ηc(1S) decays to ÏÏ and p p asB(ηc(1S)â ÏÏ)/B(ηc(1S)â p p) = 1.79 ± 0.14 ± 0.32
Observation of an Excited Bc+ State
Using 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+Ï+Ï- 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 Bcâ(2S31)+ state reconstructed without the low-energy photon from the Bcâ(1S31)+âBc+Îł decay following Bcâ(2S31)+âBcâ(1S31)+Ï+Ï-. A second state is seen with a global (local) statistical significance of 2.2Ï (3.2Ï) 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 the inelastic pp cross-section at a centre-of-mass energy of 13TeV
The cross-section for inelastic proton-proton collisions at a centre-of-mass energy of 13TeV is measured with the LHCb detector. The fiducial cross-section for inelastic interactions producing at least one prompt long-lived charged particle with momentum p > 2 GeV/c in the pseudorapidity range 2 < η < 5 is determined to be Ï acc = 62:2 ± 0:2 ± 2:5mb. The first uncertainty is the intrinsic systematic uncertainty of the measurement, the second is due to the uncertainty on the integrated luminosity. The statistical uncertainty is negligible. Extrapolation to full phase space yields the total inelastic proton-proton cross-section Ï inel = 75:4 ± 3:0 ± 4:5mb, where the first uncertainty is experimental and the second due to the extrapolation. An updated value of the inelastic cross-section at a centre-of-mass energy of 7TeV is also reported
Updated Determination of Dâ°âDÂŻâ°Mixing and CP Violation Parameters with Dâ°âKâșÏâ» Decays
We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of Dâ°âKâșÏâ» to Dâ°âKâ»Ïâș rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of 5.0ââfbâ»Âč recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be xâČÂČ=(3.9±2.7)Ă10â»â”, yâČ=(5.28±0.52)Ă10â»Âł, and R[subscript D]=(3.454±0.031)Ă10â»Âł. Without this assumption, the measurement is performed separately for Dâ° and D[over ÂŻ]â° mesons, yielding a direct CP-violating asymmetry A[subscript D]=(-0.1±9.1)Ă10â»Âł, and magnitude of the ratio of mixing parameters 1.00<|q/p|<1.35 at the 68.3% confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed
Observation of Dâ° Meson Decays to Î âșÏâ»ÎŒâșΌ⻠and KâșKâ»ÎŒâșΌ⻠Final States
The first observation of the Dâ°âÏâșÏâ»ÎŒâșΌ⻠and Dâ°âKâșKâ»ÎŒâșΌ⻠decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to 2ââfbâ»Âč of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay Dâ°âKâ»Ïâș[ÎŒâșÎŒâ»][subscript Ïâ°/Ï], where the two muons are consistent with coming from the decay of a Ïâ° or Ï meson. The results are B(Dâ°âÏâșÏâ»ÎŒâșÎŒâ»)=(9.64±0.48±0.51±0.97)Ă10â»â· and B(Dâ°âKâșKâ»ÎŒâșÎŒâ»)=(1.54±0.27±0.09±0.16)Ă10â»â·, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated
Observation of the Decay Î0bâÎ+cÏâÂŻÎœ
The first observation of the semileptonic b-baryon decay Îb0âÎc+Ï-ÎœÂŻÏ, with a significance of 6.1Ï, is reported using a data sample corresponding to 3 fb-1 of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The Ï- lepton is reconstructed in the hadronic decay to three charged pions. The ratio K=B(Îb0âÎc+Ï-ÎœÂŻÏ)/B(Îb0âÎc+Ï-Ï+Ï-) is measured to be 2.46±0.27±0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Îb0âÎc+Ï-ÎœÂŻÏ)=(1.50±0.16±0.25±0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Îb0âÎc+Ï-Ï+Ï-. The ratio of semileptonic branching fractions R(Îc+)B(Îb0âÎc+Ï-ÎœÂŻÏ)/B(Îb0âÎc+ÎŒ-ÎœÂŻÎŒ) is derived to be 0.242±0.026±0.040±0.059, where the external branching fraction uncertainty from the channel Îb0âÎc+ÎŒ-ÎœÂŻÎŒ contributes to the last term. This result is in agreement with the standard model prediction
Measurement of branching fractions of charmless four-body Î<sub>b</sub> <sup>0</sup> and Î<sub>b</sub> <sup>0</sup> decays
A search for charmless four-body decays of Îb 0 and Îb 0 baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb experiment and corresponds to an integrated luminosity of 3 fbâ1. Six decay modes are observed, among which Îb 0 â pKâÏ+Ïâ,Îb 0 â pKâK+Kâ,Îb 0 â pKâÏ+Ïâ and Îb 0 â pKâÏ+Kâ are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the Îb 0 baryon) are determined relative to the Îb 0 â Îc +Ïâ decay.[Figure not available: see fulltext.].</p
Updated determination of D 0 - D 0 mixing and C P violation parameters with D 0 â K + Ï -
We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of D0âK+Ï- to D0âK-Ï+ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of 5.0 fb-1 recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be xâČ2=(3.9±2.7)Ă10-5, yâČ=(5.28±0.52)Ă10-3, and RD=(3.454±0.031)Ă10-3. Without this assumption, the measurement is performed separately for D0 and D0 mesons, yielding a direct CP-violating asymmetry AD=(-0.1±9.1)Ă10-3, and magnitude of the ratio of mixing parameters 1.00<|q/p|<1.35 at the 68.3% confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed
Prompt and nonprompt J/Ï production and nuclear modification in pPb collisions at s<sub>NN</sub>=8.16 TeV
The production of J/Ï mesons is studied in proton-lead collisions at the centre-of-mass energy per nucleon pair sNN=8.16 TeV with the LHCb detector at the LHC. The double differential cross-sections of prompt and nonprompt J/Ï production are measured as a function of the J/Ï transverse momentum and rapidity in the nucleonânucleon centre-of-mass frame. Forward-to-backward ratios and nuclear modification factors are determined. The results are compared with theoretical calculations based on collinear factorisation using nuclear parton distribution functions, on the colour glass condensate or on coherent energy loss models.</p
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