1,173 research outputs found
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
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
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 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
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
A study of CP violation in the decays B±â[K+K-Ï+Ï-]Dh± (h= K, Ï) and B±â[Ï+Ï-Ï+Ï-]Dh±
The first study of CP violation in the decay mode B±â[K+K-Ï+Ï-]Dh± , with h= K, Ï , is presented, exploiting a data sample of protonâproton collisions collected by the LHCb experiment that corresponds to an integrated luminosity of 9 \,fb - 1 . The analysis is performed in bins of phase space, which are optimised for sensitivity to local CP asymmetries. CP -violating observables that are sensitive to the angle Îł of the Unitarity Triangle are determined. The analysis requires external information on charm-decay parameters, which are currently taken from an amplitude analysis of LHCb data, but can be updated in the future when direct measurements become available. Measurements are also performed of phase-space integrated observables for B±â[K+K-Ï+Ï-]Dh± and B±â[Ï+Ï-Ï+Ï-]Dh± decays
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