2,173 research outputs found
Measurement of forward Z â e+eâ production sâs=8 TeV
A measurement of the cross-section for Z-boson production in the forward region of pp collisions at 8 TeV centre-of-mass energy is presented. The measurement is based on a sample of Z â e+eâ decays reconstructed using the LHCb detector, corresponding to an integrated luminosity of 2.0 fbâ1. The acceptance is defined by the requirements 2.0 20 GeV for the pseudorapidities and transverse momenta of the leptons. Their invariant mass is required to lie in the range 60-120 GeV. The cross-section is determined to beS
Precise measurements of the properties of the B1(5721)0,+ and B *2(5747)0,+ states and observation of B+,0Ïâ,+ mass structures
Invariant mass distributions of B+Ïâ and B0Ï+ combinations are investigated in order to study excited B mesons. The analysis is based on a data sample corresponding to 3.0 fbâ1 of pp collision data, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses and widths of the B1(5721)0,+ and B2(5747)0,+ states are reported. Clear enhancements, particularly prominent at high pion transverse momentum, are seen over background in the mass range 5850-6000 MeV in both B+Ïâ and B0Ï+ combinations. The structures are consistent with the presence of four excited B mesons, labelled B J (5840)0,+ and B J (5960)0,+, whose masses and widths are obtained under different hypotheses for their quantum numbersS
Observation of the B0âÏ0Ï0 decay from an amplitude analysis of B0â(Ï+Ïâ)(Ï+Ïâ)decays
Protonâproton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to an integrated luminosity of 3.0fbâ1, are analysed to search for the charmless B0âÏ0Ï0decay. More than 600 B0â(Ï+Ïâ)(Ï+Ïâ)signal decays are selected and used to perform an amplitude analysis, under the assumption of no CP violation in the decay, from which the B0âÏ0Ï0decay is observed for the first time with 7.1 standard deviations significance. The fraction of B0âÏ0Ï0decays yielding a longitudinally polarised final state is measured to be fL=0.745+0.048â0.058(stat) ±0.034(syst). The B0âÏ0Ï0branching fraction, using the B0âÏKâ(892)0decay as reference, is also reported as B(B0âÏ0Ï0)=(0.94±0.17(stat)±0.09(syst)±0.06(BF))Ă10â6S
Study of the rare B0s and B0s decays into the Ï+ÏâÎŒ+ÎŒâfinal state
A search for the rare decays B0sâÏ+ÏâÎŒ+ÎŒâand B0âÏ+ÏâÎŒ+ÎŒâis performed in a data set corresponding to an integrated luminosity of 3.0fbâ1collected by the LHCb detector in protonâproton collisions at centre-of-mass energies of 7 and 8TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5â1.3GeV/c2and with muon pairs that do not originate from a resonance are considered. The first observation of the decay B0sâÏ+ÏâÎŒ+ÎŒâand the first evidence of the decay B0âÏ+ÏâÎŒ+ÎŒâare obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be B(B0sâÏ+ÏâÎŒ+ÎŒâ) =(8.6 ±1.5(stat) ±0.7(syst) ±0.7 (norm)) Ă10â8and B(B0âÏ+ÏâÎŒ+ÎŒâ) =(2.11±0.51(stat)±0.15(syst)±0.16(norm))Ă10â8, where the third uncertainty is due to the branching fraction of the decay B0âJ/Ï(âÎŒ+ÎŒâ)Kâ(892)0(âK+Ïâ), used as a normalisation.S
Measurement of the CP-violating phase ÎČin B0âJ/ÏÏ+Ïâdecays and limits on penguin effects
Time-dependent CPviolation is measured in the (â)B0âJ/ÏÏ+Ïâchannel for each Ï+Ïâresonant final state using data collected with an integrated luminosity of 3.0fbâ1in ppcollisions using the LHCb detector. The final state with the largest rate, J/ÏÏ0(770), is used to measure the CP-violating angle 2ÎČeffto be (41.7 ±9.6+2.8â6.3)âŠ.This result can be used to limit the size of penguin amplitude contributions to CPviolation measurements in, for example, (â)B0sâJ/ÏÏdecays. Assuming approximate SU(3) flavour symmetry and neglecting higher order diagrams, the shift in the CP-violating phase Ïsis limited to be within the interval [â1.05âŠ, +1.18âŠ] at 95% confidence level. Changes to the limit due to SU(3) symmetry breaking effects are also discussed.S
Study of the kinematic dependences of Î 0b production in pp collisions and a measurement of the Î 0bâââÎ +c Ï â branching fraction
The kinematic dependences of the relative production rates, fÎ0b/fd, of Î 0b baryons and B 0 mesons are measured using Î 0bâââÎ +c Ï â and BÂŻ0 âD+Ïâ decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fbâ1 at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, p T, and pseudorapidity, η, of the beauty hadron, in the studied kinematic region 1.5 < p T < 40 GeV/c and 2 < η < 5. Using a previous LHCb measurement of fÎ0b/fd in semileptonic decays, the branching fraction âŹ(Î 0bâââÎ +c Ï â) =â(4.30â±â0.03 +â0.12ââ0.11â±â0.26â±â0.21) Ă 10ââ3 is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of fÎ0b/fd and the fourth is due to the b BÂŻ0 âD+Ïâ branching fraction. This is the most precise measurement of a Î 0b branching fraction to date.S
Measurement of the inelastic pp cross-section at a centre-of-mass energy of âs = 7 TeV
The cross-section for inelastic proton-proton collisions, with at least one prompt long-lived charged particle of transverse momentum p T > 0.2GeV/c in the pseudorapidity range 2.0 < η < 4.5, is measured by the LHCb experiment at a centre-of-mass energy of âs = 7 TeV. The cross-section in this kinematic range is determined to be Ï accinel = 55.0 ± 2.4 mb with an experimental uncertainty that is dominated by systematic contributions. Extrapolation to the full phase space, using PYTHIA 6, yields Ï inel = 66.9 ± 2.9 ± 4.4 mb, where the first uncertainty is experimental and the second is due to the extrapolation.S
Measurement of CP violation parameters and polarisation fractions in B0sâJ/ÏKâ0 decays
The first measurement of CP asymmetries in the decay B0sâJ/ÏKâ(892)0 and an updated measurement of its branching fraction and polarisation fractions are presented. The results are obtained using data corresponding to an integrated luminosity of 3.0 fbâ1 of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Together with constraints from B 0 â J/Ï Ï 0, the results are used to constrain additional contributions due to penguin diagrams in the CP -violating phase Ï s , measured through B 0s decays to charmonium.S
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