904 research outputs found
Measurement of Ï production in pp collisions at âs=13 TeV
The production cross-sections of Ï(1S), Ï(2S) and Ï(3S) mesons in proton-proton collisions at âs=13 TeV are measured with a data sample corresponding to an integrated luminosity of 277 ± 11 pbâ1 recorded by the LHCb experiment in 2015. The Ï mesons are reconstructed in the decay mode Ï â ÎŒ+ÎŒâ. The differential production cross-sections times the dimuon branching fractions are measured as a function of the Ï transverse momentum, pT, and rapidity, y, over the range 0 < pT < 30 GeV/c and 2.0 < y < 4.5. The ratios of the cross-sections with respect to the LHCb measurement at sâ=8 TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.S
Measurement of the CKM angle Îł using B± â DK± with DâââK0SÏ+Ïâ,âK0SK+Kâ decays
A binned Dalitz plot analysis of B± â DK± decays, with DâââK 0SÏ+ÏââandâDâââK 0SK+Kâ, is used to perform a measurement of the CP-violating observables x± and y±, which are sensitive to the Cabibbo-Kobayashi-Maskawa angle Îł. The analysis is performed without assuming any D decay model, through the use of information on the strong-phase variation over the Dalitz plot from the CLEO collaboration. Using a sample of proton-proton collision data collected with the LHCb experiment in 2015 and 2016, and corresponding to an integrated luminosity of 2.0 fbâ1, the values of the CP violation parameters are found to be xâ = (9.0 ± 1.7 ± 0.7 ± 0.4) Ă 10â2, yâ = (2.1 ± 2.2 ± 0.5 ± 1.1) Ă 10â2, x+ = (â7.7 ± 1.9 ± 0.7 ± 0.4) Ă 10â2, and y+ = (â1.0 ± 1.9 ± 0.4 ± 0.9) Ă 10â2. The first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty (on the strong-phase measurements. These values are used to obtain Îłâ=â(87 +â11ââ12)â,ârBâ=â0.086 +â0.013ââ0.014, and ÎŽB = (101±11)°, where rB is the ratio between the suppressed and favoured B-decay amplitudes and ÎŽB is the corresponding strong-interaction phase difference. This measurement is combined with the result obtained using 2011 and 2012 data collected with the LHCb experiment, to give Îłâ=â(80 +â10ââ9)â, rB = 0.080 ± 0.011, and ÎŽB = (110 ± 10)°.S
Observation of the ÎâbâJ/ÏÎKâdecay
The observation of the decay ÎâbâJ/ÏÎKâis reported, using a data sample corresponding to an integrated luminosity of 3 fbâ1, collected by the LHCb detector in ppcollisions at centre-of-mass energies of 7and 8 TeV. The production rate of Îâbbaryons detected in the decay ÎâbâJ/ÏÎKâis measured relative to that of Î0bbaryons using the decay Î0bâJ/ÏÎ. Integrated over the b-baryon transverse momentum pT<25 GeV/cand rapidity 2.0 <y <4.5, the measured ratio is
fÎ
â
b
fÎ0
b
B(Î
â
b
â J/ÏÎKâ
)
B(Î0
b
â J/ÏÎ)
= (4.19±0.29 (stat)± 0.15 (syst))Ă10â2,
where fÎâband fÎ0bare the fragmentation fractions of b âÎâband b âÎ0btransitions, and Brepresents the branching fraction of the corresponding b-baryon decay. The mass difference between Îâband Î0bbaryons is measured to be
M(Î
â
b )â M(Î0
b ) = 177.08±0.47 (stat)± 0.16 (syst)MeV/c2.S
Measurement of D ±s production asymmetry in pp collisions at âs=7 and 8 TeV
The inclusive D ±s production asymmetry is measured in pp collisions collected by the LHCb experiment at centre-of-mass energies of âs=7 and 8 TeV. Promptly produced D ±s mesons are used, which decay as D ±sâââÏϱ, with ÏâââK+Kâ. The measurement is performed in bins of transverse momentum, pT, and rapidity, y, covering the range 2.5 < pT < 25.0 GeV/c and 2.0 < y < 4.5. No kinematic dependence is observed. Evidence of nonzero D ±s production asymmetry is found with a significance of 3.3 standard deviations.S
Measurement of the J/Ï pair production cross-section in pp collisions at âs=13 TeV
The production cross-section of J/Ï pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of âs=13 TeV, corresponding to an integrated luminosity of 279 ±11 pbâ1. The measurement is performed for J/Ï mesons with a transverse momentum of less than 10 GeV/c in the rapidity range 2.0 < y < 4.5. The production cross-section is measured to be 15.2 ± 1.0 ± 0.9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/Ï pair are measured and compared to theoretical predictions.S
Central exclusive production of J/Ï and Ï(2S) mesons in pp collisions at âs=13 TeV
Measurements are reported of the central exclusive production of J/Ï and Ï(2S) mesons in pp collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2.0 < η < 4.5, are measured to be
ÏJ/ÏâÎŒ+ÎŒâ=435±18±11±17 pbÏÏ(2S)âÎŒ+ÎŒâ=11.1±1.1±0.3±0.4 pb.
The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.S
Measurements of prompt charm production cross-sections in pp collisions at âs=5 TeV
Production cross-sections of prompt charm mesons are measured using data from pp collisions at the LHC at a centre-of-mass energy of 5 TeV. The data sample corresponds to an integrated luminosity of 8.60 ± 0.33 pbâ1 collected by the LHCb experiment. The production cross-sections of D 0, D +, D +s, and D â+ mesons are measured in bins of charm meson transverse momentum, p T, and rapidity, y. They cover the rapidity range 2.0 < y < 4.5 and transverse momentum ranges 0 < p T < 10 GeV/c for D 0 and D + and 1 < p T < 10 GeV/c for D +s and D â+ mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of 1 < p T < 8 GeV/c are determined to be
Ï(ppâD0X)=1004±3±54ÎŒb,Ï(ppâD+X)=402±2±30ÎŒb,Ï(ppâD+sX)=170±4±16ÎŒb,Ï(ppâDâ+X)=421±5±36ÎŒb,
where the uncertainties are statistical and systematic, respectively.S
Observation of the decay BÂŻ0sâÏc2K+Kâ in the Ï mass region
The BÂŻ0sâÏc2K+Kâ decay mode is observed and its branching fraction relative to the corresponding Ïc1 decay mode, in a ±15 MeV/c2 window around the Ï mass, is found to be
B(BÂŻ0sâÏc2K+Kâ)B(BÂŻ0sâÏc1K+Kâ)=(17.1±3.1±0.4±0.9)%,
where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the branching fractions of radiative Ïc decays. The decay mode BÂŻ0sâÏc1K+Kâ allows the B0s mass to be measured as
m(B0s)=5366.83±0.25±0.27 MeV/c2,
where the first uncertainty is statistical and the second systematic. A combination of this result with other LHCb determinations of the B 0s mass is made.S
Evidence for an ηc(1S)Ïâ resonance in B0 â ηc(1S)K+Ïâ decays
A Dalitz plot analysis of B0 â ηc(1S)K +Ïâ
decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies
of âs = 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 4.7 fbâ1. A satisfactory description of
the data is obtained when including a contribution representing an exotic ηc(1S)Ïâ resonant state. The significance
of this exotic resonance is more than three standard deviations, while its mass and width are 4096 ± 20 +18
â22 MeV and
152±58 +60
â35 MeV, respectively. The spin-parity assignments
J P = 0+ and J P = 1â are both consistent with the data. In
addition, the first measurement of the B0 â ηc(1S)K +Ïâ
branching fraction is performed and gives
B(B0â ηc(1S)K +Ïâ) = (5.73 ± 0.24 ± 0.13 ± 0.66) Ă 10â4,
where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external
branching fractionsS
Study of prompt D0 meson production in pPb collisions at âsNN=5 TeV
Production of prompt D0 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 nbâ1 recorded at a nucleon-nucleon centre-of-mass energy of âsNN=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 â < 4.0 and â5.0 < y â < â2.5 in the nucleon-nucleon centre-of-mass system.S
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