2,145 research outputs found
A comparison of CPU and GPU implementations for the LHCb experiment run 3 trigger
The Large Hadron Collider beauty (LHCb) experiment at CERN is undergoing an upgrade in preparation for the Run 3 data collection period at the Large Hadron Collider (LHC). As part of this upgrade, the trigger is moving to a full software implementation operating at the LHC bunch crossing rate. We present an evaluation of a CPU-based and a GPU-based implementation of the first stage of the high-level trigger. After a detailed comparison, both options are found to be viable. This document summarizes the performance and implementation details of these options, the outcome of which has led to the choice of the GPU-based implementation as the baseline
Compatibility and combination of world W -boson mass measurements
The compatibility of W-boson mass measurements performed by the ATLAS, LHCb, CDF, and D0 experiments is studied using a coherent framework with theory uncertainty correlations. The measurements are combined using a number of recent sets of parton distribution functions (PDF), and are further combined with the average value of measurements from the Large ElectronâPositron collider. The considered PDF sets generally have a low compatibility with a suite of global rapidity-sensitive DrellâYan measurements. The most compatible set is CT18 due to its larger uncertainties. A combination of all mW measurements yields a value of mW=80, 394.6±11.5 MeV with the CT18 set, but has a probability of compatibility of 0.5% and is therefore disfavoured. Combinations are performed removing each measurement individually, and a 91% probability of compatibility is obtained when the CDF measurement is removed. The corresponding value of the W boson mass is 80, 369.2±13.3 MeV, which differs by 3.6Ï from the CDF value determined using the same PDF set
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
Evidence for the decay B0SâKÂŻâ0ÎŒ+ÎŒâ
A search for the decay B0SâKÂŻâ0ÎŒ+ÎŒâ is presented using data sets corresponding to 1.0, 2.0 and 1.6 fbâ1 of integrated luminosity collected during pp collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the B0SâKÂŻâ0ÎŒ+ÎŒâ decay is determined to be B(B0sâKÂŻâ0ÎŒ+ÎŒâ)=[2.9±1.0(stat)±0.2(syst)±0.3(norm)]Ă10â8, where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement.S
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