The interference between the K+K- S-wave and P-wave amplitudes in B_s -> J/psi K+K- decays with the K+K- pairs in the region around the phi(1020) resonance is used to determine the variation of the ...difference of the strong phase between these amplitudes as a function of K+K- invariant mass. Combined with the results from our CP asymmetry measurements in B_s -> J/psi phi decays, we conclude that the B_s mass eigenstate that is almost CP =+1 is lighter and decays faster than the mass eigenstate that is almost CP =-1. This determines the sign of the decay width difference DeltaGamma_s == Gamma_L -Gamma_H to be positive. Our result also resolves the ambiguity in the past measurements of the CP violating phase phi_s to be close to zero rather than pi. These conclusions are in agreement with the Standard Model expectations.
The charged-particle production ratios p¯/p, K −/K +, π −/π +, (p+p¯)/(π++π−), (K ++K −)/(π ++π −) and (p+p¯)/(K++K−) are measured with the LHCb detector using 0.3 nb−1 of pp collisions delivered by ...the LHC at s√=0.9 TeV and 1.8 nb−1 at s√=7 TeV. The measurements are performed as a function of transverse momentum p T and pseudorapidity η. The production ratios are compared to the predictions of several Monte Carlo generator settings, none of which are able to describe adequately all observables. The ratio p¯/p is also considered as a function of rapidity loss, Δy≡y beam−y, and is used to constrain models of baryon transport.
The production of B ± mesons in proton-proton collisions at s√ = 7 TeV is studied using 35 pb−1 of data collected by the LHCb detector. The B ± mesons are reconstructed exclusively in the B ± → J/ψK ...± mode, with J/ψ → μ + μ −. The differential production cross-section is measured as a function of the B ± transverse momentum in the fiducial region 0 < p T < 40 GeV/c and with rapidity 2.0 < y < 4.5. The total cross-section, summing up B + and B −, is measured to be σ(pp → B ± X, 0 < p T < 40 GeV/c, 2.0 < y < 4.5) = 41.4 ± 1.5 (stat.) ± 3.1 (syst.) μb.
The angular distributions and the partial branching fraction of the decay B0→K*0μ+μ− are studied by using an integrated luminosity of 0.37 fb−1 of data collected with the LHCb detector. The ...forward-backward asymmetry of the muons, AFB, the fraction of longitudinal polarization, FL, and the partial branching fraction dB/dq2 are determined as a function of the dimuon invariant mass. The measurements are in good agreement with the standard model predictions and are the most precise to date. In the dimuon invariant mass squared range 1.00-6.00 GeV2/c4, the results are AFB=−0.06+0.13−0.14±0.04, FL=0.55±0.10±0.03, and dB/dq2=(0.42±0.06±0.03)×10−7 c4/GeV2. In each case, the first error is statistical and the second systematic.
The prompt production of the charmonium χc1 and χc2 mesons has been studied in proton–proton collisions at the Large Hadron Collider at a centre-of-mass energy of s=7 TeV. The χc mesons are ...identified through their decays χc→J/ψγ with J/ψ→μ+μ− using 36 pb−1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two χc spin states, σ(χc2)/σ(χc1), has been determined as a function of the J/ψ transverse momentum, pTJ/ψ, in the range from 2 to 15 GeV/c. The results are in agreement with the next-to-leading order non-relativistic QCD model at high pTJ/ψ and lie consistently above the pure leading-order colour-singlet prediction.
I will review a selection of LHCb results on the production of heavy quarkonium states in pp collisions, including recent results on J/psi and Upsilon(nS)(n = 1, 2, 3) production at radicals = 8 TeV, ...as well as preliminary results on J/psi production in proton-lead collisions at radicals sub(NN) = 5 TeV.
A search for the lepton-flavor-violating decays B 0 s → e ± μ ∓ and B 0 → e ± μ ∓ is performed with a data sample, corresponding to an integrated luminosity of 1.0 fb − 1 of p p collisions at √ s ...= 7 TeV , collected by the LHCb experiment. The observed number of B 0 s → e ± μ ∓ and B 0 → e ± μ ∓ candidates is consistent with background expectations. Upper limits on the branching fractions of both decays are determined to be B ( B 0 s → e ± μ ∓ ) < 1.1 ( 1.4 ) × 10 − 8 and B ( B 0 → e ± μ ∓ ) < 2.8 ( 3.7 ) × 10 − 9 at 90% (95%) confidence level (C.L.). These limits are a factor of 20 lower than those set by previous experiments. Lower bounds on the Pati-Salam leptoquark masses are also calculated, M LQ ( B 0 s → e ± μ ∓ ) > 101 TeV / c 2 and M LQ ( B 0 → e ± μ ∓ ) > 126 TeV / c 2 at 95% C.L., and are a factor of 2 higher than the previous bounds.
The LHCb Experiment is a hadronic precision experiment at the LHC accelerator aimed at mainly studying b-physics by profiting from the large b-anti-b-production at LHC. The challenge of high trigger ...efficiency has driven the choice of a readout architecture allowing the main event filtering to be performed by a software trigger with access to all detector information on a processing farm based on commercial multi-core PCs. The readout architecture therefore features only a relatively relaxed hardware trigger with a fixed and short latency accepting events at 1 MHz out of a nominal proton collision rate of 30 MHz, and high bandwidth with event fragment assembly over Gigabit Ethernet. A fast central system performs the entire synchronization, event labelling and control of the readout, as well as event management including destination control, dynamic load balancing of the readout network and the farm, and handling of special events for calibrations and luminosity measurements. The event filter farm processes the events in parallel and reduces the physics event rate to about 2 kHz which are formatted and written to disk before transfer to the offline processing. A spy mechanism allows processing and reconstructing a fraction of the events for online quality checking. In addition a 5 Hz subset of the events are sent as express stream to offline for checking calibrations and software before launching the full offline processing on the main event stream.
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