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The LHCb experiment has been taking data at the Large Hadron Collider (LHC) at CERN since the end of 2009. One of its key detector components is the Ring-Imaging Cherenkov (RICH) system. This provides charged particle identification over a wide momentum range, from 2–100 GeV/c. The operation and control, software, and online monitoring of the RICH system are described. The particle identification performance is presented, as measured using data from the LHC. Excellent separation of hadronic particle types (π, K, p) is achieved.
Using data collected with the LHCb detector in proton–proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays B¯s0→Ds*Xμ-v¯ and B¯s0→D0K+Xμ-v¯ are detected. Two structures are observed in the D0K+ mass spectrum at masses consistent with the known Ds1+(2536) and Ds2*(2573)+ mesons. The measured branching fractions relative to the total B¯s0 semileptonic rate are B(B¯s0→Ds2*+Xμ-v¯)/B(B¯s0→D0→Xμ-v¯)=(3.3±1.0±0.4)%, B(B¯s0→Ds1*+Xμ-v¯)/B(B¯s0→D0→Xμ-v¯)= (5.4±1.2±0.5)%, where the first uncertainty is statistical and the secon...
We present a measurement of the time-dependent CP-violating asymmetry in Bs0→J/ψϕ decays, using data collected with the LHCb detector at the LHC. The decay time distribution of Bs0→J/ψϕ is characterized by the decay widths ΓH and ΓL of the heavy and light mass eigenstates, respectively, of the Bs0-B̅ s0 system and by a CP-violating phase ϕs. In a sample of about 8500 Bs0→J/ψϕ events isolated from 0.37  fb-1 of pp collisions at √s=7  TeV, we measure ϕs=0.15±0.18(stat)±0.06(syst)  rad. We also find an average Bs0 decay width Γs≡(ΓLH)/2=0.657±0.009(stat)±0.008(syst)  ps-1 and a decay width difference ΔΓs≡ΓLH=0.123±0.029(stat)±0.011(syst)  ps-1. Our measurement is insensitive to the transformation (ϕs,ΔΓs)...
So far only the channel has been used. Here we report on a measurement using an LHCb data sample of 0.41 fb−1, in the CP odd eigenstate J/ψf0(980), where f0(980)→π+π−. A time-dependent fit of the data with the lifetime and the difference in widths of the heavy and light eigenstates constrained to the values obtained from yields a value of the CP violating phase of −0.44±0.44±0.02 rad, consistent with the Standard Model expectation.
A search for the decays View the MathML source and B0→μ+μ− is performed with 0.37 fb−1 of pp collisions at View the MathML source collected by the LHCb experiment in 2011. The upper limits on the branching fractions are View the MathML source and B(B0→μ+μ−)<3.6×10−9 at 95% confidence level. A combination of these results with the LHCb limits obtained with the 2010 dataset leads to View the MathML source and B(B0→μ+μ−)<3.2×10−9 at 95% confidence level.
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