Roadmap for selected key measurements of LHCb

379 pagesSix of the key physics measurements that will be made by the LHCb experiment, concerning CP asymmetries and rare B decays, are discussed in detail. The "road map" towards the precision measurements is presented, including the use of control channels and other techniques to understand the performance of the detector with the first data from the LHC

Measurements of the Branching fractions for B_(s) -> D_(s)πππ and Λ_b^0 -> Λ_c^+πππ

Branching fractions of the decays $H_b\to H_c\pi^-\pi^+\pi^-$ relative to $H_b\to H_c\pi^-$ are presented, where $H_b$ ($H_c$) represents B^0-bar($D^+$), $B^-$ ($D^0$), B_s^0-bar ($D_s^+$) and $\Lambda_b^0$ ($\Lambda_c^+$). The measurements are performed with the LHCb detector using 35${\rm pb^{-1}}$ of data collected at $\sqrt{s}=7$ TeV. The ratios of branching fractions are measured to be B(B^0-bar -> D^+\pi^-\pi^+\pi^-)/ B(B^0-bar -> D^+\pi^-) = 2.38\pm0.11\pm0.21 B(B^- -> D^0\pi^-\pi^+\pi^-) / B(B^- -> D^0\pi^-) = 1.27\pm0.06\pm0.11 B(B_s^0-bar -> D_s^+\pi^-\pi^+\pi^-) / B(B_s^0-bar -> D_s^+\pi^-) = 2.01\pm0.37\pm0.20 B(\Lambda_b^0->\Lambda_c^+\pi^-\pi^+\pi^-) / B(\Lambda_b^0 -> \Lambda_c^+\pi^-) = 1.43\pm0.16\pm0.13. We also report measurements of partial decay rates of these decays to excited charm hadrons. These results are of comparable or higher precision than existing measurements

First observation of Bs -> J/psi f0(980) decays

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the hadronic decay Bs -> J/psi f0(980) is observed. This CP eigenstate mode could be used to measure mixing-induced CP violation in the B_s system. Using a fit to the pi+ pi- mass spectrum with interfering resonances gives R_{f0/phi} = [Gamma(Bs -> J/psi f0, f0 -> pi+ pi-)]/[Gamma(Bs -> J/psi phi, phi -> K+K-)] = 0.252^{+0.046+0.027}_{-0.032-0.033}, where the uncertainties are statistical and systematic, respectively

Determination of f_s/f_d for 7 TeV pp collisions and a measurement of the branching fraction of the decay Bd->D-K+

The relative abundance of the three decay modes $B_d \to D^- K^+$, $B_d \to D^- \pi^+$ and $B_s \to D_s^- \pi^+$ produced in 7 TeV $pp$ collisions at the LHC is determined from data corresponding to an integrated luminosity of 35 pb$^{-1}$. The branching fraction of $B_d \to D^- K^+$ is found to be $\cal B (B_d \to D^- K^+) = (2.01 \pm 0.18^{\textrm{stat}} \pm 0.14^{\textrm{syst}})\times 10^{-4}$. The ratio of fragmentation fractions \fsfdt is determined through the relative abundance of $B_s \to D_s^- \pi^+$ to $B_d \to D^- K^+$ and $B_d \to D^-\pi^+$, leading to $f_s/f_d = 0.253 \pm 0.017 \pm 0.017 \pm 0.020$, where the uncertainties are statistical, systematic, and theoretical respectively

Search for the rare decays Bs -->mumu and Bd -->mumu

A search for the decays Bs-->mumu and Bd-->mumu is performed with about 37 pb^{-1} of pp collisions at sqrt{s} = 7 TeV collected by the LHCb experiment at the Large Hadron Collider at CERN. The observed numbers of events are consistent with the background expectations. The resulting upper limits on the branching ratios are BR(Bs-->mumu) < 5.6 x 10^{-8} and BR(Bd-->mumu) <1.5 x 10^{-8} at 95% confidence level

Measurement of the B-s(0) -> J/psi K-S(0) branching fraction

The B s0→J/ψK S0 branching fraction is measured in a data sample corresponding to 0.41fb -1 of integrated luminosity collected with the LHCb detector at the LHC. This channel is sensitive to the penguin contributions affecting the sin2β measurement from B 0→J/ψK S0. The time-integrated branching fraction is measured to be B(B S0→J/ψK S0)=(1.83±0.28)×10 -5. This is the most precise measurement to date. © 2012 CERN

Measurement of the ratio of branching fractions B(B-0 -> K*(0)gamma)/B(B-s(0) -> phi gamma)

The ratio of branching fractions of the radiative B decays B0→K *0γ and B0s→φγ has been measured using 0.37fb -1 of pp collisions at a center of mass energy of √s=7TeV, collected by the LHCb experiment. The value obtained is B(B0→K *0γ)B(B0s→φγ)=1.12±0.08- 0.04-0.08+0.06+0.09, where the first uncertainty is statistical, the second systematic, and the third is associated with the ratio of fragmentation fractions f s/f d. Using the world average for B(B0→K *0γ)=(4.33±0.15)×10 -5, the branching fraction B(B0s→φγ) is measured to be (3.9±0.5)×10 -5, which is the most precise measurement to date. © 2012 CERN

Measurements of the branching fractions and CP asymmetries of B-+/- -> J/psi pi(+/-) and B-+/- -> psi(2S)pi(+/-) decays

A study of B ±→J/ψπ ± and B ±→ψ(2S)π ± decays is performed with data corresponding to 0.37fb -1 of proton-proton collisions at √s=7TeV. Their branching fractions are found to be B(B ±→J/ψπ ±)=(3.88±0. 11±0.15)×10 -5andB(B ±→ψ(2S) π ±)=(2.52±0.26±0.15)×10 -5,where the first uncertainty is related to the statistical size of the sample and the second quantifies systematic effects. The measured CP asymmetries in these modes are ACPJ/ψπ=0.005±0.027±0. 011andACPψ(2S)π=0.048±0.090±0.011 with no evidence of direct CP violation seen. © 2012 CERN