The Large Hadron Collider beauty experiment (LHCb) is a single-arm forward spectrometer dedicated to the study of B-meson decays in p - p collisions at the Large Hadron Collider (LHC). The LHCb ...detector has excellent tracking and particle identification capabilities. The LHCb Silicon Tracker (ST) is composed of two silicon micro-strip detectors with long readout strips. The performance of these two detectors with the first high energy p - p collisions are presented here. A detailed study of the detectors intrinsic resolution and efficiency has been performed along with precise time alignment using collision data. The latest Silicon Tracker performance results and comparison to expectations are presented.
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma and Bs0 phi gamma has been measured using an integrated luminosity of 1.0 fb-1 of pp collision data collected by the LHCb ...experiment at a centre-of-mass energy of sqrt(s)=7 TeV. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.23 +/- 0.06(stat.) +/- 0.04(syst.) +/- 0.10(fs/fd), where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for BR(B0 -> K*0 gamma), the branching fraction BR(Bs0 -> phi gamma) is measured to be (3.5 +/- 0.4) x 10^{-5}. The direct CP asymmetry in B0 -> K*0 gamma decays has also been measured with the same data and found to be A(CP)(B0 -> K*0 gamma) = (0.8 +/- 1.7(stat.) +/- 0.9(syst.))%. Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations.
A search for charmless three-body decays of B0 and B0s mesons with a KS0 meson in the final state is performed using the pp collision data, corresponding to an integrated luminosity of 1.0 /fb, ...collected at a centre-of-mass energy of 7 TeV recorded by the LHCb experiment. Branching fractions of the B0(s) -> KS0 h+ h'- decay modes (h(') = \pi, K), relative to the well measured B0 -> KS0 \pi+ \pi- decay, are obtained. First observation of the decay modes B0s -> KS0 K+/- \pi-/+ and B0s -> KS0 \pi+ \pi- and confirmation of the decay B0 -> KS0 K+/- \pi-/+ are reported. The following relative branching fraction measurements or limits are obtained BF(B0 -> KS0 K+/- \pi-/+) / BF(B0 -> KS0 \pi+ \pi-) = 0.128 +/- 0.017 (stat.) +/- 0.009 (syst.), BF(B0 -> KS0 K+ K-) / BF(B0 -> KS0 \pi+ \pi-) = 0.385 +/- 0.031 (stat.) +/- 0.023 (syst.), BF(B0s -> KS0 \pi+ \pi-) / BF(B0 -> KS0 \pi+ \pi-) = 0.29 \pm 0.06 (stat.) +/- 0.03 (syst.) +/- 0.02 (f_s/f_d), BF(B0s -> KS0 K+/- \pi-/+) / BF(B0 -> KS0 \pi+ \pi-) = 1.48 +/- 0.12 (stat.) +/- 0.08 (syst.) +/- 0.12 (f_s/f_d), BF(B0s -> KS0 K+ K-) / BF(B0 -> KS0 \pi+ \pi-) E 0.004;0.068 at 90% CL.
A study of $D^+\pi^-$, $D^0 \pi^+$ and $D^{*+}\pi^-$ final states is performed using pp collision data, corresponding to an integrated luminosity of 1.0 $fb^{-1}$, collected at a centre-of-mass ...energy of 7 TeV with the LHCb detector. The $D_1(2420)^0$ resonance is observed in the $D^{*+}\pi^-$ final state and the $D^*_2(2460)$ resonance is observed in the $D^+\pi^-$, $D^0 \pi^+$ and $D^{*+}\pi^-$ final states. For both resonances, their properties and spin-parity assignments are obtained. In addition, two natural parity and two unnatural parity resonances are observed in the mass region between 2500 and 2800 MeV. Further structures in the region around 3000 MeV are observed in all the $D^{*+}\pi^-$, $D^+\pi^-$ and $D^0 \pi^+$ final states.
The results of searches for B0(s) -> J/{\psi} p pbar and B+ -> J/{\psi} p pbar {\pi}+ decays are reported. The analysis is based on a data sample, corresponding to an integrated luminosity of 1.0 ...fb^-1 of pp collisions, collected with the LHCb detector. An excess with 2.8 {\sigma} significance is seen for the decay B0s -> J/{\psi} p pbar and an upper limit on the branching fraction is set at the 90 % confidence level: B(B0s -> J/{\psi} p pbar) < 4.8 x 10^-6, which is the first such limit. No significant signals are seen for B0 -> J/{\psi} p pbar and B+ -> J/{\psi} p pbar {\pi}+ decays, for which the corresponding limits are set: B(B0 -> J/{\psi} p pbar) < 5.2 x 10^-7, which significantly improves the existing limit; and B(B+ -> J/{\psi} p pbar {\pi}+) < 5.0 x 10^-7, which is the first limit on this branching fraction.
A key ingredient to searches for physics beyond the Standard Model in $B^{0}_{s}$ mixing phenomena is the measurement of the $B^{0}_{s}$-$\bar{B}^{0}_{s}$ oscillation frequency, which is equivalent ...to the mass difference $\Delta m_{s}$ of the $B^{0}_{s}$ mass eigenstates. Using the world's largest $B^{0}_{s}$ meson sample accumulated in a dataset, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb experiment at the CERN LHC in 2011, a measurement of $\Delta m_{s}$ is presented. A total of about 34,000 $B^{0}_{s}\rightarrowD^{-}_{s}\pi^{+}$ signal decays are reconstructed, with an average decay time resolution of 44 fs. The oscillation frequency is measured to be \mbox{$\Delta m_{s}$ = 17.768 $\pm$ 0.023 (stat) $\pm$ 0.006 (syst) ps$^{-1}$}, which is the most precise measurement to date.
The angular distributions and the partial branching fraction of the decay $B^{0} \rightarrow K^{*0} \mu^+ \mu^-$ are studied using an integrated luminosity of $0.37\,fb^{-1}$ of data collected with ...the LHCb detector. The forward-backward asymmetry of the muons, $A_{\mathrm{FB}}$, the fraction of longitudinal polarisation, $F_{\mathrm{L}}$, and the partial branching fraction, $\mathrm{d}{\mathcal B}/\mathrm{d}q^{2}$, 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 $1.00-6.00{\mathrm{\,Ge\kern -0.1em V}}^2/c^4$, the results are $A_{\mathrm{FB}}=-0.06\,^{+0.13}_{-0.14} \pm 0.04$, $F_{\mathrm{L}}=0.55\pm 0.10\pm 0.03$ and $\mathrm{d}{\mathcal B}/\mathrm{d}q^{2}=(0.42 \pm 0.06\pm 0.03) \times 10^{-7}c^4/{\mathrm{\,Ge\kern -0.1em V}}^2$. In each case, the first error is statistical and the second systematic.
A search for Bs -> mu+ mu- and B0 -> mu+ mu- decays is performed using 1.0 fb^-1 of pp collision data collected at \sqrt{s}=7 TeV with the LHCb experiment at the Large Hadron Collider. For both ...decays the number of observed events is consistent with expectation from background and Standard Model signal predictions. Upper limits on the branching fractions are determined to be BR(Bs -> mu+ mu-) < 4.5 (3.8) x 10^-9 and BR(B0 -> mu+ mu-) < 1.0 (0.81) x 10^-9 at 95% (90%) confidence level.
First observations of the Cabibbo suppressed decays B0bar -->D+ K- pi+ pi- and B- --> D0 K- pi+ pi- are reported using 35 pb^{-1} of data collected with the LHCb detector. Their branching fractions ...are measured with respect to the corresponding Cabibbo favored decays, from which we obtain B(B0bar --> D+ K- pi+ pi-)/B(B0bar --> D+ pi- pi+ pi-)=(5.9\pm1.1\pm0.5) x 10^{-2} and B(B- --> D0 K- pi+ pi-)/B(B- --> D0 pi- pi+ pi-)=(9.4\pm1.3\pm0.9) x 10^{-2}, where the uncertainties are statistical and systematic, respectively. The B- --> D0 K- pi+ pi- decay is particularly interesting, as it can be used in a similar way to B- --> D0 K- to measure the CKM phase gamma.
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