Alignment of the LHCb detector with Kalman filter fitted tracks

The LHCb detector, operating at the Large Hadron Collider at CERN, is a single arm spectrometer optimised for the detection of forward b and anti-b production for b physics studies. The reconstruction of vertices and tracks is done by silicon micro-strip and gaseous straw-tube based detectors. To obtain excellent momentum, mass and vertex resolutions, the detectors need to be aligned well within the hit resolution for a given detector. We present a general and easy to configure alignment framework which uses the closed from method of alignment with Kalman filter fitted tracks to determine the alignment parameters. This allows us to use the standard LHCb track model and fit, and correctly take complexities such as multiple scattering and energy loss corrections into account. With this framework it is possible to align any detector for any degree of freedom

Alignment of LHCb tracking stations with tracks fitted with a Kalman filter

The LHCb detector, operating at the Large Hadron Collider at CERN, is a single arm spectrometer optimized for the detection of the forward b anti-b production for b physics studies. The reconstruction of vertices and tracks is done by silicon micro-strips and gaseous straw-tube based detectors. In order to achieve good mass resolution for resonances the tracking detectors should be aligned to a precision of the order of ten microns. A software framework has been developed to achieve these goals and has been tested in various configurations. After a description of the software, we present alignment results and show in particular for the first time that a global $\chi^2$ solving for alignment using a locally parameterized track trajectory can be achieved

Application of vertex and mass constraints in track-based alignment

The software alignment of planar tracking detectors using samples of charged particle trajectories may lead to global detector distortions that affect vertex and momentum resolution. We present an alignment procedure that constrains such distortions by making use of samples of decay vertices reconstructed from two or more trajectories and putting constraints on their invariant mass. We illustrate the method by using a sample of invariant-mass constrained vertices from D^0 --> K^- pi^+ decays to remove a curvature bias in the LHCb spectrometer.Comment: 18 pages, 6 figure

First observation of Bs -> D_{s2}^{*+} X mu nu decays

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays Bs -> Ds+ X mu nu and Bs -> D0 K+ X mu nu are detected. Two structures are observed in the D0 K+ mass spectrum at masses consistent with the known D^+_{s1}(2536) and $D^{*+}_{s2}(2573) mesons. The measured branching fractions relative to the total Bs semileptonic rate are B(Bs -> D_{s2}^{*+} X mu nu)/B(Bs -> X mu nu)= (3.3\pm 1.0\pm 0.4)%, and B(Bs -> D_{s1}^+ X munu)/B(Bs -> X mu nu)= (5.4\pm 1.2\pm 0.5)%, where the first uncertainty is statistical and the second is systematic. This is the first observation of the D_{s2}^{*+} state in Bs decays; we also measure its mass and width.Comment: 8 pages 2 figures. Published in Physics Letters

Prompt K_short production in pp collisions at sqrt(s)=0.9 TeV

The production of K_short mesons in pp collisions at a centre-of-mass energy of 0.9 TeV is studied with the LHCb detector at the Large Hadron Collider. The luminosity of the analysed sample is determined using a novel technique, involving measurements of the beam currents, sizes and positions, and is found to be 6.8 +/- 1.0 microbarn^-1. The differential prompt K_short production cross-section is measured as a function of the K_short transverse momentum and rapidity in the region 0 < pT < 1.6 GeV/c and 2.5 < y < 4.0. The data are found to be in reasonable agreement with previous measurements and generator expectations.Comment: 6+18 pages, 6 figures, updated author lis

The J/ψ→μμJ/\psi \to \mu\mu selection

This note presents a possible selection algorithm for \jpsimumu at LHCb with a total selection efficiency of $\epsilon_{total} = 5.11\% \pm 0.07\%$ for inclusive \jpsi events.The retention rates for $b$-inclusive and minimum bias events are RR_{b-\incl} = (1.26 \pm 0.08) \times 10^{-3} and $RR_{MB} = (0.1 \pm 0.2) \times 10^{-4}$. The expected annual number of \jpsi events is $(2.29 \pm 0.03) \times 10^{9}$. The reconstructed mass for a sample of 100 \kilo inclusive \jpsi events is M_{J/\psi} = 3096.33 \pm 0.07 \mevctwo with a mass resolution of \sigma_{J/\psi} = 9.943 \pm 0.058 \mevctwo

LHCb: Alignment of the LHCb Detector with Kalman Filter Fitted Tracks

We report on an implementation of a global chisquare algorithm for the simultaneous alignment of all tracking systems in the LHCb detector. Our algorithm uses hit residuals from the standard LHCb track fit which is based on a Kalman filter. The algorithm is implemented in the LHCb reconstruction framework and exploits the fact that all sensitive detector elements have the same geometry interface. A vertex constraint is implemented by fitting tracks to a common point and propagating the change in track parameters to the hit residuals. To remove unconstrained or poorly constrained degrees of freedom (so-called weak modes) the average movements of (subsets of) alignable detector elements can be fixed with Lagrange constraints. Alternatively, weak modes can be removed with a cutoff in the eigenvalue spectrum of the second derivative of the chisquare. As for all LHCb reconstruction and analysis software the configuration of the algorithm is done in python and gives detailed control over the selection of alignable degrees of freedom and constraints. The study the performance of the algorithm on simulated events and first LHCb data