Impact of misalignments on the analysis of B decays

This note investigates the effects of a misaligned tracking system on the analysis of B decays. Misalignment effects of both the vertex locator and the inner and outer T-stations have been studied. $z$-scaling effects of the vertex locator are also considered. It is proven that misalignments of the order of the detector single-hit resolutions have little or negligible effects on the quality of the reconstruction and of the analysis of B decays. The studies were performed with a sample of $B^0_{(s)} \to h^+h^{'-}$ decays, but the impact of misalignments on the performance of the pattern recognition algorithms and on the primary vertex resolutions, assessed for the first time, are rather general and not restricted to $B^0_{(s)} \to h^+h^{'-}$ decays

LHCb VELO software alignment, Part III: the alignment of the relative sensor positions

The LHCb Vertex Locator contains 42 silicon sensor modules. Each module has two silicon sensors. A method for determining the relative alignment of the silicon sensors within each module from data is presented. The software implementation details are discussed. Monte-Carlo simulation studies are described that demonstrate an alignment precision of 1.3 micron is obtained in the sensor plane

Alignment procedure of the LHCb Vertex Detector

LHCb is one of the four main experiments of the Large Hadron Collider (LHC) project, which will start at CERN in 2008. The experiment is primarily dedicated to B-Physics and hence requires precise vertex reconstruction. The silicon vertex locator (VELO) has a single hit precision of better than 10 micron and is used both off-line and in the trigger. These requirements place strict constraints on its alignment. Additional challenges for the alignment arise from the detector being retracted between each fill of the LHC and from its unique circular disc r/phi strip geometry. This paper describes the track based software alignment procedure developed for the VELO. The procedure is primarily based on a non-iterative method using a matrix inversion technique. The procedure is demonstrated with simulated events to be fast, robust and to achieve a suitable alignment precision.Comment: accepted for publication in NIM

ReDecay: A novel approach to speed up the simulation at LHCb

With the steady increase in the precision of flavour physics measurements collected during LHC Run 2, the LHCb experiment requires simulated data samples of larger and larger sizes to study the detector response in detail. The simulation of the detector response is the main contribution to the time needed to simulate full events. This time scales linearly with the particle multiplicity. Of the dozens of particles present in the simulation only the few participating in the signal decay under study are of interest, while all remaining particles mainly affect the resolutions and efficiencies of the detector. This paper presents a novel development for the LHCb simulation software which re-uses the rest of the event from previously simulated events. This approach achieves an order of magnitude increase in speed and the same quality compared to the nominal simulation

B Physics at the LHC

The LHC is scheduled to start its first physics data taking period later in 2009. Primarily LHCb but also ATLAS and CMS will start a rich B physics programme with the potential of revealing New Physics in the heavy flavour sector. This contribution will cover the prospects for B physics at the LHC with particular emphasis to early measurements. This includes CP violation measurements in $B^0_d$ and $B^0_s$ decays, searches for rare decays such as $B^0_s$ $\rightarrow$ $\mu\mu$, as well as semileptonic and radiative channels

LHCb VELO software alignment - PART II: the alignment of the VELO detector-halves

The software alignment of the Vertex Locator (VELO) is a critical component of the LHCb alignment strategy. This note demonstrates a potential algorithm to perform the alignment of the VELO detector-halves. The approach described in this document, and the tools developed, are also applicable to the alignment of the other LHCb sub-systems and the global relative alignment of the sub-detectors

A Monte Carlo simulation free method of measuring lifetimes using event-by-event acceptance functions at LHCb

A set of innovative methods and tools for precision lifetime and lifetime-difference measurements in hadronic B decays at LHCb is presented. All methods are purely data-driven and Monte Carlo simulation independent, a particularly important feature if lifetime measurements are to be made in the early period of LHCb's data taking. The methods and tools are shown to work in detailed simulation studies, including both Toy and Full Monte Carlo simulation studies of possible systematic biases in the measurements

The algorithm for FIR corrections of the VELO analogue links and its performance

The data from the VELO front-end is sent to the ADCs on the read-out board over a serial analogue link. Due imperfections in the link, inter-symbol cross talk occurs between adjacent time-bins in the transfer. This is corrected by an FIR filter implemented in the pre-processing FPGA locacted on the read-out board. This note reports on a method to determine the coefficients for the filter using date taken in-situ. Simulations are presented that show the performance of the methods as it is implemented in the LHCb read-out board. The effectiveness of the algorithm is demonstrated by the improvements in tracking performance on beam test data it brings

Precision scans of the pixel cell response of double sided 3D pixel detectors to pion and x-ray beams

hree-dimensional (3D) silicon sensors offer potential advantages over standard planar sensors for radiation hardness in future high energy physics experiments and reduced charge-sharing for X-ray applications, but may introduce inefficiencies due to the columnar electrodes. These inefficiencies are probed by studying variations in response across a unit pixel cell in a 55μm pitch double-sided 3D pixel sensor bump bonded to TimePix and Medipix2 readout ASICs. Two complementary characterisation techniques are discussed: the first uses a custom built telescope and a 120GeV pion beam from the Super Proton Synchrotron (SPS) at CERN; the second employs a novel technique to illuminate the sensor with a micro-focused synchrotron X-ray beam at the Diamond Light Source, UK. For a pion beam incident perpendicular to the sensor plane an overall pixel efficiency of 93.0±0.5% is measured. After a 10o rotation of the device the effect of the columnar region becomes negligible and the overall efficiency rises to 99.8±0.5%. The double-sided 3D sensor shows significantly reduced charge sharing to neighbouring pixels compared to the planar device. The charge sharing results obtained from the X-ray beam study of the 3D sensor are shown to agree with a simple simulation in which charge diffusion is neglected. The devices tested are found to be compatible with having a region in which no charge is collected centred on the electrode columns and of radius 7.6±0.6μm. Charge collection above and below the columnar electrodes in the double-sided 3D sensor is observed

Performance of the LHCb Vertex Detector Alignment Algorithm determined with Beam Test Data

LHCb is the dedicated heavy flavour experiment at the Large Hadron Collider at CERN. The partially assembled silicon vertex locator (VELO) of the LHCb experiment has been tested in a beam test. The data from this beam test have been used to determine the performance of the VELO alignment algorithm. The relative alignment of the two silicon sensors in a module and the relative alignment of the modules has been extracted. This alignment is shown to be accurate at a level of approximately 2 micron and 0.1 mrad for translations and rotations, respectively in the plane of the sensors. A single hit precision at normal track incidence of about 10 micron is obtained for the sensors. The alignment of the system is shown to be stable at better than the 10 micron level under air to vacuum pressure changes and mechanical movements of the assembled system.Comment: accepted for publication in NIM