Simulation of Heavily Irradiated Silicon Pixel Sensors and Comparison with Test Beam Measurements

Charge collection measurements performed on heavily irradiated p-spray DOFZ pixel sensors with a grazing angle hadron beam provide a sensitive determination of the electric field within the detectors. The data are compared with a complete charge transport simulation of the sensor which includes signal trapping and charge induction effects. A linearly varying electric field based upon the standard picture of a constant type-inverted effective doping density is inconsistent with the data. A two-trap double junction model implemented in the ISE TCAD software can be tuned to produce a doubly-peaked electric field which describes the data reasonably well. The modeled field differs somewhat from previous determinations based upon the transient current technique. The model can also account for the level of charge trapping observed in the data.Comment: 8 pages, 11 figures. Talk presented at the 2004 IEEE Nuclear Science Symposium, October 18-21, Rome, Italy. Submitted to IEEE Transactions on Nuclear Scienc

Selection of events with beauty and tau with the ATLAS and CMS detectors

The expected selection performance for events with b quarks and $\tau$ leptons in the final state with the ATLAS and CMS detectors are discussed. Reconstruction tools and trigger strategies are also reviewed

Track and Vertex Reconstruction with the CMS Detector at LHC

Because of the high charged particle multiplicity expected in proton-proton collisions at the LHC experiment,track and vertex reconstructions are challenging tasks. Main track and vertex reconstruction techniques used in the CMS experiment are described in the following. Both the track and vertex reconstruction problems can be decomposed into a pattern recognition stage and an estimation of the track and vertex parameters. Main algorithms used in CMS are based on the least-squares methods, but depending on the specific application robustifications of the least-squares algorithms can be more suitable. Several robustification techniques will be described

Position Determination of Pixel Hits

This Note presents a description of the algorithms used to determine the position of pixel hits and its error. Two estimators of the position and error of the pixel clusters have been developed. Each two estimator can be used at a different step of the track reconstruction. One can be applied initially, at the track seeding stage. The other can be used when the approximate trajectory is known. The studies of the spatial resolution of pixel hits as a function of the track impact angles are also described

Track reconstruction, primary vertex finding and seed generation with the Pixel Detector

The Pixel Detector is the innermost detector of the tracking system of the Compact Muon Solenoid (CMS) experiment. It provides the most precise measurements which contribute to the full track reconstruction. It also allows standalone track reconstruction, which is particularly useful for online event selection (called High-Level Triggering). The reconstruction algorithms using the Pixel Detector are presented, including pixel track reconstruction, primary vertex finding and seed generation

Track-Parameter Evaluation and Primary-Vertex Finding with the Pixel Detector

Two algorithms for primary-vertex finding based on charged particle tracks reconstructed with three pixel hits are presented in this note. The evaluation of the track parameters is also described. These algorithms are shown to be suitably fast and efficient for the CMS High-Level Trigger

Search for H→bb‾H \to b\overline{b} in Association with a ttbar Pair at CMS

The discovery of a low mass Higgs boson is particularly challenging because the leading decay mode is H -> b bbar for a Higgs mass mH gamma gamma. Nevertheless, the degree to which the Higgs is manifested in a variety of channels and modes could hold important clues to its true identity, and whether it heralds from a more rich Higgs sector than that of the Standard Model. A potentially promising channel is the production of Higgs in association with a t tbar pair. The search for H -> b bbar is enhanced by properties of top quark decays that allow a dramatic reduction in possible backgrounds. These events contain four energetic b jets and fall into three salient subclasses depending upon whether neither, one, or both of the W bosons in the event decay to electrons or muons and their respective neutrinos. In this note we present results of studies of all three subclasses of t tbar H events in CMS with an integrated luminosity of 60 fb^-1. The search for a low mass Higgs in t tbar H relies upon every ubsystem in the CMS experiment and relies particularly strongly upon the CMS Tracking System. It is very challenging

Fitting of Event Topologies with External Kinematic Constraints in CMS

The resolution of the measured objects in the final state of proton collisions at the Large Hadron Collider can be improved by forcing well-defined kinematic hypotheses on the event. The kinematic constraints proposed by the hypotheses can be applied by means of Lagrange multipliers in a general event-by-event least square fitting technique. The resulting chi-square of the fit can be interpreted as the probability of the proposed kinematic hypotheses to be true for the observed event. This note describes both the general mathematical concept of kinematic fitting and its implementation within the analysis framework of the Compact Muon Solenoid experiment. The performance of the method is demonstrated in a few typical case-studies where relative improvements are emphasized