The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 pb −1 of data collected in pp collisions at √ s = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum p T larger than a few GeV/c is above 95% over the whole region of pseudorapidity covered by the CMS muon system, |η| < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with p T above a few GeV/c is higher than 90% over the full η range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with p T below 100 GeV/c and, using cosmic rays, it is shown to be better than 10% in the central region up to p T = 1 TeV/c. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.
The inclusive b-jet production cross section in pp collisions at a center-ofmass energy of 7 TeV is measured using data collected by the CMS experiment at the LHC. The cross section is presented as a function of the jet transverse momentum in the range 18 < p T < 200 GeV for several rapidity intervals. The results are also given as the ratio of the b-jet production cross section to the inclusive jet production cross section. The measurement is performed with two different analyses, which differ in their trigger selection and b-jet identification: a jet analysis that selects events with a b jet using a sample corresponding to an integrated luminosity of 34 pb −1 , and a muon analysis requiring a b jet with a muon based on an integrated luminosity of 3 pb −1 . In both approaches the b jets are identified by requiring a secondary vertex. The results from the two methods are in agreement with each other and with next-to-leading order calculations, as well as with predictions based on the pythia event generator.
The central component of the CMS detector is the largest silicon tracker ever built. The precise alignment of this complex device is a formidable challenge, and only achievable with a significant extension of the technologies routinely used for tracking detectors in the past. This article describes the full-scale alignment procedure as it is used during LHC operations. Among the specific features of the method are the simultaneous determination of up to 200 000 alignment parameters with tracks, the measurement of individual sensor curvature parameters, the control of systematic misalignment effects, and the implementation of the whole procedure in a multiprocessor environment for high execution speed. Overall, the achieved statistical accuracy on the module alignment is found to be significantly better than 10 µm.
A: Muon tomography system built by 2-D readout high spatial resolution Multi-gap Resistive Plate Chamber (MRPC) detector is a project in Tsinghua University. In 2013, we had developed a prototype of muon tomography system named TUMUTY, now we try to develop larger sensitive area and smarter structure MRPC detector to upgrade the system to a car detection system, which is used to detect high Z metal hidden in cars or other objects. For the system, 2 layers ×3 detectors are needed to get the incident particle's track, and the setting is the same for the outgoing track. Therefore, there will four layers containing twelve detectors in total, and its detection area will reach 1 × 3 m 2 . An encoding readout method is suggested to minimize the number of the readout electronics, which reduces the complexity and the cost of the system. In this paper, we measured the performance of 12 MRPCs used for the system.
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