Measurement of The W Boson Production Cross Section and Search for the W' in The Muon Channel from pp Collisions at sqrt(s) = 7 TeV with the ATLAS Detector at the LHC

[摘要] This thesis reports the first measurement of the weak gauge boson W^{+-} production cross section in proton-proton collisions at center-of-mass energy of 7 TeV at the Large Hadron Collider with the ATLAS experiment. Data used in this measurement were collected by the ATLAS detector from March 30 to October 31, 2010 with an integrated luminosity of 35.2 pb^{-1}. The cross section measurement was carried out using the muon decay channel from the process of W->munu. The experimental signature is an isolated muon with large transverse momentum and a large momentum imbalance in the transverse plane w.r.t. the beam direction in the event. The large momentum imbalance is due to the neutrino escaping detection. The key elements of the measurement include studies of the muon trigger efficiency, the event selection optimization, the signal acceptance and associated systematic uncertainties, and the background estimation. With a total of 145226 candidates selected and a background estimation of 8461.6+-6.9(stat)+-1509.3(sys)+-188.0(lumi), the total cross section times branching ratio sigma_W*Br(W->munu) is measured to be 10.15+-0.025(stat)+-0.56(sys)+-0.35(lumi) nb, which is consistent with the Next-to-Leading order Standard Model prediction of 10.46+-0.52 nb. The W^+/W^- charge ratio is measured to be 1.56+-0.01(stat)+-0.09(sys), which is consistent with the theoretical prediction of 1.433^{+0.032}_{-0.020}. Using the same datasets, a search for a new gauge boson W;; is conducted with the same munu final state. No experimental signature of W;; in munu decay channel is observed. A 95% confidence level of lower mass limit for W;; is set at 1.32 TeV. This limit has exceeded the limit set by Tevatron experiments which have collected data with much higher integrated luminosity (~5.3 fb^{-1}) from ppbar collisions at center-of-mass energy of 1.96 TeV.

[发布机构] University of Michigan

[效力级别] Search for W"

[关键词] Electroweak W Boson Production;Search for W"Muon Final State;ATLAS Experiment;LHC;Physics;Science;Physics