A measurement of the single-top-quark t-channel production cross section in pp collisions at √ s = 7 TeV with the CMS detector at the LHC is presented. Two different and complementary approaches have been followed. The first approach exploits the distributions of the pseudorapidity of the recoil jet and reconstructed top-quark mass using background estimates determined from control samples in data. The second approach is based on multivariate analysis techniques that probe the compatibility of the candidate events with the signal. Data have been collected for the muon and electron final states, corresponding to integrated luminosities of 1.17 and 1.56 fb −1 , respectively. The single-topquark production cross section in the t-channel is measured to be 67.2±6.1 pb, in agreement with the approximate next-to-next-to-leading-order standard model prediction. Using the standard model electroweak couplings, the CKM matrix element |V tb | is measured to be 1.020 ± 0.046 (meas.) ± 0.017 (theor.).
Keywords: Hadron-Hadron Scattering
Conclusions 21The CMS collaboration 27
IntroductionSingle top quarks can be produced through charged-current electroweak interactions. Due to the large top-quark mass, these processes are well suited to test the predictions of the standard model (SM) of particle physics and to search for new phenomena. Measurements of the single-top-quark production cross section also provide an unbiased determination of the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V tb |. Single-top-quark production was observed in proton-antiproton collisions at the Tevatron collider with a centre-of-mass energy of 1. by a factor of 20 at the Large Hadron Collider (LHC) with respect to the Tevatron. The first measurements of the single-top-quark production cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV were performed by the Compact Muon Solenoid (CMS) [4] and ATLAS [5,6] experiments.Previous measurements are compatible with expectations based on approximate nextto-leading-order and next-to-next-to-leading-logarithm (NLO+NNLL) perturbative quantum chromodynamics (QCD) calculations. In these calculations, three types of parton scattering processes are considered: t-channel and s-channel processes, and W-associated single-top-quark production (tW). The dominant contribution to the cross section is expected to be from the t-channel process with a cross section of σ th t-ch. = 64.6 +2.1 −0.7for a top-quark mass of m t = 172.5 GeV/c 2 .This paper extends the previous CMS measurement [4] of the t-channel cross section. The single-top-quark production cross section measurement is based on pp collision data at √ s = 7 TeV collected during 2011 with the CMS experiment, corresponding to integrated luminosities of 1.17 and 1.56 fb −1 with muon and electron final states, respectively. Events with leptonically decaying W bosons are selected: t → bW → b ν ( = e or µ). This measurement is used to determine the CKM matrix element |V tb |.The t-channel event signature (figure 1)...