Observation of the Associated Production of a Single Top Quark and aWBoson inppCollisions ats=8 

Abstract

The first observation of the associated production of a single top quark and a W boson is presented. The analysis is based on a data set corresponding to an integrated luminosity of 12.2 fb(-1) of proton-proton collisions at sqrt[s] = 8 TeV recorded by the CMS experiment at the LHC. Events with two leptons and a jet originating from a b quark are selected. A multivariate analysis based on kinematic and topological properties is used to separate the signal from the dominant tt background. An excess consistent with the signal hypothesis is observed, with a significance which corresponds to 6.1 standard deviations above a background-only hypothesis. The measured production cross section is 23.4 ± 5.4 pb, in agreement with the standard model prediction.

Top-Quark Physics at the LHC

“…n/a tW -ch., CMS [170] 1.03 ± 0.12(exp) ± 0.04(theo) > 0.78 RB, CMS [171] 1.014 ± 0.003(stat) ± 0.032(syst) > 0.975 Table 3. Most precise values and limits for |V tb | 2 as extracted from single top-quark cross-section measurements and from RB.…”

“…Most recently, the CMS collaboration reported an observation of the process based on 8 TeV data [170]. Similarly to previous analyses, a multivariate analysis technique makes use of kinematic and topological properties to separate the signal from the dominant tt background.…”

Polarization of top quark as a probe of its chromomagnetic and chromoelectric couplings in tW production at the Large Hadron Collider

“…The dominant one is tt pair production which occurs through gluon fusion and quark-antiquark annihilation. The second mechanism is single top production [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Since the latter proceeds via weak interaction, top quarks tend to have large polarization [28,29].…”

“…These three modes are completely different kinematically and can be separated from one another. Of these, the t-channel [33][34][35] and the W t [36,37] processes have been observed at the LHC. Despite having smaller cross section than top pair production, singletop production is an important tool to study effects which may not be accessible in top pair production.…”

Single top and $V$$_{tb}$ measurements

“…Thus tt constitutes an irreducible background to the tWchannel signal. Still it had been discovered experimentally at the LHC in the di-lepton (ee, eµ and µ µ) final states, independently by CMS and ATLAS collaborations with Run-I data collected at √ s = 8 TeV [10,11]. These measurements have been combined [12,13] taking…”