Measurement of the t-channel single-top-quark production cross section and of the |Vtb| CKM matrix element in pp collisions at sqrt(s) = 8 TeV

Measurements are presented of the t-channel single-top-quark production cross section in proton-proton collisions at s? = 8 TeV. The results are based on a data sample corresponding to an integrated luminosity of 19.7 fb?1 recorded with the CMS detector at the LHC. The cross section is measured inclusively, as well as separately for top (t) and antitop (t?) , in final states with a muon or an electron. The measured inclusive t-channel cross section is ? t-ch. = 83.6 ± 2.3 (stat.) ± 7.4 (syst.) pb. The single t and t? cross sections are measured to be ? t-ch.(t) = 53.8 ± 1.5 (stat.) ± 4.4 (syst.) pb and ? t-ch. (t?) = 27.6 ± 1.3 (stat.) ± 3.7 (syst.) pb, respectively. The measured ratio of cross sections is R t-ch. = ? t-ch.(t)/? t-ch. (t?) = 1.95 ± 0.10 (stat.) ± 0.19 (syst.), in agreement with the standard model prediction. The modulus of the Cabibbo-Kobayashi-Maskawa matrix element V tb is extracted and, in combination with a previous CMS result at s? = 7 TeV, a value |V tb| = 0.998 ± 0.038 (exp.) ± 0.016 (theo.) is obtained.