Model-independent extraction of pipeVtqpipe matrix elements from top-quark measurements at hadron colliders

Current methods to extract the quark-mixing matrix element pipeVtbpipe from single-top-production measurements assume that pipeVtbpipe>>pipeVtdpipe,pipeVtspipe: top quarks decay into b quarks with 100 % branching fraction, s-channel single-top production is always accompanied by a b quark and initial-state contributions from d and s quarks in the t-channel production of single top quarks are neglected. Triggered by a recent measurement of the ratio, 0. 90 ±0. 04 performed by the D0 collaboration, we consider a pipeVtbpipe extraction method that takes into account non zero d- and s-quark contributions both in production and decay. We propose a strategy that allows to extract consistently and in a model-independent way the quark-mixing matrix elements pipeVtdpipe, pipeVtspipe, and pipeVtbpipe from the measurement of R and from single-top measured event yields. As an illustration, we apply our method to the Tevatron data using a CDF analysis of the measured single-top event yield with two jets in the final state, one of which is identified as a b-quark jet. We constrain the pipeVtqpipe matrix elements within a four-generation scenario by combining the results with those obtained from direct measurements in flavor physics and determine the preferred range for the top-quark decay width within different scenarios. © 2012 Springer-Verlag / Società Italiana di Fisica.