Measurement of B(t->Wb)/B(t->Wq) at sqrt(s) = 1.96 TeV

TL;DR

This paper measures the ratio of branching fractions of top quarks decaying to Wb versus Wq at the Tevatron, providing results consistent with the Standard Model and setting limits on the CKM matrix element |V_tb|.

Contribution

First measurement of R = B(t->Wb)/B(t->Wq) at Tevatron, including novel analysis of events without identified b-jets to improve sensitivity.

Findings

Measured R = 1.03 +0.19 -0.17, consistent with Standard Model

Set lower limit R > 0.61 at 95% CL

Set lower limit |V_tb| > 0.78 at 95% CL

Abstract

We present the measurement of R = B(t->Wb)/B(t->Wq) in ppbar collisions at sqrt(s) = 1.96 TeV, using 230 pb-1 of data collected by the DO experiment at the Fermilab Tevatron Collider. We fit simultaneously R and the number of selected top quark pairs (ttbar), to the number of identified b-quark jets in events with one electron or one muon, three or more jets, and high transverse energy imbalance. To improve sensitivity, kinematical properties of events with no identified b-quark jets are included in the fit. We measure R = 1.03 +0.19 -0.17 (stat+syst), in good agreement with the standard model. We set lower limits of R > 0.61 and |V_tb| > 0.78 at 95% confidence level.