Measurement of masses in the t t-bar system by kinematic endpoints in pp collisions at sqrt(s) = 7 TeV

TL;DR

This paper presents a measurement of the top-quark, W-boson, and neutrino masses using kinematic endpoints in dilepton t t-bar events from 7 TeV proton-proton collisions, demonstrating a method applicable to new physics scenarios.

Contribution

It introduces a simultaneous mass measurement technique using endpoint determinations in kinematic distributions, applicable even when multiple masses are unknown or partially constrained.

Findings

Measured top-quark mass as 173.9 GeV with uncertainties.

Validated mass determination methods for scenarios with multiple unknown masses.

Provided a framework for analyzing decay chains with missing particles.

Abstract

A simultaneous measurement of the top-quark, W-boson, and neutrino masses is reported for t t-bar events selected in the dilepton final state from a data sample corresponding to an integrated luminosity of 5.0 inverse femtobarns collected by the CMS experiment in pp collisions at sqrt(s) = 7 TeV. The analysis is based on endpoint determinations in kinematic distributions. When the neutrino and W-boson masses are constrained to their world-average values, a top-quark mass value of M[t] = 173.9 +/- 0.9 (stat.) +1.7/-2.1 (syst.) GeV is obtained. When such constraints are not used, the three particle masses are obtained in a simultaneous fit. In this unconstrained mode the study serves as a test of mass determination methods that may be used in beyond standard model physics scenarios where several masses in a decay chain may be unknown and undetected particles lead to underconstrained kinematics.