Optimisation of variables for studying dilepton transverse momentum distributions at hadron colliders

TL;DR

This paper proposes new variables, including a scaled extit{a}_T and a novel extit{ extphi}^*_ ext{Eta}, to improve the experimental resolution of dilepton transverse momentum measurements at hadron colliders, enhancing QCD tests.

Contribution

It introduces a new variable, extphi^*_ ext{Eta}, based solely on lepton directions, which offers higher experimental precision for studying dilepton transverse momentum distributions.

Findings

Dividing extit{a}_T and extit{Q}_T by dilepton invariant mass improves resolution.

extphi^*_ ext{Eta} is more precisely measured than previous variables.

Enhanced variables enable more stringent QCD tests and better Monte Carlo tuning.

Abstract

In future measurements of the dilepton ($Z/\gamma^*$) transverse momentum, \Qt, at both the Tevatron and LHC, the achievable bin widths and the ultimate precision of the measurements will be limited by experimental resolution rather than by the available event statistics. In a recent paper the variable \at, which corresponds to the component of \Qt\ that is transverse to the dilepton thrust axis, has been studied in this regard. In the region, \Qt\ $<$ 30 GeV, \at\ has been shown to be less susceptible to experimental resolution and efficiency effects than the \Qt. Extending over all \Qt, we now demonstrate that dividing \at\ (or \Qt) by the measured dilepton invariant mass further improves the resolution. In addition, we propose a new variable, \phistarEta, that is determined exclusively from the measured lepton directions; this is even more precisely determined experimentally than the above variables and is similarly sensitive to the \Qt. The greater precision achievable using such variables will enable more stringent tests of QCD and tighter constraints on Monte Carlo event generator tunes.