A simple event weighting technique: optimizing the measurement of the forward-backward asymmetry of Drell-Yan dilepton and top-antitop pairs at hadron colliders

Abstract

We describe a simple technique for optimizing the extraction of the forward-backward asymmetry (A fb ) of Drell-Yan lepton pairs (e + e − , μ + μ − ) produced inpp and pp collisions at hadron colliders. The method employs simple event weights which are functions of the rapidity and | cos θ | decay angle of the lepton pair. It yields the best estimate of the acceptance corrected parton level (qq) forward backward asymmetry as a function of final state dilepton mass (M ). Typically, when compared to the simple count method, the technique reduces the statistical errors by 20% forpp, and 40% for pp collisions, respectively. The method is equivalent to using the maximum likelihood method, but is much easier to implement. The technique can be used to search for new high mass and large width Z' bosons which may be best detected through the observation of deviations from the Standard Model expectation for the forwardbackward asymmetry. The technique can also be applied in the extraction of the foward-backward asymmetry in the production of top-antitop pairs.

Using Drell–Yan forward–backward asymmetry to reduce PDF uncertainties in the measurement of electroweak parameters

“…In addition, there are new techniques that can be used [16,17] to greatly reduce the experimental systematic uncertainty in asymmetry measurements.…”

First Measurement of the Angular Coefficients of Drell-Yane+e−Pairs in theZMass Region frompAaltonen1, González2, Amerio3 et al. 2011Phys. Rev. Lett.Self Cite511250View full textAdd to dashboardCite

“…For the q q ! Ã =ZG annihilation process, pQCD at the order of s predicts that the angular coefficients A 0 and A 2 are equal [4][5][6][7] and can be analytically described by…”

Publisher’s Note: Measurement of sin2θefflept using e+eAaltonen1 2017Phys. Rev. D110350View full textAdd to dashboardCite

“…The asymmetry in this analysis is measured using the event-weighting method [45], which is equivalent to measurements of A fb in | cos ϑ| bins with these simplifying assumptions: ( A) + = ( A) − in each | cos ϑ| bin, and Eq. (1) describes the angular distributions.…”

“…In the unbinned measurement, their numerator and denominator weights contain: 1) factors to cancel the angular dependencies of their event difference (N + −N − ) and sum (N + +N − ), respectively, and 2) the ξ 2 factor for the statistical combination of these events with events from other angular regions. The method is equivalent to using a maximum-likelihood technique, and for an ideal detector the statistical precision of A fb is expected to be about 20% better relative to the direct counting method [45]. However, detector resolution and limited acceptance degrade the ideal gain.…”