Driving Missing Data at Next-to-Leading Order

TL;DR

This paper evaluates the use of gamma + 2-jet production measurements to predict Z + 2-jet backgrounds with missing energy at the LHC, demonstrating the reliability of this method at next-to-leading order.

Contribution

It provides a detailed NLO analysis of gamma + 2-jet and Z + 2-jet production ratios, validating gamma measurements as a background estimator for new physics searches.

Findings

Ratios at NLO are similar across different computational approaches.

Gamma + 2-jet production is a reliable background estimator.

Photon isolation criteria differences are minimal at high transverse momentum.

Abstract

The prediction of backgrounds to new physics signals in topologies with large missing transverse energy and jets is important to new physics searches at the LHC. Following a CMS study, we investigate theoretical issues in using measurements of gamma + 2-jet production to predict the irreducible background to searches for missing energy plus two jets that originates from Z + 2-jet production where the Z boson decays to neutrinos. We compute ratios of gamma + 2-jet to Z + 2-jet production cross sections and kinematic distributions at next-to-leading order in alpha_s, as well as using a parton shower matched to leading-order matrix elements. We find that the ratios obtained in the two approximations are quite similar, making gamma + 2-jet production a theoretically reliable estimator for the missing energy plus two jets background. We employ a Frixione-style photon isolation, but we also show that for isolated prompt photon production at high transverse momentum the difference between this criterion and the standard cone isolation used by CMS is small.