Standard Model backgrounds to supersymmetry searches

TL;DR

This paper surveys Standard Model backgrounds to supersymmetry searches, with a focus on multijet plus missing energy signatures. It categorizes backgrounds as irreducible, reducible, and instrumental, and reviews the status of theoretical tools for modeling Z+jets, W+jets, ttbar+jets, and QCD multijets, highlighting the need for data-driven validation and control regions at the LHC. The authors stress that robust background estimation and internal cross-checks are essential to avoid misinterpreting SM mismodeling as signals of new physics. They advocate a cautious, validation-driven approach where experiments drive background understanding, supported by evolving theory tools and inter-experiment consistency checks.

Abstract

This work presents a review of the Standard Model sources of backgrounds to the search of supersymmetry signals. Depending on the specific model, typical signals may include jets, leptons, and missing transverse energy due to the escaping lightest supersymmetric particle. We focus on the simplest case of multijets and missing energy, since this allows us to expose most of the issues common to other more complex cases. The review is not exhaustive, and is aimed at collecting a series of general comments and observations, to serve as guideline for the process that will lead to a complete experimental determination of size and features of such SM processes.

Figures (20)

• Figure 1: Possible topologies for the final states of gluino decays.
• Figure 2: Example of an expected supersymmetry signal and relative backgrounds in the multijet+missing transverse energy final state Vahsen .
• Figure 3: QCD multijet rates as a function of the effective mass variable $M_{\mathrm{eff}}$, defined in eq. (\ref{['eq:susycuts']}), in events without missing transverse energy requirement.
• Figure 4: Left: the jet $E_{\mathrm T}$ spectrum in D0, before and after removal of the so-called it hot-cells, namely additional detector noise adding energy to the jet reconstruction. Right: the missing $E_{\mathrm T}$ spectrum at CDF, before and after the clean-up of all sources of spurious energy deposits.
• Figure 5: Distribution of the $M_{\mathrm{eff}}$ variable for the $Z$+4 jet process, with $Z\to\nu\bar{\nu}$. The different histograms represent the evolution of the background when additional signal cuts are imposed to the final state.