Monojet versus the rest of the world I: t-channel models

Michele Papucci,Kathryn M Zurek,Alessandro Vichi

doi:10.1007/jhep11(2014)024

Abstract

Monojet searches using Effective Field Theory (EFT) operators are usually interpreted as a robust and model independent constraint on direct detection (DD) scattering cross-sections. At the same time, a mediator particle must be present to produce the dark matter (DM) at the LHC. This mediator particle may be produced on shell, so that direct searches for the mediating particle can constrain the effective operator being applied to monojet constraints. In this first paper, we do a case study on t-channel models in monojet searches, where the (Standard Model singlet) DM is pair produced via a t-channel mediating particle, whose supersymmetric analogue is the squark. We compare monojet constraints to direct constraints on single or pair production of the mediator from multi-jets plus missing energy searches and we identify the regions where the latter dominate over the former. We show that computing bounds using supersymmetric simplified models and in the narrow width approximation, as done in previous work in the literature, misses important quantitative effects. We perform a full event simulation and statistical analysis, and we compute the effects of both on- and off-shell production of the mediating particle, showing that for both the monojet and multi-jets plus missing energy searches, previously derived bounds provided more conservative bounds than what can be extracted by including all relevant processes in the simulation. Monojets and searches for supersymmetry (SUSY) provide comparable bounds on a wide range of the parameter space, with SUSY searches usually providing stronger bounds, except in the regions where the DM particle and the mediator are very mass degenerate. The EFT approximation rarely is able to reproduce the actual limits. In a second paper to follow, we consider the case of s-channel mediators.

Highlights

Crossing symmetry connects dark matter (DM) production at a hadron collider and direct detection (DD) cross-sections whenever both the partons and the DM involved in the scattering are close to being onshell, with very little sensitivity to the details of the interaction
The constraints from monojet searches can be compared against squark pair production, with each squark decaying to the DM plus a jet, so that these models can be constrained by looking at final states containing at least two jets plus MET
Having validated our results and established our method in the previous section, we will provide a complete scan of results in the mDM − mM plane, extracting a constraint on the effective Effective Field Theory (EFT) scale Λ ≡ mM /gM, that can be used for translating our results to the DD plane

Summary

Introduction

Crossing symmetry connects DM production at a hadron collider and DD cross-sections whenever both the partons and the DM involved in the scattering are close to being onshell, with very little sensitivity to the details of the interaction. Previous works simulated squark pair production and extracted the constraint on the coupling from the relevant squark-neutralino simplified model interpretations of the jets+MET searches [30,31,32,33,34,35,36,37]. This is expected to be valid for DM couplings parametrically smaller than the strong coupling constant and in the narrow-width approximation (NWA). In many regions of the mediator mass and DM mass parameter space, the jets+MET constraints close the parameter space where monojets by themselves are unconstraining

Objectives

Results

Conclusion