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

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.

Measurement of beauty and charm production in deep inelastic scattering at HERA and measurement of the beauty-quark mass

“…New ways of running the searches and expressing the bounds will be a necessity, the main options being simplified and, indeed, benchmark models (see e.g. [12][13][14][15][16][17][18][19] for previous examples).…”

Scalar simplified models for dark matter

“…By specifying the spin and gauge quantum numbers of the dark matter and the mediators, the parameter space can be made relatively small, allowing an easy conversion of bounds between experiments and theories. Previous papers have discussed colored mediators [33][34][35], which result in t-channel production of dark matter in a manner very similar to squarks in supersymmetry. Other works have considered vector and axial vector Z models [29,36,37], which cause s-channel dark matter production at colliders.…”

Forbidden dark matter at the weak scale via the top portal

“…Instead, we consider "simplified models", effective low-energy theories that capture DM-SM interactions via dimension-4 Lagrangian terms [14][15][16][17][18][19][20][21][22][23][24][25]. In these models the new physics sector usually comprises of no more than the DM state and a mediator.…”