Including the Z in an Effective Field Theory for dark matter at the LHC

Sacha Davidson

doi:10.1007/jhep10(2014)084

Abstract

An Effective Field Theory for dark matter at a TeV-scale hadron collider should include contact interactions of dark matter with the partons, the Higgs and the Z. This note estimates the impact of including dark matter-Z interactions on the complementarity of spin dependent direct detection and LHC monojet searches for dark matter. Their effect is small, because they are suppressed by electroweak couplings and the contact interaction self-consistency condition $C/\Lambda^2 < 4\pi/\hat{s}$. In this note, the contact interactions between the Z and dark matter are parametrised by derivative operators; this is convenient at colliders because such interactions do not match onto the quark-dark matter contact interactions.

Highlights

JHEP10(2014)084 possible SM-gauge invariant interactions of the dark matter with other on-shell particles
The contact interactions between the Z and dark matter are parametrised by derivative operators; this is convenient at colliders because such interactions do not match onto low energy quark-dark matter contact interactions
These can interfere with the contact interactions studied in previous analyses, but contribute differently at colliders from in direct detection, so the linear combination of operator coefficients constrained at high and low energy will be different

Summary

Estimated limits from the LHC

Dark matter particles are invisible to the LHC detectors, so pair production of χs can be searched for in events with missing transverse energy (E/T ), which can be identified by jet(s) radiated from the incident partons. The Z exchange looks like a contact interactions for large p2Z = Mi2nv ≫ m2Z , where Mi2nv is the invariant mass-squared of the dark matter pair This is a useful approximation, because the arguments below suggests that most χχevents arise at larger Mi2nv. With the Minv cutoff ranging from 800 GeV to 2 TeV, requiring that the dark matter contribute ∼ 880 → 2200 GeV, for cuL,A = cuR,A = cdL,A = cdR,A = 1. This compares favourably to the CMS bound of. The parameters ruled out by the first and second eqs. of (3.2) are represented as the central regions in figure 2

From the TeV to the MeV

Discussion