Light dark matter and $Z'$ dark force at colliders

TL;DR

The paper investigates light dark matter ($M_{\chi} \lesssim 10$ GeV) interacting via a leptophobic $Z'$ mediator, bridging collider and direct-detection inquiries. It analyzes monojet$+${\not{E}}_{T}$ signals and direct dijet searches, emphasizing the role of the mediator's mass $M_{Z'}$ and width; a kinetic-width treatment is essential for broad resonances. Results show that for $250\ \mathrm{GeV} \lesssim M_{Z'} \lesssim 4\ \mathrm{TeV}$, dijet resonance searches typically constrain the model more strongly than monojet$+${\not{E}}_{T}$ searches, especially in the spin-independent case where collider bounds become competitive or superior for $M_{\chi}\lesssim 5$ GeV, and the spin-dependent case where collider limits are robust. The work demonstrates a clear complementarity: collider searches probe mediator properties directly while translating into constraints on the DM–nucleon cross section, guiding future experimental strategies in the low-mass DM frontier.

Abstract

Light Dark Matter, $<10$ GeV, with sizable direct detection rate is an interesting and less explored scenario. Collider searches can be very powerful, such as through the channel in which a pair of dark matter particle are produced in association with a jet. It is a generic possibility that the mediator of the interaction between DM and the nucleus will also be accessible at the Tevatron and the LHC. Therefore, collider search of the mediator can provide a more comprehensive probe of the dark matter and its interactions. In this article, to demonstrate the complementarity of these two approaches, we focus on the possibility of the mediator being a new $U(1)'$ gauge boson, which is probably the simplest model which allows a large direct detection cross section for a light dark matter candidate. We combine searches in the monojet+MET channel and dijet resonance search for the mediator. We find that for the mass of $Z'$ between 250 GeV and 4 TeV, resonance searches at the colliders provide stronger constraints on this model than the monojet+MET searches.