Broadening dark matter searches at the LHC: mono-X versus darkonium channels

Abstract

Current searches for dark matter at the LHC focus on mono-X signatures: the production of dark matter in association with a Standard Model (SM) particle. The simplest benchmark introduces a massive spin-1 mediator, the Z boson, between the dark matter χ and the SM. Limits derived from mono-X channels are most effective when the mediator can decay into two on-shell dark matter particles: M Z 2M χ . We broaden the experimental reach into the complementary region, where the Z mediator is much lighter than the dark matter. In this scenario the Z mediates an effective longrange force between the dark matter, thereby facilitating the formation of darkonium bound states, as is common in many dark sector models. The darkonium becomes active when M χ > M Z /α eff , where α eff is the effective fine-structure constant in the dark sector. Moreover, the darkonium could decay back into SM quarks, without producing missing transverse momentum in the detector. Considering multijet final states, we reinterpret existing searches to constrain the simple Z benchmark beyond the region probed by mono-X searches. Assuming a baryonic Z mediator and a Dirac dark matter, direct detection bounds can be loosened by giving a small Majorana mass to the dark matter. We also consider the interplay between mono-X and darkonium channels at future high energy colliders, which is at the frontier of probing the model parameter space. * This is different from fixed energy colliders where the η D and Υ D channels are comparably important [24].

Dark CP violation and gauged lepton or baryon number for electroweak baryogenesis

“…6). The annihilation cross section is [46] where v rel is the relative velocity between χ andχ particles before the annihilation, and in the last step we take the limit that m 0 ≫ M Z 0 . Requiring that χ obtains the observed relic abundance [29] through this annihilation mechanism, we get…”

Higgs portal to dark QED

“…2 In order for the dark muonium state to be actually formed, the lifetime of Mu D should be longer than the bound state lifetime, the timescale required for forming the bound state. This can be achieved by having a small enough mass splitting Δm (but still large enough to suppress direct detection constraints; see [18] for a quantitative discussion), which we assume to be the case throughout the discussions below.…”

“…The overclosure constraint could be alleviated if additional annihilation channels of the dark matter exist, which necessitates going beyond the minimal Higgs portal scenario. One of the goals of the present work is to consider a simple extension of the minimal Higgs portal model, by including a light dark photon, which is a very popular hypothetical particle in "dark sector" scenarios [11][12][13][14][15][16][17][18][19] but is less commonly considered in Higgs portal models. More specifically, we propose that the Higgs boson is the portal to dark QED, where the dark electron is a dark matter candidate.…”

Leptophobic dark matter and the baryon number violation scale

“…We will examine the simplest theories in the next section and discuss the origin of these effective operators. [10][11][12][13][14][15][16][17][18], and for a complete list of effective operators in dark matter models see, for example, Ref. [19].…”