Semivisible Jets: Dark Matter Undercover at the LHC

Abstract

The dark matter may be a composite particle that is accessible via a weakly coupled portal. If these hidden-sector states are produced at the Large Hadron Collider (LHC), they would undergo a QCD-like shower. This would result in a spray of stable invisible dark matter along with unstable states that decay back to the Standard Model. Such "semi-visible" jets arise, for example, when their production and decay are driven by a leptophobic Z resonance; the resulting signature is characterized by significant missing energy aligned along the direction of one of the jets. These events are vetoed by the current suite of searches employed by the LHC, resulting in low acceptance. This Letter will demonstrate that the transverse mass-computed using the final-state jets and the missing energy-provides a powerful discriminator between the signal and the QCD background. Assuming that the Z couples to the Standard Model quarks with the same strength as the Z 0 , the proposed search can discover (exclude) Z masses up to 2.5 TeV (3.5 TeV) with 100 fb −1 of 14 TeV data at the LHC.The existence of dark matter provides one of the strongest motivations for physics beyond the Standard Model, and its discovery is one of the core missions for the Large Hadron Collider (LHC) program. Under the assumption that the dark-matter particle is neutral and stable, it escapes the detector and manifests as missing transverse energy ( E T ). The LHC collaborations have developed a comprehensive search strategy to look for signals with significant E T , accompanied by jets and/or leptons (see, e.g.[1] for a review). These searches are typically cast in terms of a Simplified Model [2] for supersymmetry or an effective theory of dark-matter interactions [3,4]. Yet if one relaxes the assumption that the dark sector is weakly coupled, a new class of dark-matter signatures emerge that evade this entire suite of analyses. Namely, it is possible that the dark matter has been lurking undercover within hadronic jets. The purpose of this Letter is to propose a straightforward discovery strategy for these "semi-visible" jets.Semi-visible jets may occur if the dark matter is the stable (or meta-stable) remnant of a more complicated dark sector. The dynamics of non-trivial dark sectors have been explored in many contexts, e.g. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In these models, the dark sector contains a dark-matter candidate(s) and possibly new force carriers and/or matter fields. Note that we are agnostic about how much of the cosmological relic density is accounted for by this dark-matter candidate. Messenger states that couple the dark sector to the Standard Model (SM) can exist. If the messenger is accessible at colliders, dark-sector states can be produced, leading to unique signatures such as large particle multiplicities, displaced vertices, multiple resonances, and lepton or photon jets [20][21][22][23][24][25][26][27][28][29][30][31][32][33].Another possibility is that the final state resulting from strongly coupled hidden secto...

Simplified SIMPs and the LHC

“…Before to go on, we mention that other scenarios with a strongly coupled hidden sector that may lead to LHC signals somewhat analogous to trackless jets have been proposed recently, see [21,22]. If necessary, those may provide a further motivation for the kind of experimental study we discuss in the following sections.…”

Strongly interacting dark sectors in the early Universe and at the LHC through a simplified portal

“…We therefore consider an analysis proposed in Ref. [21,22], which is based on the transverse jet mass…”

Classification of dark pion multiplets as dark matter candidates and collider phenomenology

“…Third, there has recently been an increasing amount of work dedicated to discovering jets of dark hadrons, or so called dark jets. From a theoretical point of view, this includes emerging jets [16], semivisible jets [17] and softbombs [18]. From an experimental point of view, collider searches have been performed in Ref.…”

“…Generically, both stable and unstable dark pions can be produced in a parton shower. Assuming the unstable pions decay hadronically, this will result in the production of semivisible jets [17,59,60]. These roughly look like generic jets, but are accompanied by collinear stable particles that escape the detector and contribute to the missing transverse energy (MET).…”