Theory, phenomenology, and experimental avenues for dark showers: a Snowmass 2021 report

Abstract

In this work, we consider the case of a strongly coupled dark/hidden sector, which extends the Standard Model (SM) by adding an additional non-Abelian gauge group. These extensions generally contain matter fields, much like the SM quarks, and gauge fields similar to the SM gluons. We focus on the exploration of such sectors where the dark particles are produced at the LHC through a portal and undergo rapid hadronization within the dark sector before decaying back, at least in part and potentially with sizeable lifetimes, to SM particles, giving a range of possibly spectacular signatures such as emerging or semi-visible jets. Other, non-QCD-like scenarios leading to soft unclustered energy patterns or glueballs are also discussed. After a review of the theory, existing benchmarks and constraints, this work addresses how to build consistent benchmarks from the underlying physical parameters and present new developments for the pythia Hidden Valley module, along with jet substructure studies. Finally, a series of improved search strategies is presented in order to pave the way for a better exploration of the dark showers at the LHC.6 Summary and Perspectives 90 7 Acknowledgements 92 * The spin-0 states also include the flavor-singlet η v , which, as discussed in Eq. 15, can be relatively heavy. However there is no way to take this into account for separateFlav=off.† Although the spin-1 states include the flavor-singlet ωv, analogous to the spin-0 η v , it is expected to be close in mass to the other spin-1 states, as noted in sec. 4.1.1.

Leptons lurking in semi-visible jets at the LHC

“…, N f }, where N f is the number of dark flavors. Confinement of this Yang Mills theory at a scale v is guaranteed only for N f < 3N c [37]. In our study, we assume a minimal two dark flavors model (N f = 2) with mass degenerate q v,i states.…”

“…Even for mass degenerate dark quarks, the dark pseudoscalar π v and dark vector ρ v mesons masses can differ according to the hidden sector non-perturbative dynamics. Setting v as overall mass scale for dark mesons, lattice QCD fits in [37] have been used to predict the masses of dark vector mesons m ρ v from the input ratio m π v / v . As a benchmark, the hadronization scale v has been set to 5 GeV and the ratio m π v / v = 1.6, therefore fixing m π in the heavy quarkonium region at 8 GeV and m ρ v ∼ 15 GeV.…”

Boosting indirect detection of secluded dark matter sector

“…If the light species couple to mediators with relatively large coupling [18] and the mediator is much lighter than the relic DM, the hierarchy between the energy and mass of the light species will induce copious radiations of the mediator after the annihilation. The phenomenon is known as dark shower [19][20][21][22]. The boostness of light species opens up a new window to produce many kinds of light degrees of freedom in the dark sector.…”