Phenomenology of Hidden Valleys at Hadron Colliders

TL;DR

This work analyzes confining Hidden Valleys that couple to the Standard Model via TeV-scale operators, focusing on a concrete $Z'$-mediated scenario with a single light $v$-quark. It derives production mechanisms (on-threshold $v\bar{v}$ bound states and open-flavor production), models hadronization with a modified Quark Combination Model and Longitudinal Phase Space Approximation, and studies prompt $v$-hadron decays through the mediator, yielding narrow $m_{vh}$ dilepton resonances. A comprehensive set of event-shape and resonance-based cuts is developed to separate HV signals from SM backgrounds, with a detailed assessment of LHC reach (notably near the $Z'$ peak), showing substantial sensitivity despite challenging backgrounds. The results highlight a general strategy for discovering low-mass hidden sectors at hadron colliders by leveraging non-inclusive observables and narrow dilepton resonances, offering a blueprint applicable to a broad class of HV models.

Abstract

We study the phenomenology of, and search techniques for, a class of "Hidden Valleys." These models are characterized by low mass (well below a TeV) bound states resulting from a confining gauge interaction in a hidden sector; the states include a spin-one resonance that can decay to lepton pairs. Assuming that the hidden sector communicates to the Standard Model (SM) through TeV suppressed operators, taking into account the constraint from the $Z$ pole physics at LEP, searches at Tevatron may be difficult in the particular class of Hidden Valleys we consider, so that we concentrate on the searches at the LHC. Hidden Valley events are characterized by high multiplicities of jets and leptons in the final state. Depending on the scale of confinement in the hidden sector, the events are typically more spherical, with lower thrust and higher incidences of isolated leptons, than those from the SM background processes. Most notably, high cluster invariant mass and very narrow, low mass resonances in lepton pairs are the key observables to identify the signal. We use these characteristics to develop a set of cuts to separate the Hidden Valley from SM, and show that with these cuts LHC has a significant reach in the parameter space. Our strategies are quite general and should apply well beyond the particular class of models studied here.