Phenomenology of Hidden Valleys at Hadron Colliders (0712.2041v2)

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.

• The paper presents a novel hidden valley framework where low-mass v-hadrons emerge from a confining hidden sector mediated by a heavy Z' boson.
• It employs kinematic cuts and event shape analyses, revealing that resonant muon pair production can effectively distinguish signals from Standard Model backgrounds.
• The results demonstrate that the LHC can probe extensive hidden valley parameter space, offering fresh insights into physics beyond the Standard Model.

Analysis of Hidden Valleys at Hadron Colliders

The paper "Phenomenology of Hidden Valleys at Hadron Colliders" by Tao Han et al. presents a detailed exploration of hidden valley models and how they manifest in collider experiments. The emphasis is on a specific class of hidden sectors mediated by a heavy gauge boson, often a $Z'$, which is theoretically well-motivated and amenable to detection at the Large Hadron Collider (LHC).

Key Concepts and Theoretical Insights

The paper introduces hidden valley models that feature low mass bound states, referred to as $v$-hadrons, generated by a new confining gauge interaction within a hidden sector. Such sectors only weakly couple to the Standard Model (SM) via heavy mediators like $Z'$ bosons. The possibility of these hidden sectors opens avenues to novel signals at colliders, distinct from the established SM phenomena.

The hidden sectors are configured with low mass $v$-hadrons contrasting with the heavier mediators like $Z'$. These $v$-hadrons decay into pairs of leptons, most notably muons, making their detection feasible at the LHC. The paper explores the dynamics of these hidden sectors and addresses their implications for collider observables. The interaction between the hidden and standard model sectors occurs through high-dimensional operators, typically suppressed by a scale related to the mediator’s mass.

Experimental Strategy and Analysis

The authors provide a methodological approach for differentiating hidden valley signals from SM processes at the LHC. They model events characterized by a high multiplicity of jets and leptons, leading to distinct event shapes. Such events are typically more spherical, with lower thrust and higher multiplicity of isolated leptons compared to SM background processes.

Among the critical observables identified are the invariant mass of clusters within the event, which is anticipated to be high due to the high confinement scale in the hidden sector. Narrow resonances in the invariant mass of lepton pairs, particularly muon pairs, are highlighted as the most distinctive signals. The authors propose and validate a set of kinematic cuts designed to isolate these signals from SM backgrounds such as $b\bar b$ or Drell-Yan production.

Results and Implications

The paper demonstrates that with appropriate selection criteria, a significant range of the hidden valley parameter space can be probed at the LHC. They quantify the large event reach in terms of mediator mass and coupling, concluding that hidden vally signals stand out above typical backgrounds like $t\bar t$.

The results imply a robust capability for the LHC to explore scenarios involving hidden sectors and weakly interacting particles—scenarios that potentially evade detection in conventional searches. This capability suggests broader, untapped phenomenological possibilities within high-energy physics, sparking interest in search strategies incorporating non-standard event characteristics like multijet sphericity and resonant pair production.

Future Directions

While the paper successfully demonstrates the potential of searching for a specific class of hidden valley models, it also hints at the richness of phenomenology that remains to be explored further. The paper advocates for extending searches to other mediator types, such as Higgs sectors or graviton models, and investigating various mass gaps and matter content configurations within the hidden sector.

The work positions itself within a larger dialogue about physics beyond the Standard Model, suggesting that hidden sectors may provide answers to unsolved problems like dark matter composition and may uniquely influence astrophysical and cosmological phenomena. As such, continued refinement of experimental techniques and theoretical models will be essential in leveraging potential hidden sectors, impacting both collider physics and broader theoretical landscapes in particle physics.