Dark Matter Benchmark Models for Early LHC Run-2 Searches: Report of the ATLAS/CMS Dark Matter Forum (1507.00966v1)

Abstract: This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations.

• The paper presents simplified benchmark models for dark matter searches at LHC Run-2, focusing on vector, scalar, and colored mediator interactions.
• It employs advanced simulation tools such as POWHEG and MadGraph to analyze mediator mass, coupling strengths, and kinematic distributions.
• The study informs experimental strategies by integrating fit-for-purpose simulations and reweighting methods to enhance detection sensitivity.

Insights into Dark Matter Benchmark Models for Early LHC Run-2 Searches

The document "Dark Matter Benchmark Models for Early LHC Run-2 Searches" presents a comprehensive paper undertaken by the ATLAS/CMS Dark Matter Forum to evaluate and propose simplified models for dark matter (DM) searches at the Large Hadron Collider (LHC). This report delineates a prioritized selection of benchmark models that gauge interactions between the Standard Model (SM) and potential dark matter candidates. The focus is on designing early LHC Run-2 searches that optimize detection sensitivity and enhance understanding of DM phenomena in collider experiments.

Key Models and Methodologies

The Forum identifies several classes of simplified models, notably those involving scalar and vector mediators exchanged in both \schannel and \tchannel interactions. These include:

1. Vector and Axial-Vector Mediators (s-channel): Interaction models assume a Dirac fermion DM that produces missing transverse momentum (\MET) signatures. Parameters such as mediator mass (\mMed), coupling strength, and DM mass (\mDM) are varied to understand their impact on kinematic distributions.
2. Scalar and Pseudoscalar Mediators (s-channel): These models incorporate the Yukawa couplings of mediators to SM particles analogously to the SM Higgs. The kinematics are explored at the loop level due to the coupling nature, which is significant only at subleading order in QCD corrections.
3. Colored Scalar Mediators (t-channel): \tchannel interactions with colored scalar mediators provide distinctive topologies that include additional jets, complicating the overall search strategy but enriching the dataset with identifiable signal signatures.
4. Spin-Two Mediators: While less explored, the use of spin-two mediators such as Kaluza-Klein gravitons are acknowledged as possibilities within models of extra dimensions.

The Forum utilized simulation tools such as \powheg and \madgraph to generate these models with varying levels of precision, from leading order to matched next-to-leading order with parton showers. This approach provides a benchmark for sensitivity predictions against varying energy scales and particle branching ratios.

Implications and Future Directions

The report extensively covers the need for fit-for-purpose simulation models, emphasizing the importance of adapting parton distribution functions (PDFs), renormalization, and factorization scales. It highlights the necessity of integrating fast reweighting techniques to accommodate dynamic perturbations in theoretical parameters like coupling constants and mediator widths.

By addressing the uncertainty in going from model-specific to more generalized EFT interpretations, the paper suggests caution when extrapolating these models’ findings to larger, non-collider-based phenomena. However, it underscores the value of providing a balance of EFT and simplified model results to ensure comprehensive data usability.

Contributions to Dark Matter Research

This document equips experimentalists with practical guidelines for simulating and validating collider-based DM searches, contributing significantly to the interpretative framework needed for aligning LHC results with indirect detection experiments. It heightens the dialogue around model-independent reconstruction of DM interactions, a crucial step in reconciling collider findings with astrophysical and cosmological DM signals.

As the LHC continues to deliver high-luminosity data, future research will benefit from these foundational exercises in model interpretation, fostering novel approaches to uncover the fundamental nature of dark matter. The Forum’s work represents a consensus-driven push towards utilizing LHC capabilities to unravel the properties of elusive dark matter candidates, serving as a linchpin in bridging experiment, theory, and cosmological observations.