Dark sector searches with the CMS experiment (2405.13778v2)

Abstract: Astrophysical observations provide compelling evidence for gravitationally interacting dark matter in the universe that cannot be explained by the standard model of particle physics. The extraordinary amount of data from the CERN LHC presents a unique opportunity to shed light on the nature of dark matter at unprecedented collision energies. This Report comprehensively reviews the most recent searches with the CMS experiment for particles and interactions belonging to a dark sector and for dark-sector mediators. Models with invisible massive particles are probed by searches for signatures of missing transverse momentum recoiling against visible standard model particles. Searches for mediators are also conducted via fully visible final states. The results of these searches are compared with those obtained from direct-detection experiments. Searches for alternative scenarios predicting more complex dark sectors with multiple new particles and new forces are also presented. Many of these models include long-lived particles, which could manifest themselves with striking unconventional signatures with relatively small amounts of background. Searches for such particles are discussed and their impact on dark-sector scenarios is evaluated. Many results and interpretations have been newly obtained for this Report.

• The paper presents a comprehensive CMS analysis of dark sector searches using Run 2 data to constrain dark matter interactions and mediator properties.
• It employs mono-X, dijet, and long-lived particle channels to derive limits on vector and axial-vector mediators and dark matter cross sections.
• The study highlights advances in reconstruction techniques and the potential of future HL-LHC data to further explore dark sector phenomena.

Overview of Dark Sector Searches with the CMS Experiment

The paper under review presents a comprehensive analysis of dark sector searches conducted using data from the CMS experiment at the Large Hadron Collider (LHC) at CERN. The paper takes advantage of the vast datasets from Run 2 (2016–2018) and explores a variety of physics channels to probe theoretical models that extend the Standard Model (SM) of particle physics.

In light of the compelling astrophysical and cosmological evidence suggesting the presence of dark matter (DM), various physics beyond the standard model (BSM) scenarios are considered. These models generally predict new particles and interactions that could populate a "dark sector". The analyses are broadly categorized based on the final states of interest: those involving invisible signatures, visible signatures, and long-lived particles.

Invisible Signatures

Invisible final states typically emerge from DM particles that escape the detector without interaction, resulting in missing transverse momentum (\ptmiss). Mono-X searches like monojet, mono-\PZ, and mono-photon are pivotal in this category. These searches focus on identifying a single SM particle recoiling off the invisible DM candidates. The paper reports significant constraints on models with vector and axial-vector mediators, translating these constraints into limits on DM-nucleon cross sections based on spin-independent and dependent interpretations.

Visible Signatures

Beyond invisible signatures, the CMS experiment has studied events where mediators decay entirely into SM particles, offering a complementary view of potential discovery. The analysis extends into dijet and dilepton resonance searches. High-mass resonance searches, in particular, scrutinize events for massive new gauge bosons such as \PZpr bosons. These analyses provide stringent bounds on the mediator mass and coupling constants, extending our understanding of DS models over a wide mass spectrum.

Long-Lived Particles

The investigation of long-lived particles (LLPs) forms another core aspect, exploring scenarios where particles produced in the collider have significant lifetimes and decay at measurable distances from the interaction point. These include signatures of displaced leptons and displaced jets, leveraging unique CMS capabilities to tag non-prompt decay vertices and delayed signals in calorimetry. Such searches are sensitive to a rich array of theoretical constructs, including stealth supersymmetry and hidden bottomonium states.

Interpretation and Implications

The analyses reiterate CMS's sensitivity to BSM physics across various domains, yielding critical exclusion regions in the parameter space of DM models. The data disfavor certain mass and coupling configurations, refining the landscape of viable theories. Beyond direct particle discovery, such limits tighten constraints on extensions of the SM, such as the Higgs-portal scenario and models with scalar or pseudoscalar mediators.

Prospects and Future Work

Looking ahead, future runs at the LHC, including the High-Luminosity LHC (HL-LHC), promise significantly enhanced data samples. This expansion will amplify CMS's sensitivity to DS phenomena, due to both greater precision in existing channels and expanded trigger capabilities. In addition, the ongoing development of innovative reconstruction techniques is expected to further broaden the reach of LLP searches, potentially unveiling new states predicted by these complex theoretical models.

In summary, the ongoing experimental journey at CMS not only narrows down the parameter space for DM but also inspires theoretical advances, ensuring that searches for the dark sector remain a dynamic and integral part of modern particle physics. The methodologies and results comprehensively discussed in this paper underline the CMS experiment's leadership in probing BSM scenarios at the energy frontier.