Beyond the Standard Model Physics at the HL-LHC and HE-LHC (1812.07831v4)

Abstract: This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3~\mathrm{ab}^{-1}$ of data taken at a centre-of-mass energy of $14~\mathrm{TeV}$, and of a possible future upgrade, the High Energy (HE) LHC, defined as $15~\mathrm{ab}^{-1}$ of data at a centre-of-mass energy of $27~\mathrm{TeV}$. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by $20-50\%$ on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics.

• The paper evaluates supersymmetric models, projecting gluino discoveries up to 3.2 TeV and top squark reaches of 1.7 TeV at the HL-LHC with extended limits at the HE-LHC.
• The paper analyzes dark matter production channels, including monojet signatures, to probe mediator masses up to approximately 2.65 TeV.
• The paper demonstrates enhanced detection strategies for long-lived particles by leveraging upgraded detectors to identify displaced vertices and atypical decay signatures.

Overview of Beyond the Standard Model Physics at the HL-LHC and HE-LHC

The collaborative report “Beyond the Standard Model (BSM) Physics at the HL-LHC and HE-LHC” explores the potential of the High Luminosity (HL-LHC) and High Energy (HE-LHC) phases of the Large Hadron Collider (LHC) for probing BSM phenomena. This comprehensive analysis includes contributions from theorists and experimentalists focusing on a wide variety of BSM models. A multiplicity of signatures, including supersymmetric particles, dark matter candidates, and long-lived particles, are evaluated in terms of their detectability at future collider upgrades.

Supersymmetry and Naturalness

Central to the report is the exploration of supersymmetric (SUSY) models, which address the Hierarchy Problem through new fermionic and bosonic partners for Standard Model (SM) particles. The document evaluates the prospects of discovering colored SUSY partners such as gluinos and top squarks at HL-LHC, projecting their discovery potential up to around 3.2 TeV and 1.7 TeV, respectively. For HE-LHC, the reach extends significantly beyond these values due to the increased c.o.m. energy of 27 TeV. Additionally, the systematic incorporation of enhanced experimental techniques and detector upgrades is emphasized, reflecting the plan to mitigate hurdles faced in current searches.

Dark Matter and Associated Production Channels

A significant emphasis is placed on dark matter (DM) searches through several production channels. Monojet signatures—where DM recoils against the high-energy jet—are rigorously analyzed, predicting the HL-LHC can probe mediator masses up to approximately 2.65 TeV under optimized systematics. This sensitivity increases for HE-LHC, further constraining the parameter space of simplified DM models.

Research capitalizes on associated production channels, such as DM with heavy flavor quarks and electroweak gauge bosons, leveraging the HL-LHC's ability to differentiate these processes from background. Scalar and vector mediators are explored, with projected discovery potential for mediator masses reaching up to scales beyond 1 TeV, illustrating a multifaceted strategy to cover extensive regions in the DM landscape.

Long Lived Particles and Their Novel Signatures

Long-lived particles (LLPs), though challenging due to their atypical decay signatures, receive substantial attention. The HL-LHC and HE-LHC provide strategic platforms for these explorations through enhanced detectors capable of identifying displaced vertices and other signature anomalies. For instance, disappearing track signatures associated with nearly degenerate SUSY spectra provide a promising avenue for detecting electroweakinos at these future collider stages.

Prospects for BSM Phenomenology

Besides SUSY and DM models, the HL-LHC and HE-LHC's ability to probe other BSM phenomena is underscored, such as lepton flavor violation, vector-like quarks, and scalar resonances, enhancing the understanding of the SM's robustness against potential extensions. The tunnel and infrastructure preparations pivotal to realizing an HE-LHC are discussed, aiming to maximize its physics output within feasibility constraints.

Conclusion

The report stands as an instrumental resource in outlining the scope and potential of the LHC's experimental future. By quantifying both current constraints and future opportunities, it acts as a strategic plan for navigating the complexity of BSM physics, heralding advances in high-energy physics that could reshape fundamental understanding. The collective expertise applied in this report ensures a robust analysis valuable for shaping the next decade's experimental high-energy physics landscape, pushing the boundaries well beyond what is achievable with the LHC today.