Search

This is the third out of five chapters of the final report [1] of theWorkshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted tothe 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 asimplified model fashion and in a more model-dependent one. A long list ofcontributions from the theory and experimental (ATLAS, CMS, LHCb) communitieshave been collected and merged together to give a complete, wide, andconsistent view of future prospects for BSM physics at the consideredcolliders. On top of the usual standard candles, such as supersymmetricsimplified models and resonances, considered for the evaluation of futurecollider potentials, this report contains results on dark matter and darksectors, long lived particles, leptoquarks, sterile neutrinos, axion-likeparticles, heavy scalars, vector-like quarks, and more. Particular attention isplaced, especially in the study of the HL-LHC prospects, to the detectorupgrades, the assessment of the future systematic uncertainties, and newexperimental techniques. The general conclusion is that the HL-LHC, on top ofallowing to extend the present LHC mass and coupling reach by $20-50\%$ on mostnew physics scenarios, will also be able to constrain, and potentiallydiscover, new physics that is presently unconstrained. Moreover, compared tothe HL-LHC, the reach in most observables will generally more than double atthe HE-LHC, which may represent a good candidate future facility for a finaltest of TeV-scale new physics.

We present the activities of the 'New Physics' working group for the 'Physicsat TeV Colliders' workshop (Les Houches, France, 1-19 June, 2015). Our reportincludes new physics studies connected with the Higgs boson and its properties,direct search strategies, reinterpretation of the LHC results in the buildingof viable models and new computational tool developments. Important signaturesfor searches for natural new physics at the LHC and new assessments of theinterplay between direct dark matter searches and the LHC are also considered.

In this paper, we describe the potential of the LHCb experiment to detect stealth physics. This refers to dynamics beyond the standard model that would elude searches that focus on energetic objects or precision measurements of known processes. Stealth signatures include long-lived particles and light resonances that are produced very rarely or together with overwhelming backgrounds. We will discuss why LHCb is equipped to discover this kind of physics at the Large Hadron Collider and provide examples of well-motivated theoretical models that can be probed with great detail at the experiment., (© 2022 IOP Publishing Ltd.)

We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of standard model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). In most cases the LLP lifetime can be treated as a free parameter from the [Formula: see text]m scale up to the Big Bang Nucleosynthesis limit of [Formula: see text] m. Neutral LLPs with lifetimes above [Formula: see text]100 m are particularly difficult to probe, as the sensitivity of the LHC main detectors is limited by challenging backgrounds, triggers, and small acceptances. MATHUSLA is a proposal for a minimally instrumented, large-volume surface detector near ATLAS or CMS. It would search for neutral LLPs produced in HL-LHC collisions by reconstructing displaced vertices (DVs) in a low-background environment, extending the sensitivity of the main detectors by orders of magnitude in the long-lifetime regime. We study the LLP physics opportunities afforded by a MATHUSLA-like detector at the HL-LHC, assuming backgrounds can be rejected as expected. We develop a model-independent approach to describe the sensitivity of MATHUSLA to BSM LLP signals, and compare it to DV and missing energy searches at ATLAS or CMS. We then explore the BSM motivations for LLPs in considerable detail, presenting a large number of new sensitivity studies. While our discussion is especially oriented towards the long-lifetime regime at MATHUSLA, this survey underlines the importance of a varied LLP search program at the LHC in general. By synthesizing these results into a general discussion of the top-down and bottom-up motivations for LLP searches, it is our aim to demonstrate the exceptional strength and breadth of the physics case for the construction of the MATHUSLA detector.

A light pseudo-scalar that is copiously produced at the LHC may still be allowed by present searches. While masses above 65 GeV are effectively covered by di-photon searches, the lower mass window can be tested by a new search for boosted di-tau resonances. We test this strategy on a set of composite Higgs models with top partial compositeness, where most models can be probed with an integrated luminosity below 300 fb - 1 .