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Alidra, M. et al, & Torro Pastor, E. (2021). The MATHUSLA test stand. Nucl. Instrum. Methods Phys. Res. A, 985, 164661–9pp.
Abstract: The rate of muons from LHC pp collisions reaching the surface above the ATLAS interaction point is measured as a function of the ATLAS luminosity and compared with expected rates from decays of W and Z bosons and b- and c-quark jets. In addition, data collected during periods without beams circulating in the LHC provide a measurement of the background from cosmic ray inelastic backscattering that is compared to simulation predictions. Data were recorded during 2018 in a 2.5 x 2.5 x 6.5 m(3) active volume MATHUSLA test stand detector unit consisting of two scintillator planes, one at the top and one at the bottom, which defined the trigger, and six layers of RPCs between them, grouped into three (x, y)-measuring layers separated by 1.74 m from each other. Triggers selecting both upward-going tracks and downward-going tracks were used.
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Alimena, J. et al, Hirsch, M., Mamuzic, J., Mitsou, V. A., & Santra, A. (2020). Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider. J. Phys. G, 47(9), 090501–226pp.
Abstract: Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments-as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER-to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the high-luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity 'dark showers', highlighting opportunities for expanding the LHC reach for these signals.
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ATLAS Collaboration(Aad, G. et al), Ahuja, S., Aikot, A., Cabrera Urban, S., Cantero, J., Carrion Martinez, C., et al. (2026). Search for massive, long-lived particles in events with displaced vertices and displaced muons in pp collisions at √s=13.6 TeV with the ATLAS experiment. Phys. Lett. B, 878, 140509–23pp.
Abstract: A search is presented for massive long-lived particles in events featuring at least one displaced vertex and at least one displaced muon, using proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider from 2022 to 2024 at a centre-of-mass energy of 13.6 TeV. The data sample corresponds to an integrated luminosity of 164 fb(-1). The analysis targets scenarios in which long-lived particles decay inside the ATLAS inner detector, resulting in a topology of at least one massive, displaced vertex (DV) with multiple associated tracks, and at least one muon with a large transverse impact parameter relative to the primary interaction point. The muon is not required to be associated with the DV. Two signal regions are defined by the transverse distance of the reconstructed DV from the interaction point. Background contributions are estimated by using fully data-driven techniques. No significant excess above the expected background is observed. Upper limits at 95% confidence level are set on the visible cross-section and on the production cross-sections of several benchmark models of R-parity-violating supersymmetry.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Search for heavy long-lived charged particles with the ATLAS detector in pp collisions at sqrt(s)=7 TeV. Phys. Lett. B, 703(4), 428–446.
Abstract: A search for long-lived charged particles reaching the muon spectrometer is performed using a data sample of 37 pb(-1) from pp collisions at sqrt(s) = 7 TeV collected by the ATLAS detector at the LHC in 2010. No excess is observed above the estimated background. Stable (tau) over bar sleptons are excluded at 95% CL up to a mass of 136 GeV, in GMSB models with N(5) = 3 , m(messenger) = 250 TeV, sign(mu) = 1 and tan beta = 5. Electroweak production of sleptons is excluded up to a mass of 110 GeV. Gluino R-hadrons in a generic interaction model are excluded up to masses of 530 GeV to 544 GeV depending on the fraction of R-hadrons produced as (g) over bar -balls.
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Borsato, M. et al, Zurita, J., Henry, L., Jashal, B. K., & Oyanguren, A. (2022). Unleashing the full power of LHCb to probe stealth new physics. Rep. Prog. Phys., 85(2), 024201–45pp.
Abstract: 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.
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