Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider
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.
© 2020 The Author(s). Published by IOP Publishing Ltd. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 23 May 2019; Accepted 17 September 2019; Published 2 September 2020. We are very grateful to Andreas Albert, Tao Huang, Laura Jeanty, Joachim Kopp, Matt LeBlanc, Larry Lee, Haolin Li, Simone Pagan Griso, Michele Papucci, Matt Strassler, and Tien-Tien Yu for helpful conversations and comments on the draft. J Beacham acknowledges support from the US Department of Energy (DOE) and the US National Science Foundation (NSF). G Cottin acknowledges support from the Ministry of Science and Technology of Taiwan (MOST) under Grant No. MOST-107-2811-M-002-3120 and CONICYT-Chile FONDECYT Grant No. 3190051. N Desai was supported in part by the OCEVU Labex (ANR-11-LABX-0060) and the A *MIDEX project (ANR-11-IDEX-0001-02) funded by the 'Investissements d'Avenir' French government program managed by the ANR. J A Evans is supported by DOE grant DE-SC0011784. S Knapen is supported by DOE grant DE-SC0009988. A Lessa is supported by the Sao Paulo Research Foundation (FAPESP), project 2015/20570-1. Z Liu is supported in part by the NSF under Grant No. PHY-1620074, and by the Maryland Center for Fundamental Physics. S Mehlhase is supported by the BMBF, Germany. M J Ramsey-Musolf is supported by DOE grant DE-SC0011095. The work of P Schwaller has been supported by the Cluster of Excellence 'Precision Physics, Fundamental Interactions, and Structure of Matter' (PRISMA+ EXC 2118/1) funded by the German Research Foundation (DFG) within the German Excellence Strategy (Project ID 39083149). The work of J Shelton is supported in part by DOE under grant DE-SC0017840. The work of B Shuve is supported by NSF under grant PHY-1820770. X C Vidal is supported by MINECO through the Ramón y Cajal program RYC-2016-20073 and by XuntaGal under the ED431F 2018/01 project. Contributors: M Adersberger is supported by the BMBF, Germany. The work of C Alpigiani, A Kvam, E Torro-Pastor, M Profit, and G Watts is supported in part by the NSF. Y Cui is supported in part by DOE Grant DE-SC0008541. J L Feng is supported in part by Simons Investigator Award #376204 and by NSF Grant No. PHY-1620638. I. Galon is supported by DOE Grant DE-SC0010008. K Hahn is supported by DOE Grant DE-SC0015973. J Heisig acknowledges support from the F R S-FNRS, of which he is a postdoctoral researcher. The work of F Kling was supported by NSF under Grant No. PHY-1620638. H. Lubatti thanks the NSF for support. P Mermod was supported by Grant PP00P2_150583 of the Swiss National Science Foundation. S Mishra-Sharma is partially supported by the NSF CAREER Grant PHY-1554858 and NSF Grant PHY-1620727. V Mitsou acknowledges support by the Generalitat Valenciana (GV) through MoEDAL-supporting agreements and the GV Excellence Project PROMETEO-II/2017/033, by the Spanish MINECO under the project FPA2015-65652-C4-1-R, by the Severo Ochoa Excellence Centre Project SEV-2014-0398 and by a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. J Prisciandaro is supported by funding from FNRS. M Reece is supported by DOE Grant DE-SC0013607. D Robinson is supported in part by NSF grant PHY-1720252. D Stolarski is supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC). S Trojanowski is supported by Lancaster-Manchester-Sheffield Consortium for Fundamental Physics under STFC grant ST/L000520/1. S Xie is supported by the California Institute of Technology High Energy Physics Contract DE-SC0011925 with the DOE. This manuscript has been partially authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the US Department of Energy, Office of Science, Office of High Energy Physics.
Submitted - 1903.04497.pdf