Explore the Lifetime Frontier with MATHUSLA

Cristiano Alpigiani

doi:10.1051/epjconf/201818202004

Abstract

Many extensions of the Standard Model (SM) include particles that are neutral, weakly coupled, and long-lived that can decay to final states containing several hadronic jets. Long-lived particles (LLPs) can be detected as displaced decays from the interaction point, or missing energy if they escape. ATLAS and CMS have performed searches at the LHC and significant exclusion limits have been set in recent years. However, the current searches performed at colliders have limitations. An LLP does not interact with the detector and it is only visible once it decays. Unfortunately, no existing or proposed search strategy will be able to observe the decay of non-hadronic electrically neutral LLPs with masses above GeV and lifetimes near the limit set by Big Bang Nucleosynthesis (cπ ~ 107 - 108 m). Therefore, ultra-long-lived particles (ULLPs) produced at the LHC will escape the main detector with extremely high probability. MATHUSLA (MAssive Timing Hodoscope for Ultra Stable neutraL pArticles) is a surface detector, which can be implemented with existing technology and in time for the high luminosity LHC upgrade to find such ultra-long-lived particles, whether produced in exotic Higgs decays or more general production modes. The MATHUSLA detector will consist of resistive plate chambers (RPC) and scintillators with a total sensitive area of 200 x 200 m2. It will be installed on the surface, close to the ATLAS or CMS detectors. A small-scale test detector (~ 6m2) is going to be installed on the surface above ATLAS in November 2017. It will consist of three layers of RPCs used for timing/tracking and two layers of scintillators for timing measurements. It will be placed above the ATLAS interaction point to estimate cosmic backgrounds and proton-proton backgrounds coming from ATLAS during nominal LHC operations.

Highlights

The discovery of the Higgs boson at the LHC completed the Standard Model (SM), and focused attention on the many central features of our universe that the SM does not address: dark matter (DM), neutrino mass, particle-antiparticle asymmetry (Baryogenesis), hierarchy problem
Many BSM (Beyond the Standard Model) theoretical constructs proposed in the past few years that address these phenomena contain long-lived particles with macroscopic decay lengths limited only by Big Bang Nucleosynthesis (BBN) of about cτ 107 − 108 m
The detector signature is a hadronic jet displaced from the IP and no track connecting it to the IP

Summary

The hidden sector

The discovery of the Higgs boson at the LHC completed the SM, and focused attention on the many central features of our universe that the SM does not address: dark matter (DM), neutrino mass, particle-antiparticle asymmetry (Baryogenesis), hierarchy problem (naturalness). The detector signature is a hadronic jet displaced from the IP and no track connecting it to the IP. The kinetic mixing of a γd results in dark photons that decay to lepton pairs giving rise to a pair of displaced lepton vertices in the detector. The hidden sector particles have no SM quantum numbers and once produced travel through the detector unabated. Once they decay to SM particles a detector signal is observed. The proposed MATHUSLA detector [11], which is a dedicated large volume, air filled detector located on the surface above and somewhat displaced from the ATLAS or CMS IPs, will be sensitive to lifetimes of 107 m with the expected integrated luminosity of High Luminosity LHC (HL-LHC)

The MATHUSLA detector

The MATHUSLA test module

MATHUSLA and cosmic rays