Near or Far Detectors? Optimizing Long-Lived Particle Searches at Electron-Positron Colliders

Abstract

We explore the discovery potential for long-lived particles at the 250-GeV ILC. The goal is to investigate possible gains of a dedicated far detector over the main detector ILD. For concreteness, we perform our study for sub-GeV axion-like particles a produced via e + e − → aγ or e + e − → Zγ → (aγ)γ and decaying into pairs of charged leptons. In the ideal case of zero background and perfect detection efficiency, we find that far detectors placed in the planned underground cavities or a large cuboid on the ground can enhance the sensitivity to long-lived pseudo-scalars at best moderately. On the other hand, the ILD itself is a perfect environment to search for long-lived particles, due to its excellent angular coverage and radial thickness. For long-lived particles produced with cross sections of a few picobarns, the ILD could probe lifetimes up to 300 ns, or proper decay lengths up to 100 m, in 250 fb −1 of data. For axion-like particles produced through weak interactions, the ILC can reach an even higher sensitivity than searches for displaced vertices in meson decays at Belle II. Our findings apply similarly to other proposed electron-positron experiments with a high angular coverage, such as the FCC-ee and CEPC.

Searching for a single photon from lightest neutralino decays in R-parity-violating supersymmetry at FASER

“…Long-lived particles (LLPs) have in recent years received increased attention [40][41][42][43][44][45]. LLPs are predicted in a wide range of BSM models such as split SUSY, RPV-SUSY, a class of portal-physics models [axion-like particles (ALPs), heavy neutral leptons, a dark Higgs scalar, dark photons], and models of neutral naturalness -which are often related to the non-vanishing neutrino masses or dark matter.…”

Probe of axion-like particles in vector boson scattering at a muon collider

“…Since the ALPs are not directly relevant for the QCD axion, heavy ALPs can be detected at colliders. The production of the ALPs was studied in the pp [12][13][14][15][16][17][18][19] and heavyion [13,18,[20][21][22] collisions at the LHC, as well as at future colliders [23][24][25][26][27][28][29][30][31], including electron-ion scattering [32,33]. For a review on the axions and ALPs, see [9,[34][35][36][37][38][39] and references therein.…”

Triggering long-lived particles in HL-LHC and the challenges in the first stage of the trigger system

“…This includes the development of new detectors like FASER [63], MATHUSLA [64,65] and CODEX-b [66,67], and hardware specifically designed for search of displaced physics at the LHC's general purpose detectors along with application of innovative analysis techniques that utilise a variety of information from the different sub-detectors at HL-LHC. There are several proposals for dedicated detectors for LLP searches at future colliders like FCC-ee [68,69]. For FCC-hh, a transverse detector, DELIGHT [19], and a forward detector, FOREHUNT [70] have been proposed.…”