LLP2026: 16th workshop of the Long-Lived Particle Community

Proposing GRENDEL: a new dedicated LLP detector at the LHC

30 Jun 2026, 17:00

20m

Ray Dolby Centre

Talk 15'

Speakers

Federico Leo Redi (U. of Bergamo and INFN Milan (IT)) Matthew Daniel Citron (University of California Davis (US))

Description

We propose GRENDEL (GalleRy ExperimeNt for Decays of Exotic LLPs), a dedicated LLP detector to be installed in the existing PX56 drainage gallery at CMS Point 5. The gallery sits approximately 22 m above the CMS interaction point, with CMS detector material and 15--20 m of rock and concrete providing shielding from hadronic backgrounds and roughly 70 m of overburden suppressing the cosmic-ray muon flux. The existing tunnel geometry provides an air-filled decay volume of ~740m3 requiring no new civil engineering. We consider two potential technologies for tracking the decays of LLPs within the decay volume: extruded scintillator strips and scintillating fibres. We present the detector concept, its integration in PX56, the expected background, and projected sensitivities for several LLP benchmark models produced through Higgs, heavy-flavour, and electroweak processes. With 3 ab-1 of data at the HL-LHC, GRENDEL achieves leading sensitivity for LLPs with masses from 1-55 GeV (reaching sensitivity to Higgs decay branching ratios below 2x10⁻⁵ for 40 GeV LLPs). The GRENDEL detector will be documented in a paper soon to be released on arXiv.

Presentation materials

ws_LLP2026_GRENDEL_260630.pdf