Proposal to use LHC general-purpose detectors in “beam-dump” measurements for long-lived particles

We propose a novel scheme for performing a beam-dump-like experiment with the general-purpose detectors (ATLAS and CMS) at the LHC. Collisions of high-energy protons result in jets containing a number of energetic hadrons and electromagnetic objects that are essentially “dumped” to hadronic and electromagnetic calorimeters, respectively, and induce the production of secondary hadrons, electrons, and photons in calorimetric showers. We envision a situation where new physics particles are produced by the interactions of these secondary particles inside the calorimeters. For proof of principles, we consider the axion-like particles (ALPs) produced via the Primakoff process in the presence of their interaction with photons at CMS. We argue that the drift tube chambers and the ME0 module of the muon system can serve as detectors to record the photons from the ALP decay, demonstrating that assuming the background level can be controlled as discussed in this work, the resulting sensitivity reach is competitive due to their close proximity to the signal source points. We further show that the LHC does not suffer from a barrier, dubbed beam-dump “ceiling”, that typical beam-dump experiments hardly surpass. This gives the LHC great potential to explore a wide range of parameter space. This analysis can be extended to investigate various types of light mediators with couplings to the Standard Model leptons and quarks.