Speaker
Description
Future electron–positron linear colliders can extend their physics reach beyond the interaction point through beam-dump searches using intense spent beams. Proposed ILC main-beam-dump experiments use a long dump–shield–decay-volume configuration to search for long-lived particles, with penetrating muons and neutrons as key backgrounds.
EBES, located at the third switchyard of the KEK LINAC, which supplies electron and positron beams to SuperKEKB, provides a complementary lower-energy realization of such beyond-collider physics. It searches for short-lived sub-GeV axion-like particles (ALPs) in the relatively high-mass, large-coupling region through their decays into two photons. Its compact 1.4 m shield preserves sensitivity to short lifetimes while allowing penetrating beam-induced backgrounds to reach the detector.
We evaluate these backgrounds using two layers of highly granular silicon pad sensors developed for the ILC silicon–tungsten electromagnetic calorimeter (SiW-ECAL). Their fine transverse segmentation and sensitivity to minimum-ionizing particles enable measurements of charged-particle backgrounds and pad-by-pad detector response. Data from 7 GeV electron and 4 GeV positron beams are compared to quantify beam-condition-dependent variations in background composition and muon flux. PHITS-derived corrections for geometrical acceptance, pad-selection efficiency, and energy-window efficiency, combined with a cosmic-ray MIP calibration, convert observed counts into absolute background rates per unit beam charge.
Although direct extrapolation is limited by differences in beam energy and geometry, this analysis tests secondary-particle production, transport, and detector-response models relevant to future linear-collider beam-dump experiments. It also demonstrates how highly granular collider-calorimeter sensors can support BSM searches beyond the interaction point.