Investigation of Low-Energy Particle Remnants in High-Energy Collisions at the LHC with a Skipper-CCD detector

TL;DR

This study utilizes a novel skipper-CCD detector placed near the LHC collision point to search for low-energy particles, setting constraints on millicharged particles and demonstrating the detector's potential for new physics exploration.

Contribution

First deployment of a skipper-CCD detector at the LHC to probe low-energy particles produced in high-energy collisions, establishing new experimental constraints and demonstrating detector viability.

Findings

No significant beam-related low-energy signals detected.

Observed a slight increase in event rate after Pb-Pb collisions.

Placed 95% C.L. constraints on millicharged particles.

Abstract

We deployed MOSKITA $\sim$33 m away from the CMS collision point, the first skipper-CCD detector probing low-energy particles produced in high-energy collisions at the Large Hadron Collider (LHC). In this work, we search for beam-related events using data collected in 2024 during beam-on and beam-off periods. The dataset corresponds to integrated luminosities of 113.3 fb$^{-1}$ and 1.54 nb$^{-1}$ for the proton-proton and Pb-Pb collision periods, respectively. We report observed event rates in a model-independent framework across two ionization regions: $\leq20e^-$ and $>20e^-$. For the low-energy region, we perform a likelihood analysis to test the null hypothesis of no beam-correlated signal. We found no significant correlation during proton-proton and Pb-Pb collisions. For the high-energy region, we present the energy spectra for both collision periods and compare event rates for images with and without luminosity. We observe a slight increase in the event rate following the Pb-Pb collisions, coinciding with a rise in the single-electron rate, which will be investigated in future work. Using the low-energy proton-proton results, we place 95% C.L. constraints on the mass-millicharge parameter space of millicharged particles. Overall, the results in this work demonstrate the viability of skipper-CCD technology to explore new physics at high-energy colliders and motivate future searches with more massive detectors.