[논문 리뷰] Searching for supermassive charged gravitinos in underground experiments

Krzysztof A. Meissner, Hermann Nicolai|arXiv (Cornell University)|2023. 06. 22.

Dark Matter and Cosmic Phenomena인용 수 15

한 줄 요약

요약: 이 논문은 JUNO에 초점을 맞춰 지하 검출기에서 전하를 가진 안정적인 초대질량 중성중성미자(gravitino) 탐색을 제안하며, 느리면서 질량이 큰 입자에 의해 직선으로 이어지는 세 번 이상의 핵 반발의 연관 시퀀스라는 특이한 시그니처를 예측한다.

ABSTRACT

We examine possible experimental signatures that may be exploited to search for stable supermassive particles with electric charges of $O(1)$ in future underground experiments, and the upcoming JUNO experiment in particular. The telltale signal providing a unique signature of such particles, would be a correlated sequence of three or more nuclear recoils along a straight line, corresponding to the motion of a non-relativistic ($β\lesssim 10^{-2}$) particle that could enter the detector from any direction. We provide some preliminary estimates for the expected event rates.

연구 동기 및 목표

• Motivation: test the unconventional DM candidate of ultra-massive, electrically charged gravitinos as part of a Planck-scale unification proposal.
• Goal: identify unique experimental signatures that distinguish such particles from standard neutrino backgrounds in underground detectors, with emphasis on JUNO.
• Approach: assess interaction regimes and observable signals along the particle's track, and provide rough event-rate estimates dependent on flux and detector properties.

제안 방법

• Treat the particle as effectively infinitely massive due to its Planck-scale mass and analyze its electromagnetic interactions with atoms in a detector material.
• Qualitatively categorize interaction regimes as (i) grazing interaction with outer electrons, (ii) near-nucleus interactions with partial shielding, and (iii) close encounters causing nuclear recoils.
• Identify observable signals: ionization, electronic excitation without ionization, and nuclear recoils along the track, with emphasis on detectable nuclear recoils from central collisions.
• Estimate observable light production and PMT response uncertainties, noting that precise quantum-chemical treatment is not yet available.
• Compute a conservative geometric-cross-section–based recoil rate and discuss potential enhancements from long-range electromagnetic interactions.

실험 결과

연구 질문

• RQ1 What experimental signatures would uniquely indicate the passage of a supermassive charged gravitino in an underground detector?
• RQ2 Can JUNO (or similar experiments) discriminate such signals from neutrino-induced processes and other backgrounds?
• RQ3 What are the expected event-rate signatures given plausible fluxes and detector dimensions?
• RQ4 What is the minimum velocity (beta) regime for detectable nuclear recoils from such particles?
• RQ5 How many recoils along a track are needed to claim evidence for these particles, and how directionally distributed might they be?

주요 결과

• A distinctive signature would be a correlated sequence of at least three nuclear recoils along a straight line, corresponding to the slow, non-relativistic motion of the Particle through the detector.
• The Particle can traverse the Earth with minimal energy loss due to its large mass and small cross sections, making deeper detectors preferable for discovery.
• For a detector like JUNO (R ~ 18 m), the probability distribution for recoils along the track yields notable chances of N≥3 recoils, e.g., at PR=1.0 the probabilities are N=3: 0.105 and N=4: 0.041; at PR=0.5 the corresponding values are N=3: 0.029 and N=4: 0.006; at PR=1.5 the values are N=3: 0.164 and N=4: 0.093.
• Using a flux estimate of about 0.03 m^-2 yr^-1 sr^-1 and JUNO's area, the paper rough-forecasts of order hundreds of events per year from all directions, modulo substantial uncertainties.
• The triple-recoil (or double recoil) signature could be detectable with appropriate trigger/electronics adjustments in JUNO, and would be distinguishable from neutrino interactions which do not produce straight-line recoil sequences.