[論文レビュー] Searching for supermassive charged gravitinos in underground experiments

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

Dark Matter and Cosmic Phenomena被引用数 15

ひとこと要約

この論文は、地下検出器で安定した超大質量重力子を電荷約±2/3eで探索することを提案しており、 JUNO に焦点を当て、遅くて極めて大質量の粒子の直線上に沿って連動する3回以上の核反跳の特徴的な署名を予測している。

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.

研究の動機と目的

• 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.

提案手法

• 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.

実験結果

リサーチクエスチョン

• 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?

主な発見

• 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.