Constraints on millicharged particles with low-threshold germanium detectors at Kuo-Sheng Reactor Neutrino Laboratory

Abstract

Relativistic millicharged particles (χq) have been proposed in various extensions to the Standard Model of particle physics. We consider the scenarios where they are produced at nuclear reactor core and via interactions of cosmic-rays with the earth's atmosphere. Millicharged particles could also be candidates for dark matter, and become relativistic through acceleration by supernova explosion shock waves. The atomic ionization cross section of χq with matter are derived with the equivalent photon approximation. Smoking-gun signatures with significant enhancement in the differential cross section are identified. New limits on the mass and charge of χq are derived, using data taken with a point-contact germanium detector with 500 g mass functioning at an energy threshold of 300 eV at the Kuo-Sheng Reactor Neutrino Laboratory.Big Bang nucleosynthesis [12,13], and direct laboratory experiments [14][15][16].The theme of this article is to report new direct laboratory limits on χ q using data acquired by an n-type Point-Contact Germanium (PCGe) detector with sub-keV sensitivity and excellent energy resolution. The PCGe technology [17] is being used in the studies of coherent neutrino nucleus elastic scattering, as well as searches of "light" WIMPs [18][19][20][21] and neutrinoless double beta decay.This article is organized as follows. Three cases of χ q are selected for investigations, whose origins and flux estimations are given in Section II. The interaction of χ q with matter and the derivation of cross sections are discussed in Section III. Physics constraints on χ q derived from data taken with the PCGe at the Kuo-Sheng Reactor Neutrino Laboratory (KSNL) [17,[22][23][24][25] are presented in Section IV. II. SOURCES OF MILLICHARGED PARTICLES A. Nuclear Reactor-χqNuclear reactor cores are powerful sources of γ-rays and therefore have been used for searches of axions [26,27], dark photons [28,29], and millicharged neutrinos [30]. Approximately half of the γ-radioactivity are of "prompt" origins directly from highly excited fission frag-arXiv:1808.02719v2 [hep-ph]

Neutrino millicharge and other electromagnetic interactions with COHERENT-2021 data

“…The strongest upper limit on the millicharge neutrino is Q ν ≤ 2 × 10 −15 e from the time arrival dispersion and the energy spread of neutrinos from SN1987A [30]. The laboratory bounds from the ν − e are also several orders of magnitude smaller in size than the bounds of this study [20][21][22][23][24][25][26][27][28][29]. For instance, the TEXONO experiment derives the limit, Q ν ≤ 2.1 × 10 −12 e. However, this difference can be easily understood from the kinematical considerations discussed in this work, while as it was shown here, the robustness of the bounds totally depends on the experimental details.…”

“…From the theoretical considerations, there is no upper limit available on the millicharge neutrinos. All the known limits are experimental [20][21][22][23][24][25][26][27][28][29] or observational [30][31][32][33][34].…”

First results from a search for coherent elastic neutrino-nucleus scattering (CE$ν$NS) at a reactor site

“…At higher energies, they provide the ability to differentiate single-site from multiple-site interactions [12]. As a result, they have found applications in dark matter searches [15,16], neutrinoless double-beta decay experiments [17][18][19], ongoing attempts at CEνNS detection [6,[20][21][22], and exotic decays [23]. A compact detector profile, illustrated by this work, allows to envision their use as eminently-fieldable reactor monitoring devices with nuclear non-proliferation applications [24,25].…”

Constraints on bosonic dark matter with low threshold germanium detector at Kuo-Sheng reactor neutrino laboratory

“…Data taken with the nPCGe detector have been adopted to place constraints on milli-charged neutrino [21] and dark matter cosmic ray [22], as well as heavy sterile neutrinos as dark matter [13]. The data presented in this article were acquired over 628.…”