Phys. Rev. D 106, 063026 (2022) - Search for relativistic fractionally charged particles in space

Search for relativistic fractionally charged particles in space

F. Alemanno et al. (DAMPE Collaboration)

Phys. Rev. D 106, 063026 – Published 29 September 2022

Abstract

More than a century after the performance of the oil drop experiment, the possible existence of fractionally charged particles (FCPs) still remains unsettled. The search for FCPs is crucial for some extensions of the Standard Model in particle physics. Most of the previously conducted searches for FCPs in cosmic rays were based on experiments underground or at high altitudes. However, there have been few searches for FCPs in cosmic rays carried out in orbit other than AMS-01 flown by a space shuttle and BESS by a balloon at the top of the atmosphere. In this study, we conduct an FCP search in space based on on-orbit data obtained using the Dark Matter Particle Explorer (DAMPE) satellite over a period of five years. Unlike underground experiments, which require an FCP energy of the order of hundreds of GeV, our FCP search starts at only a few GeV. An upper limit of $6.2 \times 10^{- 10} {cm}^{- 2} {sr}^{- 1} s^{- 1}$ is obtained for the flux. Our results demonstrate that DAMPE exhibits higher sensitivity than experiments of similar types by three orders of magnitude that more stringently restricts the conditions for the existence of FCP in primary cosmic rays.

Received 18 May 2022
Accepted 8 September 2022

DOI:https://doi.org/10.1103/PhysRevD.106.063026

Physics Subject Headings (PhySH)

Cosmic ray & astroparticle detectors Cosmic ray composition & spectra Cosmic rays & astroparticles Particle astrophysics

Particles & FieldsGravitation, Cosmology & AstrophysicsEnergy Science & Technology

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Vol. 106, Iss. 6 — 15 September 2022

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Figure 1
The structure of the DAMPE detector.
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Figure 2
The angle difference between the BGO track and STK track. The (a) and (b) panels depict the distributions of angle difference in the YOZ and XOZ planes, respectively. The angle differences obtained from the on-orbit data (black dots) and MC proton (pink solid line) agree well within [ $- 4 °$ , $+ 4 °$ ].
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Figure 3
The distributions of charges measured by the PSD (a) and STK (b). The spectra obtained from on-orbit data (black dots) and MC protons (red line) are normalized with ordinate values in arbitrary units and are consistent. The FCP (green line) is well distinguished from singly charged particles. The log scale distributions for the PSD and STK are shown in the insets.
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Figure 4
The charge distributions from the PSD and STK and the definition of the signal region. The charge distributions for the PSD and STK are shown in panels (a) and (b), respectively. The event counts are scaled to arbitrary units. The solid green lines correspond to MC FCPs and the dashed blue lines are for MC protons. With the help of the integrals of FCP charges represented by the solid black lines, the signal region is defined based on the distributions presented in panels (a) and (b). The red lines in panels (c) and (d) represent the signal region for FCPs where the charge values for the PSD and STK are $0.84 e$ and $0.79 e$ , respectively. All background proton MIP events fall outside the region, as depicted in panel (c). Injections from the bottom surface to the top surface of DAMPE are simulated and excluded as well. The combined efficiency of the signal region for FCPs is approximately 86.0%, as depicted in panel (d).
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Figure 5
The distribution of PSD-STK charge for on-orbit data. The red lines indicate the signal region for FCPs. The signal region is defined to cover candidate FCP event, while rejecting the proton background. No candidate event is observed to lie within the signal region. The portion above 1.1e of both PSD and STK charges corresponds to the events that inject from the bottom to the top of DAMPE. These events are low-energy secondary particles of extensive air showers.
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Figure 6
FCP ux upper limit versus electric charge from different cosmic ray experiments. The results of underground experiments which require the particles to have energy above $\sim 100 s GeV$ are shown in the left panel. The results of space experiments which detect the particles above a few GeV due to the limitation of geomagnetic cuto are shown in the right panel. The DAMPE upper limit (red dot) is lower than those from AMS-01 [25] (light red cross) and BESS [26] (red inverted triangle). The results of the underground experiments such as LSD [20] (blue triangles), Kamiokande II [19] (blue full diamond), MACRO [21] (blue dashed line), CDMS II [23] (blue dotted line), and MAJORANA [24] (blue solid line) are shown also.
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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for relativistic fractionally charged particles in space

F. Alemanno et al. (DAMPE Collaboration)

Phys. Rev. D 106, 063026 – Published 29 September 2022

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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for relativistic fractionally charged particles in space

F. Alemanno et al. (DAMPE Collaboration)

Phys. Rev. D 106, 063026 – Published 29 September 2022

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