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  • Open Access

Search for the Pair Production of Dark Particles X with KL0→XX, X→γγ

C. Lin et al. (KOTO Collaboration)
Phys. Rev. Lett. 130, 111801 – Published 13 March 2023
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    Abstract

    We present the first search for the pair production of dark particles X via KL0→XX with X decaying into two photons using the data collected by the KOTO experiment. No signal was observed in the mass range of 40–110  MeV/c2 and 210–240  MeV/c2. This sets upper limits on the branching fractions as B(KL0→XX)<(1–4)×10−7 and B(KL0→XX)<(1–2)×10−6 at the 90% confidence level for the two mass regions, respectively.

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    • Received 23 September 2022
    • Accepted 8 February 2023

    DOI:https://doi.org/10.1103/PhysRevLett.130.111801

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Particle dark matterParticle decaysParticle production
    1. Physical Systems
    Hypothetical particlesKaons
    Particles & Fields

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    Vol. 130, Iss. 11 — 17 March 2023

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    Images

    • Figure 1
      Figure 1

      Cross-sectional view of the KOTO detector. The names with (without) underline are dedicated to charged particle (photon) detection.

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    • Figure 1
      Figure 1

      Cross-sectional view of the KOTO detector. The names with (without) underline are dedicated to charged particle (photon) detection.

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    • Figure 2
      Figure 2

      Distribution of the photon pair invariant mass that is closest to Mπ0 (Mγγ closest to Mπ0) after imposing all the cuts against the KL0→3π0 background except for the ΔMDF2 cut. The dots and the histograms indicate the data and the MC prediction, respectively.

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    • Figure 2
      Figure 2

      Distribution of the photon pair invariant mass that is closest to Mπ0 (Mγγ closest to Mπ0) after imposing all the cuts against the KL0→3π0 background except for the ΔMDF2 cut. The dots and the histograms indicate the data and the MC prediction, respectively.

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    • Figure 3
      Figure 3

      Distribution of Zvtx after imposing all the cuts except for the Zvtx cut. The dots and the histograms indicate the data and the MC prediction, respectively. The blue dashed histogram indicates the KL0→XX distribution for MX=70  MeV/c2 assuming the branching fraction of 5×10−6.

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    • Figure 3
      Figure 3

      Distribution of Zvtx after imposing all the cuts except for the Zvtx cut. The dots and the histograms indicate the data and the MC prediction, respectively. The blue dashed histogram indicates the KL0→XX distribution for MX=70  MeV/c2 assuming the branching fraction of 5×10−6.

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    • Figure 4
      Figure 4

      Distribution of Zvtx versus average MX after imposing all the cuts except for the Zvtx cut. The thick red box represents the signal region. The dots indicate the data.

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    • Figure 4
      Figure 4

      Distribution of Zvtx versus average MX after imposing all the cuts except for the Zvtx cut. The thick red box represents the signal region. The dots indicate the data.

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    • Figure 5
      Figure 5

      Signal acceptance versus MX. The red diamond, blue triangle, black circular markers indicate the acceptance after imposing all the cuts, all but the ΔMDF2 cut, and further excluding the cuts against the KL0→π0π0 background, respectively.

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    • Figure 6
      Figure 6

      Upper limit (UL) of B(KL0→XX) for different MX at the 90% C.L. The dark (light) gray region indicates the exclusion by the cuts against the KL0→π0π0 background (the ΔMDF2 cut).

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