Abstract

The sensitivity to dark matter signals at neutrino experiments is fundamentally challenged by the neutrino rates, as they leave similar signatures in their detectors. As a way to improve the signal sensitivity, we investigate a dark matter search strategy which utilizes the timing and energy spectra to discriminate dark matter from neutrino signals at low-energy, pulsed-beam neutrino experiments. This strategy was proposed in our companion paper Phys. Rev. Lett.124 (2020) 121802 [1], which we apply to potential searches at COHERENT, JSNS2, and CCM. These experiments are not only sources of neutrinos but also high intensity sources of photons. The dark matter candidate of interest comes from the relatively prompt decay of a dark sector gauge boson which may replace a Standard-Model photon, so the delayed neutrino events can be suppressed by keeping prompt events only. Furthermore, prompt neutrino events can be rejected by a cut in recoil energy spectra, as their incoming energy is relatively small and bounded from above while dark matter may deposit a sizable energy beyond it. We apply the search strategy of imposing a combination of energy and timing cuts to the existing CsI and LAr data of the COHERENT experiment as concrete examples, and report a mild excess beyond known backgrounds. We then investigate the expected sensitivity reaches to dark matter signals in our benchmark experiments.

Highlights

  • Searches for dark matter candidates at neutrino experiments using high intensity, O(1) GeV particle beams are intriguing [1, 12,13,14,15,16]

  • While many of the low-energy, high-intensity frontier experiments possibly would enjoy the advantage of a combination of energy and timing cuts in terms of dark matter searches, we focus on the COHERENT [15, 17, 18], JSNS2 [19,20,21], and Coherent Captain-Mills (CCM) [22,23,24] experiments to apply our search techniques for

  • The neutrinos here can carry an energy up to Eν ≈ mμ/2 = 52.5 MeV so that the resultant recoil energy spectrum can be more broadly distributed. Given these features of the prompt and delayed neutrino-induced background events, we propose to apply a combination of an energy cut and a timing cut in order to suppress the SM neutrino backgrounds but retain as many dark matter signal events as possible

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Summary

Models: dark matter scenarios

We discuss various new physics scenarios which can be probed with the proposed search strategy. E− and N denote stable particle species, electron and nucleus, respectively, and χ represents the possibility that χ turns into a different species in the scattering process [28,29,30,31] Such an intermediary particle may undergo a multi-step cascade decay depending on the model details, and some of the stable decay products (including neutrinos) again may repeat the aforementioned procedure:. Some of the decay products may be SM particles so that they directly leave visible signatures at the detector While such a possibility is interesting per se and similar strategies are applicable, we focus on the case with stable new physics particles such as dark matter in this study

Production of dark matter
Detection of dark matter
Benchmark experiments and simulations
Benchmark experiments
Estimating dark matter fluxes
Timing spectrum of dark matter events
Data analysis
Interpretations
Excess and dark matter interpretations — CsI data
Excess and dark matter interpretations — LAr data
Constraining parameter space
Interpretations in other dark matter scenarios
Conclusions
A Phase-space suppression of cascade photons
Findings
B Derivation of timing spectra
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