Prospects of detecting cosmic ray up-scattered dark matter with DUNE

TL;DR

The paper addresses the challenge of detecting sub-GeV dark matter by exploring cosmic-ray boosted DM (CRDM) that attains detectable energies through interactions with galactic CRs. It adopts a Z' mediator model with vector or axial-vector couplings, computes the CRDM flux including inelastic channels via the GENIE framework, and evaluates DUNE's sensitivity to DM–nucleon and DM–nucleus scattering across coherent, quasi-elastic, and deep inelastic processes. The main findings show that DUNE can reach sensitivity to DM–nucleon cross sections comparable to dedicated direct-detection experiments for spin-independent interactions and also constrain spin-dependent interactions with competitive reach, thanks to DIS contributions that are especially impactful for axial-vector couplings. This work highlights the potential of a neutrino detector like DUNE to probe nucleon-coupled DM in the sub-GeV regime and emphasizes the importance of accurate QE/DIS modeling and atmospheric neutrino backgrounds for CRDM searches, inviting further cross-experiment and background-uncertainty studies.

Abstract

Detection of sub-GeV dark matter (DM) particles in direct detection experiments is inherently difficult, as their low kinetic energies in the galactic halo are insufficient to produce observable recoils of the heavy nuclei in the detectors. On the other hand, whenever DM particles interact with nucleons, they can be accelerated by scattering with galactic cosmic rays. These cosmic-ray-boosted DM particles can then interact not only through coherent elastic scattering with nuclei, but also through scattering with individual nucleons in the detectors and produce outgoing particles at MeV to GeV kinetic energies. The resulting signal spectrum overlaps with the detection capabilities of modern neutrino experiments. One future experiment is the Deep Underground Neutrino Experiment (DUNE) at the Sanford Underground Research Facility. Our study shows that DUNE has a unique ability to search for cosmic-ray boosted DM with sensitivity comparable to dedicated direct detection experiments in the case of spin-independent interactions. Importantly, DUNE's sensitivity reaches similar values of DM-nucleon cross sections also in the case of spin-dependent interactions, offering a key advantage over traditional direct detection experiments.

Figures (6)

• Figure 1: Differential cross sections for the scattering of DM with kinetic energy $T_\chi=1\,$GeV with a proton initially at rest for the cases of vector and axial-vector couplings. The mediator and DM masses are set to $m_{Z'} = 1\,$GeV and $m_\chi=1\,$GeV, respectively, further, the values $Q_\chi^V = Q_\chi^A = Q_q^V = Q_q^A =1$ for all quarks $q$ and $g_{Z'}=0.1$ are assumed. The dashed lines correspond to the elastic scattering given by formula \ref{['dsig_dq2']}, the dotted lines correspond to the DIS contribution obtained from the GENIE module Berger:2018urf, and the solid lines correspond to the sum of these two contributions.
• Figure 2: Differential cross sections for the scattering of DM with kinetic energy $T_\chi=1\,$GeV with an argon nucleus initially at rest for the cases of vector and axial-vector couplings, obtained from the GENIE module Berger:2018urf. The values of the couplings and DM and mediator masses are the same as in figure \ref{['fig:comSig']}. The dashed and dotted lines correspond to QE scattering and DIS, respectively. The solid lines correspond to the sum of these two contributions. The dot-dashed line depicts the simple estimate of the QE cross section from the sum of elastic cross sections for nucleons initially at rest. The grid lines depict the maximum kinematically allowed momentum transfer $Q^2_{\max}$ for the elastic scattering of DM with a nucleon at rest ($\sim 2\,$GeV$^2$) and with an argon nucleus at rest ($\sim 10\,$GeV$^2$), see appendix \ref{['ap:kinematics']} for details.
• Figure 3: CRDM flux coming to the Earth's atmosphere. For the vector couplings (top), the solid lines correspond to the flux of the DM particles accelerated by the elastic and inelastic DM scattering with CR protons and He, C, and O nuclei. In contrast, the dotted lines correspond to scattering with protons only. On the other hand, only elastic scattering with the four most abundant CR nuclei is considered for the dashed lines. For the axial-vector couplings (bottom), the solid lines depict scattering with only CR protons (the contribution of the heavier spin-0 nuclei is subdominant in this case). The dashed lines again correspond to the flux from elastic scattering only.
• Figure 4: Number of events given 400 kiloton*years of data-taking in the signal region $\cos \theta_z \geq 0.1$ possibly seen in DUNE for a fixed value of $g_{Z'}$ and vector (left) or axial-vector (right) couplings. The solid lines correspond to the full CRDM flux induced by both elastic and inelastic scattering with CR and both QE scattering and DIS of DM with argon nuclei in the detector. The dashed lines correspond to elastic-only contribution to the CR-DM scattering, whereas the dotted lines correspond to QE-only scattering with argon. Finally, the dashed gray line corresponds to the detection threshold derived in appendix \ref{['sec:atmnu']}.
• Figure 5: Sensitivity of the DUNE detector assuming 400 kiloton*years of data taking and considering only statistical errors on the number of background neutrino events (red region). Other colored regions correspond to complementary constraints. In particular, the brown regions depict the CRDM bounds by Xenon1T Diurba:2024dqo and Borexino Dent:2019krz for similar mediator scenarios as considered in our work. Further, different shades of green depict bounds on halo DM by direct detection experiments while shades of blue are used for cosmological constraints, see the main text for details. The gray region correspond to parameter space where our DM scenarios would become non-perturbative.