Search for Cosmic-Ray Boosted Sub-GeV Dark Matter Using Recoil Protons at Super-Kamiokande

We report a search for cosmic-ray boosted dark matter with protons using the $0.37\text{megaton}\times \mathrm{years}$ data collected at Super-Kamiokande experiment during the 1996–2018 period (SKI-IV phase). We searched for an excess of proton recoils above the atmospheric neutrino background from the vicinity of the Galactic Center. No such excess is observed, and limits are calculated for two reference models of dark matter with either a constant interaction cross section or through a scalar mediator. This is the first experimental search for boosted dark matter with hadrons using directional information. The results present the most stringent limits on cosmic-ray boosted dark matter and exclude the dark matter–nucleon elastic scattering cross section between $10^{-33}{\mathrm{cm}}^2$ and $10^{-27}{\mathrm{cm}}^2$ for dark matter mass from $1\mathrm{MeV}/c^2$ to $300\mathrm{MeV}/c^2$.

Figure 1

The selection efficiencies for the proton sample. The red dotted line indicates the reduction efficiency of the FCFV sample above 30 MeV. The blue dashed line represents the efficiency after precuts. The green solid line is the efficiency after the MVA cut.

Figure 2

The angle between proton ring and the GC for events in the proton sample, without (upper) and with (lower) the zenith angle cut. The black points indicate data with statistical uncertainty. The blue bands indicate MC expectation with systematic uncertainty.

Figure 3

Constraints on dark matter–nucleon cross section. Solid lines show the upper limit while dashed lines indicate the sensitivity. The green lines are calculated with a constant cross-section model. The blue lines are the cross sections at the nonrelativistic limit (${\sigma }_{\mathrm{NR}}$) for the scalar mediator model. The shaded sage green region indicates the PANDAX-II CRDM exclusion region [36]. The shaded maroon region shows the CRESST-III exclusion region [47], and the shaded gray region shows the constraints via Migdal effect from CDEX-1B [48] and XENON1T [49].