Detecting Light Dark Matter via Inelastic Cosmic Ray Collisions

Direct detection experiments relying on nuclear recoil signatures lose sensitivity to sub-GeV dark matter for typical galactic velocities. This sensitivity is recovered if there exists another source of flux with higher momenta. Such an energetic flux of light dark matter could originate from the decay of mesons produced in inelastic cosmic ray collisions. We compute this novel production mechanism—a cosmic beam dump experiment—and estimate the resulting limits from XENON1T and LZ. We find that the dark matter flux from inelastic cosmic rays colliding with atmospheric nuclei can dominate over the flux from elastic collisions with relic dark matter. The limits that we obtain for hadrophilic scalar mediator models are competitive with those from MiniBoone for light MeV-scale mediator masses.

Figure 1

Dark matter flux from cosmic rays for elastic collisions in dotted orange with $m_{\chi }=1\mathrm{MeV}$, and for inelastic collisions with $\mathrm{BR}({\pi }^0\to \gamma \chi \chi )=6\times {10}^{-4}$ in solid green and $\mathrm{BR}(\eta \to \pi \chi \chi )=5\times {10}^{-3}$ in solid red.

Figure 2

90% C.L. limits on the spin-independent dark matter-nucleon cross section as a function of dark matter mass for a fixed branching ratio (top) and as a function of branching ratio for a fixed dark matter mass (bottom), as labeled. The inelastic cosmic ray dark matter limits from XENON1T [5] are indicated in red and green for the flux originating from meson $M=\eta$ and ${\pi }^0$ decays, respectively, and in orange for elastic cosmic ray dark matter. The dashed lines are projections for the future LZ experiment [13]. Other limits in grey are taken from Ref. [3] [based on CRESST [25], cosmic microwave background (CMB) [26], and gas cloud cooling [27] ], and from Milky Way satellites [28].

Figure 3

90% C.L. limits from inelastic cosmic ray dark matter flux from $\eta$ decays in red, for a hadrophilic scalar mediator of mass $m_S$ with up-quark coupling $g_u$, setting $g_{\chi }=1$, $m_{\chi }=m_S/3$. The solid line denotes current limits from XENON1T [5]; the dashed line are future projections for the LZ experiment [13]. Current MiniBoone limits from Ref. [14] are shown in grey.