Monochromatic dark neutrinos and boosted dark matter in noble liquid direct detection

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Monochromatic dark neutrinos and boosted dark matter in noble liquid direct detection

David McKeen and Nirmal Raj

Phys. Rev. D 99, 103003 – Published 13 May 2019

Abstract

If dark matter self-annihilates into neutrinos or a second component of (“boosted”) dark matter that is nucleophilic, the annihilation products may be detected with high rates via coherent nuclear scattering. A future multi-ten-tonne liquid xenon detector such as DARWIN, and a multi-hundred-tonne liquid argon detector, argo, would be sensitive to the flux of these particles in complementary ranges of 10–1000 MeV dark matter masses. We derive these sensitivities after accounting for atmospheric and diffuse supernova neutrino backgrounds, and realistic nuclear recoil acceptances. We find that their constraints on the dark neutrino flux may surpass neutrino detectors such as Super-Kamiokande, and that they would extensively probe parametric regions that explain the missing satellites problem in neutrino portal models. The XENON1T and Borexino experiments currently restrict the effective baryonic coupling of thermal boosted dark matter to $≲ 10 - 100 \times$ the weak interaction, but darwin and argo would probe down to couplings 10 times smaller. Detection of boosted dark matter with baryonic couplings $\sim 10^{- 3} - 10^{- 2} \times$ the weak coupling could indicate that the dark matter density profile in the centers of galactic halos become cored, rather than cuspy, through annihilations. This work demonstrates that, alongside liquid xenon, liquid argon direct detection technology would emerge a major player in dark matter searches within and beyond the wimp paradigm.

Received 20 December 2018

DOI:https://doi.org/10.1103/PhysRevD.99.103003

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)

Particle dark matter Particle interactions

Particles & Fields

Authors & Affiliations

David McKeen and Nirmal Raj

TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada

Article Text

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Issue

Vol. 99, Iss. 10 — 15 May 2019

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Images

Figure 1
Left. Differential cross section for coherent scattering of neutrinos with xenon and argon nuclei, for neutrino energies 30 MeV and 300 MeV. Argon, being lighter, recoils to higher energies. The effect of the Helm form factor, which suppresses the cross section at high recoil energies, is seen here as a bump in the cross section and is only important at recoil energies $≳ 10^{3} keV$ —which far exceeds the cutoff $\sim 10^{2} keV$ below which we accept events for our study. Right. The scattering rate of dark neutrinos [ $G_{T} = G_{F}$ in Eq. (3)] per tonne-year of exposure at liquid xenon and argon detectors, assuming dark matter annihilation cross section $⟨ σ_{ann} v ⟩ = 10^{- 23} {cm}^{3} / s$ and an NFW halo profile. Events are integrated in the recoil energy window 5 keV–100 keV for xenon and 17 keV–110 keV for argon; the lower ends of these ranges correspond to neutrino energy $≃ 17 MeV$ . Also shown for reference is the rate of atmospheric and diffuse supernova neutrinos, which make up our primary irreducible background.
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Figure 2
90% c.l. sensitivities of the liquid xenon darwin (left) and liquid argon argo (right) detectors, with fiducial masses of 40 tonnes and 300 tonnes respectively, to $⟨ σ_{ann} v ⟩ \times$ the coupling of the annihilation products to nucleons (normalized to the Fermi constant), as a function of dark matter mass. An nfw halo profile is assumed. The sensitivities are shown for 1, 5 and 10 years of exposure, and for nuclear recoil acceptances of 30% and 50% for darwin, and 60% and 80% for argo. The electronic recoil rejection is assumed to be at a level that renders background leakage from solar neutrino-electron scattering negligible. See Sec. 2c for more details.
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Figure 3
Left. Same sensitivities as Fig. 2, of the detectors darwin (with 10 years of run-time and 50% nr acceptance), argo (with 10 years of run-time and 80% nr acceptance), and XENON1T after 1 tonne-year of exposure. Also shown is the bound from proton recoils in borexino (derived in Appendix pp2). For all these bounds an nfw halo profile is assumed. These are compared with sensitivities from a possible extragalactic flux, which we compute using the approximate method described in Sec. 2a. Right. Comparison of darwin and argo sensitivities (as shown in the left panel) to a Galactic flux of dark neutrinos from the channel $χ \bar{χ} \to ν_{τ} {\bar{ν}}_{τ}$ , with current and future neutrino detectors. Direct detection would surpass the bound from Super-K relic neutrino searches [9] and that derived by Yuksel, et al. [2] in the dark matter mass range 35 MeV–800 MeV. If dark neutrinos are produced instead as mass eigenstates in majoron-mediated dark matter annihilations, $χ \bar{χ} \to ν_{i} {\bar{ν}}_{i}$ ( $i = 1$ ,2,3), the bounds from neutrino experiments would be weakened by an $O (10)$ factor while the darwin and argo sensitivities are not affected. See Sec. 2c for more details.
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Figure 4
A simple diagnostic to distinguish between dark neutrinos and boosted dark matter, as described in Sec. 2d. Shown here is the ratio of background-subtracted events at darwin and argo after equal run-times, as a function of dark matter mass. Since neutrinos scatter preferentially on neutrons whereas boosted dark matter scatters equally on neutrons and protons, and since xenon and argon contain different numbers of nucleons, this ratio separates the two cases.
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Figure 5
Interpretation of our results in the left panel of Fig. 3 in terms of the neutrino portal dark matter model described in Sec. 3a. Bounds are shown in the plane of the effective coupling $Y_{τ}$ [Eq. (12)] vs dark matter mass, with regions above the curves excluded. Dashed black curves indicate parameters that result in suppression of the growth of structures below a mass cutoff of $1 0^{9}$ and $1 0^{7}$ solar masses, thus explaining the “missing satellites” problem. These regions are seen to be extensively probed by direct detection. The dashed orange curve denotes parameters that correspond to a dark matter-nucleon scattering cross section associated with the standard “neutrino floor” in xenon. The dashed blue line corresponds to a thermal annihilation cross section $= 10^{- 25} {cm}^{3} / s$ .
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Figure 6
Interpretation of our constraints on $(G_{T}^{2} / G_{F}^{2}) ⟨ σ_{ann} v ⟩$ vs dark matter mass in the left panel of Fig. 3, in terms of the boosted dark matter models described in Sec. 3b. Left. Bounds as a function of dark matter mass on the baryonic coupling $G_{B}$ (normalized to the Fermi constant $G_{F}$ ) such that the boosted dark matter flux is obtained for a thermal annihilation cross section $= 10^{- 25} {cm}^{3} / s$ . The bounds obtained by Cherry, et al. [20] used lux data. The erstwhile bound from borexino proton recoils (derived in Appendix pp2) and the current bound from XENON1T are seen to be stronger. Darwin and argo can be seen to probe $G_{B}$ all the way down to the weak coupling $G_{F}$ in the $m_{DM}$ range $\sim 25 - 100 MeV$ . Right. Addressing the core-cusp problem with boosted dark matter detection. Shown are values of $G_{B} / G_{F}$ ruled out by borexino and XENON1T, and those to be probed by darwin and argo, for an annihilation cross section [Eq. (14)] that would ensure that dark matter is depleted from halo cores.
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