Dark matter detection in two easy steps

Abstract

Multi-component dark matter particles may have a more intricate direct detection signal than simple elastic scattering on nuclei. In a broad class of well-motivated models the inelastic excitation of dark matter particles is followed by de-excitation via $\gamma$-decay. In experiments with fine energy resolution, such as many $0\nu 2\beta$ decay experiments, this motivates a highly model-independent search for the sidereal daily modulation of an unexpected $\gamma$ line. Such a signal arises from two-step WIMP interaction: the WIMP is first excited in the lead shielding and subsequently decays back to the ground state via the emission of a monochromatic $\gamma$ within the detector volume. We explore this idea in detail by considering the model of magnetic inelastic WIMPs, and take a sequence of CUORE-type detectors as an example. We find that under reasonable assumptions about detector performance it is possible to efficiently explore mass splittings of up to few hundreds of keV for a WIMP of weak-scale mass and transitional magnetic moments. The modulation can be cheaply and easily enhanced by the presence of additional asymmetric lead shielding. We devise a toy simulation to show that a specially designed asymmetric shielding may result in up to $30\%$ diurnal modulations of the two-step WIMP signal, leading to additional strong gains in sensitivity.Comment: 14 pages, 14 figure

The dark penguin shines light at colliders

“…at direct detection experiments [59][60][61][62][63][64]. The typical momentum exchange in the direct and indirect detection experiments is very small, therefore it is reasonable to use the EFT description even when the mediators are light with respect to collider energies.…”

Physics motivation for a pilot dark matter search at Jefferson Laboratory

“…DM-electron scattering can easily yield multiGeV electron recoils for the mediator masses of interest, and are therefore particularly visible. Third, and most significantly, we consider a new signal that arises when the DM states have O(1) mass splittings and have appreciable inelastic interactions, as in [9][10][11][12][13][14][15][16]. In this case, the up-scattering of a dark matter state χ into an excited state ψ is followed by a prompt decay ψ → χe + e − ( Figure 1(b), right).…”

“…Processes analogous to both a) and b) can also exist if DM is a scalar -see Sec. II B 1 could be seen if DM states are split by MeV, so that DM scattering produces energetic e + e − pairs (considered in other contexts in [9,11,14,16,[25][26][27][28][29]). …”

“…However, most of these efforts are designed to find heavy (10−1000 GeV) DM candidates and sharply lose sensitivity to lighter (sub-GeV) states whose signals are either too feeble or lie in highbackground regions. Even direct-detection experiments [3][4][5] and proposals [6][7][8] that are expanding sensitivity to GeV-scale DM rely on an elastic scattering channel that is absent or highly suppressed in many DM scenarios [9][10][11][12][13][14][15][16].…”

X-ray line from exciting dark matter

“…In such a scenario, dark matter can upscatter in rock, then decay electromagnetically in a detector, and was proposed as an explanation of the DAMA modulation. Indeed, a search at CUORE for precisely this hybrid (vector+dipole) scenario has recently been proposed [19]. Taking the recent X-ray cluster results for normalization, this gives a specific target to look at, both as an anomalous peak at 3.56 keV in the bolometer spectrum as well as for modulation in that peak.…”