Abstract
Identifying the true theory of dark matter depends crucially on accurately characterizing interactions of dark matter (DM) with other species. In the context of DM direct detection, we present a study of the prospects for correctly identifying the low-energy effective DM-nucleus scattering operators connected to UV-complete models of DM-quark interactions. We take a census of plausible UV-complete interaction models with different low-energy leading-order DM-nuclear responses. For each model (corresponding to different spin–, momentum–, and velocity-dependent responses), we create a large number of realizations of recoil-energy spectra, and use Bayesian methods to investigate the probability that experiments will be able to select the correct scattering model within a broad set of competing scattering hypotheses. We conclude that agnostic analysis of a strong signal (such as Generation-2 would see if cross sections are just below the current limits) seen on xenon and germanium experiments is likely to correctly identify momentum dependence of the dominant response, ruling out models with either “heavy” or “light” mediators, and enabling downselection of allowed models. However, a unique determination of the correct UV completion will critically depend on the availability of measurements from a wider variety of nuclear targets, including iodine or fluorine. We investigate how model-selection prospects depend on the energy window available for the analysis. In addition, we discuss accuracy of the DM particle mass determination under a wide variety of scattering models, and investigate impact of the specific types of particle-physics uncertainties on prospects for model selection.
Highlights
Identifying the true theory of dark matter depends crucially on accurately characterizing interactions of dark matter (DM) with other species
Several studies have previously explored different aspects of the direct detection inverse problem: Ref. [18] focused on a subset of UV completions and limited to standard nuclear responses; Refs. [19, 20] investigated an incomplete set of effective field theory (EFT) operators that provoke only the standard nuclear response; Ref. [14] looked at a broad set of operators, turning on one operator at a time; Ref. [21] looked at a complete EFT but isolated a single nuclear response at a time; and Ref. [22] explored “simplified models”
For the baseline analysis, we focus on xenon, germanium (“Ge”), iodine (“I”), and fluorine (“F”) targets, with an outlook towards some existing and proposed experiments (LZ [42], SuperCDMS Snolab [43], sodium–iodide experiments [44], and fluorine–based bubble–chamber experiments [45], respectively)
Summary
The nuclear recoil energy spectrum is the number count of nuclear recoil events observed per recoil energy ER, per unit time, per unit target mass, vesc,lab dR dER (ER). Ρχ mT mχ vf (v) dσT dER (ER, v)d3v This quantity is the observable output of most direct detection experiments. It is a function of the experimental parameters, astrophysics inputs, particle properties of DM, and nuclear properties of target material. The ultimate goal of direct detection analysis is to reconstruct both the normalization and functional form of dσT /dER from nuclear recoil data. The total rate R of events (per target mass, per time) is an integral of the differential rate within the nuclear-recoil energy window of a given experiment. The total expected number of events for exposure Tobs (typically in kilogram-years) is N ≡ RTobs
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