[Paper Review] Effective Field Theory Analysis of CDMSlite Run 2 Data

SuperCDMS Collaboration, M. F. Albakry+128 more|arXiv (Cornell University)|May 24, 2022

Particle Detector Development and Performance4 citations

TL;DR

This paper applies effective field theory (EFT) to analyze CDMSlite Run 2 data to search for weakly interacting massive particle (WIMP) dark matter signals, using Bayesian inference with four prior combinations to assess systematic uncertainties. The study finds that the flat prior on WIMP mass and flat-log prior on coupling amplitude (Prior 1) provides the most reliable sampling and is selected for the main analysis, yielding consistent 95% credibility contours across EFT operators with minimal bias.

ABSTRACT

CDMSlite Run 2 was a search for weakly interacting massive particles (WIMPs) with a cryogenic 600 g Ge detector operated in a high-voltage mode to optimize sensitivity to WIMPs of relatively low mass from 2 - 20 GeV/$c^2$. In this article, we present an effective field theory (EFT) analysis of the CDMSlite Run 2 data using an extended energy range and a comprehensive treatment of the expected background. A binned likelihood Bayesian analysis was performed on the recoil energy data, taking into account the parameters of the EFT interactions and optimizing the data selection with respect to the dominant background components. Energy regions within 5$σ$ of known activation peaks were removed from the analysis. The Bayesian evidences resulting from the different operator hypotheses show that the CDMSlite Run 2 data are consistent with the background-only models and do not allow for a signal interpretation assuming any additional EFT interaction. Consequently, upper limits on the WIMP mass and coupling-coefficient amplitudes and phases are presented for each EFT operator. These limits improve previous CDMSlite Run 2 bounds for WIMP masses above 5 GeV/$c^2$.

Motivation & Objective

• To investigate the presence of WIMP dark matter signals in CDMSlite Run 2 data using effective field theory (EFT) formalism.
• To evaluate the impact of different prior distributions on WIMP mass and coupling coefficient amplitude in Bayesian inference.
• To determine the most robust prior combination for extracting reliable 95% credibility contours on WIMP mass and coupling strength.
• To assess sampling quality and potential biases introduced by flat versus flat-log priors in high-dimensional parameter spaces.
• To compare Bayesian evidences across prior combinations while maintaining consistent parameter space volume for fair comparison.

Proposed method

• Applies effective field theory (EFT) to model WIMP-nucleon interactions in CDMSlite, using dimension-6 operators to describe dark matter scattering.
• Employs Bayesian inference with likelihood functions derived from the observed recoil energy spectrum in CDMSlite Run 2.
• Uses four distinct prior combinations: flat or flat-log priors on WIMP mass and coupling coefficient amplitude, with limits set to span ~13 orders of magnitude.
• Modifies prior ranges to cover only two orders of magnitude around the 95% posterior contour to improve sampling efficiency for flat priors.
• Compares 95% credibility contours across all prior combinations to evaluate consistency and sampling quality.
• Selects Prior 1 (flat mass, flat-log amplitude) as the optimal combination due to superior sampling and consistency with other priors.

Experimental results

Research questions

• RQ1 Which prior combination on WIMP mass and coupling amplitude yields the most reliable and well-sampled 95% credibility contours in EFT analysis of CDMSlite Run 2 data?
• RQ2 How do flat and flat-log priors affect the sampling of high-mass and low-amplitude regions in the parameter space?
• RQ3 To what extent do different prior choices introduce bias in the inferred WIMP coupling strengths and masses?
• RQ4 Are the 95% credibility contours from different prior combinations consistent within a factor of ~2.5, indicating robustness?
• RQ5 Does the choice of prior significantly alter the Bayesian evidence or upper limits on WIMP coupling, especially in regions with low event counts?

Key findings

• The 95% credibility contours for all EFT operators are consistent across the four prior combinations within a factor of ~2.5, indicating robustness to prior choice.
• Prior 1—flat prior on WIMP mass and flat-log prior on coupling amplitude—was selected as the optimal combination due to superior sampling quality and consistency.
• Sampling issues were observed in Prior 3 (flat-log mass, flat-log amplitude) and Prior 4 (flat-log mass, flat amplitude), particularly in high-mass and low-amplitude regions.
• Wiggles in the 95% contours for Prior 3 and 4, especially visible in Operator 𝒪₁₀, suggest poor sampling and potential artifacts from inadequate coverage.
• The flat prior on amplitude fails to sample low-amplitude regions effectively, and when combined with flat-log mass (Prior 4), leads to poorly sampled regions along the 95% contour.
• The choice of Prior 1 does not introduce notable bias, as Prior 2 and Prior 3 performed similarly, validating the robustness of the main analysis results.