Results of a Search for Sub-GeV Dark Matter Using 2013 LUX Data (1811.11241v3)

Abstract: The scattering of dark matter (DM) particles with sub-GeV masses off nuclei is difficult to detect using liquid xenon-based DM search instruments because the energy transfer during nuclear recoils is smaller than the typical detector threshold. However, the tree-level DM-nucleus scattering diagram can be accompanied by simultaneous emission of a Bremsstrahlung photon or a so-called "Migdal" electron. These provide an electron recoil component to the experimental signature at higher energies than the corresponding nuclear recoil. The presence of this signature allows liquid xenon detectors to use both the scintillation and the ionization signals in the analysis where the nuclear recoil signal would not be otherwise visible. We report constraints on spin-independent DM-nucleon scattering for DM particles with masses of 0.4-5 GeV/c$^2$ using 1.4$\times10^4$ kg$\cdot$day of search exposure from the 2013 data from the Large Underground Xenon (LUX) experiment for four different classes of mediators. This analysis extends the reach of liquid xenon-based DM search instruments to lower DM masses than has been achieved previously.

• The paper introduces novel detection methodologies by exploiting Bremsstrahlung and Migdal effects to enhance sensitivity to sub-GeV dark matter.
• The experiment employs a dual-phase TPC with enhanced spatial resolution and low-energy response to accurately capture both electron and nuclear recoils.
• The findings set upper limits on the spin-independent DM-nucleon cross-section, paving the way for future experiments like LUX-ZEPLIN to explore light dark matter.

Detection of Sub-GeV Dark Matter Using Advanced Techniques in LUX

The paper presents an investigation into the elusive domain of sub-GeV dark matter (DM) detection, focusing on data obtained from the Large Underground Xenon (LUX) experiment conducted in 2013. This research utilizes innovative detection methodologies, enhancing the sensitivity of liquid xenon-based time projection chambers (TPCs) to DM particles of lower mass ranges—particularly those spanning 0.4-5 GeV/c². Such an advancement in DM detection is facilitated by exploiting the Bremsstrahlung and Migdal effects, which augment traditional nuclear recoil (NR) signals with measurable electron recoil (ER) components, facilitating characteristics observable in liquid xenon detectors.

Methodology and Experimental Setup

The paper explores two key mechanisms—Bremsstrahlung and the Migdal effect—as avenues to capture scattering events that emit ER signatures. These novel detection channels allow the observation of DM interactions via the ER component, produced alongside NR events, thereby making low-mass DM particles detectable with higher precision. The LUX experiment's dual-phase TPC, with its distinctive 50% detection efficiency power for ER at energies as low as 1.24 keV, is pivotal in this detection process. By contrasting scalar and vector mediators in their interactions, this paper examines these DM-nucleus scatterings, providing a pathway to gauge cross-sections against the backdrop of hypothesized sub-GeV DM particles.

A critical factor in enhancing detection beneath the keV range is spatial resolution. This experimental setup takes advantage of both scintillation (S1) and ionization (S2) signals to triangulate the three-dimensional vertices of particle interactions, an approach which aids in effective background discrimination and event localization.

Results and Implications

The experiment notably extends the sensitivity range of liquid xenon detectors to lower DM masses, attributing this advancement to the addition of Bremsstrahlung photons and Migdal electrons in the detected signals. The results demonstrate bounds on the spin-independent DM-nucleon cross-section, crucial for understanding not just traditional hypothesis spaces but also newly considered areas in DM particle physics.

Upper limits are set across sub-GeV masses, revealing a capacity to challenge and refine theoretical models that propose light DM particles. While current results align with predicted background-only hypotheses, these findings mark a pathway forward, not only for LUX but also for next-generation detectors like the LUX-ZEPLIN (LZ) that aim to achieve greater detection breadth.

Future Directions

The implications of this work underscore the continued evolution of DM detection methodologies, emphasizing the utility of advanced signal processing and modeling in expanding detection thresholds. Future developments may capitalize on these refined techniques to reconcile the ongoing challenges of DM searches—that is, to potentially unveil new physics beyond the Standard Model's purview.

Ultimately, this research contributes to an incremental yet indispensable understanding of particle physics by broadening the accessible parameter space for DM candidates and guiding the design of future experimental setups designed to probe the DM sector with enhanced sensitivity and precision.