Dark matter direct search result from InDEx run2 at JUSL

TL;DR

This study reports InDEx run2 at JUSL using two C2H2F4 superheated droplet detectors operated at a threshold of $1.95$ keV to achieve a $7.2$ kg-days exposure and constrain low-mass WIMPs via a profile likelihood analysis. No WIMP signal is observed, yielding 90% C.L. upper limits of about $1.55 imes10^{-40}$ cm$^2$ at $M_ ext{χ} obreak[=]20.4$ GeV/$c^2$ (SI) and $7.97 imes10^{-38}$ cm$^2$ at $M_ ext{χ} obreak[=]21.0$ GeV/$c^2$ (SD on fluorine), representing an improvement over Run1. The work emphasizes the advantageous hydrogen content for low-mass reach, documents neutron-background modeling with FLUKA/FLAIR, and outlines prospects for lower thresholds and larger detectors to approach near-zero background and potentially MeV-scale WIMP sensitivity.

Abstract

The Indian Dark matter search Experiment (InDEx) has been initiated at Jaduguda Underground Science Laboratory (JUSL) to explore the low mass region of dark matter. The detectors used by InDEx are superheated droplet detectors with active liquid C2H2F4. The run1 of InDEx was with 2.47 kg-days of exposure at a threshold of 5.87 keV. In the present work, the run2 of InDEx, the detectors were set at 1.95 keV thresholds with an active liquid mass of 70.4 g. For a runtime of 102.48 days, the experimental results set constraint on spin-independent at 20.4 GeV/c2 and on spin-dependent at 21.0 GeV/c2 WIMP mass respectively. There is a shift of the most sensitive WIMP mass towards the lower region and an improvement of the sensitivity limit over the InDEx run1.

Figures (6)

• Figure 1: Experimental setup of InDEx run2 at JUSL and the detectors (inset).
• Figure 2: Block diagram of the experimental setup.
• Figure 3: Typical signal from the neutron calibration run. Inset: figure rise time.
• Figure 4: Rise time vs N$_{peak}$ distribution for the triggered events of InDEx run2 and neutron calibration. The vertical and horizontal lines correspond to the cut values.
• Figure 5: Present (red solid line) and projected sensitivity (black dashed line) of InDEx along with the results from SIMPLE PhysRevLett.108.201302 (purple solid line), PICASSO BEHNKE201785 (green solid line), PICO PhysRevD.100.022001 (aqua solid line), LUX-ZEPLIN PhysRevLett.131.041002 (magenta solid line), InDEx run1 kumar2025resulttetrafluoroethanec2h2f4superheated (blue solid line) and the theoretically predicted region essig2023snowmass2021cosmicfrontierlandscapebattaglieri2017cosmicvisionsnewideas (gray contour region) on WIMP-nucleon SI cross section with 90% C.L.