17.12.2019Light Dark Matter Results Published

XENON1T’s new letterdetails an “S2-only analysis”, where events without S1s are still considered. Advances in detector construction and analytic techniques have led to a background levels that is one thousand times lower than what was achieved in previous S2-only searches.

For example, the S2 electron cloud becomes broader as it drifts upward, like a drop of ink that spreads out in water. The deeper the event, the broader the cloud, and the longer the S2 signal lasts. Thus, XENON1T could reject most of the events at the top and bottom, even without the S1, by rejecting very short and very long S2 signals.

Theorists predict that dark matter would collide with the heavy xenon nuclei and produce nuclear recoils. In this case, the S2-only technique is sensitive to energies 2-3 times lower than traditional analyses. We consequently find improved constraints on light dark matter. On the other hand, dark matter might collide with electrons that surround the nucleus, producing electronic recoils. These interactions create much larger S2 signals than nuclear recoils of the same S1 size. S2-only searches thus improve the energy threshold for these models by as much as a factor of ten. Combined with the lower background, XENON1T’s S2-only results enhance the constraints on such models by several orders of magnitude.

This letter was also featured in a synopsis from APS Physics.