Results released from first 34 days of the XENON1T experiment

Understanding all the detailed physics going on inside the world’s most sensitive dark matter detector is a great challenge to work on. — Bart Pelssers, PhD student, Stockholm University, Oskar Klein Centre

The first results have just been released from XENON1T (“Xenon One Ton”), the most sensitive dark matter detection experiment in the world. Dark matter has not yet been detected but these results push the limits for the detection of a specific kind of dark matter particle (Weakly Interacting Massive Particles) lower than those from previous experiments.  This is after collecting data for just 34 days.

This experiment consists of a liquid xenon central detector surrounded by ultra-pure water which shields the detector. When particles collide with the xenon nucleus it emits light and electrons that the experiment can detect. Xenon can also be made very pure and it is dense enough that the inner part of the xenon nucleus is almost completely isolated from radioactivity from the detector itself as well as outside.  The XENON1T experiment is located underneath a mountain in the Gran Sasso Underground Laboratory in Italy in order to shield the detector from cosmic rays.

The XENON collaboration contains scientists from 10 different countries, including a number of Oskar Klein Centre researchers. Given these results the dark matter community will be watching this experiment closely to see what it finds after analyzing a larger amount of data. In fact, more than 60 new days of data have already been recorded!

Note how quickly the sensitivity of these experiments increases — the last result from XENON100 was made with 100kg of xenon and a detector that could fit in a living room while the new one is suspended in a three-story tank of water. One should also take a second to look at the green band– that shows the region the upper limit would be in 68% of the time. It is huge! That is because we are looking for very rare events, and so any statistical fluctuation or misestimated background could move our result a lot. That we find a result like the one we show is a good indication that we already understand our detector quite well. — Knut Morå, PhD student, Stockholm University, Oskar Klein Centre

The spin-independent WIMP-nucleon cross section sensitivity limits as a function of WIMP mass at 90% confidence level for this run of XENON1T (in black). Results from previous experiments are shown.  The 1- and 2σ sensitivity bands are shown in green and yellow.
The spin-independent WIMP-nucleon cross section sensitivity limits as a function of WIMP mass at 90% confidence level for this run of XENON1T (in black). Results from previous experiments are shown. The 1- and 2σ sensitivity bands are shown in green and yellow.

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