Last week I had the opportunity to present the XENON1T experiment at the Recontres de Moriond electroweak conference in La Thuile Italy in the beautiful Aosta Valley. This meeting is one of the most important meetings for LHC physics, but has slowly expanded to encapsulate a variety of topics, including the hunt for dark matter. The conference program and slides are available on indico. The XENON1T presentation focused on our dark matter search results from last spring as well as the upcoming result using about a factor of 10 more exposure, which is under intense preparation for release. The whole presentation is available from the indico page but here is one slide from it:
Here we discuss how we were able to increase the amount of liquid xenon we use for our dark matter search from ~1000kg to ~1300kg. The top left plot shows an example larger search volume (red) compared to the smaller volume used for the first result. But it’s not so simple as just adding volume. While our inner detector is completely free of WIMP-like background, the outer radii contain background components that can mimic WIMPs. This is illustrated in the bottom right plot where the background-free inner volume (right) is contrasted with the full search volume containing the outer radial sections (left). The full volume has a contribution from PTFE (Teflon) surface background (green contour and points) that is absent as soon as we consider only the inner volume.
Our statistical interpretation has been updated so it is smart enough to take this into account. We parameterize our entire search region in both radial and spatial dimensions with expected signal and background distributions described at each location. This allows us to fully exploit the sensitivity of our innermost background-free volumes while also gaining a modest improvement from the outermost ones.