Author Archives: Michael Murra

Latest XENON1T results at ICHEP2018 in Seoul

The XXXIX International Conference on High Energy Physics (ICHEP2018) was taking place from July 4 – 11, 2018 in Seoul, Korea. After a warm welcome in this modern and traditional metropolis with over 10 million citizens, I was invited to present the recent results from XENON1T in a Dark Matter parallel session.

Here is one slide of my talk visualizing the spatial distribution of the unblinded and de-salted events.

Spatial distribution of unblinded and de-salted data.

The left plot shows the X- and Y- distribution, while the right plot indicates the radius R versus depth Z for the same set of data. The enlarged fiducial volume of 1.3 tons with respect to the first result, is highlighted by the pink line. For the analysis, a core volume (green line) was defined to distinguish WIMP-like events over neutron-like background events. The different events are visualized by pie charts, where the color code resembles the relative probability from each background component assigned by the best-fit. The larger a pie is, the more “WIMPy” it is. As you can see, only a few “WIMPy” events were found that are comparable to the background model expectations. From this, we derived the most stringent limits on spin-independent WIMP-nucleon cross sections.

At the end of my talk,  I also reported on the status of XENONnT, which will feature a 10x higher sensitivity than XENON1T. One main task is radon mitigation, one of the dominant backgrounds, which is visualized in this slide.

Radon mitigation for XENONnT

In a first step, a careful material selection needs to be made to avoid radon emanation from the start. Then, a new high throughput radon distillation column is under development to further reduce the radon contribution. Additionally, a new custom-made radon-free magnetically-coupled piston pump was built and installed at XENON1T in June 2018. With that, the radon budget in XENON1T was reduced by almost half (45%), which is an important step for the future XENONnT experiment.

The full talk is publicly available here.

XeSAT2017: Online krypton and radon removal for the XENON1T experiment

This talk by Michael Murra (slides) was presented at the XeSAT2017 conference in Khon Kaen, Thailand, from 3. – 7. April 2017.

The  main background for the XENON1T experiment are the intrinsic contaminants krypton and radon in the xenon gas. Instead of purifying the xenon once before starting the science run we were able to operate our distillation column in a closed loop with the XENON1T detector system running during its commissioning phase. This resulted into reducing the krypton concentration quickly below 1 ppt (parts per trillion, 1 ppt = 10^(-12) mol/mol) without emptying and refilling of the detector.

In addition, the column was operated in the same closed loop in inverse mode in order to reduce Rn-222 by about 20% during the first science run.

This so-called online removal for both noble gases along with the working principle of the distillation system are presented within this talk.