Tag Archives: XENONnT

A Larger Cleanroom for a Larger XENONnT

Assembly of XENONnT Cleanroom at LNGS. Foto: Roberto Corrieri/XENON

The upcoming XENONnT detector, the next phase in our dark matter program, will have a dark matter target about three times larger than that of XENON1T. This means that all dimensions of the instruments are about 50% larger and thus require more space for the cleaning of the detector components and for detector assembly. For this reason, the class ISO-5/6 XENON cleanroom is currently being moved to a new above-ground space at LNGS, where it is re-built with a 50% increased footprint and a partially increased height.

The last action seen by the “old” cleanroom before its decommissioning were very successful tests of the TPC electrodes for XENONnT.

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.

XENON1T at the first Rucio Community Workshop at CERN

Everything scales up! Even the amount of acquired raw data in XENON1T. To handle data transfers easily, the XENON collaboration decided to let the Rucio Scientific Data Managment software do all the work. Rucio is developed at CERN and meant to manage scientific data. Data transfers, book keeping, easy data access and safety against data loss are its big advantage.

XENON1T is taking about one Terabyte of raw data per day. The detector is located at the Laboratori Nazionali del Gran Sass (LNGS) in Italy and the data need to be shipped out to dedicated computing centers for data reduction and analysis.

Individual Rucio clients access dedicated GRID disk space on world wide distributed computer facilities. Everything is controlled by a Rucio server which keeps track on storage locations, data sizes and transfers within the computer infrastructure. Rucio is developed in Python and its distribution becomes very simple.

The First Rucio Community Workshop was held at CERN on 1st and 2nd of March. Since Rucio was developed for the ATLAS collaboration, other experiments like XENON and AMS started to use Rucio a while ago. Nowadays, more collaborations such as EISCAT 3D, LIGO or NA62 (just to mention a few) became interested. The workshop allowed to meet all each other: developers and users discussed several use cases and how to improve Rucio for individual collaborations.

The XENON1T data distribution from https://indico.cern.ch/event/676472/contributions/2905755/

The XENON1T data distribution framework

We presented our integration of Rucio in the existing data handling framework. XENON1T raw data are distributed to five computing centers in Europe and the US. Each one is connected to the European Grid Interface (EGI) or the Open Science Grid (OSG) for data reduction (“processing”). Raw data are processed on the GRID and the reduced data sets are provided for the analysts on Research Computing Center (RCC) in Chicago. Beyond this, the XENON collaboration will continue to use Rucio for the upcoming XENONnT upgrade.

Towards a Neutron Veto System for the XENONnT Upgrade

Once a year the Spring-Meeting of the German Physics Society (DPG “Deutsche Physikalische Gesellschafft”) takes place. This year I had the opportunity to talk about the planned neutron Veto for XENONnT in Würzburg (19.-23.3.2018).

In order to maximize the fiducial volume, we want to veto nuclear recoils. Therefore we are working on a neutron veto system based on Gadolinium loaded liquid scintillator. The plan is to use acrylic boxes, which can be filled with liquid scintillator before being placed around the TPC cryostat.

Building on the experience of DOUBLE CHOOZ, we developed a first LAB-based liquid scintillator doped with 0.1 % Gadolinium and two wavelength shifters. Three measurements were performed to test the optical properties, transmission, emission and relative light yield. From the transmission measurement, we learned that the attenuation length of the scintillator at a wavelength of 430nm is 7.1m. The emission measurement shows the shifting due to the wavelength shifters to the visible wavelength. And with the relative light yield measurement we can compare an unloaded scintillator sample with the Gd-loaded sample. The light yield for the loaded scintillator decreases to 74% of the unloaded sample.

Our next steps will be to find a supplier who can provide us with a large and pure amount of the Gadolinium-Complex and to build a setup for neutron tagging measurements.