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First results from a Search for New Physics in Electronic Recoils from XENONnT

Press information, Friday, July 22, 2022. For immediate release.

The paper is available on the arxiv and directly here (pdf) . Slides as they were presented at the IDM conference are also available here (pdf).

XENONnT, the latest detector of the XENON Dark Matter program, shows an unprecedentedly low background which facilitates searches for new, very rare phenomena with high sensitivity. First results clarify an exciting excess observed in the predecessor XENON1T and set strong limits on new physics scenarios.

The XENONnT experiment was designed to look for elusive dark matter particles. The detector holds almost 6000 kg of ultrapure liquid xenon as a target for particle interactions; it is installed inside a water Cherenkov active muon and neutron veto, deep underground at the INFN Laboratori Nazionali del Gran Sasso in Italy. Despite the challenging pandemic situation, XENONnT was constructed and subsequently commissioned between spring 2020 and spring 2021. XENONnT took the first science data over 97.1 days, from July 6 to November 10, 2021.

Experiments of this type require the lowest possible levels of natural radioactivity of any kind, both from sources intrinsically present in the liquid xenon target and from construction materials and the environment. The former, dominated by radon, is the most difficult to reduce and its elimination represents the holy grail of current searches at the sensitivity level of XENONnT. However, the XENON collaboration has been instrumental in reducing radon to an unprecedentedly low-level, thanks to extensive material screening and the successful operation of an online cryogenic distillation column that actively removes radon from the xenon.

Two years ago, the XENON collaboration announced the observation of an excess of electronic recoil events in the XENON1T experiment. The result triggered a lot of interest and many publications since this could be interpreted as a signal of new physics beyond known phenomena. Interactions with electrons in the atomic shell within the liquid xenon from solar axions, neutrinos with an anomalous magnetic moment, axion-like particles, or hypothetical dark sector particles might induce so-called “electronic recoil” signals. Today the XENON collaboration has released the first results from its new and more sensitive experiment, XENONnT, with one-fifth of the electronic recoil background of its predecessor, XENON1T. The absence of an excess in the new data indicates that the origin of the XENON1T signal was trace amounts of tritium in the liquid xenon, one of the hypotheses considered at the time. In consequence, this leads now to very strong limits on new physics scenarios originally invoked to explain an excess.

With this new result, obtained through a blind analysis, XENONnT makes its debut, with an initial exposure slightly larger than 1 tonne x year. The existing data are being further analyzed to search for weakly interacting massive particles (WIMPs), one of the most promising candidates of Dark Matter in the Universe. XENONnT is meanwhile collecting more data, aiming for even better sensitivity as part of its science program for the next years.

XENON at the 2019 Swiss-Austrian Physical Society Meeting

Five members of the University of Zurich group participated at the 2019 Swiss-Austrian Physical Society Meeting in Zurich, Switzerland.

Adam Brown contributed with a poster on the XENONnT upgrades and status and Ricardo Peres on the software for the supernova early warning system:

Giovanni Volta, Michelle Galloway and Chiara Capelli contributed with talks on the general XENON1T results, the ongoing search for dark absorption and the analysis on high energy events respectively. The full talks are linked. Below a key slide from each talk is shown: the spin-independent elastic WIMP-nucleon scattering limit at 90% CL still are the most sensitive limits on WIMP dark matter. The motivation for light dark matter searches is becoming more and more pressing. And our reconstruction of single-site and multiple-site interactions for the neutrinoless double beta decay search significantly improves our capability to contribute to this exciting science channel.

Talk at Lepton Photon 2019

A talk on the measurement of the double electron capture half-life of xenon-124 with the XENON1T experiment was given at the Lepton Photon 2019 conference in Toronto in August 2019. Ethan Brown from Rensselaer Polytechnic Institute presented this exciting result, demonstrating the power of the ultra-low background in XENON1T. This yielded the measurement of the longest process ever directly observed at 1.8×10^22 years, a trillion times longer than the age of the Universe.

Some of the dark matter search results were also presented in this talk, advertising the incredible success of the XENON program and the science reach of the XENON1T experiment in rare event detection.

XENON talk at Patras Workshop

A talk on the XENON project was given at the 15th Patras Workshop on Axions, WIMPs and WISPs, which was held in Freiburg (Germany) in the first week of June. Andrea Molinario from the Gran Sasso Science Institute and Laboratori Nazionali del Gran Sasso presented the most recent results from the data analysis of XENON1T, in particular the search for WIMP-nucleon spin-dependent and spin-independent interactions. The sensitivity of this search will be much-improved upon by the upcoming XENONnT phase of the experiment.

The first observation of 124Xe double electron capture and the measurement of the half-life of the process were also shown (this topic had a dedicated talk by Sebastian Lindemann). In the second part of his talk, Andrea gave an update on the status of XENONnT. The presentation is available here.

XENON1T talk at Low Radioactivity Technique 2019

Our latest XENON1T paper on details of our analysis was presented at the Low Radioactivity Techniques, a conference focused on low background experiments. In the talk (that you can find here), the response model of the detector, the challenges of background modeling, as well as the used techniques were described. In a low background experiment is often hard to asses the expected distribution of events due to lack of statistics and to many subtle effects. In the talk a novel technique was described to introduce a well-motivated systematic uncertainty to the background model based on a calibration sample, which can be relevant to other low background experiments.

XENON on skis

XENON was present at the ALPS conference in Austria. Chiara Capelli from University of Zurich gave a talk on behalf of the XENON collaboration. The talk focused on the latest XENON1T results on spin-independent and spin-dependent WIMPs, and on the newest results on two-neutrinos double electron capture, with a final status on the XENONnT upgrade. The talk is available here.

On March 8, 2019, Shigetaka Moriyama presented the status of the XENONnT experiment at the international symposium on “Revealing the history of the Universe with underground particle and nuclear research” in Sendai, Japan. The symposium is held by a Japanese research community working on underground experiments and developing low background techniques. Its members are interested in the physics goals of XENONnT as well as its radon reduction technique and will enhance the experiment with Super-Kamiokande’s water Cherenkov technology developed in Kamioka, Japan, for the SK-Gd project. Super-Kamiokande developed this technology to measure the diffuse relic neutrino flux from past supernovae.

At the Sendai meeting, this community is summarizing its achievements over last five years and aims to secure new funding for the next five years by expanding its activity through internationalization and the inclusion of new physics topics such as history of stars, galaxies, and the origin of the heavy elements in the Universe.

Its HP is here and the slides are available here.

Outline the XENONnT Computing Scheme at the 2nd Rucio Community Workshop in Oslo

Oslo welcomed all 66 participants of the second Rucio Community Workshop with pleasant weather and a venue which offered an astonishing view about the capital of Norway.
The opensource and contribution model of the Rucio data management tool captures more and more attention from numerous fields. Therefore, 21 communities reported this year about the implementation of Rucio in their current data workflows, discussed with the Rucio developing team possible improvements and chatted among each other during the coffee breaks to learn from others experiences. Among the various communities were presentations given by the DUNE experiment, Belle-2 and LSST. The XENON Dark Matter Collaboration presented the computing scheme of the upcoming XENONnT experiment. Two keynote talks from Richard Hughes-Jones (University of Maryland) and Gundmund Høst (NeIC) highlighted the concepts of the upcoming generation of academic networks and the Nordic e-Infrastructure Collaboration.

After the successful XENON1T stage with two major science runs, a world-leading limit for spin-indepenent Dark Matter interactions with nucleons and further publications, the XENON1T experiment stopped data taking in December 2018. We aim for two major updates for the successor stage of XENONnT: a larger time projection chamber (TPC) which holds ~8,000 kg of liquid xenon with 496 PMTs for signal readout and an additional neutron veto detector based on Gadolinium doped water in our water tank. That requires upgrades in our current data management and processing scheme, which was presented last year at the first Rucio Community Workshop. Fundamental change is the new data processor STRAX which allows us much faster data processing. Based on the recorded raw data, the final data product will be available at distinct intermediate processing stages which depend on each other. Therefore, we stop using our “classical” data scheme of raw data, processed data and minitrees, and instead aim for a more flexible data structure. Nevertheless, all stages of the data are distributed with Rucio to connected grid computing facilities. STRAX will be able to process data from the TPC, the MuonVeto and the NeutronVeto together to allow coincident analysis.

The data flow of the XENONnT experiment

The data flow of the XENONnT experiment. A first set data is processed already at the LNGS. All data kinds are distributed with Rucio to the analysts.

Reprocessing campaigns are planed ahead with HTCondor and DAGMan jobs at EGI and OSG similar to the setup of XENON1T. Due to the faster data processor, it becomes necessary to outline a well-established read and write routine with Rucio to guarantee quick data access.
Another major update in the XENONnT computing scheme becomes the tape backup location. Because of the increased number of disks and tape allocations in the Rucio catalogue, we will abandon the Rucio independent tape backup in Stockholm and use dedicated Rucio storage elements for storing the raw data. The XENON1T experiment collected ~780 TB of (raw) data during its life time which are all managed by Rucio. The XENON Collaboration is looking forward to continuing this success story with XENONnT

XENON1T at Lake Louise

Physics meets winter sports at the Lake Louise Winter Institute, a particle physics conference held annually in the beautiful Canadian Rockies. On February 12, 2019, Evan Shockley from University of Chicago presented at the conference on behalf of the XENON collaboration. The talk focused on the latest, world-leading WIMP results, and included a status update on XENON1T and its imminent upgrade, XENONnT. The talk is available here.

XENONnT will feature a larger detector and even lower background than XENON1T, making it ~10 times more sensitive to interactions from dark matter and other rare processes. With installation coming later this year, it’s an exciting time for the XENON collaboration and the field of dark matter research!


XENON1T at the annual meeting of the Swiss Physical Society, 2018

Two members of the University of Zurich group gave talks on XENON1T at the annual meeting of the Swiss Physical Society in Lausanne, Switzerland. Chiara Capelli presented the latest news from the experiment and in particular the recently presented limit on spin-independent WIMP-nucleon cross-section, while Adam Brown spoke about the ongoing work searching for the inelastic scattering of WIMPs.

One of the key slides from Chiara’s talk is below. In the top-right you can see the WIMP-search data pre-unblinding, and in the bottom-right the efficiency for detecting nuclear recoils which happen in our fiducial volume. In the full talk, which is available here, she also presented the final limit and then gave a update on the preparations for the detector upgrade to XENONnT which are ongoing at the University of Zurich.

Adam’s talk focussed instead on an alternative possibility of searching for WIMPs via their inelastic scattering off xenon nuclei. During the interaction the nucleus is excited, and so the usual nuclear recoil signal would be observed in coincidence with the 39.6 keV gamma ray from the de-excitation of the nucleus. One of the attractions of this search channel, which is however less sensitive than elastic scattering, is that it distinguishes between spin-dependent and spin-independent WIMP interactions: a spin-dependent interaction is needed to change the nuclear spin state during its excitation. Again, the full talk is available online here.