Scientists from the international XENON collaboration, an international experimental group including the Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University; the Institute for Space-Earth Environmental Research (ISEE), Nagoya University; the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo; the Institute for Cosmic Ray Research (ICRR), The University of Tokyo; and the Graduate School of Science, Kobe University, announced today the first results from XENONnT, the latest detector of the XENON Dark Matter program. XENON collaboration reported that 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.

From Nagoya University, Professor. Yoshitaka Itow (KMI, ISEE, IAR), Associate Professor. Shingo Kazama (KMI, analysis coordinator of the XENONnT experiment), JSPS Research Fellowship for Young Scientists, PD (ISEE) Masatoshi Kobayashi are involved in the collaboration.

The analysis for this result was quite challenging as new detector requires a deep understanding of its characteristics.Additionally, the pandemic of the COVID -19 made it difficult to coordinate the international analysis team as most of them had to be performed remotely. We are proud of our effort on analysis to achieve the world lowest background detector which enabled us to have a conclusion for the excess observed in XENON1T with the first data of XENONnT.  Although no hint for new physics was observed in this result, the analysis for the WIMPs, which is the most important and promising candidate of the dark matter, is still ongoing. I would like to keep doing my best for the research of dark matter and new physics, to reveal the mystery behind them.

Shingo KAZAMA (Associate Professor/KMI and analysis coordinator of the XENONnT experiment)

It is very exciting to release our first result from XENONnT. Despite difficulties due to the worldwide pandemic, our collaboration spent a lot of effort to realize the XENONnT. I am also proud of my contribution to the construction, commissioning and data taking as one of run coordinators onsite. Currently we are working on the analysis for WIMPs, and the detector is taking data with upgrade for the further lower background level. I would like to continue studying to find the new physics such as dark matter.

Masatoshi KOBAYASHI (JSPS Research Fellowship for Young Scientists, PD/ISEE)

Press Release

July 22, 2022
XENON collaboration
Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University (KMI)
Institute for Space-Earth Environmental Research, Nagoya University (ISEE)
Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo (Kavli IPMU)
Institute for Cosmic Ray Research, The University of Tokyo (ICRR)
Graduate School of Science, Kobe University

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.

* The XENON collaboration is an international experimental group including Nagoya University, the University of Tokyo, and Kobe University from Japan. Japanese groups are contributing for the gadolinium loaded water cerenkov based neutron veto system initially developed by Super-Kamiokande group; the liquid xenon purification system with the experience from the XMASS experiment; and data analysis as one of analysis coordinators. 
Our research related to XENON1T and XENONnT experiments are supported by: JSPS Kakenhi (18H03697, 18KK0082, 19H05802, 19H05805, 19H00675, 19H01920, 21H05455, 21H04466, 22H00127) and JST FOREST JPMJFR212Q.

Reference URL: Press release by XENON collaboration (English)

http://xenonexperiment.org

Paper details

Journal: Title: Search for New Physics in Electronic Recoil Data from XENONnT 
Author: XENON Collaboration
Pre-print: http://xenonexperiment.org , submitted to Physical Review Letter

Figure.1：XENON researchers working to assemble a bottom PMT array for the  XENONnT detector. The TPC cage is seen hehind. Credit: Luigi Di Carlo for the XENON collaboration