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The XENON collaboration today presented the results of XENONnT, the latest generation experiment of the XENON project, dedicated to the direct search for dark matter in the form of weakly interacting massive particles (WIMPs). With an initial exposure of just over 1 tonne.year and a blind analysis, the data are consistent with the assumption of background alone. XENONnT therefore sets new limits on the interaction of WIMPs with ordinary matter. Thanks to a fivefold lower background, XENONnT has considerably improved the results of the XENON1T experiment, which was obtained with a similar exposure.
The XENONnT experiment was designed to search for dark matter particles with an order of magnitude higher sensitivity than its predecessor. The cylindrical detector at the heart of the experiment is a Time Projection Chamber (TPC). About 1.5 metres high and 1.5 metres in diameter, it is filled with ultra-pure liquid xenon maintained at -95°C. A mass of 5900 kg of xenon out of the 8600 kg required for the operation of the detector constitutes the active target for the interactions with the particles. It is installed inside a Cherenkov veto for muons and neutrons, deep inside the Gran Sasso National Laboratories (INFN) in Italy. XENONnT was built and commissioned between spring 2020 and spring 2021 and took its first scientific data on 97.1 days, from 6 July to 10 November 2021.
The signature of an interaction between a WIMP and a xenon atom is a tiny flash of scintillation light accompanied by a handful of ionising electrons. These are driven by an applied electric field up the CPT where they are then extracted by a stronger electric field into the xenon gas above the liquid, producing a second scintillation signal. Both light signals are detected by ultra-sensitive photodetectors, which provide energy and position information in 3D, event by event.
Dark matter experiments require the lowest possible level of natural radioactivity, both from sources intrinsically present in the liquid xenon target, from building materials and from the environment. The latter is dominated by radon atoms that are constantly emitted from detector materials and are extremely difficult to reduce. The XENON collaboration has pioneered technologies to reduce radon to unprecedented levels, from material selection campaigns to an in-line cryogenic distillation system that actively removes radon from xenon. Another important radioactive background comes from neutrons generated by the radioactivity of detector materials. In XENONnT, its impact has been reduced by a new neutron veto detector installed in the water tank around the xenon cryostat. This allows neutron events that could mimic the WIMP signature to be recognised and eliminated. The XENONnT detector is so sensitive to rare interactions that even neutrinos, the most elusive particles known to date, must be taken into account in the background model.
With this result, XENONnT strengthens the previous constraints from the first short exposure.
XENONnT is collecting more data, with improved detection conditions and an even lower background level thanks to a further improvement of the online radon removal system, with the aim of increasing the sensitivity of WIMPs over the next few years.
Mor information about the XENON project on the web https://xenonexperiment.org/
Informations about Xenon Subatech team involved in the collaboration : http://www-subatech.in2p3.fr/en/research/research-team/xenon/about
View of the interior of the water tank, with the TPC surrounded by the neutron detection system in the centre
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As part of the XEMOX research project, a delegation from Subatech's Xenon team visited the French Mox fuel assembly plant Orano-Melox in mid January. The XEMOX project aims at unlocking possible secrets still present in Mox fuel by using the new hyper-sensitive gamma camera technology "XEMIS" including liquid xenon and used for the new 3-photon medical imaging at the Nantes University Hospital.
On the photo from left to right : Dominique Thers, Nicolas Beaupère et Eugène Semenov from Xenon tema Subatech; Abibatou Ndiaye (Orano), Thierry Gervais (Orano), Marco Cologna (Joint Research Center)
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A prototype of the DAMIC-M detector was installed in December 2021 in the Modane underground laboratory in the Frejus tunnel. First results from the joint work of researchers and PhD students from Subatech and LPNHE laboratories, the University of Chicago and the University of Washington, are expected in the coming months.
Links to DAMIC-M experience :
https://damic.uchicago.edu
www.damicm.cnrs.fr
The detector cor, two skippers CCDs. Working team* and the last screw placed by Claudia de Dominicis, PhD student in Subatech
*From left to right : Michelangelo Traina, PhD LPNHE, Jonty Paul, PhD U. Chicago, Alvaro Chavarria, Professeur University of Washington, spokesperson DAMIC at Snolab, Paolo Privitera, Professeur University of Chicago, spokesperson DAMICM, Claudia De Dominicis, PhD Subatech, Mariangela Settimo, researcher Subatech
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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.
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.
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.
Data (points) and model (lines) from XENON1T and XENONnT experiments.
With a background 5 times lower, XENONnT reaches an unprecedented sensitivity. No signal from new physics has been observed.
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Avec le niveau de bruit de fond le plus bas jamais atteint par une chambre à projection temporelle au xénon liquide, XENON1T s'est avéré être l'expérience de détection directe de matière sombre la plus sensible sur terre pour des candidats ayant une masse supérieure à 3 GeV/c2. Bien que XENON1T ait été principalement conçue pour rechercher des reculs nucléaires entre des particules massives interagissant faiblement (Weakly Interacting Massive Particles, WIMPs) et des atomes de xénon à des énergies de l’ordre du keV, le niveau sans précédent de radioactivité atteint a rendu l’expérience XENON1T également adaptée pour d’autres recherches d’événements rares issus de reculs électroniques à faibles O(keV) et aussi plus hautes O(MeV) énergies. Parmi ces recherches, la désintégration double beta sans émission de neutrino (0ν2β) du 136Xe recouvre un intérêt particulier car l’observation d'une telle décroissance radioactive permettrait d’accéder à l’échelle de masse du neutrino et de répondre à une des grandes questions actuelles de la physique des particules : quelle est la nature des neutrinos ? Sont-ils des particules de Dirac (particule et antiparticule sont deux états distincts) ou de Majorana (particule et antiparticule sont le même état) ? Avec le but de répondre à cette question, les membres de l’équipe Xénon de SUBATECH sont très engagés dans l’analyse de la 0ν2β au sein de la Collaboration XENON. En particulier, le travail de thèse de Chloe Therreau a mené au résultat majeur montré sur la couverture de EPJC 80/08 dans l’image ci-après (lien vers l'article).
Avant ce travail, les chambres à projection temporelle double phase au xénon, conçues pour rechercher des WIMPs, étaient caractérisées par une détérioration de la résolution en énergie pour les énergies de recul électronique supérieures à ∼100 keV. Dans l'expérience XENON1T, nous avons développé une méthode de correction du signal qui a permis de bien reconstruire les signaux d'intérêt dans une plus large gamme d'énergie. En particulier, nous avons démontré qu'à l’énergie du signal de la 0ν2β du 136Xe (~2,46 MeV), la résolution en énergie relative (à 1-?) est aussi basse que (0,80 ± 0,02)%. L’excellent résultat de XENON1T ouvre de nouvelles fenêtres pour les détecteurs double phase au xénon pour la recherche simultanée de matière noire et d'autres événements rares.