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39-488: Their first announcement was an excess of events recorded after 56 days. Juan Collar, who presented the results to a conference at the University of California, was quoted: "If it's real, we're looking at a very beautiful dark-matter signal". This signal conflicts with other searches that have failed to find any evidence, such as XENON and LUX but appears to confirm results from DAMA . They observed an annual modulation in

78-584: A 30 GeV/ c WIMP mass. Due to nearly half of natural xenon having odd spin states ( Xe has an abundance of 26% and spin-1/2; Xe has an abundance of 21% and spin-3/2), the XENON detectors can also be used to provide limits on spin dependent WIMP-nucleon cross sections for coupling of the dark matter candidate particle to both neutrons and protons. XENON10 set the world's most stringent restrictions on pure neutron coupling. The second phase detector, XENON100, contains 165 kg of liquid xenon, with 62 kg in

117-418: A dual phase time projection chamber (TPC), which utilizes a liquid xenon target with a gaseous phase on top. Two arrays of photomultiplier tubes (PMTs), one at the top of the detector in the gaseous phase (GXe), and one at the bottom of the liquid layer (LXe), detect scintillation and electroluminescence light produced when charged particles interact in the detector. Electric fields are applied across both

156-520: A dual phase time projection chamber (TPC). The experiment detects scintillation and ionization signals produced when external particles interact in the liquid xenon volume, to search for an excess of nuclear recoil events against known backgrounds. The detection of such a signal would provide the first direct experimental evidence for dark matter candidate particles. The collaboration is currently led by Italian professor of physics Elena Aprile from Columbia University . The XENON experiment operates

195-539: A few cases mass spectrometry was performed on low mass plastic samples. In doing so the design goal of <10 events/kg/day/keV was reached, realising the world's lowest background rate dark matter detector. The detector was installed at the Gran Sasso National Laboratory in 2008 in the same shield as the XENON10 detector, and has conducted several science runs. In each science run, no dark matter signal

234-747: A fiducial volume of about 2 tons. The detector is housed in a 10 m water tank that serves as a muon veto. The TPC is 1 m in diameter and 1 m in height. The detector project team, called the XENON Collaboration, is composed of 135 investigators across 22 institutions from Europe, the Middle East, and the United States. The first results from XENON1T were released by the XENON collaboration on May 18, 2017, based on 34 days of data-taking between November 2016 and January 2017. While no WIMPs or dark matter candidate signals were officially detected,

273-483: A flawed optic fiber cable in OPERA receiver of the laboratory, resulting in late arrival of the clock signal to which the neutrinos' arrivals were compared. Although the official statement published by OPERA does not declare any anomaly in the velocity of the neutrinos, and therefore the case is completely solved, the development of the story has given the community pause for thought. In 2014 Borexino measured directly, for

312-465: A member of the coordinating group ILIAS . The laboratory consists of a surface facility, located within the Gran Sasso and Monti della Laga National Park , and extensive underground facilities located next to the 10 km long Traforo del Gran Sasso freeway tunnel. The first large experiments at LNGS ran in 1989; the facilities were later expanded, and it is now the largest underground laboratory in

351-468: A researcher of Institute of Nuclear Physics in Lyons, France, presented preliminary findings that indicated neutrinos produced at CERN were arriving at OPERA detector about 60 ns earlier than they would if they were travelling at the speed of light. This faster-than-light neutrino anomaly was not immediately explained. The results were subsequently investigated and confirmed to be wrong. They were caused by

390-532: Is designed to reach a sensitivity (in a small part of the mass-range probed) where neutrinos become a significant background. As of 2019, the upgrade was on-going and first light was expected in 2020. The XENONnT detector was under construction in March 2020. Even with the problems posed by COVID-19, the project was able to finish construction and move forwards into commissioning phase by mid 2020. Full detector operations commenced in late 2020. In September 2021, XENONnT

429-505: Is referred to as the S2 signal. This technique has proved sensitive enough to detect S2 signals generated from single electrons. The detector allows for a full 3-D position determination of the particle interaction. Electrons in liquid xenon have a uniform drift velocity. This allows the interaction depth of the event to be determined by measuring the time delay between the S1 and S2 signal. The position of

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468-506: Is the largest underground research center in the world. Situated below Gran Sasso mountain in Italy , it is well known for particle physics research by the INFN . In addition to a surface portion of the laboratory, there are extensive underground facilities beneath the mountain. The nearest towns are L'Aquila and Teramo . The facility is located about 120 km from Rome . The primary mission of

507-486: The Italian Gran Sasso National Laboratory , is a deep underground detector facility featuring increasingly ambitious experiments aiming to detect hypothetical dark matter particles. The experiments aim to detect particles in the form of weakly interacting massive particles (WIMPs) by looking for rare nuclear recoil interactions in a liquid xenon target chamber. The current detector consists of

546-514: The LZ experiment published its first results too excluding cross sections above 9.2 × 10 − 48 c m 2 {\displaystyle 9.2\times 10^{-48}cm^{2}} at 36 GeV with 90% confidence level. 42°25′14″N 13°30′59″E  /  42.42056°N 13.51639°E  / 42.42056; 13.51639 Laboratori Nazionali del Gran Sasso Laboratori Nazionali del Gran Sasso ( LNGS )

585-608: The Majorana /Dirac nature of the neutrino, called CUORE (Cryogenic Underground Observatory for Rare Events), is operating in the laboratory (as of 2018). The detector is shielded with lead recovered from an ancient Roman shipwreck, due to the ancient lead's lower radioactivity than recently minted lead. The artifacts were given to CUORE from the National Archaeological Museum in Cagliari . In September 2011, Dario Autiero,

624-521: The OPERA and ICARUS detectors, in a study of neutrino oscillations that will improve on the results of the Fermilab to MINOS experiment. In May 2010, Lucia Votano , Director of the Gran Sasso laboratories, announced, "The OPERA experiment has reached its first goal: the detection of a tau neutrino obtained from the transformation of a muon neutrino , which occurred during the journey from Geneva to

663-599: The Gran Sasso Laboratory." This was the first observed tau neutrino candidate event in a muon neutrino beam, providing further evidence that neutrinos have mass. (Research first determined that neutrinos have mass in 1998 at the Super-Kamiokande neutrino detector. ) Neutrinos must have mass for this transformation to occur; this is a deviation from the classic Standard Model of particle physics , which assumed that neutrinos are massless. An effort to determine

702-627: The TPC measures 20 cm in diameter and 15 cm in height. An analysis of 59 live days of data, taken between October 2006 and February 2007, produced no WIMP signatures. The number of events observed in the WIMP search region is statistically consistent with the expected number of events from electronic recoil backgrounds. This result excluded some of the available parameter space in minimal Supersymmetric models , by placing limits on spin independent WIMP-nucleon cross sections down to below 10 × 10  cm for

741-481: The XENON1T collaboration reported an excess of electron recoils: 285 events, 53 more than the expected 232 with a statistical significance of 3.5σ. Three explanations were considered: existence of to-date-hypothetical solar axions , a surprisingly large magnetic moment for neutrinos, and tritium contamination in the detector. Multiple other explanations were given later by others groups and in 2021 an interpretation of

780-454: The electrons produced from a charged particle interaction in the TPC. These electrons are drifted to the top of the liquid phase by the electric field. The ionization is then extracted into the gas phase by the stronger electric field in the gaseous phase. The electric field accelerates the electrons to the point that it creates a proportional scintillation signal that is also collected by the PMTs, and

819-404: The event in the x-y plane can be determined by looking at the number of photons seen by each of the individual PMTs. The full 3-D position allows for the fiducialization of the detector, in which a low-background region is defined in the inner volume of the TPC. This fiducial volume has a greatly reduced rate of background events as compared to regions of the detector at the edge of the TPC, due to

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858-585: The event rate that could indicate light dark matter. The annual modulation has continued to be seen in 3 years of data. However more recent work has shown that the excess of events attributed to a tentative dark matter signal was in fact due to an underestimated background from surface events. After accounting for this background there is no evidence for a signal in data from the CoGeNT experiment and no tension with null results from other experiments. XENON The XENON dark matter research project, operated at

897-463: The experiments from cosmic rays . Providing about 3400 metres of water equivalent (mwe) shielding, it is not the deepest underground laboratory, but the fact that it can be driven to without using mine elevators makes it very popular. Since late August 2006, CERN has directed a beam of muon neutrinos from the CERN SPS accelerator to the Gran Sasso lab, 730 km away, where they are detected by

936-464: The first direct observation of two-neutrino double electron capture in xenon-124 nuclei. The measured half-life of this process, which is several orders of magnitude larger than the age of the Universe, demonstrates the capabilities of xenon-based detectors to search for rare events and showcases the broad physics reach of even larger next-generation experiments. This measurement represents a first step in

975-496: The first time, the neutrinos from the primary proton-proton fusion process in the Sun. This result is published on Nature . This measurement is consistent with the expectations derived from the standard solar model of J. Bahcall along with the theory of solar neutrino oscillations as described by MSW theory . In 2020 Borexino measured also solar neutrinos originated from CNO cycle , a fusion process common in giant stars but uncommon in

1014-434: The laboratory is to host experiments that require a low background environment in the fields of astroparticle physics and nuclear astrophysics and other disciplines that can profit of its characteristics and of its infrastructures. The LNGS is, like the three other European underground astroparticle laboratories ( Laboratoire Souterrain de Modane , Laboratorio subterráneo de Canfranc , and Boulby Underground Laboratory ),

1053-416: The laboratory provides 3100 m of water-equivalent shielding. The detector was placed within a shield to further reduce the background rate in the TPC. XENON10 was intended as a prototype detector, to prove the efficacy of the XENON design, as well as verify the achievable threshold, background rejection power and sensitivity. The XENON10 detector contained 15 kg of liquid xenon. The sensitive volume of

1092-449: The liquid and gaseous phase of the detector. The electric field in the gaseous phase has to be sufficiently large to extract electrons from the liquid phase. Particle interactions in the liquid target produce scintillation and ionization . The prompt scintillation light produces 178 nm ultraviolet photons. This signal is detected by the PMTs, and is referred to as the S1 signal. The applied electric field prevents recombination of all

1131-489: The ratio of S2/S1 can be used as a discrimination parameter to distinguish electronic and nuclear recoil events. This ratio is expected to be greater for electronic recoils than for nuclear recoils. In this way backgrounds from electronic recoils can be suppressed by more than 99%, while simultaneously retaining 50% of the nuclear recoil events. The XENON10 experiment was installed at the underground Gran Sasso laboratory in Italy during March 2006. The underground location of

1170-551: The results not as dark matter particles but of as dark energy particles candidates called chameleons has also been discussed. In July 2022 a new analysis by XENONnT discarded the excess. XENONnT is an upgrade of the XENON1T experiment underground at LNGS. Its systems will contain a total xenon mass of more than 8 tonnes. Apart from a larger xenon target in its time projection chamber the upgraded experiment will feature new components to further reduce or tag radiation that otherwise would constitute background to its measurements. It

1209-417: The search for the neutrinoless double electron capture process, the detection of which would provide insight into the nature of the neutrino and allow to determine its absolute mass. As of 2019, the XENON1T experiment has stopped data-taking to allow for construction of the next phase, XENONnT. The XENON1T detector operated 2016–2018, with the detector operations ending at the end of 2018. In June 2020,

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1248-403: The self-shielding properties of liquid xenon. This allows for a much higher sensitivity when searching for very rare events. Charged particles moving through the detector are expected to either interact with the electrons of the xenon atoms producing electronic recoils, or with the nucleus, producing nuclear recoils. For a given amount of energy deposited by a particle interaction in the detector,

1287-457: The sensitivity to WIMPs . In September 2018 the XENON1T experiment published its results from 278.8 days of collected data. A new record limit for WIMP-nucleon spin-independent elastic interactions was set, with a minimum of 4.1 × 10  cm at a WIMP mass of 30 GeV/ c . In April 2019, based on measurements performed with the XENON1T detector, the XENON Collaboration reported in Nature

1326-498: The spin dependent WIMP-nucleon cross section. An axion result was published in 2014, setting a new best axion limit. XENON100 operated the then-lowest background experiment, for dark matter searches, with a background of 50 mDRU (1 mDRU=10 events/kg/day/keV). Construction of the next phase, XENON1T, started in Hall B of the Gran Sasso National Laboratory in 2014. The detector contains 3.2 tons of ultra radio-pure liquid xenon, and has

1365-424: The target region and the remaining xenon in an active veto. The TPC of the detector has a diameter of 30 cm and a height of 30 cm. As WIMP interactions are expected to be extremely rare events, a thorough campaign was launched during the construction and commissioning phase of XENON100 to screen all parts of the detector for radioactivity. The screening was performed using high-purity Germanium detectors . In

1404-461: The team did announce a record low reduction in the background radioactivity levels being picked up by XENON1T. The exclusion limits exceeded the previous best limits set by the LUX experiment , with an exclusion of cross sections larger than 7.7 × 10  cm for WIMP masses of 35 GeV/ c . Because some signals that the detector receives might be due to neutrons, reducing the radioactivity increases

1443-554: The world. There are three main barrel vaulted experimental halls, each approximately 20 m wide, 18 m tall, and 100 m long. These provide roughly 3×20×100=6,000 m (65,000 sq ft) of floor space and 3×20×(8+10×π/4)×100=95,100 m (3,360,000 cu ft) of volume. Including smaller spaces and various connecting tunnels, the facility totals 17,800 m (192,000 sq ft) and 180,000 m (6,400,000 cu ft). The experimental halls are covered by about 1400 m of rock, protecting

1482-459: Was observed above the expected background, leading to the most stringent limit on the spin independent WIMP-nucleon cross section in 2012, with a minimum at 2.0 × 10  cm for a 65 GeV/ c WIMP mass. These results constrain interpretations of signals in other experiments as dark matter interactions, and rule out exotic models such as inelastic dark matter, which would resolve this discrepancy. XENON100 has also provided improved limits on

1521-452: Was taking science data for its first science run, which was ongoing at the time. On 28 July 2023 the XENONnT published the first results of its search for WIMPs, excluding cross sections above 2.58 × 10 − 47 c m 2 {\displaystyle 2.58\times 10^{-47}cm^{2}} at 28 GeV with 90% confidence level, jointly on the same date

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