Search

We propose a major upgrade to the existing PandaX-4T experiment at the China Jinping Underground Laboratory. The new experiment, PandaX-xT, will be a multi-ten-tonne liquid xenon, ultra-low background, and general-purpose observatory. The full-scaled PandaX-xT contains a 43-t liquid xenon active target. Such an experiment will significantly advance our fundamental understanding of particle physics and astrophysics. The sensitivity of dark matter direct detection will be improved by nearly two orders of magnitude compared to the current best limits, approaching the so-called “neutrino floor” for a dark matter mass above 10 GeV/c2, providing a key test to the Weakly Interacting Massive Particle paradigm. By searching for the neutrinoless double beta decay of 136Xe isotope in the detector, the effective Majorana neutrino mass can be measured to a 10–41 meV/c2 sensitivity, providing a key test to the Dirac/Majorana nature of neutrinos. Astrophysical neutrinos and other ultra-rare interactions can also be measured and searched for with an unprecedented background level, opening up new windows of discovery. Depending on the findings, PandaX-xT will seek the next stage upgrade utilizing isotopic separation of natural xenon. [ABSTRACT FROM AUTHOR]

A search for the neutrinoless quadruple beta decay of 136Xe was conducted with the liquid-xenon detector XMASS-I using 327 kg ×800.0 days of the exposure. The pulse shape discrimination based on the scintillation decay time constant which distinguishes γ-rays including the signal and β-rays was used to enhance the search sensitivity. No significant signal excess was observed from the energy spectrum fitting with precise background evaluation, and we set a lower limit of the half life of 3.7 × 1024 years at 90% confidence level. This is the first experimental constraint of the neutrinoless quadruple beta decay of 136Xe.

We have searched for exotic neutrino-electron interactions that could be produced by a neutrino millicharge, by a neutrino magnetic moment, or by dark photons using solar neutrinos in the XMASS-I liquid xenon detector. We observed no significant signals in 711 days of data. We obtain an upper limit for neutrino millicharge of 5.4×10−12e at 90% confidence level assuming all three species of neutrino have common millicharge. We also set flavor-dependent limits assuming the respective neutrino flavor is the only one carrying a millicharge, 7.3×10−12e for νe, 1.1×10−11e for νμ, and 1.1×10−11e for ντ. These limits are the most stringent yet obtained from direct measurements. We also obtain an upper limit for the neutrino magnetic moment of 1.8×10−10 Bohr magnetons. In addition, we obtain upper limits for the coupling constant of dark photons in the U(1)B−L model of 1.3×10−6 if the dark photon mass is 1×10−3 MeV/c2, and 8.8×10−5 if it is 10 MeV/c2.

Dark matter is one of the greatest mysteries of the Universe. The attributes of the dark matter particles, which make up about 86% of the mass of our Universe, are still obscure. LUX‐ZEPLIN (LZ) will be the most sensitive direct detection dark matter experiment to detect the faint interactions between the dark and ordinary matter. The LZ experiment employs the technology of a dual‐phase xenon time projection chamber (TPC) in combination with a novel active neutron veto to detect Weakly Interacting Massive Particles (WIMPs), one of the propitious dark matter candidates. For a 1,000 live day run, the projected spin‐independent cross‐section sensitivity of LZ is 1.6 × 10−48 cm2 for a 40 GeV c−2 mass WIMP. LZ will also probe the sensitivity to neutrinoless double beta (0νββ) decay of 136Xe. For 1,000 live days, the median exclusion sensitivity to the half‐life of 0νββ decay of 136Xe is predicted to be 1.06 × 1026 years. The LZ experiment is currently under construction and it will start commissioning by the end of 2020. [ABSTRACT FROM AUTHOR]

Abstract The XENON1T experiment aims for the direct detection of dark matter in a detector filled with 3.3 tons of liquid xenon. In order to achieve the desired sensitivity, the background induced by radioactive decays inside the detector has to be sufficiently low. One major contributor is the $$\beta $$ β -emitter $$^{85}$$ 85 Kr which is present in the xenon. For XENON1T a concentration of natural krypton in xenon $$\mathrm {^{nat}\mathrm{Kr/Xe}\,

LUX (Large Underground Xenon) was a dark matter experiment, which was housed at the Sanford Underground Research Facility (SURF) in South Dakota until late 2016, and previously set world-leading limits on Weakly Interacting Massive Particles (WIMPs), axions and axion-like particles (ALPs). This proceeding presents an overview of the LUX experiment and discusses the most recent analysis efforts, which are probing various dark matter models and detection techniques. In particular, studies of signals from inelastic scattering processes and of single scintillation photon events have improved the sensitivity of the experiment to low mass WIMPs. Additionally, a model-independent search for modulations in the LUX electron recoil rate is presented, demonstrating the most sensitive annual modulation search to date. [ABSTRACT FROM AUTHOR]

LZ is a second-generation Dark Matter experiment to conduct searches for weakly interacting massive particles. It is expected that the detector will reach a sensitivity for spin-independent elastic WIMP-nucleon cross-section of 1. 6 × 1 0 − 48 cm 2 at a mass of 40 GeV/c 2 in 1000 days of operation. Aside from Dark Matter particle interactions, the detector will also be sensitive to solar and supernova neutrinos as well as neutrinoless double beta decay from 136Xe. Background sources such as 222Rn and 85Kr must be significantly suppressed. This will be assured by radioactive screening of detector components and purification of xenon. The design of the LZ detector, radioactive background expectations and projected WIMP sensitivity are presented in this article. [ABSTRACT FROM AUTHOR]

A search for dark matter (DM) with mass in the sub-GeV region (0.32–1 GeV) was conducted by looking for an annual modulation signal in XMASS, a single-phase liquid xenon detector. Inelastic nuclear scattering accompanied by bremsstrahlung emission was used to search down to an electron equivalent energy of 1 keV. The data used had a live time of 2.8 years (3.5 years in calendar time), resulting in a total exposure of 2.38 ton-years. No significant modulation signal was observed and 90% confidence level upper limits of 1.6 × 10 − 33 cm2 at 0.5 GeV was set for the DM-nucleon cross section. This is the first experimental result of a search for DM mediated by the bremsstrahlung effect. In addition, a search for DM with mass in the multi-GeV region (4–20 GeV) was conducted with a lower energy threshold than previous analysis of XMASS. Elastic nuclear scattering was used to search down to a nuclear recoil equivalent energy of 2.3 keV, and upper limits of 2.9 × 10 − 42 cm2 at 8 GeV was obtained. [ABSTRACT FROM AUTHOR]

Abstract A search for Weakly Interacting Massive Particles (WIMPs) was conducted with the single-phase liquid-xenon detector XMASS through inelastic scattering in which 129Xe nuclei were excited, using an exposure (327 kg × 800.0 days) 48 times larger than that of our previous study. The inelastic excitation sensitivity was improved by detailed evaluation of background, event classification based on scintillation timing that distinguished γ -rays and β -rays, and simultaneous fitting of the energy spectra of γ -like and β -like samples. No evidence of a WIMP signal was found. Thus, we set the upper limits of the inelastic channel cross section at 90% confidence level, for example, 4.1 × 10 − 39 cm 2 for a 200 GeV/ c 2 WIMP. This result provides the most stringent limits on the SD WIMP-neutron interaction and is better by a factor of 7.7 at 200 GeV/ c 2 than the existing experimental limit. [ABSTRACT FROM AUTHOR]

Abstract A large-area Multi-Pixel Photon Counter (MPPC) sensitive to vacuum ultra violet (VUV) light has been developed for the liquid xenon (LXe) scintillation detector of the MEG II experiment. The LXe detector is designed to detect the 52.8 MeV photon from the lepton flavour violating decay μ + → e + γ and is based on 900 ℓ LXe with a highly granular scintillation readout by 4092 VUV-MPPCs with an active area of 139 mm 2 each, totalling 0. 57 m 2. The VUV-MPPC shows an excellent performance in LXe, which includes a high photon detection efficiency (PDE) up to 21% for the LXe scintillation light in the VUV range, a high gain, a low probability of the optical cross-talk and the after-pulsing, a low dark count rate and a good single photoelectron resolution. The large active area of the VUV-MPPC is formed by connecting four independent small VUV-MPPC chips in series to avoid the increase of the sensor capacitance and thus, to have a short pulse-decay-time, which is crucial for high rate experiments. Performance tests of 4180 VUV-MPPCs produced for the LXe detector were also carried out at room temperature prior to the installation to the detector and all of them with only a few exceptions were found to work properly. The design and performance of the VUV-MPPC are described in detail as well as the results from the performance tests at room temperature. [ABSTRACT FROM AUTHOR]

Abstract Neutrinoless double beta decays in liquid xenon produce a significant amount of Cherenkov light, with a photon number and angular distribution that distinguishes these events from common backgrounds. A GEANT4 simulation was used to simulate Cherenkov photon production and measurement in a liquid xenon detector and a multilayer perceptron was used to analyze the resulting distributions to classify events based on their Cherenkov photons. Our results show that a modest improvement in the sensitivity of neutrinoless double beta decay searches is possible using this technique, but the kinematics of the neutrinoless double beta decay and electron scattering in liquid xenon substantially limit this approach. [ABSTRACT FROM AUTHOR]

A search for dark matter was conducted by looking for an annual modulation signal due to the Earth's rotation around the Sun using XMASS, a single phase liquid xenon detector. The data used for this analysis was 359.2 live days times 832 kg of exposure accumulated between November 2013 and March 2015. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the target nuclei, the exclusion upper limit of the WIMP–nucleon cross section 4.3×10−41 cm2 at 8 GeV/c2 was obtained and we exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c2 range at ∼10−40 cm2. The result of a simple modulation analysis, without assuming any specific dark matter model but including electron/γ events, showed a slight negative amplitude. The p-values obtained with two independent analyses are 0.014 and 0.068 for null hypothesis, respectively. We obtained 90% C.L. upper bounds that can be used to test various models. This is the first extensive annual modulation search probing this region with an exposure comparable to DAMA/LIBRA.

Double electron capture is a rare nuclear decay process in which two orbital electrons are captured simultaneously in the same nucleus. Measurement of its two-neutrino mode would provide a new reference for the calculation of nuclear matrix elements whereas observation of its neutrinoless mode would demonstrate lepton number violation. A search for two-neutrino double electron capture on 124Xe is performed using 165.9 days of data collected with the XMASS-I liquid xenon detector. No significant excess above background was observed and we set a lower limit on the half-life as 4.7×1021 years at 90% confidence level. The obtained limit has ruled out parts of some theoretical expectations. We obtain a lower limit on the 126Xe two-neutrino double electron capture half-life of 4.3×1021 years at 90% confidence level as well.

Biexcitonic collision kinetics with prescribed diffusion in the ion track core have been applied for scintillation response due to heavy ions in liquid argon. The quenching factors q = EL/E, where E is the ion energy and EL is the energy expended for luminescence, for 33.5 MeV/n 18O and 31.9 MeV/n 36Ar ions in liquid Ar at zero field are found to be 0.73 and 0.46, compared with measured values of 0.59 and 0.46, respectively. The quenching model is also applied for 80–200 keV Pb recoils in α-decay, background candidates in direct dark matter searches, in liquid argon. Values obtained are ~0.09. A particular feature of Birks’ law has been found and exploited in evaluating the electronic quenching factor qel in liquid Xe. The total quenching factors qT for 0.5–20 keV Xe recoils needed for weakly interacting massive particle (WIMP) searches are estimated to be ~0.12–0.14, and those for Pb recoils of 103 and 169 keV are 0.08 and 0.09, respectively. In the calculation, the nuclear quenching factor qnc = Eη/E, where Eη is the energy available for the electronic excitation, is obtained by Lindhard theory and a semi-empirical theory by Ling and Knipp. The electronic linear energy transfer plays a key role.

Abstract A search for dark matter using an underground single-phase liquid xenon detector was conducted at the Kamioka Observatory in Japan, particularly for Weakly Interacting Massive Particles (WIMPs). We have used 705.9 live days of data in a fiducial volume containing 97 kg of liquid xenon at the center of the detector. The event rate in the fiducial volume after the data reduction was (4.2 ± 0.2) × 10 − 3 day − 1 kg − 1 ke V ee − 1 at 5 ke V ee , with a signal efficiency of 20%. All the remaining events are consistent with our background evaluation, mostly of the "mis-reconstructed events" originated from 210Pb in the copper plates lining the detector's inner surface. The obtained upper limit on a spin-independent WIMP-nucleon cross section was 2.2 × 10 − 44 cm 2 for a WIMP mass of 60 GeV/c 2 at the 90% confidence level, which was the most stringent limit among results from single-phase liquid xenon detectors. [ABSTRACT FROM AUTHOR]

Abstract We report a new liquid xenon Compton camera, called XEMIS2 (XEnon Medical Imaging System), developed to image for the first time small animals using 3 γ imaging. This technique proposes an alternative to reduce the administered radiopharmaceutical activity while preserving diagnostic image quality using liquid xenon as detection medium. Given the success of its predecessor, a small dimension liquid xenon time projection chamber called XEMIS1, we are currently building a larger scale detector for preclinical applications. This second prototype, XEMIS2, is a single phase liquid xenon cylindrical camera with a large axial field of view for full-body small animal imaging. XEMIS2 holds around 200 kg of xenon and it has been designed to enable high-efficiency and simultaneous detection of the three γ -rays emitted by a 44Sc radionuclide. The innovative geometry of XEMIS2 will allow to discriminate and measure the position and deposited energy of most Compton interactions inside the detector. In order to manage such a large quantity of xenon, an innovative high-pressure subsystem known as ReStoX has been developed and successfully qualified. ReStoX allows to maintain the xenon in liquid state at the desired temperature and pressure, transfer the xenon into XEMIS2 and store it during long term periods. XEMIS2 will be installed at a non controlled radioactive area of Nantes Hospital. The goal is to evaluate image quality of a 20 min whole-body preclinical exam with an injected activity of 20 kBq. Highlights • The first 3 gamma whole-body small animal scanner is presented. • The XEMIS2 camera is a single-phase liquid xenon detector with a 24 cm axial field of view. • A dedicated 32-channels low power circuit called XTRACT is described. • ReStoX is an advanced cryogenic system developed to liquefy, recover and store the xenon. • A reconstructed image using the innovative 3 gamma reconstruction algorithm is reported. [ABSTRACT FROM AUTHOR]

Abstract Hidden photons and axion-like particles are candidates for cold dark matter if they were produced non-thermally in the early universe. We conducted a search for both of these bosons using 800 live-days of data from the XMASS detector with 327 kg of liquid xenon in the fiducial volume. No significant signal was observed, and thus we set constraints on the α ′ / α parameter related to kinetic mixing of hidden photons and the coupling constant g A e of axion-like particles in the mass range from 40 to 120 keV/ c 2 , resulting in α ′ / α < 6 × 10 − 26 and g A e < 4 × 10 − 13. These limits are the most stringent over this mass range derived from both direct and indirect searches to date. [ABSTRACT FROM AUTHOR]

Abstract Noble liquid radiation detectors have long been afflicted by spurious electron emission from their cathodic electrodes. This phenomenon must be understood and mitigated in the next generation of liquid xenon (LXe) experiments searching for WIMP dark matter or neutrinoless double beta decay, and in the large liquid argon (LAr) detectors for the long-baseline neutrino programmes. We present a systematic study of this spurious emission involving a series of slow voltage-ramping tests on fine metal wires immersed in a two-phase xenon time projection chamber with single electron sensitivity. Emission currents as low as 10 − 18 A can thus be detected by electron counting, a vast improvement over previous dedicated measurements. Emission episodes were recorded at surface fields as low as ∼ 10 kV/cm in some wires and observed to have complex emission patterns, with average rates of 10–200 counts per second (c/s) and outbreaks as high as ∼ 106 c/s. A fainter, less variable type of emission was also present in all untreated samples. There is evidence of a partial conditioning effect, with subsequent tests yielding on average fewer emitters occurring at different fields for the same wire. We find no evidence for an intrinsic threshold particular to the metal-LXe interface which might have limited previous experiments up to fields of at least 160 kV/cm. The general phenomenology is not consistent with enhanced field emission from microscopic filaments, but it appears instead to be related to the quality of the wire surface in terms of corrosion and the nature of its oxide layer. This study concludes that some surface treatments, in particular nitric acid cleaning applied to stainless steel wires, can bring about at least order-of-magnitude improvements in overall electron emission rates, and this should help the next generation of detectors achieve the required electrostatic performance. [ABSTRACT FROM AUTHOR]

Abstract The Large Underground Xenon experiment (LUX) searches for dark matter using a dual-phase xenon detector. LUX uses a custom-developed trigger system for event selection. In this paper, the trigger efficiency, which is defined as the probability that an event of interest is selected for offline analysis, is studied using raw data obtained from both electron recoil (ER) and nuclear recoil (NR) calibrations. The measured efficiency exceeds 98% at a pulse area of 90 detected photons, which is well below the WIMP analysis threshold on the S2 pulse area. The efficiency also exceeds 98% at recoil energies of 0.2 keV and above for ER, and 1.3 keV and above for NR. The measured trigger efficiency varies between 99% and 100% over the fiducial volume of the detector. [ABSTRACT FROM AUTHOR]

We present the performances and characterization of an array made of S13370-3050CN (VUV4 generation) Multi-Pixel Photon Counters manufactured by Hamamatsu and equipped with a low power consumption preamplifier operating at liquid xenon temperature ( ∼ 175 K). The electronics is designed for the readout of a matrix of maximum dimension of 8 × 8 individual photosensors and it is based on a single operational amplifier. The detector prototype presented in this paper utilizes the Analog Devices AD8011 current feedback operational amplifier, but other models can be used depending on the application. A biasing correction circuit has been implemented for the gain equalization of photosensors operating at different voltages. The results show single photon detection capability making this device a promising choice for future generation of large scale dark matter detectors based on liquid xenon, such as DARWIN. [ABSTRACT FROM AUTHOR]

We report on a liquid xenon gravity assisted recovery method for nuclear medical imaging applications. The experimental setup consists of an elevated detector enclosed in a cryostat connected to a storage tank called ReStoX. Both elements are part of XEMIS2 (XEnon Medical Imaging System): an innovative medical imaging facility for pre-clinical research that uses pure liquid xenon as detection medium. Tests based on liquid xenon transfer from the detector to ReStoX have been successfully performed showing that an unprecedented mass flow rate close to 1 ton per hour can be reached. This promising achievement as well as future areas of improvement will be discussed in this paper. [ABSTRACT FROM AUTHOR]

Large liquid argon detectors have become widely used in low rate experiments, including dark matter and neutrino research. However, the optical properties of liquid argon are not well understood at the large scales relevant for current and near-future detectors. The index of refraction of liquid argon at the scintillation wavelength has not been measured, and current Rayleigh scattering length calculations disagree with measurements. Furthermore, the Rayleigh scattering length and index of refraction of solid argon and solid xenon at their scintillation wavelengths have not been previously measured or calculated. We introduce a new calculation using existing data in liquid and solid argon and xenon to extrapolate the optical properties at the scintillation wavelengths using the Sellmeier dispersion relationship. [ABSTRACT FROM AUTHOR]

In the MEG II experiment, Multi-Pixel Photon Counters (MPPC) sensitive to vacuum ultraviolet (VUV) light are used in the liquid xenon gamma-ray detector under a high-intensity muon beam environment. In the commissioning phase of the detector with the beam, a significant degradation in the Photon Detection Efficiency (PDE) for VUV light was observed, while the degradation in the PDE for visible light was much less significant. This wavelength dependence of the damage level suggests that the radiation damage is localized to the surface of the MPPC where incoming VUV photons create electron–hole pairs. The study also found that the original PDE level could be restored by thermal annealing. [ABSTRACT FROM AUTHOR]

Positron targets are a critical component of future Linear Colliders. Traditional targets are composed of high-Z metals that become brittle over time due to constant bombardment by high-power electron beams. We explore the possibility of a liquid xenon target which is continuously refreshed and therefore not susceptible to the damage mechanisms of traditional solid targets. Using the GEANT4 simulation code, we examine the performance of the liquid xenon target and show that the positron yield is comparable to solid targets when normalized by radiation length. Additionally, we observe that the peak energy deposition density (PEDD) threshold for liquid xenon is higher than for commonly employed metal targets, which makes it an attractive, non-toxic positron target alternative. We develop parameter sets for demonstration applications at FACET-II and future Linear Colliders. [ABSTRACT FROM AUTHOR]

We developed two complementary ways to measure the position of SiPMs inside liquid xenon detector for MEG II experiment; one uses laser tools and the other uses an X-ray beam. We measured the position of all SiPMs to an accuracy of 320 μ m. • Precise alignment of SiPMs in liquid xenon detector with X-ray and laser. • The SiPM array is scanned with X-ray beam that makes a local energy deposit. • Reconstructed 3D SiPM array from an image taken by a laser scanner. • Reasonable thermal contraction was observed from the comparison. • Consistent shape of the SiPM array measured by two measurements. [ABSTRACT FROM AUTHOR]

The nEXO experiment will operate an ultra-low background time projection chamber filled with 5 t of isotopically enriched liquid xenon (LXe) for the search for the neutrinoless double beta decay in Xe-136. The detector will use 4 m 2 of silicon photomultipliers (SiPMs) operated at about − 104 ∘ C to collect the scintillation light. There are strong requirements on the background levels, light collection efficiency and SiPM performance to set the most stringent limits on the half-life. Detecting the 0 ν β β -decay would have wide-spread implications for neutrino physics. The SiPMs need to be sensitive to the vacuum-ultraviolet scintillation light of LXe at 178 nm which is not given for off-the-shelf SiPMs. The SiPM performance requirements adopted by nEXO are (among others) a photon detection efficiency of at least 15% at 178 nm , a correlated avalanche probability of less than 20% and a low dark-rate. Additionally, the VUV-reflectance of the SiPM surface in LXe is an important parameter for optimal light collection and thus the energy resolution of nEXO. We present measurements with state-of-the-art VUV-sensitive SiPMs focusing on the surface VUV-reflectance in liquid xenon. • SiPM surfaces reflect up to 17% of incident VUV light when immersed in liquid xenon. • Due to the surface micro-structure, reflectance spectra reveal additional artefacts. • Knowing the surface reflectivity is vital for simulating large scale LXe detectors. [ABSTRACT FROM AUTHOR]

The coherent elastic neutrino-nucleus scattering (CEvNS) plays a crucial role at the final evolution of stars. The detection of it would be of importance in astroparticle physics. Among all available neutrino sources, galactic supernovae give the highest neutrino flux in the MeV range. Among all liquid xenon dark matter experiments, XMASS has the largest sensitive volume and light yield. The possibility to detect galactic supernova via the CEvNS-process on xenon nuclei in the current XMASS detector was investigated. The total number of events integrated in about 18 s after the explosion of a supernova 10 kpc away from the Earth was expected to be from 3.5 to 21.1, depending on the supernova model used to predict the neutrino flux, while the number of background events in the same time window was measured to be negligible. All lead to very high possibility to detect CEvNS experimentally for the first time utilizing the combination of galactic supernovae and the XMASS detector. In case of a supernova explosion as close as Betelgeuse, the total observable events can be more than ∼ 10 4 , making it possible to distinguish different supernova models by examining the evolution of neutrino event rate in XMASS. [ABSTRACT FROM AUTHOR]

The MEG II experiment is an upgrade of the MEG experiment to search for the charged lepton flavor violating decay of muon, μ + → e + γ . The MEG II experiment is expected to reach a branching ratio sensitivity of 4 × 10 − 14 , which is one order of magnitude better than the sensitivity of the current MEG experiment. The performance of the liquid xenon (LXe) γ -ray detector will be greatly improved with a highly granular scintillation readout realized by replacing 216 photomultiplier tubes (PMTs) on the γ -ray entrance face with 4092 Multi-Pixel Photon Counters (MPPCs). For this purpose, we have developed a new type of MPPC which is sensitive to the LXe scintillation light in vacuum ultraviolet (VUV) range, in collaboration with Hamamatsu Photonics K.K. We have measured the performance of the MPPC in LXe, and an excellent performance has been confirmed including high photon detection efficiency ( > 15 % ) for LXe scintillation light. An excellent performance of the LXe detector has been confirmed by Monte Carlo simulations based on the measured properties of the MPPC. The construction of the detector is in progress, aiming to start physics data taking in 2017. [ABSTRACT FROM AUTHOR]

We report the measurement of the emission time profile of scintillation from gamma-ray induced events in the XMASS-I 832 kg liquid xenon scintillation detector. Decay time constant was derived from a comparison of scintillation photon timing distributions between the observed data and simulated samples in order to take into account optical processes such as absorption and scattering in liquid xenon. Calibration data of radioactive sources, 55 Fe, 241 Am, and 57 Co were used to obtain the decay time constant. Assuming two decay components, τ 1 and τ 2 , the decay time constant τ 2 increased from 27.9 ns to 37.0 ns as the gamma-ray energy increased from 5.9 keV to 122 keV. The accuracy of the measurement was better than 1.5 ns at all energy levels. A fast decay component with τ 1 ∼ 2 ns was necessary to reproduce data. Energy dependencies of τ 2 and the fraction of the fast decay component were studied as a function of the kinetic energy of electrons induced by gamma-rays. The obtained data almost reproduced previously reported results and extended them to the lower energy region relevant to direct dark matter searches. [ABSTRACT FROM AUTHOR]

In this study we report on the analysis of isothermal spectra of NH 3 and ND 3 solutions in liquid xenon at 203 K using newly developed and validated least-squares approaches to investigate the its self-associating behavior. For both species we observe clear dimer bands in the spectral area of the ν 1 +ν 4, ν 3 +ν 4 and ν 1 +ν 2, ν 3 +ν 2 combination bands. The analysis of the N−D stretching area, allows us to characterize clear contributions of dimers and trimers. The analysis of the N H stretching area is hampered by the occurrence of a time dependent band due to solid water traces during the experiments. For NH 3 we also performed an investigation of the N H bending region, ν 2 , which demonstrated a small dimer absorption band. These obtained results compare well with literature data. [ABSTRACT FROM AUTHOR]

The MEG experiment searches for the muon lepton flavor violating decay, μ + → e + γ . An upgrade of the experiment is ongoing, aiming at reaching a sensitivity of Br ( μ + → e + γ ) = 4 × 10 − 14 , an order of magnitude better than the sensitivity of the current MEG. To achieve this goal, all of the detectors are being upgraded. In MEG, the energy, position and timing of the gamma ray were measured by a liquid Xe calorimeter, which consists of 900 l of liquid Xe and 846 2-in. round-shaped photo-multiplier tubes (PMTs). In the upgrade, the granularity at the gamma ray incident face will be improved by replacing 216 PMTs with 4092 SiPMs (MPPCs) with an active area of 12×12 mm 2 each. The energy resolution for the gamma ray is expected to improve by a factor of 2, because the efficiency to collect scintillation light will become more uniform. The position resolution is also expected to improve by a factor of 2. In collaboration with Hamamatsu Photonics K.K., we have successfully developed a high performance MPPC for our detector. It has excellent photon detection efficiency for the liquid xenon scintillation light in VUV range. The size of the chips is large so that it can cover large area with a manageable number of readout channels. The characteristics of the MPPCs are being tested in liquid Xe, and also at the room temperature. The results of the tests will be presented, together with the expected performance of the upgraded detector. [ABSTRACT FROM AUTHOR]

We describe a new positron emission time-of-flight apparatus using liquid xenon. The detector is based in a liquid xenon scintillating cell. The cell shape and dimensions can be optimized depending on the intended application. In its simplest form, the liquid xenon scintillating cell is a box in which two faces are covered by silicon photomultipliers and the others by a reflecting material such as Teflon. It is a compact, homogenous and highly efficient detector which shares many of the desirable properties of monolithic crystals, with the added advantage of high yield and fast scintillation offered by liquid xenon. Our initial studies suggest that good energy and spatial resolution comparable with that achieved by lutetium oxyorthosilicate crystals can be obtained with a detector based in liquid xenon scintillating cells. In addition, the system can potentially achieve an excellent coincidence resolving time of better than 100 ps. [ABSTRACT FROM AUTHOR]

The liquid xenon (LXe) gamma-ray detector in the MEG II experiment measures the energy, position and timing of the gamma-ray from μ + → e + γ , and it is the key to the unprecedented sensitivity of the experiment. All the photo sensors of 4092 VUV MPPCs and 668 PMTs were read out for the first time and a physics data collection started in 2021. The detector response was monitored all through the beam time, and the LXe detector operated stably. The timing and energy resolution were measured using the gamma-rays from the π 0 decays after charge exchange reaction of charged pions in a liquid hydrogen target. The detector has been successfully commissioned and is ready for the long physics run. [ABSTRACT FROM AUTHOR]

The Light-only Liquid Xenon (LoLX) experiment is designed to study the properties of light emission and transport in liquid xenon (LXe) using silicon photomultipliers (SiPMs). In addition, we also plan to perform long-term stability studies of the SiPMs in LXe. Another important goal of the LoLX experiment is to characterize and utilize the differences in spectrum and timing of Cherenkov and scintillation light production to develop a background discriminator for low-background LXe experiments such as, neutrino-less double beta decay searches. In this paper we present the project status and perspectives. [ABSTRACT FROM AUTHOR]

We report the studies and optimization of scintillation light measurements in an updated version of the XEMIS1 prototype for the development of the XEMIS2 camera. A novel monolithic liquid xenon Compton camera, named XEMIS2 (XEnon Medical Imaging System), attempts to achieve low-activity small-animal imaging using the 3-gamma imaging technique. This emerging detector relies on the time projection chamber technique: it will be able to perform a simultaneous detection of the three γ -rays emitted by a specific radionuclide, such as scandium-44, and to produce a good quality image with a remarkable diminution of radiopharmaceutical activity at the same time. Vacuum Ultraviolet (VUV) scintillation light and ionization charge carriers generated from the recoiling particles within the detector are detected and used to reconstruct the interaction position and deposited energy. A cost-effective self-triggering scintillation signal read-out and data acquisition (DAQ) system has been developed to achieve a continuous data read-out with negligible electronics dead time. The DAQ prototype has been installed and qualified in an updated version of the XEMIS1 detector. It reaches the performance specifications in scintillation light measurements. Moreover, scintillation signals can also be used for the virtual segmentation of the monolithic detection volume through the matching algorithm of the scintillation and ionization signals based on the Light Collection Map (LCM). This spatial pre-localization of the physical events, called the virtual fiducialization of the active volume, is used to lower the detector occupancy rate when the administered activity is increased to lessen the examination time. The XEMIS1 experimental LCMs indicate that each PMT owns an individual field of view so as to segment the active volume virtually. The preparation work for the XEMIS2 camera operation has been completed in the updated XEMIS1 detector while the XEMIS2 scintillation light measurement system is under commissioning in Nantes Centre Hospitalier Universitaire. • The XEMIS2 camera oriented to the whole-body small animal 3-gamma medical imaging is presented. • The XEMIS2 system is a monolithic liquid xenon Compton camera with a 24 cm axial field of view. • A cost-effective 16-channel self-triggering scintillation signal front-end read-out electronics named XSRETOT is reported. • The XEMIS1 experimental light collection maps can be used for the virtual segmentation of the monolithic detection volume. [ABSTRACT FROM AUTHOR]

The MEG II experiment is searching for new physics beyond the SM (e.g. SUSY-GUT, SUSY-seesaw) through the lepton flavor violating μ + → e + γ decay with ten times better sensitivity than the MEG experiment. The MEG collaboration published the result of B (μ + → e + γ) < 4. 2 × 1 0 − 13 at 90% C.L. in 2016, which was thirty times better result than the previous limit. As the sensitivity of the MEG experiment was already limited by the accidental background, the MEG detector had to be upgraded to reach one order of magnitude better sensitivity. The MEG experiment utilized 846 2 inch PMTs to detect scintillation light in a 900 l liquid xenon γ calorimeter. In the MEG II experiment, 216 2 inch PMTs on the γ incident face were replaced with 4092 MPPCs (SiPMs produced by Hamamatsu) to improve the energy and position resolutions. We started the detector commissioning with the full electronics readout channels for the first time in 2021, and soon after, we started the physics data taking. Here the LXe detector status including initial photon sensor calibration and performance will be summarized together with the expected detector performance. The PDE decrease of the SiPM observed in the high rate muon beam environment and our possible remedy will also be discussed. [ABSTRACT FROM AUTHOR]

The self-associating behavior of pyrrole in liquid xenon was investigated by analyzing a data set of 185–113 infrared spectra obtained for different concentrations recorded at a constant temperature of 203 K. Analysis of the data using a recently developed least-squares approach allows the vibrational spectra of the monomer and of the different oligomers to be isolated. Apart from the monomer transitions, intense absorption bands originating from pyrrole trimers are observed in almost every spectral region including regions for which no data have yet been reported. Apart from these bands, weak features proving the presence of pyrrole dimer and pyrrole tetramer in the solutions are also reported. The weak character of the dimer bands observed and the low concentrations of these species deduced are explained by the fact that the cryosolutions studied are in chemical equilibrium and by the fact that due to strong cooperative effect present in the trimer, the complexation equilibria are strongly shifted towards the latter species, thereby strongly reducing the equilibrium concentrations of dimer and tetramer. [ABSTRACT FROM AUTHOR]

Tetraphenyl butadiene (TPB) is widely used in particle detectors as a wavelength shifter. In this work we studied the stability of TPB thin films when immersed in liquid xenon (LXe). The thin films were deposited on glass and quartz substrates by thermal evaporation. Morphological and chemical surface properties were monitored before and after immersion into LXe by scanning electron microscopy and X-ray photoelectron spectroscopy. No appreciable changes have been detected with these two methods. Grain size and surface chemical composition were found to be identical before and after submersion into LXe. However, the film thickness, measured via optical transmission in the ultraviolet–visible wavelength regions, decreased by 1.6 μg/cm 2 (24%) after immersion in LXe during 20 h. These results suggest the necessity of using a protective thin film over the Tetraphenyl butadiene when used as a wavelength shifter in LXe particle detectors. [ABSTRACT FROM AUTHOR]

The structure of the barrel calorimeter of the CMD-3 detector is presented in this work. The procedure of energy calibration of the calorimeter and the method of photon energy restoration are described. The distinctive feature of this barrel calorimeter is its combined structure; it is composed of two coaxial subsystems: a liquid xenon calorimeter and a crystalline CsI calorimeter. The calorimeter spatial resolution of the photon conversion point is about 2 mm, which corresponds to an angular resolution of ∼6 mrad. The energy resolution of the calorimeter is about 8% for photons with energy of 200 MeV and 4% for photons with energy of 1 GeV. [ABSTRACT FROM AUTHOR]

We present an updated model of light and charge yields from nuclear recoils in liquid xenon with a simultaneously constrained parameter set. A global analysis is performed using measurements of electron and photon yields compiled from all available historical data, as well as measurements of the ratio of the two. These data sweep over energies from 1 - 300~\keV and external applied electric fields from 0 - 4060~\V/cm. The model is constrained by constructing global cost functions and using a simulated annealing algorithm and a Markov Chain Monte Carlo approach to optimize and find confidence intervals on all free parameters in the model. This analysis contrasts with previous work in that we do not unnecessarily exclude data sets nor impose artificially conservative assumptions, do not use spline functions, and reduce the number of parameters used in NEST v0.98. We report our results and the calculated best-fit charge and light yields. These quantities are crucial to understanding the response of liquid xenon detectors in the energy regime important for rare event searches such as the direct detection of dark matter particles. [ABSTRACT FROM AUTHOR]

The emission spectrum of cryogenic liquid xenon in the vacuum ultraviolet region was measured by irradiating liquid xenon with gamma-rays from a radioactive source. To achieve a high signal-to-noise ratio, we employed coincident photon counting. Additionally, the charge of the photo-sensor signals was measured to estimate the number of detected photons accurately. In addition, proper corrections were incorporated for the wavelength; response functions of the apparatus obtained using a low-pressure mercury lamp, and photon detection efficiencies of the optical system were considered. The obtained emission spectrum is found to be in the shape of a Gaussian function, with the center at 57,199±34 (stat.)±33 (syst.) cm −1 (174.8±0.1 (stat.)±0.1 (syst.) nm) and the full width at half maximum of 3328±72 (stat.)±65 (syst.) cm −1 (10.2±0.2 (stat.)±0.2 (sys.) nm). These results are the most accurate values obtained in terms of the data acquisition method and the calibration for the experimental system and provide valuable information regarding the high-precision instruments that employ a liquid-xenon scintillator. [ABSTRACT FROM AUTHOR]

The liquid xenon (LXe) γ-ray detector for the MEG II experiment is based on a highly granular scintillation readout with Multi-Pixel Photon Counters (MPPCs). Here we report on the development of a large-area MPPC sensitive to LXe scintillation light in deep-UV range for the MEG II LXe detector. A prototype model of the deep-UV MPPC with an active area of 12 × 12 mm 2 was successfully tested in LXe, showing an excellent performance such as a high photon detection efficiency for the LXe scintillation light (about 20% at Δ V = 2.5 V ), a high internal gain (about 10 6 at Δ V = 2.5 V ) and an excellent single photoelectron resolution. The sensor chip of the MPPC is segmented into four sectors, which are then connected in series in order to reduce the overall sensor capacitance. The signal fall time of about 135 ns for the non-segmented sensor was significantly reduced down to 25 ns with the series-connected sensor segments. The preliminary results on the performance of the deep-UV MPPC are presented. [ABSTRACT FROM AUTHOR]

A new medical imaging technique based on the precise 3D location of a radioactive source by the simultaneous detection of 3 γ rays has been proposed by Subatech laboratory. To take advantage of this novel technique a detection device based on a liquid xenon Compton telescope and a specific ( β + , γ ) emitter radionuclide, 44 Sc, are required. A first prototype of a liquid xenon time projection chamber called XEMIS1 has been successfully developed showing very promising results for the energy and spatial resolutions for the ionization signal in liquid xenon, thanks to an advanced cryogenics system, which has contributed to a high liquid xenon purity with a very good stability and an ultra-low noise front-end electronics (below 100 electrons) operating at liquid xenon temperature. The very positive results obtained with XEMIS1 have led to the development of a second prototype for small animal imaging, XEMIS2, which is now under development. To study the feasibility of the 3 γ imaging technique and optimize the characteristics of the device, a complete Monte Carlo simulation has been also carried out. A preliminary study shows very positive results for the sensitivity, energy and spatial resolutions of XEMIS2. [ABSTRACT FROM AUTHOR]

The LUX (Large Underground Xenon) experiment aims at the direct detection of dark matter particles via their collisions with xenon nuclei. The 370 kg two-phase liquid xenon time projection chamber measures simultaneously the scintillation and ionization from interactions in the target. The ratio of these two signals provides very good discrimination between potential nuclear recoil and electronic recoil signals to search for WIMP-nucleon scattering. The LUX detector operates at the Sanford Underground Research Facility (Lead, South Dakota, USA) since February 2013. First results were presented in late 2013 setting the world׳s most stringent limits on WIMP-nucleon scattering cross-sections over a wide range of WIMP masses. A 300 day run beginning in 2014 will further improve the sensitivity and new calibration techniques will reduce systematics for the WIMP signal search. [ABSTRACT FROM AUTHOR]

In this paper we present thermal cycling experiments of GridPix radiation imaging detectors, in view of a potential application in a cryogenic experiment. The robustness of the GridPix detector is studied for various grid designs, as well as various mechanical and thermal surroundings. The grid design variations had insignificant effect on the grid strength. A low cool-down rate as well as good thermal contact are crucial for the durability of the grid. Further, additional strengthening at the grid edges proved necessary to maintain the integrity of the structure during thermal cycling, which was done using globtop adhesive. The combination of these measures led to 100% survival rate after thermal cycling down to −130 °C. [ABSTRACT FROM AUTHOR]

We perform a theoretical study of the scintillation efficiency of the low energy region crucial for liquid xenon dark matter detectors. We develop a computer program to simulate the cascading process of the recoiling xenon nucleus in liquid xenon and calculate the nuclear quenching effect due to atomic collisions. We use the electronic stopping power extrapolated from experimental data to the low energy region, and take into account the effects of electron escape from electron--ion pair recombination using the generalized Thomas-Imel model fitted to scintillation data. Our result agrees well with the experiments from neutron scattering and vanishes rapidly as the recoil energy drops below 3 keV. [ABSTRACT FROM AUTHOR]

The Timepix readout chip with its 65k pixels on a sensitive area of 14 mm×14 mm provides a fine spatial resolution for particle tracking or medical imaging. We explore the operation of Timepix in a dual-phase xenon environment (around −110 °C). Used in dual-phase xenon time projection chambers, e.g. for dark matter search experiments, the readout must have a sufficiently low detection limit for small energy deposits. We measured the electronic pixel noise of three bare Timepix chips. For the first time Timepix readout chips were cooled to temperatures as low as −125 °C. In this work, we present the results of analysing noise transition curves recorded while applying a well-defined charge to the pixel׳s input. The electronic noise reduces to an average of 99e − , a reduction of 23% compared to operation at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: The MEG experiment is searching for the lepton flavor violating decay, , with the highest sensitivity. A major upgrade of the experiment is planned where the performance of the liquid xenon (LXe) detector is expected to be significantly improved. The current 2-in. photomultiplier tubes (PMT) on the incident face will be replaced with smaller photo-sensors such as multi-pixel photon counters (MPPC) in order to improve the resolutions and the efficiency. A UV-sensitive MPPC operational in LXe is under development in collaboration with Hamamatsu Photonics. A high photon detection efficiency (PDE) of 17% to LXe scintillation light is achieved with a prototype with an active area of 12×12mm2 and a single-photoelectron peak is clearly observed. The engineering design of the detector and the development of the related technologies such as the signal transmission and assembly are also steadily in progress. [Copyright &y& Elsevier]