PandaX 暗物质探测实验

PandaX是一个位于四川锦屏地下实验室的大型粒子与天体物理稀有事件探测实验装置。PandaX的一期和二期实验利用二相型氙时间投影室技术来直接探测弱相互作用暗物质粒子。PandaX一期实验已经完成,它使用了120 kg氙以检验以往其他实验所发现的疑似信号,其结果在标准假设下否定了这些疑似信号。PandaX二期升级了探测器,使用了500 kg的氙,预期在2015年晚些时候正式开始数据采集以寻找暗物质,将有望拓展暗物质探测的极限。     

Development of the liquid level meters for the PandaX dark matter detector

The two-phase xenon detector is at the frontier of dark matter direct search. This kind of detector uses liquid xenon as the sensitive target and is operated in two-phase (liquid/gas) mode, where the liquid level needs to be monitored and controlled in sub-millimeter precision. In this paper, we present a detailed design and study of two kinds of level meters for the PandaX dark matter detector. The long level meter is used to monitor the overall liquid level while short level meters are used to monitor the inclination of the detector. These level meters are cylindrical capacitors that are custom-made from two concentric metal tubes. Their capacitance values are read out by a universal transducer interface chip and are recorded by the PandaX slow control system. We present the developments that lead to level meters with long-term stability and sub-millimeter precision. Fluctuations (standard deviations) of less than 0.02 mm for the short level meters and less than 0.2 mm for the long level meter were achieved during a few days of test operation.     

Development of the liquid level meters for the PandaX dark matter detector

The two-phase xenon detector is at the frontier of dark matter direct search. This kind of detector uses liquid xenon as the sensitive target and is operated in two-phase （liquid/gas） mode, where the liquid level needs to be monitored and controlled in sub-millimeter precision. In this paper, we present a detailed design and study of two kinds of level meters for the PandaX dark matter detector. The long level meter is used to monitor the overall liquid level while short level meters are used to monitor the inclination of the detector. These level meters are cylindrical capacitors that are custom-made from two concentric metal tubes. Their capacitance values are read out by a universal transducer interface chip and are recorded by the PandaX slow control system. We present the developments that lead to level meters with long-term stability and sub-millimeter precision. Fluctuations （standard deviations） of less than 0.02 mm for the short level meters and less than 0.2 mm for the long level meter were achieved during a few days of test operation.     

Simultaneous measurement of ionization and scintillation from nuclear recoils in liquid xenon for a dark matter experiment

We report the first measurements of the absolute ionization yield of nuclear recoils in liquid xenon, as a function of energy and electric field. Independent experiments were carried out with two dual-phase time-projection chamber prototypes, developed for the XENON dark matter project. We find that the charge yield increases with decreasing recoil energy, and exhibits only a weak field dependence. These results are the first unambiguous demonstration of the capability of dual-phase xenon detectors to discriminate between electron and nuclear recoils down to 20 keV, a key requirement for a sensitive dark matter search.     

Development of a two-phase xenon dark matter detector

The current status of the development study focused on building a novel two-phase xenon detector for dark matter search is described. Discrimination of the radioactive background is based on particle identification that comes from the analysis of the scintillation-to-ionization ratio. Electroluminescence (proportional scintillation) is used for “amplification” of the ionization signal.     

EDELWEISS experiment: Direct search for dark matter

The EDELWEISS experiment is aimed at direct searches for nonbaryonic cold dark matter by means of cryogenic germanium detectors. It is deployed at the LSM underground laboratory in the Frejus tunnel, which connects France and Italy. The results of the experimentmade it possible to set a limit on the spin-independent cross section for the scattering of weak-interacting massive particles (WIMP) at a level of 10^?6 pb. Data from 21 detectors of total mass about 7 kg are being accumulated at the present time.     

PandaX limits on the light dark matter with a light mediator in the singlet extension of MSSM

Using the latest PandaX limits on the light dark matter(DM) with a light mediator, we check their implication on the parameter space of the general singlet extension of MSSM(without Z_3 symmetry), which can have a sufficient DM self-interaction to solve the small-scale structure problem. We find that the PandaX limits can tightly constrain the parameter space, depending on the coupling λ between the singlet and doublet Higgs fields. For the singlet extension of MSSM with Z_3 symmetry, the so-called NMSSM, we also demonstrate the PandaX constraints on its parameter space, which gives a light DM with the correct relic density but without sufficient self-interaction to solve the small-scale structure problem. We find that in NMSSM, the GeV dark matter with a sub-GeV mediator is tightly constrained.     

直接探测暗物质和中国暗物质实验

The nature of dark matter in our universe is one of the most challenging problems in science today. A most probable class of dark matter is the weakly interacting massive particles (WIMPs), which exhibit a wide range of features. Current experiments searching for dark matter aim for direct detection via the elastic scattering off ordinary matter in terrestrial detectors. This paper will present the main methods, status and roadmap for the direct detection of dark matter. The world's deepest laboratory, China Jinping underground laboratory and its extension, will also be described. Finally, we will give a detailed introduction to the research history, detection technologies, current results, and future prospects of China dark matter experiment (CDEX).     

Searching for sub-MeV boosted dark matter from xenon electron direct detection

Direct detection experiments tend to lose sensitivity in searches for sub-MeV light dark matter candidates due to the threshold of recoil energy.However,such light dark matter particles could be accelerated by energetic cosmic rays,such that they could be detected with existing detectors.We derive constraints on the scattering of a boosted light dark matter particle and electron from the XENON100/1T experiment.We illustrate that the energy dependence of the cross section plays a crucial role in improving both the detection sensitivity and also the complementarity of direct detection and other experiments.     

A large scale double beta and dark matter experiment: GENIUS

The recent results from the HEIDELBERG-MOSCOW experiment have demonstrated the large potential of double beta decay to search for new physics beyond the Standard Model. To increase by a major step the present sensitivity for double beta decay and dark matter search much bigger source strengths and much lower backgrounds are needed than used in experiments under operation at present or under construction. We present here a study of a project proposed recently [1], which would operate one ton of ‘naked’ enriched GErmanium-detectorsinliquid NItrogenas shielding in an Underground Setup (GENIUS). It improves the sensitivity to neutrino masses to 0.01 eV. A ten ton version would probe neutrino masses even down to 10^?3 eV. The first version would allow to test the atmospheric neutrino problem, the second at least part of the solar neutrino problem. Both versions would allow in addition significant contributions to testing several classes of GUT models. These are especially tests of R-parity breaking supersymmetry models, leptoquark masses and mechanism and right-handed W-boson masses comparable to LHC. The second issue of the experiment is the search for dark matter in the universe. The entire MSSM parameter space for prediction of neutralinos as dark matter particles could be covered already in a first step of the full experiment with the same purity requirements, but using only 100 kg of ⁷⁶Ge or even of natural Ge making the experiment competitive to LHC in the search for supersymmetry. The layout ofthe proposed experiment is discussed and the shielding and purity requirements are studied using GEANT Monte Carlo simulations. As a demonstration of the feasibility of the experiment first results of operating a ‘naked’ Ge detector in liquid nitrogen are presented.     

First dark matter search results from the PandaX-I experiment

We report on the first dark-matter (DM) search results from PandaX-I, a low threshold dual-phase xenon experiment operating at the China JinPing Underground Laboratory. In the 37-kg liquid xenon target with 17.4 live-days of exposure, no DM particle candidate event was found. This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results. The minimum upper limit, 3.7 × 10^?44 cm², for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of 49GeV/c² at 90% confidence level.     

First dark matter results from the XENON100 experiment

The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso in Italy, is designed to search for dark matter weakly interacting massive particles (WIMPs) scattering off 62 kg of liquid xenon in an ultralow background dual-phase time projection chamber. In this Letter, we present first dark matter results from the analysis of 11.17 live days of nonblind data, acquired in October and November 2009. In the selected fiducial target of 40 kg, and within the predefined signal region, we observe no events and hence exclude spin-independent WIMP-nucleon elastic scattering cross sections above 3.4 × 10??? cm2 for 55 GeV/c2 WIMPs at 90% confidence level. Below 20 GeV/c2, this result constrains the interpretation of the CoGeNT and DAMA signals as being due to spin-independent, elastic, light mass WIMP interactions.     

Inelastic dark matter at the LHC

The dark matter sector may be more complicated than anticipated. An inelastically scattering dark matter with a mass splitting above one MeV will make direct detection experiments hopeless, and render LHC the primary chance for discovery. We perform a model-independent study of inelastic dark matter at the LHC, concentrating on the parameter space with the mass splitting between the excited and ground states of dark matter above a few hundred MeV. The generic signatures of inelastic dark matter at the LHC are displaced pions together with a monojet plus missing energy, and can be tested at the 7 TeV LHC.     

Liquid xenon as a dark matter detector. Prospects for nuclear recoil discrimination by photon timing

Two mechanisms lead to liquid xenon scintillatlon, and are excited differently by incident electrons and by heavy charged nuclei. This could be used to discriminate nuclear recoil events from radioactive background in a search for hypothetical Galactic dark matter particles. To achieve low energy threshold a likelihood analysis is proposed using the time intervals between detected photons. Results are presented of Monte Carlo simulations, showing the background rejection achievable as a function of the number of detected photons. Some comments are included on background discrimination by simultaneous measurement of scintillation and ionization signals.     

First results from the XENON10 dark matter experiment at the Gran Sasso National Laboratory

The XENON10 experiment at the Gran Sasso National Laboratory uses a 15 kg xenon dual phase time projection chamber to search for dark matter weakly interacting massive particles (WIMPs). The detector measures simultaneously the scintillation and the ionization produced by radiation in pure liquid xenon to discriminate signal from background down to 4.5 keV nuclear-recoil energy. A blind analysis of 58.6 live days of data, acquired between October 6, 2006, and February 14, 2007, and using a fiducial mass of 5.4 kg, excludes previously unexplored parameter space, setting a new 90% C.L. upper limit for the WIMP-nucleon spin-independent cross section of 8.8x10(-44) cm2 for a WIMP mass of 100 GeV/c2, and 4.5x10(-44) cm2 for a WIMP mass of 30 GeV/c2. This result further constrains predictions of supersymmetric models.     

Dark matter searches by the Boulby Collaboration and liquid xenon prototype development

The current status of direct dark matter searches by the Boulby Dark Matter Collaboration is presented with the latest result from the ZePLiN I liquid xenon detector. An upper limit in the interaction cross section per nucleon of ～1×10^?6 pb for a WIMP mass of 100 GeV is found. Details of ZePLiN’s II and III—two future liquid xenon dark matter are presented. Extensive two-phase liquid-gas xenon prototype work has been undertaken and results of characterization studies are presented. The detector response to internal alpha and external gamma and neutron sources is shown. The potential discrimination power of the two-phase technique is displayed. Finally, prospects for the future dark matter search program are discussed.