We report results of a search for light Dark Matter WIMPs with CDEX-1 experiment at the China Jinping Underground Laboratory, based on 53.9 kg-days of data from a p-type point-contact germanium detector enclosed by a NaI(Tl) crystal scintillator as anti-Compton detector. The event rate and spectrum above the analysis threshold of 475 eVee are consistent with the understood background model. Part of the allowed regions for WIMP-nucleus coherent elastic scattering at WIMP mass of 6-20 GeV are probed and excluded. Independent of interaction channels, this result contradicts the interpretation that the anomalous excesses of the CoGeNT experiment are induced by Dark Matter, since identical detector techniques are used in both experiments. PACS numbers: 95.35.+d, 98.70.Vc

The CDEX-1 experiment conducted a search of low-mass (< 10 GeV/c 2 ) Weakly Interacting Massive Particles (WIMPs) dark matter at the China Jinping Underground Laboratory using a ptype point-contact germanium detector with a fiducial mass of 915 g at a physics analysis threshold of 475 eVee. We report the hardware set-up, detector characterization, data acquisition and analysis procedures of this experiment. No excess of unidentified events are observed after subtraction of known background. Using 335.6 kg-days of data, exclusion constraints on the WIMP-nucleon spinindependent and spin-dependent couplings are derived.PACS numbers: 95.35.+d, 98.70.Vc

Weakly Interacting Massive Particles (WIMPs) are the candidates of dark matter in our universe. Up to now any direct interaction of WIMP with nuclei has not been observed yet. The exclusion limits of the spin-independent cross section of WIMP-nucleon which have been experimentally obtained is about 10 −7 pb at high mass region and only 10 −5 pb at low mass region. China Jin-Ping underground laboratory CJPL is the deepest underground lab in the world and provides a very promising environment for direct observation of dark matter. The China Dark Matter Experiment (CDEX) experiment is going to directly detect the WIMP flux with high sensitivity in the low mass region. Both CJPL and CDEX have achieved a remarkable progress in recent two years. The CDEX employs a point-contact germanium semi-conductor detector PCGe whose detection threshold is less than 300 eV. We report the measurement results of Muon flux, monitoring of radioactivity and Radon concentration carried out in CJPL, as well describe the structure and performance of the 1 kg PCGe detector CDEX-1 and 10kg detector array CDEX-10 including the detectors, electronics, shielding and cooling systems. Finally we discuss the physics goals of the CDEX-1, CDEX-10 and the future CDEX-1T detectors.

The China Dark Matter Experiment Collaboration reports the first experimental limit on weakly interacting massive particles (WIMPs) dark matter from 14.6 kg-days of data taken with a 994 g p-type point-contact germanium detector at the China Jinping underground laboratory where the rock overburden is more than 2400 m. The energy threshold achieved was 400 eVee. According to the 14.6 kg-day live data, we placed the limit of N ¼ 1:75 Â 10 À40 cm 2 at a 90% confidence level on the spin-independent cross section at a WIMP mass of 7 GeV before differentiating bulk signals from the surface backgrounds.There are many pieces of evidence from astroparticle physics and cosmology which indicate that about one quarter of the mass of our Universe is composed of dark matter [1]. The nature of dark matter is unknown, except that it is coupled with matter via gravity. One of the possible candidates for dark matter is weakly interacting massive particles (WIMPs, denoted by ), as motivated by many new theories beyond the standard model [2]. Direct detection of WIMP dark matter has been attempted with different detector technologies in the particle physics domain [3].In recent years, several experiments have expanded their coverage down to low-mass WIMPs with m < 10 GeV [4][5][6][7][8][9]. A point-contact germanium detector can reach an energy threshold of hundreds of eV while keeping almost the same energy resolution as the traditional coaxial germanium detector [10]. Thus, it can be a good choice for a low-mass dark matter search. Based on our previous work [11], the China Dark Matter Experiment (CDEX) Collaboration has formally started a program aimed at the direct detection of low-mass WIMPs using a ton-scale germanium array detector system [12]. As the first step, in 2011 the CDEX phase I experiment (CDEX-1) started to test and run its first prototype p-type point-contact germanium (PPCGe) detector with a crystal mass of 994 g. The experiment took place at the China Jinping underground laboratory (CJPL), which was established at the end of 2010. With 2400 m of rock overburden, CJPL is the deepest operational underground laboratory for particle physics in the world. The cosmic ray flux in CJPL is down to 61:7 y À1 m À2 [13], and this makes it a very good site for ultra-low-background experiments such as dark matter search, double beta decay, and so on.The point-contact germanium detectors have also been used by several experiments [4,9] to directly search for low-mass WIMPs. Due to the relative shallow cosmic ray shielding, CoGeNT and TEXONO used muon veto detectors to decrease the direct and indirect background contributions from cosmic ray muons. The muon veto method can decrease the background contribution of the * Corresponding author. yueq@mail.tsinghua.edu.cn † Participating as a member of the TEXONO Collaboration.PHYSICAL REVIEW D 88, 052004 (2013) 1550-7998= 2013=88(5)=052004(5) 052004-1

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