The DArk Matter Particle Explorer (DAMPE), one of the four scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Sciences, is a general purpose high energy cosmic-ray and gamma-ray observatory, which was successfully launched on December 17th, 2015 from the Jiuquan Satellite Launch Center. The DAMPE scientific objectives include the study of galactic cosmic rays up to $\sim 10$ TeV and hundreds of TeV for electrons/gammas and nuclei respectively, and the search for dark matter signatures in their spectra. In this paper we illustrate the layout of the DAMPE instrument, and discuss the results of beam tests and calibrations performed on ground. Finally we present the expected performance in space and give an overview of the mission key scientific goals.Comment: 45 pages, including 29 figures and 6 tables. Published in Astropart. Phy

For the first time, we present an extensive study of stars with individual non-LTE (NLTE) abundances for 17 chemical elements from Li to Eu in a sample of stars uniformly distributed over the −2.62 [Fe/H] +0.24 metallicity range that is suitable for the Galactic chemical evolution research. The star sample has been kinematically selected to trace the Galactic thin and thick disks and halo. We find new results and improve earlier ones as follows: (i) the element-to-iron ratios for Mg, Si, Ca, and Ti form a metal-poor (MP) plateau at a similar height of 0.3 dex, and the knee occurs at common

An energy threshold of (220±10) eV was achieved at an efficiency of 50% with a four-channel ultra-low-energy germanium detector each with an active mass of 5 g. This provides a unique probe to WIMP dark matter with mass below 10 GeV. With a data acquisition live time of 0.338 kg-day at the Kuo-Sheng Laboratory, constraints on WIMPs in the galactic halo were derived. The limits improve over previous results on both spin-independent WIMP-nucleon and spin-dependent WIMPneutron cross-sections for WIMP mass between 3−6 GeV. Sensitivities for full-scale experiments are projected. This detector technique makes the unexplored sub-keV energy window accessible for new neutrino and dark matter experiments.PACS numbers: 95.35.+d, 98.70.Vc There is compelling evidence from cosmological and astrophysical observations that about one quarter of the energy density of the universe can be attributed to Cold Dark Matter(CDM), whose nature and properties are still unknown [1]. Weakly Interacting Massive Particles (WIMP, denoted by χ) are the leading candidates for CDM. There are intense experimental efforts[2] to look for WIMPs through direct detection of nuclear recoils in χN→χN elastic scattering or in the studies of the possible products through χχ annihilations. The Kuo-Sheng(KS) Laboratory[12] is located at 28 m from a 2.9 GW reactor core with an overburden of about 30 meter-water-equivalence. Limits on neutrino magnetic moments(µ ν )[13] with a 1.06-kg germanium detector(HPGe) at a threshold of 5 keV were reported [14]. These data also allowed the studies of reactor electron neutrinos [15] and reactor axions [16]. A background level of ∼ 1 event kg −1 keV −1 day −1 (cpkkd) at 20 keV, comparable with those of underground CDM experiments, was achieved. The current goal is to develop detectors with kg-scale target mass, 100 eV-range threshold and lowbackground specifications for the studies of WIMPs, µ ν and neutrino-nucleus coherent scatterings [17].Ultra-low-energy germanium detectors(ULEGe) is a matured technique for sub-keV soft X-rays measurements. They typically have modular mass of 5−10 g while detector arrays of up to 30 elements have been constructed. Compared with Al 2 O 3 , Ge provides enhancement in χN spin-independent couplings(σ SI χN ) due to the A 2 dependence [1,18], where A is the mass number of the target isotopes. The isotope 73 Ge (natural isotopic abundance of 7.73%) comprises an unpaired neutron such that it can provide additional probe to the spin-dependent couplings of WIMPs with the neutrons(σ SD χn ). The nuclear recoils from χN interactions in ULEGe only give rise to ∼20% of the observable ionizations compared with electron recoils at the same energy. The suppression ratio is called the quenching factor(QF) [19]. For clarity, all ULEGe measurements discussed hereafter in this article are electron-equivalent-energy, unless otherwise stated.The ULEGe array consists of 4-element each having an active mass of 5 g [20]. Standard ultra-low-background specifications were adopted in its construction and ch...

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

We present results on light weakly interacting massive particle (WIMP) searches with annual modulation (AM) analysis on data from a 1-kg mass p-type point-contact germanium detector of the CDEX-1B experiment at the China Jinping Underground Laboratory. Datasets with a total live time of 3.2 yr within a 4.2 yr span are analyzed with analysis threshold of 250 eVee. Limits on WIMP-nucleus (χ-N ) spin-independent cross sections as function of WIMP mass (mχ) at 90% confidence level (C.L.) are derived using the dark matter halo model. Within the context of the standard halo model, the 90% C.L. allowed regions implied by the DAMA/LIBRA and CoGeNT AM-based analysis are excluded at >99.99% and 98% C.L., respectively. These results correspond to the best sensitivity at mχ<6 GeV/c 2 among WIMP AM measurements to date. PACS numbers: 95.35.+d, 98.70.Vc Compelling cosmological evidence indicates that about one-quarter of the energy density of the Universe manifests as dark matter [1], a favored candidate of which is the weakly interacting massive particle (WIMP, denoted as χ). In direct laboratory searches of WIMPs conducted with WIMP-nucleus (χ-N ) elastic scattering, positive evidence of WIMPs can only be established by assuming detailed knowledge of the background. The annual modulation (AM) analysis, on the other hand, only requires the background at the relevant energy range is stable with time. It can provide smoking-gun signatures for WIMPs independent of background modeling. Within the astrophysical dark matter halo model [2], the expected χ-N rates have distinctive AM features with maximum intensity in June and a period of 1 yr due to the Earth's motion relative to the galaxy dark matter distribution.Positive results were concluded at significance of 12.9 σ and 2.2 σ from AM-based analysis of DAMA/LIBRA [3][4][5] and CoGeNT [6-8] experiments, respectively. However, these interpretations are challenged by integrated rate experiments with liquid xenon [9-11], cryogenic bolometer [12][13][14] and ionization germanium [15][16][17][18][19] detectors, when the data were analyzed in certain scenarios where the dark matter particle properties and distributions in the Milky Way's halo are precisely defined. Comparison of AM data with differnet targets is also model dependent. The AM-allowed regions of DAMA/LIBRA and CoGeNT have been probed and excluded by AM analysis from the XMASS-1 experiment [20,21], which is limited by the diminishing sensitivities of the liquid xenon techniques at light WIMP masses (m χ ) below 6 GeV/c 2 . The and COSINE-100 [23] experiments aim to resolve this tension by a model-independent test of DAMA/LIBRA's obser-arXiv:1904.12889v2 [hep-ex]

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