Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session H16: Dark Matter I |
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Sponsoring Units: DPF Chair: Josh Klein, University of Pennsylvania Room: 251D |
Sunday, April 17, 2016 8:30AM - 8:42AM |
H16.00001: DarkSide-50 WIMP search results with low radioactivity argon Xin Xiang Located at the Laboratori Nazionali del Gran Sasso, DarkSide-50 is the first physics detector of the DarkSide dark matter search program. The experiment features a dual-phase Time Projection Chamber as the WIMP detector, surrounded by an organic liquid-scintillator neutron veto and a water-Cherenkov muon detector. We report the results from the first use of low radioactivity argon extracted from underground sources in a dark matter search. We have determined that underground argon is depleted in $^{39}$Ar by a factor $(1.4\pm 0.2) \times10^3$ relative to atmospheric argon whose $^{39}$Ar activity is 1 bq/kg. The underground argon is also found to contain $(2.05 \pm 0.13)$ mBq/kg of $^{85}$Kr. We find no evidence for dark matter in the form of WIMPs in 70.9 live-days of data with a fiducial mass of $(36.9\pm 0.6)$ kg. When combined with our preceding search with an atmospheric argon target, we set a $90 \%$ C.L. upper limit on the WIMP-nucleon spin-independent cross section of $2.0\times10^{-44}$ cm$^2$ $(8.6\times10^{-44}$ {cm}$^2$, $8.0\times10^{-43}$ cm$^2$) for a WIMP mass of 100 GeV/c$^2$ (1 TeV/c$^2$, 10 TeV/c$^2$). DS-50 will continue dark matter search with the underground argon target for a total of 3 years. See also the DS-50 presentations by E. Edkins and G. Koh. [Preview Abstract] |
Sunday, April 17, 2016 8:42AM - 8:54AM |
H16.00002: Nuclear Recoil Calibration of DarkSide-50 Erin Edkins DarkSide-50 dark matter experiment is a liquid argon time projection chamber (TPC) surrounded by a liquid scintillator active neutron veto, designed for the direct detection of Weakly Interacting Massive Particles (WIMPs). The success of such an experiment is dependent upon a detailed understanding of both the expected signal and backgrounds, achieved using radioactive calibration sources of known energies. Nuclear recoils provide a measurement of both the expected signal and the most dangerous background, as nuclear recoils from neutrons cannot be distinguished from a dark matter signal on an event-by-event basis in the TPC. In this talk, I will present the DS-50 calibration system, and analysis of the results of the calibration of DarkSide-50 to nuclear recoils using radioactive neutron sources. See also the DS-50 presentations by X. Xiang and G. Koh. [Preview Abstract] |
Sunday, April 17, 2016 8:54AM - 9:06AM |
H16.00003: Pulse shape discrimination in DarkSide-50 Guangyong Koh Dark matter detection with liquid argon relies heavily on pulse shape discrimination to distinguish between the dominant electron recoil (ER) signal from electromagnetic background, and the nuclear recoil (NR) signal expected from a WIMP dark matter candidate. The DarkSide-50 (DS-50) deployment with atmospheric argon (Nov 2013--Jun 2014) provides a high-statistics sample of ER events from $^{39}$Ar beta decay for predicting ER contamination in any NR region in the ongoing campaign (since Apr 2015) with underground argon (which is naturally depleted in $^{39}$Ar). With the underground argon, the most common background changes from single-sited $^{39}$Ar beta decays to often-multi-sited gamma interactions. I will discuss the impact of this on pulse shape discrimination, and in particular on the use of our high-statistics $^{39}$Ar sample in determining the effectiveness of pulse shape discrimination on multi-sited events. See also the DS-50 presentations by X. Xiang and E. Edkins. [Preview Abstract] |
Sunday, April 17, 2016 9:06AM - 9:18AM |
H16.00004: Darkside-20k: A 20 ton Liquid Argon Dark Matter Experiment Henning Back The Darkside-20k detector is the next step in the Darkside dark matter search program at the Laboratori Nazionali del Gran Sasso in Italy. The Darkside detectors have grown in fiducial mass starting with 10kg in Darkside10, to 50 kg in Darkside50, and finally a proposed 20,000 kg fiducial mass, Darkside20k. The Darkside detectors are dual-phase argon TPCs that combine the very powerful scintillation pulse-shape analysis and ionization information to discriminate against background events. Two unique aspects to the Darkside program is the use of an external neutron veto based on borated liquid scintillator, and the use of low radioactivity argon from underground sources as the target. Argon from the atmosphere has an $^{39}$Ar activity of 1Bq/kg, which would be the limiting background, but the underground argon is essentially free of $^{39}$Ar. Additionally, the detector is placed in a water Cherenkov muon veto. Combining all these techniques allows Darkside-20k to achieve a background-free 100 t-yr exposure accumulated in a 5 yr run. Darkside-20k is expected to start operations in 2020 with data taking starting in 2021, and will be sensitive to WIMP-nucleon interaction cross sections of 1×10$^{-47}$ cm$^{2}$ (1x10$^{-46}$ cm$^{2}$) for WIMPs of 1 TeV/c$^{2}$ (10 TeV/c$^{2}$) mass [Preview Abstract] |
Sunday, April 17, 2016 9:18AM - 9:30AM |
H16.00005: Measuring Sub-keV Ionization Yields in Liquid Argon for Dark Matter and Coherent Neutrino Scattering Searches Brian Lenardo, Adam Bernstein, Kareem Kazkaz, Sergey Pereverzev, Finn Rebassoo, Samuele Sangiorgio, Mani Tripathi, Jingke Xu Liquid argon is widely used as a detector medium in particle physics, and is a promising technique for the future in the detection of neutrinos and possibly more exotic particles. Low energy recoils in argon are of special interest: coherent elastic neutrino-nucleus scattering (CENNS) and elastic scattering of dark matter in the form of low mass WIMPs are both expected to produce nuclear recoils at sub-keV energies. This regime that is largely unexplored in today's argon detectors. To properly model and analyze experimental data, an understanding of liquid argon response to nuclear recoils (signal) and electronic recoils (background) is needed at these energies. We present here a new measurement of the electronic recoil ionization yield of liquid argon at 0.27 keV using an Ar-37 calibration source dissolved in the liquid. The measurement spans a range of applied electric fields, and is the lowest energy multi-field calibration in liquid argon to date. We will describe the experiment, explain the analysis, and compare our results to existing models of ionization in liquid argon. These data provide information on the backgrounds in searches for low energy nuclear recoils and inform detector response models for existing and future experiments. [Preview Abstract] |
Sunday, April 17, 2016 9:30AM - 9:42AM |
H16.00006: Results from the PandaX-II Commissioning Run Xiang Xiao The PandaX dark matter experiment searches WIMP-nucleon scattering signals in the China JinPing Underground Laboratory (CJPL) with a rock burden of 2400 m, employing dual-phase xenon time projection chamber technology. After the completion of PandaX-I, the upgraded experiment, PandaX-II, has been equipped with a 580 kg active xenon target. A commissioning run was carried out in CJPL late in 2015. In this talk, I will present the results from the commissioning run, as well as give an update of the current status of the experiment. [Preview Abstract] |
Sunday, April 17, 2016 9:42AM - 9:54AM |
H16.00007: ABSTRACT WITHDRAWN |
Sunday, April 17, 2016 9:54AM - 10:06AM |
H16.00008: Search for dark matter in monojet events in proton-proton collisions at $\sqrt{s}$=13 TeV Sonaina Undleeb We will present a search for dark matter in proton-proton collisions at center-of-mass energy of 13 TeV. A search has been performed using events containing a single energetic jet and large missing transverse momentum. The data were collected by the CMS detector at the LHC and correspond to an integrated luminosity of 2.1 fb$^{-1}$. The results of search will be discussed in terms of various dark matter benchmark models. [Preview Abstract] |
Sunday, April 17, 2016 10:06AM - 10:18AM |
H16.00009: Stealth Dark Matter: Model, lattice calculations, and constraints David Schaich A new strongly coupled dark sector can produce a well-motivated and phenomenologically interesting composite dark matter candidate. I will review a model recently proposed by the Lattice Strong Dynamics Collaboration in which the composite dark matter is naturally ``stealthy'': Although its constituents are charged the composite particle itself is electroweak neutral with vanishing magnetic moment and charge radius. This results in an extraordinarily small direct detection cross section dominated by the dimension-7 electromagnetic polarizability interaction. I will present direct detection constraints on the model that rely on our non-perturbative lattice calculations of the polarizability, as well as complementary constraints from collider experiments. Collider bounds require the stealth dark matter mass to be $m > 300$~GeV, while its cross section for spin-independent scattering with xenon is smaller than the coherent neutrino scattering background for $m > 700$~GeV. [Preview Abstract] |
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