New Experiment With Sphere:

Transcription

1 1 New Experiment With Sphere: Dark Matter search with spherical gas detector. 11 th International Conference on the Identification of Dark Matter July 18 th 2016

2 Overview of a spherical gas detector: - Spherical cavity filled with gas. - Sphere is grounded and HV is applied on a spherical sensor. -Particle ionizes gas. -Primary electrons drift toward the sensor. -Close to the sensor, secondary electron are produced following Polya distribution. -Signal is induced by secondary ion's motion. -This signal is processed by a pre-amplifier and digitized. Advantages: -Possibility to use large range of target mass. -Sub-keV energy threshold. -Identification of point like energy deposition 2

3 Particles identification: Typical measured pulse: Track events Amplitude Rise time Point like events 3

4 Sedine detector: 60 cm diameter detector. Placed in the LSM Located in Frejus tunnel at France/Italia border under 4800 mwe. The sphere is enclosed in a cubic shielding made of: cm of copper - 10 cm of lead - ~30 cm of polyethylene 4

5 Sedine detector: Energy calibration Volume calibration done with 37 Ar source 5

6 Anticipated background events, simulation of pulses: Compton electron Pb 210 decays product Analysis threshold at 150 kev. Pulse simulations include homogeneous radial field, diffusion (Magboltz), current induction (Ramo), amplification (Polya distribution single electron), amplifier RC (50 µs). 6

7 Sedine detector: Comparison of simulation with AmBe neutron data. Good agreement 7

8 WIMP search run: -Data taking continuously during 42 days with: -Use of 3100 mbars gas mixture, 99.3% Neon % CH 4 => 310 g of sensitive mass -High voltage on the sensor set to 2520V, no sparks and gain around Seal mode, no recirculation. -Loss of gain 4% along 42 days monitored with 210 Po line. -Variation of ± 4% on daily scale. -Amplifier Camberra 2006 with 50 µs RC decay constant. -DAQ sampling frequency, 2 Mhz. 8

9 WIMP search run: µs Confirmation of strong component of surface events in data ROI 1) Conservative analysis Apply soft threshold cut at 150 ev Side bands used to normalize volume/compton and surface populations and predict expected contribution in ROI Select ROI where to set maximum component of WIMP 2) Given expected shapes of contributions of backgrounds in ROI, set limit on WIMP from BDT analysis (optimization of cuts wrt WIMP mass) kev 9

10 WIMP search run: 10

11 Sedine detector: Main background contribution: Cobalt 60 on copper A contamination of 1 mbq/kg brings a background event rate of 0.3 to 0.5 evts/kev/kg/days at low energy. => Impose a limit of time exposure on ground for pure copper. 2 months at see level give 30 µbq/kg Geant4 simulation 11

12 Sedine detector: Main background contribution: Lead 210 on inner surface Decays of Pb210 and Bi210 produce about 0.1 evts/kg/day for a contamination of 1 nbq/cm 2. This could be solve using chemical cleaning. First cleaning Second cleaning Amplitude spectrum before and after cleaning. Effect of cleaning: -High energy events : 180 mhz -> ~2 mhz -Low energy events : 400 mhz -> ~20 mhz 12

13 From NEWS-LSM to NEWS-SNO: 140 cm diameter copper sphere LSM SNOLAB Contamination in copper: - 1 µbq/kg for Uranium and Thorium µbq/kg for Cobalt 60 13

14 NEWS-SNO background budget estimation: 14

15 NEWS Collaboration Queen s University Kingston Gilles Gerbier, P di Stefano, R Martin, T Noble, B Cai, A Brossard, A Kamaha, P Vasquez ds, Q Arnaud, K Dering, J Mc Donald, M Clark, and summer students Copper vessel and gas set-up specifications, calibration, project management Gas characterization, laser calibration, on smaller scale prototype Simulations/Data analysis IRFU (Institut de Recherches sur les Lois fondamentales de l Univers)/CEA Saclay -I Giomataris, M Gros, C Nones, I Katsioulas, T Papaevangelou, A Gigagnon, JP Bard, JP Mols, XF Navick, Sensor/rod (low activity, optimization with 2 electrodes) Electronics (low noise preamps, digitization, stream mode) DAQ/soft LSM (Laboratoire Souterrain de Modane), IN2P3, U of Chambéry - F Piquemal, M Zampaolo, A DastgheibiFard Low activity archeological lead Coordination for lead/pe shielding and copper sphere Thessaloniki University I Savvidis, A Leisos, S Tzamarias, C Elefteriadis, L Anastasios Simulations, neutron calibration Studies on sensor LPSC (Laboratoire de Physique Subatomique et Cosmologie) Grenoble - D Santos, JF Muraz, O Guillaudin Quenching factor measurements at low energy with ion beams Technical University Munich A Ulrich Gas properties, ionization and scintillation process in gaz Pacific National Northwest Lab E Hoppe Low activity measurements, Copper electroforming Associated lab : TRIUMF - F Retiere Future R&D on light detection, sensor June 2016

16 THANK YOU 16

17 BACKUP SLIDES

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