Zhimin Wang Liu Ruoqing , Tang ChenYang , Charling Tao, Changgen Yang , Changjiang Dai,

1. Spherical Time Projection Chamber (STPC) for future neutrino and dark matter experiments(or Spherical Proportional Counter) Zhimin Wang Liu Ruoqing, Tang ChenYang, Charling Tao, Changgen Yang , Changjiang Dai, Tsinghua & IHEP 2014-10-12, Shanghai

2. A Simple New Gas DetectorDeveloped by IoanisGiomataris, Saclay, France • Natural focusing: • large volumes can be instrumented with a small readout surface and few (or even one) readout lines • 4p coverage: better signal • Still some spatial information achievable: • Signal time dispersion • Other practical advantages: • Symmetry: lower noise and threshold with large volume • Low capacity • No field cage • Simplicity: few materials. They can be optimized for low radioactivity. • Low cost

4. A prototype • D=1.3 m • V=1 m3 • Spherical vessel made of Cu (6 mm thick) • P up to 5 bar possible (up to 1.5 tested up to now) • Vacuum tight: ~10-6 mbar (outgassing: ~10-9 mbar/s)

5. Typical spectra

6. RunwithAr/CH4 + 3g 3He @ 200 mb SPC 130cm Ø @ LSM NB: no start => risetime records place and/or history of energydeposition 210Po 5.3 MeV If localisedenergydeposition, rise time depends of radius (diffusion) n capt on 3He 764 keV Rise time (s) alpha If track, rise time depends on orientation of track (different drift times) 222Rn 218Po 214Po derivative de/dx Amplitude

7. RunwithAr/CH4 + 3g 3He @ 200 mb SPC 130cm Ø @ LSM 210Po 5.3 MeV from 210Pb @ Cu surface R = 15 cm 210Po 5.3 MeV Taux 400 capt/j n capt on 3He 764 keV Rise time (s) n capt on 3He => p + T 3 2 1 Unwanted Radon daughter deposit on surface 222Rn 218Po 214Po Amplitude 2 : fast neutron expected here

8. Basic performance • Mixtures tested: • Ar+10% CO2 • Ar+2% Isobutane • Pressures from 0.25 up to 1.5 bar tested up to now • High gains (>104) achieved with simple spherical electrode • No need to go to very high V (better for minimizing absorption)

9. Applications • Dark Matter • Coherent neutrino scattering • Double beta decay • Axion • SN neutrino monitoring ----------------------------------------------------------------------------------- • Neutron spectroscopy • Neutron counter for industrial application • Low level neutron counting • Radon low level counting • Atmospheric neutron and Muon monitoring • Gamma ray spectroscopy in harsh environment • …

10. Some physics applications arXiv:1401.7902Gerbier et al. DM WIMP Reactor neutrino

11. doi:10.1088/1742-6596/203/1/012030 LSM neutron flux From Savvidisilias

12. An international working group “NEWS” from G. Gerbier

13. Activities at IHEP &Tsinghua Detector performance studies • Plan to measure neutrons in Jinping with 1g He3

14. STPC goals • NEWS network: 4m detector. Where? • Jinping? • SNO? Gerbier in Canada with 10 M$ grant • Training for low radioactivity gaseous detector for large volume TPC • Solar neutrino (HELLAZ like) • Directional Dark Matter (also an old idea!)

15. Hellaz simulation (1997?) 1995-1998 The HELLAZ solar pp neutrino project Tom Ypsilantis, Jacques Séguinot et al… , with a Micromegas

16. Dark matter detection with hydrogen proportional counters G. Gerbier, J. Rich, M. Spiro, C. Tao Nuclear Physics B - Proceedings SupplementsVolume 13, February 1990, Pages 207-208 Comments : for some DM types not Mass but Number of nuclei is important

17. Gaseous detectors are beautiful! • 1975-1979 Cylindrical Drift chamber in PhD thesis back for Fermilab DIS muon CHIO in Smithsonian (Washington DC) • 1979-1982: UA1 Central Detector 1st W event in UA1 CD Personalinterest for > 20 years Technology OK and keeps improving For DM: needs detection from >2 nuclei AND directionality!!! Is our science case compelling enough? CDM vs WDM debate

18. Directional DM Detectors • CYGNUS 2013: 4th Workshop on Directional Detection of Dark Matter Tatsuhiro Naka and KentaroMiuchi- 2013 J. Phys.: Conf. Ser.469 011001 Workshop Series Boulby 2007 , MIT 2009, Aussois2011 • Many projects: DMTPC, NEWAGE, DRIFT, MIMAC • emulsions

19. MIMAC MIMAC bi-chamber prototype 1311.0616 • The MIMAC bi-chamber prototype is composed of two chambers sharing the same cathode being the module of the matrix • active volume (V 5:8 l) • 70%CF4 + 28%CHF3 + 2%C4H10 at a pressure of 50mbar. The primary electron- ion pairs produced by a nuclear recoil in one chamber of the matrix are detected by driving the electrons to the grid of a bulk micromegasand producing the avalanche in a very thin gap (256 mu). • Track reconstruction in MIMAC. The anode is read every 20 ns. The 3D track is reconstructed, from the consecutive number of images

20. Bi-chamber prototype at the LaboratoireSouterrain de Modane The bi-chamber prototype at the LaboratoireSouterrain de Modane in June 2012. The bi-chamber module is identified in red and the bluer volume in blue. The position of peaks of Cd (3.2 keV), Cr (5.4 keV), Fe (6.4 keV), Cu (8.1 keV) and Pb (10.5 and 12.6 keV) tted by a linear calibration in ADC channels as a function of time, highlighting the gain stability during the data taking period. 4. Preliminary analysis of the first months of data taking The first available data set of the bi-chamber prototype was started on July 5th 2012

21. Background in LSM

23. Electron vs nuclei recoil The length [cm] vs. Energy [ADC channel] of electrons and proton recoils produced by neutrons of 144 keV in pure isobutane (C4H10) at 50 mbar. The maximum of the proton energy corresponds to 144 keV. (Right): The NIS (normalized integrated straggling) for recoil events (in black) and for electrons (in blue).

25. 1.5 keV He4 recoils

26. 3D-Track reconstruction 34 keV

27. Some tracks in MIMAC 8 keV hydrogen nucleus in 350 mbar 4He+5%C4H10, a fluorine nucleus leaving 50 keV in ionization in 55 mbar (70% CF4 + 30% CHF3) and a 5.5 MeV alpha particle in 350 mbar 4He+5%C4H10

29. MIMAC 1m3 in preparation

30. WIMP distribution