1. Ilias Savvidis Aristotle University of Thessaloniki Development of a Spherical Proportional Counter for low energy neutrino detection via Coherent Scattering Ilias Savvidis Aristotle University of Thessaloniki Collaboration I Savvidis 1, I Giomataris 2, E Bougamont 2, I Irastorza 4, S Aune 2, M Chapelier 2, Ph Charvin 2, P Colas 2, J Derre 2, E Ferrer 2, G Gerbier 2, M Gros 2, P Mangier 2, XF Navick 2, P Salin 5, J D Vergados 6 and M Zampalo 3 1 : Aristotle University of Thessaloniki, Greece 2 : IRFU, Centre d'études de Saclay, 91191 Gif sur Yvette CEDEX, France 3. LSM, Laboratoire Souterrain de Modane, France 4: University of Saragoza, Spain 5 : LSBB, France 6: University of Ioannina, Greece

2. Outline The detector characteristics The neutrino sources and spectra Low energy calibration The sub keV x-ray detection The low energy Ar recoil detection Conclutions

3. The detector Volume = 1 m3, Cu 6 mm Gas leak < 5x10-9mbar/s. Gas mixture Argon + 2%CH4.Pressure up to 5 bar Internal electrode at high voltage. Read-out of the internal electrode 15 mm

4. Radial TPC with spherical proportional counter read-out Saclay-Thessaloniki-Saragoza 5.9 keV 55 Fe signal Very low electronic noise: low threshold Good fit to theoretical curve including avalanche induction and electronics E=A/R 2 20  s Simple and cheap single read-out Robustness Good energy resolution Low energy threshold Efficient fiducial cut 15 mm A Novel large-volume Spherical Detector with Proportional Amplification read-out, I. Giomataris et al., JINST 3:P09007,2008 C= R in = 7.5 mm <.1pF

5. The electric field problem Good energy resolution →perfect electric field (spherical capacitor electric field)

6. Electrostatic field (simulation results) LEFT: 15 mm sphere, 1mm Cu cable covered with 3mm PE RIGHT: 15 mm sphere, 1mm Cu cable covered with 3mm PE + graphite (ground). Distance sphere to graphite 4mm No field correction With field correction

7. The three sensors which has been used

8. Alpha particle spectroscopy and thermal neutrons Rn-222: 5.49 MeV alpha Po-218: 6.00 MeV alpha Po-214: 7.68 MeV alpha Resolution: σ=1.5% Gas: 98% Ar + 2% CH4,P=200 mbar Underground thermal neutron peak in LSM, after rise time cut. 3gr He-3 in the sphere R=417 evts/d, Φth.neutron = 1.9 10-6 n/cm2/s n + He-3 → p + H-3 + 765 keV 765 keV

9. neutrinos antineutrinos super nova explosion nuclear reactor core Spherical Proportional Counter Can we detect the neutrinos?

10. Neutrino detection via coherent elastic scattering

11. Neutrino Sources Neutrino energy-spectra emitted in Core-collapse Supernova Typical Reactor Antineutrino Spectrum Other neutrino sources: Geoneutrinos, Solar neutrinos

12. The maximum recoiling energy versus the neutrino energy (both in units of the recoiling mass). The nuclear recoil energy versus the neutrino energy. From top to bottom nuclear targets with A=4, 20, 40, 84, 131 for the elements He, Ne, Ar, Kr and Xe respectively. The energy of the recoil nucleus Xe He Ar

13. Nuclear reactor neutrinos: With present prototype at 10 m from the reactor, after 1 year run (2x10 7 s)  assuming full detector efficiency: -Xe (  ≈ 2.16x10 -40 cm 2 )  x    neutrinos detected, T max =146 eV - Ar (  ≈ 1.7x10 -41 cm 2 )  x    neutrinos detected, T max =480 eV - Ne (  ≈ 7.8x10 -42 cm 2 )  x    neutrinos detected, T max =960 eV Supernova neutrinos: -For a detector of radius 4 m with a gas under 10 Atm and a typical supernova in our galaxy, i.e. 10 kpc away, one finds 1, 30, 150, 600 and 1900 events for He, Ne, Ar, Kr and Xe respectively (Y. Giomataris, J. D. Vergados, Phys.Lett.B634:23-29,2006) Response of the detector to the reactor and supernova neutrinos

14. The detector’s characteristics for neutrino detection Low electronic noise Low energy threshold ( ̴ 100eV) Low energy recoil nucleus detection Separation of the recoil signals from the cosmic rays

15. Low energy calibration the 8 keV Cu –x rays (Ne + 5% CH4, P=500 mbar) 8 keV Cu-X Cosmic rays UV Lamp Electronic noise UV LampCosmic rays 8 keV Cu-X after cosmic rays cut-off

16. Sub-keV x-ray detection Peaks observed from the 241 Am radioactive source through aluminium and polypropylene foil. On the left the Carbon (270 eV) peak is shown, followed by the Aluminium peak (1.45 keV), the escape peak (E.P.) of Iron in Argon (3.3 keV), the escape peak of Copper in Argon (5 keV), the Iron peak (6.4 keV), the Copper peak (8 keV) and the Neptunium peak (13.93 keV).

17. Low energy Ar recoils detection using Am-Be neutron source (Thessaloniki, Nuclear Physics Laboratory) Am-Be source

18. Shielding Pb= 9cm Fe= 5cm PE= 2cm

19. P=250 mbar, 5%CH4+4%N2 Left: No source Bottom: Am-Be Ar recoils

20. P=175 mbar, 5%CH4+4%N2 Left: No source Am-Be + Cs-137 (γ 661keV) Cs-137 (γ 661keV) Ar recoils γ 661keV

21. P=50 mbar, 5%CH4+4%N2 Left: No source Am-Be Ar recoils 8 keV Cu-X

22. Cs-137 (γ 661keV) Am-Be P=50 mbar, 5%CH4+4%N2 8 keV Cu-X

23. Am-Be : No source P=50 mbar, 5%CH4+4%N2

24. Conclusions We have developed a new detector with: large mass good energy resolution low sub-keV energy threshold radial geometry with spherical proportional amplification read-out robustness and low cost.

25. Next step A new detector with low radiation materials is under construction Quenching factor measurement for the low energy particles Development of a new 8mm sensor for higher gain and stable for long time counting. Sub-keV Ar recoil detection from neutron scattering Separation of the Ar recoil signals from the cosmic rays