1. Second Workshop on large TPC for low energy rare event detection, Paris, December 21 st, 2004

2. MUNU is an elastic scattering experiment which probes in particular the neutrino magnetic moment e e e - -  e  e e e T E T m    1 2 2 2 The contribution of the magnetic moment term increases with decreasing neutrino and electron recoil energy In order to study the magnetic moment of neutrino we need a low neutrino energy source and a low electron detection threshold

3.  lab =10 13. cm -2. s -1 distance =18m 20 m.w.e e source - nuclear reactor (2800 MWth) Bugey, France E =(0  8 MeV) Neutrinos are mostly produced in the  decay of fission fragments of the four major fuel isotopes : 235 U(54%), 239 Pu(33%), 241 Pu(6%), 238 U(7%)

4. However the low energy part of the reactor neutrino spectrum 0  1.8 MeV has never been measured and it is known only from calculations T (keV) Neutrino/keV/fis REACTOR NEUTRINO SPECTRUM used by MUNU Above 1.8 MeV the neutrino spectrum can be reconstructed from the measured β spectra of the fission fragments

5. The central tracking detector is a 1m 3 Time Projection Chamber L =162 cm  90 cm acrylic vessel 11.4 (3.8) kg CF 4 gas at 3 (1)bar pressure Why do we use CF4? absence of free protons (no ) high density ( 3.7 g /l at 1 bar ) low Z (less multiple scattering )

6. Anti-Compton Detector and Passive Shielding served as active and passive veto against Compton electrons, muons and cosmics 2 x 24 PMT Anti-Compton  reac e-e- steel vessel L =380 cm  = 200 cm 10m 3 liquid scintillator NE235 Anti Compton veto muons and Compton electrons with 99.9 % efficiency Passive shielding 15 cm Pb and 8 cm polyethylene boron to absorb external gammas + neutrons TPC

7. Neutrino candidates are single electrons with clearly distinguishable start and end of tracks (blobs) inside of a fiducial volume (R<42 cm) Neutrino Candidates

8. Visual scanning analysis determines from the Kinematics: incident neutrino energy   Te,  rea ) determines from the fitting :  rea

11. muon proton Examples of background events at 3-bar pressure   -  EM shower

12. 500 keV 700 keV Examples of electron events at 3-bar pressure 900 keV1100 keV 1200 keV

13. Forward –Normalized Background Analysis Downward (B) X Y 0° 90° 180° -90°   dre a Backward (B) REACTOR Forward (S+B) E > 0, cos   > 0 E > 0, cos (  -   ) < 0 E   cos  reac > 0 E   cos(  -  reac ) > 0 Normalized Background =(Upward +Downward +Backward)/ 3 Signal = Forward – Normalized Background Upward (B)

14. Results 3-bar Forward –Normalized Background Analysis Energy distributions of the background electrons 66.6 days reactor-on T > 700 keV T Upward Downward Backward Background electrons are 1154 ± 34 in total

15. Energy distributions of the forward (S+B) and normalized background electrons (B), 66.6 d reactor-on T > 700 keV Forward Normalized Background T Forward electrons are 455 ± 21 Normalized Background electrons are 385 ± 11

16. Energy distributions of the forward (B) and normalized background electrons (B), 16.7 days reactor-off Forward electrons are 133 ± 11 Normalized Background electrons are 147 ± 7 T > 700 keV Forward Normalized Background T -0.8 ± 0.8 cpd

17. measured : 1.05 ± 0.36 cpd expected    0  0 ± 0  cpd T e >700 keV T (keV) Counts  = 0  = 9.0 x 10 -11  B 70 events for 66.6 days 1.05 ± 0.36 cpd  < 9.0 x 10 -    (90%CL) Energy distribution of the forward – NB electrons 66.6 d reactor-on T > 700 keV

19. Calibrations with 54 Mn and 137 Cs 54 Mn T(keV) data MC 137 Cs T(keV) data MC

20. R% T (keV) R % (3-bar)R%(1bar) 2002410 400157.6 60011.46.4 100085 TPC energy resolutions at 1-bar and 3-bar 3-bar 1-bar Energy resolution at 1-bar is about 2 times better then that at 3-bar

21. Examples of background events at 1-bar pressure muon  proton EM shower

22. 100 keV Examples of electron events at 1-bar pressure 140 keV 190 keV 500 keV 700 keV

23. Results 1-bar Forward –Normalized Background Analysis Energy distributions of the background electrons 5.3 d reactor-on T > 200 keV Upward Downward Backward T Background electrons are 326 ± 18 in total

24. Energy distributions of the forward (S+B) and normalized background electrons (B) 5.3 d reactor-on Forward electrons are 124 ± 11 Normalized Background electrons are 109 ± 6 T Forward Normalized Background T > 200 keV

25. Energy distribution of the forward – NB electrons 5.3 days reactor-on 15 events for 5.3 days above 200 keV 2.89 ± 2.39 cpd measured : 2.89 ± 2.39 cpd expected    0  : 0.49 ± 0  12  cpd T e > 200 keV This is the first measurement of the recoil electron spectrum from e - scattering down to 200 keV T > 200 keV T

26. Present experimental situation Direct measurements of  at reactors UC Irvine group :  reac   x 10 -10  B  CL) Rovno experiment :  reac  x 10 -10    CL) TEXONO experiment :  reac  x 10 -10    CL) Solar neutrino experiments Super Kamiokande experiment :  sol < 1.5 x 10 -10  B (90%CL )  < 1.0 x 10 -10  B (90%CL),PLB 564 (2003) New:  < 9.0 x 10 -11   (90%CL) MUNU experiment

27. The  of the reconstructed peak at 662 keV is 100 keV (15 %) The technology of MUNU could be used for detecting solar neutrinos E  (keV) reconstructed 662 keV photopeak from the Compton scattering of  e -, E  (T e,  e ) E  (keV) Reconstructed 662 keV γ-ray from 137 Cs TPC + AntiCompton Neutrino energy E can be reconstructed from T e,  e Test with 662 keV  -ray from 137 Cs

28. EXO-gas, double beta decay in 136 Xe

29. e -, 232 Th  (E)/E=3.4 % at 1.59 MeV  (E)/E= 2.7 % at 2.48 MeV Gotthard 5 bar xenon  (from cathode), 210 Po ( 238 U chain) quenching (  /e - )=1/6.5  (E)/E=1.1 % at 2.48 MeV ! Energy resolution F=0.19, W=22 eV  (E)/E=0.13 % at 2.48 MeV !