2. I. Giomataris NOSTOS Neutrino studies with a tritium source Neutrino Oscillations with triton neutrinos The concept of a spherical TPC Measurement of the angle  , Neutrino magnetic moment, Neutrino decay, Weinberg angle measurement at low energy, Supernova sensitivity The first prototype Conclusions

3. I. Giomataris

4. The idea Study neutrino-electron elastic scattering with very-low energy neutrinos from a strong tritium source (E ≈14 keV) Detect low energy electron recoils (T max = 1.27 keV) by a spherical gaseous TPC surrounding the tritium source The oscillation length is shorter than the length of the detector The modulation will be contained and seen in the TPC Reconstruction of the relevant oscillation parameters by a single experiment I. Giomataris, J. Vergados, hep-ex/0303045 J. Bouchez, I Giomataris DAPNIA-01-07

5. I. Giomataris The new strategy (I. Giomataris, J. Vergados, hep-ex/0303045 ) L 32 = 4  /  m 2 32  m 2 32 = 2.510 -3,   keV L 13 = L 12 /50 = 13 mfully contained in the TPC (radius=10m) New challenge :   measurement The sensitivity depends on statistics, backgrounds and systematics >10 4 neutrino-electron interactions must be detected and localized Tritium source activity can be measured on-line at <1% Background level can be measured and subtracted (source on-off) Fitting the oscillation will suppress systematics

6. I. Giomataris 200 Mcurie T 2 source 3000 m 3 spherical TPC volume 5x10 30 e - with Xe at p=1 bar NOSTOS Neutrino OScillation Tritium Outgoing Source

7. I. Giomataris The advantages of the spherical TPC Natural focusing system reasonable size detector Provides a full 4  coverage enhancement of the detected signal Allows a good determination of the depth of the interaction point by measuring the time dispersion of the signal: The electric field is V 0 = the applied high voltage, R 1 = the internal radius, R 2 = the external radius  t =  L /v d,  L = D√r At low fields: v d ≈ E and D ≈1/√ E  t ≈ 1/E 3/2 ≈ r 3 The time dispersion is highly enhanced in the spherical case Estimation of the depth of the interaction < 10 cm

8. I. Giomataris Two Micromegas signals at 3 mm distance in depth 3 mm drift Precise determination of the depth

9. I. Giomataris Cu escape Fe escape Ar Low energy spectrum from Micromegas in CAST

10. I. Giomataris Energy distribution of detected neutrinos, E th = 200 eV 14 keV

11. I. Giomataris Detected neutrinos-versus distance, sin 2 2  13 =.17, E th =200 eV The effect of the unknown neutrino energy distribution is small Fitting the curve we extract the oscillation parameters with a single experiment

12. I. Giomataris Neutrino-electron elastic scattering cross section e e e e e-e- e-e- e-e- e-e- w-w- z0z0 G.’t Hooft, Phys. Lett. B37,195(1971) For T<<1 keV d  /dT = a(2sin 4  w +sin 2  w +1/4) High accuracy measurement of the Weinberg angle at very-low energy!! Test the weak interaction at long distances

13. I. Giomataris  Neutrino magnetic moment sensitivity d  /dT ≈ (  ) 2 (1-T/E )/T << 10 -12  B Actual limit 10 -10  B

14. I. Giomataris Low cost Very high pressure None4127He Moderate costNone365.4Ne Low cost 42 Ar activity: <1000/y below 1keV 42 Ar T=33y,E max =565keV 263Ar It needs high purification Expensive 85 Kr161Xe CommentsRadioactivityW(eV)Pressure (bar) Noble gas Target properties with 5.10 30 electrons, 1000 events/year Reasonable goal: operate with Ar or Ne at pressures >10 bars >10 4 events/year to tackle a total number of events of 10 5 Good news : The HELLAZ prototype provide gains of about 10 6 with He at 20 bar

15. I. Giomataris Supernova sensitivity Detect recoils from coherent neutrino-nucleus interaction High cross section:  ≈  N 2 E 2 ≈ 2.5x10 -39 cm 2, Xe and E=10 MeV and 1.5x10 -38 cm 2 at 25 MeV For a a typical supernova explosion and the spherical TPC deterctor: ≈ 15,000 detected with Xe at 1 bar for a distance of 10kpc ≈ 15,000 at 10 bar pressure !!! ≈ 30 at 700 kpc (Extragalactic detection !!!) The challenge is again at the low-energy threshold detection T max = 1500 eV for E = 10 MeV Detection efficiency independent of the neutrino flavor

16. I. Giomataris Plans 1.3 m prototype is under construction - Laboratory study of the radial spatial accuracy - Laboratory study of the electron attenuation length First investigations on the availability of the tritium source High gain operation of the detector at high pressure operation must be investigated with various gas candidates

17. I. Giomataris NOSTOS 1 rst prototype Schedule 2003-2004 Laboratory tests From 2004 Operation in underground laboratory

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20. Tests and studies with the 1.3 m prototype Laboratory tests with various gas mixtures up to 5 bar Total mass 1 - 25 Kgr (He, Ne, Ar, Xe, CF 4 ) First underground investigations 1. Measure the background level in the sub-keV range 2. Optimize the detector parameters, pitch, pulse shaping, gas mixture etc.. If the background level is satisfactory 1. Search for low mass dark matter candidates 2. Search for WIMPs trapped in the solar system 3. WIMP search in spin dependant interactions (CF 4 target) Possible investigations with reactor neutrinos : coherent neutrino-nucleon scattering (>100/day detected neutrinos)

21. I. Giomataris Summary and Outlook The purpose of the new experiment is to establish the phenomenon of neutrino oscillations with a different experimental technique and measure the angle   High sensitivity measurement of the neutrino magnetic moment Measurement of the Weinberg angle at very-low energy High sensitivity for supernova neutrinos Increase as much as possible the gas pressure will provide very-high statistics