2. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 NOSTOS a new low energy neutrino experiment Detect low energy neutrinos from a tritium source using a spherical gaseous TPC Study neutrino oscillations, magnetic moment, Weinberg angle at low energy SUPERNOVA detection sensitivity The first Saclay prototype Preliminary results and short term experimental program HELLAZ? Conclusions An idea by I. Giomataris from Saclay (France)

3. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 The idea (I. Giomataris, J. Vergados, hep-ex/0303045 ) Use a large spherical TPC surrounding the tritium source Detect low energy electron recoils (T max =1.27keV) produced by neutrino-electron scattering L 13 = L 12 /50 = 13 m E=14 keV The oscillation length is comparable to the radius of the TPC Measure  13 and  m 2 by a single experiment The background level can be measured and subtracted The neutrino flux can be measured with a high accuracy <1%

4. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

5. 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

6. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 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

7. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 Energy distribution of detected neutrinos, Recoil energy threshold E th = 200 eV Neutrino energy (keV) 14 keV

8. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 Detected neutrinos-versus distance, sin 2 2  13 =.17, E th =200 eV 3 years of running at p= 1 bar of Xenon The effect of the unknown neutrino energy distribution is small Fitting the curve we extract the oscillation parameters with a single experiment Preliminary

9. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 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 5x10 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

10. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005  Neutrino magnetic moment sensitivity d  /dT=cons(  ) 2 (1-T/E )/T << 10 -12  B Actual limit 10 -10  B

11. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 Detect recoils from coherent neutrino-nucleus interaction High cross section in Xenon: For E = 10 MeV  ≈  N 2 E 2 ≈ 2.5x10 -39 cm 2, T max = 1.500 keV For E = 25 MeV  ≈ 1.5x10 -38 cm 2, T max = 9 keV For a a typical supernova explosion and the spherical TPC detector Filled with Xe at 10 bar we expect : ≈ 100,000 events at 10 kpc!!! ≈ 20 at 700 kpc (Extragalactic sensitivity !!!) Detection efficiency independent of the neutrino flavor The challenge is again at the low-energy threshold detection Supernova sensitivity

12. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 1 st challenge : low background level in the sub-keV range Good news from the Micromegas-CAST detector Cu Fe Ar Low energy spectrum from Micromegas in CAST escape Same detector in MODANE underground : Few counts/day (100 eV threshold)

13. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 2 nd challenge : high gain at high gas pressure - Good news from the Micromegas of the HELLAZ project Single electron detection with high time resolution with Micromegas. They reached gains of >10 5 at p=20 bars in helium !! - High gain at high pressure Xenon is challenging ISSUES Use a low ionization potential quencher (C6H8, TEA, TMAE..) Double amplification Resistive anode

14. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 1.3 m Volume = 1 m 3 P=5 bars Cu 6 mm 1 st prototype (old LEP cavity) Gas leak < 5x10 -9 mbar/s Gas mixture Argon + 10%CO2 (5.7) Pressure up to 5 bar (26.5 kgr Xe) Internal electrode at high voltage Read-out of the internal electrode 10 mm

15. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 First results Low pressure operation 250 mbar - 1100 mbar High voltage 7 kV- 15 kV Cosmic ray signals well observed Low energy x-ray signals observed Satisfactory gain > 5x10 4 Signal stable during 1 week

16. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 Future short-term investigations Tests of the 1 st prototype and optimize the amplification structure Optimize the detector for very-high gain operation Measure the attenuation length of drifting electrons Optimize the energy resolution Measure the accuracy of the depth measurement by the time dispersion of the signal Optimize mechanics and electronics, use low-radioactivity materials Improve the simulation program Calculate (or measure?) the quenching factor in various gases (Xe, Ar..). Underground measurement of the background level at low energy If satisfactorymeasure the neutrino-nucleus coherent scattering with reactor neutrinos Design a 4-m in diameter demonstrator and evaluate it as Supernova detector

17. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 4-m 2 nd 4-m demonstrator A simple and cheap Galactic supernova detector Xe P max =10 bars1000 events/explosion 50 m shield is enough (deploy in the see or lake?) We should assure stability for 100 years Cost estimate : 300k€ (2/3 Xe) ==> Ar: 100 k€ (60 bar) 1 channel read-out Maybe no active detector (field big enough if central ball small enough) The idea is to provide these cheap detectors to receptive universities. They would be maintained by the faculty and their students. The resulting network would tell not only WHEN Supernovae happen, but also WHERE. For that, 5 to 10 spheres have to be installed around the world First sphere: here underwater in Pylos at 600 m depth, hence no security problem?

18. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 HELLAZ? Hellaz was T. Ypsilantis idea to measure solar neutrinos in a cylindrical TPC filled with 20 bar He. Solar neutrinos (pp and Be 7 ) would elastically scatter the He nuclei, produce e - whose energy and direction relative to the sun would be measured. Then the neutrino energy can be reconstructed. Monte-Carlo showed that with 2000 m 3 we had 1000 events / year. The energy threshold had to do with the e - track length that had to be > 2 cm at the beginning, hence 100 keV e -, that is around 200 keV neutrinos. To get the angular resolution, all possible information had to be gathered, hence the “digital” TPC where each individual ionisation e - was identified. The end-detector best suited is Giomataris parallel plate Micromegas (160 m 2 ). But it was difficult to get Micromegas to have single electron gain at 20 bar. This was finally solved, together with getting X-Y information. Here, instead of a 20 m long, 5 m in diameter constant E TPC, we think of the tritium 8.5 m radius TPC where the field would be reversed: the anode would be the external sphere, covered by Micromegas (300 m 2 ). Advantages:- best volume per surface ratio (less background) - best mechanical strength (thinner ==> less background) - good information on the interaction positionéz@”dzxzpositionéz@”dzxz

19. P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 CONCLUSIONS The spherical TPC project allows a simple and low cost detection scheme and offers an ambitious experimental program : Neutrino oscillations, neutrino magnetic moment studies with measurement of the Weinberg angle at low energy using an intense tritium source Low-cost Supernova detector A first prototype is operating in Saclay as a first step to NOSTOS Conference in Paris 9 & 10 dec 2004. Interested people should contact philippe.gorodetzky@cern.ch