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

1. NOSTOS a new low energy neutrino experiment An idea by I. Giomataris from Saclay (France) • 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 P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

2. The idea (I. Giomataris, J. Vergados, hep-ex/0303045 ) • Use a large spherical TPC surrounding the tritium source • Detect low energy electron recoils (Tmax=1.27keV) produced by neutrino-electron scattering P(e e)  1 sin2213 sin2(L/L13) • L13= L12/50 = 13 m • The oscillation length is comparable to the radius of the TPC • Measure q13and dm2by a single experiment • The background level can be measured and subtracted • The neutrino flux can be measured with a high accuracy <1% E=14 keV  P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

3. Tritium Produced by neutrons on Li6 or He3 Half life 12.26 years, Energy Maximum 18.6 keV, Average energy 5.7 keV, power 4 kWatt/20 Kgr Neutrino production: 7x1018/s/20 Kgr T  He3 e v 8000000 electron neutrino 7000000 6000000 dN/dT 5000000 4000000 3000000 2000000 1000000 0 0 2 4 6 8 10 12 14 16 18 20 T(keV) P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

4. NOSTOS NOSTOS N Neutrino • 200 Mcurie T2source eutrino OS T Tritium ritium O Outgoing OScillation cillation utgoing S Source ource • 3000 m3spherical TPC volume • 5x1030e-with Xe at p=1 bar P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

5. The advantages of the spherical TPC • Natural focusing system reasonable size detector • Provides a full 4p coverage signal enhancement of the detected • Allows a good determination of the depth of the interaction point by measuring the time dispersion of the signal: The electric field is R2R1 V0 r2 R1R2 E  V0= the applied high voltage, R1= the internal radius, R2= the external radius st= sL/vd, sL= D√r At low fields: vd≈E and D≈1/√ E  s st≈1/E3/2 ≈ r3 The time dispersion is highly enhanced in the spherical case Estimation of the depth of the interaction << 10 cm P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

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

7. Detected neutrinos-versus distance, sin22q13=.17, Eth=200 eV 3 years of running at p= 1 bar of Xenon The effect of the unknown neutrino energy distribution is small Preliminary Fitting the curve we extract the oscillation parameters with a single experiment P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

8. Target properties with 5x1030electrons, 1000 events/year Noble gas Pressure (bar) W(eV) Radioactivity Comments 85Kr Xe 1 16 It needs high purification Expensive 42Ar T=33y,Emax=565keV Ar 3 26 Low cost 42Ar activity: <1000/y below 1keV Ne 5.4 36 None Moderate cost He 27 41 None Low cost Very high pressure Reasonable goal: operate with Ar or Ne at pressures >10 bars >104events/year to tackle a total number of events of 105 P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

9. Neutrino magnetic moment sensitivity << 10-12m mB d ds s/dT=cons( /dT=cons(m mn n) )2 2(1 (1- -T/E T/En n)/T )/T 3 Actual limit 10-10m mB 2.5 *10-47 2 ds/dT(cm2/keV) 10-12mB 1.5 1 weak 0.5 0 0.01 0.1 1 2 T (keV) P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

10. Supernova sensitivity Detect recoils from coherent neutrino-nucleus interaction High cross section in Xenon: For En= 10 MeV s≈ N2E 2 ≈ 2.5x10-39cm2,Tmax= 1.500 keV For En= 25 MeV s≈ 1.5x10-38cm2,Tmax= 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 P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

11. 1stchallenge : low background level in the sub-keV range Good news from the Micromegas-CAST detector Low energy spectrum from Micromegas in CAST Cu Fe escape Ar Same detector in MODANE underground : Few counts/day (100 eV threshold) P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

12. 2ndchallenge : 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 >105 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 P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

13. 1stprototype (old LEP cavity) 1.3 m • Gas leak < 5x10-9mbar/s • Gas mixture Argon + 10%CO2 (5.7) Cu 6 mm • Pressure up to 5 bar (26.5 kgr Xe) • Internal electrode at high voltage 10 mm • Read-out of the internal electrode Volume = 1 m3 P=5 bars P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

14. 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 > 5x104 •Signal stable during 1 week P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

15. Future short-term investigations • Tests of the 1stprototype 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 satisfactory scattering with reactor neutrinos measure the neutrino-nucleus coherent • Design a 4-m in diameter demonstrator and evaluate it as Supernova detector P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

16. 2nd4-m demonstrator A simple and cheap Galactic supernova detector Xe Pmax=10 bars 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) 1000 events/explosion 4-m 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. 1 channel read-out For that, 5 to 10 spheres have to be installed around the world Maybe no active detector (field big enough if central ball small enough) First sphere: here underwater in Pylos at 600 m depth, hence no security problem? P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

17. HELLAZ? Hellaz was T. Ypsilantis idea to measure solar neutrinos in a cylindrical TPC filled with 20 bar He. Solar neutrinos (pp and Be7) 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 m3we 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 m2). 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 m2). Advantages: - best volume per surface ratio (less background) - best mechanical strength (thinner ==> less background) - good information on the interaction positionéz@”dzxz P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

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