1. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay NOSTOS: a spherical TPC to detect low energy neutrinos Igor G. Irastorza CEA/Saclay NOSTOS NOSTOS A new concept: the spherical TPC. A new concept: the spherical TPC. A first prototype: the Saclay sphere. A first prototype: the Saclay sphere. Results and prospects. Results and prospects. Additional physics Additional physics

2. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay e-e- e NOSTOS experiment E max =18.6 keV ~14 keV ~14 keV GOAL: detection of very low energy neutrinos from a tritium source GOAL: detection of very low energy neutrinos from a tritium source

3. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay NOSTOS experiment Oscillations at “room” scale… Oscillations at “room” scale… G. Gounaris, CERN seminar 23-09-04 “room-size” neutrino oscillations Oscillation of a 10 keV e

4. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay NOSTOS Scheme Large Spherical TPC Large Spherical TPC 10 m radius 10 m radius 200 MCi tritium source in the center 200 MCi tritium source in the center Neutrinos oscillate inside detector volume L 23 =13 m Neutrinos oscillate inside detector volume L 23 =13 m Measure  13 and more… Measure  13 and more…

5. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay The spherical TPC concept The spherical TPC concept (I. Giomataris, J. Vergados, NIM A530 (04) 330-358 [hep-ex/0303045] ) Drifting charges MICROMEGAS readout (max E=1.27 keV)

6. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay The spherical TPC concept: Advantages Natural focusing: Natural focusing: –large volumes can be instrumented with a small readout surface and few (or even one) readout lines 4  coverage: better signal 4  coverage: better signal Still some spatial information achievable: Still some spatial information achievable: –Signal time dispersion Other practical advantages: Other practical advantages: –Symmetry: lower noise and threshold –Low capacity –No field cage Simplicity: few materials. They can be optimized for low radioactivity. Simplicity: few materials. They can be optimized for low radioactivity. Low cost Low cost The way to obtain large detector volumes keeping low background and threshold

7. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay Source & Target Source: 200MCi (20 kg) Tritium Source: 200MCi (20 kg) Tritium Target: Several possibilities as target gas: Target: Several possibilities as target gas: Detailed calculation/simulation in progress to assess expected signal/sensitivity, taking into account atomic effects (Gounaris et al. hep-ex/0409053) Detailed calculation/simulation in progress to assess expected signal/sensitivity, taking into account atomic effects (Gounaris et al. hep-ex/0409053)

8. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay Experimental challenges: within reach Threshold  easily achievable, to be demonstrated with underground tests Threshold  easily achievable, to be demonstrated with underground tests Background  simulations planned, to be demonstrated with underground tests Background  simulations planned, to be demonstrated with underground tests Radial resolution  being demonstrated by Saclay sphere Radial resolution  being demonstrated by Saclay sphere Stability  first results positive, more planned Stability  first results positive, more planned Scaling up  intermediate size prototypes being designed Scaling up  intermediate size prototypes being designed Electrostatics  some ideas being demonstrated by Saclay sphere Electrostatics  some ideas being demonstrated by Saclay sphere

9. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First prototype: the Saclay sphere D=1.3 m D=1.3 m V=1 m 3 V=1 m 3 Spherical vessel made of Cu (6 mm thick) Spherical vessel made of Cu (6 mm thick) P up to 5 bar possible (up to 1.5 tested up to now) P up to 5 bar possible (up to 1.5 tested up to now) Vacuum tight: ~10 -6 mbar (outgassing: ~10 -9 mbar/s) Vacuum tight: ~10 -6 mbar (outgassing: ~10 -9 mbar/s)

10. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First prototype: the Saclay sphere Simple multiplication structure: small (10 mm Ø) sphere Simple multiplication structure: small (10 mm Ø) sphere Internal electrode at HV Internal electrode at HV Readout of the internal electrode Readout of the internal electrode 10 mm

11. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First tests: Gain Ar + 10% CO 2 High gains (>10 4 ) achieved with simple spherical electrode High gains (>10 4 ) achieved with simple spherical electrode No need to go to very high V (better for minimizing absorption) No need to go to very high V (better for minimizing absorption)

12. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First tests: Gain Ar + 2% Isobutane High gains (>10 4 ) achieved High gains (>10 4 ) achieved No need to go to very high V even at high P No need to go to very high V even at high P P up to 1.5 bar tested up to now P up to 1.5 bar tested up to now

13. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First results 5.9 keV 55 Fe signal 5.9 keV 55 Fe signal Very low electronic noise: low threshold Fit to theoretical curve including avalanche induction and electronics: system well understood

14. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First results Runs of 55 Fe, 109 Cd and Cosmic Rays Runs of 55 Fe, 109 Cd and Cosmic Rays Better resolution obtained in more recent tests with Isobutane (analysis in progress) Better resolution obtained in more recent tests with Isobutane (analysis in progress) 55Fe 5.9 keV Ar escape 55 Fe spectrum with Ar+CO 2

15. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay Pulse deconvolution Response function including the ion induction + electronics effects associated to one single point charge. Response function including the ion induction + electronics effects associated to one single point charge. Remove the slow tail of the pulses Remove the slow tail of the pulses Recover the time (=radial) structure of the primary e - cloud Recover the time (=radial) structure of the primary e - cloud This analysis will not be needed when a fast readout (MICROMEGAS) will be available This analysis will not be needed when a fast readout (MICROMEGAS) will be available

16. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First results Clear time dispersion effect observed in deconvoluted pulses correlated with distance drifted Clear time dispersion effect observed in deconvoluted pulses correlated with distance drifted 60 cm drift 50 cm drift 40 cm drift 30 cm drift 20 cm drift 10 cm drift Template pulses (average of 20 sample pulses) In Ar+CO2 P=0.25 bar

17. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First results Even with a very simple (and slow) readout, we have proved the use of dispersion effects to estimate the position of the interation (at least at ~10 cm level). Even with a very simple (and slow) readout, we have proved the use of dispersion effects to estimate the position of the interation (at least at ~10 cm level). Further tests are under preparation to better calibrate (external trigger from Am source ) Further tests are under preparation to better calibrate (external trigger from Am source ) Average time dispersion of 5.9 keV deconvoluted events VS. Distance drifted No source run (cosmics) Ar+CO2 P=0.25 bar

18. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay First results Stability: Stability: –tested up to ~2 months. –No circulation of gas. Detector working in sealed mode. (1 pass through an oxysorb filter) No absorption observed No absorption observed –Signal integrity preserved after 60 cm drift. –Not high E needed to achieve high gain. Robustness Robustness

19. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay Next steps Electrostatics Electrostatics –Field shaping rings –More ambitious ideas in mind for the future: charging systems without electrical contact (like the ones in electrostatic accelerators)

20. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay Next steps : Micromegas as NOSTOS readout Very fast signals: will allow to measure precisely time (and space) dispersion, i.e. radial coordinate of event. Very fast signals: will allow to measure precisely time (and space) dispersion, i.e. radial coordinate of event. Spherical MICROMEGAS (?) (or series of flat elements) Spherical MICROMEGAS (?) (or series of flat elements) 2 Typical MICROMEGAS pulses

21. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay NOSTOS Additional Physics Neutrino magnetic moment Best limit from the MUNU experiment: Best limit from the MUNU experiment:  e < 10 -10  B [MUNU coll., PLB 564 (03)] NOSTOS sensitivity could be down to 10 -12  B NOSTOS sensitivity could be down to 10 -12  B McLaughlin & Volpe PLB 591 (04) 229 10 -12  B 10 -11  B NO MM

22. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay NOSTOS Additional Physics Weinberg angle at low energies High accuracy measurement of the Weinberg angle at very low energy High accuracy measurement of the Weinberg angle at very low energy 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) Important: atomic effects Important: atomic effects

23. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay NOSTOS Additional Physics Neutrino-nucleus interaction  ≈ N 2 E 2 [D. Z. Freedman, Phys. Rev.D,9(74)1389] n Recoil energy: E max =(2E ) 2 /2AM E mean =E max /3 Could be measured by a miniNOSTOS close to a nuclear reactor

24. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay NOSTOS Additional Physics Neutrino-nucleus interaction 1 m 3 detector (present prototype!!) (gas at 5 bar) at 10m from a reactor after 1 year run (2x10 7 s), assuming full detector efficiency: Xe (  ≈ 2.16x10 -40 cm 2 ), 2.2x10 6 neutrinos int., E max =146 eV Ar (  ≈ 1.7x10 -41 cm 2 ), 9x10 4 neutrinos int., E max =480 eV Ne (  ≈ 7.8x10 -42 cm 2 ), 1.87x10 4 neutrinos int., E max =960 eV Challenge : Very low energy threshold Challenge : Very low energy threshold We need to calculate and measure the quenching factor We need to calculate and measure the quenching factor  from nuclear reactor miniNOSTOS – flux=10 13 /cm 2 /s – ~ 3 MeV

25. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay NOSTOS Additional Physics Neutrinos from supernovae with a 4 m sphere coherent neutrino-nucleus interaction High cross sections and reasonable recoiling energies: – –For E =10 MeV:  ≈ 2.5x10 -39 cm 2, E max = 1.5 keV – –For E =25 MeV:  ≈ 1.5x10 -38 cm 2, E max = 9 keV – –(Xenon assumed) For a a typical supernova explosion and the D=4 m spherical TPC detector: Detection efficiency independent of the neutrino flavor Detection efficiency independent of the neutrino flavor The challenge is again at the low-energy threshold detection The challenge is again at the low-energy threshold detection ~ 100 events detected with Xe at 1 bar for a distance of 10kpc ~ 1000 events at 10 bar pressure !!! 4m prototype

26. Large TPC Workshop, Paris, 20-21 December 2004Igor G. Irastorza, CEA Saclay Conclusions Spherical TPC concept introduced in the framework of NOSTOS proposal Spherical TPC concept introduced in the framework of NOSTOS proposal Promising as a simple way to obtain large detector volumes, keeping low background and low threshold Promising as a simple way to obtain large detector volumes, keeping low background and low threshold First prototype already working in Saclay First prototype already working in Saclay First encouraging results: low threshold, stability, no absorption, dispersion vs. drift observed. First encouraging results: low threshold, stability, no absorption, dispersion vs. drift observed. To be done next: optimize electrostatics, develop more calibration systems, assess background (test underground) To be done next: optimize electrostatics, develop more calibration systems, assess background (test underground) Highly exciting physics program could be done by NOSTOS: neutrino oscillations, magnetic moment, Weinberg angle, Neutrino-nucleus interaction, Supernova detection,… Highly exciting physics program could be done by NOSTOS: neutrino oscillations, magnetic moment, Weinberg angle, Neutrino-nucleus interaction, Supernova detection,…