1. LRT2004 Sudbury, 12-14 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.

2. LRT2004 Sudbury, 12-14 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…

3. LRT2004 Sudbury, 12-14 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)

4. LRT2004 Sudbury, 12-14 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

5. LRT2004 Sudbury, 12-14 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)

6. LRT2004 Sudbury, 12-14 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

7. LRT2004 Sudbury, 12-14 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)

8. LRT2004 Sudbury, 12-14 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

9. LRT2004 Sudbury, 12-14 December 2004Igor G. Irastorza, CEA Saclay First tests Mixtures tested: Mixtures tested: –Ar+10% CO 2 –Ar+2% Isobutane Pressures from 0.25 up to 1.5 bar tested up to now Pressures from 0.25 up to 1.5 bar tested up to now 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)

10. LRT2004 Sudbury, 12-14 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

11. LRT2004 Sudbury, 12-14 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

12. LRT2004 Sudbury, 12-14 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

13. LRT2004 Sudbury, 12-14 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

14. LRT2004 Sudbury, 12-14 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 test are under preparation to better calibrate (external trigger from Am source ) Further test 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

15. LRT2004 Sudbury, 12-14 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.

16. LRT2004 Sudbury, 12-14 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)

17. LRT2004 Sudbury, 12-14 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

18. LRT2004 Sudbury, 12-14 December 2004Igor G. Irastorza, CEA Saclay NOSTOS Additional Physics Neutrino magnetic moment Neutrino magnetic moment Test of weak interaction at low energy (Weinberg angle) Test of weak interaction at low energy (Weinberg angle) Supernovae (neutrino-nucleus scattering) Supernovae (neutrino-nucleus scattering) McLaughlin & Volpe PLB 591 (04) 229 10 -12  B 10 -11  B NO MM

19. LRT2004 Sudbury, 12-14 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)