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NOSTOS: a spherical TPC to detect low energy neutrinos Igor G. Irastorza CEA/Saclay

NOSTOS: a spherical TPC to detect low energy neutrinos Igor G. Irastorza CEA/Saclay. NOSTOS A new concept: the spherical TPC. A first prototype: the Saclay sphere. Results and prospects. NOSTOS Scheme. Large Spherical TPC 10 m radius 200 MCi tritium source in the center

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NOSTOS: a spherical TPC to detect low energy neutrinos Igor G. Irastorza CEA/Saclay

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  1. NOSTOS:a spherical TPC to detect low energy neutrinosIgor G. Irastorza CEA/Saclay • NOSTOS • A new concept: the spherical TPC. • A first prototype: the Saclay sphere. • Results and prospects. Igor G. Irastorza, CEA Saclay

  2. NOSTOS Scheme • Large Spherical TPC • 10 m radius • 200 MCi tritium source in the center • Neutrinos oscillate inside detector volume L23=13 m • Measure q13 and more… Igor G. Irastorza, CEA Saclay

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

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

  5. Source & Target • Source: 200MCi (20 kg) Tritium • 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) Igor G. Irastorza, CEA Saclay

  6. Experimental challenges: within reach • Threshold easily achievable, to be demonstrated with underground tests • Background simulations planned, to be demonstrated with underground tests • Radial resolution being demonstrated by Saclay sphere • Stability  first results positive, more planned • Scaling up  intermediate size prototypes being designed • Electrostatics some ideas being demonstrated by Saclay sphere Igor G. Irastorza, CEA Saclay

  7. First prototype: the Saclay sphere • D=1.3 m • V=1 m3 • Spherical vessel made of Cu (6 mm thick) • P up to 5 bar possible (up to 1.5 tested up to now) • Vacuum tight: ~10-6 mbar (outgassing: ~10-9 mbar/s) Igor G. Irastorza, CEA Saclay

  8. Simple multiplication structure: small (10 mm Ø) sphere Internal electrode at HV Readout of the internal electrode First prototype: the Saclay sphere 10 mm Igor G. Irastorza, CEA Saclay

  9. First tests • Mixtures tested: • Ar+10% CO2 • Ar+2% Isobutane • Pressures from 0.25 up to 1.5 bar tested up to now • High gains (>104) achieved with simple spherical electrode • No need to go to very high V (better for minimizing absorption) Igor G. Irastorza, CEA Saclay

  10. First results • 5.9 keV 55Fe signal • Very low electronic noise: low threshold • Fit to theoretical curve including avalanche induction and electronics: system well understood Igor G. Irastorza, CEA Saclay

  11. First results • Runs of 55Fe, 109Cd and Cosmic Rays • Better resolution obtained in more recent tests with Isobutane (analysis in progress) 55Fe spectrum with Ar+CO2 Ar escape 55Fe 5.9 keV Igor G. Irastorza, CEA Saclay

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

  13. First results Template pulses (average of 20 sample pulses) In Ar+CO2 P=0.25 bar • 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 Igor G. Irastorza, CEA Saclay

  14. 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). • 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 Igor G. Irastorza, CEA Saclay

  15. First results • Stability: • tested up to ~2 months. • No circulation of gas. Detector working in sealed mode. (1 pass through an oxysorb filter) • No absorption observed • Signal integrity preserved after 60 cm drift. • Not high E needed to achieve high gain. Igor G. Irastorza, CEA Saclay

  16. Next steps • Electrostatics • Field shaping rings • More ambitious ideas in mind for the future: charging systems without electrical contact (like the ones in electrostatic accelerators) Igor G. Irastorza, CEA Saclay

  17. Next steps: Micromegas as NOSTOS readout • 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) 2 Typical MICROMEGAS pulses Igor G. Irastorza, CEA Saclay

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

  19. Conclusions • 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 • First prototype already working in Saclay • 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) Igor G. Irastorza, CEA Saclay

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