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Study of low energy nuclear recoils in several noble gases

Study of low energy nuclear recoils in several noble gases. S. Andriamonje a , S. Aune a , P. Colas a , E. Ferrer-Ribas a , Y. Giomataris a , I. G . Irastorza a , J . Pancin a , P. Salin b , I. Savvidis c. Proposal for nTOF phase II. a DAPNIA, CEA/Saclay, France b APC, Paris, France

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Study of low energy nuclear recoils in several noble gases

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  1. Study of low energy nuclear recoils in several noble gases S. Andriamonjea, S. Aunea, P. Colasa, E. Ferrer-Ribasa, Y. Giomatarisa, I. G . Irastorzaa, J . Pancina, P. Salinb, I. Savvidisc Proposal for nTOF phase II a DAPNIA, CEA/Saclay, France b APC, Paris, France c U. Thessaloniki, Greece Igor G. Irastorza, CEA Saclay

  2. Goals and Motivation • Quenching factor at low energies (~1 keV) • Detection of coherent neutrino-nucleus interaction: very low energy nuclear recoils • Development of a very low threshold massive detector: the spherical TPC concept • Neutrinos from supernovae and others.. • Nuclear recoil “imaging” • Direction of the nuclear recoil will open the way to unmistakable signatures in WIMP dark matter searches • Micromegas could prove it in nTOF Igor G. Irastorza, CEA Saclay

  3. High Voltage Shield E Drift Gaseous Volume The spherical TPC concept • Spherical drift region with spherical E field • Ionization drift focusing towards the center • Central electrode with amplification structure • Simple spherical electrode • Spherical Micromegas (in development) • Temporal pattern of the pulse induced in the central electrode is recorded Igor G. Irastorza, CEA Saclay

  4. Advantages of the spherical TPC • Natural focusing: large volumescan be instrumented • Spatial information achievable (Signal time dispersion) • Extremely low capacity: very low thresholdachievable. • No field cage • Simplicity: few materials. They can be optimized for low radioactivity. • Low cost The way to obtain large detector volumes keeping low background and threshold • Offer the way to detect coherent neutrino-nucleus interactions Igor G. Irastorza, CEA Saclay

  5. 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) The Saclay sphere Igor G. Irastorza, CEA Saclay

  6. Saclay prototype: first results Demonstration prototype built and working in Saclay 55Fe calibration with Ar + Isobutane (2%) • 5.9 keV 55Fe signal 5.9 keV Ar escape • Very low threshold (~100 eV) !! Igor G. Irastorza, CEA Saclay

  7. Spherical TPC: applications • Coherent neutrino-nucleus interaction n n n Cross section enhanced by coherence Recoil energy: Emax =(2En)2/2AM Emean=Emax/3 s ≈ N2En2 [D. Z. Freedman, Phys. Rev.D,9(74)1389] Standard Model effect, but not yet experimentally observed Igor G. Irastorza, CEA Saclay

  8. Neutrino nucleus interaction • 1 m3 detector (present prototype!!) • (gas at 5 bar) at 10m from a reactor • after 1 year run (2x107s), assuming full detector efficiency: n from nuclear reactor Spherical TPC • n flux=1013/cm2/s • <En> ~3 MeV Xe (s ≈ 2.16x10-40 cm2), 2.2x106 neutrinos int., Emax=146 eV Ar (s ≈ 1.7x10-41 cm2), 9x104 neutrinos int., Emax=480 eV Ne (s ≈ 7.8x10-42 cm2), 1.87x104 neutrinos int., Emax=960 eV • Challenge : Very low energy threshold (but clearly feasible if more energetic neutrinos: spallation source) • We need to calculate and measure the quenching factor Igor G. Irastorza, CEA Saclay

  9. Supernova neutrinos • coherent neutrino-nucleus interaction • High cross sections and reasonable recoiling energies: • For En=10 MeV: s ≈ 2.5x10-39 cm2, • Emax = 1.5 keV • For En=25 MeV: s ≈ 1.5x10-38 cm2 , • Emax = 9 keV • (Xenon assumed) • For a a typical supernova explosion and the D=4 m spherical TPC detector: 4m prototype ~ 100 events detected with Xe at 1 bar for a distance of 10kpc ~ 1000 events at 10 bar pressure !!! • Detection efficiency independent of the neutrino flavor • The challenge is again at the low-energy threshold detection Igor G. Irastorza, CEA Saclay

  10. Nuclear recoils in a Micromegas • MICROMEGAS already measured nuclear recoils in nTOF-I Detection scheme for nTOF-I • For nTOF-II: • no converter • 2D strips/pixels • lower threshold per strip/pixel Igor G. Irastorza, CEA Saclay

  11. Count rate from MICROMEGAS – nTOF-I • For nTOF-II: • no converter: we focus on nuclear recoils • 2D strips/pixels: better identification of good events • lower threshold per strip/pixel: S. Andriamonje et al NIM (2001) Igor G. Irastorza, CEA Saclay

  12. Quenching factor ionization of an nuclear recoil E • QF = • Method 1: • Using the whole recoil spectrum measured. • Recoil energy of single events is not determined but overall spectrum may be estimated. • Problem: control of systematics • Method 2: • Recoil energy event-by-event is measured (by detecting dispersed neutron). • QF determined event-by-event • Problem: low counting ionization of an electron recoil same E Igor G. Irastorza, CEA Saclay

  13. PMT PMT PMT PMT PMT Proposed setup - outline Dispersed neutron detectors nTOF neutron beam MICROMEGAS Igor G. Irastorza, CEA Saclay

  14. Proposed setup • 1st (easy) option • Small MICROMEGAS • QF calculated from integral spectra • 2nd option • Medium MICROMEGAS (~100 cm3) • Several neutron detectors (~10) placed at several angles (at 1-2 m) provide recoil energy • QF calculated event by event, more precisely. Simulations on course to estimate precise numbers… Igor G. Irastorza, CEA Saclay

  15. Nuclear recoil track “imaging”Motivation Background is isotropic • WIMP Dark Matter: the unmistakable signature While the signal is not Igor G. Irastorza, CEA Saclay

  16. Nuclear recoil track “imaging” • Examples of ion trajectories in (1 atm) gases: (simulations with SRIM) ~1 mm 400 mm 100 keV Ar recoiling in pure Ar gas 100 keV Ne recoiling in pure Ne gas Igor G. Irastorza, CEA Saclay

  17. Nuclear recoil track “imaging” • Mixtures of gases ~900 mm ~800 mm 100 keV Ar recoiling in Ar(20%)/He(80%) gas 50 keV Ne recoiling in Ne(50%)/He(50%) gas Igor G. Irastorza, CEA Saclay

  18. Nuclear recoil track “imaging” • Helium • Questions: • can nuclear recoils at sub-mm scale be detected and their direction determined? • Down to which energies? • With which accuracy? • MICROMEGAS is a promising tool for that ~1 mm 5 keV He recoiling in pure He gas Igor G. Irastorza, CEA Saclay

  19. Micromegas + Medipix2 The MediPix2 pixel CMOS chip • H. van der Graaf, NIKHEF, presented at IPRD 2004, Siena • NIM A540 (05) 55Fe Cathode (drift) plane Drift space: 15 mm Micromegas Baseplate MediPix2 pixel sensor Brass spacer block Printed circuit board Aluminum base plate Igor G. Irastorza, CEA Saclay

  20. Igor G. Irastorza, CEA Saclay

  21. ~14 mm Some example events… He/Isobutane 80/20 Medipix+Micromegas • H. van der Graaf, NIKHEF, presented at IPRD 2004, Siena • NIM A540 (05) δ-ray? Igor G. Irastorza, CEA Saclay

  22. ~14 mm Some example events… He/Isobutane 80/20 Medipix+Micromegas • H. van der Graaf, NIKHEF, presented at IPRD 2004, Siena • NIM A540 (05) Igor G. Irastorza, CEA Saclay

  23. ~14 mm Some example events… 55Fe source, 1 s integration AR/Isobutane Medipix+Micromegas • H. van der Graaf, NIKHEF, presented at IPRD 2004, Siena • NIM A540 (05) Igor G. Irastorza, CEA Saclay

  24. ~14 mm Some example events… 55Fe source, 10 s integration AR/Isobutane Medipix+Micromegas • H. van der Graaf, NIKHEF, presented at IPRD 2004, Siena • NIM A540 (05) Igor G. Irastorza, CEA Saclay

  25. Zoom on single clusters… • H. van der Graaf, NIKHEF, presented at IPRD 2004, Siena • NIM A540 (05) ~500 mm Start seeing the photoelectron track A similar setup in nTOF should be able to see nuclear recoils track at a sub-mm scale. Igor G. Irastorza, CEA Saclay

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