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GNO and the pp - Neutrino Challenge

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mira
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T.Kirsten/GNO. GNO and the pp - Neutrino Challenge. Till A. Kirsten Max-Planck-Institut für Kernphysik, Heidelberg for the GNO Collaboration NDM03 Nara/Japan June 9-14, 2003 a. Solar Neutrino Energy Spectrum. GNO - Gallium Neutrino Observatory. detection of low energy solar neutrinos.

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  1. T.Kirsten/GNO GNO and the pp - Neutrino Challenge Till A. Kirsten Max-Planck-Institut für Kernphysik, Heidelberg for the GNO Collaboration NDM03 Nara/Japan June 9-14, 2003 • a

  2. Solar Neutrino Energy Spectrum

  3. GNO - Gallium Neutrino Observatory detection of low energy solar neutrinos Purpose: Basic interaction: 71Ga(ne,e)71Ge (Ethr = 233 keV) EC, t = 16.49 days 7Be 27% n signal composition: CNO 8% pp+pep 55% 8B 10% 72 SNU 35 SNU 10 SNU Tot: 128+9-7 SNU 13 SNU Technique: Radiochemical Target: 103 tons of GaCl3 acidic solution containing 30 tons of natural gallium Chemical extraction of 71Ge every 3-4 weeks Detection of 71Ge decay with gas proportional counters  9 71Ge counts detected per extraction Expected signal (SSM): More details can be found on the webpage www.lngs.infn.it/site/exppro/gno/Gno_home.htm

  4. GNO Collaboration • Dip. Di Fisica dell’Università di Milano “La Bicocca” e INFN sez. Milano • INFN Laboratori Nazionali del Gran Sasso • Dip. Di Fisica dell’Università di Roma “Tor Vergata” e INFN sez. Roma II • Dip. Di Ingegneria Chimica e dei Materiali Università dell’Aquila • Max Planck Institut fur Kernphysik – Heidelberg • Physik Dep. E15 – Technische Universitaet – Muenchen

  5. Jun 1994 – Oct 1994 1st51Cr source experiment PL B342 (1995) 440 PL B447 (1999) 127 Feb. 1997 End of Solar Data Taking Oct 1995 – Feb 1996 2nd source 51Cr experiment PL B420 (1998) 114 Feb 1997 – Apr 1997 Test of the detector with 71As PL B436 (1998) 158 Start of GNO data taking Apr 1998 – Now GALLEX Construction of the detector 1986 - 1990 GALLEX I data taking 15 Solar runs, 5 Blanks PL B285 (1992) 376 PL B285 (1992) 390 May 1991 – May 1992 83.4 ± 19 SNU GALLEX Final Result 1594 days – 65 runs: 77.5± 7.7 SNU

  6. Significance of Deficit in Time

  7. Neutrino Source Exposure

  8. Source results

  9. Arsenic Tests Repeated tests under variable respectively purposely unfavorable conditions with respect to: method and magnitude of carrier addition Mixing-and extraction conditions standing time to exclude witholdings (classical or ‘hot-atom’-effects) Method: Triple-batch comparison:  30 000 71As atoms in: Tank sample External sample Calibration sample (-spectrometry) Result: Recovery 99+ %

  10. GNO – Results completed 52 solar runs 1547 days still counting 7 solar runs 200 days blanks 10 +2 GNO65.2 ± 6.4 ± 3.0 SNU (L 70. ± 10. K 62. ± 8.) GALLEX 77.5 ± 6.2 +4.3-4.7SNU GALLEX+GNO70.8 ± 4.5 ± 3.8 SNU

  11. GALLEX - GNODavis plot GNO 52 solar runs GALLEX 65 solar runs

  12. GALLEX +GNO Seasonal variations Winter-Summer(statistical error only): GNO only (52 SRs): Winter (26 SR): 59.6+8.1-7.7 SNU Summer (26 SR): 67.7+8.7-8.3 SNU W-S: -8 ± 16 SNU GNO + Gallex (117 SRs): Winter (60 SR): 68.1+6.0-5.8 SNU Summer (57 SR): 73.5+6.4-6.2 SNU W-S: -5 ± 12 SNU

  13. Improvements * Neural network analysis

  14. Why sub-MeV Neutrinos? • Solar Physics • 98 % of all solar neutrinos are sub-MeV • ( 7 ~ 7 % , pp ~ 91 % ) • The pp- neutrino flux is coupled to the solar luminosity. It is a fundamental astrophysical parameter that should definitely be measured, as precisely as possible. Stringent limitations (or observation) of departures from the standard solar model are obtained if the flux of pp neutrinos could be deduced.

  15. 2. Neutrino Physics (a) Below 1 MeV, the vacuum oscillation domain takes over from the matter oscillation domain at >1 MeV. Also there could be hidden effects only at < 1MeV (e.g., sterile admix-tures?) (b) Narrow down on tang2θ12 . To obtain Δ  15%, the pp-flux must be determined to  3 %

  16. Depression Factor vs. Energy

  17. Ga SNU contours in the LMA region Holanda + Smirnov PRD 66(2002)113005

  18. How? The best promise is with low threshold real time experiments like (n-e) scattering or (n, e-γ) (e.g. Xe) e.g. In-Lens Yet:When ??? 7Be :soon (Borexino, Kamland?)pp :> 4 years (at least) Meanwhile : pp = GNO(pp+7Be) minus BOREXINO (7Be)!

  19. An important Asset: GNO is a running experiment. Continuation and improvements are (relatively) low cost and effort. Yet: How precisely can we get before the advent of real time sub-MeV data ?

  20. Outset on which we must improve (see Bahcall and Pena-Garay, hep-ph 0305159) pp-flux: (1.01  0.02) x BP00 SSM (1) (with luminosity constraint) 7Be-flux:(0.97 +0.28-0.54) x BP00 SSM (1) tang2θ12 = = 0.42 +0.08-0.06 (LMA: Δm2 = ( 7.3 +0.4-0.5) x 10-5 eV2 ; no hope to improve on this from GNO/Borexino) fGa,cc = 0.55  0.03 (1)

  21. CC / NC Response

  22. Determination of the pp-neutrino flux from GNO and Borexino

  23. Deduction of the pp-flux

  24. Survival probabilities Survival probabilities 2 3 P (ne ne) 4 3 5 4 1 2 5 1 Ppp = 0.57 +- 10% Ppep = 0.53 +- 5% P7 = 0,56 +- 8% P8 = 0.33 +- 20% PCNO = 0.55 +- 8% E (MeV) C. Cattadori, N. Ferrari

  25. Capture cross sections Capture cross sections n type s Err % Transitions Signal/SSM % Errors from s 10-46 cm2 % GS 1,2 >2 (with MSW LMA) GS 1,2 >2 pp 11.72 +- 2.3 100 - - 0.311 pep 204 -7 +17 82 6 12 0.012 7Be 71.7 -3 +7 94 6 - 0.150 8B 24000 -15 +32 12 6 82 0.030 N 60.4 -3 +6 94 6 - 0.014 O 113.7 -5 +12 86 6 8 0.023 TOT 0.541 +-2.1 -0.4+1.7 -0.9 +3.5

  26. Future Plans in GNO

  27. Future Neutrino Source Exposures

  28. Source Feasibility and Status An intense feasibility study, including test irradiations with actual GALLEX enriched chromium, revealed that the RIAR reactor research institute at Dimitrovgrad (Russia) can produce sources up to 6.5MegaCurie with the available material. The immediate project is a 3MCi source for GNO (next major experimental step)

  29. Quotation of J. Bahcall „Simple neutrino scenarios fit well the existing data, which – with the exception of the chlorine and gallium radiochemical experiments – all detect only solar neutrinos with energies above 5 MeV. Perhaps these higher energy data have not yet revealed the full richness of the weak interaction phenomena.” Nucl.Phys. Proc. Suppl. B118 (2003) 86