1. 1 Retrospect of GALLEX / GNO Till Kirsten Max-Planck-Institut für Kernphysik Heidelberg / Germany 1Retrospect 2Recent update 3Why did we stop?

2. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 2 GALLEX / GNO, SAGE Radiochemical Method (product accumulation) Ga 71 + e  Ge 71 + e - Low threshold! (0.233 MeV) recall: Cl- experiment 1 RETROSPECT

3. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 3 Purpose: detection of low energy solar neutrinos 71 Ga( e,e) 71 Ge (E thr = 233 keV) Basic interaction: EC,  = 16.49 days  signal composition: Technique: Expected signal (SSM):  9 71 Ge counts detected per extraction Radiochemical Target: 103 tons of GaCl 3 acidic solution containing 30 tons of natural gallium Chemical extraction of 71 Ge every 3-4 weeks Detection of 71 Ge decay with gas proportional counters Tot: 126 +9 -7 SNU 72 SNU 33 SNU 9 SNU 12 SNU 8 B 10% CNO 7% 7 Be 26% pp+pep 57% Conception of the Gallium Neutrino Experiment GALLEX (later GNO)

4. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 4 Why sub-MeV Neutrinos?  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 must definitely be measured, as precisely as possible. Stringent limitations (or obser- vation) of departures from the standard solar model can be obtained if the flux of pp neutrinos is deduced, provided that, as it is now possible, neutrino properties are properly folded in.

5. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 5  Below ~1-2 MeV, the vacuum oscillation domain takes over from the matter oscillation domain at > 2 MeV. Also there could be hidden effects only at < 2 MeV from C. Pena-Garay

6. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 6 Radiochemical experiments  cumulative measurement of the integral solar neutrino interaction rate (as opposed to real-time event detection)  no spectral or directional information After long time operation of these first generation experiments (Cl, Ga), the statistical errors equal the intrinsic systematic errors. The success of these experiments implies their end. However, they have been crucial in paving the way into the excitement of the third millenium!

7. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 7 1986 - 1990 May 1991 – May 1992 Construction of the detector GALLEX I data taking 15 Solar runs, 5 Blanks PL B285 (1992) 376 PL B285 (1992) 390 Jun 1994 – Oct 19941 st 51 Cr source experiment PL B342 (1995) 440 Oct 1995 – Feb 19962 nd source 51 Cr experiment PL B420 (1998) 114 Feb 1997 – Apr 1997Test of the detector with 71 As PL B436 (1998) 158 Apr 1998 – Apr 2003 GNO data taking 83.4 ± 19 SNU GALLEX Final Result 1594 days – 65 runs: 77.5 ± 7.7 SNU Feb. 1997End of Solar Data Taking PL B447 (1999) 127 PL B490 (2000) 16 PLB B616(2005)174 GALLEX/GNO Time Table

8. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 8 Granada, June 8th, 1992 GALLEX announces first observation of solar pp-neutrinos at „Neutrino 92“

9. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 9 de Rujula

10. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 10 GALLEX RESULT IMPLICATIONS (1992) PL B285 (1992) 376  60 % of the SSM expectation  Definite deficit of 7 Be (or pp-) neutrinos observed  105 % of pp- expectation  Hydrogen fusion in the solar interior experimentally observed

11. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 11 Significance of Deficit in Time

12. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 12 GALLEX Final Result 1594 days – 65 runs: 77.5 ± 7.7 SNU

13. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 13 Cr source experiments

14. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 14 Cr source results

15. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 15 Arsenic Tests Repeated tests under variable and purposely unfavorable conditions respective to the  standing time  mixing- and extraction conditions  method and magnitude of carrier addition to exclude witholdings (classical or ‘hot-atom’-effects) Method Triple-batch comparison  30 000 71 As atoms added to: Tank sample External sample Calibration sample (  -spectrom.) Result: Recovery 99+ %

16. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 16 GALLEX 65 Solar runs = 1594 d 23 Blank runs GNO 58 Solar runs = 1713 d 12 Blank runs 62.9 +5.5 –5.3 ± 2.5 SNU 77.5 ± 6.2 ± 4.5 SNU 51 Cr source-, 71 As experiments GALLEX + GNO results

17. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 17 GNO 62.9 ± 6.0 5.9 SNU GALLEX77.5 ± 7.6 7.8 SNU GALLEX+GNO69.3 ± 5.5 SNU SAGE 66.9 ± 5.3 5.0 SNU Range of SSM predicted rates: No oscillations: 122 – 131 SNU With oscillations 68 – 72 SNU (global fit) FINAL RESULTS

18. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 18 2 RECENT UPDATE Results of a recent complete re-analysis of the Gallex data * (using ~10 5 Ge-decays per counter) not allowed before completion of the low rate measurment phase (solar runs) - Improved Rn-cut efficiency (multi-year low-rate - Counter efficiency error reduction after full calibration experiment) - full PSA instead of RTA Also for Cr-source data -Counter efficiency error reduction after full calibration (as above) - solar subtraction to include also GNO data * F. Kaether, PhD Thesis, Heidelberg University, July 2007

19. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 19 GALLEX Periods (new vs. old) old (RTA) new (PSA ect.)

20. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 20 GALLEX77.5 ± 7.6 7.8 SNU re-evaluated73.1 ± 7.1 7.3 SNU GNO (unchanged)62.9 ± 6.0 5.9 SNU GALLEX+GNO69.3 ± 5.5 SNU re-evaluated 67.5 ± 5.1 SNU Updated Results

21. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 21 Cr- source update Mean S1+S2: 93 ± 8% (1  ) Gallex PL (1998) Re-evaluated: 88 ± 8% (1  ) Thesis Kaether (2007) The expectation value for ground state only is 95 ± 1% Bahcall PR C (1997) Our 71 As-experiment excludes Ge-yield errors >1% Consequences  The excited state contribution is probably close to 0, instead of (5 ± 3)% as estimated by Bahcall. Supported also by the SAGE Cr-source result.  The 71 Ge production rate prediction on Ga (without oscillatons) must be reduced by ~2 SNU from 7 Be- (32.7 SNU instead of 34.8 SNU). [no change for pp- ]

22. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 22 Oscillation parameters If the LMA(MSW) solution is the correct explanation of the SNO/SK data, then vacuum oscillations must dominate below 1 MeV and the mixing angle is estimated as  = 32  1.6 degrees (B-PG04) From our data we extract the e-e survival probability P ee for pp-neutrinos after subtraction of the 8 B and 7 Be contributions based on the experimentally deter- mined 8 B- (SNO/SK) and 7 Be- (Borexino) neutrino fluxes as P ee (pp only) = 0.52 ± 0.12 THE RESULTS IMPLY THE EXPERIMENTAL VERIFI- CATION OF THE SOLAR MODEL AND OF THE NEUTRINO OSCILLATION MECHANISMNS AT sub-MeV ENERGIES THAT ARE OTHERWISE INACCESSIBLE

23. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 23 Partitioning of the Gallium Cake SNUP ee Experim. measured68 ± 5GX/GNO 7 Be exp 22 ± 70.68 ± 0.20Borexino 8 B exp 4 ± 10.33 ± 0.08SK + SNO 13 N, 15 O4.5 +1 -3 ~0.5 (assumed) - pep1.5 ±.5~0.5 (assumed) - pp only36 ± 80.52 ± 0.12Gallium (Experiments, SSM and LMA)

24. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 24 3WHY DID WE STOP? Reasons that existed to continue GNO as long as real-time pp-neutrino detection was (and still is) a long way to go Continous pp-neutrino monitoring is an astrophysical necessity pp-observations simultaneously with Borexino real-time beryllium neutrino observations Further neutrino source experiments to improve the knowledge of relevant cross sections

25. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 25 Reflections on the causes for the termination of the experiment Quote: „ The Gallium Neutrino Observatory (GNO) is the price that Italy‘s underground lab is paying to get back on its feet after a small chemical spill nearly two years ago“ (Toni Feder, Physics Today, May 2004) No confusion: The spill occured in Hall C (Borexino) GALLEX/GNO (in Hall A) never spilled a single drop of liquid. Ironically, GALLEX introduced the double spill tray safety conception in 1986, almost 20 years before it now became mandatory for the Laboratory The GALLEX corpse feeded Borexino for survival (the laws of nature)

26. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 26 The End April 6, 2005 : GNO17, the last regular (semi-annual) GNO meeting was held in Assergi Febr 28, 2006: Final Celebration Ceremony for GALLEX/GNO at Gran Sasso, ending a successful fifteen year period that started with the Inauguration Ceremony on November 30, 1990 (Gallium was sold in April 2007 to Recapture Metals Inc., Ontario, Canada)

27. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 27 GALLEX- Inauguration at GRAN SASSO 30.11.1990 The Future In n… years: Determine pp-neutrino flux directly with low threshold real-time experiments (Xe, Borexino,…?) n = 3,4,5,6…?

28. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 28 In memoriam

29. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 29 Luciano Paoluzi † 2002

30. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 30 Michael Altmann † 31 July 2006

31. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 31 Nicola Ferrari † 31 July 2006

32. Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 2007 32 Keith Rowley † 29 October 2006