GNO and the pp - Neutrino Challenge  T.Kirsten/GNO 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

Purpose: detection of low energy solar neutrinos 71 Ga( e,e) 71 Ge (E thr = 233 keV) Basic interaction: EC,  = 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: SNU 72 SNU 35 SNU 10 SNU 13 SNU 8 B 10% CNO 8% 7 Be 27% pp+pep 55% More details can be found on the webpage GNO - Gallium Neutrino Observatory

 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 GNO Collaboration

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 st 51 Cr source experiment PL B342 (1995) 440 Oct 1995 – Feb 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 – Now Start of GNO data taking 83.4 ± 19 SNU GALLEX Final Result 1594 days – 65 runs: 77.5 ± 7.7 SNU GALLEX Feb. 1997End of Solar Data Taking PL B447 (1999) 127

Significance of Deficit in Time

Neutrino Source Exposure

Source results

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:  As atoms in: Tank sample External sample Calibration sample (  -spectrometry) Result: Recovery 99+ %

GNO – Results completed52 solar runs1547 days still counting 7 solar runs 200 days blanks GNO 65.2 ± 6.4 ± 3.0 SNU (L 70. ± 10. K 62. ± 8.) GALLEX77.5 ± SNU GALLEX+GNO 70.8 ± 4.5 ± 3.8 SNU

GALLEX - GNO Davis plot GALLEX 65 solar runs GNO 52 solar runs

GALLEX +GNO Seasonal variations Winter-Summer (statistical error only): GNO only (52 SRs): Winter (26 SR): SNU Summer (26 SR): SNU W-S: -8 ± 16 SNU GNO + Gallex (117 SRs): Winter (60 SR): SNU Summer (57 SR): SNU W-S: -5 ± 12 SNU

Improvements ItemGallexGNO Target size0.8% Chemical yield2.0% Counting efficiency (active volume determ.) 4.0%2.3% Pulse shape cuts2.0%1.3% * Event selection (others)0.3%0.6% Side reactions1.2 SNU Rn-cut inefficiency1.2 SNU0.8 SNU 68 Ge contamination +1.8 SNU -2.6 SNU - * Neural network analysis

Why sub-MeV Neutrinos? 1.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.

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 tang2θ 12. To obtain Δ  15%, the pp-flux must be determined to  3 %

Depression Factor vs. Energy

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

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

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 ?

Outset on which we must improve (see Bahcall and Pena-Garay, hep-ph ) pp-flux: (1.01  0.02) x BP00 SSM (1  ) (with luminosity constraint) 7 Be-flux: ( ) x BP00 SSM (1  ) tang 2 θ 12 = = (LMA: Δm 2 = ( ) x eV 2 ; no hope to improve on this from GNO/Borexino) f Ga,cc = 0.55  0.03 (1  )

CC / NC Response

Determination of the pp-neutrino flux from GNO and Borexino

Deduction of the pp-flux

E (MeV) P ( e  e ) Survival probabilities P pp = % P pep = % P 7 = 0, % P 8 = % P CNO = % C. Cattadori, N. Ferrari Survival probabilities

Capture cross sections type  Err% TransitionsSignal/SSM % Errors from  cm2 %GS 1,2 >2 (with MSW LMA) GS 1,2 >2 pp pep Be B N O TOT Capture cross sections

Future Plans in GNO

Future Neutrino Source Exposures

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 6.5 MegaCurie with the available material. The immediate project is a  3 MCi source for GNO (next major experimental step)

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