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Carla Maria Cattadori INFN Milano and Milano Bicocca Physics Department

Results from Solar Neutrino Radiochemical Experiments (with main emphasis on Gallium) Neutrino 2004, Paris 13-18 June 2004 . Carla Maria Cattadori INFN Milano and Milano Bicocca Physics Department. Results from Solar Neutrino Radiochemical Experiments.

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Carla Maria Cattadori INFN Milano and Milano Bicocca Physics Department

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  1. Results from Solar Neutrino Radiochemical Experiments(with main emphasis on Gallium)Neutrino 2004, Paris 13-18 June 2004 Carla Maria Cattadori INFN Milano and Milano Bicocca Physics Department

  2. Results from Solar Neutrino Radiochemical Experiments • Generalities about solar neutrinos and radiochemical experiments • Results of Chlorine, SAGE, GALLEX/GNO • Impact on • Neutrino Physics • Astrophysics • “Technological” results • Are precision measurements possible,with radiochemical experiments ? • Conclusions Carla Maria Cattadori

  3. Radiochemical experiments provided at the end of the ´60 the first indication of solar neutrino flux anomaly at Earth. (22 years after the Pontecorvo idea to exploit the reaction ne(N,N´)e-) to detect neutrinos.) Since then, they have continuously performed measurements of solar neutrino capture rate at Earth that, until year 2000 (before SNO), were of invaluable importance both to determine (Dm2,sin22q12) and for solar astrophysics. Nowadays, in the SNO + KamLAND era, their role is changed; having almost no weight in the neutrino oscillation parameters determination (3 values over 44SK+ 34 SNO + 13 KL +3 Rchem= 94) they are still the only experiments that have detected sub-MeV (7Be, pp) neSun. Therefore they are the experimental verification at low energy of solar models neutrino oscillation mechanism Generalities on radiochemical experiments Carla Maria Cattadori

  4. Generalities on radiochemical experiments • Nowadays, in the neutrino community, radiochemical experiment are considered like turtles (“protected” ancient animals): • they are slow, low statistic experiment • they are sensitive only to ne • they measure only one quantity (the integral solar neutrino interaction rate). • they do not measure spectrum or incoming direction of solar neutrinos. • It is common opinion that having reached a statistical accuracy almost equal to the systematic accuracy they have almost accomplished their role. Carla Maria Cattadori

  5. Generalities on radiochemical experiments • CC experiments sensitive only to ne. Proposed by Pontecorvo in 1946. • N' (unstable) is then separated from the target with physical-chemical techniques and then quantitatively measured observing its decay back in N. • as • 1 Solar Neutrino Unit [SNU] = 1 n interaction/sec each 1036 target atoms. • Ntarget = 1029-1030nuclei,namely O(10-100) tons of target to have O(1) n interaction/day Carla Maria Cattadori

  6. The Pioneer: Chlorine Experiment 37Cl(ne,e)37Ar (Ethr = 813 keV) KshellEC t = 50.5 d 37Cl + 2.82 keV (Auger e-, X) The interaction pep+hep0.15 SNU ( 4.6%) 7Be 0.65 SNU (20.0%) 8B 2.30 SNU (71.0%) CNO 0.13 SNU ( 4.0%) Tot 3.23 SNU± 0.681s nSignal Composition: (BP04+N14 SSM+ n osc) Expected Signal (BP04 + N14) 8.2 SNU+1.8–1.81s Carla Maria Cattadori

  7. The Chlorine experiment Carla Maria Cattadori

  8. Results of Chlorine experiment • First measurement of solar neutrino interaction rate • Raised the problem of missing neutrinos • Opened a field of research that is not yet closed. Davis awarded in 2002, with the Nobel prize together with Koshiba and R. Giacconi • “for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos" R = 2.56 ± 0.16 ± 0.16 SNU = 2.56 ± 0.23 Constancy of the solar neutrino flux (over 23 years): no correlation has been found between RnSun and the solar cycle (many speculation on this item in the ‘90) Carla Maria Cattadori

  9. SAGE - The Russian-American Gallium Experiment Gallium experiments Carla Maria Cattadori

  10. SAGE Carla Maria Cattadori

  11. 71Ga(ne,e)71Ge (Ethr = 233 keV) K,L shellEC t = 16.5 d 71Ga + 10 keV, 1 keV (Auger e-, X) GALLIUM Experiments Gallium Experiments The interaction (proposed by Kuzmin in 1966) pp + pep 41.7 SNU ( 62%) 7Be 19.0 SNU (28 %) CNO 2.6 SNU ( 3.9 %) 8B 4.1 SNU ( 6.1 %) Tot 67.4 SNU+2.6–2.31s No osc 127 SNU +12–10 nSignal Composition: (BP04 +N14 SSM+ n osc) 0.6n int. per day in GNO (1 in SAGE), but due to decay during exposure + ineff., 4.771Ge decay detected per extraction (28 days exposure). Expected Signal (SSM + n osc) Carla Maria Cattadori

  12. New !! Gallium Experiments 68.1 ± 3.75 (5.5%) New combined value Carla Maria Cattadori

  13. SAGEJanuary 1990 – December200314 years – 121runs66.9 +5.3-5.0 SNU See poster session ! 51Cr source experiments Carla Maria Cattadori

  14. GNO 58 Solar runs = 1713 d 12 Blank runs GALLEX 65 Solar runs = 1594 d 23 Blank runs 77.5 ± 6.2 ± 4.5 SNU 62.9 +5.5–5.3 ± 2.5 SNU 51Cr source, 71As experiments See poster session ! Carla Maria Cattadori

  15. Balance of the signal in L/K region within 1s, events are equally distributed between L and K window, as expected from counting efficiencies Carla Maria Cattadori

  16. The signal is validated for both SAGE and GALLEX/GNO by 1 keV Event energy distribution Important! No other peaks appear in the spectrum 10 keV tfit = 16.6 ± 2.1 days t76Ge = 16.5 days Event time distribution. Analysis: M.L. analysis. Null hypothesys: 1 decaying isotope + flat backgrd (independent /each run) Carla Maria Cattadori

  17. GALLEX/GNO seasonal variation analysis bi-monthly binning of the whole data set perihelion aphelion Flat: c2= 2.7 (5 d.o.f.), C.L.: 75% Elliptical: c2= 3.0 (5 d.o.f.) C.L.: 70% Carla Maria Cattadori

  18. GALLEX +GNO Seasonal variations Included in the analysis by Fogli and Lisi Winter-Summer(statistical error only): GNO only (58 SRs): Winter (32 SR): 58.7+7.1-6.8 SNU Summer (26 SR): 69.0+8.8-8.3 SNU W-S: -10 ± 11 SNU(expected from 1/d2: +2.5) GNO + Gallex (123 SRs): Winter (66 SR): 66.5+5.6-5.4 SNU Summer (57 SR): 74.1+6.4-6.2 SNU W-S: -7.6 ± 9 SNU(expected from 1/d2: +2.5) Carla Maria Cattadori No excess in W-S, as expected for LMA !!

  19. SAGE survey of time modulations No evidence of time modulation binning the all data set monthly, bimonthly, yearly. Carla Maria Cattadori

  20. Search for time modulations in GALLEX/GNO data Claim from Sturrock and Caldwell of a significant peak in the periodogram plot of GALLEX data (and also SK) astro-ph/0103154 and subsequent (1 / years) Lomb–Scargle analysis is a Fourier analysis for data not equally spaced in time. We have repeated the analysis, found the same periodogram, but we don’t agree on the significance of the signal at 13.5 y-1 Random gaussian fluctuations Carla Maria Cattadori

  21. Lomb-Scargle analysis L.-S. time series analysis of 58 simulated GNO-like runs power 40 SNU error on single sun 0.1% CL frequency (y-1) power 25 SNU error on single sun 0.1% CL Carla Maria Cattadori frequency (y-1)

  22. 1 = 69.3 SNU Rule out modulations with frequency < 12 y-1 and amplitude > 40% of signal Time modulation exclusion plot from GALLEX/GNO data Carla Maria Cattadori

  23. GALLEX GNO The capture rate published by both experiments has monotonically decreased in the last 5-6 years Carla Maria Cattadori

  24. m = 63 s = 43 m = 89 s = 55 m = 73 s = 52 GNO GALLEX GALLEX+GNO SAGE Carla Maria Cattadori

  25. combining SAGE and GALLEX/GNO period Jan 1990 – December 2003 68.1 ± 3.75 (5.5%) * this value is before the efficiencies re-evaluation * reduction of systematic obtained in GNO has not been propagated back to GALLEX Carla Maria Cattadori

  26. …. all this means that • it has been of crucial importance to proceed with the data taking so long. • RGa published by both experiments, has monotonically decreased in the last 6-7 years. The statistical significance of this decreasing in each experiment is low, but the joint probability….. • given the relevance that Gallium capture rate has and will have once the 7Be flux will be available from Borexino or Kamland, it is important that both collaborations investigate once more if necessary to select “golden data set”, (difficult and dangerous action!!) then perform a joint analysis to provide their joint best evaluation of Rnon Gallim (debate in the collaborations about this item) Carla Maria Cattadori

  27. Determination of Gallium-ne capture cross section Ga-ne capture cross sections are needed to compute fluxes from rate At low energy ( < 410 keV, namely for pp ns) only g.s.-g.s.transitions are present;for this transitioncross sections are evaluated from 71Ge E.C. good accuracy ( 2.3% at 1) At the 7Be energies, the first two excited state (at 175 and 500 keV) must be considered; BGT estimated from (p,n) reactions; estimated accuracy –3% +5% Direct measurement desirable Carla Maria Cattadori

  28. Experimental situation Two GALLEX and one SAGE calibrations, with strong 51Cr sources Rmeas= 0.93 ±0.07 Rtheo Improvements are well possible irradiating with a 2MCi source f.i. 20 tons of metallic gallium Final accuracy 5% or better = theoretical accuracy to addrees the question: corrections to g.s.-e.s. only or to g.s.-g.s. also? GALLEX sources: 1.71 MCi 1.87 MCi SAGE source 0.52 MCi Carla Maria Cattadori

  29. SAGE is at the moment irradiating 13.2 tons of its metallic Gallium with a 37Ar n source 614 kCi strenght: En (37Ar) > En (51Cr) improved sensitivity for second 71Ge e.s. 330 Kg of Ca2O3 SAGE 37Ar source: see details in SAGE poster Carla Maria Cattadori

  30. Gas processing efficiencies evaluation Data from neutrino source experiments can be used to infer on the cross section only once the extraction + gas processing efficiencies are exactly determined, and “hot chemistry” effect are excluded.This has been done by the GALLEX collaboration, spiking the target with O(10000) atoms of 37As, that beta decay to 76Ge, kinematically mimicking then interaction.The processing efficiency has been found to be correctly extimated (from the methods routinely adopted at each run) =100% with 1% error. Carla Maria Cattadori

  31. Impact of Gallium experimental results on neutrino oscillation parameters determination. Almost irrelevant with the actual experimental accuracy in the actual experimental scenario Carla Maria Cattadori

  32. 10 10 10-4 10-3 10-2 10-1 1 10-4 10-3 10-2 10-1 1 Allowed (Dm2,tan2q12) regions from Radiochemical experiments -4 Ga experiments are more sensitive to tan2q12 than toDm2 Carla Maria Cattadori

  33. Oscillation parameters vs (Ga rate + SSM) Theta=32.5° Theta=35° Theta=37.5° Theta=28.5° Theta=30° 0.954 0.970 Fpp 0.983 1.000 1.016 Carla Maria Cattadori Comments: No sensitivity within the presently allowed oscillation parameter region

  34. Impact of Gallium Results on Astrophysics Carla Maria Cattadori

  35. Solar Models R previsions for Radiochemical experiments from LUNA experiment on 14N(p,g)15O New S0(14N+p) = 1.77 keV ± 0.2 Columns 2,3,4 from BP04 Carla Maria Cattadori increased accuracy in 7Be(p,g)8B measurement

  36. …… to summarize BP00 with Z/Xold= 0.0229 BP04 = BP00 + New data on EOS, Nucl Phys.(Cross sections) N14 = BP04 + S0(14N+p) = 1.77 keV ± 0.2 BP04+ = BP04 + Z/Xnew=0.0176 to be compared with Carla Maria Cattadori

  37. Solar Models R previsions for Radiochemical experiments † (best fit point all solar + KamLAND data. 8B flux free, other fluxes from BP00) * (best fit point all solar + KamLAND data; all n fluxes free+ lum. constr.) Carla Maria Cattadori

  38. Comparison of solar model predictions with experimental results • Neutrinos prefer a Sun having “low metallicity” solar interior, as the recent photospheric measurements indicate • when this data are included in the SSM  tension with helioseismology as the depth of the convective zone goes to 0.726 Rsun (instead of 0.713 as measured i.e. 18% discrepancy). Carla Maria Cattadori

  39. and knowing from experiments RGa which is given by the sum of all the neutrino components, weighted by the cross section and Pee LCNOestimate from Gallium experimental results imposing the luminosity constraint Assumption: nuclear fusion reactions are the only source of energy in the Sun Carla Maria Cattadori

  40. Gallium Uncertainties for evaluation of pp and CNO n flux Carla Maria Cattadori

  41. …..it is possible to estimate at the same time Fpp and FCNO once we know the 8B, 7Be, pep fluxes • 8B take from experiments • 7Be take from SSM • pep strictly related to pp Carla Maria Cattadori

  42. Important!Here the solar model N14 (Bahcall nomenclature) is used as reference, i.e. the unity on the Y axis take already into account the reduced flux due to new S0(14N) measurement 3  limit 3  luminosity constraint 2  1  best fit Carla Maria Cattadori

  43. Carla Maria Cattadori

  44. Finally with the listed assumptions and from the capture rate measured in Gallium experiments it is possible to determine Fantastic agreement !! Carla Maria Cattadori

  45. …. for 8B and 7Be F(8B)meas = (0.89 ± 0.04ex ± 0.23theo) F(8B) BP04 + N14 F(7Be)meas = (0.91+0.24-0.62 ex ± 0.11theo) F(7Be) BP04+N14 from BP04 Carla Maria Cattadori

  46. GALLEX/GNO - all uncertainties Comments: perfect agreement of Ga rate with SSM + oscillation scenario F(pp) probed at 2% level (1 sigma) F(CNO) < 3.5 SSM (2 sigma) But to be totally model independent we need a measurement of F(Be) at 10% 0.954 Experimental constraint Experimental constraint 0.970 SSM prediction Fpp SSM prediction 0.983 1.000 1.016 Measured Carla Maria Cattadori R = 69.3 +- 5.5 SNU

  47. GNO- all uncertainties Comments: GNO is compatible with SSM + oscillation scenario at the level of 1 s low values of the CNO flux are favored 0.954 0.970 Fpp 0.983 1.000 1.016 GNO is at border of physical region Measured Carla Maria Cattadori R = 62.9 +- 6.0 SNU

  48. GALLEX- all uncertainties Comments: GALLEX is compatible with SSM + oscillation scenario within 2s The effect of GNO is important in the probe of the solar luminosity 0.954 0.970 Fpp 0.983 1.000 1.016 Measured Carla Maria Cattadori R = 77.5 +- 7.7 SNU

  49. Gallium- 5% error 0.954 0.970 Fpp BP00 0.983 1.000 1.016 Carla Maria Cattadori R = 70.0 +- 3.5 SNU

  50. Are precision measurements possible with Gallium radiochemical experiments? Carla Maria Cattadori

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