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TAUP 2001 - LNGS 8-12 September 2001

TAUP 2001 - LNGS 8-12 September 2001. Updated results from GNO at LNGS. C.Cattadori – INFN Milano. on behalf of the GNO collaboration. Summary: Introduction Major changes GNO vs GALLEX Update of GNO meas. of solar n e interaction rate 16 new solar runs + 6 blanks

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TAUP 2001 - LNGS 8-12 September 2001

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  1. TAUP 2001 - LNGS 8-12 September 2001 Updated results from GNO at LNGS C.Cattadori – INFN Milano on behalf of the GNO collaboration • Summary: • Introduction • Major changes GNO vs GALLEX • Update of GNO meas. of solar ne interaction rate • 16 new solar runs + 6 blanks • and combination with GALLEX • Neural Network analyis • Future plans • Conclusions

  2. Motivations: Measure the low energy solar neutrinos interaction rate, whose flux is strictly related to solar luminosity (i.e. model independent), with an accuracy of 5 SNU, examine its constancy over 1 solar cycle with a sensitivity of ~ 15 %. 71Ga(ne,e)71Ge (Ethr = 233 keV) EC t = 16.5 d 71Ga Basic interaction PP 73 SNU (56%) 7Be 35 SNU (27%) CNO 9 SNU ( 7%) 8B 12 SNU (10%) Tot 129 SNU+8–6 1s n Signal Composition: (BP00 SSM) Expected Signal (SSM) 1.2 n int. per day, but due to decay during exposure + ineff., 9 71Ge decay detected per extraction (28 days exposure)

  3. Radiochemical - Target: 30 t of natGa (12 t of 71Ga) in 102 t of Ga3Cl acid sol. Technique Detector description and operation See f.i. PL B490(2000)16 PL B314(1993)445 What is a run? Add 1 mg of carrier In synthesis lab Extract GeCl4 12 h GeCl4 10 h t0 In tank GeH4 + Xe in counter V =1cc Wait 21-28 d for SR 1 d for blanks Counter in shielding Stop counting Remove counter 6 months

  4. What did change between GALLEX and GNO ? • Collaboration (a restricted part of the GALLEX coll. + l’Aquila Univ.) • Analog electronics (LV,HV, preamp and amp,analog BW from 100 MHz  300 MHz) • Digital electronics (no multiplexing, 1 digitizer per line @ 5Gs/s and DAQ • The resulting noise figure is < 2 mV r.m.s. @ 300 MHz on digitizer • Counter calibration with an X ray tube • More severe criteria to select counter to be used in solar runs • Revaluation of residual bckgr due to internal Rn • Counter type and passive shielding • Extraction and sinthesys plants • Target and tank. What did not change

  5. This presentation • GNO II results relative to • 16 exposures 27-28 days long called Solar Runs (SR) • 6 exposures 1 day long called Blank Runs (BL) • From 13-jan-2000 untill 3-may-2001 • 17 extraction performed, only 1 run lost due to HV instability • counting live time 97% ; DAQ stops only for calibrations, monthly counter connection and improvements and or maintenance . • Analysis • The results presented here are obtained from our Standard Analysis based on two parameter (E-RT) Selection criteria • If the neural network analysis will pass all the validation steps, all the GNO runs will be reanalized and both the single run and the global run values could eventually change.

  6. GNO results updated at 3-may-01

  7. Algoritm for determination of E window (starting from Ce calibration) • Re-evaluation of Rn inefficiencies in the removal of Rn bckgr events • eineff = 7% ±5% (eineff = 9% ± 5% until PLB490 (2000)16) • Rn cut (3h dead time after ovfl only in first 30 days)  increase live time of meas of 1% • Introduced in side reaction subtraction the atm neutrino contribution (0.3 ± 0.3) SNU. Side reaction subtraction new value 4.55 SNU (old value 4.25 SNU) • 2 counter filled with 69Ge for absolute determination of volume efficiency. The newly determined values are used for the 6 runs (2 in GNO I + 4 in GNO II). • PLB490 (2000)16 This update • GNO I L ev. 80 +17.5– 16.2 71.1 +16.4–15.1 • GNO I K ev. 57.2 +12.4– 11.4 59.5 +12.9–11.9 • GNO I L+K 65.8 +10.2– 9.6 64.2 +10.1–9.5 Refinement of the GNO I results

  8. GNO II single Solar Runs For GNO I single runs see PLB 490(2000)16

  9. GNO II single Solar Runs (follows) For GNO I single runs see PLB 490(2000)16

  10. Starting point: pulses from counters 800 mV 1100 mV A typical 0.5 keV event TDF 2 TDF 1 400 ns 400 ns Bi Po TDS 8 ms 800 ms

  11. Energy dist. of fast ev. Time dist. of selected events Superimposed the N(t)=a + b exp(-t/t) which gives the best Log(L) GNO counts/day/run Red – fast ev. t < 50 days Black – fast ev. t > 50 days Time [d] Energy [keV] 35 runs Time dist. of selected events. GALLEX counts/day/run Reduction of the bckgr GNO vs Gallex 30% 65 runs from 0.1 c/d/run to 0.07 c/day/run Time [d]

  12. GNO II Blank Runs Why Blank Runs? To check each 3 month the proper functionality of the whole setup (no tailig effect,background from isotopes other than 71Ge, ecc)

  13. Time dist. of selected ev. Superimposed the N(t)=a + b exp(-t/t) which gives the best Log(L) t=16.48 days 6 GNO blanks counts/day/run Time [d] counts/day/run 35 GNO solar runs Time [d]

  14. 100 runs GALLEX GNO GALLEX + GNO 73.9  4.7 (stat) 4.0 (sys)

  15. Single runs SNU values distributions Test of the hypothesis of constant signal over the entire period of GNO Ratio of L test 2(L/L) is distributed as a c2 2[L(single runs)/L(global dist)] = 31.2 D.O.F. = 34 C.L. = 60% 2L[(GNO1 + GNO2)/L(global dist)] = 0.4816 D.O.F. = 1 C.L. = 50% GALLEX GNO

  16. Single runs SNU values distributions GALLEX + GNO 2L[(GNO1 + GALLEX single runs)/L(global dist)] =93.677 D.O.F. = 83 C.L. = 19%

  17. Single run excess counts distribution Red histogram of single run GALLEX + GNO Blue simulation of 1000 runs where N71 and Bckgr fluctuate following a Poisson distribution around actual values N71 found in run

  18. Seasonal variations expected in GNO in the 2n MSW scenario Fogli et al. hep/ph/9910387

  19. K 71Ge b/g K main flag 71Ge L b/g L main flag A powerful alternative analysis: Neural Network The selection of events from solar runs can be carried out using a 3-levels neural network instead of Rise Time cuts (standard analysis) In the input neurons of the neural network there are five parameters coming from the fit of the pulse and characterizing its shape. (L ev: RT, c2, spread of the charge cloud) (K ev : the same as for L+ A1/A2 and dt for double peaks) The output is a flag value in 0÷1; if the flag is greater than 0.5 the event is accepted as 71 Ge, else it is rejected as background Distribution functions of the output flag for a sample of data containing both 71Ge and b/g events

  20. Fit of the pulses (Fit-data) amplified Fit function Charge dist. function

  21. Training of the Neural Network The NN is trained with genuine 71Ge pulses (from calibrations) as true examples and b/g from 137Cs or 222Rn as false examples. The number and the type of the training examples must be carefully chosen, as the overall efficiency of the network is very sensitive to these parameters Event selection efficiencies Noise rejection efficiencies Conclusions Although the Ge-efficincies are slighly smaller than the corrisponding values for the rise-time analysis, the NN is able to reject backgrond from b/g more efficiently. When the Rn meas. is analyzed with the fit+NN and after the Rn cuts (3h after alpha ev, 15 min before BiPO ev.) the inefficiency is 0. (inefficiency is 7% ± 5% for RT selection)

  22. Time distribution of selected events 35 GNO runs RT ev selection Reduction of bckgr NN vs RT analysis 15% NN ev selection

  23. Single runs SNU values distributions GNO NN selection

  24. Future plans • Last validation steps of the new NN analysis  increase S/N. • Next publication probably before end 2001 • Direct and absolute determination of volume efficiencies of all counters • by 69Ge measurements  reduce systematic < 3% (spring 2002 ?) • Production of a new 2.5 MCi 51Cr source to perform a 3rd irradiation Average 0.93 ± 0.08 (PLB420(1998)114) Later corrections 0.89 ± 0.07 Now take the echem from 71As exp. (1.00 ±0.01)%  the source exp. gives results on cross section 71Ga(ne,e)71Ge

  25. Proposal for a new source experiment Possibility to irradiate 11.5 Kg of Cr at SM3 reactor of RIAR (Dimitrovgrad) for 50 days to obtain a source 2.6 Mci on site (LNGS) The expected accuracy will be better than 8% When taken togheter with others exposure results this will lead to an Accuracy on s(750 keV) 5% New detector for 71Ge counting R&D work in an advanced phase but the technique is very different And an eventaual implementation on site not so near.

  26. Conclusions • GNO experiment is running smoothly and with a very high duty cycle since • may 1998 and GALLEX + GNO since 1991 • The updatedGNOresults (35 solar runs) is 68.9 ± 7.3 (stat)± 3.2 (sys) • and when combined with GALLEX73.9  4.7 (stat) 4.0 (sys) • Exp/SSM = 0.57 + 0.047 % • no seasonal variation is observed in the GALLEX+ GNO data • Winter-Summer = -9  10 SNU • the systematic error will be reduced before middle 2002 at 3% level • a new pulse analysis has been developped and if definetely validated will • be applied at the whole GNO data set.

  27. if refined at a 5% level, Gallium measurements give important constraints in the oscillation scenario f.i. (non)observation of seasonal effects, and when the 7Be meas will be available the very important PP flux will be derived. • high values of the GALLIUM exp. favour SMA, • Low values of “ “ “LOW and LMA • To reach the 5% accuracy level we have to improve • Statistic ( increase the target mass and continuously measure) • Join GNO and SAGE targets Why not? • Systematics (work is going on) • Knowledge of the cross section better then 5% (new source exp)

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