TAUP 2001 - LNGS 8-12 September 2001

Updated results from GNO at LNGS

C.Cattadori – INFN Milano

Summary:

• Introduction• Major changes GNO vs GALLEX• Update of GNO meas. of solar e interaction rate

16 new solar runs + 6 blanks and combination with GALLEX• Neural Network analyis • Future plans• Conclusions

Summary:

• Introduction• Major changes GNO vs GALLEX• Update of GNO meas. of solar e interaction rate

16 new solar runs + 6 blanks and combination with GALLEX• Neural Network analyis • Future plans• Conclusions

on behalf of the GNO collaboration

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 %.

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 %.

Basic interactionBasic interaction

71Ga(e,e)71Ge (Ethr = 233 keV)EC = 16.5 d 71Ga

71Ga(e,e)71Ge (Ethr = 233 keV)EC = 16.5 d 71Ga

Signal Composition:(BP00 SSM) Signal Composition:(BP00 SSM)

PP 73 SNU (56%)7Be 35 SNU (27%)CNO 9 SNU ( 7%)8B 12 SNU (10%)Tot 129 SNU +8

–6 1

PP 73 SNU (56%)7Be 35 SNU (27%)CNO 9 SNU ( 7%)8B 12 SNU (10%)Tot 129 SNU +8

–6 1

Expected Signal (SSM)Expected Signal (SSM)

1.2 int. per day, but due to decay during exposure + ineff., 9 71Ge decay detected per

extraction (28 days exposure)

1.2 int. per day, but due to decay during exposure + ineff., 9 71Ge decay detected per

extraction (28 days exposure)

TechniqueTechnique Radiochemical - Target: 30 t of natGa (12 t of 71Ga) in 102 t of Ga3Cl acid sol.Radiochemical - Target: 30 t of natGa (12 t of 71Ga) in 102 t of Ga3Cl acid sol.

See f.i. PL B490(2000)16PL B314(1993)445

See f.i. PL B490(2000)16PL B314(1993)445

Detector descriptionand operation

Detector descriptionand operation

What is a run?What is a run?

Add 1 mg of carrier

ExtractGeCl4

12 h

Wait 21-28 d for SR 1 d for blanks

GeCl4

GeH4 + Xein counter V =1cc

10 ht0

In tank

In synthesis lab

Counter in shielding 6 months

Stop countingRemove counter

What did change between GALLEX and GNO ?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

What did not changeWhat did not change• Counter type and passive shielding• Extraction and sinthesys plants• Target and tank.

This presentationThis 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 .

AnalysisThe 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.

GNO results updated at 3-may-01GNO results updated at 3-may-01

Selection SR SNU N71Ge

N. Bckgr

GNO-I L 19 71.1 +16.4 –15.1 45 128

GNO-I K 59.5 +12.9 –11.9 43 76

GNO-I L+K 64.2 +10.1 –9.5 88 204

GNO-II L 16 81.5 +18.2 –17.0 43 82

GNO-II K 68.9 +14.3 –13.0 41 59

GNO-II L+K 74.1 +11.2 –10.7 84 141

GNO L 35 75.9 +12.1 –11.5

GNO K 64.0 + 9.4 – 8.9

GNO L+K 68.9 ± 7.3 (stat) ± 3.2 (sys)

GALLEX L 65 74.4 ± 10

GALLEX K 79.5 ± 8.2

GALLEX L+K 77.5 ± 6.2 (stat) ± 4.5 (sys)

•Algoritm for determination of E window (starting from Ce calibration)

•Re-evaluation of Rn inefficiencies in the removal of Rn bckgr events ineff = 7% ± 5% (ineff = 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

•Algoritm for determination of E window (starting from Ce calibration)

•Re-evaluation of Rn inefficiencies in the removal of Rn bckgr events ineff = 7% ± 5% (ineff = 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

GNO II single Solar RunsGNO II single Solar Runs

Run lable

Start exp.End exp.

Exptime

Chem Yield

Counting

SNUL+K

A024 13-01 / 9-02-00 27 91.2 165 77 +51 –39

A025 9-02 / 8-03-00 28 94.8 168 29 +51 –33

A026 8-03 / 5-04-00 28 97.7 167 3 +36 –24

A028 6-04 / 3-05-00 27 94.7 168 143 +57 –47

A029 3-05/31-05/00 28 93.0 166 81 +51 –39

A030 31-05/28-06-00 28 98.1 Lost

A032 29-06/26-07-00 27 93.9 168 69 +58 –46

A033 26-07/23-08-00 28 94.1 168 89 +48 –38

For GNO I single runs see PLB 490(2000)16

GNO II single Solar Runs (follows)GNO II single Solar Runs (follows)

Run lable

Start exp.End exp.

Exptime

Chem Yield

Counting SNUL+K

A034 23-08/20-09-00 28 97.2 167 47 +52 –40

A036 21-09/18-10-00 27 95.4 167 60 +41 –29

A037 18-10-/15-11-00 28 93.9 168 -12 +36 –24

A038 15-11/12-12-00 27 98.1 167 119 +54 –44

A040 13-12/10-01-01 28 96.2 164 103 +60 –49

A041 10-01/07-02-01 28 95 167 88 +44 –34

A042 7-02-01/7-03-01 28 97.8 140+ 51 +47 –36

A044 8-03/4-04-01 27 92.3 115 + 118 +63 –53

A045 4-04-01/3-05-01 29 95.1 100 + 62 +40 –32

For GNO I single runs see PLB 490(2000)16

800 mV 1100 mV

400 ns 400 ns

8 s800 s

TDF 1

TDF 2

Bi Po TDS

A typical 0.5 keV event

Starting point: pulses from counters

GALLEX

Time [d]

cou

nts

/day

/ru

n

Time dist. of selected events.

GNO

Time [d]

cou

nts

/day

/ru

n

Time dist. of selected events

Superimposed the N(t)=a + b exp(-t/)which gives the best Log(L)

Energy [keV]

Red – fast ev. t < 50 daysBlack – fast ev. t > 50 days

Energy dist. of fast ev.

65 runs

35 runs

from 0.1 c/d/run to 0.07 c/day/run

GNO II Blank RunsGNO II Blank Runs

Run lable

Start exp.End exp.

ExpTime

[d]

Chem Yield[%]

Counting[d]

ExcsCnts

BckgCnts160 d

A023 12-01/13-01-00 27 91.2 165 1.4 8.6

A027 5-04 / 6-04-00 28 94.8 166 0.0 15.0

A031 28-06 / 29-06-00 28 97.7 164 0.0 11.0

A035 20-09 / 21-09-00 27 94.7 166 1.7 5.3

A039 12-12/13-12-00 28 93.0 165 1.3 8.7

A043 7-03/8-03-01 28 98.1 166 0.7 9.3

3.7 59.3

Average per run

0.85 ± 0.73

9.65 ± 3.2

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)

Time [d]

35 GNO solar runsco

un

ts/d

ay/r

un Time dist. of selected ev.

Superimposed the N(t)=a + b exp(-t/)which gives the best Log(L)=16.48 days

6 GNO blanks

Time [d]

cou

nts

/ day

/ru

n

GALLEX + GNO 73.9 4.7 (stat)(sys)GALLEX + GNO 73.9 4.7 (stat)(sys)

Single runs SNU values distributions

GALLEX

GNO

Test of the hypothesisof constant signal over the entireperiod of GNO

Ratio of L test2(L/L) is distributed as a 2

2[L(single runs)/L(global dist)] = 31.2D.O.F. = 34C.L. = 60%

2L[(GNO1 + GNO2)/L(global dist)] = 0.4816

D.O.F. = 1C.L. = 50%

Single runs SNU values distributions

GALLEX+

GNO

2L[(GNO1 + GALLEX single runs)/L(global dist)]

=93.677

D.O.F. = 83

C.L. = 19%

Red histogram of single run GALLEX + GNOBlue simulation of 1000 runs where N71 and Bckgr fluctuate following a Poisson distribution around actual values

N71 found in run

Single run excess counts distribution

Fogli et al. hep/ph/9910387

Seasonal variations expected in GNO in the 2 MSW scenario

Distribution functions of the output flag for a sample of data containing both 71Ge and events

K main flag

71Ge

L main flag

71Ge

A powerful alternative analysis:Neural Network

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)

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, 2, 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

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, 2, 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

Charge dist. function

(Fit-data) amplified

Fit function

Fit of the pulses

Training of the Neural Network

The NN is trained with genuine 71Ge pulses (from calibrations) as true examples and 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

Training of the Neural Network

The NN is trained with genuine 71Ge pulses (from calibrations) as true examples and 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 efficienciesEvent selection efficienciesNN RT

L evnts 95.3% 96.6%

K evnts 94.0% 96.3%

Noise rejection efficienciesNoise rejection efficienciesNN RT

L evnts 87.8% 65.7%

K evnts 77.1% 73.5%

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 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)

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 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)

Time distribution of selected events 35 GNO runs

Time distribution of selected events 35 GNO runs

Single runs SNU values distributions

GNO NN selection

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

Intensity exp/theo

I (may 1995) 63.4 +1.1 -1.6 1.01 ± 0.11

II (sept 1996) 69.1+3.3 -2.1 0.85 ± 0.11

Average 0.93 ± 0.08 (PLB420(1998)114)Later corrections 0.89 ± 0.07

Now take the chem from 71As exp. (1.00 ±0.01)% the source exp. gives results on cross section 71Ga(e,e)71Ge

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 anAccuracy on (750 keV) 5%

New detector for 71Ge countingR&D work in an advanced phase but the technique is very differentAnd an eventaual implementation on site not so near.

Conclusions

•GNO experiment is running smoothly and with a very high duty cycle since may 1998 and GALLEX + GNO since 1991

•The updated GNO results (35 solar runs) is 68.9 ± 7.3 (stat) ± 3.2 (sys) and when combined with GALLEX 73.9 4.7 (stat)(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.

• 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)

•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.