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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

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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 86 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)
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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
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What did change between GALLEX and GNO ?

• Collaboration (a restricted part of the GALLEX
  coll. lAquila Univ.)
• Analog electronics (LV,HV, preamp and amp,analog
  BW from 100 MHz ? 300 MHz)
• Digital electronics (no multiplexing, 1 digitizer
  per line _at_ 5Gs/s and DAQ
• The resulting noise figure is lt 2 mV r.m.s. _at_
  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
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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.

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GNO results updated at 3-may-01
Selection SR SNU N 71Ge 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 LK 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 LK 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 LK 68.9 7.3 (stat) 3.2 (sys) 68.9 7.3 (stat) 3.2 (sys) 68.9 7.3 (stat) 3.2 (sys)
GALLEX L 65 74.4 10
GALLEX K 79.5 8.2
GALLEX LK 77.5 6.2 (stat) 4.5 (sys) 77.5 6.2 (stat) 4.5 (sys) 77.5 6.2 (stat) 4.5 (sys)
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• 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

Refinement of the GNO I results
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GNO II single Solar Runs
Run lable Start exp. End exp. Exp time Chem Yield Counting SNU LK
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
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GNO II single Solar Runs (follows)
Run lable Start exp. End exp. Exp time Chem Yield Counting SNU LK
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
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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
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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
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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)
Run lable Start exp. End exp. Exp Time d Chem Yield Counting d Excs Cnts Bckg Cnts 160 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
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Time dist. of selected ev. Superimposed the
N(t)a b exp(-t/t) which gives the best
Log(L) t16.48 days
counts/day/run
35 GNO solar runs
Time d
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100 runs
GALLEX
GNO
GALLEX GNO 73.9 ? 4.7 (stat)? 4.0 (sys)
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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 2L(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.
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GALLEX
GNO
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Single runs SNU values distributions
GALLEX GNO
2L(GNO1 GALLEX single runs)/L(global
dist) 93.677 D.O.F. 83 C.L. 19
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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
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Seasonal variations expected in GNO in the 2n
MSW scenario
Fogli et al. hep/ph/9910387
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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 01 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
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Fit of the pulses
(Fit-data) amplified
Fit function
Charge dist. function
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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
NN RT
L evnts 95.3 96.6
K evnts 94.0 96.3
NN 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 b/g more efficiently. When the Rn
meas. is analyzed with the fitNN 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)
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Time distribution of selected events 35 GNO runs
RT ev selection
Reduction of bckgr NN vs RT analysis 15
NN ev selection
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Single runs SNU values distributions
GNO NN selection
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• 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 lt 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) 69.13.3 -2.1 0.85 0.11
Average 0.93 0.08 (PLB420(1998)114) Lat
er 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
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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 RD work in an advanced phase but
the technique is very different And an eventaual
implementation on site not so near.
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• 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)? 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.

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• 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)