Results from Solar Neutrino Radiochemical Experiments (with main emphasis on Gallium) Neutrino 2004, Paris 13-18 June 2004

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

3
Generalities on radiochemical experiments
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.

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 1029-1030 nuclei, namely O(10-100) tons
  of target to have O(1) n interaction/day

6
The Pioneer Chlorine Experiment
The interaction
pephep 0.15 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 0.68 1s
n Signal Composition (BP04N14 SSM n osc)
Expected Signal (BP04 N14)
8.2 SNU 1.81.8 1s
7
The Chlorine experiment
Name Location ne interaction reaction Target comp. and mass Exp. Time d d Data taking
Name Location Lab overburden Target comp. and mass Exp. Time d d Data taking
Chlorine (Homestake Mine)South Dakota USA ne(37Cl,37Ar)e- C2Cl4 615 tons Liquid 60-120 50.5 1964- 1994
Chlorine (Homestake Mine)South Dakota USA 4200 mwe C2Cl4 615 tons Liquid 60-120 50.5 1964- 1994
Name Location Data used for R determination N runs Average efficiency Hot chem check Source calib
Chlorine (Homestake Mine)South Dakota USA 1970-1994 108 ltegtextr 95 ltegtsynth (95.8 0.7) ltegtcount 42 36Cl No
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 Rn
Sun and the solar cycle (many speculation on this
item in the 90)
9
Gallium experiments
10
SAGE
Collaboration ne interaction reaction Target comp. and mass Exp. Time d Data taking
Collaboration Lab overburden Target comp. and mass Exp. Time d Data taking
GALLEX/ GNO LNGS Italy D (MPIK,TUM), I (INFN), F (CEA), USA (BNL), Israel ne(71Ga,71Ge)e- GaCl3 HCl in H2O 103 t (30 t Ga) 21-28 28 1991-2003
GALLEX/ GNO LNGS Italy D (MPIK,TUM), I (INFN), F (CEA), USA (BNL), Israel 3500 mwe 0.6 m h m2-1 GaCl3 HCl in H2O 103 t (30 t Ga) 21-28 28 1991-2003
SAGE Baksan Kabardino Balkaria RU (INR, RAS) USA (LNL,BNL) ne(71Ga,71Ge)e- Metallic Ga 50 tons 28 1990-ongoing
SAGE Baksan Kabardino Balkaria RU (INR, RAS) USA (LNL,BNL) 4800 mwe 0.1 m h m2-1 Metallic Ga 50 tons 28 1990-ongoing
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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 2.62.3 1s No
osc 127 SNU 12 10
n Signal Composition (BP04 N14 SSM n osc)
0.6 n int. per day in GNO (1 in SAGE), but due to
decay during exposure ineff., 4.7 71Ge decay
detected per extraction (28 days exposure).
Expected Signal (SSM n osc)
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Gallium Experiments
Data taking N runs Average Efficieny Tank to counter Hot chem check Source calib Rex SNU
GALLEX/GNO LNGS Italy 1991-2003 stopped 123 97 71As Yes twice 51Cr source 69.3 4.1 3.6 5.9 5.2 69.3 5.5
SAGE Baksan Kabardino Balkaria 1990-ongoing 121 90 No Yes 51Cr 37Ar 66.9 3.9 3.6 5.8 5.2 66.9 5.3 5.0
68.1 3.75 (5.5)
New combined value
13
SAGE January 1990 December200314 years 121
runs 66.9 5.3-5.0 SNU
See poster session !
51Cr source experiments
14
GNO 58 Solar runs 1713 d 12 Blank runs
GALLEX 65 Solar runs 1594 d 23 Blank runs
62.9 5.5 5.3 2.5 SNU
77.5 6.2 4.5 SNU
51Cr source, 71As experiments
See poster session !
15
Balance of the signal in L/K region
L K LK
GALLEX 74.4 10 79.5 8.2 77.5 6.2
GNO 68.2 8.9 8. 5 59.5 6.9 6.6 62.9 5.5 5.3
GALLEX/ GNO 70.9 6.6 67.8 5.3 69.3 4.1
SAGE 64.0 5.9-5.7 69.1 5.3-5.1 66.9 3.9-3.8
within 1s, events are equally distributed between
L and K window, as expected from counting
efficiencies
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)
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
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) 58.77.1-6.8
SNU Summer (26 SR) 69.08.8-8.3 SNU W-S -10
11 SNU (expected from 1/d2 2.5)
GNO Gallex (123 SRs) Winter (66 SR)
66.55.6-5.4 SNU Summer (57 SR) 74.16.4-6.2
SNU W-S -7.6 9 SNU (expected from 1/d2 2.5)
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.
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)
LombScargle analysis is a Fourier analysis for
data not equally spaced in time.
We have repeated the analysis, found the same
periodogram, but we dont agree on the
significance of the signal at 13.5 y-1
Random gaussian fluctuations
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
frequency (y-1)
22
Time modulation exclusion plot from GALLEX/GNO
data
23
GALLEX GNO
The capture rate published by both experiments
has monotonically decreased in the last 5-6 years
24
m 63 s 43
m 89 s 55
m 73 s 52
GNO
GALLEX
GALLEXGNO
SAGE
25
combining SAGE and GALLEX/GNO period Jan 1990
December 2003
68.1 3.75 (5.5)
SAGE SAGE SAGE SAGE
Period Jan 90 Oct 99 Jan 90 Dec 03
N runs 70 51 121
Rn 75.4 7.0 6.8 3.5 3.0 lt 60 ?? 66.9 3.9 3.8 3.6 3.2
GALLEX/GNO GALLEX/GNO GALLEX/GNO GALLEX/GNO
Period May 91 Jan 97 Apr 98 Mar 03 May 91 Mar 03
N runs 65 58 123
Rn 77.5 6.2 4.3 4.7 62.9 5.4 2.5 69.3 4.1 3.6
this value is before the efficiencies
re-evaluation reduction of systematic obtained
in GNO has not been propagated back to GALLEX
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 Rn on Gallim (debate in the
  collaborations about this item)

27
Determination of Gallium-ne capture cross section
Ga-ne capture cross sections are needed to
compute fluxes from rate At low energy ( lt 410
keV, namely for pp ns) only g.s.-g.s.transitions
are presentfor this transition cross 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
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
29
SAGE 37Ar source see details in SAGE poster
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 the n interaction.The
processing efficiency has been found to be
correctly extimated (from the methods routinely
adopted at each run) 100 with 1 error.
31
Impact of Gallium experimental results on
neutrino oscillation parameters determination.
Almost irrelevant with the actual experimental
accuracy in the actual experimental scenario
32
Allowed (Dm2,tan2q12) regions from Radiochemical
experiments
-4
Ga experiments are more sensitive to tan2q12 than
to Dm2
33
Oscillation parameters vs (Ga rate SSM)
Theta32.5
Theta35
Theta28.5
Theta37.5
Theta30
0.954
0.970
Fpp
0.983
1.000
1.016
Comments No sensitivity within the presently
allowed oscillation parameter region
34
Impact of Gallium Results on Astrophysics
35
Solar Models R previsions for Radiochemical
experiments
from LUNA experiment on 14N(p,g)15O New S0(14Np)
1.77 keV 0.2
Flux (cm-2s-1) BP00 BP04 BP04 N14 BP04 N14 Pee Dm2 7.1x10-5 eV2 q12 32.5
pp (109) 59.5 ( 1) 5.94 ( 1) 59.8 60.3 0.578 (vac)
pep (108) 1.40 ( 2) 1.40 ( 2) 1.42 1.44 0.531(vac)
hep (103) 9.24 7.88 ( 16) 7.93 8.09 0.3 matter
7Be (109) 4.77 ( 10) 4.86 ( 12) 4.86 4.65 0.557 vac
8B (106) 5.05 20-16 5.79 ( 23) 5.77 5.24 0.324 matter
13N (108) 5.48 21-17 5.71 2.30 0.557 vac
15O (108) 4.80 25-19 5.03 1.79 0.541 vac
17F (106) 5.63 25-25 5.91 3.93
Columns 2,3,4 from BP04
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(14Np) 1.77 keV 0.2 BP04 BP04
Z/Xnew0.0176 to be compared with
37
Solar Models R previsions for Radiochemical
experiments
Experimental Dm2, tan2q12 from experiments BP00 BP04 BP04 N14 BP04 N14
SNO/ SK 5.21 0.27 (cm-2s-1) 7.1, 0.45 7.3, 0.42 1.00 6 -6 1.01 6 -6
SNO/ SK 5.21 0.27 (cm-2s-1) no osc 5.05 20 -16 5.79 ( 23) 5.77 5.24
Cl 2.56 0.23 SNU 7.1, 0.45 7.3, 0.42 3.06 0.04 2.79 0.18 3.35 ( 21) 3.23 2.95
Cl 2.56 0.23 SNU no osc 7.6 1.3 1.1 8.5 1.8 1.8 8.2 7.7
Ga 68.1 3.75 SNU 7.1, 0.45 7.3, 0.42 69.4 2.6 65.8 4.5 67.7 5.5 69.3 5.3 67.7 5.3
Ga 68.1 3.75 SNU no osc 128 9 -7 131 12 10 127 12 10 127 12 10
(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.)
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).

39
LCNO estimate from Gallium experimental results
imposing the luminosity constraint
Assumption nuclear fusion reactions are the only
source of energy in the Sun
40
Gallium Uncertainties for evaluation of pp and
CNO n flux
Parameter Parameter Uncertainty Rga Uncertainty (SNU)
Theta /- 2.5 SNOkamSK 2.9
7Be 10 SSM 1.9
Cross section GS -GS 2.3 1.5
Cross section GS ES(1,2) 50 0.7
Cross section GS-ESgt2 35 1.5
8B 9 SNO 0.4
pep 1.5 SSM 0.1
4.2
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

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
43
(No Transcript)
44
Finally with the listed assumptions and from the
capture rate measured in Gallium experiments it
is possible to determine
RGa Fpp 109 cm-2 s-1 Fpp / Fpp (BP04N14)
69.3 Old 59.9 (1 0.02 0.01theo) 1.00(2)
68.1 New 58.8 (1 0.02) 0.98(4)
Fantastic agreement !!
45
. for 8B and 7Be
F(8B)meas (0.89 0.04ex 0.23theo) F(8B) BP04
N14
F(7Be)meas (0.910.24-0.62 ex 0.11theo)
F(7Be) BP04N14
from BP04
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) lt 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
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
R 62.9 - 6.0 SNU
48
GALLEX- all uncertainties
Comments GALLEX is compatible with SSM
oscillation scenario within 2 s 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
R 77.5 - 7.7 SNU
49
Gallium- 5 error
0.954
0.970
Fpp BP00
0.983
1.000
1.016
R 70.0 - 3.5 SNU
50
Are precision measurements possible with Gallium
radiochemical experiments?
51
Gallium- 3 error
Delta theta 1.5 - cross section measured at 1
Comments Errors at the level of SSM
uncertainties in pp flux
0.954
0.970
Fpp
0.983
1.000
1.016
52
Achievable accuracies
3 years of running 4 weeks runs 60
efficency 70 SNU signal Systematic error 2.5
SNU ( GNO) not large improvements
possible 30 tons 80 tons 160 tons (GNO)
(available gallium) Det.evt.s 195
519 1040 Total accuracy 7 SNU 4 SNU 3 SNU
53
Technological results

• Few atoms chemistry
• Low level counting techniques
• Intense neutrino sources production (intensity
  calibration, know-how to produce and manipulate
  safely etc..)
• Radiochemistry techniques
• Radon counting and quantitative determination at
  level of few atoms.
• Ultra-low activity miniaturized proportional
  counters

54
Conclusions

• Radiochemical experiments have provided along
  the last 40 years measurements of solar ne
  interaction rate on 37Cl and on 71Ga
• they confirm at sub-Mev energies the neutrino
  oscillation scenario and the standard solar model
• The update value for the neutrino capture rate on
  Gallium is
• 68.1 3.7 from 244 GALLEXGNOSAGE runs
• Gallium experiments have demonstrated to be
  reliable and have been calibrated with high
  intensity neutrino sources.Chlorine and GALLEX
  experiments has experimentally excluded hot
  chenistry effects
• No time modulations (seasonal, monthly,
  bimonthly, yearly) have been found ? with the
  actual accuracy we can state that the neutrino
  flux is constant

55
Taking F(8B)meas (0.89 0.04ex 0.23theo)
F(8B) BP04 N14
F(7Be)meas (0.910.24-0.62 ex 0.11theo)
F(7Be) BP04N14
RGa Fpp 109 cm-2 s-1 Fpp / Fpp (BP04N14)
69.3 Old 59.9 (1 0.02 0.01theo) 1.00(2)
68.1 New 58.8 (1 0.02) 0.98(4)
56
Extra slides
57
Radiochemical experimental technique
Add carrier 1mg 72,74,76 Ge in GALLEX 250mg
72,74,76 Ge in SAGE 0.1 cc STP 36,38Ar in
Chlorine exp.
Extraction Ga GeCl4 with N2 Cl Ar with
He stream
2. Extracted gas in counter
1. Exposure
In synthesis lab
Gallium (GeH4 Xe), Chlorine (Ar CH4) in
counter V 1cc
Wait Exposure time
t0
Stop counting Remove counter
Counter in shielding
3.
6 months for 76Ge 12 months for 37Ar
58
Results of Chlorine experiment
59
Results of Chlorine experiment
Learning phase of these experiments is very long !
60
GALLEX GNO

• Test hypothesis of time constancy of n signal
• Test of Likelihood Ratio ? C.L. 5.6
• c2 flat fit 13.6 (6 d.o.f.)? C.L. 3.4

61
Improvements
Many improvements resulting in a reduction of a
factor of ? 2 in the systematic error
Item Gallex GNO
Target size 0.8 0.8
Chemical yield 2.0 2.0
Counting efficiency (active vol determination) 4.0 2.2
Pulse shape cuts 2.0 1.3
Event sel. (others) 0.3 0.6
Side reactions 1.2 SNU 1.2 SNU
Rn-cut inefficiency 1.2 SNU 0.5 SNU
68Ge contamination 1.8 SNU-2.6 SNU -
Neural network analysis
62
Composition of the Gallium signal
RGa Fpp spp Ppp FCNO sCNO PCNO F8 s8 P8
F7 s7 P7 Fpep spep Ppep
LSun Fpp app FCNO aCNO F8 a8 F7 a7
Fpep apep
F a s P (SNOSKKAM) s P (SNU)
pp 59.8 BP04N14 1.310 11.7 0.578 40.4
7Be 4.86 BP04N14 1.260 71.7 0.557 19.4
N 0.323 BP04N14 0.346 60.2 0.557 1.1
O 0.254 BP04N14 2.157 115 0.541 1.5
8B 0.00521 SNO 0.663 24500 0.324 4.1
pep 0.142 BP04N14 1.192 15.7 0.531 1.2
TOT 67.7
RGa 69.3 5.5 SNU
FN 1.14 FO
63
Solar Models previsions for R (int.rate) in
Radiochemical Experiments
new meas.from LUNA exp. of S0(14Np) 1.77 keV
0.2 14N(p,g)15O
(Z/X)old0.0229
64
Solar Models R previsions for Radiochemical
experiments
65
Generalities on radiochemical experiments
ne interaction reaction Target comp. and mass Exp. Time d d Data taking
Lab overburden Target comp. and mass Exp. Time d d Data taking
Chlorine (Homestake Mine)South Dakota USA ne(37Cl,37Ar)e- C2Cl4 600 tons Liquid 60-120 50.5 1964- 1993
Chlorine (Homestake Mine)South Dakota USA 4400 mwe C2Cl4 600 tons Liquid 60-120 50.5 1964- 1993
GALLEX/ GNO LNGS Italy ne(71Ga,71Ge)e- GaCl3 HCl in H2O 100 t (30 t Ga) 21-28 28 16 1991-2003
GALLEX/ GNO LNGS Italy 2700 mwe GaCl3 HCl in H2O 100 t (30 t Ga) 21-28 28 16 1991-2003
SAGE Baksan Kabardino Balkaria ne(71Ga,71Ge)e- Metallic Ga 55-49 tons 28 16 1990-ongoing
SAGE Baksan Kabardino Balkaria 4800 mwe Metallic Ga 55-49 tons 28 16 1990-ongoing
66
Generalities on radiochemical experiments
Data used for R determination N runs Average efficiency Hot chem check Source calib Rex SNU
Chlorine (Homestake Mine)South Dakota USA 1970-1993 106 0.958 0.007 36Cl No 2.55 0.17 0.18 6.6 7 2.6 0.3
GALLEX/GNO LNGS Italy 1991-2003 124 ?? 37As Yes twice 51Cr source 69.3 4.1 3.6 5.9 5
SAGE Baksan Kabardino Balkaria 1990-ongoing 104 ?? No Yes 51Cr 37Ar 70.5 4.8 3.7 6.8 5.2 70.5 6.0