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Carla Maria Cattadori INFN Milano and Milano Bicocca Physics Department

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### 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

- 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

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 experimentsCarla Maria Cattadori

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

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

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

The Chlorine experiment

Carla Maria Cattadori

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

Carla Maria Cattadori

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

SAGEJanuary 1990 – December200314 years – 121runs66.9 +5.3-5.0 SNU

See poster session !

51Cr source experiments

Carla Maria Cattadori

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

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

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

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

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 !!

SAGE survey of time modulations

No evidence of time modulation binning the all data set monthly, bimonthly, yearly.

Carla Maria Cattadori

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

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)

Rule out modulations with frequency < 12 y-1 and amplitude > 40% of signal

Time modulation exclusion plot from GALLEX/GNO dataCarla Maria Cattadori

The capture rate published by both experiments has monotonically decreased in the last 5-6 years

Carla Maria Cattadori

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

…. 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

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

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

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 posterCarla Maria Cattadori

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

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

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

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

Impact of Gallium Results on Astrophysics

Carla Maria Cattadori

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

…… 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

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

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

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 constraintAssumption: nuclear fusion reactions are the only source of energy in the Sun

Carla Maria Cattadori

…..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

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

Finally with the listed assumptions and from the capture rate measured in Gallium experiments it is possible to determine

Fantastic agreement !!

Carla Maria Cattadori

…. 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

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

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

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

Are precision measurements possible with Gallium radiochemical experiments?

Carla Maria Cattadori

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

Carla Maria Cattadori

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 SNU4 SNU 3 SNU

Carla Maria Cattadori

Technologicalresults

- 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

Carla Maria Cattadori

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 GALLEX+GNO+SAGE 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

Carla Maria Cattadori

Taking 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

Carla Maria Cattadori

Extra slides

Carla Maria Cattadori

Radiochemical experimental technique

Add carrier

1mg 72,74,76 Ge in GALLEX

250mg 72,74,76 Ge in SAGE

0.1 cc STP36,38Ar 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

Carla Maria Cattadori

Results of Chlorine experiment

Carla Maria Cattadori

Results of Chlorine experiment

Learning phase of these experiments is very long !

Carla Maria Cattadori

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%

Carla Maria Cattadori

Improvements

Many improvements resulting in a reduction of

a factor of 2 in the systematic error

* Neural network analysis

Carla Maria Cattadori

Composition of the Gallium signal

RGa = Fppspp Ppp + FCNOsCNO PCNO + F8s8 P8 + F7s7 P7 + Fpepspep Ppep

LSun = Fppapp + FCNOaCNO + F8a8 + F7a7 + Fpepapep

RGa = 69.3 ± 5.5 SNU

FN = 1.14 FO

Carla Maria Cattadori

Solar Models previsions for R (int.rate) in Radiochemical Experiments

new meas.from LUNA exp. of

S0(14N+p) =

1.77 keV ± 0.2

14N(p,g)15O

(Z/X)old=0.0229

Carla Maria Cattadori

Solar Models R previsions for Radiochemical experiments

Carla Maria Cattadori

Generalities on radiochemical experiments

Carla Maria Cattadori

Generalities on radiochemical experiments

Carla Maria Cattadori

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