GALLEXGALLEX--GNO GNO experiments: status and experiments: status and

reportsreportsSecond International Summer Student School on Neutrino Physics in Memory of Bruno Pontecorvo

September 2003

R. BernabeiUniv. Roma - Tor Vergata and INFN-Roma2

GallexCollaboration

GallexGallexCollaborationCollaboration

• Max-Planck-Institut für Kernphysik (MPIK)-Heidelberg, Germany• Istitut für Technische Chemie, Forschungzentrum Karlsruhe (FZK) –

Germany• Laboratori Nazionali del Gran Sasso (LNGS) - L'Aquila, Italy• Dipartimento di Fisica, Universitá di Milano e INFN - Italy• Physik Department E15, Technische Universität München (TUM) -

München, Germany• Observatoire de la Côte d'Azur, Département Cassini - France• Department of Environmental and Energy Research, the Weizmann Institute

of Science (WI) – Israel• Dipartimento di Fisica, II Universitá di Roma `Tor Vergata' e INFN, Sezione

di Roma 2 - Italy• DAPNIA/Service de Physique des Particules, CEA/Saclay – France• Brookhaven National Laboratory (BNL) - USA

GNO Collaboration

GNO GNO CollaborationCollaboration

Dip. Di Fisica dell’Università di Milano “La Bicocca” e INFN sez. Milano

INFN Laboratori Nazionali del Gran Sasso

Dip. Di Fisica dell’Università di Roma “Tor Vergata” e INFN sez. Roma II

Dip. Di Ingegneria Chimica e dei Materiali Università dell’Aquila

Max Planck Institut fur Kernphysik – Heidelberg

Physik Dep. E15 – Technische Universitaet – Muenchen

• Purpose: measurement of the low energy solar neutrino interaction rate which is related to the sun luminosity (i.e. model-independent), with an accuracy of 5 SNU (GNO) and investigation of its time dependence on a solar cycle with a sensitivity ~15% (GNO) .

• Basic interaction: νe + 71Ga → e- + 71Ge Ethr = 0.233 MeV ~ 1.2 capture/day expected by SSM71Ga EC, τ=16.49 days

• Exp. site: Gran Sasso underground laboratory (3300 m.w.e.)

• Target: 103 tons of GaCl3 acidic solution ⇒ 30 tons of natGa (12 tons of 71Ga) in GaCl3 + HCl

• Technique: radiochemical, chemical extraction of 71Ge every 3-4 weeks; detection of 71Ge decay with gas proportional counters

• Expected signal (SSM): ~ 9 71Ge counts detected per extraction

GALLEX/GALLEX/GNOGNO

TankLNGS

νν’s from the SUN’s from the SUN

ν ν signal compositionsignal compositionSolar neutrino energy spectrum

8B 10% CNO

8%

7Be 27%72 SNU

35 SNU

10 SNU

13 SNU

pp+pep 55%

Tot: 128+9-7 SNU

• 3-4 weeks of exposure to the solar neutrinos (SR) or 1 day for blank run (BR).

• 71Ge (GeCl4) extracted in water fluxing ~ 3000 m3 of nitrogen in the solution

• 71Ge (~ 95%-98%) converted in GeH4 (gas) and used together with Xe gas to fill a miniaturized proportional counter

• Counting of the 71Ge nuclei through its decays

• Expected signal (SSM): 1.2 n inter./day, but due to decay duringexposure + ineff. ~9 71Ge counts detected per extraction

Miniaturized Proportional Counter

PLB490(2000)16PLB314(1993)445

Extraction and counting procedures Extraction and counting procedures -- 11

Extraction and counting procedures Extraction and counting procedures -- 22

Decay processes for 71Ge detection71Ge (EC) → 71Ga* → 71Ga (t1/2 = 11.4 d)

% Auger (keV) X-ray (keV)41.5 10.37 -

K 41.2 1.12 9.255.3 0.11 10.26

L 10.3 1.30 -M 1.7 0.16 -

{ → fast pulses with the respect to those due to natural radioactivity

L-window

K-window

RED: background pulseBLU: fast event pulse of 71Ge decayExpected energy distribution

GALLEX: GALLEX: data taking and resultdata taking and result• 1986 – 1990 Construction of the detector

• May 1991 – May 1992 GALLEX I data taking: 15 SR + 5 blanks83.4 ± 19 SNU

• 14 May 1991 - 23 Jan 1997 GALLEX 65 SR + 36 blanks

• Jun 1994 - Oct 1994 51Cr ν source experiment 11 runs

• Oct 1995 - Feb 1996 51Cr ν source experiment 7 runs

• Feb 1997 - Apr 1997 Tests with 71As

• Apr 1998 – now GNO data taking

PLB285(1992)376, PLB285(1992)390

PLB342(1995)440

PLB420(1998)114

PLB436(1998)158

PLB314(1993)445, PLB327(1994)377, PLB357(1995)237, PLB388(1996)384, PLB447(1999)127

FINAL RESULT (1594 days – 65 runs):77.5 ± 7.7 (stat+syst) SNU

Observation of:→ pp fusion in the solar core→ definitive deficit of 7Be (or pp) ν

not explainable by solar physics+ reliability of the radiochemical (solar-ν) experiments (ν-sources, As-test)

GALLEX – Energy and rise time distributions

GALLEX – Energy and rise time distributions

GALLEX I + II + III

Significance of Deficit in Time

Why a Why a νν source experiment?source experiment?

To place trustworthiness of the experimental techniques (excluding unforseen effects)

How ?How ?

Exposing the experiment to a ν source of known activity and appropriate energy in the same condition than in the solar exposure

NeedsNeeds

>50 PBq build a ν source with activity allowing a precision on ≈9% in the measurements

51Cr ν energy close to solar ν detected in the experiments

(27.706 ± 0.007) T1/2 sufficient to transport the source and perform the experiment

Source constructionSource constructionChromium enriched in 50Cr activated at Grenoble nuclear reactor:

n + 50Cr → 51Cr + γ

Response of Gallex experiment to source exposureResponse of Gallex experiment to source exposure

• First observation of low enery neutrino from artificial terrestrial source

• Confirmation of solar ν deficit as measured by experiments

• Radiochemical techniques are reliable: it is possible to extract ≈10 atoms from 30 tons and to count their decay

• General check of the experiment

[1 PBq = 1015 Bq = 27.0 kCi]

Arsenic tests in GallexArsenic tests in Gallex• Introduction of about 105 atoms of 71As inside the solution

• Repeated tests under variable respectively purposely unfavorable conditions with respect to:- method and magnitude of carrier addition- mixing-and extraction conditions- standing time

• To exclude withholdings (classical or ‘hot-atom’-effects)

Arsenic tests in GallexArsenic tests in Gallex•Method: triple-batch

comparison: ≈ 30 000 71As atoms in:- tank sample, - external sample- calibration sample (γ-

spectrometry)

Recovery factor = (99.9 ± 0.8) %

GNO: the modernized and improved continuation of GALLEX

• Demanding selection of counters used in solar runs

• Internal calibration of individual counter efficiencies

• Reduction of Rn contamination inside counters (from 5-6 to 0-1 atoms/run)

• Improved internal Rn correction

• Neural network pulse shape analysis

• Improved backgrounds counts (from 0.1 to 0.06 counts/day )

• Newly structured collaboration

• New analog electronics

• New digital electronics: one Transient Digitizer for each line: led to much improved pulse shape recording

• New DAQ

• In-shield counter calibration with X-ray tube

• Re-measurement of carrier concentration with high accuracy

GNO II (from Jan00)44 SR + 12 blanks

GNO I (May98 - Jan00)19 solar runs

PLB490(2000)16

Improvements from Gallex to GNO

-

1.3 SNU

+0.7 SNU-2.0 SNU+1.8 SNU-2.6 SNU

68Ge contamination

Subtotal

0.5 SNU1.2 SNURn-cut inefficiency

1.2 SNU1.2 SNUSide reactions

0.6%3.4%

0.3%5.0%

Event sel. (others)Subtotal

1.3%*2.0%Pulse shape cuts

2.2%4.0%Counting efficiency(active vol determination)

2.0%2.0%Chemical yield

0.8%0.8%Target size

GNOGallexItem

Many improvements resulting in a reduction of a factor of ≈ 2 in thesystematic error

* Neural network analysisGALLEX GNO GNO+GALLEX

Rate (SNU) 77.5 62.9 69.3Stat. err. (SNU) 6.2 5.4 4.1Syst. err. (SNU) 4.5 2.5 3.6Tot. err. (SNU) 7.6 6.0 5.5Tot. err. (%) 9.8 9.5 7.9# of SR 65 58 123

Further minor improvements expected in a short time (analysis of counter calibration data, ...)

Example of the improvement in the systematics• 69Ge and 71Ge calibration of the PC:

• Redetermination of carrier solution concentration

• Pulse shape analysis

• Rn cut inefficiency: Gallex (9±5)%, GNO new meas. (1.7±4.7)% (ongoing)

Neural network analysis

better bckg rejection power than rise time analysis

Comparison between NN and RT analyses:

... some pictures from GNO!

Proportional counterThe columns

The synthesis line Shielding

800 mV 1100 mV

400 ns 400 ns

TDF 1 TDF 2

Example of recorded pulses in GNO

A typical 0.5 keV event:

GNO Results (31/08/2003)

Completed 58 solar runs 1713 days

Still counting 5 solar runs 30 days

Blanks 12

GNO 62.9 ± 5.4 (stat) ± 2.5 (syst) SNU

(L 68 ± 9; K 60 ± 7)

GALLEX 77.5 ± 6.2 (stat) ± 4.5 (syst) SNU

GALLEX+GNO 69.3 ± 4.1 (stat) ± 3.6 (syst) SNU

Energy distribution of fast eventsEnergy distribution of fast events

t < 50 days(50 d ~ 3τ)

t > 50 days

Lonly → 69.6 ± 10.3 SNUKonly → 62.2 ± 8.2 SNUL+K → 65.2 ± 7.1 SNU (N.N.)L+K → 69.4 ± 7.1 SNU (R.T.)

GALLEX

Time [d]

coun

ts/d

ay/r

un

Time dist. of selected events.

65 runs

GNO58 runs

Time dist. of selected events71Ge signal~276 decays

τ (71Ge) = 16.6 ± 2.1 dτtrue (71Ge) = 16.49 d

Reduction of the bckgGNO vs Gallex 30%

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

Gallex + GNO results: Davis plotTotal exposure time: 3307 d

GALLEX+GNO 70.8 ± 4.5 ± 3.8 SNU

Analysis Energy-RTGALLEX

Analyses Energy-PS/NNGNO

GALLEX 65 SR 77.5 ± 6.2 (stat) ± 4.5 (sys) SNUGNO 58 SR 62.9 ± 5.4 (stat) ± 2.5 (sys) SNU

GALLEX + GNO 123 SR 69.3 ± 4.1 (stat) ± 3.6 (sys) SNU

GNO: 276 71Ge in 1713 d exposure time

Single run distribution compared with the expectations from a constant ν interaction rate

GNO II : GNO II : example about Blank Runsexample about Blank RunsBlank Runs: to check each 3 month the proper functionality of the whole setup (no tailing effect, background from isotopes other than 71Ge, etc.)

9.65 ±3.2

0.85 ±0.73

Average per run

3.70.71.31.70.00.01.4

ExcsCnts

166

165

166

164

166

165

Counting[d]

59.39.398.117-03/8-03-01A043

8.793.0112-12/13-12-00 A039

5.394.7120-09 / 21-09-00A035

11.097.7128-06 / 29-06-00A031

15.094.815-04 / 6-04-00A027

8.691.2112-01/13-01-00A023

BckgCnts160 d

Chem Yield[%]

ExpTime[d]

Start exp.End exp.

Run

Time dist. of selected events

coun

ts/d

ay/r

un

6 GNO blanks

Time [d]

coun

t s/d

ay/r

u n

GNO58 runs

71Ge signal~276 decays

Time [d]

Flat: χ2= 2.7 (5 d.o.f.), P=75%Elliptical: χ2= 3.0 (5 d.o.f.), P=70%

aphe

lion

peri

helio

n

Rate

(SN

U)

January July

Geometrical modulation

GALLEX +GNOSeasonal variations

GALLEX +GNOSeasonal variations

Data binned with the distance from the SunData binned with the distance from the Sun

Expected geometricalmodulation +2.5 SNU

Fogli et al., hep-ph/0208026

Interpretation of solar νexpts in terms of neutrino

oscillations

McDonald, hep-ex/0209056

SNO day-night

all expts.

Typical examples:

•Direct and absolute determination of volume efficiencies of all counters by 69Ge measurements reduce systematic < 3% (within two years)

•Continued exploration of joining Gallium from SAGE and GNO in one experiment: potential for 100 tons gallium experiment, for a statistical error of ±4 SNU.

•Production of a new 3 MCi 51Cr source to perform a 3rd irradiation→ Cross section determination (in particular, at level 175 keV) to <5%(important for pp and 7Be ν’s separation) rem: Gallex result (89±7)% (this is a true

cross section due to the results from the Gallex 71As exp., chemical recovery (100±1)%) •51Cr source production ar RIAR (Dimitrovgrad) from 11kg enriched Cr (38% 50Cr); expected accuracy < 8%

•Allows also a model independent proof of non-standard neutrinos from Gallium alone (exclusion of “minimal” model, ≈90 SNU [2σ])

•Direct and absolute determination of volume efficiencies of all counters by 69Ge measurements reduce systematic < 3% (within two years)

•Continued exploration of joining Gallium from SAGE and GNO in one experiment: potential for 100 tons gallium experiment, for a statistical error of ±4 SNU.

•Production of a new 3 MCi 51Cr source to perform a 3rd irradiation→ Cross section determination (in particular, at level 175 keV) to <5%(important for pp and 7Be ν’s separation) rem: Gallex result (89±7)% (this is a true

cross section due to the results from the Gallex 71As exp., chemical recovery (100±1)%) •51Cr source production ar RIAR (Dimitrovgrad) from 11kg enriched Cr (38% 50Cr); expected accuracy < 8%

•Allows also a model independent proof of non-standard neutrinos from Gallium alone (exclusion of “minimal” model, ≈90 SNU [2σ])

0.85 ± 0.1169.1+3.3-2.1II (sept 1996)

1.01 ± 0.1163.4 +1.1-1.6I (may 1995)

expexp//theotheoIntensity (PBq)Intensity (PBq)

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

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

Why subWhy sub--MeV Neutrinos?MeV Neutrinos?

• Solar Physics: 98 % of all solar neutrinos are sub-MeV ( Φ7 ~ 7% , Φpp~91% );the pp-neutrino flux is coupled to the solar luminosity. It is a fundamental astrophysical parameter that should definitely be measured, as precisely as possible. Stringent limitations (or observation) of departures from the standard solar model are obtained if the flux of pp neutrinos could be deduced. Ga SNU contours Ga SNU contours

in the LMA regionin the LMA region

Holanda + Smirnov PRD66(2002)113005• Neutrino Physics: (a) Below 1 MeV, the

vacuum oscillation domain takes over from the matter oscillation domain at >1 MeV. Also there could be hidden effects only at < 1 MeV (e.g., sterile admixtures?). (b) Narrow down on tang2θ12. To obtain ∆ ≈ 15%, the pp-flux must be determined to ± 3%.

Conclusions

• Gallex experiment has allowed to observe for the 1st time in 1992 the pp neutrinos• Gallex experiment stated the definitive deficit of 7Be (or pp) ν not explainable by

solar physics • GNO experiment is running smoothly and with a very high duty cycle since may

1998 (5 years) and GALLEX + GNO since 1991• GNO: reduction of systematic error to 4.0%• GNO Blank run → zero-compatible• The updated GNO results (58 solar runs) is 62.9 ± 5.4 (stat) ± 2.5 (syst) and when

combined with GALLEX (123 solar runs) is 69.3 ± 4.1 (stat) ± 3.6 (sys)

• No seasonal variation is observed in the GALLEX+ GNO data Winter-Summer = -7.6 ± 9 SNU

Conclusions - 2• GNO exposure time is now equivalent to GALLEX

• The same statistics (65 solar runs) will be reached at the end of 2003

• GNO will continue the solar data taking

• At present, the gallium experiments are the only ones running with a low energy threshold (pp ν’s)

• Refinement of the rate value to take into account new information on counters …

• 2.5 MCi 51Cr source

• Collaboration with SAGE ( better signal/noise; more significant single run result…., discussions in progress)

Aims:

- increasing statistics and decreasing systematics- better knowledge of neutrino cross sections ≡ Cr source- Search for time variation (e.g. Sturrock et al.)- Improve the statistical meaning of single run result