retrospect of gallex / gno

1

Retrospect of GALLEX / GNO

Till KirstenMax-Planck-Institut für Kernphysik Heidelberg / Germany

1 Retrospect

2 Recent update

3 Why did we stop?

Till Kirsten, Max-Planck-Institut für Kernphysik Heidelberg, at TAUP 2007, Sendai September 11–15, 20072

GALLEX / GNO , SAGE

Radiochemical Method(product accumulation)

Ga71 + e Ge71 + e-

Low threshold! (0.233 MeV)

recall: Cl- experiment

1 RETROSPECT


Purpose: detection of low energy solar neutrinos71Ga(e,e)71Ge (Ethr = 233 keV)Basic interaction:

EC, = 16.49 dayssignal composition:

Technique:

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

Radiochemical

Target: 103 tons of GaCl3 acidic solution containing 30 tons of natural galliumChemical extraction of 71Ge every 3-4 weeks

Detection of 71Ge decay with gas proportional counters

Tot: 126+9-7 SNU

72

S

NU

33

S

NU

9

SN

U

12

S

NU

8 B 10

%CNO

7%

7 Be

26%

pp+

pep

57%

Conception of the Gallium Neutrino Experiment GALLEX (later GNO)


Why sub-MeV Neutrinos? 98 % of all solar neutrinos are sub-MeV ( 7 ~ 7 % , pp ~ 91 % ). The pp- neutrino flux is coupled to the solar luminosity. It is a fundamental astrophysical parameter that must definitely be measured, as precisely as possible. Stringent limitations (or obser-vation) of departures from the standard solar model can be obtained if the flux of pp neutrinos is deduced, provided that, as it is now possible, neutrino properties are properly folded in.


Below ~1-2 MeV, the vacuum oscillation domain takes over from the matter oscillation domain at > 2 MeV. Also there could be hidden effects only at < 2 MeV

from C. Pena-Garay


Radiochemical experiments

cumulative measurement of the integral solar neutrino interaction rate (as opposed to real-time event detection)

no spectral or directional informationAfter long time operation of these first generation experiments (Cl, Ga), the statistical errors equal the intrinsic systematic errors. The success of these experiments implies their end. However, they have been crucial in paving the way into the excitement of the third millenium!


1986 - 1990

May 1991 – May 1992

Construction of the detector

GALLEX I data taking15 Solar runs, 5 Blanks

PL B285 (1992) 376PL B285 (1992) 390

Jun 1994 – Oct 1994 1st 51Cr source experiment PL B342 (1995) 440

Oct 1995 – Feb 1996 2nd source 51Cr experiment PL B420 (1998) 114

Feb 1997 – Apr 1997 Test of the detector with 71As PL B436 (1998) 158

Apr 1998 – Apr 2003 GNO data taking

83.4 ± 19 SNU

GALLEX Final Result 1594 days – 65 runs: 77.5 ± 7.7 SNU

Feb. 1997 End of Solar Data Taking PL B447 (1999) 127

PL B490 (2000) 16

PLB B616(2005)174

GALLEX/GNO Time Table


Granada, June 8th, 1992GALLEX announces first observation of solar pp-neutrinos at „Neutrino 92“


Feb 28 2006 Till Kirsten at LNGS 45

de Rujula Conference Summary Talk

de Rujula


GALLEX RESULT IMPLICATIONS (1992) PL B285 (1992) 376

60 % of the SSM expectation Definite deficit of 7Be (or pp-) neutrinos observed

105 % of pp- expectation Hydrogen fusion in the solar interior experimentally observed


Significance of Deficit in Time


GALLEX Final Result 1594 days – 65 runs: 77.5 ± 7.7 SNU


Cr source experiments


Arsenic Tests

Repeated tests under variable and purposely unfavorable conditions respective to the standing time mixing- and extraction conditions method and magnitude of carrier additionto exclude witholdings (classical or ‘hot-atom’-effects)Method Triple-batch comparison 30 000 71As atoms added to:Tank sampleExternal sampleCalibration sample (-spectrom.)

Result: Recovery 99+ %


GALLEXGALLEX65 Solar runs = 1594 d23 Blank runs

GNOGNO 58 Solar runs = 1713 d12 Blank runs

62.9 62.9 ++5.55.5 –5.3–5.3 ± 2.5 SNU ± 2.5 SNU77.5 77.5 ± 6.2 ± 4.5 SNU± 6.2 ± 4.5 SNU

51Cr source-, 71As experiments


GNO 62.9 ± 6.0 5.9 SNU

GALLEX 77.5 ± 7.6 7.8 SNU

GALLEX+GNO 69.3 ± 5.5 SNU

SAGE 66.9 ± 5.3 5.0 SNU

Range of SSM predicted rates:

No oscillations: 122 – 131 SNUWith oscillations 68 – 72 SNU(global fit)

FINAL RESULTS


2 RECENT UPDATEResults of a recent complete re-analysis of the Gallex data * (using ~105 Ge-decays per counter) not allowed before completion of the low rate measurment phase (solar runs)- Improved Rn-cut efficiency (multi-year low-rate - Counter efficiency error reduction after full calibration experiment) - full PSA instead of RTAAlso for Cr-source data -Counter efficiency error reduction after full calibration (as above)- solar subtraction to include also GNO data

* F. Kaether, PhD Thesis, Heidelberg University, July 2007


GALLEX Periods (new vs. old)old (RTA)

new (PSA ect.)


GALLEX 77.5 ± 7.6 7.8 SNU

re-evaluated 73.1 ± 7.1 7.3 SNU

GNO (unchanged) 62.9 ± 6.0 5.9 SNU

GALLEX+GNO 69.3 ± 5.5 SNU

re-evaluated 67.5 ± 5.1 SNU

Updated Results


Cr- source updateMean S1+S2: 93 ± 8% (1) Gallex PL (1998)

Re-evaluated: 88 ± 8% (1) Thesis Kaether (2007)

The expectation value for ground state only is95 ± 1% Bahcall PR C (1997)

Our 71As-experiment excludes Ge-yield errors >1%Consequences The excited state contribution is probably close to 0, instead of (5 ± 3)% as estimated by Bahcall. Supported also by the SAGE Cr-source result. The 71Ge production rate prediction on Ga (without oscillatons) must be reduced by ~2 SNU from 7Be- (32.7 SNU instead of 34.8 SNU). [no change for pp-]


Oscillation parametersIf the LMA(MSW) solution is the correct explanation of the SNO/SK data, then vacuum oscillations must dominate below 1 MeV and the mixing angle is estimated as

= 32 1.6 degrees (B-PG04)From our data we extract the e-e survival probability Pee for pp-neutrinos after subtraction of the 8B and 7Be contributions based on the experimentally deter-mined 8B- (SNO/SK) and 7Be- (Borexino) neutrino fluxes as

Pee(pp only) = 0.52 ± 0.12

THE RESULTS IMPLY THE EXPERIMENTAL VERIFI-CATION OF THE SOLAR MODEL AND OF THE NEUTRINO OSCILLATION MECHANISMNS AT sub-MeV ENERGIES THAT ARE OTHERWISE INACCESSIBLE


Partitioning of the Gallium Cake

SNU Pee Experim.

measured 68 ± 5 GX/GNO7Beexp 22 ± 7 0.68 ± 0.20 Borexino8Bexp 4 ± 1 0.33 ± 0.08 SK + SNO13N, 15O 4.5 +1

-3 ~0.5(assumed) -

pep 1.5 ± .5 ~0.5(assumed) -

pp only 36 ± 8 0.52 ± 0.12 Gallium

(Experiments, SSM and LMA)


3 WHY DID WE STOP?

Reasons that existed to continue GNOas long as real-time pp-neutrino detection was (and still is) a long way to go

• Continous pp-neutrino monitoring is an astrophysical necessity

• pp-observations simultaneously with Borexino real-time beryllium neutrino observations

• Further neutrino source experiments to improve the knowledge of relevant cross sections


Reflections on the causes for the termination of the experiment

Quote: „The Gallium Neutrino Observatory (GNO) is the price that Italy‘s underground lab is paying to get back on its feet after a small chemical spill nearly two years ago“ (Toni Feder, Physics Today, May 2004)

No confusion: The spill occured in Hall C (Borexino)

GALLEX/GNO (in Hall A) never spilled a single drop of liquid. Ironically, GALLEX introduced the double spill tray safety conception in 1986, almost 20 years before it now became mandatory for the Laboratory

The GALLEX corpse feeded Borexino for survival (the laws of nature)


The End

April 6, 2005 : GNO17, the last regular (semi-annual) GNO meeting was held in Assergi

Febr 28, 2006: Final Celebration Ceremony for GALLEX/GNO at Gran Sasso, ending a

successful fifteen year period that started with the Inauguration Ceremony on November 30, 1990

(Gallium was sold in April 2007 to Recapture Metals Inc., Ontario, Canada)


GALLEX-Inaugurationat GRAN SASSO 30.11.1990

The FutureIn n… years:Determine pp-neutrino flux directly with low threshold real-time experiments (Xe, Borexino,…?) n = 3,4,5,6…?


In memoriam


Luciano Paoluzi † 2002


Michael Altmann† 31 July 2006


Nicola Ferrari † 31 July 2006


Keith Rowley † 29 October 2006

retrospect of gallex / gno

Documents

pp neutrinos

solar interior

solar luminosity

pp neutrino flux

flux of pp neutrinos

mev neutrinos

data taking15 solar

standard solar model