GNO and the pp - Neutrino Challenge T.Kirsten/GNO Till A. Kirsten Max-Planck-Institut für Kernphysik, Heidelberg for the GNO Collaboration NDM03 Nara/Japan.

GNO and the pp - Neutrino Challenge

T.Kirsten/GNO

Till A. KirstenMax-Planck-Institut für Kernphysik, Heidelberg

for the

GNO Collaboration

NDM03 Nara/JapanJune 9-14, 2003 a

Solar Neutrino Energy Spectrum

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: 128+9-7 SNU

72

S

NU

35

S

NU

10

S

NU

13

S

NU

8 B 10

%CNO

8%

7 Be

27%

pp+

pep

55%

More details can be found on the webpage www.lngs.infn.it/site/exppro/gno/Gno_home.htm

GNO - Gallium Neutrino Observatory

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

GNO Collaboration

GNO Collaboration

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 – Now Start of GNO data taking

83.4 ± 19 SNU

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

GALLEXGALLEX

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

Significance of Deficit in Time

Neutrino Source Exposure

Source results

Arsenic TestsRepeated tests under variable respectively purposely unfavorableconditions with respect to: method and magnitude of carrier addition Mixing-and extraction conditions standing timeto exclude witholdings (classical or ‘hot-atom’-effects)Method:Triple-batch comparison: 30 000 71As atoms in:Tank sampleExternal sampleCalibration sample (-spectrometry)

Result: Recovery 99+ %

GNO – ResultsGNO – Results

completed 52 solar runs 1547 days

still counting 7 solar runs 200 days

blanks 10 +2

GNO 65.2 ± 6.4 ± 3.0 SNU

(L 70. ± 10. K 62. ± 8.)

GALLEX 77.5 ± 6.2 +4.3-4.7 SNU

GALLEX+GNO 70.8 ± 4.5 ± 3.8 SNU

GALLEX - GNODavis plot

GALLEX65 solar runs

GNO52 solar runs

GALLEX +GNO Seasonal variations

GALLEX +GNO Seasonal variations

Winter-Summer (statistical error only):

GNO only (52 SRs):

Winter (26 SR): 59.6+8.1-7.7 SNU

Summer (26 SR): 67.7+8.7-8.3 SNU

W-S: -8 ± 16 SNUGNO + Gallex (117 SRs):

Winter (60 SR): 68.1+6.0-5.8 SNU

Summer (57 SR): 73.5+6.4-6.2 SNU

W-S: -5 ± 12 SNU

ImprovementsImprovements

Item Gallex GNOTarget size 0.8% 0.8%

Chemical yield 2.0% 2.0%

Counting efficiency

(active volume determ.)

4.0% 2.3%

Pulse shape cuts 2.0% 1.3%*

Event selection (others) 0.3% 0.6%

Side reactions 1.2 SNU 1.2 SNU

Rn-cut inefficiency 1.2 SNU 0.8 SNU68Ge contamination +1.8 SNU

-2.6 SNU -

* Neural network analysis

Why sub-MeV Neutrinos?

1.Solar Physics 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 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.

2. 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 < 1MeV (e.g., sterile admix-tures?)

(b) Narrow down on tang2θ12 .

To obtain Δ 15%, the pp-flux

must be determined to 3 %

Depression Factor vs. Energy

Ga SNU contours in the LMA region

Holanda + Smirnov PRD 66(2002)113005

How?The best promise is with low threshold real time experiments like

-e) scattering or (e-γ) (e.g. Xe) e.g. In-Lens

 Yet: When ???

7Be : soon (Borexino, Kamland?)pp : > 4 years (at least)

Meanwhile : pp = GNO(pp+7Be) minus BOREXINO (7Be)!

An important Asset:GNO is a running experiment. Continuation and improvements are (relatively) low cost and effort.

 Yet:

How precisely can we get before the advent of real time sub-MeV data ?

Outset on which we must improve(see Bahcall and Pena-Garay, hep-ph 0305159)

pp-flux: (1.01 0.02) x BP00 SSM (1)

(with luminosity constraint)

7Be-flux: (0.97 +0.28-0.54) x BP00 SSM (1)

 tang2θ12 = = 0.42 +0.08-0.06

(LMA: Δm2 = ( 7.3 +0.4-0.5) x 10-5 eV2 ;

no hope to improve on this from GNO/Borexino)

fGa,cc = 0.55 0.03 (1)

CC / NC Response

Determination of the pp-neutrino flux from GNO and Borexino

Deduction of the pp-flux

E (MeV)

P ( e

e)

5

4

1

32

Survival probabilities

Ppp = 0.57 +- 10%Ppep = 0.53 +- 5%P7 = 0,56 +- 8%P8 = 0.33 +- 20%PCNO = 0.55 +- 8%

12

3

4

5

C. Cattadori, N. Ferrari

Survival probabilities

Capture cross sections

type Err % Transitions Signal/SSM % Errors from 10-46 cm2 % GS 1,2 >2 (with MSW LMA) GS 1,2 >2

pp 11.72 +- 2.3 100 - - 0.311 pep 204 -7 +17 82 6 12 0.0127Be 71.7 -3 +7 94 6 - 0.1508B 24000 -15 +32 12 6 82 0.030N 60.4 -3 +6 94 6 - 0.014O 113.7 -5 +12 86 6 8 0.023

TOT 0.541 +-2.1 -0.4+1.7 -0.9 +3.5

Capture cross sections

Future Plans in GNO

Future Neutrino Source Exposures

Source Feasibility and Status

An intense feasibility study, including test irradiations with actual GALLEX enriched chromium, revealed that the RIAR reactor research institute at Dimitrovgrad (Russia) can produce sources up to 6.5 MegaCurie with the available material.The immediate project is a 3 MCi source for GNO (next major experimental step)

Quotation of J. Bahcall

„Simple neutrino scenarios fit well the existing data, which – with the exception of the chlorine and gallium radiochemical experiments – all detect only solar neutrinos with energies above 5 MeV.

Perhaps these higher energy data have not yet revealed the full richness of the weak interaction phenomena.”Nucl.Phys. Proc. Suppl. B118 (2003) 86