GNO : Gallium Neutrino Observatory
Collaboration
- Italy: Dip. di Fisica
dell' Università di Milano 'La Bicocca', and INFN sez.
di Milano, Milano; INFN, Laboratori Nazionali del Gran
Sasso (LNGS), Assergi (AQ); Dip. di Fisica, Università
di Roma 'Tor Vergata' and INFN sez. di Roma-II, Roma;
Dip. di Ingegneria Chimica e Materiali, Università
dell'Aquila , L'Aquila
- Germany: Max Planck
Institut fuer Kernphysik (MPIK), Heidelberg; Institut
fuer Technische Chemie, Forschungszentrum Karlsruhe
(Fzk), Karlsruhe; Physik Department E15, Technische
Universitaet Muenchen (TUM), Muenchen
Location of the
experiment: LNGS for solar neutrino measurements, MPIK
Heidelberg for proportional counter construction and absolute
calibrations.
National Responsible:
E.Bellotti (Mi)
1. Goal of the experiment
The goal of GNO is to monitor the low energy solar
neutrino flux with a radiochemical gallium detector underground
at Laboratori Nazionali del Gran Sasso. The measurement of the
solar neutrino flux and their energy spectrum is crucial both for
astrophysics and for particle physics (neutrino flavor
oscillations). Gallium-based radiochemical detectors are the only
working experiments able to detect the low-energy pp neutrinos,
produced in the sun in the basic reaction of the hydrogen chain.
More on the experiment
2.
Activities
during 2001
The
following physics items were achieved during 2001:
- 13 solar runs have been successfully
performed; the total number of solar runs of GNO is now
43. These runs can be added to the 65 solar runs
performed in GALLEX.
- 4 short-exposure runs (blanks) have been
successfully performed during 2001; the total number of
blanks in GNO is 8. The analysis of blanks is an
important tool to check the absence of any signal faking 71Ge
from solar neutrinos.
- Upgrade of the electronics from 12 to 16
independent counting lines (analog, digital, and DAQ)
- Development of an advanced pulse shape
analysis. Data analysis was carried on up to now with a
two parameter pulse shape cut (energy-rise-time). A more
sophisticated analysis based on fitting the whole pulse
and using a neural network to select 71Ge
events was developed; efficiency and systematic was
deeply investigated, and the new method will be adopted
starting from the next data release.
- Counter calibrations. The most relevant
systematic error of the experiment is represented by the
uncertainty in the determination of the counting
efficiency of the proportional counters. A substantial
reduction of this component (from 4% to about 1.5%) was
achieved by direct absolute calibration of several
proportional counters doped with 69Ge. It is
foreseen to calibrate all other used counters in the
future.
- A Radon test started in 1999 was
successfully completed. The aim of the test was to
improve the characterization and understanding of Rn
events, and decrease the systematic uncertainty due to
the so-called 'Rn cut' applied to the data.
- Data analysis. Data from the first 35 GNO
solar runs were analyzed and results were presented at
the TAUP 2001 conference. The neutrino interaction rate
as measured from the first 35 GNO runs is 67.7 +/- 7.2
(stat) +/- 3.2 (sys) SNU; the global result from the 65
GALLEX + 35 GNO solar runs is 73.3 +/- 4.7 (stat) +/- 4.0
(sys) SNU.
- The systematic error in GNO is
significantly reduced with respect to the GALLEX one (+/-
4.5 SNU); therefore a relevant reduction of the global
error is expected to come from continuation of the
experiment.
- Data were also analyzed in terms of
possible seasonal variations; no significant effect was
found.
The following achievements
have been obtained:
Routine
solar and blank runs execution. |
31-12-2001
|
100%
|
Development
of new pulse and data analysis methods. |
30-09-2001
|
100%
|
Milestones
2002:
Uninterrupted acquisition of
solar runs |
31-10-2002 |
Preliminary work to obtain a
51Cr neutrino source |
31-10-2002 |
51Cr neutrino
source production and Gallium solution irradiation (if
possible, within 30/04/2003). |
31-12-2002 |
3.
INFN contribution to the experiment in terms of manpower and
financial support
Manpower: 13 researchers (7.5 FTE), and support
of the LNGS workshop and chemical labs
Budget for the year 2002:1216,5 kEuro
4.Publications in refereed
journals (in 2001):
5.
Number of conference talks (in 2001): 6
6.
Undergraduate and PhD (italian groups):
Undergraduate
students: 3 students completed their 'tesi di laurea' during
2001 (1 at Università degli Studi di Milano, 1 at Phys. Dep. of
Università dell'Aquila, 1 at Chem. Dep. of Università
dell'Aquila)
7. Leadership roles and
primary responsibilities of the experiment
- E. Bellotti - principal investigator
- INFN LNGS and L'Aquila University : Ge
Extraction, maintenance and upgrade of the chemical
plants;
- INFN Milano and LNGS: hardware and
electronics for 71Ge counting;
- INFN Milano: DAQ;
- INFN Roma and LNGS: Data storage and
backup, web page;
- INFN Milano and LNGS: Data monitoring and
analysis;
- INFN Milano and MPI Heidelberg: Counter
absolute calibrations.
8.
Innovative instruments
- Development of extremely low radioactivity
techniques
- Development of extremely-low-background
cryogenic-detectors able to detect a few 71Ge
decays. These instruments, under study at TUM Muenchen,
could eventually be employed besides the gas proportional
counters presently used in GNO, with improved counting
efficiency and independent systematic.
9.
Competing experiments
Radiochemical
gallium detectors are the only one presently able to detect pp
solar neutrinos. Next generation real-time experiments able to
lower the threshold to cover the pp energy region are still in a
R&D phase and are not expected to start observations at least
in the next 5 years.
The
SAGE experiment, situated in the Baksan mine in Caucasus is the
only other radiochemical gallium solar neutrino detector in the
world. The gallium in SAGE is in metal form with a mass of about
50 tons.
10.
International committee which has reviewed the experiment
The
experiment is reviewed by the funding authorities of INFN and
periodically by the Scientific Committee of the LNGS.