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, TUM Muenchen: R&D on cryogenic detectors;
LAquila University: R&D on desorption plant.
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 2002
The
following physics items were achieved during 2002:
- 12
solar runs have been successfully performed; the total
number of solar runs of GNO is now 54. These runs can be
added to the 65 solar runs performed in GALLEX.
- 2
short-exposure runs (blanks) have been successfully
performed during 2002; the total number of blanks in GNO
is 10. The analysis of blanks is an important tool to
check the absence of any signal faking 71Ge
from solar neutrinos.
- Application
of a new advanced pulse shape analysis studied in detail
during 2001. In the past data analysis was carried out
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. Application of this method allowed
to reduce the background level by about 10%, and a better
better recognition of double pulses.
- 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. In total 15 counters have
been calibrated. The remaining few counters will be
calibrated in 2003.
- Data
analysis. Data from the first 43 GNO solar runs were
analyzed and results were presented at the Neutrino 2002
conference. The neutrino interaction rate as measured
from the first 43 GNO runs is 65.3 +/- 6.4 (stat) +/- 3.0
(sys) SNU; the global result from the 65 GALLEX + 43 GNO
solar runs is 70.8 +/- 4.5 (stat) +/- 3.8 (sys) SNU.
- The
systematic error in GNO (+/- 3.0) is significantly
reduced with respect to the GALLEX one (+/- 4.5 SNU);
therefore a relevant reduction of the global error has
been achieved by GNO.
- Data
were also analyzed in terms of possible seasonal
variations; no significant effect was found.
- We are presently considering a third exposure of the
gallium solution to an intense (>2.5 MCi~ 90 PBq)
neutrino source. At present we have a design of the
source very close to the final one provided by the
Research Institute of Atomic Reactors of Dimitrovgrad
(Ulyanovsk region, Russia) after strict contacts with the
GNO collaboration. Many technical aspects (e.g. absolute
calibration of the source, transportation) have been
investigated. The source project if finally approoved and
funded will allow to check the stability of the
experiment and improve our knowledge on the neutrino
cross section on gallium.
The following achievements
have been obtained:
- Routine solar and blank runs execution.(data from one
solar run was lost due high voltage instability) (93%)
- Preliminary work to obtain a 51Cr neutrino
source (100%)
Milestones
2003:
Completion
of 12 solar runs and of blank runs |
31-12-2003
|
Absolute
calibration of 4 proportional counters |
30-06-2003
|
Re-calibration
of the carrier concentration |
30-09-2003
|
Definition
of the final program for the 51Cr source project |
30-09-2003
|
Release
of updated results on solar neutrinos |
30-09-2003
|
3.
INFN contribution to the experiment in terms of manpower and
financial support
Manpower: 14 researchers (7.4 FTE), and support
of the LNGS workshop and chemical labs
Budget for the year 2003: 1.0 % of
the CSNII budget
4.Publications in refereed
journals (in 2002): 1
5.
Number of conference talks (in 2002): 5
6.
Undergraduate and PhD (italian groups):
1 students
(Milano Bicocca Univ.) is doing his 'tesi di laurea'.
1 PhD student
(LAquila University) is doing his PhD studies (1st year).
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.
- INFN Milano, LNGS, MPI Heidelberg, TUM Muenchen: 51Cr
Source project
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.
- High intensity neutrino source and related technologies
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.
We plan to have a more strict than in the past exchange of
information among the two experiments.
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.