Diapositiva 1

1
solar neutrino physics
3rd School on Cosmic Rays and Astrophysics August
25 to September 5, 2008 Arequipa Perú
Lino Miramonti Università degli Studi di Milano
and Istituto Nazionale di Fisica Nucleare
Homestake The first solar neutrino detector
..to see into the interior of a star and thus
verify directly the hypothesis of nuclear energy
generation in stars. Phys. Rev. Lett. 12, 300
(1964) Phys. Rev. Lett. 12, 303 (1964)
How the Sun shines
Neutrino energy spectrum as predicted by the
Solar Standard Model (SSM)
The first experiment built to detect solar
neutrinos was performed by Raymond Davis, Jr. and
John N. Bahcall in the late 1960's in the
Homestake mine in South Dakota
7Be 384 keV (10) 862 keV
(90) pep 1.44 MeV
Davis and Bahcall
Large tank of 615 tons of liquid perchloroethylene
The pp chain reaction
1 SNU (Solar Neutrino Unit) 1 capture/sec/1036
atoms
Neutrinos are detected via the reaction
ne 37Cl ? 37Ar e-
Eth 814 keV mostly 8B neutrinos
The CNO cycle
Remove and detect 37Ar (?1/235 days) 37Ar e-
? 37Cl ?e
Homestake Solar Neutrino Detector
Expected rate Only 1 atom of 37Ar every six days
in 615 tons C2Cl4!
The number of neutrino detected was about 1/3
lower than the number of neutrino expected ?
Solar Neutrino Problem (SNP)
Expected from SSM 7.6 1.3 - 1.1 SNU Detected
in Homestake 2.56 0.23 SNU
looking for pp neutrinos
Possible Explanations to the SNP
Kamiokande ? SuperKamiokande Real time detection
Until the year 1990 there was no observation of
the initial reaction in the nuclear fusion chain
(i.e. pp neutrinos). This changed with the
installation of the gallium experiments. Gallium
as target allows neutrino interaction via 2
radiochemical experiment were built in order to
detect solar pp neutrinos.

• Standard Solar Model is not right
• Homestake is wrong
• Something happens to the ?

• SuperKamiokande large water Cherenkov Detector
• 50000 tons of pure water
• 11200 PMTs

• Kamiokande large water Cherenkov Detector
• 3000 tons of pure water
• 1000 PMTs

..but
Solar models have been tested independently by
helioseismology (studies of the interior of the
Sun by looking at its vibration modes), and the
standard solar model has so far passed all the
tests. Non-standard solar models seem very
unlikely.
SuperKamiokande
ne 71Ga ? 71Ge e-
Eth 233 keV
Less model-depended
bisede
Reaction Elastic Scattering on e-
GALLEX (and then GNO)
Electrons are accelerated to speeds v gt c/n
faster than light.
Located in the Gran Sasso laboratory (LNGS) in
Italy. The tank contained 30 tonnes of natural
gallium in a 100 tonnes aqueous gallium chloride
solution
Eth 7.5 MeV (for Kamiokande) Eth 5.5 MeV (for
SKamiokande) only 8B neutrinos (and hep)

• New experiments (since about 1980) are of three
  types
• Neutrino scattering in water (Kamiokande,
  SuperKamiokande)
• Radiochemical experiments (like Homestake, but
  probing different energies) (SAGE, GALLEX)
• Heavy water experiment (SNO)

SAGE
The core of the Sun reaches temperatures of ?
15.5 million K. At these temperatures, nuclear
fusion can occur which transforms 4 Hydrogen
nuclei into 1 Helium nucleus
Located at Baksan underground laboratory in
Russia Neutrino Observatory with 50 tons of
metallic gallium running since 1990-present
Results Inferred flux ? 2 times lower than the
prediction Neutrinos come from the Sun! (Point
directly to the source)
The measured neutrino signal were smaller than
predicted by the solar model (? 60). Calibration
tests with an artificial neutrino source (51Cr)
confirmed the proper performance of the detector.
CC, NC FLUXES MEASURED INDEPENDENTLY
Sudbury Neutrino Observatory NC CC detection
Summary of all Solar neutrino experiments before
Borexino
1000 tonnes D2O (Heavy Water)
Best fit to data gives
The Total Flux of Active Neutrinos is measured
independently (NC) and agrees well with solar
model Calculations 4.7 0.5 (BPS07)
All experiments see less neutrinos than
expected by SSM .. (but SNO in case of NC)
electron neutrinos oscillate into non-electron
neutrino with these parameters
Solar Model Chemical Controversy
Borexino is able to measure for the first time
neutrino coming from the Sun in real_time with
low_energy (? 200 keV) and high_statistic.
Borexino real time at low energy
Large mixing Angle (LMA) Region MSW
from S.Abe et al., KamLAND Collab.
arXiv0803.4312v1

• One fundamental input of the Standard Solar Model
  is the metallicity (abundance of all elements
  above Helium) of the Sun
• The Standard Solar Model, based on the old
  metallicity GS98 is in agreement within 0.5
  with helioseismology (measured solar sound
  speed).
• Recent work AGS05 indicates a lower
  metallicity. ? This result destroys the agreement
  with helioseismology
• A lower metallicity implies a variation in the
  neutrino flux (reduction of ? 40 for CNO
  neutrino flux) ? A direct measurement of the CNO
  neutrinos rate could help to solve this
  controversy

A direct measurement of the CNO neutrinos rate
(never measured up to now) could give a direct
indication of metallicity in the core of the Sun
Radiochemical
Real time measurement (only 0.01 !)
SOLAR only
SNO SuperKamiokande
Homestake
Gallex/GNO SAGE
KamLAND is a detector built to measure electron
antineutrinos coming from 53 commercial power
reactors (average distance of 180 km ). The
experiment is sensitive to the neutrino mixing
associated with the (LMA) solution.
SOLAR plus KamLAND
Borexino (real time)
Rl are the rates actually measured by Clorine and
Gallium experiments f8B is measured by SNO
and SuperKamiokande f7Be 1.02 0.10 is given
by Borexino results
7Be Neutrinos Flux
Constraints on pp and CNO fluxes
Best estimate ratio prior to Borexino, as
determined with global fit to all solar (except
Borexino) and reactor data, with the assumption
of the constraint on solar luminosity (M.C.
Gonzalez-Garcia and Maltoni, Phys. Rep 460, 1
(2008)
It is possible to combine the results obtained by
Borexino on 7Be flux with those obtained by other
experiments to constraint the fluxes of pp and
CNO ?
The expected rate in Clorine and Gallium
experiments can be written as
Ratio measured by Borexino assuming the high-Z
BPS07 SSM and the constraint on solar luminosity
Performing a ?2 based analysis with the
additional luminosity constraint
Survival probability averaged over threshold for
a source i in experiment l
Ratio between measured and predicted flux
Which is the best determination of pp flux
Expected rate from a source i in experiment l
that corresponds to a 7Be neutrinos flux of
This result translates into a CNO contribution to
the solar neutrino luminosity lt 3.4 (90 C.L)
Rl,i and Pl,i are calculated in the hypothesis of
high-Z SSM and MSW LMA