Transcript Diapositiva 1 - Istituto Nazionale di Fisica Nucleare

solar neutrino physics
3rd School on Cosmic Rays and Astrophysics
August 25 to September 5, 2008
Arequipa – Perú
Lino Miramonti
“…..to see into the
interior of a star and
thus verify directly the
hypothesis of nuclear
energy generation in
stars.”
Homestake: The first
solar neutrino detector
How the Sun shines
Neutrino energy spectrum
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:
as predicted by the
384 keV (10%)
Solar Standard Model (SSM)
862 keV (90%)
pep:
Phys. Rev. Lett. 12, 300 (1964);
Phys. Rev. Lett. 12, 303 (1964);
Davis and Bahcall
Large tank of 615 tons of
liquid perchloroethylene
1.44 MeV
The pp chain reaction
Neutrinos are detected via the reaction:
ne+ 37Cl → 37Ar + eThe CNO cycle
Eth = 814 keV
mostly 8B
neutrinos
Remove and detect
37Ar
Homestake Solar
Neutrino Detector
(1/2=35 days): 37Ar + e-  37Cl* + ne
Expected rate: Only 1 atom of 37Ar every six days in 615 tons C2Cl4!
1 SNU (Solar Neutrino Unit) = 1 capture/sec/1036 atoms
Università degli Studi di Milano and Istituto Nazionale di Fisica Nucleare
Expected from SSM: 7.6 + 1.3 - 1.1 SNU
The number of neutrino detected was about 1/3 lower than the
Detected in Homestake: 2.56 ± 0.23 SNU number of neutrino expected → Solar Neutrino Problem (SNP)
…looking for pp neutrinos …
Kamiokande  SuperKamiokande: Real time detection
Possible Explanations to the SNP
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
..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.
Kamiokande large water
SuperKamiokande large water
Cherenkov Detector
Cherenkov Detector
•3000 tons of pure
water
•1000 PMTs
Reaction: Elastic Scattering on e-
bisede
Non-standard solar models seem very
unlikely.
n  e  n  e 
•Homestake is wrong
SuperKamiokande
•50000 tons of pure
water
•11200 PMTs
ne+ 71Ga → 71Ge + e-
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 = 5.5 MeV (for SKamiokande)
SAGE
only 8B neutrinos (and hep)
•Neutrino scattering in water (Kamiokande,
SuperKamiokande)
•Radiochemical experiments (like Homestake, but
probing different energies) (SAGE, GALLEX)
•Heavy water experiment (SNO)
The core of the Sun reaches temperatures of  15.5 million K.
Baksan underground
laboratory
in Russia
AtLocated
these at
temperatures,
nuclear
fusion can
occur which transforms 4
Hydrogen nuclei into 1 Helium nucleus
Results:
Neutrino Observatory with 50 tons of metallic gallium
running since 1990-present
Inferred flux  2 times lower than the prediction
Neutrinos come from the Sun! (Point directly to the source)
•Something happens to the n
Less model-depended
GALLEX (and then GNO)
Electrons
are
accelerated
to
speeds v > c/n
“faster than light”.
Eth = 7.5 MeV (for Kamiokande)
New experiments (since about 1980) are of three types:
Eth = 233 keV
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:
6
 2 1
   3.41  0.45  00..45
48 10 cm s
CC  1.68
 0.06
0.06
NC  4.94
 0.21
0.21
ES  2.35
 0.22
0.22
08
(stat.) 00..09
(syst.)
The Total Flux of Active Neutrinos is
measured independently (NC) and
agrees well with solar model
Calculations: 4.7 ± 0.5 (BPS07)
38
(stat.) 00..34
(syst.)
15
(stat.) 00..15
(syst.)
(In unitsof 106 cm2s1 )
CC  n
e

 NC  n e  n   n 

ES  n e  0.154(n   n  )
CC
029
Pee 
 0.34  0.023(stat.) 00..031
12
NC
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:
5
m  7.6 10 eV
sin 2 212  0.87
2
12
Large mixing Angle (LMA) Region: MSW
2
Solar Model Chemical Controversy
from S.Abe et al., KamLAND
Collab. arXiv:0803.4312v1
Borexino: real time at low energy
•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).
SOLAR only
•Recent work [AGS05] indicates a lower metallicity. → This result destroys the
agreement with helioseismology
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 %!)
Gallex/GNO
SAGE
Homestake
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.
SNO &
SuperKamiokande
•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
SOLAR plus
KamLAND
7Be
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.
Neutrinos Flux 
i
m easuredvalue
f i  SSM 
i
predicted value
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)
24
f Be  1.0310..03
Rl are the rates actually measured by Clorine and Gallium experiments:
Constraints on pp and CNO fluxes
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:
Rl SNU    Rl ,i f i Peel ,i
source
l  Ga, Cl
experiment i  pp, pep, CNO,7Be,8B
i
f Be  1.02  0.10
that corresponds to a
7Be neutrinos flux of:
f8B is measured by SNO and SuperKamiokande:
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 ν;
Expected rate from
a source “i” in
experiment “l”
Ratio between
measured and
predicted flux

Survival probability averaged over
threshold for a source “i” in
experiment “l”
Rl,i and Pl,i are calculated in the
hypothesis of high-Z SSM and
MSW LMA

f7Be =1.02 ±0.10 is given by Borexino results;
Performing a 2 based analysis with the additional luminosity
constraint;
f pp  1.00400..008
020
(1 )
Which is the best determination of pp flux
fCNO  3.90 (90% C.L.) This result translates into a CNO contribution to
the solar neutrino luminosity <
3.4% (90% C.L)