The document summarizes information about the Sun and discusses several particle physics experiments related to the Sun. It provides basic facts about the Sun such as its temperature, age, composition and total luminosity. It then discusses three specific topics - solar neutrinos, solar axions, and WIMPs in relation to the Sun. For solar neutrinos, it explains their production through the pp-chain and CNO cycle and discusses several past experiments that detected solar neutrinos such as Homestake, SAGE, GALLEX, Kamiokande and Super-Kamiokande, and SNO. It notes the "solar neutrino problem" of a discrepancy between predicted and observed solar neutrino fluxes. For solar axions, it defines what

1. The Sun
and
the particle physics
Vladislav Kobychev
Insitute for Nuclear Research, Kiev, Ukraine

2. 1. The Sun: basic facts
2. Solar neutrinos
3. Solar axions
4. The Sun and WIMPs

3. Basic facts on the Sun:
•Central temperature: 15 710 000 K 1.4 keV
•Surface temperature: 6000 K
•Age: 4.6·109 yr.
•Distance from Earth: R = 150·106 km (1 Astr. Unit)
•Diameter: D = 2R = 1.4·106 km (108 x D )
•Mass: M = 2·1030 kg (300 000 x the Earth's mass)
•Average density: 1400 kg/m3 (1.4 x water)
(central density: 150 x water).
•Composition: 74% H, 24% He, 2% of heavy elements
•Solar energy reaching Earth:
1400 W/m2 (solar constant)
•Total luminosity:
L =1400 W/m2 x 4 x R2 = 4·1026 W
The Sun is a very typical star:
nothing special. The only special feature
(for us) is that it is the closest star.

4. Production of solar neutrinos
pp-chain:
pp, pep, 7Be & 8B neutrinos

5. Production of solar neutrinos
Net reaction:
p+ + p+ + p+ + p+ + e– + e–
4He (p+ + p+ + n0 + n0)
e e

6. e - what
does it
mean?
The Standard Model of particle physics forbids
conversion between different kinds (flavours) of
neutrino and considers them massless.

7. Production of solar neutrinos
CNO-chain:
13N, 15O & 17F neutrinos

8. Production of solar neutrinos
Every second, the Sun produces 2·1038 electron
neutrinos, and almost all of them escape to the
space (very weakly interacting with the matter).
On Earth, the solar neutrino flux is
~60 000 000 000 neutrinos/(cm2 s).

10. Several experiments have been carried out to measure
the solar neutrino flux.
Homestake:
Homestake: radiochem. Cl-Ar experiment.
Cl-
SAGE and GALLEX/GNO: radiochem. Ga-Ge –
GALLEX/GNO: Ga-
large fraction of pp neutrinos + 7Be neutrinos.
Kamiokande and Super-Kamiokande: water
Super-Kamiokande:
Cherenkov -- 8B neutrinos.
SNO: heavy water -- 8B neutrinos + neutral
SNO:
current reactions with muon and tau neutrino
+ elastic scattering of all flavours.
Borexino:
Borexino: liquid scintillator -- the first experiment
to detect low-energy solar neutrinos in real time
low-

11. History of solar neutrino experiments:

12. Homestake experiment
The Homestake solar neutrino
experiment was in the Homestake
gold mine in South Dakota. The
detector was constructed at
Brookhaven National Laboratory in
the late 1960s by a collaboration led
by Dr. Raymond Davis, and has been
operated continuously since 1970
(taken over by UPenn in 1984). The
detector was a big tank containing
615 tons of liquid perchloroethylene
(C2Cl4).
Neutrino detection via the reaction:
e + 37Cl e - + 37Ar, Eth = 0.814 MeV
Collection of radioactive 37Ar (few tens atoms per
month!) from all the tank into a small counter.

13. Homestake Construction (1966)

14. Homestake Experiment
The Solar Neutrino Unit (SNU) = 1 neutrino
interaction per second per 1036 atoms
But 1036 atoms is ~ 240 million tons of
chlorine
Homestake could contain ~1030 atoms
So, Homestake counted only ~2.5 neutrinos
per day (2.55 ± 0.25 SNU)
Based on the Standard Solar Model, one
should expect 8 ± 1 SNU
“Solar neutrino problem”

15. Homestake experiment
The Nobel result* obtained by
Davis:
The flux of solar neutrinos is
~3 times less then the
predicted.
predicted.
*) The Nobel Prize in Physics, 2002

16. Solar neutrino problem
•All existing experiments on
detecting of solar neutrinos
gave 1/3 to 1/2 of the
predicted neutrino flux
(Standard Solar Model +
weak interactions theory)
•Beside this, different
experiments gave different
(and disagreeing)
experiment-to-theory ratios.

17. Solar neutrino problem

18. Solar neutrino problem
Possible solutions:
1. We don’t understand the solar interior
2. We don’t understand the behaviour of neutrino

19. Neutrino oscillations
If electron, muon and tau lepton
numbers don’t conserve, the neutrino of
one flavour can transform to other one.
This requires neutrino masses should
be non-zero and different mass states
non-
should have different masses.
The neutrino oscillations were predicted
by Bruno Pontecorvo in 1957 by
analogy with the observed neutral kaon
oscillations.

20. Solar neutrino oscillations
Before SNO all the
experiments detected only
electron Solar neutrinos.
SNO found that the most
of the flux of solar neutrino
are not electron ones.
ones.
Flux of mu and
But the solar core emits
tau neutrinos
only electron neutrinos, so
neutrinos,
neutrinos have to flavour
oscillate flying from the
solar core to the Earth.
It is possible only in the Flux of electron
case when the flavour neutrinos
states of neutrino do not
coincide with their mass
states, and these mass
states have to have
(different) masses:
disagreement with the
Standard Model!

22. MSW Effect
The neutrino oscillations are resonantly gained when
the neutrino flux propagates through matter with
slowly changing density (Mikheev-Smirnov-
(Mikheev-Smirnov-
Wolfenstein effect). The effective mass of neutrino
depends on the density of electrons in the matter, and
in some point where the effective masses of different
neutrino flavours crosses, the oscillation
enhancement appears.
MSW effect explains the observed difference of solar
neutrino fluxes in different experiments:
Low energy (pp) neutrinos (SAGE, GALLEX)
(pp) GALLEX)
survive with higher probability:
probability:
Pee P( e e) = 56%.
56%.
High energy (8B) neutrinos survive with lower
probability:
probability:
Pee ~ 32% (theory, SNO)
even their passage through Earth can have an
observed effect (day-night assimmetry)
(day- assimmetry)
No good data for intermediate energies.

23. MSW Effect

24. R N

25. Laboratori Nazionali del Gran Sasso

26. Abruzzo, Italy Laboratori
120 km of Rome Nazionali del
Gran Sasso
External Buildings Asserg (AQ)
of the Laboratory Italy
~3500 m w.e.
1 km of depth
detector26and
supplementary equipment

27. BOREXINO

28. BOREXINO

29. Steel sphere
278 t PC+PPO
(R=6,85 m):
(1,5 g/l)
- 2212 PMT (8”);
- 1350 m3
PC+DMP (5.0 g/l)
2100 m3 water tank:
Two 0.125 mm
- R=9 m, H=16,9 m;
nylon spheres:
- 208 PMT in water,
- R=4,25 m;
looking outwards;
- R=5,5 m
- shielding from
-(Rn-barrier)
, &n

31. Physical program
of :
Monoenergetic
= 862 keV) solar 7Be
keV)
neutrinos;
neutrinos;
pep & CNO neutrinos;
Antineutrino from reactors
and the Sun;
Sun;
Geoneutrinos;
Geoneutrinos;
Supernova neutrinos (?) …
Rate of (SSM, MSW-LMA),
prediced for

33. Registration of
Neutrinos scatter on electrons of liquid organic scintillator
(pseudo-cumene):
(pseudo-cumene):
Low threshold of registration;
registration;
Good energy resolution;
resolution;
Good space reconstructions.
reconstructions.
BUT…
No directional sensitivity;
sensitivity;
No selection between events and other (natural
radioactivity).
radioactivity).
!! HIGHEST REQUIREMENTS TO RADIOPURITY
OF SCINTILLATOR AND OTHER MATERIALS !!

34. RADIOPURITY
Uranium
Thorium 10-6 g/g in natural substances (human body etc.)
10-17 g/g in Borexino scintillator
Potassium 10-4…10-2 g/g in natural substances
~300 g in a 70 kg human body
(4000 decays/s of 40K)
10-14 g/g in Borexino scintillator
The center of the Borexino detector is possibly
the most radiopure place in the Universe.

35. Data collection
The collected data
allow to reconstruct
for every event:
•Total absorbed energy
•Position (±10 cm)
•Kind of particle (alpha,
beta, muons)

36. The preliminary result of Borexino
49 ± 3stat ± 4syst 7Be / (day · 100 t)
(day

37. Comparison with theor.predictions
for :
exp.: 49 ± 3stat ± 4syst evt./(day · 100 t)
49
75 ± 4 evt./(day · 100 t) without oscillations
evt.
49 ± 4 evt./(day · 100 t) with MSW-LMA
evt. MSW-
oscillations
m122 = 7,92·10–5 2, sin2 12 = 0,314)
for the Standard Solar Model BPS07(GS98)

38. Axions
Axion is a hypothetical neutral massive particle, introduced
to theory in connection with the problem of strong CP-violation.
The QCD includes the so-called -phase, which is experimentally
very small (0 or, at least, <10–10), but its smallness is not required
by the theory ( -phase can take any value between 0 and ).
Peccei and Quinn (1977) proposed a mechanism to make
-phase equal 0 by introducing a new symmetry, with being a
dynamical variable, of zero value at the minimal energy state. The
spontaneous violation of the PQ symmetry creates the Goldstone
boson, which was named axion by Frank Wilczek.
Axions are considered as one of the best candidates for the
Dark Matter particles, because they are massive and their
interaction with normal matter should be extremelly small.
23.03.2009
23.03.2009 « » 6

39. Axion interactions
DFSZ-axion hadronic axion
Compton
effect Primakoff’s effect Bremsstrahlung
Mass of axion varies from 10–18 to 1 MeV in different
variants of theory. Spin/parity of axion is 0–
(pseudoscalar particle). The leptonic axion (DFSZ-
axion) interacts with leptons directly, the hadronic axion
(KSZV-axion) – only with hadrons.

40. Laboratory search for solar axions
Based on axion-photon conversion in magnetic field.
External
field
Axion
Axion

41. Laboratory search for solar axions
The predicted solar axion luminosity for DFSZ-axions:
2
ma3
La 3.6 10 L
1
Their mean energy is predicted to be 4.2 keV.
In order to registrate the axions, they are converted to
X-ray quanta with strong transversal magnetic field.
X-rays are then detected by an appropriate detector.
The most sensitive experiment of this kind is the axio-
helioscope CAST (CERN), using a huge de-
comissioned accelerator magnet.

42. Laboratory search for solar axions
Resonant absorption of solar axions.
The thermal excitation of low-energy nuclear levels
(of few keV, f.i., 57Fe) can be excited in the solar core
(T= 1.4 keV). These levels can (in some conditions)
deexcite via emission of an axion which escapes from
the Sun almost freely. In Earth, the axion can
resonantely excite a nucleus of the same kind which
then deexcites by emission of a detectable gamma
quantum. Many experiments are based on this
scheme.
Modification: the level of the nucleus-emitter is
populated not by thermal excitation, but in a nuclear
reaction (for example, the 478 keV excited level of 7Li
is populated by the electron capture of 7Be in the pp-
chain with ~10% branching ratio)

43. Solar axions: continuous spectrum
axions:
(Primakoff’s effect: photon-to-axion
photon-to-
conversion in the electric field of a nucleus)
43

44. 57Fe
14.4 keV
The monoenergetic lines can also be present
in the solar axion spectrum. 44

45. Solar Core Laboratory
57Fe 57Fe
14.4 keV 14.4 keV
gaNN a gaNN
1. Thermal excitation 3. Resonant excitation of a
2. Emission of a target 57Fe nucleus by the axion.
monoenergetic axion. 4. Emission of gamma quantum.
5. Detection.
The method was proposed: Moriyama [PRL 75(1995)3222].
proposed:
Other natural isotopes with low-lying levels, de-excitated
via M1-transitions, can be (and are) also used; for 45
example, 83Kr (9.4 keV).

46. 57Fe(‘iron’) solar axions allow to exclude axion
mass values between ~14.4 keV and (on today)
0.216 keV [T. Namba, PLB 645 (2007) 398].
Other possibility – non-thermal excitation of source nuclei.
non-
7Li is created
in the pp-
chain (the
main energy
source of the
Sun).
46

47. Solar Core Laboratory
7Li 7Li
7Be
477.6 keV 477.6 keV
gaNN a gaNN
1. Level population via 3. Resonant excitation of a
electron capture of 7Be target 7Li nucleus by the axion.
2. Emission of 4. Emission of gamma quantum.
a monoenergetic axion. 5. Detection.
First exp.: M. Krcmar et al. [PRD 64 (2001) 115016]
(ma < 32 keV).
keV).
Best limit: A.V. Derbin et al. [JETP Lett. 81 (2005) 365]
limit:
(ma < 16 keV).
47

48. Our experiment:
1. Lithium fluoride (LiF) was chosen
as a target due to:
a) its high density of Li nuclei in
comparison to other Li compounds;
b) chemical passivity;
c) non-hygroscopicity.
non-
2. Few samples of LiF (powder of
99.99% purity, single crystal) were
placed in two HPGe detectors in
Laboratori Nazionali del Gran Sasso
(3800 m w.e.). 48

49. If we would observe a gamma peak at 478
keV with area S, mass of axion would be
ma = 1.55×1011 × (S tN7)1/4 eV
– efficiency of the detector,
t – time of measurement,
N7 – number of 7Li nuclei in the sample.
ma < 13.9 keV
(90% C.L.)
49

50. LiF(W) single crystals
Total mass is ~550 g.
50

51. Of course, the search for mono-energetic axions from
the Sun can be performed also without resonant
nucleus as a target (the resonant target only allows to
decrease its mass by increasing the cross-section).
Such the searches were carried out by Borexino and
CAST collaborations (both are mentioned above) for 7Li
solar axions.

52. Geophysical search for solar axions
Another interesting idea: we have a lot of iron within
the Earth core; let us consider it as a target for “iron”
solar axions. The resonant absorption of 14.4 keV
axions by 57Fe nuclei would heat the Earth core, and
the thermal flow through the Earth surface outwards
(measured: ~42 TW) would give us the upper limit on
probability of such the process.
Taking into account that the part of this heat flow is
produced by radioactive transitions (U, Th, K) in the
Earth crust, we can set the upper limit on the hadronic
axion mass of ma<1.6 keV.
Danevich et al., Kinematics and Physics of Celestial
Bodies, 25(2009)102.

53. Indirect search for WIMPs by their annihilations
within the Sun
The Dark Matter is non-barionic matter which
dominates in the Universe but is “invisible” – it is still
observed only by its gravitaitonal influence to the
normal matter. The most common hypothesis is that
the DM consists of Weakly Interacting Massive
Particles – WIMPs. They are stable and have a mass
of tens GeV or more. There are many direct
experiments to search for WIMPs, but indirect
observations are possible too. One of ways to observe
WIMPs indirectly is the search for high-energy
neutrinos emitted by annihilating WIMPs captured by
the Sun.

54. Indirect search for WIMPs by their annihilations
within the Sun
The neutrinos from WIMPs annihilation with energy of
GeVs or tens GeV can escape from the Sun and be
detected by an appropriate high-energy neutrino (HEN)
detector. The collaborations IMB, Kamiokande, AMANDA
and MACRO already tried to extract such the information
from their observations.
For example, AMANDA detector is placed within ice many-
km layer on the South pole. A HEN from the Sun
propagates through Earth and interacts with rock or ice
under the detector. This interaction creates a high-energy
muon that keeps the direction of the primary neutrino
moving; the PMTs of AMANDA will see an upwarding
muon by emission of Cherenkov light in ice. So,
surprisingly, this kind of observation of the Sun should be
carried out in night, when the Sun is below the horison.

55. Conclusions
I have briefly reviewed the particle physics experiments
which are using the Sun as a unique strong source of
weakly interacting particles, known or hypothetical
(neutrinos, axions and axion-like particles). As it is a very
wide area of research, I have focused upon the
experiments I participated myself.
1. Observations of solar neutrinos demonstrate that they
transforms (oscillates) from electron to muon and tau
neutrino and give information on their properties (masses,
mixing angles, magnetic moments etc.). By-product: our
solar models are correct.
2. Different models of hypothetical axions are checked by
using the Sun as a source.
3. Hypothetical WIMPs captured by the Sun and
ahhihilating in its core can be detected by observation of
high-energy neutrinos – annihilation products.