The SunThe Sunandand

the particle physicsthe particle physicsVladislav Kobychev

Insitute for Nuclear Research, Kiev, Ukraine

1.1. The Sun: basic factsThe Sun: basic facts2.2. Solar neutrinosSolar neutrinos3.3. Solar axionsSolar axions4.4. The Sun and WIMPsThe Sun and WIMPs

•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

Basic facts on the Sun:

The Sun is a very typical star:nothing special. The only special feature(for us) is that it is the closest star.

Production of solar neutrinosProduction of solar neutrinospp-chain:pp, pep, 7Be & 8B neutrinos

Production of solar neutrinosProduction of solar neutrinosNet reaction:

p+ + p+ + p+ + p+ + e– + e–

4He (p+ + p+ + n0 + n0)e e

The Standard Model of particle physics forbidsconversion between different kinds (flavours) ofneutrino and considers them massless.

e - whatdoes itmean?

CNO-chain:13N, 15O & 17F neutrinos

Production of solar neutrinosProduction of solar neutrinos

Every second, the Sun produces 2·1038 electronneutrinos, and almost all of them escape to thespace (very weakly interacting with the matter).

On Earth, the solar neutrino flux is~60 000 000 000 neutrinos/(cm2 s).

Production of solar neutrinosProduction of solar neutrinos

Several experiments have been carried out to measureSeveral experiments have been carried out to measurethe solar neutrino flux.the solar neutrino flux.

HomestakeHomestake: radiochem. Cl: radiochem. Cl--Ar experiment.Ar experiment.SAGESAGE andand GALLEX/GNOGALLEX/GNO: radiochem. Ga: radiochem. Ga--GeGe ––large fraction of pp neutrinos +large fraction of pp neutrinos + 77Be neutrinos.Be neutrinos.KamiokandeKamiokande andand SuperSuper--KamiokandeKamiokande: water: waterCherenkovCherenkov ---- 88B neutrinos.B neutrinos.SNOSNO: heavy water: heavy water ---- 88B neutrinos + neutralB neutrinos + neutralcurrent reactions with muon and tau neutrinocurrent reactions with muon and tau neutrino+ elastic scattering of all flavours.+ elastic scattering of all flavours.BorexinoBorexino: liquid scintillator: liquid scintillator ---- the first experimentthe first experimentto detect lowto detect low--energy solar neutrinos in real timeenergy solar neutrinos in real time

History of solar neutrino experiments:History of solar neutrino experiments:

Homestake experimentHomestake experimentTheThe Homestake solar neutrinoHomestake solar neutrinoexperimentexperiment was in the Homestakewas in the Homestakegold mine in South Dakota.gold mine in South Dakota. TheThedetector was constructed atdetector was constructed atBrookhaven National Laboratory inBrookhaven National Laboratory inthe late 1960s by a collaboration ledthe late 1960s by a collaboration ledby Dr. Raymond Davis, and has beenby Dr. Raymond Davis, and has beenoperated continuously since 1970operated continuously since 1970(taken over by UPenn in 1984).(taken over by UPenn in 1984). TheThedetector was a big tank containingdetector was a big tank containing615 tons of liquid perchloroethylene615 tons of liquid perchloroethylene(C(C22ClCl44).).

Neutrino detection via the reaction:Neutrino detection via the reaction:

ee ++ 3737ClCl ee -- ++ 3737Ar,Ar, EEthth == 0.814 MeV0.814 MeVCollection of radioactiveCollection of radioactive 3737Ar (few tens atoms perAr (few tens atoms per

month!) from all the tank into a small counter.month!) from all the tank into a small counter.

Homestake Construction (1966)Homestake Construction (1966)

Homestake ExperimentHomestake Experiment

The Solar Neutrino Unit (SNU) = 1 neutrinoThe Solar Neutrino Unit (SNU) = 1 neutrinointeraction per second per 10interaction per second per 103636 atomsatomsBut 10But 103636 atoms is ~ 240 million tons ofatoms is ~ 240 million tons ofchlorinechlorineHomestake could contain ~10Homestake could contain ~103030 atomsatomsSo, Homestake counted only ~2.5 neutrinosSo, Homestake counted only ~2.5 neutrinosper day (2.55per day (2.55 ±± 0.25 SNU)0.25 SNU)Based on the Standard Solar Model, oneBased on the Standard Solar Model, oneshould expect 8should expect 8 ±± 1 SNU1 SNU“Solar neutrino problem”“Solar neutrino problem”

Homestake experimentHomestake experiment

TheThe Nobel result*Nobel result* obtained byobtained byDavis:Davis:

The flux of solar neutrinos isThe flux of solar neutrinos is~~3 times less then the3 times less then thepredictedpredicted..

*) The Nobel Prize in Physics, 2002*) The Nobel Prize in Physics, 2002

Solar neutrino problemSolar neutrino problem•All existing experiments ondetecting of solar neutrinosgave 1/3 to 1/2 of thepredicted neutrino flux(Standard Solar Model +weak interactions theory)•Beside this, differentexperiments gave different(and disagreeing)experiment-to-theory ratios.

Solar neutrino problemSolar neutrino problem

Solar neutrino problemSolar neutrino problemPossible solutions:1. We don’t understand the solar interior2. We don’t understand the behaviour of neutrino

Neutrino oscillationsNeutrino oscillations

If electron, muon and tau leptonIf electron, muon and tau leptonnumbers don’t conserve, the neutrino ofnumbers don’t conserve, the neutrino ofone flavour can transform to other one.one flavour can transform to other one.This requires neutrino masses shouldThis requires neutrino masses shouldbe nonbe non--zero and different mass stateszero and different mass statesshould have different masses.should have different masses.The neutrino oscillations were predictedThe neutrino oscillations were predictedby Bruno Pontecorvo in 1957 byby Bruno Pontecorvo in 1957 byanalogy with the observed neutral kaonanalogy with the observed neutral kaonoscillations.oscillations.

Solar neutrino oscillationsSolar neutrino oscillationsBeforeBefore SNO all theSNO all theexperimentsexperiments detected onlydetected onlyelectronelectron Solar neutrinos.Solar neutrinos.SNOSNO found that the mostfound that the mostof the flux of solarof the flux of solar neutrinoneutrinoare not electron onesare not electron ones..But the solar core emitsBut the solar core emitsonly electron neutrinosonly electron neutrinos,, sosoneutrinos have to flavourneutrinos have to flavouroscillateoscillate flying from theflying from thesolar core to the Earth.solar core to the Earth.It is possible only in theIt is possible only in thecase when the flavourcase when the flavourstates of neutrino do notstates of neutrino do notcoincide with their masscoincide with their massstates, and these massstates, and these massstates have to havestates have to have(different) masses:(different) masses:disagreement with thedisagreement with theStandard Model!Standard Model!

Flux of electronneutrinosFl

ux o

f mu

and

tau

neut

rinos

MSW EffectMSW EffectThe neutrino oscillations are resonantly gained whenThe neutrino oscillations are resonantly gained whenthe neutrino flux propagates through matter withthe neutrino flux propagates through matter withslowly changing densityslowly changing density (Mikheev(Mikheev--SmirnovSmirnov--Wolfenstein effect). The effective mass of neutrinoWolfenstein effect). The effective mass of neutrinodepends on the density of electrons in the matter, anddepends on the density of electrons in the matter, andin some point where the effective masses of differentin some point where the effective masses of differentneutrino flavours crosses, the oscillationneutrino flavours crosses, the oscillationenhancement appears.enhancement appears.MSW effect explains the observed differenceMSW effect explains the observed difference of solarof solarneutrino fluxes in different experiments:neutrino fluxes in different experiments:

Low energy (Low energy (pppp) neutrinos) neutrinos ((SAGE, GALLEXSAGE, GALLEX))survive with higher probabilitysurvive with higher probability::PPeeee PP(( ee ee)) == 56%56%..High energy (High energy (88B) neutrinos survive with lowerB) neutrinos survive with lowerprobabilityprobability::

PPeeee ~ 32% (theory, SNO)~ 32% (theory, SNO)even their passage through Earth can have aneven their passage through Earth can have anobserved effect (dayobserved effect (day--night assimmetrynight assimmetry))

No good data for intermediate energies.No good data for intermediate energies.

MSW EffectMSW Effect

RR NN

Laboratori Nazionali del Gran SassoLaboratori Nazionali del Gran Sasso

2626

Abruzzo, Italy120 km of Rome

LaboratoriNazionali delGran Sasso

Asserg (AQ)Italy~3500 m w.e.1 km of depth

detector andsupplementary equipment

External Buildingsof the Laboratory

BOREXINOBOREXINO

BOREXINOBOREXINO

Two 0.125 mmnylon spheres:- R=4,25 m;- R=5,5 m-(Rn-barrier)

278 t PC+PPO(1,5 g/l)

Steel sphere(R=6,85 m):- 2212 PMT (8”);- 1350 m3

PC+DMP (5.0 g/l)

2100 m3 water tank:- R=9 m, H=16,9 m;- 208 PMT in water,looking outwards;- shielding from

, & n

MonoenergeticMonoenergetic = 862 = 862 keVkeV)) solarsolar 77BeBe

neutrinosneutrinos;;pep &pep & CNO neutrinos;CNO neutrinos;Antineutrino from reactorsAntineutrino from reactorsand the Sunand the Sun;;GeoneutrinosGeoneutrinos;;Supernova neutrinosSupernova neutrinos (?) …(?) …

Rate of (SSM, MSW-LMA),prediced for

Physical programPhysical programofof :

Neutrinos scatter on electrons of liquid organic scintillatorNeutrinos scatter on electrons of liquid organic scintillator(pseudo(pseudo--cumene)cumene)::

Low threshold of registrationLow threshold of registration;;Good energy resolutionGood energy resolution;;Good space reconstructionsGood space reconstructions..

BUT…BUT…No directional sensitivityNo directional sensitivity;;No selection betweenNo selection between events andevents and otherother ((naturalnaturalradioactivityradioactivity).).

!!!! HIGHEST REQUIREMENTS TO RADIOPURITYHIGHEST REQUIREMENTS TO RADIOPURITYOFOF SCINTILLATOR AND OTHER MATERIALSSCINTILLATOR AND OTHER MATERIALS !!!!

Registration of

RADIOPURITYRADIOPURITYUraniumThorium 10-6 g/g in natural substances (human body etc.)

10-17 g/g in Borexino scintillator

Potassium~300 g in a 70 kg human body

(4000 decays/s of 40K)

10-14 g/g in Borexino scintillator

10-4…10-2 g/g in natural substances

The center of the Borexino detector is possiblythe most radiopure place in the Universe.

The collected dataallow to reconstructfor every event:•Total absorbed energy•Position (±10 cm)•Kind of particle (alpha,

beta, muons)

Data collection

4499 ±± 33statstat ±± 44systsyst77BeBe / (/ (dayday ·· 100100 tt))

The preliminary result of BorexinoThe preliminary result of Borexino

exp.: 4exp.: 499 ±± 33statstat ±± 44systsyst evt./(day · 100 t)evt./(day · 100 t)

7575 ±± 44 evtevt..//((dayday ·· 100100 tt)) without oscillationswithout oscillations

4949 ±± 44 evtevt..//((dayday ·· 100100 tt)) withwith MSWMSW--LMALMAoscillationsoscillations

mm121222 == 77,,92·1092·10––55 22,, sinsin22

1212 == 00,,314)314)for the Standard Solar Modelfor the Standard Solar Model BPS07(GS98)BPS07(GS98)

Comparison with theor.predictionsComparison with theor.predictionsforfor ::

AxionsAxion 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 experimentallyvery small (0 or, at least, <10–10), but its smallness is not requiredby 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. Thespontaneous violation of the PQ symmetry creates the Goldstoneboson, which was named axion by Frank Wilczek.

Axions are considered as one of the best candidates for theDark Matter particles, because they are massive and theirinteraction with normal matter should be extremelly small.

2323..0303.200.20099 « » « » 66

Axion interactions

Mass of axion varies from 10–18 to 1 MeV in differentvariants 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.

DFSZ-axion

BremsstrahlungComptoneffect Primakoff’s effect

hadronic axion

Based on axion-photon conversion in magnetic field.

Laboratory search for solar axions

Axion

Axion

Externalfield

The predicted solar axion luminosity for DFSZ-axions:

23

1106.3 a

amLL

Their mean energy is predicted to be 4.2 keV.In order to registrate the axions, they are converted toX-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.

Laboratory search for solar axions

Laboratory search for solar axionsResonant 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 fromthe Sun almost freely. In Earth, the axion canresonantely excite a nucleus of the same kind whichthen deexcites by emission of a detectable gammaquantum. Many experiments are based on thisscheme.

Modification: the level of the nucleus-emitter ispopulated not by thermal excitation, but in a nuclearreaction (for example, the 478 keV excited level of 7Liis populated by the electron capture of 7Be in the pp-chain with ~10% branching ratio)

4343

Solar axionsSolar axions:: continuous spectrumcontinuous spectrum(Primakoff’s effect: photon(Primakoff’s effect: photon--toto--axionaxionconversion in the electric field of a nucleus)conversion in the electric field of a nucleus)

4444

5757FeFe14.4 keV14.4 keV

The monoenergetic lines can also be presentThe monoenergetic lines can also be presentin the solar axion spectrum.in the solar axion spectrum.

4545

5757FeFe14.4 keV14.4 keV

a

5757FeFe14.4 keV14.4 keV

gaNN gaNN

Other natural isotopes with low-lying levels, de-excitatedvia M1-transitions, can be (and are) also used; forexample, 83Kr (9.4 keV).

The method was proposedThe method was proposed:: Moriyama [PRL 75(1995)3222].Moriyama [PRL 75(1995)3222].

Solar CoreSolar Core LaboratoryLaboratory

1. Thermal excitation1. Thermal excitation2. Emission of a2. Emission of a

monoenergetic axion.monoenergetic axion.

3. Resonant3. Resonant excitation of aexcitation of atargettarget 5757Fe nucleus byFe nucleus by the axion.the axion.

4. Emission of4. Emission of gamma quantum.gamma quantum.5. Detection.5. Detection.

4646

5757Fe (‘iron’) solarFe (‘iron’) solar axions allow to excludeaxions allow to exclude axionaxionmass valuesmass values between ~14.4 keV and (on today)between ~14.4 keV and (on today)0.216 keV [T. Namba, PLB 645 (2007) 398].0.216 keV [T. Namba, PLB 645 (2007) 398].

Other possibilityOther possibility –– nonnon--thermalthermal excitationexcitation of source nuclei.of source nuclei.77LiLi is createdis createdin thein the pppp--chain (thechain (themain energymain energysource of thesource of theSun).Sun).

4747

77LiLi477.6 keV477.6 keV

a

1. Level population via1. Level population viaelectron captureelectron capture ofof 77BeBe

2. Emission of2. Emission ofa monoenergetic axion.a monoenergetic axion.

gaNN gaNN

First exp.:First exp.: M. KrcmarM. Krcmar et al.et al. [PRD 64 (2001) 115016][PRD 64 (2001) 115016]((mmaa < 32 keV)< 32 keV)..Best limitBest limit:: A.V. DerbinA.V. Derbin et al.et al. [JETP Lett. 81 (2005) 365][JETP Lett. 81 (2005) 365]((mmaa < 16 keV).< 16 keV).

77LiLi477.6 keV477.6 keV

77BeBe

Solar CoreSolar Core LaboratoryLaboratory

3. Resonant3. Resonant excitation of aexcitation of atargettarget 77Li nucleus byLi nucleus by the axion.the axion.

4. Emission of4. Emission of gamma quantum.gamma quantum.5. Detection.5. Detection.

4848

Our experiment:Our experiment:

1. Lithium fluoride (LiF) was chosen1. Lithium fluoride (LiF) was chosenas a target due to:as a target due to:a) its high density of Li nuclei ina) its high density of Li nuclei incomparison to other Li compounds;comparison to other Li compounds;b) chemical passivity;b) chemical passivity;c) nonc) non--hygroscopicity.hygroscopicity.

2. Few samples of LiF (powder of2. Few samples of LiF (powder of99.99% purity, single crystal) were99.99% purity, single crystal) wereplaced in two HPGe detectors inplaced in two HPGe detectors inLaboratori Nazionali del Gran SassoLaboratori Nazionali del Gran Sasso(3800 m w.e.).(3800 m w.e.).

4949

mmaa << 13.913.9 keVkeV(90% C.L.)(90% C.L.)

If we would observe a gamma peak at 478keV with area S, mass of axion would bema = 1.55×1011 × (S tN7)1/4 eV

– efficiency of the detector,t – time of measurement,N7 – number of 7Li nuclei in the sample.

5050

LiF(W) single crystalsLiF(W) single crystals

Total mass is ~550 g.Total mass is ~550 g.

Of course, the search for mono-energetic axions fromthe Sun can be performed also without resonantnucleus as a target (the resonant target only allows todecrease its mass by increasing the cross-section).Such the searches were carried out by Borexino andCAST collaborations (both are mentioned above) for 7Lisolar axions.

Another interesting idea: we have a lot of iron withinthe Earth core; let us consider it as a target for “iron”solar axions. The resonant absorption of 14.4 keVaxions by 57Fe nuclei would heat the Earth core, andthe thermal flow through the Earth surface outwards(measured: ~42 TW) would give us the upper limit onprobability of such the process.

Taking into account that the part of this heat flow isproduced by radioactive transitions (U, Th, K) in theEarth crust, we can set the upper limit on the hadronicaxion mass of ma<1.6 keV.Danevich et al., Kinematics and Physics of CelestialBodies, 25(2009)102.

Geophysical search for solar axions

The Dark Matter is non-barionic matter whichdominates in the Universe but is “invisible” – it is stillobserved only by its gravitaitonal influence to thenormal matter. The most common hypothesis is thatthe DM consists of Weakly Interacting MassiveParticles – WIMPs. They are stable and have a massof tens GeV or more. There are many directexperiments to search for WIMPs, but indirectobservations are possible too. One of ways to observeWIMPs indirectly is the search for high-energyneutrinos emitted by annihilating WIMPs captured bythe Sun.

Indirect search for WIMPs by their annihilationswithin the Sun

The neutrinos from WIMPs annihilation with energy ofGeVs or tens GeV can escape from the Sun and bedetected by an appropriate high-energy neutrino (HEN)detector. The collaborations IMB, Kamiokande, AMANDAand MACRO already tried to extract such the informationfrom their observations.

For example, AMANDA detector is placed within ice many-km layer on the South pole. A HEN from the Sunpropagates through Earth and interacts with rock or iceunder the detector. This interaction creates a high-energymuon that keeps the direction of the primary neutrinomoving; the PMTs of AMANDA will see an upwardingmuon by emission of Cherenkov light in ice. So,surprisingly, this kind of observation of the Sun should becarried out in night, when the Sun is below the horison.

Indirect search for WIMPs by their annihilationswithin the Sun

ConclusionsConclusionsI have briefly reviewed the particle physics experimentswhich are using the Sun as a unique strong source ofweakly interacting particles, known or hypothetical(neutrinos, axions and axion-like particles). As it is a verywide area of research, I have focused upon theexperiments I participated myself.

1. Observations of solar neutrinos demonstrate that theytransforms (oscillates) from electron to muon and tauneutrino and give information on their properties (masses,mixing angles, magnetic moments etc.). By-product: oursolar models are correct.2. Different models of hypothetical axions are checked byusing the Sun as a source.3. Hypothetical WIMPs captured by the Sun andahhihilating in its core can be detected by observation ofhigh-energy neutrinos – annihilation products.