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PoS(CRA School)030 http://pos.sissa.it/ llation phenomena and change estake mine in South Dakota in g and . More o test the validity of solar models. flux value, giving birth to the Solar our neighborhood , is ilt in order to understand the origin in which four are fused and h. Thanks to neutrinos detection it is cal point of view from its beginning to i Fisica Nucleare e Commons Attribution-NonCommercial-ShareAlike Licence. ∗ [email protected] Speaker. their nature while travelling from the corepossible of to the infer and to to Eart prove howThis the paper Sun introduces shines. solar physics fromour a days. histori reactions take place in the core of the Sun. On two of them undergo a betathan decay 40 to years become ago neutrons, it releasin was suggested to detect solar neutrinos t Neutrino Problem. Since then differentof experiments were this bu discrepancy. Now we know that neutrinos undergo osci being fused into in the -proton chain reaction The first measurement of the neutrino1968. flux The took experiment place detected in only the one Hom third of the expected ∗ Copyright owned by the author(s) under the terms of the Creativ c

4th School on Cosmic Rays andAugust Astrophysics, 25- September 04, 2010 Sao Paulo Brazil Lino Miramonti Universit degli Studi di Milano and Istituto Nazionale d Solar neutrinos: from their productiondetection to their E-mail: PoS(CRA School)030 , kg 30 10 · t 0.13%, kilometers, lar system. Its Lino Miramonti ore, a radiative f gas in a process ater. The radiative responds to about the Sun, while he- other elements are cleus [1], [2]. One ective zone is where yers by photons. The e the three most abun- ; at these temperatures . lear fusion takes place. Kelvin (putting it in the mass of about 2 K ize of about 0.5 degrees. kes up 78.5% of the mass 6 of gravity compression the 10 · mass of the Sun and is where ntages are by relative number 5 . 15 332,800 1392 26-37 d 149 1.41 274 ≈ ) km 6 ) 2 m 2 6 s / m Characteristics of the Sun. Characteristics of the Sun. Table 1: Mean distance to Earth (10 Density Surface gravity Mass (Earth=1) Mean diameter (10 Rotation period . In the Sun there are also traces of neon, sodium, magnesium, aluminum, silicon 1 Starting from the center of the Sun and moving outwards we can distinguish a c In any atom heavier than helium is called a "metal" atom The Sun is is a medium-sized star and by far the biggest celestial body in the so Spectroscopy measurements show that hydrogen makes up about 94% of As we said, the core of the Sun reaches temperatures of 1 distance from the Earth isthat about corresponds 150 to million 109 kilometers. EarthAll With diameters, planets a orbit it diameter around appears of the 1392000 to Sun have because an of angular its s enormous gravity. It has a (accounting for about 99.86%333000 of times the the Earth’s total mass. massG2 The spectral effective of surface class). temperature the The is characteristics solar 5780 of system) the Sun that are summarized cor in table 1 lium makes up about0.11% 6% of of this the quantity is solar composeddant material, by "metals" and , , all and the other that ar elements make up jus phosphorus, sulfur, potassium, and iron.of The atoms. previous If quoted one uses perce theof percentage the by mass, Sun, one helium finds that 19.7%,0.54%. hydrogen oxygen ma 0.86%, carbon 0.4%, iron 0.14%, and the Solar neutrinos 1. ”Our” star: the Sun nuclear fusion can occur transforming 4 hydrogen nuclei into 1 helium nu 2. How the Sun shines zone and a convective zone. Theenergy, core from accounts nuclear fusion, for is about generated. 10%core of Due to the is the very enormous hot amount andThe Sun’s dense. core is At at these about 15.5zone high million is temperatures K where and and it the densities is energyradiative nuc about is 150 zone transported times denser includes from than the approximately w energy core 85% in to of the the the outer colder 15% Sun’s outercalled of la radius. convection. the Sun’s The radius is conv transported by the bulk motion o PoS(CRA School)030 , 2 2 at + H mc (3.1) (2.1) He 1 d then 4 energy = MeV . + 7 E After this . e nucleus W H 3 1 . 26 + 10 drogen nuclei. Lino Miramonti , releasing two · n. The first step MeV 596 million tons He ays take 10000 to He that is 26 4 4 42 846 neutrinos but in this . . J orm 2 protons into 2 ping into space. The → 0 the core of the Sun is 12 , releasing a as + − tron emitting a positron e He H produce a light of ν 3 10 2 · + + 3 . + 4 e He 3 + = 2 H ) . Using Einstein’s equation s 2 ) / → m 7% 8 . e H 0 ν 1 , which is heavier than the mass of 1 10 energy · ≈ + + kg ( 3 + ( + H 27 · e 1 − kg 3 85% of the case He + kg 27 . Finally, after millions of years, two of the helium (protons) into deuterium 10 4 n − · ≈ 27 H → − 10 1 → · MeV H 10 p · 6943 1 . · 49 . 4 5 0477 . is 6 0477 + . H γ 1 + He . e 3 ν → H 1 is converted into the energy which is released by Sun. + . The difference is 0 H kg 2 : 27 produced can fuse together to make the common helium isotope and is named PPI chain. − He 3 10 He · 3 MeV missing mass In the previous reaction (2.1) we started with 4 protons and ended up with 1 H Each second about 600 million tons of hydrogen are converted into about The combined mass of of 4 By far the most important reaction in the Sun is the proton-proton chain reactio The 5.5 MeV gamma rays are absorbed by only a few millimeters of solar plasma an The net reaction is: According to the Standard Model of particle physics, there are 3 types of 86 . 6466 . we find that each fusion releases 0 which is composed of 2 protonsneutrons; and in 2 this neutrons. inverse beta Thisand means decay an we a electron had proton neutrino to (see transf eq. 3.1) becomes a neu of helium-4. The remainingincluding 4 radiation million in tons the (actually form 4.26 of light. million The tons) current are converted of into the Sun is 3 hydrogen nuclei; this last fusion happens in 3. What about neutrinos? 6 involves the fusion of two hydrogen nuclei re-emitted again in random directions and170000 at years slightly to lower energy. reach The the gammaconverted surface into r several of million the of Sun. visiblephotons light escape Each as photons gamma visible (some ray light. eV) created before in esca one proton changes into a neutron and a neutrino: first reaction the deuterium produced canhelium, fuse with another hydrogen to 12 reaction only an is emitted. 3.1 From protons to helium nucleus: The ppI chain nuclei Solar neutrinos helium nucleus has a massThis that is smaller than the combined masses of the four hy PoS(CRA School)030 − e MeV . 42 . 0 tron) has a MeV decays beta + e B 42 ν Lino Miramonti 8 . + captures a proton + der to form helium e Li . While neutrinos emitted 7 ∗ + B 8 H neutrinos are the ones emitted reaction. In this reaction 2 pp ; this last can capture an neutrinos in the of → H : 1 Be nd their mass energy is carried off by H 7 hep + 1 , + H 1 pep H 1 23% the three body reaction can occur . 0 respectively. The reaction. Neutrinos emitted in this reaction and form ≈ B H 8 1 He 4 + or H Li 1 4 . Figure 3 shows the neutrino energy spectrum as 7 4 neutrinos emitted in the decay of ; this chain is named PPII chain. The B to the Q-value of the reaction, that is 0 this chain is named PPIII chain. . 8 . He He 4 and MeV 4 MeV MeV + Be + emitting a positron and an electron neutrino. Or, with a much 7 42 . 022 He . 77%, in the remnent . 1 He He 4 can interact with a 4 to 0 4 + 99 is produced it can capture a proton (this happens with a very small → γ → 2 He ≈ H 3 MeV He → 1 Be 3 . Figure 2 summarizes the different paths of the pp chain. The figure 8 1%) in order to form − + e . e ν 0 Li + 15%) 7 and + + ≈ ; e ( e ≈ J H ν neutrinos the ones emitted in the three bodies fusion 19 H 2 He − + 1 4 → 10 pep + · e 6 H . + 1 1 Neutrino energy spectrum emitted in the + ≈ Be fusion, neutrinos in the of − 8 9%) or a . e eV pp Be The PPI chain just described is not the only one in which protons fuse in or Figure 1 shows the spectrum of neutrinos emitted in the 1 The positron immediately annihilates with one of the hydrogen’s electrons, a At the beginning of the proton-proton chain, the reaction Solar neutrinos are labeled according to the reaction in which they are emitted 7 → 2 3 4 , 99 + ∗ B H He ≈ nuclei. For instance, once 8 ( probability) and directly create a 3.2 From protons to helium nucleus: The ppII and ppIII chains and creates two higher probability, ( we have 3 bodies incontinuous the spectrum extending final from state; 0 this means that the emitted neutrino (like the elec have energy extending from 0 two photons also shows the different neutrino contributions 3 Figure 1: Solar neutrinos 1 happens with a probability of in the PoS(CRA School)030 pep ocrhomatic ( Lino Miramonti tar like the Sun heavier than re 3). eated energy is given Model (SSM). ino contribution of the pp chain (see trum ranging from 0 to the Q-value of the 5 ); neutrinos emitted in reactions that have two bodies in the final state are mon Neutrino energy spectrum as predicted by the Solar Standard hep and B 8 , Th efigure shows the different paths with the different neutr Figure 3: pp ), see figure 2. The pp chain is not the only reaction that transforms protons into helium. In a s Be 7 Solar neutrinos and in reactions that have threereaction bodies ( in the final state have a continuous spec text). Figure 2: predicted by the Solar Standard Model (SSM). 3.3 From protons to helium nucleus: The CNO cycle about 98% of the energy isby created the in CNO pp cycle. chain; the Thethe remaining Sun. CNO 1-2% In cycle of this becomes the cycle the cr there dominant is source also an of emission energy of in neutrinos (dashed line in figu PoS(CRA School)030 B 8 (4.2) (5.2) (4.1) (5.1) is the and N we need th Dakota 2 Be 7 cm r day. Lino Miramonti 45 Solar Standard electron neutri- − of about 35 days eriments and real 2 / 1 . usly from 1970 until hloroethylene, which τ P) which has been for per month in 615 tons MeV atoms were extracted and Ar 37 42 . Ar 37 allowing the detection of e − ν − e e + keV + dE + ∗ ) Y E Ar Cl 814 ( 1 and a cross section of about 10 + 37 37 σ 1 = A Z ) is the cross section of solar neutrinos and 6 − → → ) E s th → ( 2 E − E ( − Cl e Φ X σ A Z 37 + Z cm + + ν N e Ar e ν 10 ν 37 is the flux, ) are radioactive and decay by electron capture with a E ( Φ target atoms (that correspond to ktons of matter) to produce one event pe Ar neutrinos which, as we said, have a maximum energy of 0 : 37 ∗ 30 pp Cl . 4 Neutrinos were detected via the reaction: The first solar neutrino experiment took place in the Homestake gold mine in Sou In radiochemical experiments the reactions involve isotopes which interacting With a typical neutrino flux of 10 There are two possible ways to detect solar neutrinos: radiochemical exp where The number of detected neutrinos was about 1/3 lower than expected by the Once a month, after bubbling helium through the tank, the The The production rate of the daughter nucleus is given by The energy threshold of this reaction is 37 Cl 2 [3]. The detector consisted inwas a chosen large because tank containing it 615 is1994. tons rich of in liquid chlorine.The perc experiment operated continuo about 10 5. Homestake: The first solar neutrino detector nos produce other radioactive isotopes and an electron. time experiments. counted. The number of atoms created was only about 5 atoms of Model. This discrepancy is themany essence years an of important the problem Solar among Neutrino physicists. Problem (SN number of target atoms. into Solar neutrinos 4. How to detect Solar Neutrinos? but not C PoS(CRA School)030 (7.1) neutrinos s built, the B 8 ause they are Lino Miramonti sion chain (i.e. ns scattered by oming neutrino st one is to con- n easy task. The pected neutrinos, n 1982-83 [4]. It tomultiplier tubes guish the different king at its vibration [5]. so only ormation about single wrong, i.e. the Home- the Sun. tains the same direction in real time experiments icted correctly. After all, ens to the neutrinos while r viewed by 11200 PMTs. been tested independently MeV MeV 5 . 5 d, non-standard solar models particle passes through matter at a ltraviolet. The radiation is emitted . 5 7 = = th s polarize the molecules of that medium, th ed particle and the refraction index of the E E − e + x ν 7 → − e + x ν detector for a total mass of 3000 tons of pure water. In real 5 neutrinos are less model-dependent and hence more robust to pp neutrinos). pp neutrinos are detected. At the beginning of ’90s a much bigger detector wa Until 1990 there were no observations of the initial reaction in the nuclear fu As we have seen radiochemical experiments integrate in time and in energy bec The number of detected neutrinos was about 1/2 lower than the number of ex The first real time solar neutrino detector, Kamiokande, was built in JapanI The energy threshold of the reaction in Kamiokande is Cherenkov radiation is an electromagnetic radiation emitted when a charged There are three possible explanations to the Solar Neutrino Problem. The fir hep 5 the detection of slow and need time to produceindividual measurable results. energy This values. causes the However, lossit of unlike is inf radiochemical possible experiments, to obtainneutrino contributions. single Furthermore, values given and that therefore theof scattered a the electron impinging spectrum main neutrino, energy it to isand possible distin so to to infer the point direction at of its the source. origin This of proved the that inc neutrinosaggravating actually the come Solar from Neutrino Problem. 8. Looking for pp neutrinos: Gallex and SAGE time neutrino experiments scientists studyan the impinging bluish neutrino light 7.1. produced In by the(PMT). the Kamiokande the electro light is recorded by 1000 pho consisted in a large water Cherenkov speed greater than thewhich speed then of turn light back in rapidlyunder that to a medium. their cone ground The shaped state,medium. charged zone; emitting particle its radiation in angle the depends near on u the velocity of the charg sider that the Standard Solar Modelby is helioseismology not (that correct; is but the solar science models thatmodes), have studies and the the interior standard of solar the model Sunseem has by very passed loo unlikely. all The tests so second far. onestake Indee is detector to could consider be that inefficient Homestake itsto could reactions detect be would a not handful have of beenthird atoms pred one, per and the week strangest in hypothesis, is moretravelling to from than consider the 600 that core something tons of happ of the material Sun to is the not Earth. a 7. Kamiokande and SuperKamiokande: Real time detection and SuperKamiokande, where the active mass was ofIn 50000 the tons of SuperKamiokande pure the wate energy threshold was lowered to Solar neutrinos 6. Possible explanations to the SNP PoS(CRA School)030 ird, [9]. (9.1) (8.1) 3 ν , 2 ν , 1 M matrix in ν Lino Miramonti by linear combi- le 2 and figure 5 3 coincide with their ν ry in Italy, 30 tonnes ts were built in order iment, located in the , by the standard solar 2 O, see later). ν d vice versa. . , 1 ino oscillations. nd consider the oscillation ν 0 to be detected as a muon or tau 06 02 05 03 . . . . confirmed the efficiency of both de- = 0 0 0 0 − . t e ± ± ± ± Cr    51 + 1 2 3 59 46 58 34 keV . . . . ν ν ν Ge    233 71 U 8 ; but since one of the three mixing angles is very are different from mass eigenstates = → = 23 τ th θ ν E    , Ga , e τ µ µ 13 are related to the mass states 71 ν ν ν ν θ τ , , + e ν SAGE 0 e    , ν 12 Super-K 0 ν µ θ Homestake 0 ν , e Gallex and GNO 0 ν . τ ν observed vs expected ratio in the four experiment (before SN , µ neutrinos; both employing the reaction: ν pp ), and because two of the mass states are very close in mass compared to the th 13 ←→ θ Table 2: 60%). e ν ≈ is the Pontecorvo-Maki-Nakagawa-Sakata matrix and is the analog of the CK Neutrinos have the peculiar property that their flavour eigenstates do not The probability of an electron neutrino produced at The neutrino flavour states The energy threshold of this reaction is There are three mixing angles: All experiments detected fewer neutrinos than expected from the SSM! Tab In the Gallex experiment, located at the Gran Sasso underground laborato Calibration tests with an artificial neutrino source U small (i.e. Flavour eigenstates can be expressed in terms of mass eigenstate system an for solar neutrinos we can restrictbetween the six neutrino cases to only 2 cases a 9. What happens to neutrinos? 9.1 neutrino oscillations the hadronic sector of the Standard Model. This effect is known as neutr summarizes the observed vs expected ratio for all experiments. of natural gallium were employedBaksan [6] underground [7], laboratory, while there in were the 50 tons soviet-american of exper metallic gallium [8] Solar neutrinos prove the validity of the Solar Standardto Model. detect Two solar radiochemical experimen nation: tectors. Once again the measuredmodel neutrino ( signal was smaller than predicted neutrino is: mass eigenstates. Flavor eigenstates PoS(CRA School)030 + x ν (9.2) 0 to be = t Lino Miramonti uum oscillations 12]. nce from the neu- uced at [10] [11]. . The Sun is made 6 gy neutrinos flavour τ rgy. For high energy ν t ated in Creighton Mine os through their interac- vatory and µ ν (in GeV) and two fundamental 0 to be detected as a muon or tau L E 2 E m . See figure 4. 4 ∆ 2 it is possible to determine the two funda- can interact through neutral current (NC) MeV sin L τ 2 ν . θ , − 2 is different from θ µ 2 2 e ν 2 , ν . 9 e 3 sin ν − )= gcm τ , and sin µ ) can interact through charge current (CC) scattering ν 2 e ν eV → ( e 2 2 ν ( m P − . and a detector at distance 2 1 2 E m m (in km) and the energy of the neutrinos ∆ = L 2 and m ∆ θ . This means that the interaction of − e Survival probability vs energy of an electron neutrino at t= + x ν The core of the Sun has a density of about 150 As we have already pointed out, the probability of an electron neutrino prod Neutrino oscillations can be enhanced by traveling through dense matter So, for a given energy This probability depends upon two experimental parameters that are the dista The Sudbury Neutrino Observatory (SNO) is a neutrino observatory loc The advantage of this detector is to detect CC and NC fluxes independently [ 6 → − Solar neutrinos neutrino. of up/down quarks and electrons; all neutrinos e 9.2 The Mikheyev Smirnov Wolfenstein Effect (MSW) or Matter Effec Figure 4: equally, but only electron neutrinos 9.3 Neutrino survival probability mental parameters detected as a muon orneutrinos tau flavour neutrino change after is dominated a by certain matter oscillations,change distance while depends is for on low dominated ener its by ene vacuumand oscillations. matter driven The oscillations regime is transition expected between between 1 vac 10. Detecting all neutrino types: The Sudbury Neutrino Obser parameters that are trino source to detector in Sudbury, Canada. It wastions turned with on 1000 in tons May of 1999 heavy to water detect viewed by solar 9600 neutrin photomultiplier tubes. PoS(CRA School)030 ≈ = 2 12 (10.5) (10.4) (10.2) (10.3) (10.1) gy ( m ES) on ∆ eory; while ts "see" fewer Lino Miramonti te the total flux us to reconstruct tron of the heavy breaking it into its acuum oscillations. is given of all neutrino ino contributions. lectron neutrinos. confirming that actually with parameters NC 1 3 ognize two regions, as we 1 ll neutrino flavour types. 1 rvatory experiment in case τ φ − nge is dominated by matter ν − ∼ s s 2 2 94 68 − − . . and 4 1 cm µ cm = ν 6 6 while for e 1 NC CC 10 τ 10 ν φ φ − ν · · φ s x − φ ) ) 2 . . ν e is: − + + + µ syst ν syst n NC cm p ( ( φ φ 6 + + 34 38 09 08 . . . . + p 0 0 10 p 0 0 e e 10 · − + − + ν ν ) ) ) → φ . φ . → 5 . d and via d = 0 = stat stat + ( + ( ± CC x e is given only from NC CC φ 21 21 7 06 06 ν . . ν . . . φ φ 0 0 0 0 4 CC − + ( − + ( φ 94 68 . . during their voyage from the core of the Sun to the surface of the 4 1 87 corresponding to the Large Mixing Angle (LMA) of the Mikheyev . τ = = 0 ν = oscillate into non-electron neutrino NC CC φ φ e and 12 ν ϑ µ 2 ν 2 . τ ν φ and sin , µ 2 ν φ eV , ) and high statistic [13]. The detection principle is based on elastic scattering ( 5 e ν − φ Borexino is able to measure neutrino coming from the Sun in real time with low ener Electron neutrinos The measured flux via NC reaction is comparable with the one expected from th Figure 5 reports the summary of all solar neutrino experiments. All experimen As we have pointed out in previous paragraphs, real time experiments allow In the charged current interaction, the impinging neutrino converts the neu As we can see in equation 10.3 In equation 10.4 we reporte the measured flux and in equation 10.5 we repor If we plot the survival probability vs energy (see figure 4) we can rec In the neutral current interaction, the neutrino dissociates the deuteron, keV 10 · are converted into 6 e . 200 the ratio between the measured flux via 7 neutrinos than expected by SSM exceptof for the neutral Sandbury currents. Neutrino Obse the complete spectrum and hence to disentangle the different electron neutr types Earth where they are detected. water deuteron into a proton (eq. 10.1). This reaction is possible only for e calculated with the solar standard model (BPS07). said in the previous paragraph.oscillations, For while high for energy low neutrinos energyThe flavuor neutrinos regime cha flavour transition change is expected is between dominated 1-2 by MeV. v 11. To measure in real time below 1 MeV: The Borexino detector constituent neutron and proton (eq. 10.2). This reaction is possible for a ν Solar neutrinos Smirnov Wolfenstein effect. PoS(CRA School)030 n of the neu- Lino Miramonti l chemical con- . 7 le to measure the theory raised the versy giving a di- unded by different nature during their ming from the Sun of the Sun. A lower neutrinos can bring r the world, to solve tons e same detector. 100 40% for CNO neutrino flux. ≈ ≈ . This corresponds to a radioactivity 9-10 g / g 16 ld. In order to have a signal to noise ratio on the − events due to natural radioactivity. The neutrino γ − β 11 neutrinos. Beside this, it will be able to measure for the first Summary of all Solar neutrino experiments. Be 7 intrinsic contamination cannot exceed 10 Figure 5: Th 232 and U 238 induced events cannot be distinguished from other ν More than 40 years have passed since the first detection of neutrinos co The main goal of Borexino is to obtain a direct measure in the low energy regio The 7 took place. Thesolar lack neutrino of problem. neutrinos compared Sincethis with then mystery. the different Now experiments ones we were know expected thatvoyage built, from neutrinos all from the undergo ove the oscillations changing core their of the Sun to our detectors. Thanks to their nature, troversy. One fundamental input of the Standardmetallicity Solar implies Model a is variation the in theA neutrino flux direct with measurement reduction of of therect CNO indication neutrinos of rate metallicity could in help thesurvival to probability core solve for of this both the contro low Sun. energy and Furthermore, high Borexino energy is neutrinos ab with th 12. Conclusion time the neutrinos coming from CNO cycle therefore trying to solve the solar mode trino spectrum and in particular electrons in very high purity liquid scintillatorshielding contained media in of a decreasing nylon radiopurity. balloon surro The active fiducial mass is orders of lower than anything on Earth. signal is on the order of some tens of events/day/100 tons above thresho order of 1 the Solar neutrinos PoS(CRA School)030 ra for inviting Lino Miramonti This long race is not o to thank Ruth Silva (1985). of Canada, 94, No. 6, 219-227 (2000). ). 12 I would like to thank Marcelo Augusto Leigui de Oliveira and Oscar Saaved [1] J.N. Bahcall, Astrophys. J. 467, 475[2] (1996). J.N. Bahcall, Journal of the Royal[3] Astronomical Society R. Davis, Nobel Prize Lecture (2002). [4] K.S. Hirata et al., Phys. Rev.[5] Lett. 63, 16 Y. Fukuda (1989). et al., Phys. Rev. Lett.[6] 81, 1562 W. (1998). Hampel et al., Phys. Lett.[7] B 447, 127 M. (1999). Altmann et al., Phys. Lett.[8] B 616,174 J.N. (2005). Abdurashitov et al., Phys. Rev. Lett. 83, 4686 (1999 [9] V. Gribov and B. Pontecorvo, Phys. Lett. B 28, 493 (1969). me at this international schoolLoewenstein on and cosmic Franco rays Reseghetti and for astrophysics. the revision I of would this als article. References [12] B. Aharmim et al., Phys. Rev.[13] C 7, 045502 C (2007). Arpesella et al., Phys. Rev. Lett. 101, 091302 (2008). [10] L. Wolfenstein, Phys. Rev. D 17, 2369[11] (1978). S.P Mikheev and A.Yu. Smimov, Sov. J. Nucl. Phys. 42, 913 Solar neutrinos information about the engine thatover powers yet our end star and telling some us open how questions stars remain shine. to be solved. 13. Acknowledgements