Solar Neutrinos: Status and Prospects. Marianne Göger-Neff

Transcription

1 Solar Neutrinos: Status and Prospects Marianne Göger-Neff NIC 2014, Debrecen TU München

2 Solar Neutrinos Objective of the first solar neutrino experiment: to see into the interior of a star and thus verify directly the hypothesis of nuclear energy generation in stars. (John N. Bahcall, PRL 12, 300, 1964) Astrophysics: use neutrinos as messengers from the solar interior real-time information from the solar core do we understand fusion inside the Sun? Particle physics: use the Sun as a well(?) understood source of electron neutrinos neutrino oscillations non-standard neutrino interactions 2

3 Nuclear reactions in the solar core hydrogen burning: 4 4p He 2e 2 e 26.7 MeV p + p 2 H + e + + e pp chain ~ 99% of energy p + e + p 2 H + e 99.8% 0.2% 2 H + p 3 He + 85% 10-5 % 15% 3 He + 3 He 4 He + 2p 3 He + p 4 He + e + + e 3 He + 4 He 7 Be + CNO cycle <1% of energy poorly known not directly measured yet 12 C + p 13 N + 13 N 13 C + e + + e 13 C + p 14 N + 14 N + p 15 O % 0.1% 15 O 15 N + e + + e 7 Be + e 7 Li + + e 7 Be + p 8 B + 15 N + p 12 C + 4 He 7 Li + p 4 He + 4 He 8 B 2 4 He + e + + e 3

4 The Standard Solar Model model of a main sequence star with M = 1.989x10 33 g Input parameters: initial chemical composition X in, Y in, Z in, mixing length parameter α MLT nuclear cross sections evolve solar model to the solar age (τ = 4.57 Gyr) S ij present-day constraints: solar luminosity solar radius atmospheric composition L = 3.842x10 33 erg/s R = x10 10 cm (Z/X) atmo Output: ν fluxes and spectra density ϱ(r) and sound speed c(r) depth of the convective zone R CZ Experimental data: solar neutrinos helioseismology 4

5 The Standard Solar Model Predicted solar neutrino spectrum: Serenelli et al Total neutrino flux determined by solar luminosity: 6.5 x cm -2 s -1 5

6 The Solar Abundance Problem Significant improvements in the SSM over the past 10 years: improved cross sections 14 N(p, ) 15 O, 3 He(α, ) 7 Be new opacity calculations more accurate determination of solar surface abundancies lower solar metallicity Z reduced 7 Be, 8 B, CNO neutrino fluxes But: low Z solar models are in conflict with helioseismology ( R CZ, Y surf ) low Z high Z high Z low Z Can solar neutrino measurements decide? 6

7 Prediction of Solar Neutrino Fluxes Source Neutrino Flux [cm -2 s -1 ] SSM-GS98 high Z Neutrino Flux [cm -2 s -1 ] SSM-AGS09 low Z Difference [%] pp 5.98 (1±0.006) (1±0.006) pep 1.44 (1±0.012) (1±0.012) Be 5.00 (1±0.07) (1±0.07) B 5.58 (1±0.13) (1±0.13) N 2.96 (1±0.15) (1±0.15) O 2.23 (1±0.16) (1±0.16) F 5.52 (1±0.18) (1±0.16) CNO total 5.24 x x Serenelli et al.,apj , 2011 Can solar neutrino measurements decide? 7

8 Solar neutrino experiments Detector Target mass & material Threshold [MeV] Data taking Homestake 615 t C 2 Cl Kamiokande 3 kt H 2 O SAGE 50 t Ga present GALLEX/GNO 30.3 t GaCl Super- Kamiokande 22.5 kt H 2 O present SNO 1 kt D 2 O 5 (3.5) Borexino 300 t C 9 H present radio-chemical experiments sensitive only to ν e measure integral flux above threshold real-time experiments water-cerenkov or liquid scintillator neutrino spectroscopy 8

9 History: The Solar neutrino problem over 30 years all solar neutrino experiments measured significantly lower neutrino rates than predicted by the SSM solved by the SNO experiment 2002: CC: ν e + d p + p + e - NC: ν x + d p + n + ν x E>5 MeV ES: ν x + e ν x + e Experiment Threshold Data/ SSM Homestake (ν e + 37 Cl 37 Ar+e) Superkamiokande (ν x +e ν x +e) Sage + Gallex (ν e + 71 Ga 71 Ge+e) MeV MeV MeV NC SNO SSM 8B CC SNO NC SNO sin 12 solar 8 B neutrino flux compatible with SSM proof of neutrino oscillations 9

10 The MSW LMA oscillation scenario global analysis of solar neutrino data (+KamLAND): θ 12 = (34 ± 1) Δm 2 21 = (7.5 ± 0.2) 10-5 ev 2 survival probability for solar electron neutrinos: before Borexino Schwetz et al transition region vacuum-osc. P ee ~1 ½ sin 2 θ 12 matter-enhanced P ee ~ sin 2 θ 12 10

11 Solar Neutrinos: what next? real-time spectroscopy of low energy neutrinos: 7 Be, pep, CNO, pp SuperK, SNO Borexino Cerenkov-experiments (SNO, SuperK) measure < 10-4 of the total solar neutrino flux in real-time 11

12 1 Solar Neutrinos: what next? real-time spectroscopy of low energy neutrinos: 7 Be, pep, CNO, pp neutrino physics: test transition region MSW to vacuum oscillations (1 4 MeV) precision measurement θ 12, Δm 2 21 Non-Standard Interactions solar physics: determination of CNO flux discriminate high/ low Z SSM test luminosity constraint L ν = L

13 17 m Borexino LNGS, Italy, 3500 mwe, taking data since May 2007 Target: 270 t liquid scintillator (PC+PPO) in Ø 8.5m nylon vessel (0.1 mm thick) PMTs detection reaction: ν x + e ν x + e no signature no directional information extreme radiopurity required c( 238 U, 232 Th) < g/g reached: c ( 238 U) < g/g c ( 232 Th) < g/g 13

14 Precision measurement of 7 Be neutrino rate monoenergetic, E ν = 862 kev R (stat) 1.5 (syst) Be 1.6 cpd/100t Phys. Rev. Lett. 107, (2011) live days R no osc cpd/100t Φ Be = (4.84 ± 0.24) 10 9 cm -2 s -1 P ee = 0.51 ± 0.862MeV f Be = Φ Be /Φ SSM = 0.97 ±0.07 no oscillation 5.0 s absence of day-night-asymmetry in agreement with LMA A DN = ± 0.012(stat) ± 0.007(syst)

15 pep and CNO neutrinos pep neutrinos: E ν = 1.44 MeV Phys. Rev. Lett. 108 (2012) reduce 11 C background by 3-fold coincidence R pep = 3.1 ± 0.6(stat) ± 0.3(sys) cpd/100 t Φpep = (1.6 ± 0.3) x 10 8 cm -2 s -1 P ee = 0.62 ± 0.17 f pep = Φpep /Φ SSM = 1.1 ± Bi pep 11 C CNO neutrinos: only limits, strong correlation with 210 Bi CNO limit obtained assuming SSM R CNO < 7.1 cpd/100 t (95% c.l.) ΦCNO < cm -2 s -1 (95% C.L.) f CNO < 1.4 the strongest limit to date 15

16 Low threshold measurement of the 8 B solar ν 8 B flux measured with 3.0 MeV threshold: R B = (0.22±0.04±0.01) cpd/100 t Phys. Rev. D82 (2010) ΦB ES = (2.4 ± 0.4 ± 0.1) x 10 6 cm -2 s live days f B = ΦB /Φ SSM = 0.88 ± 0.19 no hint for up-turn, but low statistics In agreement with other measurements: Kamland coll., PRC 84, (2011)

17 The Sudbury Neutrino Sudbury, Canada, 6000 mwe 1 kton D 2 O as target, 9500 PMTs data taking Detection channels CC: ν e + d p + p + e - NC: ν x + d p + n + ν x ES: ν x + e - ν x + e - Low Energy Threshold Analysis E > 3.5 MeV no significant distortion observed CC Phys.Rev.C81:055504,

18 Kamioka, Japan, 2700 mwe 50 (22.5) ktons H 2 O PMTs (20 ) taking data since 1996 Real-time-detection of 8 B ν via ν-electron-scattering: ν x + e ν x + e Cherenkov-effect direction information 18

19 SuperKamiokande latest results detection of low energy 8 B neutrinos: search for upturn in the energy spectrum = solar matter effect SK IV: threshold 3.5 MeV 8 B flux: (2.344 ±0.034) 10 6 /cm 2 s no significant distortion observed observation of day-night asymmetry = earth-matter-effect A DN ( )% in agreement with LMA solution PRL 112, (2014) 19

20 Physics implications of the latest results LMA solution confirmed by Borexino 7 Be and pep measurement, SuperKamiokande Day-Night-Asymmetry upturn in low energy 8 B spectrum not yet observed NSI or sterile neutrinos still an option Holanda, Smirnov: Phys.Rev.D83:113011,2011 Bonventre et al, PRD 88, ,

21 Solar neutrinos and metallicity HighZ Low Z central value of 7 Be is right in the middle between predictions 7 Be measurement cannot discriminate btw. high/low Z solar models more accurate measurement & prediction needed present CNO limit not strong enough to discriminate btw. models 21

22 Solar neutrinos what next? measure CNO: solar models (high/low Z) high precision pep: Non Standard Interactions (NSI), precision test of LMA 8 B spectrum at low energies: NSI, sterile neutrinos direct measurement of pp neutrinos: test Solar luminosity improve precision on 7 Be (measurement and prediction): solar models Future Experiments ongoing: Borexino, Super-Kamiokande, SAGE liquid scintillator: SNO+, LENS, LENA liquid noble gas: XMASS, CLEAN 22

23 Borexino: phase 2 ( ) Purification effort in : reduced 210 Bi background by water extraction (50 20 cpd/100t) removed 85 Kr by nitrogen stripping (30 <7 cpd/100t) 3 years of undisturbed data taking , calibration 2015 Goals for solar neutrinos: direct detection of pp neutrinos (reduced 85 Kr and 210 Bi background) solar luminosity in neutrinos improve limit on CNO neutrinos (reduced 210 Bi background) probe metallicity reach 3σ significance of pep signal (reduced 210 Bi background) measure 7 Be neutrinos to 3% (reduced 85 Kr and 210 Bi background) improve 8 B measurement to 10% (higher statistics) precision test of LMA 23

24 SuperKamiokande future from Y. Koshio s Nu2014 wide band intelligent trigger system with 100 % efficiency > 2.5 MeV installed 24

25 location: Sudbury, Canada, 6000 mwe fill SNO with liquid scintillator 780 tons LAB+PPO, 9000 PMTs reduced 11 C background due to the depth 70 µ/day@sno+ (10 4 µ/day@borexino) 210 Bi, 85 Kr dominating background for solar ν Schedule: start scintillator filling: early 2015 background studies add 130 Te end 2015 ( bb decay ) solar phase postponed 25

26 LENA: Low Energy Neutrino Astronomy physics program: proton decay, solar neutrinos, Supernova neutrinos, DSNB, geoneutrinos, etc. scaling up Borexino (~ 100): 26

27 Solar neutrinos with LENA ~ 18 kton fiducial volume for solar neutrinos detection via: neutrino-electron-scattering (ES) e - e - CC-interaction on 13 C: 13 C + e 13 N + e - 7 Be: ~ 5400 events per day search for fluctuations on short time scale CNO & pep: ~ 360 events per day sensitive test of MSW, solar metallicity CC and NC measurement of 8 B: ~ 60 events per day (ES)/1 event per day (CC) search for spectral deformation 27

28 JUNO Jianmen Underground Neutrino Observatory (formerly Daya Bay II) 20 kt liquid scintillator, 700 mwe determination of mass ordering with reactor neutrinos also good for low-energy neutrino astronomy (solar neutrinos?) 28

29 LENS: Low energy neutrino spectroscopy In-loaded liquid scintillator clear signature of ν e -events (CC-reaction): R. Raghavan, Phys. Rev. Lett. 37, 259 (1976) C. Grieb et al.,physrevd (2007) prompt: e 115 In e 115 Sn * t=4.6 ms delayed: 115 Sn * 115 Sn ' s (116 kev, 497 kev) Q= 114 kev sensitivity to pp, 7 Be, pep, CNO, 8 B Background from β-decay of 115 In: 400 pp/year In-decays/year µ-lens: 130 l prototype running in Kimballton mine 29 simulated spectrum: 5 years, 10 t In

30 Cryogenic liquid noble gas scintillators 100 t liquid noble gas as scintillator main goal: dark matter 1 pp-event per day and ton XMASS phase-1 detector with 835 kg liquid Xe, 642 PMTs, Kamioka CLEAN prototype with 500 kg liquid Ne, 92 PMTs SNOLAB arxiv arxiv

31 Conclusions Lessons learned from Solar Neutrinos: evidence of hydrogen burning in the sun neutrino oscillations and matter-effect precise measurement of θ 12 What the future may bring: direct measurement of pp neutrinos detection of CNO neutrinos solar abundance problem search for new physics in solar neutrino interactions Solar neutrino detectors are also good for: Supernova neutrinos geo neutrinos search for sterile neutrinos with artificial sources dark matter neutrinoless double beta decay 31