Coulomb dissociation of 8 B and the solarneutrino

Coulomb dissociation of 8 B and the "solar-neutrino problem" Klaus Sümmerer, GSI Darmstadt (Germany) 1. Energy production in the Sun: • • Solar fusion reactions The "solar-neutrino problem" 2. The 7 Be(p, γ)8 B reaction • • Direct (p, γ) measurements Indirect methods 3. Coulomb dissociation of 8 B • • • Pro's and Con's of the method The GSI experiment Comparison to other results 4. The solution of the "solar-neutrino problem" • Results from SNO and other neutrino detectors 5. Outlook

Energy production in the Sun: the p-p chain Coulomb-dissociation experiments of astrophysical interest high energy neutrinos! plus small contribution by CNO-cyle (≈ 1. 5%) net result: 4 p a + 2 e+ + 2 ve + 26. 7 Me. V

Solar neutrino spectra and detection methods Coulomb-dissociation experiments of astrophysical interest 2 detection methods: 1, 2: radiochemical (cumulative) detection 3: real-time detection 1 3

Radiochemical ν-detection: The Homestake Cl experiment The Homestake-Mine chlorine experiment by Ray Davis and collaborators (1968 bis 2001): νe+37 Cl → 37 Ar (T 1/2=35 d)+e 680 t liquid CCl 4 located in Homestake Gold-Mine (USA) (1. 5 km below surface) flush Ar every 100 days Production: ~0. 5 atoms/day Measured: 2. 56 ± 0. 16(stat) ± 0. 16(syst) SNU Predicted: 8. 5 ± 0. 18 SNU (Standard Solar Model, Bahcall et al. 2004): → only 30% of the predicted flux! 1 SNU (Solar Neutrino Unit) = Is this prediction reliable? 1 νe-capture/(1036 atoms of 37 Cl∙s )

Radiochemical ν-detection: The Gallium experiments Gallium-based radiochemical experiments: SAGE, GALLEX νe + 71 Ga → 71 Ge (T 1/2=11. 4 d) + e- SAGE: 60 t liquid Ga metal (Baksan, Russia) GALLEX: 30. 3 t Ga in Ga. Cl 3 -HCl solution Gran Sasso underground laboratory (Italy) (1. 3 km below surface) Flush liquid with N 2, convert Ge. Cl 4 into Ge. H 4 Result: Predicted: 70. 8± 4. 5(stat)± 3. 8(syst) SNU 131 SNU (BP 04) → only 55% of predicted flux! GALLEX

Realtime ν-detection: (Super-) Kamiokande 1) Kamiokande (700 t of water, 1983 -1996) 2) Super-Kamiokande (50 kt of water, since 1996) in Kamioka Mine, Japan (~1 km below surface) Elastic neutrino scattering from electrons: νe + e - → e - + νe (11146 photomultipliers with 50 cm each) → Cherenkov – radiation → information on direction and energy Energy threshold: ~ 5 Me. V Result: 2. 35 ± 0. 02(stat) ± 0. 08(syst)× 106 cm-2 s-1 Prediction: 5. 8 ± 1. 3× 106 cm-2 s-1 → only 40% of the predicted flux ! Sun

The "solar-neutrino problem" Cl H 2 O Ga Possible solutions to these solar-neutrino problems: 1) The standard solar model is wrong or 2) Something is happening to the e -neutrinos between creation in the Sun and detection on Earth

Can we trust the Standard Solar Model (SSM)? Ingredients: R = 700 000 km • Measured solar properties: Radius, Mass, Luminosity, Distance, Chemical surface composition, T = 5800 K Surface oscillation frequencies, . . • Thermal equilibrium • Nuclear theory of solar-fusion reactions • Best estimate for nuclear cross sections Important ingredient for high-energy (8 B) neutrino detection: low-energy cross section of the 7 Be(p, γ)8 B reaction! Desired precision: ± 5%!

The low-energy 7 Be(p, γ)8 B cross section Thermal fusion in the Sun occurs far below the Coulomb barrier! p+7 Be cross sections σ(Ecm) S-factor: S=Ecm x σ/exp(-2πη) η=Z 1 Z 2 e 2/(ћv) for p+7 Be: S 17 C. M. energy of Gamov peak: E 0 = 1. 22 (Z 12 Z 22∙m. T 62)1/3 ke. V p+7 Be in the Sun: E 0 = 16 ke. V

The low-energy 7 Be(p, γ)8 B cross section 7 Be (t 1/2 = 53 d): Long-lived enough to make a target, but: 7 Be target areal density: ≈ 10 mg/cm 2 p intensity: 10 m. A = 6∙ 1013/s L ≈ e ∙ 5∙ 1031 cm-2 s-1 e large: a detection! s, d + 1 769 E 1 p, f 3/2 - M 1 137 7 Be+p E 1 non-resonant capture 2+ 8 B 0 ke. V 8 Be* M 1 resonant capture 769 – 137 = 632 ke. V Problems with direct-proton-capture: Ø small cross sections at low Ecm Ø problems with absolute normalization Ø sensitive to d. E/dx at low energies 2α

History of the astrophysical S 17 factor J. Bahcall Nucl. Phys. B 118 (2003) 77 www. sns. ias. edu/~jnb/

S-factor S 17 from modern proton-capture experiments In 2003, the Seattle group (Junghans et al. ) published a new dataset with much smaller error bars and a higher S 17(0) Up to 2003, all recent S 17 -results seemed to agree within errors Can we cross-check these results with an alternate method?

Alternate method: Coulomb dissociation 7 Be Baur, Bertulani and Rebel (1986): measure instead of 8 B+γ 7 Be +p + p 8 B+γ 8 B p cross sections are related by detailed balance! virtual-photon spectrum (Weizsäcker-Williams) dσCD/d. Ecm = 1/Ecm dnγ/d. Ecm σγp detailed balance σγp = 4/5 k 2/kγ 2 σpγ kγ = (Ecm+Q)/ћc k 2 = 2μEcm/ћ 2 k 2/k 2 ≈ 1000 virtual photons from high-Z target (best at relativistic energies, 200 -500 A Me. V)

Pro's and Con's of the Coulomb-dissociation method Pro CD: ØTwo fast charged particles in exit channel ØDifferent systematic errors than low-energy direct p-capture ØMethod applicable also to short-lived nuclei ØPhase-space factor enhances cross sections Contra CD: Øbad cm-energy resolution Ødnγ/d. Ecm depends on multipolarity! ØNuclear contribution? ØHigher-order effects? Best CD results for: CD works best for low Q, high Ecm! Small nuclear, large CD contribution Small higher-order effects

Multipolarity contribution to Coulomb dissociation Example: 7 Be (p, γ)8 B Direct p-capture: S 17(0) is dominated by E 1 virtual-photon spectrum: large number of E 2 photons E 2 may play a role! (theory: ~5 -10% effect)

Overview over Coulomb-dissociation experiments of 8 B Author Lab Energy Year published Motobayashi et al. RIKEN 46. 5 A Me. V 1996 Kikuchi et al. RIKEN 52 A Me. V 1998 Iwasa et al. GSI 254 A Me. V 1999 Davids et al. MSU 83 A Me. V 2001 Schümann et al. GSI 254 A Me. V 2006

The GSI 8 B Coulomb-dissociation experiment: Preparation of the 8 B beam production target 9 Be, 8 g/cm 2 12 C, Plastic (TOF-Start) 8 B, 254 Me. V/u 208 Pb-target 52 mg/cm 2 PPACs (TOF-Stop) degrader 353 Me. V/u Kao. S SIS FRS ESR

Analyzing incident 8 B and outgoing p and 7 Be at the spectrometer "Kao. S" track incoming 8 B Si microstrip detectors (SSD): pitch 100 μm; identify p, 7 Be, 8 B; measure θ 17 Magnetic spectrometer Kao. S: measure pp, p. Be construct invariant mass from θ 17, pp, p. Be Reference: F. Schümann et al. , Phys. Rev. C 73 (2006) 015806.

Identification of p and 7 Be in Si Strip detectors Identification of p, 7 Be, 8 B: energy loss in Si. Strip detectors p He 7 Be 8 B p and 7 Be from breakup in Pb target: vertex reconstruction vertex region y SSD 1/SSD 2 target SSD 3/SSD 4 p Z x 17 7 Be back-ground free measurement! z-vertex position

Results(1): Scattering angles Θ 8 1. nuclear overlap? introduce absorptive potential 2. E 2 -contribution? . Ø E 1 multipolarity gives perfect fit to data Ø E 1+E 2 deviates for large θ 8

Results(2): p-7 Be angular correlations E 1 -E 2 interference? p- Be angular correlations 7 In-plane proton angular distributions: cm Compare to two theoretical approaches: 1. first-order perturbation theory 2. dynamical QM-calculation θcm distributions are symmetric: E 1 describes data sufficiently well!

Results(3): Energy-differential cross sections experimental cross sections theoretical prediction: M 1 component: • taken from Filippone et al. (1983) • GEANT simulation to take into account experimental resolution Conversion to S factor: • compare exp. and simulated bin contents • adjust S 17(E 1, theor. ) S 17(exp)

-factors Coulomb from Coulomb Dissociation experiments S 17 -factors. S from experiments 17 GSI: 254 A Me. V E 1 only Kikuchi/RIKEN: 51 A Me. V E 1 -only Davids/MSU: 83 A Me. V E 2 component subtracted .

Comparison with S 17 factors Comparsion to S proton-capture -factors from (p, γ) experiments 17 Best fit to Seattle data: S 17(0) = 21. 5 ± 0. 6 e. V barn . GSI-2: S 17(0) = 20. 6 ± 1. 5 e. V barn Accepted (p, γ) value from 2009 Seattle workshop: S 17(0) = 20. 9 ± 0. 7 e. V barn Very good agreement with (p, γ) data!

Conclusions from 8 B Coul. Diss. experiment Ø In certain cases, CD is a useful tool to measure radiative-capture cross sections. Ø It works best at high energies (300 -500 A Me. V). Ø The 7 Be(p, γ)8 B reaction is an ideal case: Dominant E 1 multipolarity, low Q-value. Ø We found convincing evidence for a negligible E 2 contribution. Ø The GSI CD experiment agrees very well with the best (p, γ) experiment. Direct-proton capture seems still to provide more precise results. Ø S 17 is no longer the largest uncertainty in solar-model predictions of the 8 B solar neutrino flux.

The final solution to the solar-neutrino problems: ν-oscillations ØIn 2002, the Sudbury Neutrino Observatory (SNO) published direct evidence for e-neutrino flavor oscillations. ØMore papers from the Sudbury Neutrino Observatory (SNO) have confirmed the earlier results. ØThe KAMLAND experiment in Japan has directly measured reactor -antineutrino oscillations. ØThe BOREXINO experiment in Italy has measured the solar 7 Be neutrino flux.

Neutrino-flux measurements by the Sudbury Neutrino Observatory (SNO, Canada) Cherenkov detector 1100 t D 2 O (99. 92%) 9456 photomultiplier tubes ( 20 cm each) fiducial volume, surrounded by 1700 t H 2 O outer volume: 5300 t H 2 O 2 km below surface near Sudbury, Canada Aim: Measuring the total v flux including τ, μ and e neutrinos!

How SNO can detect other neutrino Direct neutrino detection in the SNO detector flavors Elastic scattering Charged current interaction: Neutral-current interaction: ES: nx + e- → nx + e- CC: ne + d → p + e- NC: nx + d → p + nx mainly sensitive to ne sensitive only to ne sensitive to all n flavors New: neutrons detected by 3 He counters!

The SNO results for the 8 B solar neutrino flux experimental total v-flux from the Sun predicted total v-flux

8 B solar neutrino fluxes: SNO experiment vs. SSM calculations Experimental solar neutrino flux: (B. Aharmin et al. , PRL 101 (2008) 111301) Best value from SNO Φexp = 5. 54 (1 ± 0. 09) 106 n/cm 2/s Standard Solar Model solar-neutrino flux: Recent changes (J. N. Bahcall and M. H. Pinsonneault, PRL 92 (2004) 121301) New 7 Be(p, γ) cross section from Seattle exp. increases Φtheo by 15% New solar-surface composition increase error on Φtheo to ± 23% Φtheo = 5. 79 (1 ± 0. 23) 106 n/cm 2/s

Kam. LAND: Detecting the disappearance of reactor antineutrinos Kam. LAND ve + p n + e+

KAMLAND results prompt energy spectrum ve survival probability L 0 = 180 km

7 Be neutrinos: Borexino at Gran Sasso (Italy) Elastic scattering: nx + e- → nx + erecoil e-: < 665 ke. V requires ultra-low background! PRL 101, 091302 (2008) 7 Be 862 ke. V line Result: counts/(day∙ 100 tons) Exp. : 43 ± 3(stat) ± 4(syst) Predicted: 48 ± 4 (with ν oscill. ) 74 ± 4 (without ν oscill. )

Neutrino oscillation parameters Confidence limits from SNO without Kam. LAND with Confidence limits from SNO plus all other neutrino experiments B. Aharmim et al. , PRL 101 (2008) 111301

Outlook: Nuclear Physics ØAll solar-fusion reactions were discussed during an "expert meeting" in Seattle in January 2009, following a similar meeting in 1998. ØThere is little chance to improve the nuclear-physics input. E. g. : ØThe low-energy cross section of the 3 He(4 He, γ)7 Be reaction (i. e. S 34) has been remeasured with better accuracy. S 34(0) = 0. 56 ± 0. 02 ke. V b old value: S 34(0) = 0. 53 ± 0. 05 ke. V b 3 He + 4 He

Outlook: Neutrino Physics Many experiments are under way to elucidate certain aspects of neutrino physics: Tokai-to-Kamiokande (T 2 K, Japan): Shoot a μ-neutrino beam from Tokai to the Super-Kamiokande detector (295 km). Look for e-appearance in Super-Kamiokande. CERN-to-Gran Sasso (CNGS, Europe): Shoot a μ-neutrino beam from CERN to the a detector at Gran Sasso (730 km). Look for τ-appearance at Gran Sasso (OPERA, ICARUS) exciting results to be expected!

Muchisimas gracias. . . Øto Frank Schümann, Fairouz Hammache, Stefan Typel, Naohito Iwasa, Peter Senger and the Kao. S collaboration for performing and analyzing the 8 B experiment, Øto Tom Aumann for lending me many neutrino slides from his habilitation talk, Øto I. Duran, D. Cortina, J. Benlliure and the nuclear-physics group at USC for very generous hospitality, Øto you for your kind attention!

Helioseismology Pressure waves at the solar surface can be detected by Doppler shifts of optical emission lines sound speeds inside the Sun. Bahcall's SSM can reproduce the measured sound speeds to a remarkable accuracy!

SNO can distinguish between neutrino interactions Anisotropy Energy spectrum direction

Super-Kamiokande: Atmospheric Neutrinos e-like neutrinos μ-like neutrinos Monte-Carlo calculations assuming nm→nt oscillations

Advantages of high incident energies E 1 contribution is maximized GSI: 254 Me. V/nucleon higher-order corrections are minimized S. Typel

Correction for feeding of excited state in 7 Be 1+ 769 E 1 M 1 429 137 7 Be+p 0 ke. V 2+ 8 B In Coul. Diss. , the 1 st excited state in 7 Be can be fed. This feeding has been measured at RIKEN and reproduced by a calculation by S. Typel. At low Erel, its contribution is small.

Check low-θ 17 = low-Erel data points typical single-event hit pattern in SSD p-7 Be opening angles θ 17 d = 6 strips = 0. 6 mm 7 Be p w Present analysis condition: sharp cutoff at d = 4 strips • Simulation of low-θ 17 response must be improved! • Low Erel cross sections will increase!

E 2 contribution found at MSU: CD of 8 B at 44, 81 A Me. V Inclusive 7 Be momentum spectra with high resolution at S 800 Asymmetries are interpreted as signs for E 1 -E 2 interference! 1 st order pert. theory dynamical theory 44 A Me. V: f=1. 0 81 A Me. V: f=0. 6 44 A Me. V: f=1. 6 81 A Me. V: f=1. 2 (same as for GSI) B. Davids and S. Typel, PRC 68, 045802 (2003) but: E 2 scaling factor is energy- dependent!

Coulomb-dissociation experimentsreactions of astrophysical interest Radiative-capture studied by Coulomb dissociation Reaction Significance Laboratory d( , )6 Li big bang GSI 7 Be(p, )8 B pp chain RIKEN, GSI, MSU 8 B(p, )9 C hot pp-chain RIKEN* 11 C(p, )12 N hot pp chain GANIL, RIKEN 12 C(p, )13 N CNO RIKEN* 12 N(p, )13 O hot pp chain RIKEN* 13 N(p, )14 O hot CNO RIKEN, GANIL 14 C(n, )15 C r-process GSI 22 Mg(p, )23 Al rp-process RIKEN *unpublished 26 Si(p, )27 P rp-process RIKEN