1. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Upper limit on the molecular resonance strengths in the 12 C+ 12 C fusion reaction X. Tang University of Notre Dame

2. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Outline Superburst puzzle Empirical relationships among the carbon isotope fusion reactions: 12 C+ 12 C, 12 C+ 13 C and 13 C+ 13 C Upper limit on the molecular resonance strengths in the 12 C+ 12 C fusion reaction Comparison with the most recent direct measurement and impact to the superburst puzzle. Future ND-ANL experiments

3. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Superbursts Rare, long duration bursts; By 2009, 15 bursts from 10 sources Kuulkers 2004, 2005; in’t Zand 2004; Remillard 2005; Keek 2008 Recurrence times 1-2 years, energies 10 42 ergs. Triggered by 12 C+ 12 C fusion in the ashes left over after the rp-process Cumming & Bildsten 2001; Strohmayer & Brown 2002; Cumming 2003; Brown 2004; Cooper & Narayan 2005; Cumming et al. 2006; Gupta et al. 2007 Normal X-Ray burst Superburst Flux time

4. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Superburst: ignited by Carbon burning Ashes from rp process deposit in the outer crust. Crust processes (EC, pycnonuclear fusion)  crust heating  crust conductivity Picture by E. Brown ~ 20m Column depth (Y) (0.5-2)x10 12 g/cm 2 ashes

5. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Superburst Puzzle: the outer crust is too cold to ignite the carbon burning! Maybe the carbon burning rate underestimated? Keek et al. (2007), Astron. & Astrophys. 479: 177. 4U 1608-522 + atmospherecore

6. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 3x10 16 MeV*b Astrophysical energy range

7. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 1.E+15 1.E+16 1.E+17 1.E+18 1.E+19 1.E+20 1234567 E c.m. (MeV) S* (MeV*b) CF88 Becker Patterson Aguilera 3x10 16 MeV*b Fit with Eilat! Astrophysical energy range

8. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 T. Spillane et al., Phys. Rev. Lett. 98, 122501 (2007) R. Cooper et al., APJ (2009) 702, 660 Possible resonances in 12 C+ 12 C

9. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 R. Cooper et al., APJ (2009) 702, 660 …. in this case, observationally inferred superburst ignition depths would accord with model predictions for a range of plausible neutron star parameters….

10. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 24 Mg(a,a’) inelastic Search the possible resonances Direct measurement The exact cross section 12 C+ 13 C 13 C+ 13 C Provide potential to model the smooth behavior 12 C+ 13 C 13 C+ 13 C Provide potential to model the smooth behavior 12 C+ 13 C 13 C+ 13 C 12 C+ 12 C 12 C( 12 C,n) 23 Mg 12 C( 12 C,p) 23 Na 12 C( 12 C,a) 20 Ne 12 C( 12 C, 8 Be) 16 O 12 C( 12 C,a) 20 Ne

11. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 10 MV FN Tandem @ ND 20 e  A 13 C - 2 e  A 13 C 2+ Thick graphite disk Carbon stripping (100 enA) Gas stripping The 12 C+ 13 C experiment ---- Full (Un- gated) ---- Gated 1.37MeV 2.74MeV Ec.m.=2.83 MeV, 1puA*28hr,379 counts Very compact beta counter 12 C( 13 C, 24 Na)p

12. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Eg. for 12 C+ 12 C, (E in MeV) Caltech 1983 Not good to compare xsec among the three systems 12 C+ 13 C 12 C+ 12 C 13 C+ 13 C

13. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Use the same conversion formula for all the three carbon systems.

14. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 The 12 C +12 C is not enhanced but suppressed! 4 nb Linear scale!

15. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 KNS and CW (Woods-Saxon type) are taken from Aguilera’s paper, PRC 73, 064601 (2006) CC and NOC are calculated with CCFULL by Hagino et al..

16. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Couple channel enhancement is not sensitive to the choices of potential. CW

17. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 First quantitative systematic description of the molecular resonance strengths CC: resonance NOC: off-resonance The observation supports Nogami-Imanishi model (1968). Linear scale!

18. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Spillane (2007) Cooper (2009) Preliminary HINDRANCE: Woods Saxon potential always over-predicts Upper limit: ~3xCF88 Lower limit: ~1/3*CF88 OR LESS X X

19. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Preliminary results from the 12 C+ 12 C fusion experiment at Caserta Uncertainties below 2.5 MeV range from 25-100% on each curve Gamma ray data correspond to the 440 keV line of 23 Na and charged particle data to P0 and P1 groups (normalization necessary) Modifications are necessary to achieve energies below 2 MeV (higher beam currents, larger efficiency, etc.) Tim Spillane, U. Conn Thesis (2007) Jim Zickefoose, U. Conn Thesis (2011) proton channel only

20. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 If the rate can not be as that high, there must be some physics missing in the superburst model. Unknown process to heat up the crust to higher temperature. Carbon burning is not the one triggering the superbust! Upper limit 4U 1608-522 +

21. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Notre Dame-ANL fusion experiment A 5 MV Pelletron with ECR source in terminal. Will be installed at the end of 2011. Simulation @ Ecm=1.5 MeV Solenoid Spectrometer for Nuclear AstroPhysics (SSNAP) Silicon Array at Notre Dame (SAND)

22. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011

23. Institute for Structure and Nuclear Astrophysics Nuclear Science Laboratory NPA5 April 7, 2011 Summary Based on an empirical correlations among three carbon isotope fusions, the upper limit for the carbon fusion reaction rate is defined. Both the strong resonance observed at E cm =2.14 MeV and the hypothetical strong resonance at E cm =1.5 MeV are not realistic. Superburst puzzle remains unsolved! Direct/Indirect(THM) measurement is urgently needed! We are developing high current accelerator and highly efficient detector arrays to conquer the challenges.