Measurement of the b-branch of 12B to the Hoyle state in 12C Hans Fynbo replacing Martin Alcorta Physics Division Argonne National Laboratory INPC 2013 Firenze, Italia

Motivation 12C 3a 0+ 12B 1+ b-decay (0+, 1+ or 2+) 2+ 1.28% 97.2% gs 4.439 7.654 Recent studies using beta-decay get a result half that of the literature value for the branching ratio to the Hoyle state It is crucial to get the correct feeding to the states in R-matrix calculations, which found evidence for 2+ in 12C at 11.1 MeV 0.8% 0+/2+ 1.2% F. Ajzenberg-Selove, NPA506, 1 (1990) S. Hyldegaard, PRC81, 024303 (2010) M. Alcorta 6/3/2013

12C Motivation 12B 0.58(2)% 1.2(3)% 1.2% 1.28(4)% KVI Literature 97.2% 0+ 12B 1+ b-decay (0+, 1+ or 2+) 2+ 1.28(4)% 97.2% gs 7.654 KVI Literature 0.58(2)% 1.2(3)% 1.2% 4.439 0.068% 0.08% 2.8×10-4% Nature2005 PRC2009,2010, PLB2009 M. Alcorta 6/3/2013

Confirm BR(7.65) using independent method b-decay (0+, 1+ or 2+) 1+ 12B 0.58(2)% 1.2(3)% 7.654 0+ 3a 1.28(4)% 0.0413(11)% 4.439 2+ 97.2% gs 0+ 12C M. Alcorta 6/3/2013

Confirm BR(7.65) using independent method 3a 0+ 12B 1+ β-decay (0+, 1+ or 2+) 2+ 1.28% 97.2% 0.58% 1.2% gs 7.654 g3% 0.58(2)% 1.2(3)% b 5% 1.28(4)% 4.439 gg 0.1% g 3% D. E. Alburger, Phys. Rev. 131, 1624 (1963). M. Alcorta 6/3/2013

Confirm BR(7.65) using independent method 3a 0+ 12B 1+ b-decay (0+, 1+ or 2+) 2+ 1.28% 97.2% 0.58% 1.2% gs 7.654 bgg 1.7(5)% 0.58(2)% 1.2(3)% 1.28(4)% 4.439 gg M. Alcorta 6/3/2013

Need to reduce Bremsstrahlung! Experiment Gammasphere at ATLAS 101 high-purity Ge detectors BGO Compton-suppression shields 2.5 pnA 11B beam, 40 MeV Thick TiD2 target to stop the beam 1.5 mg/cm2 D2 Measure 40 ms beam on/beam off T1/2 = 20.2 ms Qb = 13.37 MeV Need to reduce Bremsstrahlung! M. Alcorta 6/3/2013

Confirm BR(7.65) using independent method Unused Bonner sphere Made from CH2 Low Z for reducing Bremsstrahlung Also good at absorbing gammas + Attenuate low-energy gammas - Need to determine absolute efficiency Efficiency determined from 24Mg 4+ -> 2+ -> 0+ transition Gives absolute efficiency at 1.32 MeV Relative efficiency determined from 56Co and 152Eu sources Brad DiGiovine M. Alcorta 6/3/2013

Results Standard GS chamber With plastic housing M. Alcorta 6/3/2013

12C Results 12B 1.28% 97.2% 0.58% 1.2% 0.58(2)% 1.2(3)% 1.28(4)% 1+ 3a 0+ 12B 1+ b-decay (0+, 1+ or 2+) 2+ 1.28% 97.2% 0.58% 1.2% gs 7.654 0.58(2)% 1.2(3)% 1.28(4)% 4.439 M. Alcorta 10/25/2012

Preliminary Results BR(7.65) = 0.68(09)% The error is dominated by statistics Increase statistics using HfD2 target Can we determine Gg / G ? Gg / G = 4.12(11)x10-4 BR(4.44) = 1.28(4)% ε3.21 = 2.94(9)% Cq = 1 Preliminary F. Ajzenberg-Selove, Nucl. Phys. A506, 1 (1990) M. Alcorta 6/3/2013

Determine Radiative Width Gg Gp Q2= -287 keV a +8Be Hoyle state Q1 = -92 keV a + a M. Alcorta 6/3/2013

Determine Radiative Width Quantity Value Error(%) Q3a 379.4(2)keV 1.2 Grad/G 4.12(11) ×10-4 2.7 Markham, Austin, Gp/G 6.7(6) × 10-4 9.2 Alburger 1977 Gp 62.3(2.0) meV 2.5 Chernykh 2010 Shahabuddin 1976 NPA270 489, (1976) PRC 16, 2394 (1977). PRL 105 022501, (2010) M. Alcorta 6/3/2013

Conclusion / Outlook Determined value of BR to Hoyle state as 0.68(9)% In agreement with recent results from b-decay Confirms a 2+ at 11.1 MeV in 12C from b-decay Disagreement with literature value Method could possibly be used to constrain Gg/ G b-decay result for mirror nucleus 12N is 1.41(3)% Previous value 2.7(4)% Use same method to independently determine BR(7.65) for 12N? M. Alcorta 6/3/2013

Thank you Aarhus University, Aarhus, Denmark Physics Division, Argonne National Laboratory, Argonne, IL Western Michigan University, Kalamazoo, MI Department of Astronomy and Astrophysics, University of Chicago, IL Joint Institute for Nuclear Astrophysics, Chicago, IL Laboratorio Tandar, Buenos Aires, Argentina H.O.U Fynbo, K.L. Laursen, M. Albers, S. Almaraz-Calderon, P.F Bertone, P.F.F. Carnelli, M.P. Carpenter, B. DiGiovine, J.P. Greene, C.R Hoffman, R.V.F Janssens, T. Lauritsen, C. Nair, S.T. Marley, K.E. Rehm, D. Seweryniak, C. Ugalde, S. Zhu M. Alcorta 6/3/2013 15

EXTRAS M. Alcorta 6/3/2013 16

12C Motivation 12B R-matrix analysis (multi-channel, multi-level): 2+ 0+ 12C 3a 0+ 12B 1+ b-decay (0+, 1+ or 2+) 2+ 1.28% 97.2% gs 4.441 7.654 0.04% Beta-decay Scattering: E(0+) = 11.2(3) MeV 9.93(3) MeV G(0+)= 1.5(6) MeV 2.71(8) MeV Beta-decay Scattering: E(2+) = 11.1(3) MeV 9.8(2) MeV G(2+)= 1.4(4) MeV 0.8(2) MeV R-matrix analysis (multi-channel, multi-level): M. Alcorta 6/3/2013

Lowest 2+ resonance in 12C? E(2+)=9.8(2) MeV G(2+)=0.8(2)MeV 3- 1- 3a Stellenbosch: Freer et al. (2009): 12C(p,p´)12C Yale : Zimmerman et al. (2011): 12C(p,p´)12C 3- 1- Osaka: Itoh et al. (2011): 12C(, ´)12C Lowest 2+ resonance in 12C? 3a E(2+)=9.8(2) MeV G(2+)=0.8(2)MeV Fynbo & Freer, Physics, 4 (2011) 94. M. Alcorta 6/3/2013