Ralph Hix

Understanding Core Collapse Supernovae

Our understanding of core-collapse supernovae continues to improve as better microphysics is included in ncreasingly realistic neutrino-radiationhydrodynamic simulations.  Recent multi-dimensional models with spectral neutrino transport, which slowly develop successful explosions for a range of progenitors between 12 and 25 solar mass, have motivated changes in our understanding of the neutrino heating mechanism.  In a similar fashion, improvements in nuclear physics, most notably explorations of weak interactions on nuclei and the nuclear equation of state, continue to refine our understanding of how supernovae explode.  I will discuss recent progress on both the macroscopic and microscopic physics that affect core-collapse supernovae.

Peter von Neumann-Cosel

The talk discusses our knowledge of the low-multipolarity magnetic response in nuclei with a focus on open problems and suggestions for future research. A (not necessarily complete) list of possible topics includes quenching of the spin strength for ground-state M1, M2 and M3 transitions orbital M1 strength as a signature of mixed-symmetry states evidence for an orbital M2 “twist” mode relation between M1 and GT strengths and astrophysical implications characteristic scales of the spin M1 resonance shell-model description of cross-shell M1 transitions meson exchange current contributions to M1 transitions in sd-shell nuclei forbidden M1 transitions

Juha Äystö

Beta decay and Precision Mass Measurements

Beta decay mediated by the weak force acting in a nucleus is dominated by the allowed transitions involving proton, neutron, electron and neutrino. Decay rates (half-lives) are determined by the transition matrix elements of spin-flip (Gamow- Teller) or non-spin-flip (Fermi) transitions, coupling constants of the weak interaction and the energy available for the decay. Sine the decay rate is proportional to the fifth power of the decay energy precise determination of the energy difference between the parent and daughter states plays crucial role in understanding the weak nuclear decays. Recent developments in Penning trap mass spectrometry of exotic nuclei have contributed in an important way to studies of nuclear beta decays and their applications in nuclear structure physics [1] and in astrophysical nucleosynthesis processes [2]. On the other hand, the relative accuracy of the order of 10-9 reached in recent mass measurements [3,4] has provided the most precise value for the Vud matrix element of the CKM matrix and a test of its unitarity, a property fundamental to the electroweak standard model. Another application of high-precision mass measurements is related to the search experiments for neutrinoless double beta decay and neutrino mass [5,6].

[1] J. Hakala et al., Phys. Rev. Lett. 101 (2008) 052502
[2] V. Elomaa et al., Phys. Rev. Lett., 102 (2009) 252501
[3] T. Eronen et al., Phys. Rev. Lett. 100 (2008) 132502
[4] J. C. Hardy, I. S. Towner, Phys. Rev. C 79 (2009) 055502
[5] S. Rahaman et al., Phys. Lett. B 662 (2008) 111
[6] S. Rahaman et al., Phys. Rev. Lett. 103 (2009) 042501

Yoshitaka Fujita

Gamow Teller transitions studied by (3He,t) reactions and the comparison with analogous transitions

Gamow-Teller (GT) transition is one of the most popular nuclear weak processes of spin-isospin excitations.  It is of interest not only in nuclear physics, but also in astrophysics; it plays important roles, for example, in supernova-explosion or nuclear synthesis.  Relatively limited information can directly be obtained through the study of weak processes themselves.  However, it was found that charge-exchange reactions, such as (3He,t) reaction, which are caused by the strong interaction, can well study the GT transitions owing to the similarity of the active operator.  They could drastically extend the energy region of the GT study.  Especially, with the one-order-of-magnitude improvement of the energy resolution in the (3He,t) reaction compared with the pioneering (p,n) reaction, fine structures of GT excitations, even those of GT giant resonances (GTGR), can now be studied.  For example, determination of GT strengths for individual transitions in pf-shell nuclei with astrophysical interest is now possible up to the GTGR region.  We show that quantum number ``isospin'' plays important roles in such studies.  Under the assumption of isospin symmetry, the achieved high energy-resolution allows the comparison with the results obtained by beta decays as well as gamma decays, which are caused by the weak and electro-magnetic interaction, respectively.