Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Neutrino-Nucleus Interactions and the Core Collapse Supernova Mechanism Sk SN 1987a

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Weak reactions & Stellar Evolution Iron core mass and neutronization depend on e - capture and  decay rates for A<65 Heger, Woosley, Martinez-Pinedo & Langanke ‘01 New shell model rates reduce e - capture rates, decreasing the core neutronization

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Electron Capture Puzzle New progenitor models with reduced neutronization made little difference in collapse behavior. e - / capture on nuclei cease for A>65, allowing e - capture on protons to dominate. For these conditions, Y p is a strong function of Y e, so differences in Y e are “washed out”. Is this due to physics or our approximation? Messer, Hix, Liebendörfer & Mezzacappa ‘03

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Captures on Nuclei a la Bruenn (1985) EOS (Lattimer & Swesty 1991) identifies average heavy nucleus e - and  capture via generic 1 f 7/2  1 f 5/2 GT transition (Bethe et al 1979), quenched at N=40, with Q=  n -  p -3 MeV  decay suppressed by large  e

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Testing the effects of e - Capture on Nuclei Replaced quenching term with parameter (N p N h ) = Without quenching, e - capture on nuclei dominates until bounce. Significant impact (~.1 M  ) on the location of bounce shock formation. Messer, Hix, Liebendörfer & Mezzacappa ‘03

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Needed Electron Capture Rates Nuclei with A>120 are present in collapsing core.

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Nuclear Electron Capture Rates Shell Model calculations are currently limited to 0h  in the pf shell (A~65). Langanke et al (2003) have employed a hybrid of shell model (SMMC) and RPA to calculate a scattering of rates for A<110. Electron capture on heavy nuclei remains important throughout collapse. Langanke et al (2003)

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Approaches to Nuclear Composition Thomas-Fermi free nucleons,  particles, and a heavy nucleus Nuclear Saha Equation All nuclei for which mass and partition function are available Provides detailed composition Transitions easily to non NSE regions Lighter computational requirement Transitions easily to nuclear matter Strengths Need Both!

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Effects of Nuclear Electron Capture during Core Collapse Constructed average capture rate using Saha-like NSE and Langanke et al (2003) rates. Compared to Bruenn (1985), results in more electron capture at high densities but less electron capture at low densities. Reduces initial mass interior to the shock by 20% Hix, Messer, Mezzacappa, et al ‘03

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Effects on Shock propagation “Weaker” shock is faster. Lepton and entropy gradients are altered. Maximum excursion of the shock is 10 km further and 30 ms earlier. Hix, Messer, Mezzacappa, et al ‘03

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Changes in Neutrino Emission e burst slightly delayed and prolonged. Other luminosities minimally affected (~1%). Mean Energy altered: 1-2 MeV during collapse ~1 MeV up to 50ms after bounce ~.3 MeV at late time Hix, Messer, Mezzacappa, et al ‘03

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Convection in context Fluid instabilities which drive convection result from complete neutrino radiation-hydrodynamic problem. Hix, Messer, Mezzacappa, et al ‘03 Example: Updated nuclear electron capture inhibits proto-neutron star convection.

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Neutrino Capture on Nuclei Recent multi-group neutrino transport simulations show decreased neutronization in the innermost ejecta. Martinez-Pinedo, Hauser, Hix, Liebendörfer, Mezzacappa & Thielemann ‘03

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Only multi-D models with complete (weak/nuclear,  transport, EOS, magnetic?) physics will determine what the core collapse supernova mechanism is. This includes neutrino-nucleus interactions Discussion Modern treatment of nuclear electron capture significantly changes supernova evolution. - Homologous Core reduced by 20% - Neutrino Emission boosted 15% after bounce - Slower collapse of outer layers allows shock to propagate further

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL)

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Liebendörfer, Mezzacappa, Thielemann, Messer, Hix & Bruenn ‘01 Mezzacappa, Liebendörfer, Messer, Hix, Thielemann & Bruenn ’01 Neutrino Transport -sphere is energy dependent. Neutrino distribution is nonthermal. Gray transport unreliable. Modeling of Energy Spectrum Required Shock revitalization occurs in the semi-transparent regime. Heating rate depends on isotropy. Must also track angular dist. Boltzmann Transport is Required

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Neutrino Interactions: e ± / capture on nucleons and -nucleon elastic scattering + recoil & relativity (Reddy et al. ‘98) + weak magnetism (Horowitz ‘02) + correlations (Burrows & Sawyer ‘97, Pons et al. ‘99) -electron scattering / pair production / annihilation + e  e     (Burras, et al ‘02) + Bremsstrahlung (Hannestad & Raffelt ‘98, Burrows et al. ‘00) + Plasmon decay (Schinder & Shapiro ‘82) e - / capture on nuclei and  -nucleus elastic scattering + Inelastic Scattering (Bruenn & Haxton ‘91) Bruenn (1985) and improvements

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Herant, Benz, Hix, Fryer & Colgate ‘94 Fryer & Warren ‘02  Neutrino-Driven (beneath stalled shock) Enhances Explosions  Proto-Neutron Star (beneath neutrinospheres) boosts neutrino luminosities. enhances efficiency and boosts shock radius. Convection… Totani, Sato, Dalhed & Wilson ‘98

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Janka & Müller ‘96 Convection is no guarantee Mezzacappa, Calder, et. al ‘98

Neutrino Studies at the Spallation Neutron Source, ORNL, 8/29/03W.R. Hix (UTenn./ORNL) Stellar Evolution End Game Core collapse is the inevitable end of the life of a massive star. Question is which stars produce neutron stars (and supernovae) and which produce black holes. This division and the details of the explosions which result depend on their initial models Rauscher, Heger, Hoffman & Woosley ‘02