neutrino studies at the spallation neutron source, ornl, 8/29/03w.r. hix (utenn./ornl)...

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

Neutrino-Nucleus Interactions and the Core Collapse Supernova

Mechanism

Sk 202-69SN 1987a


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


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, Yp is a strong function of Ye, so differences in Ye are “washed out”.Is this due to physics or our

approximation?

Messer, Hix, Liebendörfer & Mezzacappa ‘03


Captures on Nuclei a la Bruenn (1985)

EOS (Lattimer & Swesty 1991) identifies average heavy nucleus e- and capture via generic 1f7/21f5/2 GT transition (Bethe et al 1979), quenched at N=40, with Q=n-p-3 MeV

decay suppressed by large e


Testing the effects of e- Capture on Nuclei

Replaced quenching term with parameter (NpNh) = 0.1-1000.

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


Needed Electron Capture Rates

Nuclei with A>120 are present in collapsing core.


Nuclear Electron Capture RatesShell 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)


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 compositionTransitions easily to non NSE regions

Lighter computational requirementTransitions easily to nuclear matter

Strengths

Need Both!


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


Effects on Shock propagation

“Weaker” shock is faster.

Lepton and entropy gradients are

altered.

Maximum excursion of the shock is 10 km

furtherand 30 ms earlier.



Changes in Neutrino Emissione 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



Convection in context Fluid instabilities which drive convection result from complete neutrino radiation-hydrodynamic problem.


Example:Updated nuclear electron capture inhibits proto-neutron star convection.


Neutrino Capture on NucleiRecent multi-group neutrino transport simulations show decreased neutronization in the innermost ejecta.

Martinez-Pinedo, Hauser, Hix, Liebendörfer, Mezzacappa & Thielemann ‘03


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

DiscussionModern 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


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

200

250

Time After Bounce [s]

General Relativistic Shock Trajectories

NH 13 MWW 15 MNH 20 MWW 25 MHW 30 MHW 35 MWW 40 M

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

200

250

Newtonian Shock Trajectories

NH 13 MNH 15 MNH 20 MWW 15 MWW 25 M

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 RequiredShock revitalization occurs in the semi-transparent regime.Heating rate depends on isotropy.Must also track angular dist.

Boltzmann Transport is Required


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 + ee (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


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


Janka & Müller ‘96

Convection is no guarantee

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.

Mezzacappa, Calder, et. al ‘98


Stellar Evolution End GameCore 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

neutrino studies at the spallation neutron source, ornl, 8/29/03w.r. hix (utenn./ornl)...

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