1、Detecting Supernova Neutrinos X.-H. Guo Beijing Normal University1ContentsI. SN neutrinos production and propagationII. Detection of SN neutrinos at neutrino experimentsIII. Possible information on small 13 from detection of SN neutrinos2I. SN neutrinos production and propagation Supernova explosion
2、: natural laboratory to study fundamental issues of physics and astrophysics. Explosion mechanism is not understood completely. Two types of SN explosion. Type I: without lines of hydrogen;Type II: with strong lines of hydrogen. Type I: Usually a white dwarf (mainly C and O) accretes material from a
3、 companion star. Energy is from thermonuclear reactions. Gives out gigantic firework display Disruption of the dwarf.3 Type II: Energy from gravitational core collapse (Zwicky can be helpful to study of intrinsic properties of neutrinos. Total energy release: approximately gravitational binding ener
4、gy of the core. Neutrinos take away about 99% of the total energy.4Core collapse process While evolving, stars get energy from burning hydrogen to helium. Then heavier helium settles to the core of the star. Towards the end of hydrogen burning, gravitational contraction heats up the core helium burn
5、ing to Carbon. Heavier carbon settles to center of core, H and He floating above it. Similar processes repeat, carbon neon oxygen silicon iron (most stable nucleus). When iron core grows to exceed Chandrasekhar mass, degenerate electron Fermi pressure fails to support gravitational pull of core, ele
6、ctron capture on Fe nuclei occurs predominantly via 56Fe + e- 56Mn +e . Absorption of electrons leads to loss of electron pressure support and begins core collapse. Core proceeds to contract under the pull of self gravitational force.5Core collapse process (cont.) When the central density 1011-1012
7、g cm-3 , electron neutrinos begin to be trapped in the core (the mean free path of neutrino ( -5/3) is smaller than the size of core ( -1/3) ). The surface determining the escape or trapping of neutrinos in the core: neutrino sphere. Neutrinos produced within (outside) neutrino sphere cannot (can) e
8、scape freely from the core. When nuclear density ( 3 X 1014 g cm-3 ) is reached in the collapsing core, repulsive nuclear force halt the collapse of inner core driving a shock wave into outer core. The shock propagates into outer core dissociate nuclei into free nucleons. Electron capture process e-
9、 + p n + e generates a huge amount of electron neutrinos and are liberated suddenly as shock waves pass through neutrino sphere: called neutronization burst. Duration of neutronization: less than 20ms. Breakout of electron neutrinos is almost simultaneous with appearance of all other neutrino specie
10、s (last for O(10) seconds): via e+e- annihilation, electron neutrino anti-electronic neutrino annihilation, and nucleon-nucleon bremsstrahlung. 6 First observations of the type II SN: Kamiokande II (11 events) and IMB (8 events) observed in 13 seconds in 1987. (Large Magellanic Cloud, closest supern
11、ova since the galactic supernova in the 17th century. Progenitor star mass 10 Msun, distance 50kpc.) Besides the information on the physical state deep inside SN, SN neutrinos can also bring information about the outer structure of SN through neutrino oscillation while neutrinos pass through mantle.
12、 Average energy of emitted neutrinos reflects temperature of matter around neutrino sphere. Interactions of electron neutrino and anti-electron neutrino are stronger than other flavor neutrinos. Since there are more neutrons than protons in the star, electron neutrino couples more strongly than anti
13、-electron neutrinos. This leads to 7Energy spectrum Since cross section of interactions depend on neutrino energy, the energy spectra of neutrinos are not simple blackbodies. As a result, the energy spectrum has a pinched shape compared with the Fermi-Dirac distribution. One popular way to parametri
14、ze neutrino spectrum is L(0) (T ): luminosity (temperature) of ; : pinching parameter; ESN(0) : total energy release. Typical values from numerical simulations are ( 3.15 T):8Level Crossing When SN neutrinos of each flavor is produced they are also mass eigenstates due to extremely high matter densi
15、ty environment. While they propagate to the surface of SN, they experience level crossing (neutrinos jump from one mass eigenstate to another) in the MSW (Mikheyev-Smirnov-Wolfenstein) resonance regions. These regions are far from the core. Two MSW resonance regions: determined by two pairs of neutr
16、ino mixing parameters: High resonance region (denser region): H 103-104 g cm-3 ; Low resonance region (less dense region): L 20200 g cm-3 . Probability that neutrinos jump from one mass eigenstate to another at the high (low) resonance layer is denoted by PH (PL) . The large mixing angle (LMA) solut
17、ion of the solar neutrino constrains PL =0. The level crossing diagrams are different for normal and inverted mass hierarchies. This leads to different forms for neutrino flux of mass eigenstates at the surface of SN. 9Crossing probability at resonance point Using Landau-Zener formula, crossing prob
18、ability was calculated at resonance region (T.K. Kuo, Rev. Mod. Phys., 1989). At high resonance region, where is adiabaticity parameter, is mixing angle, F depends on density profile and mixing angle, Ne is electron density. When 1, PH=0. PH depends on neutrino energy, neutrino mass difference, neutrino mixing angle, and SN density profile.10
