Alex Murphy 17/1/2002CERN2 The 7 stages of Core Collapse... For a ~10M star Stage Temp (K) Ashes Duration H burning 2x10 7 He few x 10 6 yrs He 2x10 8 C, O few x 10 4 yrs C 8x10 8 Ne, O ~600 yrs Ne 1.4 x10 9 O, Mg ~1 yr.. O 2x10 9 Si, S ~6 mo.. Si 3.5x10 9 Fe, Ni ~1 day Collapse ~40 x %n ~few ms 10%p +Ejecta (some of surface layers, rich in heavy elements) Fe core Si O Ne C He H Not to scale! 17/1/2002CERN3 Inside a Supernova Dense core 100 km M. 3x10 7 km 3000 km n* 10 km M. >8 M evolves ~10 7 yr Extreme temp: photodissociates nuclei back to protons, neutrons and alphas. Neutronisation: p+e - n+ e e + +e - + ; + x + x (all flavours equally) ~ few x nuclear Huge thermal emission of neutrinos ~5-10 seconds 17/1/2002CERN4 SN1987A Anglo Australian Observatory Progenitor: Sanduleak -69202, LMC about 50 kpc away. Remnant neutron star unseen maybe it went to a black hole? Neutrinos preceded light by ~2 hours ~20 events seen in IMB, Kamiokande First (and only) extra-solar neutrinos Water detectors, therefore almost certainly these were e type: e +p n+e + 17/1/2002CERN5 Supernovae: Facts and Figures Energy release ~3x10 46 J (the gravitational binding energy of the core), in about 10 seconds Equivalent to 1000 times the energy emitted by the Sun in its entire lifetime. Energy density of the core is equivalent to 1MT TNT per cubic micron. 99% of energy released is in the form of neutrinos ~1% is in the KE of the exploding matter ~0.01% is in light and thats enough to make it as bright as an entire galaxy. Probably site of the r-process. MT test (Dominic Truckee, 1962) 17/1/2002CERN6 Importance of Neutrinos in Core Collapse They facilitate the explosion: The prompt explosion stalls due to photo-nuclear dissociation Tremendous density - Core is opaque to neutrinos! Coupling of energetic neutrinos with core material Delayed explosion. Flux, energy, time profile of neutrinos provide detail of explosion mechanism Energy transport is dominated by neutrinos Less trapped than any other radiation Cooling via neutrinos (evidenced by 99% luminosity) The last interaction of the neutrinos will have been with the collapsing/radiating core Allows us to look directly at the core of a collapsing massive star! Caveat! NO self consistent core collapse computer simulations have yet been successful May REQUIRE neutrino oscillations, or maybe convection/rotation/strong magnetic fields 17/1/2002CERN7 Detecting SN Neutrinos Cross section: Weak coupling constants are small ~ cm 2 ~10 15 times smaller that traditional nuclear physics (e.g. mb) Energies: thermal, weighted by number of ways to interact before decoupling ( G. Raffelts talk yesterday for more details ) More n than p More e +n p+e - than e +p n+e + CC reactions (changes n p) easier that NC (elastic scattering) Some recent work suggests neutrino Bremsstrahlung may pinch high and low ends of spectrum. Such an observation would tell us about the EOS of dense matter Neutrinospheres at different radii = 11 MeV = 16 MeV = 25 MeV Measurement of energies: primary physics goal EOS, neutrino transport 17/1/2002CERN8 A New Detection Strategy Utilize CC & NC reactions from hi-z materials with low n-threshold. Use the higher energies of and -neutrinos to enhance their yields flavour filter Results in 2 observables: 1 neutron emission from Pb 2 neutron emission from Pb The O bservatory for M ultiflavor N eutr I nos from S upernovae 208 Pb 207 Bi Q [ 208 Pb(, 2n) 206 Pb] = MeV Q [ 208 Pb( e,e + n) 207 Bi] = -9.8 MeV Q [ 208 Pb(, n) 207 Pb] = -7.4 MeV ns Reaction thresholds Strong dependence of neutron yield on temperature Sensitivity to oscillations Dependence on temperature different for 1n and 2n channels Sensitivity to shape of energy spectrum 17/1/2002CERN9 Neutron Detection Time (ns) Energy deposited Time ( s) Energy deposited Prompt pulse Delayed pulse Require: Large Efficient Provide adequate discrimination against background Fast timing CHEAP Gadolinium loaded scintillator (liquid of plastic) Fast neutron enters High H content results in rapid energy loss. Prompt pulse After thermalisation (~30 s) capture on Gd; release of several - rays (total 8 MeV). Delayed pulse Allows two level trigger Singles while flux high Double Pulse when flux low 17/1/2002CERN10 So how to build OMNIS Underground to reduce cosmic ray rate Need large blocks of lead interleaved with scintillator planes n Lead Loaded scintillator (liquid or plastic) PF Smith Astroparticle Physics 8 (1997) 27 Astroparticle Physics 16 (2001) 75 JJ Zach, AStJ Murphy, RN Boyd, NIMS, 2001, accepted 17/1/2002CERN11 Lead Perchlorate Pb(Cl 2 O 4 ) 2 S. Elliott PRC 62 (2001) Diluted 20% (w/w) with H 2 O Transparent Crenkov light Bulk attenuation length >4m Neutron capture time ~100 s 8.6 MeV in s recoil electrons Crenkov flash Interesting chemical properties CC e events have well defined Crenkov cone energy spectrum 2.8m ~3000 5 pmts kT module 8 kpc, kT e e x No osc e Includes reactions on H 2 O PMTs 17/1/2002CERN12 Neutrino Physics Potential Presence of neutrino mass s t e t c h e s arrival time profile. Rise of leading edge is probably best measure of mass Beacom, et al PRL 85, 3568 (2000); PRD 63, (2001). Direct way to measure mass (not inferred from oscillations) e is light (