Theoretical study of supernova relic neutrinos Ken’ichiro Nakazato （ Kyushu University ） Revealing the history of the universe with underground particle and nuclear research 2016, May 13, 2016
Outline 1. Introduction 2. What does SRN spectrum depend on? involving metallicity evolution of galaxies （ K. Nakazato et al. 2015, ApJ 804, 75 ） 3. Comparison with noise BG 4. Summary
Outline 1. Introduction 2. What does SRN spectrum depend on? involving metallicity evolution of galaxies （ K. Nakazato et al. 2015, ApJ 804, 75 ） 3. Comparison with noise BG 4. Summary
History of Universe Big Bang Now • The Universe is expanding! Many generations of • Cosmological redshift stars have exploded! z denotes ``time’’.
Supernova neutrinos • Clue for puzzle in supernova physics. Burrows （ 1988 ） SN1987A @ Kamiokande
Light curves and spectra • Neutrino emission continues for 10 seconds. （ diffusion time scale ） x e e Fischer+ （ 2012 ） Nakazato+ （ 2013 ）
Supernova relic neutrinos time • The flux of neutrinos We are here! and antineutrinos emitted by all core- collapse supernovae z = 0 in the causally- reachable universe. z = 1 • Is it possible to study something from supernova relic neutrinos? z = 2
Detection status • The upper limit is near theoretical predictions. E. Mochida, master thesis
Outline 1. Introduction 2. What does SRN spectrum depend on? involving metallicity evolution of galaxies （ K. Nakazato et al. 2015, ApJ 804, 75 ） 3. Comparison with noise BG 4. Summary
What determines BG luminosity? supernova relic neutrinos • luminosity of a source → supernova physics • the source number star formation history • distance to sources – cosmological redshift for the expanding universe • Also neutrino oscillation parameters
Formulation d E 1 z dE • Supernova neutrino spectrum: • Cosmological parameters • Initial mass function: （ Salpeter ）
Formulation d E 1 z dE • Core collapse rate: cosmic star formation rate related to stellar mass distribution of galaxies （ Drory & Alvarez, 2008 ） stellar mass function SFR of galaxy
Cosmic star formation rate Cosmic star formation rate • It has a peak at redshift z ~ 1-2, but uncertainty [ M ☉ yr -1 Mpc -3 ] is large. → conversion from UV luminosity to star formation rate of galaxy → dust obscuration Observation of galaxies correction Hopkins & Beacom （ 2006 ） Note: Contribution from stars Drory & Alvarez （ 2008 ） in z > 2 is small. Theoretical model Kobayashi et al. （ 2013 ）
Formulation d E 1 z dE • Metallicity distribution function of progenitors mass metallicity relation （ Maiolino+, 2008 ） SFR of galaxy stellar mass function （ Drory & Alvarez, 2008 ）
Cosmic chemical evolution Big Bang galaxy formation, evolution Now supernovae H, He only metal increase • Old stars are low metallicity. • Low metallicity stars have massive cores. → Failed supernova progenitors are included.
Fraction of failed supernovae Fraction of failed supernovae Z M 0.02 0.004 13 M ☉ SN SN 20 M ☉ SN SN 30 M ☉ SN BH 50 M ☉ SN SN Nakazato+ （ 2015 ） • It increases with redshift because metal poor stars are abundant in high redshift universe.
Spectra of SN relic neutrinos difference of SFR difference of SFR Event [MeV -1 (22.5kt yr) -1 ] 0.16 10 Flux [cm -2 s -1 MeV -1 ] 1 0.12 high 0.1 0.08 0.01 0.04 0.001 low 0 0 10 20 30 40 50 0 10 20 30 40 50 Neutrino Energy [MeV] Positron Energy [MeV] • Uncertainty is large in low energy region. • Reflecting large uncertainty of cosmic star formation rate in high redshift universe
Spectra of SN relic neutrinos difference of t revive difference of t revive Event [MeV -1 (22.5kt yr) -1 ] 10 0.12 Flux [cm -2 s -1 MeV -1 ] 1 late 200 ms 0.08 0.1 300 ms 0.01 0.04 early 0.001 100 ms 0 0 10 20 30 40 50 0 10 20 30 40 50 Neutrino Energy [MeV] Positron Energy [MeV] • Uncertainty is large in high energy region. • If the shock revival is late, proto-neutron star is heated and neutrino spectrum gets hard.
Spectra of SN relic neutrinos difference of EOS difference of EOS Event [MeV -1 (22.5kt yr) -1 ] 10 0.12 Flux [cm -2 s -1 MeV -1 ] 1 hard Shen 0.08 0.1 0.01 0.04 LS soft 0.001 （ 220 MeV ） 0 0 10 20 30 40 50 0 10 20 30 40 50 Neutrino Energy [MeV] Positron Energy [MeV] • Uncertainty is large in high energy region. • If the EOS is hard, the black hole formation is delayed and neutrino spectrum gets hard.
Uncertainties on SRN spectrum 10 10 Flux [cm -2 s -1 MeV -1 ] cosmic SFR IMF & M min fixed. 1 1 uncertainties high 0.1 of others 0.1 from max. 0.01 0.01 SFR 0.001 low 0.001 min. 0 10 20 30 40 50 0 10 20 30 40 50 Neutrino Energy [MeV] Neutrino Energy [MeV] • Uncertainty on SRN spectrum in low energies is mainly from cosmic star formation rate. • To investigate star formation history, low energy is better and SK-Gd is promising.
Outline 1. Introduction 2. What does SRN spectrum depend on? involving metallicity evolution of galaxies （ K. Nakazato et al. 2015, ApJ 804, 75 ） 3. Comparison with noise BG 4. Summary
Formulation d E 1 z dE • Min. mass of SN progenitors: M min =8 or 10 M ☉ • Initial mass function 8 M ☉ M min 10 M ☉ Chabrier (2003); Baldry, & Glazebrook (2003, SalpeterA); Salpeter (1955)
Uncertainties of M min and IMF difference of M min difference of IMF • These uncertainties are energy-independent. • Uncertainty of IMF is largest at high energies, and as large as that of SFR at low energies.
Comparison with noise BG E. Mochida, master thesis @ SK-Gd atmospheric NC Ueno (2012) invisible & atmospheric e Abe et al. (2011) • Detectability highly depends on uncertainties. • Reduction of atmospheric NC is important.
Outline 1. Introduction 2. What does SRN spectrum depend on? involving metallicity evolution of galaxies （ K. Nakazato et al. 2015, ApJ 804, 75 ） 3. Comparison with noise BG 4. Summary
Summary • Uncertainties low energy high energy SFR large middle small middle t revive small middle EOS （ BH ） IMF large large middle middle M min • To investigate the star formation history, low energy is better and SK-Gd is promising, but reduction of atmospheric NC is important.
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