Search for the Diffuse Supernova Neutrino Background in LENA DPG-Tagung in Heidelberg M. Wurm, F. v. Feilitzsch, M. Göger-Neff, T. Marrodán Undagoitia, L. Oberauer, W. Potzel, J. Winter Technische Universität München Phys.Rev.D 75 (2007)
Diffuse Supernova Neutrino Background (DSNB): contribute to an isotropic background of v v e could be detected in LENA via v e + p → n + e + clear (delayed) coincidence signal due to e + -annihilation & n-capture current best limit on the DSN flux is given by Super-Kamiokande: (E>19MeV) ≤ 1.2 v/cm²s solid: v e dashed: v e S. Ando, astro-ph/ __ Outline DSNB Background Event Rates Spectroscopy 1/8 TU MünchenMichael Wurm LENA will improve this limit by a factor of 9: high discovery potential
LL – Lawrence Livermore TBP – Thompson, Burrows, Pinto KRJ – Keil, Raffelt, Janka DSN model calculations use … SN neutrino spectra: little experimental data spectral shape is model-dependent Supernova Rate SNR(z) contributions from high z regions are red-shifted, large uncertainties of conventional observations z=0: f SN = , likely 2.5 z>0: even larger E>10MeV: SNR(z=0) SN v spectrum E<10MeV: SNR(z>1) f SN Outline DSNB Background Event Rates Spectroscopy 2/8 TU MünchenMichael Wurm
in a pure water Čerenkov detector the n-capture is not detected. background sources reactor v e :~ 10 MeV atmospheric v e :~ 30 MeV spallation products:< 19 MeV invisible muons:> 19 MeV no observational window background subtracted statistically observational window S. Ando, astro-ph/ Outline DSNB Background Event Rates Spectroscopy 3/8 TU MünchenMichael Wurm
in a liquid-scintillator detector the n-capture can be tagged. background sources reactor v e :~ 10 MeV atmospheric v e :~ 30 MeV spallation products:< 19 MeV invisible muons:> 19 MeV observational window: 10 MeV < E < 30 MeV observational window S. Ando, astro-ph/ Outline DSNB Background Event Rates Spectroscopy 3/8 TU MünchenMichael Wurm
reactor v e flux depends on location reactor v’s atmospheric v’s Outline DSNB Background Event Rates Spectroscopy 4/8 TU MünchenMichael Wurm nuclear power plants possible detector sites _ atmospheric v e flux depends on magnetic latitude up to a factor 2 difference in flux _ DSN Pyhäsalmi Hawaii
detector siteenergy window (MeV) signal/background (10 yrs exposure, f SN = 2.5) Kamioka11.1 – /11 Frejus10.8 – /12 Kimballton10.6 – /11 Pyhäsalmi9.7 – /13 Pylos9.4 – /12 Homestake9.0 – /13 Henderson8.9 – /13 Hawaii8.4 – /12 New Zealand8.2 – /12 Outline DSNB Background Event Rates Spectroscopy 5/8 TU MünchenMichael Wurm
LENA at Pyhäsalmi (Finland) dependent on SN model (assumed f SN =2.5) LL:113 KRJ:100 TBP:60 dependent on SNR f SN = f SN = f SN = DSN event rate in 10yrs inside the energy window from 9.7 to 25 MeV background events: 13 ~25% of events are due to v’s originating from z>1! 6/8 TU MünchenMichael Wurm Outline DSNB Background Event Rates Spectroscopy
Limits on the SN Rate (z=0) by counting event numbers in the energy bin 10MeV < E v < 14MeV, one can derive a limit on f SN without using a SN v model in case of f SN =2.5: f SN ≤1.3 could be excluded at 2 after 10 years Pyhäsalmi (FIN) event rates (10-14MeV): LL2.0 f SN /yr KRJ1.5 f SN /yr TBP2.0 f SN /yr BG0.6 f SN /yr cross-check of ‘optical’ SNR measurements Outline DSNB Background Event Rates Spectroscopy 7/8 TU MünchenMichael Wurm
Constraints on SN model using MC simulations optical measurements will determine the SNR with high accuracy with this input, the spectral slope of the DSN can be used to distinguish between different SN explosion scenarios comparison of count rates in the energy bins 10MeV < E B1 < 14MeV 15MeV < E B2 < 25MeV significance levels of SN model exclusion 8/8 TU MünchenMichael Wurm Outline DSNB Background Event Rates Spectroscopy
Due to the excellent background discrimination, a liquid-scintillator detector enables a detection of the Diffuse Supernova Neutrinos in an almost background-free energy window form ~10 to 30 MeV. The discovery potential for the DSN in LENA is very high. According to current models, ~2 to 20 events per year are expected. After 10 years, statistics will be large enough to give significant constraints on both Supernova Rate and SN explosion models.