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.