Detection of the Diffuse Supernova Neutrino Background in LENA & Study of Scintillator Properties Michael Wurm DPG Spring Meeting, E15

Neutrinos from Supernovae Detection of the DSNB in LENA Michael Wurm 2/11 SN explosion: 99% of gravitational binding energy are emitted in the form of v‘s galactic rate: ~3 in 100 yrs Diffuse Supernova Neutrinos: all SN throughout the Universe contribute to an isotropic background of vs, the DSNB. all flavours are equally created fluxes are low, v e are the most likely to be detected by inverse  decay v e + p  n + e + SK limit:1.2 cm -2 s -1 for E v > 19.3 MeV S. Ando, K. Sato, astro-ph/

DSNB Predictions Detection of the DSNB in LENA Michael Wurm 3/11 Supernova Model SN 1987A: about 20 v e events detected  spectral shape is strongly model-dependent visible mainly for E v > 10 MeV LL – Lawrence Livermore Group TBP – Thompson, Burrows, Pinto KRJ – Keil, Raffelt, Janka Star Formation Rate redshift-dependent local (z=0): uncertainty compared to used model due to dust extinction high z: even higher uncertainties DSN from z > 1 are dominant for E v < 10 MeV. Detection of the DSNB would provide information both on SN explosion mechanism and on the Star Formation Rate at high redshifts. E v 10 MeV :SN models use …

DSNB Detection in LENA Detection of the DSNB in LENA Michael Wurm 4/11 detection via inverse beta decay v e + p  n + e + (Q = 1.8 MeV) 50x10 6 l of liquid scintillator containing 2.9x10 33 free protons  events in 10 years

Observational Window Detection of the DSNB in LENA Michael Wurm 5/11 In a liquid scintillator: Inverse beta decay: 1.8 MeV reactor v e :~ 10 MeV atmospheric v e :~ 30 MeV  Observation: 10 MeV < E < 30 MeV

Observational Window Detection of the DSNB in LENA Michael Wurm 6/11 In a water Čerenkov detector: Inverse beta decay: 1.8 MeV reactor v e :~ 10 MeV atmospheric v e :~ 30 MeV spallation products:< 19 MeV invisible muons:> 19 MeV  no observational window  no observational window  background substracted statistically

Reactor Background Detection of the DSNB in LENA Michael Wurm 7/11 1. reactor v e spectrum spectral form well known for E < 8 MeV measurements done by Tengblad et al. for E < 12 MeV consideration of high endpoint beta emitters like 94 Br 2. NPP power and position 200 NPP sites considered number of v e per GW of thermal power is ~ 1.3 x include v e  µ oscillations detector sitereactor v e flux 1/cm 2 s Threshold MeV DSNB events in 10 yrs Kamioka2.14 x Frejus1.63 x Pyhäsalmi1.86 x Pylos1.08 x Homestake7.51 x Hawaii1.09 x New Zealand5.38 x

Event Rates in LENA Detection of the DSNB in LENA Michael Wurm 8/11 after 10 years of measurement time in Pyhäsalmi 9.7 MeV < E v < 30 MeV: LL:54 KRJ:45 TBP:29 according to MC simulations, a separation between LL & TBP is possible at 90% C.L. after 10 years DSN spectroscopy in LENA should be possible!

Scintillator Properties Study of Scintillator Properties Michael Wurm 9/11 light yield and transparency of the scintillator are vital for energy resolution & spectroscopy!  laboratory measurements of light yield & attenuation length done in Garching & Heidelberg Scintillator Candidates: PXE (C 16 H 18 ) high light yield, high attenuation length if purified in Al 2 O 3 column, non-hazardous Dodecane (C 12 H 26 ) lowers light yield, very transparent, increases number of free protons up to 25% light yield setup attenuation setup

Photoelectron Yield Study of Scintillator Properties Michael Wurm 10/11 is the number of photons per MeV registered in the PMs. Rough estimation for LENA: Results Results for different mixtures of PXE and Dodecane:  corresponds to an energy resolution of 10 MeV!  corresponds to an energy resolution of 10 MeV! (lower limit)

Conclusions Detection of the DSNB in LENA Michael Wurm 11/11 In a 50 kt liquid scintillator detector like LENA an energy window for DSNB detection from ~10 MeV to 30 MeV can be found. For LENA in Pyhäsalmi, the lower threshold will be about 9.7 MeV, allowing the detection of SN neutrinos emitted at a redshift z>1. 29 to 54 events in 10 years are awaited for LENA within DSNB model predictions. After 10 years, the number of events provided will most likely be sufficient for a spectroscopic discrimination of some of the predicted DSNB models. Technical feasability studies concerning the light yield and attenuation length of the scintillator look very promising. LENA would allow the detection of DNSB for the first time. New observational data both on SN models and on the Star Formation Rate (up to z~2) could be obtained.