Low Energy Neutrino Astronomy with the Large Liquid Scintillator

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Low Energy Neutrino Astronomy with the Large Liquid Scintillator
Phys.Rev.D 75 (2007) 023007
Search for the
Diffuse Supernova Neutrino Background
in LENA
DPG-Tagung in Heidelberg
9.3.2007
M. Wurm, F. v. Feilitzsch, M. Göger-Neff,
T. Marrodán Undagoitia, L. Oberauer, W. Potzel, J. Winter
Technische Universität München
[email protected]
http://www.e15.physik.tu-muenchen.de/research/lena.html
Outline
DSNB
Background
Event Rates
Spectroscopy
Diffuse Supernova Neutrino Background (DSNB):
[email protected]<5 contribute to an isotropic background of v
_
_
ve could be detected in LENA via ve + p → n + e+
clear (delayed) coincidence signal due to e+-annihilation & n-capture
current best limit solid:
on theveDSN flux
dashed: ve
is given by Super-Kamiokande:
F(E>19MeV) ≤ 1.2 v/cm²s
LENA will improve this
limit by a factor of 9:
 high discovery potential
S. Ando, astro-ph/0410061
Michael Wurm
TU München
1/8
Outline
DSNB
Background
Event Rates
Spectroscopy
SN neutrino spectra:
little experimental data
 spectral shape is
model-dependent
E>10MeV: SNR(z=0)
SN v spectrum
DSN model
calculations use …
E<10MeV:
SNR(z>1)
LL – Lawrence Livermore
TBP – Thompson, Burrows, Pinto
KRJ – Keil, Raffelt, Janka
Supernova Rate SNR(z)
contributions from high z
regions are red-shifted,
large uncertainties of
conventional observations
fSN
Michael Wurm
z=0: fSN=0.7-4.2, likely 2.5
z>0: even larger
TU München
2/8
Outline
DSNB
Background
Event Rates
Spectroscopy
observational window
in a pure water Čerenkov detector
the n-capture is not detected.
background sources
reactor ve:
atmospheric ve:
spallation products:
invisible muons:
~ 10 MeV
~ 30 MeV
< 19 MeV
> 19 MeV
S. Ando, astro-ph/0410061
 no observational window  background subtracted statistically
Michael Wurm
TU München
3/8
Outline
DSNB
Background
Event Rates
Spectroscopy
observational window
in a liquid-scintillator detector
the n-capture can be tagged.
background sources
reactor ve:
atmospheric ve:
spallation products:
invisible muons:
~ 10 MeV
~ 30 MeV
< 19 MeV
> 19 MeV
S. Ando, astro-ph/0410061
 observational window: 10 MeV < E < 30 MeV
Michael Wurm
TU München
3/8
Outline
_
DSNB
Background
Event Rates
Spectroscopy
reactor ve flux
depends on location
reactor v’s
_
atmospheric ve flux
depends on magnetic latitude
up toatmospheric
a factor 2 differencev’s
in flux
DSN
nuclear power plants
possible detector sites
Michael Wurm
Pyhäsalmi
Hawaii
TU München
4/8
Outline
DSNB
Background
Event Rates
Spectroscopy
energy window
signal/background
(MeV)
(10 yrs exposure, fSN = 2.5)
Kamioka
11.1 – 28.1
79/11
Frejus
10.8 – 26.4
79/12
Kimballton
10.6 – 28.1
84/11
Pyhäsalmi
9.7 – 25.1
86/13
Pylos
9.4 – 28.1
95/12
Homestake
9.0 – 26.4
96/13
Henderson
8.9 – 27.2
98/13
Hawaii
8.4 – 29.0
106/12
New Zealand
8.2 – 27.2
105/12
detector site
Michael Wurm
TU München
5/8
Outline
DSNB
Background
LENA at Pyhäsalmi (Finland)
Event Rates
Spectroscopy
DSN event rate in 10yrs
inside the energy window
from 9.7 to 25 MeV
dependent on SN model
(assumed fSN=2.5)
LL:
KRJ:
TBP:
113
100
60
dependent on SNR
fSN=0.7 17
fSN=2.5 100
fSN=4.2 220
~25% of events are due to v’s
originating from SN @ z>1!
Michael Wurm
TU München
background events: 13
6/8
Outline
DSNB
Background
Limits on the SN Rate (z=0)
LENA @ Pyhäsalmi (FIN)
Event Rates
Spectroscopy
cross-check of ‘optical’
SNR measurements
by counting event numbers
in the energy bin
10MeV < Ev < 14MeV,
one can derive a limit on fSN
without using a SN v model
event rates (10-14MeV):
LL
2.0 fSN /yr
KRJ 1.5 fSN /yr
TBP 2.0 fSN /yr
BG
0.6 fSN /yr
in case of fSN=2.5:
fSN≤1.3 could be excluded
at 2s after 10 years
Michael Wurm
TU München
7/8
Outline
DSNB
Background
Event Rates
Spectroscopy
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 < EB1 < 14MeV
15MeV < EB2 < 25MeV
significance levels of
SN model exclusion
Michael Wurm
TU München
8/8
 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.

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