Transcript Detection of the Diffuse Supernova Neutrino Background in

Detection of the
Diffuse Supernova Neutrino
Background in LENA &
Study of Scintillator Properties
Michael Wurm
DPG Spring Meeting, 30.3.06
E15
Neutrinos from Supernovae
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, ve are the most likely
to be detected by inverse b decay
ve + p  n + e+
S. Ando, K. Sato, astro-ph/0410061
Detection of the DSNB in LENA
SK limit: 1.2 cm-2s-1
for Ev > 19.3 MeV
Michael Wurm
2/11
DSNB Predictions use …
Supernova Model
Detection of the DSNB
would provide information
both on SN explosion
mechanism and on the
Star Formation Rate at
high redshifts.
DSN from
z > 20
1 v events detected
SN 1987A:
about
e
are dominant for
 spectral
shape
is
Ev < 10
MeV.
strongly model-dependent
visible mainly for Ev > 10 MeV
LL – Lawrence Livermore Group
TBP – Thompson, Burrows, Pinto
KRJ – Keil, Raffelt, Janka
Star Formation Rate
Ev < 10 MeV
Ev > 10 MeV
: SFR(z) redshift-dependent
local (z=0): uncertainty
: SN models
compared to used
model 0.7-4.1 due to
dust extinction
high z: even higher
uncertainties
Detection of the DSNB in LENA
Michael Wurm
3/11
DSNB Detection in LENA
detection via inverse beta decay
ve + p  n + e+ (Q = 1.8 MeV)
50x106 l of liquid scintillator
containing 2.9x1033 free protons
 50-75 events in 10 years
Detection of the DSNB in LENA
Michael Wurm
4/11
Observational Window
In a liquid scintillator:
Inverse beta decay:
1.8 MeV
reactor ve:
~ 10 MeV
atmospheric ve:
~ 30 MeV
 Observation: 10 MeV < E < 30 MeV
Detection of the DSNB in LENA
Michael Wurm
5/11
Observational Window
In a water Čerenkov detector:
Inverse beta decay:
1.8 MeV
reactor ve:
~ 10 MeV
atmospheric ve:
~ 30 MeV
spallation products:
< 19 MeV
invisible muons:
> 19 MeV
 no observational window
Detection of the DSNB in LENA

background substracted statistically
Michael Wurm
6/11
Reactor Background
1. reactor ve 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 94Br
detector site
reactor ve flux
2. NPP power and position
Threshold
DSNB events
1/cm2s
MeV
in 10 yrs
Kamioka
2.14 x 106
11.1
23-48
200 NPP sites considered
Frejus
1.63 x 106
10.8
24-49
Pyhäsalmi
1.86 x
105
9.7
28-54
number of ve per GW of
thermal power is ~ 1.3 x 1017
Pylos
1.08 x 105
9.3
30-56
Homestake
7.51 x 104
9.0
31-57
Hawaii
1.09 x 104
8.4
34-60
New Zealand
5.38 x 103
8.2
35-61
Detection of the DSNB in LENA
3. include ve  µ oscillations
Michael Wurm
7/11
Event Rates in LENA
after 10 years of measurement time in Pyhäsalmi
9.7 MeV < Ev < 30 MeV:
LL:
KRJ:
TBP:
54
45
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!
Detection of the DSNB in LENA
Michael Wurm
8/11
Scintillator Properties
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:
Dodecane (C12H26)
lowers light yield, very transparent,
increases number of free protons
up to 25%
Study of Scintillator Properties
light yield setup
attenuation setup
PXE (C16H18)
high light yield, high attenuation
length if purified in Al2O3 column,
non-hazardous
Michael Wurm
9/11
Photoelectron Yield
is the number of photons per MeV registered in the PMs.
Rough estimation for LENA:
Results for different mixtures of PXE and Dodecane:
 corresponds to an energy resolution of ~3% @ 10 MeV! (lower limit)
Study of Scintillator Properties
Michael Wurm
10/11
Conclusions
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.
Detection of the DSNB in LENA
Michael Wurm
11/11