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A feasibility study for the detection of SuperNova explosions with an Undersea Neutrino Telescope
A. Leisos, A. G. Tsirigotis, S. E. TzamariasPhysics Laboratory H.O.U
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SN (GARCHING) Model In this study we consider only the flux and the reaction
HOURS(HOU Reconstruction& Simulation)
α is a function of time
e e p e n
e p e n
2 ( ), ( )0
1 1
( ), ( )
1 ( ),4 ( )
11
e
e ee e
e
e e
eee e
T
a t E t
Ea aE
a t E t
d L tE d f dtdE d E t
Eaf E e
E E
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Detector Geometrical Layout
154 Towers with a mean horizontal distance of 180mEach Tower consists of 20 bars, 6m in length and 40m apartOne MultiPMT OM at each end of the bar.
Detectors Footprint
31 3” PMTs (~30% max QE) inside a 17” glass sphere with 31 bases (total ~6.5W) Cooling shield and stemSingle vs multi-photon hit
separation Large (1260 cm2) photocade
area per OM First full prototype under test
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Neutrino Energy (MeV)
σ IBD x
10-4
1 cm
2
Neutrino Energy (MeV)
Spectrum at the source <E>=12.54 MeV
Spectrum of IBD neutrinos<E>=18.87 MeV
e p e n
Neutrino Energy (MeV)<P
ositr
on E
nerg
y> (M
eV)
Neutrino Energy (MeV)
<Pos
itron
cos
θ>Positron Energy (MeV)
Num
ber o
f eve
nts
generated
At least 1 hit in OM
<E>=17.19 MeV
<E>=19.23MeV
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Nobs int Veff
00
0
00
( ) ~:2
) 1( 0Tt
bck
tTt d S T t e
dt TS T s e dt
T 2.95s
d 10kpcT 2.95s
ρint 0.078m-3
Significance Level of discovery:Assuming that μbck is the expected number of background events then for 5σ discovery the minimum number of observed events, m, is defined as:
1
bcki e bck
i!i0
m
1 erf5
2
Time Integrated Differential Flux(d: SN distance in kpc)
number of e / cm2 / MeV
int arg0
( )( )e e
e e
e
t et
d EE dE
dE
Interaction Density
Veff nobs
ngen
Vgen
Effective Volume
5bck
bcbck bc
kkbut Tm m m T
Assuming Gaussian statistics:
Nobs T bck T bck T
S T bck T
maxGeneral Condition:
Garching Model: t0=2.35
2 ( ), ( )0
1 ( ),4 ( )
e
e ee e
T
a t E t
d L tE d f dtdE d E t
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Coincidence Level (Multiplicity)
Rate
(Hz)
K40 Coincidence rate per OM Background-I: Only K40 Decays
K40 Decay Distance (m)
Even
ts p
er O
M
(arb
. Uni
ts) Multiplicity>2
Multiplicity>4
Energy(MeV)
electron
Gamma (1.46 MeV)
K40 event sample in full WPD detector (T=2.95s)
Expe
cted
Num
ber o
f K40
bac
kgro
und
Even
tsCoincidence Level (Multiplicity)
Coincidence between the small PMTs of the same OM, within 100 ns
e.g. “Coincidence Level” or “Multiplicity” 3
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IBD event sample in full WPD detector for (Integration Time : T=2.95s )
OM Multiplicity (100ns coincidence window)
Signal: SN @ 10 kpc
Expe
cted
Num
ber o
f Eve
nts
Multiplicity>4
Multiplicity>6
Multiplicity>2
Interaction Point Distance (m) to OM
Arb
. uni
ts
K40
SN @ 10kpc
Inverse Beta Decay IBD :e p e n
K40 Decay Distance (m) to OM
Even
ts p
er O
M
(arb
. Uni
ts) Multiplicity>2
Multiplicity>4
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Background Rejection-I: K40 Decays
OM Multiplicity > 5
Q-Threshold (Q of a Small PMT > Q–Threshold) = b
Number of Small PMTS with Q > Q–Threshold > c
OM Multiplicity (100ns coincidence window)
Expe
cted
Num
ber o
f Eve
nts
K40
SN @ 10kpc
Active OM: Selection Criteria
K40
K40
K40
SN
SN
SN
Number of PMT hits per Active OM
Q-Threshold: 1 pe
Q-Threshold: 2 pe
Q-Threshold: 3 pe
Q>Q-Threshold
Q>Q-Threshold
Q>Q-Threshold
PMT hit
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Background-II: Atmopsheric muons
Εμ (GeV)
Num
ber o
f Eve
nts
Generated (MuPage)
At least 1 active OM
OM Multiplicity
K40
SN
Atmospheric μ
Num
ber o
f Eve
nts
Expected Number of Εvents in a full WPD detector (6160 Oms) in T=2.95s
K40
SN
μ
Atmospheric muons seems to be tough guys !
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Background Rejection-II: Atmospheric muons
Number of Neighbor-OMs with multiplicity > 2
Num
ber o
f OM
s with
mul
tiplic
ity >
5
Active OMs due to Atmospheric Muons
Cherenkov Light
• 94% of the background due to atmospheric muons (i.e. active Oms with multiplicity >5) has at least one neighbor OM with multiplicity >2• Only 7% of the signal has at least one neighbor OM with multiplicity >2
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OM Multiplicity > 5
Q-Threshold = b
Number of PMTS with Q>Q-Threshold > cNeighbors with multiplicity greater than 2 < 1
Simulate the Cherenkov Light Emision and the photoelectron production on the small PMTs photocathode due to:1. SN neutrinos (following the GARCHING Model) interacting inside the KM3 full detector and
producing positrons in the vicinity of the Oms.2. K40 decays producing electrons and gammas3. Atmospheric muons e.g. 107 fully simulated signal events, 1011 fully simulated K40 background events and 106 fully
simulated atmospheric muon tracks
Apply the signal selection criteria for each optical module and estimate:a) the number of SN induced events (OMs passing Certain Selection Criteria) for T=2.95s as a
function of the SN distanceb) the number of background induced events (due to K40 and atmospheric muons) for T=2.95s
Estimate the SN distance for which the observed number of events (on top of the expected background) corresponds to 5σ discovery, e.g.
a b c Signal @10 kpc
Backr. K40
Backr. Atm. μ
5 1 2 147.5 2.53 18.96
7
0
2 1/ 210max
~
2.53 18.96 21.49
1 5.96 10 47!
147.5 10 ~10 25.5
bck
bck
imbck
i
kpcSN
e mi
d kpckpc
5S
5SN
N
max
N 25.5
dN
24kpc
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a b c dmax (kpc)
5 0 0 20.7
5 1 0 21.7
5 1 1 24
5 1 2 24
5 1 3 22
5 2 0 23.5
The background rejection criteria are based on the PMT waveform amplitude/chargeCan the Time over Threshold digitization electronics provide the necessary Information?
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Pulse simulation
Pulse characteristics @ 1 p.e.Gaussian Amplitude Distribution
σ/μ 35%
Time jitter 1 ns
Rise time 2.5ns
/( ) b t cf t at e
ns
Threshold value : 0.3 μ
ToT (time over threshold)
pes
ToT
(ns)
The error-bars correspond to the RMS of the ToT distribution
K40
SN
μ
We choose the condition: ToT> 7.5 ns, to select pulses “corresponding” to more
than 1 pe
single photoelectron averaged wave form
μ
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OM Multiplicity > 5ToT-Threshold > BNumber of PMTS with ToT>ToT-Threshold > c
Neighbors with multiplicity greater than 2 < 1
Dmax=23 kpc for 5 σ discovery
Background Rejection Criteria
OM Multiplicity > 5
Q-Threshold = b
Number of PMTS with Q>Q-Threshold > c
Neighbors with multiplicity greater than 2 < 1
a b c dmax (kpc)
5 1 2 24
a B c dmax (kpc)
5 7.5ns 2 23Including pulse statistics
a B c Signal @10 kpc
Backr. K40
Backr. Atm. μ
5 7.5 ns 2 118.7 < 0.8 15.4
Livermore model ~30 kpcIcecube: dmax=50 kpc (80 strings) (2000 events) 36.9 (DC) (13 events)
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Summary
SN explosions within our Galaxy can be detected by an Underwater Neutrino Telescope .
Preliminary results for the Garching model without oscillations, indicate that a maximum distance of ~ 23 kpc for 5σ significance level can be reached
Further Studies• Other models for SN collapse (eg Livermore)
• Inclusion of matter and vacuum oscillations
• Improve selection efficiency and quality cut criteria
• Apply filters for atmospheric muons
• Directionality ?
• Energy sensitive observables ?