Transcript ANTARES Status report

ITEP winter school
Feb 12, 2008
Coincidence analysis in ANTARES:
Potassium-40 and muons
Dmitry Zaborov
(ITEP, Moscow, Russia)
 Brief overview of ANTARES experiment
 Potassium-40 calibration technique
 Adjacent floor coincidences as very basic
atmospheric muon signal
Detection principle
p, a
107
m atm
m
nm
104
p Cherenkov light
from m
n atm
nm
1-100
g
Sea floor
n cosm
Hadronic showers
from CC/NC
interactions can interaction
be detected as
n
well
Feb 12, 2008
3D PMT
array
m
g
43°
angular resolution ~ 0.3º at 10 TeV
effective area ~ 0.1 km2 in TeV range
Reconstruction of m trajectory (~ n)
from timing and position of PMT hits
D. Zaborov. Coincidence analysis in ANTARES
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Detector layout
a storey
12 lines (900 PMTs)
25 storeys / line
3 PMTs/storey
14.5 m
350 m
Horizontal layout
~70 m
40 km to
shore
100 m Junction
box
Feb 12,
2008~ -2500 D.
Sea
bed
mZaborov. Coincidence analysis in ANTARES Readout cables 3
Current status
10 detector lines
+
instrumentation
line
operational
(Feb. 2008)
N
seismometer
42°50’ N
IL07
6°10’E
L1
L5
L2
(since December 07)
L3
L9
L4
L7
~ 2 muons/sec
L6
L8
~ 5 neutrino/day
(atmospheric)
2 more lines
coming soon
Feb 12, 2008
L11
Submarine
cable
to shore
L10
L12
100 m
Junction box
* Cable path is shown only indicatively
D. Zaborov. Coincidence analysis in ANTARES
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Basic detection and calibration elements
Optical Beacon
with blue LEDs:
timing
calibration
Optical Module:
10” PMT in 17” glass sphere
photon detection
Local Control Module
(in Ti container):
Front-end ASIC,
Clock, DAQ/SC,
compass/roll/pitch
Feb 12, 2008
D. Zaborov. Coincidence analysis in ANTARES
Hydrophone:
acoustic positioning
5
In situ calibration with Potassium-40
High precision (~5%)
monitoring of OM
efficiencies
g
g
Gaussian peak on
coincidence plot
Rate of
correlated
coincidences
15 Hz
Cherenkov
e- (b decay)
40K
Peak offset
40Ca
No dependence on bioluminescent
activity has been observed - this
confirms the single photon character of
bioluminescent emission
Feb 12, 2008
Mean ≈ 0
RMS 0.7 ns
D. Zaborov. Coincidence analysis in ANTARES
MC prediction
13+/-4 Hz
(“NIM” angular
acceptance)
time
calibration
confirmed
6
Example: calibration of Line 8
Three OM sensitivity factors
si can be extracted using 3
equations
rateij = k * si * sj
I,j=1,2,3
factor k gives absolute scale;
k can be determined from Monte-Carlo
(or, in opposite, used to constrain
parameters of Monte-Carlo)
Unofficial technical plot
* No charge calibration used
* No walk correction included
Unofficial technical plot
Feb 12, 2008
OM-OM time offsets determined using
K-40 (basically single photoelectrons)
w.r.t Dark room calibration
(high amplitude laser pulse)
D. Zaborov. Coincidence analysis in ANTARES
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Time evolution (example)
Gradual decrease is probably due to
PMT gain drift
Steep changes are threshold tunings
Time delays seem stable
(within our accuracy)
Unofficial technical plot
K40 runs are taken once a week
Unofficial technical plot
Feb 12, 2008
K40 trigger can run in parallel with
other triggers (e.g. GRB trigger or
directional triggers) and can be even
used for physics analysis as is
D. Zaborov. Coincidence analysis in ANTARES
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Time evolution of average K-40 coincidence rate
tuning 2
tuning 1
start
at 12 Hz
tuning 2
-> 15.5 Hz
“degradation”
Unofficial technical plot
One year of “degradation” could be fully compensated by the tuning
* Other Lines show similar behavior
Feb 12, 2008
D. Zaborov. Coincidence analysis in ANTARES
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Delay between adjacent floors (theory)
≈ fixed number for exactly vertical muons
a wide distribution in general
Δt = L / c ≈ 50 ns
to
Δt ~ L n / c ~ 70 ns
But light hits back
of the OM
L
The most basic signal
of physics events in
ANTARES
No background
Delay
between
storeys
from
Feb 12, 2008
Δt ~ 0
D. Zaborov. Coincidence analysis in ANTARES
No systematic
errors from
trigger or
reconstruction
algorithms
10
Adjacent floor coincidences: measurement
Integral under the peak ~ muon flux
Shape is sensitive to angular
acceptance of optical modules and
angular distribution of muon flux
This plot is preliminary
Actual comparison of peak amplitude with Monte
Carlo will be made after OM angular acceptance
issues are fixed, OM efficiency is well known and all
dead time corrections applied
Low energy threshold
(compared to full reconstruction)
The analysis can be repeated for
every detector storey separately
The effect of muon flux reduction with
depth is directly (!) measured
Feb 12, 2008
D. Zaborov. Coincidence analysis in ANTARES
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Summary
• A calibration technique using Cherenkov light from
Potassium-40 decays in sea water has been developed
– Sensitivity of optical modules is now controlled using K-40
– K-40 is also a useful tool for time calibration
• A simple but powerful technique for atmospheric muon
measurement is developed based on the idea of adjacent
floor coincidences
– First results allowed to reject one of the models of OM angular
acceptance
– Depth dependence and absolute normalization of atmospheric
muon flux can be extracted using this new approach
– Possibility to reject certain hadronic interaction models or (less
likely) primary flux models is being investigated
– Promising prospects to use adjacent floor coincidences in the
trigger
Feb 12, 2008
D. Zaborov. Coincidence analysis in ANTARES
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