Pid Detector Implementation
in G4Mice
Steve Kahn
Brookhaven National Lab
10 Feb 2005
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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TOF Detector Geometry Status

TOF planes:

Positions have been upgraded:




Transverse sizes:



All stations are 2 planes arranged
orthogonal to each other.
TOF0,1,2 have 8 slabs in each plane.
NO OVERLAP.
TOF0 environment:


TOF0,1,2 are all 4848 cm.
Segmentation:


TOF0 is placed after Q6.
TOF1 is placed after Q9.
TOF2 position has been changed to
have the correct relative position
relative to the other downstream
detectors.
Low field: 100-200 g; High rate: 2.5 MHz.
TOF1,2 environment:

High field: 1-2 kg; Medium rate 0.5 MHz
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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TOF Implementation


A particle traversing the TOF scintillator will deposit energy. The number of
optical photons produced is proportional to the deposited energy.

The number of photons is attenuated traveling through the scintillator.
atten=1.4 m.

The transit time through the scintillator is delayed by an exponentially
distributed time with a decay constant decay=1.8 ns.
The rise time of the arrival time of the optical photons at each PMT is
smeared with the PMT jitter time.


= 80 ps for the fast PMT at TOF0. =175 ps for fine-mesh tubes used for
high fields at TOF1,2.
There is a gaussian amplitude resolution applied to the ADC counts.

Also there is a truncation error for the finite number of bits representing the
ADC counts.
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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What Have We Simulated?

We have generated two samples:

Sample of 20K events starting just upstream of TOF0.
 x=5 cm; x’=2 mr.
 Few of these events make it down the entire channel, however
this sample is minimally biased.

Sample of 20K events that start at z=2000 This sample gives
sufficient statistics at the downstream PID detectors.

The decay electron sample is enhanced by decreasing the decay length
by a factor of 10.

We want to keep the proper decay electron energy distribution.

We want to correct for having no upstream detector.

We need enough events in our sample.
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Muon Economics
Tof0
Ckov1
Tof1
SciFi
Tof2
Ckov2
EmCal




Muons
9617
3413
1835
1821
634
643
656
Electrons E>2.5 MeV
403
72
62
133
The above table shows the true number of muons at each detector
station.
The input beam is larger than the acceptance of the detector channel
so there are large losses expected between Tof0 and Tof1.
Electrons have E>2.5 MeV in order to suppress the background from
knock-on electrons.
The initial beam has 33% electron beam contamination.
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Transit Time for Upstream Tof
Planes
•Transit time
between Tof0 and
Tof1
•Quad fields are
currently ignored
•Pions and muons
can be
distinguished
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Transit Time through Detector
Channel
•Transit time
between Tof1 and
Tof2 (at opposite
ends of tracker).
•The arc length
variations because
of different PT
make the transit
time less effective
for distinguishing
particle ID.
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Cherenkov Systems

Upstream Ckov

C6F14 radiator with n=1.25

4 PMTs

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Threshold cherenkov:



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2 on top, 2 on bottom.
0.7 MeV for electrons
140 MeV for muons
190 MeV for pions
Downstream Ckov




Aerogel with n=1.03
12 PMTs on 12-sided polygon.
Typically on electrons visible since
pion threshold is > 500 MeV.
Requires TOF coincidence.
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Ckov1 as a Threshold Detector
•Note: According to
Kevin Tilley’s Talk this

morning, we expect
the muon beam to
have a momentum of
~241 MeV at the
Ckov1 radiator!

N pe  sin 2  c
cos  c 
1
n
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Photon Generation in the
Cherenkov Detectors


For each track that crosses the radiator with
a velocity above threshold a number of
photons are generated proportional to the
deposited energy.
We currently do not use the Cherenkov
photon facility in Geant4.



There is some question as to how well it
works with reflective surfaces.
Imaginary photons are generated in a cone
(at the č angle) around the particle direction.
Since all mirrors are at 45º w.r.t. the beam
direction, we can position the PMTs on an
imaginary plane.

The č photons that intercept the PMT circles
are “seen”.
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Efficiency of Ckov1
The histograms
show:
•Photons generated.
•Photons seen in
PMTs
•Event-by-event
efficiency.
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Ckov2 Efficiency
The histograms
show:
•Photons
generated.
•Photons seen
in PMTs
•Event-by-event
efficiency.
From
downstream
electron sample
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Ckov2 Efficiency from Electron Contamination in
Beam that Traversed the whole channel
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Ckov1: Momentum for
Different Species
Caveat:
Different
species have
same KE, not
the same
momentum!
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Č Photons Generated by Track
Traversing Radiator (for Ckov1)
KE of tracks is 120.5
MeV. Unfortunately
that means:
•P=200 MeV/c
•P=219 MeV/c
•Pe=121 MeV/c
In order for Ckov1
to be effective,
momentum must be
less than 190 MeV/c
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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EM Calorimeter



Rikard Sandstrőm has taken over the
management of the EM calorimeter. He has
completely rewritten the package.
The following plots were made with the
previous version.
Most of the previous studies have only made
use of the longitudinal shape. The transverse
shape difference between electrons and
muons could be effective in particle
identification.
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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EmCal: E1 vs. E1/ETot
Muons
Electron Sample
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Baricentric
Variable
3 Layers
Z bari
Ez


E
i i
i
All Layers
2 Layers
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Baricentric Z vs. Momentum for Muons
and Decay Electrons
Momentum
Stopping 
Muons
Decay Electrons
Zbaricentric
Feb 10, 2005
S. Kahn -- Pid Detectors in G4Mice
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Ckov II Selection Criteria


The Ckov II Detector Response currently does not have
sufficient information to properly produce a decision based on
the measurements.
The following procedure was used:
 Require a Tof II signature or the selection is indeterminate.
 If the track crossing the Ckov radiator has >0.98 (the
electron threshold) and the Ckov II – Tof II time difference
is between 0.2-1.0 ns, then it is an electron.
 Else if the energy is greater than 75 MeV it is a muon.
 Else it is indeterminate.
True mu as mu
True mu as e
True e as mu
True e as e
Feb 10, 2005
Ckov2
551
1
9
52
EmCal
586
71
0
133
S. Kahn -- Pid Detectors in G4Mice
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