feb 10, 2005 s. kahn -- pid detectors in g4micepage 1 pid detector implementation in g4mice steve...

Feb 10, 2005 S. Kahn -- Pid Detectors in G4Mice

Pid Detector Implementation in G4Mice

Steve KahnBrookhaven National Lab

10 Feb 2005


2

TOF Detector Geometry Status

TOF planes: Positions have been upgraded:

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.

Transverse sizes: TOF0,1,2 are all 4848 cm.

Segmentation: All stations are 2 planes arranged

orthogonal to each other. TOF0,1,2 have 8 slabs in each plane.

NO OVERLAP. TOF0 environment:

Low field: 100-200 g; High rate: 2.5 MHz. TOF1,2 environment:

High field: 1-2 kg; Medium rate 0.5 MHz


3

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.


4

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.


5

Muon Economics Muons Electrons E>2.5 MeV Tof0 9617 Ckov1 3413 Tof1 1835 SciFi 1821 403 Tof2 634 72 Ckov2 643 62 EmCal 656 133

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.


6

Transit Time for Upstream Tof Planes

•Transit time between Tof0 and Tof1

•Quad fields are currently ignored

•Pions and muons can be distinguished


7

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.


8

Cherenkov Systems Upstream Ckov

C6F14 radiator with n=1.25 4 PMTs

2 on top, 2 on bottom. Threshold cherenkov:

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.


9

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

N

c

cpe

1cos

sin 2


10

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”.


11

Efficiency of Ckov1

The histograms show:

•Photons generated.

•Photons seen in PMTs

•Event-by-event efficiency.


12

Ckov2 Efficiency

The histograms show:•Photons generated.•Photons seen in PMTs•Event-by-event efficiency.

From downstream electron sample


13

Ckov2 Efficiency from Electron Contamination in Beam that Traversed the whole channel


14

Ckov1: Momentum for Different Species

Caveat: Different species have same KE, not the same momentum!


15

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


16

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.


17

EmCal: E1 vs. E1/ETot

Muons

Electron Sample


18

Baricentric VariableAll Layers3 Layers

2 Layers

i

iibari E

zEZ


19

Baricentric Z vs. Momentum for Muons and Decay Electrons

Stopping

MuonsDecay Electrons

Mom

entum

Zbaricentric


20

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. Ckov2 EmCal

True mu as mu 551 586 True mu as e 1 71 True e as mu 9 0 True e as e 52 133

feb 10, 2005 s. kahn -- pid detectors in g4micepage 1 pid detector implementation in g4mice steve...

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