Muon Detector Jiawen ZHANG

Introduction The Detector Choices Simulation The structure and detector design The Expected performance Schedule

BESII detector

Worked for 12 years Leakage problem Large size (5×6cm ) Signal too slow

Signal drift time is about 0 ～ 700ns, and the trigger signal delay is about 2.4s

Solid angle (~63% )

BESIII Detector

The detector is the outmost subsystem of the BESIII detector. It includes detectors and hadron absorbers. Its main function is to identify muons from pions and other hadrons in the momentum range of 0.4—1.5GeV/c and to provide the solenoid flux return

The Detector Choices

Two possible kinds of detectors

The Plastic Streamer Tubes (PST) The Resistive plate counters (RPC)

RPC and PST are very similar, such as graphite painting, induced strips, gas mixture etc.

The Resistive plate counters (RPC)

Advantages Small dead region Fast response Lower cost No poisonous material in case of fire

Shortcoming Very high voltage (8000V), easy to produce sparks No experience

The Plastic Streamer Tubes (PST)

Larger signal pulse, good signal noise ratio Taking ALEPH detector as an example Typical strip signals around 6 mV (at BESIII detector, the strips

are shorter than ALEPH, so the signal maybe larger than 6 mV ) Rise time 10 ns and width at the base ~ 100ns Have a rather long plateau Stable operation , ALEPH has stop working, however the PST st

ill works very stably More experience At IHEP, Beijing, some people ever made many PSTs for ALEPH

Simulation

Careful simulation studies were made for initial designing and optimizing

Geant 3.21 Condition 13 radiation lengths BGO, all of the other inner detectors equal to 6cm Fe

plate

detection efficiency and contamination

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0 10 20 30 40 50 60 70

m: P=0. 35GeV p: P=0. 35GeVm: P=0. 4GeV p: P=0. 4GeV

m: P=0. 45GeV p: P=0. 45GeVm: P=0. 5GeV p: P=0. 5GeV

m: P=0. 6GeV p: P=0. 6GeVm: P=0. 7GeV p: P=0. 7GeV

m: P=0. 8GeV p: P=0. 8GeVm: P=0. 9GeV p: P=0. 9GeV

m: P=1. 0GeV p: P=1. 0GeVm: P=1. 1GeV p: P=1. 1GeV

m: P=1. 2GeV p: P=1. 2GeV

Radial thickness of Fe (cm)

Eff

icie

ncy

%

Increase the position pricisoin, considering the interaction with Fe which can produce second class of particles, and, in turn, produce more than one hit, the contamination can be reduced in the low momenta

hits position distribution

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P=0. 35Gev P=0. 4GeV

P=0. 45GeV P=0. 5GeV

P=0. 6GeV P=0. 7GeV

P=0. 8GeV P=0. 9GeV

P=1. 0GeV P=1. 1GeV

P=1. 2GeV

Radial thickness of Fe (cm)

Hit

s po

siti

on The sigma of the hit positi

on distribution of moun will be about 4 to 8cm after moun’s multiple scatters in the absorber Fe. In this case, improving the position distinguish will not help the separation of moun and pion well but increasing the electronic channels and cost.

The structure and detector design

Requirements

 High detection efficiency for muons.

 Large solid angle coverage.

 Wide momentum range (the minimum momentum ～ 400MeV).

 High rejecting factor for other charged particles.

Suitable position precision.

Structure of PST

Similar to ALEPH’s Each cell has an inner dimension of 0.9×0.9cm2, The

internal surface of comb is painted with graphite . consists of plastic (PVC) comb profile having 9 cells

each

Wires diameter 100 m Strips on the two side of the streamer tubes (x—strips

and y—strips) or one view only

General structure

Sandwiched structure with Fe as absorber material and PST

The barrel counters are subdivided into 8 sectors, and 12 layers

inner radius is ~1.5m and outer radius is about ~2.5m

Length 3.6m 11 layers Fe 2, 2, 2, 3, 3, 4, 4, 6, 6, 8 and

10cm (Total thickness 50cm)

End cap counter

Each end cap counter is divided 4 pieces

Each end, the 4 pieces are separated to two parts and supported at left and right and each part has its own railway for moving

12 layers of PSTs

Gas select

ALEPH (12.5%Ar +56.5% CO2 + 30% C4H10)

Expensive and inflammable

long plateau BESII ESC (40%Ar + 60%CO2)

cheap and safe

short plateau

Need some R&D

The Expected performance

0.4GeV/c may be the low momentum limit to identify

cos ~0.90 efficiency >95%

detection efficiency and contamination from versus momentum

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0. 3 0. 5 0. 7 0. 9 1. 1 1. 3

Momentum GeV

Efficiency

contamination

Good / separation can be obtained with momenta greater then 0.6GeV/c. With momenta less then 0.5GeV/c, the separation becomes worse. And with momenta less then 0.4GeV/c, the efficiency is rather lower. So 0.4GeV/c may be a low momentum limit to identify

Read out channels

Strips on the two side of the streamer tubes (x—strips and y—strips). Strips wide 3cm

Barrel 120×8×12＋ 55×8×12=11520＋ 5280=16800 End cap 82×2×4×2×12=15744 Total 16800+15744≈ 32500 One side view only Barrel 55×8×12=5280 End cap 82×2×4×12=7872 Total 5280+7872≈ 13100 Outer layers use wide strips, can reduce some

channels

Schedule

2001,Oct.—2003,May： R&D, Design and Lab. construction.

2003,Jun.—2005,Oct.： Chamber production and test.

2005,Nov.—2006,May： Installation.