Muon Detector

Jiawen ZHANG

16 September 2002

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

The Resistive plate counters (RPC)

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

Simulation

Careful simulation studies were made for initial designing and optimizing

Geant 3.21 Condition 13 radiation lengths CsI, all of the other inner detectors equal to

4cm Fe plate

detection efficiency and contamination

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

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Thickness of Fe(cm)

Effi

cien

cy(%

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m: P=0. 35GeV p: P=0. 35GeVm: P=0. 4GeV p: P=0. 4GeVm: P=0. 45GeV p: P=0. 45GeVm: P=0. 5GeV p: P=0. 5GeVm: P=0. 6GeV p: P=0. 6GeVm: P=0. 7GeV p: P=0. 7GeVm: P=0. 8GeV p: P=0. 8GeVm: P=0. 9GeV p: P=0. 9GeVm: P=1. 0GeV p: P=1. 0GeVm: P=1. 1GeV p: P=1. 1GeVm: P=1. 2GeV p: P=1. 2GeV

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

(cm

)

The sigma of the hit position 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.

General structure Sandwiched structure with Fe

as absorber material and RPC The barrel counters are

subdivided into 8 sectors, and 9 layers

inner radius is ~1.7m and outer radius is about ~2.6m

Length 4.1m ， (RPC length 3.8m)

8 layers Fe 3, 3, 3, 4, 4, 8, 8 and 8cm (Total thickness 41cm)

Barrel Structure Two layers RPC

composed from several parts, and they overcast to reduce the dead space

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 or right and each part has its own railway for moving

8 layers of RPCs

RPC Structure The structure of

RPC Like CMS

Small prototype and the Spacer

Prototype and the Strip

RPC Q Distribution Ar:F134A:

Iso-butane = 30:58:12

HV=8400V

Gas System Gas Mixtures

Ar+Isobutane+F134A

Need some R&D Mass Flow Control

System

High Voltage System Separate apply positive voltage to

the anodes and negative voltage to the cathodes

The modules typically operate with a total gap voltage of 8 KV

Readout System

FEC(Most of the FEC card’s properties have been described before)

discriminater Anti-errorcode shaper Buffer(XN)Ch00

discriminater Anti-errorcode shaper Buffer(XN)Ch01

discriminater Anti-errorcode shaper Buffer(XN)Ch02

discriminater Anti-errorcode shaper Buffer(XN)Ch15

Controller Trigger

System Clock

SH

IFT

RE

GS

hift In

Sh

ift Ou

t

The Expected performance

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

cos ~0.89 efficiency ~ 95%

detection efficiency and contamination from versus momentum

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

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0. 3 0. 5 0. 7 0. 9 1. 1 1. 3Momentum (GeV)

cont

amin

atio

n or

det

ecti

oneffi

cien

cy(%

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Read out channels Strips between the double layers RPC One dimension readout Strip width 4cm Readout channels Barrel 48×8×5＋ 96×8×4=4992 End cap 64×4×2×9=4608

Total 4992＋ 4608=9600

Schedule 2001,Oct.—2003,May ： R&D, Design

and Lab. construction. 2003,Jun.—2005,Oct. ： Chamber

production and test. 2005,Nov.—2006,May ： Installation.

THANKS