1. Muon Detector
Jiawen ZHANG
16 September 2002

2. BESIII m Detector
The m 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

3. The Detector Choices The Resistive plate counters (RPC) Advantages
Small dead region
Fast response
Lower cost
No poisonous material in case of fire

4. 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

5. m detection efficiency and p contamination
Increase the position pricisoin, considering the p interaction with Fe which can produce second class of particles, and, in turn, produce more than one hit, the p contamination can be reduced in the low momenta
Efficiency %
Radial thickness of Fe (cm)

6. m hits position distribution
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.
Hits position s(cm)
Radial thickness of Fe (cm)

7. The structure and detector design
Requirements
l High detection efficiency for muons.
l Large solid angle coverage.
l Wide momentum range (the minimum momentum ～400MeV).
l High rejecting factor for other charged particles.
l Suitable position precision.

8. 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)

9. Barrel Structure
Two layers RPC composed from several parts, and they overcast to reduce the dead space

10. End cap m counter Each end cap m 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

11. RPC Structure
The structure of RPC Like CMS

12. Small prototype and the Spacer

13. Prototype and the Strip

14. RPC Q Distribution
Ar:F134A: Iso-butane = 30:58:12
HV=8400V

15. Gas System Gas Mixtures Ar+Isobutane+F134A Need some R&D
Mass Flow Control System

16. 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

17. Readout System

18. Anti-errorcode shaper
FEC
(Most of the FEC card’s properties have been described before)
discriminater
Anti-errorcode shaper
Buffer(XN)
Ch00
Ch01
Ch02
Ch15
Controller
Trigger
System Clock
SHIFT REG
Shift In
Shift Out

19. The Expected performance
0.4GeV/c may be the low momentum limit to identify m
cos q ~0.89
efficiency ~ 95%

20. m detection efficiency and contamination from p versus momentum
Good m/p 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 m efficiency is rather lower. So 0.4GeV/c may be a low momentum limit to identify m.

21. 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 ＋4608=9600

22. Schedule 2001,Oct.—2003,May：R&D, Design and Lab. construction.
2003,Jun.—2005,Oct.：Chamber production and test.
2005,Nov.—2006,May：Installation.

23. THANKS