Muon Detector Jiawen ZHANG 16 September 2002

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

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

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)

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)

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.

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 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

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

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

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

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.

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.

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