RPCs of BESIII Muon Identifier  BESIII and muon identifier  R&D  Mass production  Installation Zhang Qingmin Advisor: Zhang Jiawen

The BESIII Detector Be beam pipe SC magnet Magnet yoke and muonidentifier MDC CsI calorimeter TOF It is the outmost subsystem of the BESIII detector to measure the muons, consisting of muon counters and hadron absorbers, the muon’s position and trajectory can be obtained through multi-layers measurements. To obtain a large solid angle coverage, the muon counters splitted off into two parts, namely barrel and endcap. Barrel has 9 layers, its inner radius is 1700mm and outer radius 2620mm. Endcap has 8 layers.

Muon identifier ---- Barrel & Endcap The structure of the endcap sketch map The size of each layer of the barrel part RPC

The prototype RPCs for the BESIII muon identifier were constructed by using resistive electrodes made from a special type of phenolic resin developed by us. The surface quality of these plates is improved compared to other bakelite plates that have been used to construct RPCs elsewhere. A method for adjusting the resistivity of these plates was also developed. Extensive studies were conducted by using a number of prototype RPCs in the last several years. Tests have shown prototype RPCs made by using our resistive plates without linseed oil treatment can achieve the level of performance comparable to RPCs with linseed oil treated bakelite or resistive glass electrodes. All of the follow experiments are in streamer mode. R&D of RPC

R&D ---- Amplitude vs. HV Oscilloscope traces of 100 triggered cosmic ray muons registered in a RPC prototype at 8 kV. The average signal size from a pickup electrode is about 400 mV with a 50 Ω termination. No secondary streamers were recorded secondary streamers 450mv

R&D ---- Eff. And Cnt. VS. HV Efficiencies and singles counting rates versus the high voltage up to 12 kV. This plot shows the behavior of the prototype RPC under extreme high voltages. The gas mixture used was Ar(argon) :C 2 F 4 H 2 ( Freon): C 4 H 10 (Iso-butane) = 50:42:8.

R&D ---- prototype performance Efficiency Plateau: 96-98% ~2KV

neutron irradiation other experiments R&D ---- long-term stability Beam test neutron irradiation Max: 98.8% Min: 95.3% Average: 97.2%

R&D ---- Threshold Efficiencies versus high voltage for different discrimination thresholds Singles counting rates versus high voltage for different discrimination thresholds

R&D ---- Different gas mixture

R&D ---- Temperature The efficiency and counting rate versus temperature. Efficiency curve will shift to left side at high temperatures. And the counting rate will increase exponent with temperature.

R&D ---- Different Resistivity

Gas vapor test

R&D ---- Neutron irradiation Total dose: 10 6 rad Efficiency: 1% ; 96% Cnt rate: 0.18Hz/cm 2 Dark current: 250% more than 1.5μA/m 2 Revision time: 20days

R&D ---- Electron Irradiation No obvious change !

R&D ---- γ Irradiation ( Co60 )

Mass production The RPC production for the BESIII muon identifier has started in middle of 2004 and finished in the early of The average area for the endcap RPC is 1.3m 2, barrel RPC 1.4m 2. The maximum area for the endcap RPC is 1.6m 2, barrel RPC 2.0m 2. There are 978 RPCs and the area is about 1300m 2 totally. Each bare chamber is tested to ensure their performance is meet the requirement of the muon identifier before them assembled in the module, and all of modules are tested using cosmic rays before them installed on the BESIII. // Maximum RPC we can make is 1.2mx2.4m. //

Mass production ---- Bare chamber The worker are facturing the bare chambers!

Mass production ---- Bare chamber test Test surrounding

counting rate (Hz/cm 2 ) The performance of the RPC that just produced HV7-8Kv,Eff 90%- 95% efficiency HV: 7- 8Kv; Eff.>95% Counting Rate at 7kV ( Hz /cm 2 ) More than 95% cnt.<0.6 Efficiency at 7kV More than 97% Eff.>90% More than 35% Eff.>95% Amount: 130RPCs No training

Mass production ---- Bare chamber test result ---- efficiency Training time : 1 - 3days; endcap 320RPCs, barrel 590RPCs Endcap 7.5Kv Min. 83.5% Max. 98.5% Aver.93.46% Barrel 7.5Kv Min. 85.6% Max % Aver.95.39% Endcap 8.0Kv Min % Max. 98.7% Aver.94.25% Barrel 8.0Kv Min % Max. 99.2% Aver.96.4%

Mass production ---- Bare chamber test result ---- counting rate Training time : 1 - 3days; endcap 320RPCs, barrel 590RPCs Endcap 7.5Kv Min Max Aver Barrel 7.5Kv Min Max Aver Endcap 8.0Kv Min Max Aver Barrel 8.0Kv Min Max Aver.0.130

Mass production ---- Bare chamber test result ---- dark current Training time : 1 - 3days; endcap 320RPCs, barrel 590RPCs Endcap 7.5Kv Aver Barrel 7.5Kv Aver Endcap 8.0Kv Aver Barrel 8.0Kv Aver

Mass production ---- Resistivity 0.8—5.4x10 12 eligible

 Temperature : 20±2ºC; Humidity≤50%; Ar:F134A:Iso=50:42:8  Reaching the efficiency plateau as the high voltage reaches 7.0kv and In the middle of the efficiency plateau (8.0KV)  Eff > 90%; Cnt. < 0.8Hz/cm 2 ; Cur. < 10μA/m 2  The resistivity range : 8x10 11 ~5x10 12 Ohm  So 92% RPCs of endcap up to grade and 99% RPCs of barrel up to grade. NOTE: All of the previous performance is signal RPC’s. Bare chamber performance requirements

Mass production ---- Module The worker are assembling the modules!

Mass production ---- Module test RPC Super layers module Streamer Telescope system

Mass production ---- Module test Test result of an endcap module One example of the cosmic ray test result: The plot size: 35mm*35mm; Average efficiency: 0.94 Spatial resolution: 14.6mm

…after assembling - endcap  The efficiency and current distribution of all 64 endcap modules:  Note that the average efficiency is underestimated, because the efficiency at the edge is pull down by boundary effect.  Test temperature: ℃ Mean 0.91 Mean 2.7 μA/m 2

Test Result after installation - endcap  Total efficiency and current of 64 endcap RPC modules after installation.  Test temperature: ℃ Mean 0.95 Mean 1.8μA/m2

…barrel Module size: 3800mm*1640mm Strip length: 3800mm Strip width: 33mm Average strip efficiency: 0.99 Spatial resolution: 14.2mm

…after assembling - barrel  Total efficiency and current distribution of 72 barrel modules:  Average efficiency higher than that of endcap modules, while dark current smaller than endcap modules.  Test temperature: ℃ Mean 0.98 Mean 1.1μA/m 2 Barrel After installation have not been tested!

Installation

All except three modules have been installed! After installing,the endcap are being tested!

More R&D in the future  Performance of lower resistivity Bakelite RPC in high background environment  Toughness of the Bakelite surface against the HF acid attack;  Systematic aging study;  Detailed performance study in avalanche mode.

Summary  The RPCs making with new bakelite plates that we developed have good surface quality （ ~200nm ）, it can meet with different RPC detector requirement.  The bulk resistivity range of bakelite plates is 10 9 ~10 14 Ω·cm.  The RPC avoid the problem of linseed oil and glass RPC  The RPCs have higher efficiency, lower counting rate and dark current, and good long-term stability. The end THANKS