1. Han Jifeng BESIII MUON GROUP IHEP, CAS 2006.10.28
BESIII MUON detector
Han Jifeng
BESIII MUON GROUP
IHEP, CAS

2. Outline Introduction R&D of RPC chamber Bare chamber performance
Super Module performance after assembling
Super Module performance after installation
Conclusion

3. R&D of RPC chamber
No linseed oil technique render the production process much easier;
Our bakelite’s smoothness without linseed oil is better than that of the bakelite used by BABAR;
The performance is comparable to that of RPCs with linseed oil and glass RPCs.

4. … longtime test Gas is Ar: C2H2F4:Iso-C4H10 = 50:42:8
We test one RPC prototype’s performance over one year’s period
The efficiency higher than 95%;
Counting rate smaller than 0.2Hz/cm2;

5. … performance at different discrimination threshold
Finally we choose 100mV as our discrimination threshold, to ensure our RPC could reach plateau quickly and the counting rate is acceptable.

6. …amplitude versus HV and performance at extreme high HV
Average signal amplitude versus high voltage at 8KV, the average amplitude is 450mV.
Efficiency and counting rate at extreme high voltage, we can see the efficiency is still very high when the HV is 12000V.

7. Bare chamber performance
Totally BESIII MUON system will use 1200m2 RPCs, including368 end cap RPCs and 594 barrel RPCs.
Each bare RPC should be tested before they are assembled into super module.
At 8000V, they should meet the minimum cut:
Efficiency > 0.85
Counting rate < 0.8 Hz/cm2;
Current < 20 μ A/m2;

8. Bare chamber bakelite and graphite resistivity
Bakelite resistiviey: 2×1011—2×1013Ωcm
Graphite resistiviey:
KΩ/cm2

9. Bare chamber efficiency
End cap and barrel efficiency distribution at 8000V

10. Bare chamber counting rate
End cap and barrel counting rate distribution at 8000V

11. End cap and barrel current distribution at 8000V
Bare chamber current
End cap and barrel current distribution at 8000V

12. RPC super module
One super module contains two RPC layers and one readout layer;
Totally there are 64 end cap super modules and 72 barrel super modules.

13. Performance of super module after assembling – end cap
3 streamer tubes are used as cosmic ray telescope, one test facility is made to support both streamer tubes and RPC modules.
For good event, first we fit and rebuild the cosmic ray using streamer tubes, then we calculate RPC’s efficiency by that.
Streamer tubes
RPCs

14. Boundary effect of streamer tubes
… - end cap
Boundary effect of streamer tubes
One example of the cosmic ray test result:
The plot size is 35mm*35mm;
Average efficiency is 0.94
Spatial resolution is 14.6mm

15. …after assembling – end cap
The efficiency and current distribution of all 64 end cap modules:
Note that the average efficiency is underestimated, because the efficiency at the edge is pull down by boundary effect.
Test temperature: 22-25℃
Mean 0.91
Mean 2.7 μA/m2

16. Performance of super module after assembling - barrel
Use RPCs to test RPCs.
Activation:
Barrel RPCs are much too larger than streamer tubes.
DAQ of streamer tubes is too slow.3-5Hz
Trigger:
Each RPC module give an fastor signal; when 3 of the chosen 4 modules could coincidence, it will trigger one event. Hz

17. …after assembly - barrel
8 RPCs (4 X-strips and 4 Y-strips) are tested together.
For each RPC under test: first fit the cosmic ray line use RPCs exclude itself, then calculate the expected hit of that RPC, and get the efficiency.
One good event: the left is for X strip modules and right for Y strip modules.
The round black points define the boundary of the modules, and the red triangle points mean the fired strip.

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

19. …after assembling - barrel
Total efficiency and current distribution of 72 barrel modules:
Average efficiency higher than that of endcap modules, while current smaller than endcap modules.
Test temperature: 22-25℃
The experience of producing endcap modules have helped to get a better performance of barrel modules.
Mean 0.98
Mean 1.1μA/m2

20. …-efficiency versus HV
The average efficiency of RPC modules
with different high voltage.
8000V is already in the efficiency plateau, plateau efficiency 0.96, and the plateau lasts 2000V

21. …-efficiency versus discrimination threshold
Threshold 250mV
Zone with only one layer RPC
Threshold 100mV
The average efficiency of RPC modules
with different discrimination threshold.
Our system could set discrimination threshold online.

22. Performance of super module after installation – end cap
After the RPC modules have installed into the BESIII iron, we test the efficiency again.
Trigger: use fastor of inner 4 layers, when 3 of the 4 layers could coincidence, it will give a trigger.
The test have been finished for end cap modules, while the test of barrel modules haven’t done yet.

23. …after installation – end cap
Average strip efficiency: 0.97
Spatial resolution: 16.6mm

24. … after installation – end cap
Total efficiency and current of 64 end cap RPC modules after installation.
Test temperature: 20-22℃
Mean 0.95
Mean 1.8μA/m2

25. Efficiency before and after installation
Problem after installation:
There are areas where the efficiency is very low, maybe 0.2 or less.
Maybe the spacer in that area have ripped off during the installation process.
After installation
Before installation

26. Conclusion Our RPC modules’ average efficiency is higher than 0.95.
The average current is 1.5μA/m2

27. The end
Thanks!