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BESIII Muon Counter

BESIII Muon Counter. Jiawen ZHANG BESIII Workshop June 5-6 2002. Introduction (1). Outmost subsystem Main function : M easure the muons of the end particles produced during reaction. Identify muons from hadrons (especially pions). Introduction(2). Muon counter is very important

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BESIII Muon Counter

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  1. BESIII Muon Counter Jiawen ZHANG BESIII Workshop June 5-6 2002

  2. Introduction (1) • Outmost subsystem • Main function: Measure the muons of the end particles produced during reaction. Identify muons from hadrons (especially pions).

  3. Introduction(2) • Muon counter is very important The channel of decay to muons clean • J/Ψ discovery cross section measurement is one of the important evidences • mass precise measurement on BES measured mainly through

  4. Introduction(3) In reaction, many muons are produced during D decays and  decays. The momentum distribution muons produced during D decays and  decays near 2×2.0 GeV.

  5. Introduction(4) • Lower muon end momentum • Greater cover solid angle • Higher detection efficiency • Safer working gas • Suitable location precision

  6. Detector Choice (1) Brief introduction to (RPC) • The RPC is developed by R. Santonico in the early 80’s. • Several large experiments have used it. For instance, Belle, BaBar, CMS, ATALAS, L3 and ARGO have used RPC • Much successful experience was accumulated

  7. Detector Choice(2) RPC structure • Two parallel high resistive plate electrodes • gas room • pickup strip

  8. Detector Choice(3)

  9. Detector Choice(4)

  10. RPC’s characteristics Simple and solid structure Superior time and spatial property High detection efficiency and little dead space Flexible signal readout Occupation of small space Mature technology Good radiation hardness Easy management and maintenance Big signal Long lifetime Detector Choice(5)

  11. RPC comparison with PST RPC and PST resemble very much in many places, working in streamer mode the signal read out through the pickup strip, big signal graphite to be sprayed Simple comparison of RPC and PST Time performance Spatial resolution Detection efficiency The crucial material Detector Choice(6)

  12. Monte Carlo Simulation (1) Careful simulation studies were made for initial designing and optimizing • Geant 3.21 • Condition • 13.5 radiation lengths CsI, • All of the other inner detectors equal to 5cm Fe plate

  13. Monte Carlo Simulation (2) • detection efficiency and p contamination If we choice suitable thickness of the absorber, the pion contamination to muon can be reduced to a lower level when the muons detection efficiency is ensured.

  14. Monte Carlo Simulation (3) m hits position distribution • The sigma of the hit position distribution of moun will be about 4 to 8cm • If the position resolution is to be increased, only increase the electronics readout channels, but the effect to identify muon and pion is not obvious.

  15. Monte Carlo Simulation (4) The muon detection efficiency in one dimension readout will be higher than that of 2-dimension readout

  16. Monte Carlo Simulation (5) The contamination of muon by pion will be increased, but to a very limited level. In the high momentum range, the contamination of muon by pion has no difference

  17. Monte Carlo Simulation (6) The influence of noise background • 2-dimension read-out can reduce the influence of noise background properly, and it is superior to one-dimension readout . • But we can use the time gate to reduce the noise background during the electronics readout. • If the noise of RPC reaches 1 KHz/㎡, we use 2000 ㎡ RPC, the time gate width is 100ns, for every event, will record 2000㎡×1000 Hz/㎡×10-7s=0.2 signal, so the physics analysis will not be affected .

  18. Overall Structure (1) • High detection efficiency for muon • Large solid angle coverage • Large momentum range (the minimum momentum ～400MeV) • Ability of rejects other charged particles • Appropriate positioning precision

  19. Overall Structure(2) The barrel muon counter is subdivided into 8 pieces. Its inner radius is 1700mm and its outer radius 2600mm.

  20. Overall Structure(3) • The barrel part has 10 layers of RPC and 9 layers of absorbing iron • 9 layers of absorbing iron, thickness of each layer being respectively 3, 3, 3, 4, 4, 8, 8, 8, and 8cm. The total Fe thickness is about 49cm. • 4cm gap for arrangement the RPC

  21. Overall Structure(4) • The barrel part adopts the rectangle RPC of different size to overlap the arrangement in order to reduce its dead space

  22. Overall Structure(5) • The end cap muoncounter has nine layers of counters and nine layers of absorbing iron. • 9 layers of absorbing iron, thickness of each layer being respectively 3, 3, 3, 3, 3, 4, 8, 8, and 8cm. The total Fe thickness is about 43cm • 4cm gap for arrangement the RPC

  23. Overall Structure(6) • 4 pieces at each end • 2cm iron between every two pieces • each piece consists of 4 trapezoids of right angle RPC • pushed into the gap of the yoke from the left side or the right side

  24. The RPC Structure (1) • The RPC consists of two parallel sheets of 2.0mm Bakelite. • The bulk resistivity of the Bakelite is 1011-1012Ω·cm at room temperature. • The plates are separated by 2.0mm thick circular spacers made of insulating material. • The span between every spacer is 100mm. • The mixture gas of certain proportion passes the gap of the plates as working gas.

  25. The RPC Structure (2) • The placesround the gap are sealed with T-shape spacer made of insulating material • This spacer can reduce the dark current, and guarantee the span of the resistive plate, guarantee the glue thickness and the binding strength

  26. The RPC Structure (3) • The outer surface of the Bakelite is coated with graphite. The surface resistivity adopts 105—106Ω/□. • When graphite is sprayed to the resistive plate, it will not be sprayed to the place which corresponds to the place of spacers for the reduction of the dark current

  27. The RPC Structure (4) • The two layers of RPC and one layer of aluminum pickup strip between the two layers of absorbing iron constitute a superlayer

  28. High Voltage System • apply positive voltage to the anodes and negative voltage to the cathodes • The modules typically operate with a total gap voltage of 8—9 KV • Each layer of the barrel RPC uses one group of high voltage, including one positive and one negative high voltage • Each end is divided into 3 groups, with 3 layers forming one group • One CEAN high voltage crate, controlled by computer

  29. Gas System (1) • argon＋F134A＋isobutane • control system adopts the mass flow control system • The flow rates from the mass flow controller are monitored via a network connection and the high voltage is automatically lowered if a deviation from the desired flow rate is detected • The flow rate is controlled to approximately one volume change per day

  30. Gas System (2)

  31. The Expected Performance (1) • the total solid angle coverage of the barrel and end cap parts will reach 0.89 • monolayer location resolution in Φ direction is 1.2 cm, • The minimum momentum of muon that can be detected reaches 0.35 GeV , momentum larger than 0.4 GeV, the detection efficiency can reach 95% in different degrees of angle

  32. The Expected Performance (2) Muon separation efficiency and contamination from pion versus momentum

  33. The R&D of Muon counter • The selection of RPC material and research on the technology of surface treatment • The research on readout strip • The choice of gas • The influence of environmental temperature and humidity • The choice of spacer and sealed material • The shape and the structure of the spacer and seal frame • To make a test model according to the design of RPC and carry out an overall test of its performance

  34. Schedule

  35. Estimated Budget

  36. Thanks

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