Post on 19-Jan-2016
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BESIII detector --- design considerations and its
realization
Yifang Wang
Detector design• Physics motivation
• Characteristics of particles(type, energy, angular distribution, …)
• Specifications(range, resolution, …)
• Choice of the detector based on requirements
• Reference of existing apparatus
• Constraints(cost, technology, experience, schedule, …)
What to measure ?• Momentum: tracking detector(gaseous) to measure the
trajectory of particles in a magnetic field
drift chamber , TPC, …
• Energy: scintillator detector(solid , liquid)to measure energy loss of particles
plastic scintillator, liquid scintillator,
Crystal(CsI, NaI, BGO, …), …
• Lifetime: vertex detector(silicon, gaseous)
• Particle PID
gas detector: streamer tube, RPC, … as muon chamber
TOF , Cerenkov
多丝 电磁 强子 µ 子室 径迹室 量能器 量能器
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BESIII BESIII 探测器探测器
Main components
• Small cell, He gas based drift chamber
• CsI(Tl) crystal calorimeter
• Superconducting magnet of 1T
• PID system based on TOF
• RPC muon chamber system
Why no vertex chamber ?• Physics requirement:
– D tagging – Low energy, extremely short vertex– Material budget too high for low energy particles
• Technical challenge:– Silicon detector technology not available in China
• Cost issues– Silicon detector and related equipment very
expensive
• We planed to have a scintillator fiber vertex detector for trigger, but later it was removed
Why helium based drift chamber• Choice between drift chamber and
– TEC: 50 s, too high material budget– TPC: 200 s: worse resolution
• Our choice: – Gas: He+C3H8
• Less material: He• Good balance between dE/dX, multiple scattering, …
– Wires: Al/W • balance between wire types, dimension, …
– Good rate capabilities: small cell– Good single wire resolution ~ 130 s– Balance between wires, multiple scattering, …
• Experience at IHEP for large wire chambers• Cost
Experience • Good choice at the design phase
– Uncertainty: multiple scattering ~ diffusion– Chamber parameters
• Critical item: mechanical structure– Good practice: two prototypes for mechanics– Malpractice: failed twice the endplate
• Well organized other manufacture plan:– Feedthrough– Wiring machine– Carbon fiber structure
• Well organized wiring and testing• Critical path: cosmic-ray test• Final: installation
Why CsI(Tl) Calorimeter
• Good energy resolution
• Good angular resolution
• High cost
• Other choices:– Other crystal calorimeter: too expensive– Lead-fiber: not so good performance– LAr: technically difficult
Experience • Good choice to use CsI(Tl) • Good practice to select three crystal suppliers• Good price• Well organized crystal and component tests• Critical item: Mechanical structure
– Careful design: two major designs– Three independent calculations– Many experimental tests
• To be assembled soon
No hadron calorimeter
• Low energy
• Segmented muon chamber partially for it
Why TOF for PID ?• Many choices:
– Aerogel: not enough light, no space– CCT: not enough light– DIRC: too expensive, no space– MRPC: technically not available, need R&D
• TOF: not a best choice for physics, but a good balance between costs and physics
• Many design options: one or two layers, thickness, wrapping, PMT, scintillator, …
• Good beam tests: first at IHEP• K/Pi separation: 0.8 GeV • Need upgrade
Why RPC for muon chamber
• Choices: – RPC– Streamer tubes
• Why RPC:– No wire, realiable– Low cost– Good future
• Well organized production• Good quality control• Not enough R&D
Why super-conducting magnet• Choice: normal & super-conducting• Pro & cons:
– High costs– High tech & high risk– Good for physics performance
• Good decision: Super-conducting; do-it-ourseves; contract with Wang NMR
• Key items: – supporting structure– Wiring– Assembly & testing– Valve box
Experience
• Good choice of contractor• Reasonably organized• Lack of experience• Problems:
– Assembly– Valve box– Vacuum
• Successfully tested on Sep. 19 at 8:00 am
Electronics, trigger and DAQ
• Many technical choices
• Interface !!!
• Good collaboration with universities
• Mixture of latest and mature technology
• No ASIC
• Good organization
• Good quality control
Good technical support
• Grounding
• Radiation monitoring
• Slow control
• Cooling
• Gas
• electricity
Offline software
• Very late for the software structure
• Lack of manpower: from BELLE
• Pushed by new force: Gaudi
• Well organized, progressing well
• To be tested soon
Cost control• Why:
– Funding never enough– Maximize the physics potential– A basic skill for all physicists
• Detailed investigation • Group examination of budget• A set of rules:
– multi-quotation and comparison– Bidding: MDC machenics– Negotiation– Group purchasing
• Budget control
Example:
CsI, SSM
Example: MDC mechanicsmagnet yoke VME crates
Risk analysis and control
• Single out the risky item– SSM
• Single out the risky process– Winding
• Prototyping
• Know how
• Organization: make sure no mistakes
Quality control• Rules and regulations
• Documentation
• Education
• Process control
• Regular inspection
• Review
Organization: budget and CPM
• Technical design and specification
• Detailed budget: – good for understanding the project – Good for proceeding the project
• CPM Planning– Parallel work– schedule
• Planning: quality, budget and schedule
Summary
• BESIII is an international project– Physics motivation– Technical challenge – Management
• Careful planning is a key for its success
• A unique chance for young students