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

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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