BESIII detector --- design considerations and its realization

1. BESIII detector --- design considerations and its realization Yifang Wang

2. 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, …)

3. 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

4. 多丝 电磁 强子 µ 子室 径迹室 量能器 量能器

6. BESIII 探测器

7. 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

8. 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

9. Why helium based drift chamber • Choice between drift chamber and • TEC: 50 ms, too high material budget • TPC: 200 ms: 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 ms • Balance between wires, multiple scattering, … • Experience at IHEP for large wire chambers • Cost

10. 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

11. 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

12. 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

13. No hadron calorimeter • Low energy • Segmented muon chamber partially for it

14. 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

15. 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

16. 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

17. Experience • Good choice of contractor • Reasonably organized • Lack of experience • Problems: • Assembly • Valve box • Vacuum • Successfully tested on Sep. 19 at 8:00 am

18. 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

19. Good technical support • Grounding • Radiation monitoring • Slow control • Cooling • Gas • electricity

20. 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

21. Cost control Example: CsI, SSM • 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: MDC mechanics magnet yoke VME crates

22. Risk analysis and control • Single out the risky item • SSM • Single out the risky process • Winding • Prototyping • Know how • Organization: make sure no mistakes

23. Quality control • Rules and regulations • Documentation • Education • Process control • Regular inspection • Review

24. 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

25. 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