1. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 1 VETO AND XPC: Preliminary ideas Outline: Mechanical structure Gas mixture study Aging tests Glass RPC R&D Conclusion

2. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 2 Mechanical structure Mechanical structure The XPC frame drawing is ready (E.Tatananni). A real scale prototype (1,46x9 m2) is foreseen for the end of the year. Frame calculations (C. Zarra) NOT concluded because personal problems of Chiara. We need an engineer for it (XPC, VETO and glass RPC)

3. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 3 Float Glass: Bakelite Stable resistivity (hopping conductivity)  =10 12 -10 13  cm at normal temperature Resistivity depends only on temperature  =  0 10 (T-20)/25 Well known industrial technology BELLE EXPERIMENT  =10 10 -10 12  cm at normal temperature resistivity increases with the integrated charge (ionic conductivity) Need a surface treatment with linseed oil L3, BaBar ARGO EXPERIMENTS 2 kV compound

4. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 4 gas study (1) We have been tested 4 components gas mixture (argon+TFE+Isobutane+SF6) With this choice the presence of an avalanche precursor is apparent The precursor is prompt (good timing), the streamer is not (large jitter) The electronics exploit the good timing of precursor (low thr) and the big amplitude of streamer (high thr=noise suppressor) precursor streamer

5. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 5 gas study (2)

6. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 6 gas study (3) single streamer peak Multistreamer peaks Efficiency knee

7. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 7 gas study (time resolution) By using SF6 + proper electronics: 1 ns resolution “everywhere” (safe operation) Efficiency knee

8. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 8 gas study (time resolution) Single thr time distribution (knee voltage) Double thr time distroibution (knee voltage) Gaussian shape TFE+argon +isobutane+SF6=48+47+4+1 % Single threshold distribution Precursor driven distribution

9. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 9 OPERA: gas study (charge) With SF 6 the peak charge is 1/3 than w/o. The afterpulses increases for TFE<48% and/or Isobutane<4% No SF6

10. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 10 OPERA: gas study (summary) No SF6 SF6>0.6% small streamer, big precursor ISO-butane>4% photon absorption TFE>48% little afterpulsing TFE>36% good timing

11. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 11 Aging: long term operation After 5 months of operation, better performance (lower counting level). Tests are still in progress

12. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 12 Aging: GIF irradiation Good efficiency after 7 mC/cm2 (corresponding to more than 30 years of operation in the hall C)

13. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 13 Aging: temperature tests Avalanche modeStreamer mode Differently from Bakelite, Glass RPC do not suffer high temperatures

14. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 14 Aging: humidity test Water vapour seriously damages the Glass RPC: It is a threshold effect

15. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 15 Aging: Glass RPC recovery Bubbling the gas through 28% ammonia there is a full recovery after 2 weeks

16. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 16 RPC design: new spacers No glue overflowing electrode glue spacer Field lines never cross the spacer (no charging up)

17. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 17 RPC production Real scale prototype from: GT (glass and bachelite) G&A (glass) LNGS (reference detectors)

18. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 18 Time schedule (XPC): Mechanical structure XPC): Final design ready: to be discussed with magnet, TT and PT people. december: real scale model Glass RPC R&D July: large area prototype with 2 and 3 mm glass electrodes. End of the year: choice between glass and bachelite

19. C.Gustavino, XPC and VETO, LNGS OPERA meeting, may 2003 19 VETO System: Same conceptual structure and detectors as XPC. Schedule and responsability must be defined soon.