1. Beam Test Result Jeewon SEO World lab fellow

2. T10 Beam Test 14. Oct. ~ 20. Nov. 2009 ALICE TOF 10 gap chamber and 24 gap MRPC was tested with different percentages of SF 6. SF 6 ◦ Property : Highly electronegative ◦ Disadvantages  Expensive cost  Global warming gas

3. 10 Gap MRPC Gap size : 250 ㎛ Aluminum box volume : 200ℓ Gas flow rate : 20ℓ/h (O 2 content was kept at 100 ppm)

4. Beam Test Setup -5GeV/c beam of π -, μ -. Trigger selected 10 ㎜ⅹ 10 ㎜ beam spot (130 triggers/spill in every 20 seconds)

5. Data Acquisition

6. Slewing Correction Time = T chamber – T ave T ave : average time of the timing scintillators

7. Time Resolution σ res = √( σ ch 2 -σ sc 2 ) σ res : time resolution σ ch : measured time of signals σ sc : jiter of scintillators Ave(S1,S2)-Ave(S3,S4)

8. Efficiency and Streamer Plateau SF60 %2 %4 %6 %8 %10 % Streamer free and efficient >90% operation range 10.6~11.6 kV10.8~13 kV11~13.2 kV11.2~13.4 kV11.4~13.6 kV11.6~13.8 kV 1 kV2.2 kV The knee of the efficiency plateau moves to high voltage when the percentage of SF 6 increase. Breakdown at 11.8 kV with the pure freon Break down at 11.8kV with pure freon Break down at 11.8kV with pure freon

9. Time resolution with various percentage of SF 6 Time resolution is independent of the fraction of SF6.

10. 24 Gap MRPC 160 ㎛ gaps (total thickness : 3.84 ㎜ ) Gas flow rate : 20ℓ/h (box volume : 30ℓ) -> O 2 content was kept at 20 ppm Threshold : 40 fC

11. Data Acquisition NINO mounted on chamber inside gas volume

12. Compare time of one MRPC with another Time resolution obtained by measuring time difference between two chambers Timing scintillators are not used.

13. Efficiency and Time resolution T diff = (T mean ) MRPC1 -(T mean ) MRPC2 The best resolution is 20.8 ps with pure freon and 19.1 ps with added 5% SF 6. Efficiency plateau is shifted to a lower voltage with the pure freon. The streamer-free and efficient operation range Pure freon : 1.6 kV (10.6kV ~ 12.2kV) 5% SF 6 : 2 kV (11kV ~ 13 kV)

14. Conclusion 10 gap MRPC ◦ Break down at 11.8kV with pure freon. ◦ Work with 2% SF 6, obtaining the time resolution below 50 ps with a 2.2 kV range. -> Seems to need the SF6 to avoid breakdown 24 gap MRPC ◦ Work satisfactorily with pure freon SF 6 effect ◦ Shift the efficiency plateau to a higher voltage ◦ Shift in streamer production to higher voltage ◦ For 24 gap MRPC, the efficient operation range without streamer is broader when SF6 added. Time resolution is independent of SF 6 fraction.