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First look at vacuum and background conditions in ALICE

A. Alici (INFN, Bologna), A. Di Mauro (CERN) LBS, 16/04/12. First look at vacuum and background conditions in ALICE. Introductory remarks.

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First look at vacuum and background conditions in ALICE

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  1. A. Alici (INFN, Bologna), A. Di Mauro (CERN) LBS, 16/04/12 First look at vacuum and background conditions in ALICE

  2. Introductory remarks • During Xmas stop two sectors have been opened on both sides of IP2 to remove TCTVB (at ~ 80 m) and insert new TCTVA (at 120 m) (ZDC collimators shadowing issue) • NEG cartridge has been installed on TDI to improve pumping power • Issue with online bkgd rate from V0 trigger detector (large fluctuations), only qualitative assessment available • Few runs reconstructed and available for offline analysis, some preliminary results will be shown ALICE background, LBS #35

  3. ALICE vacuum layout VGPB.623.4L2 120m VGPB.623.4R2 120m ALICE background, LBS #35

  4. FILLS overview and BKGD3 (BCM RS32) FILL 2508 840b FILL 2509 840b FILL 2497 624b B=0 FILL 2500 624b B=0 FILL 2501 624b B=0 FILL 2505 624b B=0 FILL 2493 624b B=0 FILL 2514 1092b FILL 2491 624b FILL 2513 1092b FILL 2516 1092b FILLS 2488 2489 2490 264b ALICE background, LBS #35

  5. Gauges on vacuum chamber, TDI, ex-TCTVB 264b 624b 840b 1092b • 514 (vacuum chamber) silent up to 840b, degradation with 1092b • 231 (TDI) at level comparable to 2011 in same beam conditions • 120 and 123 bad on first fill with 624b, • then slowly recovering, R slightly better than L ALICE background, LBS #35

  6. 768b TDI, Apr 2011 624b

  7. TDI, Apr 2012 624b

  8. Gauges next to new TCTVAs 264b 624b 840b 1092b Jumps related to steps in beam intensity, conditioning in progress ALICE background, LBS #35

  9. Gauges in UX25 624b 264b 840b 1092b * FILLS with B=0 190, 220 and 222 very bad on first fill with B=0 (624b), afterwards slowly recovering, again silent with B on *TRIP OF TPC FIELD CAGE ALICE background, LBS #35

  10. FILLS overview and BKGD4 (V0) 624b 264b 840b 1092b FILLS with B=0 ALICE background, LBS #35

  11. V0 timing V0A V0C IP beam2 beam1 340cm ~11.3ns 90cm ~3ns V0A+V0C ≈ 14.3ns V0A-V0C ≈ 8.3ns collisions IP beam1 ~-11.3ns ~3ns V0A+V0C ≈ -8.3ns V0A-V0C ≈ -14.3ns Bkgd1 (BGA) IP beam2 ~11.3ns ~-3ns V0A+V0C ≈ 8.3ns V0A-V0C ≈ 14.3ns Bkgd2 (BGC) ALICE background, LBS #35

  12. First results from offline analysis Beam background from C side ≈ 30% of total triggers. Beam background from A side ≈ 7% of total triggers.

  13. Larger pressure on R side, in the first hours of the fill RUN 177858 ALICE background, LBS #35

  14. First results from offline analysis Measured background rate per bunch is linearly proportional to the product of the beam intensities and the vacuum pressure in LSS2. 1092 bunches 840 bunches fit to 840b data ALICE background, LBS #35

  15. Summary • As expected, vacuum and beam-gas background issues have been observed, in particular correlated to sectors opened during winter stop • High pressure observed also in UX25 during B=0 fills, improving with time and disappearing when ramping up again ALICE solenoid and dipole • No clear improvement of TDI so far • High BKGD rate (~ 2-300 KHz, depending on vacuum) ALICE background, LBS #35

  16. Backup slides ALICE background, LBS #35

  17. ALICE layout Beam 1 BCM-A 8 sensors z = + 6 m, r = 10 cm Beam 2 BCM C 7 sensors z = -18.5 m, r=10 cm 17 ALICE background, LBS #35

  18. The V0 detector ITS V0A rin=8 cm rout=100 cm V0C rin=8 cm rout= 76 cm SPD V0C V0A 340 cm 90 cm Two arrays of scintillator counters (V0A and V0C). Time spectra allow beam-gas events rejection 18 ALICE background, LBS #35

  19. V0 timing features (example) CINT1-B V0A V0C IP beam2 beam1 340cm ~11.3ns 90cm ~3ns V0A+V0C ≈ 14.3ns V0A-V0C ≈ 8.3ns collisions IP beam1 Beam background from beam2 ~-11.3ns ~3ns V0A+V0C ≈ -8.3ns V0A-V0C ≈ -14.3ns Bkgd1 (BGA) Beam background from beam1 IP satellites beam2 ~11.3ns ~-3ns V0A+V0C ≈ 8.3ns V0A-V0C ≈ 14.3ns Bkgd2 (BGC) ALICE background, LBS #35

  20. V0A V0C V0A V0C V0A V0C IP IP IP beam1 beam2 beam1 beam2 340cm ~11.3ns 90cm ~3ns ~11.3ns ~-3ns ~-11.3ns ~3ns V0A+V0C ≈ 14.3ns V0A-V0C ≈ 8.3ns V0A+V0C ≈ -8.3ns V0A-V0C ≈ -14.3ns V0A+V0C ≈ 8.3ns V0A-V0C ≈ 14.3ns collisions Bkgd2 Bkgd1 ALICE background, LBS #35

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