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Update on background conditions in ALICE

A. Alici (Centro Fermi,INFN Bologna) , A. Di Mauro (CERN) LBS, 18/06/12. Update on background conditions in ALICE. ALICE vacuum layout. A. C. A side. 70 m 69.7 m. VGPB.623.4L2. VGI.500.4L2. 120m. C side. 70 m 69.7 m. VGPB.623.4R2. VGI.500.4R2. 120m. 17/05/2012. 2.

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Update on background conditions in ALICE

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  1. A. Alici (Centro Fermi,INFN Bologna) , A. Di Mauro (CERN) LBS, 18/06/12 Update on background conditions in ALICE

  2. ALICE vacuum layout A C A side 70 m 69.7 m VGPB.623.4L2 VGI.500.4L2 120m C side 70 m 69.7 m VGPB.623.4R2 VGI.500.4R2 120m 17/05/2012 2 ALICE background, LBS #37

  3. Introduction • Reminder: • Ideal running condition: vacuum better than ~ 5E-09 mbar in LSS2 and UX25 • Condition to ramp up gaseous detectors: vacuum < 1.5E-08 mbar in LSS2 and UX25 (BKGD rate < 150 KHz) • during winter stop: • sectors on both sides were opened to remove TCTVB and install TCTVA • NEG cartridge has been installed in TDI to improve pumping power • ALICE main trigger detector (V0) , providing BKGD online monitoring (in particular BKGD2 in logging DB), is OFF until running conditions are reached, to prevent ageing (already observed) due to large rates at beginning of fills • Issues for gaseous detectors operation, event size (constraints on trigger modes), integrated luminosity ALICE background, LBS #37

  4. L-side vacuum overview 10/05-16/06 FILL 2735 FILL 2609 1E-8 Vacuum conditions dominated by TDI, p> 1E-08 mbar for most of fills duration, no improvements with time ALICE background, LBS #37

  5. R-side vacuum overview 10/05-16/06 FILL 2609 FILL 2735 Vacuum conditions dominated by large recombination chamber, improving with time ALICE background, LBS #37

  6. L and R Large recombination chambers comparison 10/05-16/06 Impact of TDI (?) Difference between L and R large recombination chamberprobably related to TDI ALICE background, LBS #37

  7. Comparison with 2011 vacuum FILL 2267 (last pp in 2011) FILL 2718 ALICE background, LBS #37

  8. Comparison TDI.4L2 – TDI.4R8 No issues for P8 TDI! ALICE background, LBS #37

  9. BKGD overview 10/05-16/06 KHz BKGD rate at beginning of fill ~ 500 KHz, i.e. 4 times larger than collision rate Gaseous detectors are ramped up when bkgd+collision rate is < 200 KHz ALICE background, LBS #37

  10. FILL 2692 KHz ALICE background, LBS #37

  11. FILL 2712 KHz ALICE background, LBS #37

  12. FILL 2717 KHz ALICE background, LBS #37

  13. FILL 2718 KHz ALICE background, LBS #37

  14. Offline analysis of BKGD in FILL 2621 beam-bkgd side A ≈ 9.8% beam-bkgd side C ≈ 9.5% After Beam-Background removal (V0 timing and SPD cluster vs. tracklet selection) 76% of total triggers left. Data taking started when bkgd2< 100 KHZ ALICE background, LBS #37

  15. FILL 2621 KHz ALICE background, LBS #37

  16. Overview of running time in May-June Data taking with all detectors can start typically after 7 h from SB declaration ALICE background, LBS #37

  17. Impact on physics program • Due to beam induced background MB data taking is quite difficult, switched to RARE triggers running (with small % of MB): • data volume too large (TPC event size > 2MB instead of nominal 600kB) • not possible to record MB data at 900 Hz • critically exceeds storage + bandwidth budget • Integrated luminosity from main-satellites collision scheme is also an issue: • our target luminosity = 2 Hz/ub ~100 kHz V0AND (collision rate) • currently we get 1/3 of “target” luminosity when TPC turns on • Overall trend for target integrated luminosity -> achieved only 3% in RARE and 20% in MB ALICE background, LBS #37

  18. Summary • After increase to 1380 b, vacuum conditions degraded significantly and presently are worst than last ppfills in 2011 • A-side is dominated by TDI, no improvements with NEG cartridge, probably due to high impedance of connection which could not be changed during the winter stop • C-side is dominated by the large vacuum chamber (but overall a factor 3 better than A-side) • ALICE data taking with all detectors is limited to last hours of fills, large background affects also event size and trigger running modes, so far achieved only small fraction of target integrated luminosity ALICE background, LBS #37

  19. Backup slides ALICE background, LBS #37

  20. 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 20 ALICE background, LBS #37

  21. 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 21 ALICE background, LBS #37

  22. V0 timing properties 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 #37

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