1. Latest background observations in ALICE Latest background observations in ALICE A. Alici (INFN, Bologna), A. Di Mauro (CERN) LBS, 19/09/11

2. ALICE status after TS All fills from 2090 to 2103 could not be used, ALICE was safe all the time Physics runs have been taken in fills 2104, 2105, 2110, 2117 and 2124; however, gaseous detectors (including the TPC) could not always be ramped up 2

3. Two weeks ago vacuum around P2 3 FILL 2093 FILL 2092 FILL 2090 FILL 2091 FILL 2094 FILL 2086

4. FILLS 2092-2100, V0-AND rate 4 542 KHz

5. FILL 2092 5 542 KHz

6. Last week vacuum around P2 6 FILL 2124 FILL 2117 FILL 2110 FILL 2105 FILL 2104 FILL 2103 FILL 2101 RC improvment, TDI degradation in fill

7. FILL 2104 7

8. FILL 2105 8

9. FILL 2110 9

10. 10

11. FILL 2117 11

12. FILL 2117 12

13. FILL 2124 13

14. FILL 2124 14 COMPARING FILLS 2117 AND 2124 -> STRONGER CORRELATION OF V0AND WITH VGPB.123 ?

15. V0AND vs Bran 15

16. run 159285 see next slide bkgd/all (MinBias) normalized @ L=1Hz/ub vs. vacuum pressure (VGPB.123.4L2) BKGD vs p (after TDI) before TS

17. run 159285 FILL 2029

18. p=1.1E-8 mbar r=140kHz BG side A 4.8% BG side C 0.3% FILL 2032

19. BG side A 4.3% BG side C 1.8% run158777 L=1Hz/ub run158875 L=1Hz/ub BG side A 4.6% BG side C 0.4% FILL 2010 FILL 2011 Effect of RC vacuum before TS

20. run161088 L=0.6Hz/ub run161129 L=2.4Hz/ub BG side A 9.6% (5.8% ) BG side C 12.3% (7.4%) BG side A 2.2% (5.3%) BG side C 2.4% (5.7%) FILL 2104 FILL 2105 Effect of RC vacuum after TS

21. Conclusions From fill 2110 observed improvement of vacuum and bkgd, still far from status before TS From fill 2110 observed improvement of vacuum and bkgd, still far from status before TS Conditions are still not “optimal”, V0AND ~ 300 KHZ i.e. 4-5 times larger Conditions are still not “optimal”, V0AND ~ 300 KHZ i.e. 4-5 times larger Target pressure for acceptable bkgd is ~3x10 -9 mbar 21

22. Backup slides 22

23. ALICE layout23 Beam 1 Beam 2 BCM C 7 sensors z = -18.5 m, r=10 cm BCM-A 8 sensors z = + 6 m, r = 10 cm

24. The V0 detector24 Two arrays of scintillator counters (V0A and V0C). Time spectra allow beam-gas events rejection V0A SPD 340 cm 90 cm V0A r in =8 cm r out =100 cm V0C r in =8 cm r out = 76 cm ITS V0C

25. 25 beam1 IP 340cm ~11.3ns 90cm ~3ns V0AV0C V0A+V0C ≈ 14.3ns V0A-V0C ≈ 8.3ns beam1 IP ~-11.3ns~3ns V0A+V0C ≈ -8.3ns V0A-V0C ≈ -14.3ns beam2 IP V0A+V0C ≈ 8.3ns V0A-V0C ≈ 14.3ns ~11.3ns~-3ns V0 timing features beam2 collisions Bkgd1 (BGA) Bkgd2 (BGC) CINT1-B Beam background from beam1 Beam background from beam2 satellites