Latest background observations in ALICE

A. Alici (INFN, Bologna), A. Di Mauro (CERN)LBS, 19/09/11

ALICE status after TS

All fills from 2090 to 2103 could not be used, ALICE was safe all the timePhysics 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

Two weeks ago vacuum around P2

3

FILL 2093

FILL 2092

FILL 2090FILL 2091 FILL 2094

FILL 2086

FILLS 2092-2100, V0-AND rate

4

542 KHz

FILL 2092

5

542 KHz

Last week vacuum around P2

6

FILL 2124

FILL 2117FILL 2110

FILL 2105FILL 2104

FILL 2103FILL 2101

RC improvment,TDI degradation in fill

FILL 2104

7

FILL 2105

8

FILL 2110

9

FILL 2110

10

FILL 2117

11

FILL 2117

12

FILL 2124

13

FILL 2124

14

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

V0AND vs Bran

15

run 159285see next slide

bkgd/all (MinBias) normalized @ L=1Hz/ub vs. vacuum pressure (VGPB.123.4L2)

BKGD vs p (after TDI) before TS

run 159285

FILL 2029

p=1.1E-8 mbarr=140kHz

BG side A 4.8%

BG side C 0.3%run 123L 123R 514L 514R

159379 1.2E-8 1.9E-9 1.4E-8 1.3E-9

FILL 2032

run 123L 123R 514L 514R

158875 1.2E-8 1E-9 1.1E-8 1E-9

run 123L 123R 514L 514R

158777 1.1E-8 2E-9 2E-8 1.4E-8

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

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%)

run 123L 123R 514L 514R

161129 3.5E-9 5E-9 2.5E-8 3.8E-8

run 123L 123R 514L 514R

161088 1.2E-9 7.5E-9 3.3E-8 6.2E-8

FILL 2104

FILL 2105

Effect of RC vacuum after TS

Conclusions

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 largerTarget pressure for acceptable bkgd is ~3x10-9 mbar

21

Backup slides

22

ALICE layout

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Beam 1

Beam 2

BCM C 7 sensorsz = -18.5 m, r=10 cm

BCM-A8 sensorsz = + 6 m, r = 10 cm

The V0 detector

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Two arrays of scintillator counters (V0A and V0C). Time spectra allow beam-gas events rejection

V0A SPD

340 cm 90 cm

V0Arin=8 cm rout=100 cm

V0Crin=8 cm rout= 76 cm

ITS

V0C

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beam1

IP

340cm~11.3ns

90cm~3ns

V0A V0C

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