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
23
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
25
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