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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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alice vacuum layout
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

introduction
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

l side vacuum overview 10 05 16 06
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

r side vacuum overview 10 05 16 06
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

l and r large recombination chambers comparison 10 05 16 06
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

comparison with 2011 vacuum
Comparison with 2011 vacuum

FILL 2267 (last pp in 2011)

FILL 2718

ALICE background, LBS #37

comparison tdi 4l2 tdi 4r8
Comparison TDI.4L2 – TDI.4R8

No issues for P8 TDI!

ALICE background, LBS #37

bkgd overview 10 05 16 06
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

fill 2692
FILL 2692

KHz

ALICE background, LBS #37

fill 2712
FILL 2712

KHz

ALICE background, LBS #37

fill 2717
FILL 2717

KHz

ALICE background, LBS #37

fill 2718
FILL 2718

KHz

ALICE background, LBS #37

offline analysis of bkgd in fill 2621
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

fill 2621
FILL 2621

KHz

ALICE background, LBS #37

overview of running time in may june
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

impact on physics program
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

summary
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

slide19
Backup slides

ALICE background, LBS #37

alice layout
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

the v0 detector
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

v0 timing properties
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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