ALICE muon trigger (bakelite RPCs): performance and issues Dark rate - - PowerPoint PPT Presentation

ALICE muon trigger (bakelite RPCs): performance and issues

Performance:

• Efficiency: stable and uniform (>95%)
• Cluster size: stable and in line with R&D values
• Dark rate: stable, < 0.05 Hz/cm2
• Dark current: globally stable

Issues:

• A few RPCs show an important increase of

dark current (apparently not correlated with the integrated charge)

• A few issues with gas tightness

(mechanical stress on beaks at in/outlets) Average RPC current vs average RPC hit rate

Dark rate distribution 2011 vs Dark rate distribution 2013

Average RPC efficiency vs time

ALICE muon trigger (bakelite RPCs): extrapolation to Run 2, 3 and 4

JINST 7 T12002 (2012)

• Extrapolated Mhits/cm2 at the end of Run 2: 165 on average, 290 for the most exposed RPC
• Extrapolated Mhits/cm2 at the end of Run 4: 300 on average, 500 for the most exposed RPC

N.B. : these extrapolated rates and fluences do not include any safety factors Beam and ageing tests (Nucl. Phys. B.PS 158 2006 149) in the present running mode: rate capability ~60 Hz/cm2 , certified lifetime ~500 Mhits/cm2

• > operation in Run 3 and Run 4 is at the limit of the detector capabilities

in the present running mode (maxi avalanche, charge/hit ~ 100 pC)

• > upgrade the FEE electronics by adding amplification, so that RPCs can work at lower gain
• Based on the measured correlation between

luminosity and counting rate (extrapolation + energy rescaling)

• Counting rate in Pb-Pb at 6x1027s-1cm-2 :

30 Hz/cm2 on average 55 Hz/cm2 for the most exposed RPC

• Counting rate in pp at 1031 s-1 cm-2:

9 Hz/cm2 on average 15 Hz/cm2 for the most exposed RPC (does not include the rate from beam-gas, which could be on the same order of magnitude)

ALICE : Muon Tracking cathode pad chamber performance during RUN I

• The Muon Tracking detector managed to collect high

precision data for physics analysis.

• The cluster charge distribution over different data

taking periods are very similar.

• The variation of the peak of cluster charge

distribution is due the different voltage setup.

• The Muon Tracker achieved position resolution of

250 𝜈𝑛 and 800 𝜈𝑛 in the bending and non-bending planes, respectively.

• Most importantly, Muon Tracker managed to measure

the 𝐾/𝜔 and Υ resonances at mass resolution of ~70 MeV and ~100 MeV, respectively, which was the design criteria of the detector.

TOF matching efficiency defined as the ratio of the tracks matched at TOF to those reconstructed using the ALICE tracking detectors. It is not the MRPC efficiency because it is also affected by:

• TOF geometrical acceptance
• Uncertainties in the track extrapolation
• Interaction with materials in front of the TOF
• Track-TOF matching algorithm inefficiency

Agreement between data and MC within 1%. MRPC detection efficiency in the MC is set to 98.5%, determined by assuming 99.5% of efficiency in the center of the readout pads, as measured from test beam results, and a small drop close to the pad boundaries

(GeV/c)

T

p

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

TOF matching efficiency

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Data p-Pb January 2013 Data pp May 2012 Data pp March 2011

The TOF matching efficiency was stable throughout the

• years. The bump at low pT is due to different material

budget in front of the TOF before and after 2012.

ALICE TOF (glass MRPCs): performance and issues

(GeV/c)

T

p

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

TOF matching efficiency

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

MC p-Pb 2013 Data p-Pb 2013

(GeV/c)

T

p 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Ratio

0.9 1 1.1

• Eur. Phys. J. Plus Volume 128,

Issue 4 (2013)

• active are of 141 m2, 152928 readout

channels.

• made of 1593 glass MRPCs (10 gas gaps 250

μm width) operated in saturated avalanche mode.

• gas mixture C2H2F4/SF6 (93:7).
• low noise rate ≈ 0.5 Hz/pad (1 pad = 2.5 ×

3.5 cm2 pick-up element).

• Eur. Phys. J. Plus Volume 128,

Issue 4 (2013)

ALICE TOF (glass MRPCs): performance and issues

The MRPCs current increased linearly with the LHC luminosity with no sign of the deviations related to the

• ccurrence of abnormal noise current.

Charged particle rate at TOF has been estimated offline considering the TOF raw hit multiplicity per event and the ALICE interaction rate. From this rate and the total current of the MRPCs we compute an average induced charge of 6 pC per track.

• Eur. Phys. J. Plus Volume 128,

Issue 4 (2013)

ISSUES:

• 25 out of 1593 (1.6%) MRPCs OFF at the end of Run 1 due to HV failures. Problems not in the MRPCs

(no high currents nor discharges between anode and cathode), most probably in the HV connectors or

• distributors. Problems are inside the gas tight volume or in zone difficult to access. Not clear whether

we can improve that situation during LS1.

• Major troubles in Run1 due to LV power supplies working in B-field (DCDC converters). New design

validated (no failures with a sample of new DCDCs operated in ALICE during all 2012), full replacement under way.

• Few % of readout channels OFF due to broken or noisy readout electronics boards.

Current drawn in p-Pb at 1029 cm-2s-1 was ~ 130μA (less than 100nA per MRPC

• r 1 uA/m2).

Estimated rate in p-Pb at 1029 cm-2s-1 is ~ 14 Hz/cm2 (good agreement with expectations from FLUKA simulations).

• avg. lumi = 2.4 1027 cm-2s-1
• max. lumi = 6 1027 cm-2s-1
• Integrated charge at the end of Run1: 0.2 mC/cm2
• Extrapolated charge at the end of Phase I: 1.9 mC/cm2
• Extrapolated charge at the end of Phase II: 2.8 mC/cm2

Calculations doesn’t account for beam-gas (results should not change significantly) With ageing tests at CERN GIF we didn’t observe any sign of degradation nor increase of dark current after collecting a total amount of 14 mC/cm2. A search for HF in the outgoing gas, using gas chromatography, gave negative results (below 0.02 ppm). A MRPC that collected a charge of 10 mC/cm2 was carefully measured before and after irradiation; we did not observe any efficiency and time resolution degradation (Nucl. Instr. Meth. A 533 (2004) 93–97). NO UPGRADE FORESEEN

ALICE TOF (glass MRPCs): extrapolated background

• Charged particle rate in Pb-Pb at 2.4

1027cm-2s-1 : 38 Hz/cm2

• Charged particle rate in Pb-Pb at 6 1027cm-

2s-1 : 94 Hz/cm2

MRPCs tested at CERN GIF showed no loss in performance up to 1 kHz/cm2 (Nucl. Instr. Meth. A490(2002) 58). Pb-Pb at 6 1027cm-2s-1 (5.5 TeV/NN) from FLUKA: 95 Hz/cm2

Scenarios used in the extrapolations (1/2)

Year System Luminosity 2015 pp – min bias (24 weeks) 1029-1030 cm-2s-1 Pb-Pb – 4 weeks 1027 cm-2s-1 - leveled 2016 pp – rare triggers (24 weeks) 5-10 1030 cm-2s-1 Pb-Pb – 4 weeks 1027 cm-2s-1 - leveled 2017 pp – rare triggers (24 weeks) 5-10 1030 cm-2s-1 p-Pb – min bias (2 weeks) 0.5-1 1028 cm-2s-1 - leveled p-Pb – rare triggers (2 weeks) 1 1029 cm-2s-1 - leveled RUN2: RUN3: 2020 pp (1y for detector recommissioning) 6 1030 cm-2s-1 2021 Pb-Pb 2.85 nb-1 2.4 1027 cm-2s-1 - leveled 2022 Pb-Pb 2.85 nb-1 at low magnetic field 2.4 1027 cm-2s-1 - leveled

• Table from RLIUP workshop (29-31 October 2013). In the above calculations we

considered scenarios with largest luminosity values.

• Values from ALICE Upgrade LoI. For pp we considered the peak luminosity.

Scenarios used in the extrapolations (2/2)

Year System Luminosity 2025 pp (1y for detector recommissioning) 6 1030 cm-2s-1 2026 Pb-Pb 2.85 nb-1 2.4 1027 cm-2s-1 - leveled 2027 Pb-Pb 1.42 nb-1 2.4 1027 cm-2s-1 - leveled p-Pb 50nb-1 1029 cm-2s-1 - leveled 2028 Pb-Pb 2.85 nb-1 2.4 1027 cm-2s-1 - leveled RUN4:

• Values from ALICE Upgrade LoI. For pp we considered the peak luminosity.