Status & Readiness of the ATLAS Muon Spectrometer

Workshop of the Americas NYU August 4, 2009

J. Chapman - University of Michigan

on behalf of the ATLAS Muon Groups

Particular Thanks to C. Ferretti, D. Levin, E. Diehl & A. Belloni (Harvard)

Overview Status

• Hardware almost completed – Status at closure: – MDT Endcap fibers replaced – RPC nearing 95.5% coverage – TGC ready soon, after 7 months • ATLAS DAQ functioning well – CSC working to reach design L1 rate

• Most data from 2008 runs

• Muon Sub-detector will be ready for collisions!

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Outline

•

Very Quick Detector Description

•

Sub-detectors Status

•

Detector Control System Status

•

Challenges to Precision Calibration

•

Alignment System – next talk

•

Commissioning Results

•

Conclusions

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ATLAS Muon Spectrometer

•

Three stations in an air-core toroidal magnetic field (superconducting) (barrel: |η|<1.4 , endcap: 1.6<|η|<2.7)

• Four different technologies: – Monitored Drift Tubes (MDT): precision chambers in the bending direction – Cathode Strip Chambers (CSC): precision chambers at |η|>2.0

– Resistive Plate Chambers (RPC): trigger |η|<1.05 + 2 nd – Thin Gap Chambers (TGC): trigger 1.05<|η|<2.4 + 2 nd coordinate coordinate MDT CSC RPC TGC #chambers 1150 32 606 3588 #channels 354k 30.7k

373k 318k Resolution (RMS) 35 μm (z&R) 40 μm (R) 10 mm (z) 2-6 mm (R) 3-7 mm (φ) 5 mm (φ) 10 mm (φ) •

Performance goal: stand-alone Δp/p~10% at 1 TeV



sagitta ~ 500 μm along

Q

measured with a resolution ~50μm

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Spectrometer Layout

Side View Beam View

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Muons cross 3 layers of precision chambers for sagitta measurement Trigger chambers are placed on both sides of middle precision layer (+ a few elsewhere)

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Monitored Drift Tubes

• System features low failures – Readout channels: ~0.2% – T-sensors: ~0.3% – B-sensors: ~0.5% – Alignment: ~1-2% • Final actions taken – Fiber replacement C & A side – Replaced a few faulty cards & sensors, sealed gas leaks – Switched barrel mezzanines to 50MHz & exchanged a few cards that did not operate successfully at higher speed • Single-hit efficiency above 99% • Hit resolution near design value Chambers in DAQ (2009)

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MDT Occupancy

1090/1150 Chambers installed – 99.6% operational

TGC vs MDT correlation Lines

↔

noisy channels

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MDT Occupancy – chamber

Φ vs η

Hot spots due to access shafts circled

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EE Chamber Installation

• Additional MDTs – EEL Sector 5 installed – Mounted on Toroid • Other sectors soon – EELA11 next – EELA14 follows

• Side C follows A

– Schedule is uncertain

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RPC Status

• 95.5% operative (out of 396 towers) • < 4% broken HV connectors or electronic components • < 1% leaky gas channels • Temperature problem forces top sectors to run at 9.2kV (9.6kV) 4-August-2009

Workshop of the Americas (NYU) – J. Chapman

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RPC Performance

• Cosmic data provides good evaluation of RPC – Hit efficiency in the high 90% region – expect the tails to be reduced with HV tuning – Resolution is as expected • Timing calibration for trigger is underway

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RPC Performance with MDT tracks

- Events triggered by RPCs with ¾ majority From: G.Aielli

- Only 1 MDT track reconstructed by MuonBoy - Look at 4 th layer when trigger justified offline by 3 layers

BM BM

113860 113860 with HV=9.6kV, Vth=-1V 4-August-2009 normalized to strip pitch

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TGC Status

• • •

All chambers installed with final gas CO 2 : n-C 5 H 12 (55:45) Now: 3 chambers (less than 0.8‰) are problematic TGC trigger worked very well during DAQ periods Fall 2008 data

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TGC trigger timing

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TGC Performance

• Low rate of faulty channels – ~0.02% in Middle Layer – ~0.5% in Inner Layer – No holes in coverage • L1 rate limited to 45kHz – Redundant information removed. Ready for tests • Last runs (HV+gas) in 2008 – MDT/TGC work halted runs – Oil contamination of gas damaged vessel. System will be back mid August 2009

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CSC Status

• 2 of 128 panels unusable – covered by redundancy • New ROD firmware progress – Current status: max L1 rate < 1kHz; – ROD crashes after ~1k events fixed – Test stand & two SLAC engineers at CERN for redesign effort • Commissioning the CSC with cosmics is difficult – Low probability to hit CSC – Only 50k events in 2008 with 199, 4-hit segments in CSC.

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Securing & Maintaining Precision

• Knowing the drift time R-T function & offset t 0 .

– Depends on gas temperature, composition, & pressure – Depends on pulse amplitude (time walk) & wire sag – Depends on electronics delays & trigger timing (t 0 ) • Knowing the chamber alignment & B-field • Sensitivity figures: – Drift velocity at wall is ~20

μ

m/ns (50

μ

m in 2.5ns) –

D

t of 7 o C corresponds to ~ 17ns ( many

s

) – Wire sag for largest chambers ~ 500

m

m – Plots for other variables visible in gas monitor

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•

MDT Detector Control System

The DCS provides initialization of the chambers and reads out

– – – – – –

voltages/temperatures of ~18k F.E. electronic cards and power supply over 13k temperature sensors ~2k Hall probes gas parameters alignment system ...

T>25°C •

Note: 7 o C variation from bottom to top!

T<18°C

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MDT Gas Monitoring & Prompt Calibrations

Recycler

(D. Levin, N. Amram et al)

• Track gas quality via maximum drift time

gas supply line

• Compare behavior of MDT gas for supply and exhaust lines • Precision: below 1ns in the maximum drift time measurement, once/hour • Universal Time-to-Radius (RT) relations published every two hours • Gas volume exchange – Muon Spectrometer ~2 weeks refresh – Gas Monitor ~2 hours

gas exhaust

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MDT gas Drift-time (T max ) & Cavern Humidity

ns D

t

=

720-685ns = 35ns Oct 2007 Dec 2008 • Monitoring TDC spectra continuously since August 2007 • Results displayed at mdtgasmon.grid.umich.edu

• Transients due to gas system interventions or occasional component failures • Overall variation in maximum drift time caused by gas mixture change from – External humidity – Intentional water vapor injection

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MDT Calibration with Cosmic-rays

• Difficult due to asynchronous nature of cosmic rays with LHC clock



25ns and variable TOF between trigger and precision chambers. Recovered by t 0 -tuning algorithm.

• Dedicated L2 stream



3 centers for all chambers in 24h • Collision data critical to obtain final precision

Residuals vs. Radius

t 0

fit 4-August-2009

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Segment Reconstruction Performance

Outer layers Inner layer • • • •

Performance from clean sample: No shower (#segments/event<20) Track passing at least 2 stations Extrapolation pass the 3 Segment on each station rd station

Efficiency(ε)= #Seg(found)/#Seg(expect)

Fall 2008 <ε>=98.4%

4-August-2009

For cosmic rays

o

enlarged single-hit error (1 mm)

o o

relaxed matching angle minimum 3 hits per segment

Workshop of the Americas (NYU) – J. Chapman

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Track Reconstruction

MDT hits distribution peaked at 12, 14 and 20 (expected) Tails: overlap small-large sectors

Number of hits

Track residual ~ 250 μm worse than segment residual (expected): - misalignment - multiple scattering 4-August-2009

Workshop of the Americas (NYU) – J. Chapman

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Inner Detector vs. Spectrometer

Δp(top-bottom) 2 x 3 Gev loss in calorimeters

Cosmic ray passing in the Inner Detector split in two tracks at the perigee.

3 GeV loss in the calorimeter.

MS tracks corrected for the E loss compared with ID tracks ΔP[GeV/c]

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Conclusions

• • • • •

Hardware: status very good (nearing completion) Trigger:

–

Coverage much improved from 2008

–

Timing between detector elements still being tuned Calibration:

–

Calibration centers returning constants in 36 hours

–

Fine tuning of constants awaiting collision data Alignment: Chamber position & orientation known Track segment finding, reconstruction efficiency, & resolution is improving & will continue to improve

Still a lot of work to do, but the ATLAS Muon Spectrometer is ready for beam

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Backup Slides

Alignment Issues

Layers, Locations, & Labels

EO EM EI

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Fake Segments

Form pattern recognition: 1 track should to give 1 segment/station From noise hits: study #segments far from the only track in the event

Fall 2008 avg=1.1

Fall 2008 avg=2.3·10 -4

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ATLAS Muon Detector

4-August-2009

Endcap 1.05<| η|<2.7

three wheels (Small, Big, Outer) of TGC + MDT/CSC Barrel | η|<1.05: I=inner, M=middle, O=outer layers of RPC + MDT in S=small and L=large sectors

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• • • •

MDT/CSC Status

1090/1150 MDT + 32/32 CSC chambers installed Shutdown: recovered ~7k MDT tubes, replaced MDT BW optical fibers, doubled speed for all MDT readout electronics Now: > 99.5 % MDT channels operational and 99.9% of the chambers are read by the ATLAS DAQ + 98.5 % CSC layers Work continuing on CSC readout Driver (ROD) firmware

Inner, Middle and Outer MDT occupancy (Fall 08): sector vs.

ηID

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• • •

Precision Chambers Alignment

Grid of ~12k optical sensors monitoring/reconstructing chamber position, rotation angles and deformations Track-based alignment used for global positions (Endcap Wheels-Barrel and Spectrometer-ID) After shutdown over 99% of the devices working and the degradation due to a few missing sensors is negligible

4-August-2009

Barrel Endcap

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Barrel Alignment: Large vs. Small Sectors

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Alignment in the Barrel

• • •

10 5 μ ± (20 GeV) enough to align at 30 μm (Small sectors: 5×statistics) Initial geometry + alignment traces displacement in relative mode Track + alignment parameters inside one global fit (correlations included)

•

Tracks (magnetic field off runs)

–

Close to the IP (precision plane)

– – –

Traversing 3 stations Straight line fit inner-outer MDT Residuals in the middle chamber ~ sagitta = 22±7 μm

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Alignment in the Endcap

•

Corrected sagitta = 2±27 μm

– – –

3 segments tracks (EI-EM-EO) in the same sector Angle segments-straight line EI-EO segments < 5/50 mrad (sagitta only) At least 1 trigger phi hit (good 2nd coordinate measurement)

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Spectrometer Overview

• Designed to trigger on and measure muons with Pt

≳

GeV with resolution 3% < 250 GeV to 10% @ 1 TeV.

3 • Magnetic field from air-core torroids: barrel + 2 endcap • Trigger detectors (trigger + 2nd coordinate measurement) – 0<

η

<1.0 (Barrel) Resistive Plate Chambers (RPC) 373k chan – 1.0<

η

<2.4 (Endcap) Thin Gap Chambers (TGC) 318k chan • Precision detectors

– 0<η<2.0

Monitored Drift Chambers (MDT) 354k chan – Monitored

⇨

Positions monitored by an alignment system – 2.0<

η

<2.7 Cathode Strip Chambers (CSC) 30.7k chan • Alignment – determine chamber positions to ~50

μ

m – Separate optical alignment systems for barrel & endcap complemented by alignment with tracks

.

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