1998 IEEE Nuclear Science Symposium, Toronto, Canada High-Precision, Large-Volume Particle Tracking U. Bratzler* Outline (Example: Muon Tracking in ATLAS)

1998 IEEE Nuclear Science Symposium, Toronto, Canada

High-Precision, Large-Volume

Particle Tracking

U. Bratzler*

Outline(Example: Muon Tracking in ATLAS)• Introduction• Requirements• Tracking System• Performance• Summary

Tracking in High Energy and Nuclear Physics, N3-1, November 10, 1998

*Mailing Address: MPI fuer Physik, Foehringer Ring 6, D-80805 Munich, Germany

U. Bratzler; NSS98, High-Precision, Large-Volume, Particle Tracking - Introduction

ATLAS Detector

Outer Dimensions: ~22 m x 40 mp-p collisions at E(CM) = 14 TeVLuminosity = 1034 /cm2/s

Muon Momentum Measurement

Muon Momentum Measurement

Tracking volume: Three measuring “stations” (I=Inner, M=Middle, O=Outer)Barrel: sagitta in middle station (vector-vector measurement in two stations)Endcaps: point-angle measurement

Toroidal B-Field, 0.5-2 T, parallel to chamber wires---> defines particle track bending plane (R-Z)Magnet: Superconducting air-core system, 8 coils in barrel, 8 coils in each endcap.

U. Bratzler; High-Precision, Large-Volume, Particle Tracking - Introduction

Tracking: MDTs, CSCs; Trigger: RPCs, TGCs)

BI

BM

BO

EM EO

EI

-track

-track

Z

R

RequirementsMuon momentum measurement precision:

Typical values: ~2 % for 100 GeV Muons ~10% for 1 TeV Muons

===> Requirement for tracking precisionTypical deflection/bending of 1 TeV Muons: 500 m

===> Track measuring accuracy: 50 m (rms) (sagitta alignment error: < 30 m (rms))

===> Requires very precise knowledge of sense wire positions of tracking chambers throughout the tracking volume.

Additionally: ATLAS/LHC Conditionsp-p bunch crossing rate: 40 MHz (~15 evts/crossing)Background: ~ 10-100 Hz/cm2, up to 1 kHz/cm2

Typical operation duration: 10-15 yearsLarge-volume/large-area detector coverage==>efficient, economic, chamber production, high mechanical precision, light/stiffness, ‘granularity’, long-term robustness/aging.

U. Bratzler; High-Precision, Large-Volume, Particle Tracking - Requirements

Example: Momentum Resolution Degradation

===> Mechanical precision, alignment essential. Plus: detector (drift tube) spatial resolution.


Example: Background Rates


===> Tracking chambers must work in particle background environment.

Tracking System

Decision for:

Large-area coverage with drift tube chambers,special chambers for high particle flux regions.

Design Philosophy:

Build muon chambers as precise as possible

plus

Monitor and record their mechanicaldeformations, starting at production, and

monitor chamber positions in ATLAS,through the lifetime of the experiment.

Monitored Drift Tube (MDT) Chambers(Cathode Strip Chambers for large -regions)

U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Tacking System

U. Bratzler; High-Precision, Large-Volume Particle Tracking - Tracking System

Muon System Layout

MDT Chambers:•1,200 chambers, 370,000 channels (tubes), total area: 5,500 m2

(Three layers, in Endcap and Barrel; projective to IP)

Cathode Strip Chambers:•67,000 channels, 32 chambers, area: 27 m2

The Monitored Drift Tube (MDT) Chamber

2 Multilayers (~ 400 Al tubes with sense wires)Multilayer: 3 or 4 layers of tubesSpacer support structure, 4 alignment monitors

Typical size: 2 m x 4 m x 0.3 mPrecision: ~ 400 wire positions known to 20 m (RMS)

Match of gravitational sags. (ECs: trapezoidal)


Chamber Instrumentation


• Multi-board system (pre-amps, ASDs, DCS, TDC) • Gas service bar, inter-tube gas connections• Faraday cages

Front-EndElectronics

Leading and trailing edges, slope of leading edge,multi-hit information

The Monitored Drift Tube

Tube: high-precision Al extrusion - cathode diameter: 30 mm, wall thickness: 400 m, typical length: 4 m

Wire: W-Re, gold-plated, 50-m diam. - anode

Endplugs: gas, H.V./signal, wire precision.

Challenge:Wire centering to < 10 m, 370,000 MDTs, costs.

Tolerances on:Length: +0.5 mm, wall thickness: +20 m, OD: +0 m -30 m, straightness: 30 m/30 cm

U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Tracking System

Alignment


Example: Barrel Chambers (I, M, O stations)

In-plane: 4 independent systems, 3-point meas.Projective (IP): aligns chamber stationsAxial (Z-axis): aligns chambers along beam axis (multi-point alignment systems).Typical Chamber alignment precision: ~20 m.(Alignment systems intrins. precision: ~1-5 m.)

Alignment Systems

RASNIK System: 3-point relative alignm. system

ALMY-MPA System: multi-point system (~10)


CCD with ~ 400,000 pixels, pixel size ~ 7 x 7 m2

arbitrary large mask (range) Precision: ~ 1 m, rotations: ~ 25 rad

Two-sided transparentSi strip detectors20 x 20 to 30 x 30 mm2

Laser Diode, single-modeoptical fibers, collimator,2 mm Gaussian profileMeasure charge distrib.on Si strips

Precision: < 5 m, rotations: 3 to 10 rad (calibr.)Other systems: BCAM, STAMP

Examples:

[Backup]

Alignment Systems (cont.)

STAMP System:

BCAM System:


Note: Names of proposed systems indicate application type and/or institute where developped.

PerformanceMonitored Drift Tube(Proportional drift tube)Gas pressure: 3 bar absGas gain: 2 x 104

Gas mixuture: Ar/CO2

- other gases are beinginvestigated (ageing)Typical H.V: 3.25 kV,vd: ~30 m/nsTrack position: from measured td

Spatial resolution: < 80 m

Example:

U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Performance

Particle Backgrounds, Pulse Height, Resolution

U. Bratzler; High-Precision, Large-Volume, Particle Tracking - Performance

Photon Background (other tests):High-intensity muon beam (up to 200 Hz/cm2)plus 3.7 MBq 60Co-source ---> photon background: 100 Hz/cm2

Note: 600 keV photons from 60Co ---> comptonscattering off e- in Al ===> similar to mainbackground processes at LHC===> Average resolution deterioration: 5% (10-200 Hz/cm2)Res. deterioration due to rate effects acceptable.

Data points: measureddeteriorationof gas gainas function ofmuon rate (solid curve: simulation)

System Tracking Performance


Note: 4 tube layers/multilayer (“444”)Typical track reconstruction efficiencies: 98% (444), 97% (333) (with particle occupancy of < 5 %)

Typical event (simulated) where one muon trackis found and registered by all MDT stations - inpresence of typical expected LHC background:

Detector System Acceptance and Momentum Resolution

U. Bratzler; High-Precision, Large-Volume, Particle Tracking - Performance

DATCHA - Demonstration of ATLAS CHamber AlignmentAlignment system tests with real-size chamberstations (CERN and SACLAY).Example: CERN setup, using cosmic rays:


===>Alignment system monitors chamber movements well below 10 m level.

Summary

U. Bratzler; High-Precision, Large-Volume, Particle Tracking - Summary

From numerous prototype constructions, perform-ance simulations, DATCHA and other extensive tests, one can expect:

• All chambers needed produced within coming 4-5 years (~ 2 weeks per chamber, at 14 production sites), within specifications and cost.

• Alignment systems fulfill specifications, monitor chambers with micron precision.===> Muon tracking precision: 50 m===> Design momentum resolution, with values: 2% for 100 GeV muons, 10% for 1 TeV muons.• Detector Layout: good detector coverage, employing a system of 1,200 chambers, with total active area of 5,500 m2.

• Track reconstruction efficiency of ~97 % (tower) [Physics events: di-, four-: 80-95 % range.]

Realizable with the concept of Monitored DriftTube Chambers (large-area coverage), andCathode Strip Chambers for high flux regions.

1998 IEEE Nuclear Science Symposium, Toronto, Canada High-Precision, Large-Volume Particle Tracking U. Bratzler* Outline (Example: Muon Tracking in ATLAS)

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