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 Munich, Germany

U. Bratzler; NSS98, High- Precision, Large-Volume, Particle Tracking - Introduction ATLAS Detector Outer Dimensions: ~22 m x 40 m p-p collisions at E(CM) = 14 TeV Luminosity = /cm 2 /s 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, 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 Z R

Requirements Muon momentum measurement precision : Typical values: ~2 % for 100 GeV Muons ~10% for 1 TeV Muons ===> Requirement for tracking precision Typical 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 Conditions p-p bunch crossing rate: 40 MHz (~15 evts/crossing) Background: ~ Hz/cm 2, up to 1 kHz/cm 2 Typical operation duration: years Large-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. U. Bratzler; High-Precision, Large-Volume, Particle Tracking - Requirements

Example: Background Rates U. Bratzler; High-Precision, Large-Volume, Particle Tracking - Requirements ===> 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 mechanical deformations, 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 m 2 (Three layers, in Endcap and Barrel; projective to IP) Cathode Strip Chambers: 67,000 channels, 32 chambers, area: 27 m 2

The Monitored Drift Tube (MDT) Chamber 2 Multilayers (~ 400 Al tubes with sense wires) Multilayer: 3 or 4 layers of tubes Spacer support structure, 4 alignment monitors Typical size: 2 m x 4 m x 0.3 m Precision: ~ 400 wire positions known to 20  m (RMS) Match of gravitational sags. (ECs: trapezoidal) U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Tacking System

Chamber Instrumentation U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Tacking System Multi-board system (pre-amps, ASDs, DCS, TDC) Gas service bar, inter-tube gas connections Faraday cages Front-End Electronics 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: 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 U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Tracking System Example: Barrel Chambers (I, M, O stations) In-plane: 4 independent systems, 3-point meas. Projective (IP): aligns chamber stations Axial (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) U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Tracking System CCD with ~ 400,000 pixels, pixel size ~ 7 x 7  m 2 arbitrary large mask (range) Precision: ~ 1  m, rotations: ~ 25  rad Two-sided transparent Si strip detectors 20 x 20 to 30 x 30 mm 2 Laser Diode, single-mode optical fibers, collimator, 2 mm Gaussian profile Measure 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: U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Tracking System Note: Names of proposed systems indicate application type and/or institute where developped.

Performance Monitored Drift Tube (Proportional drift tube) Gas pressure: 3 bar abs Gas gain: 2 x 10 4 Gas mixuture: Ar/CO 2 - other gases are being investigated (ageing) Typical H.V: 3.25 kV, v d : ~30  m/ns Track position: from measured t d 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/cm 2 ) plus 3.7 MBq 60 Co-source ---> photon background: 100 Hz/cm 2 Note: 600 keV photons from 60 Co ---> compton scattering off e - in Al ===> similar to main background processes at LHC ===> Average resolution deterioration: 5% ( Hz/cm 2 ) Res. deterioration due to rate effects acceptable. Data points: measured deterioration of gas gain as function of muon rate (solid curve: simulation)

System Tracking Performance U. Bratzler; High-Precision, Large-Volume, Particle 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 track is found and registered by all MDT stations - in presence 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 Alignment Alignment system tests with real-size chamber stations (CERN and SACLAY). Example: CERN setup, using cosmic rays: U. Bratzler; High-Precision, Large-Volume, Particle Tracking -Performance ===>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 produc- tion 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 m 2. Track reconstruction efficiency of ~97 % (tower) [Physics events: di- , four-  : % range.] Realizable with the concept of Monitored Drift Tube Chambers (large-area coverage), and Cathode Strip Chambers for high flux regions.