The ZEUS Micro Vertex Detector

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The ZEUS Micro Vertex Detector
Vertex 2001 Workshop Brunnen, Switzerland 23-28
September 2001

• Vincenzo Chiochia
• DESY - Hamburg
• for the ZEUS MVD Group

ZEUS MVD Group Bonn Univ., DESY-Hamburg,
DESY-Zeuthen, Hamburg Univ., KEK-Japan, NIKHEF,
Oxford Univ., Padova, Torino, Bologna, Firenze
Univ. and INFN, UCL.
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Outlook

• Technical specifications and design
• Assembly steps
• Detector tests before installation
• Measurements with cosmic ray setup
• Test Beam measurements
• Radiation monitoring

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Technical requirements and design constraints for
a vertex detector

• Requirements
• Three spatial measurements in two projections for
  each track
• lt20 mm intrinsic hit resolution for perpendicular
  tracks
• Impact parameter resolution of order 100 mm
• High efficiency (gt97)

• Constraints
• Elliptical beampipe to give space to synchrotron
  radiation (max diameter 12 cm)
• Central Tracker inner diameter 32 cm
• Bunch crossing time 96 ns
• Operating at room temperature
• Extended interaction region in z direction

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The MVD layout
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Silicon microstrip detectors

• n-doped silicon wafers (300 mm thickness) with p
  implantations (12 or 14 mm wide), HAMAMATSU PH.
  K.K.
• 512 readout channels.
• Using the capacitive charge sharing, the
  analogue readout of one strip every 6 allows a
  good resolution (lt20 mm) despite the readout
  pitch of 120 mm.
• Highest coupling to the front end electronics if
  

Cc gtgt Cint gt Cb
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Ladder and module structure
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Production summary

• Half-Modules production
• Front-end chips Helix 3.0, 0.8 mm CMOS AMS, 128
  channels. 70 wafers (58 chip/wafer). Yield 70
• Hybrids Test of 4 chips in chain
• Final yield after improvement of production and
  transportation 70.
• Detectors
• Category A Idarklt10 mA _at_ 200 V category B
  Idarklt50 mA _at_ 100 V
• Overall yield after Long Term Test 94.5 (6
  production steps)
• Overall yield between hybrid gluing and laser
  scan 98.3 (3 production steps)

• Ladder production
• Consists of positioning, gluing and 3D survey.
• Readout tests before and after module gluing
• Total of 30 pieces produced plus 2 spares and 1
  prototype.
• 4 rejected Half-Modules

• Wheel production
• 4 wheels produced. 4 weeks assembly. 1.5 year
  overall
• 2 damaged modules during assembly
• Tests Electrical, laser scan, survey

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Ladder installation

• Half cylinder
• 15 ladders
• 300 sensors, 75.000 channels
• Assembly 7 weeks
• 2 technicians 2 physicists
• Full time

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3D survey
forward flange overview

• Bullets position compared to design

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Wheels assembly

• L-shaped carbon fiber half ring with seven
  straight sections
• Supported by three points to half cylinder

• The sensors are mounted side by side and stagged
  by 3 mm with an active overlap of 2 mm
• The long side of the support provides housing for
  cooling pipes and supports the hybrides

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Laser alignment measurement
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Assembly timeline

• Feb-Oct 00 303 ladders produced at NIKHEF (1.5
  ladder/week)
• Mid Oct 00 Start read out chain preparation at
  DESY. First tests with a prototype ladder
• Oct-Dec 00 Bottom MVD half assembly (15
  ladders4 half wheels) at NIKHEF
• Mid Dec 00 MVD bottom half at DESY. Start laser
  alignment measurements and read out tests
• Dec-Feb 00/01 Top MVD half assembly at NIKHEF
• Mid Feb 01 MVD top half at DESY. Start tests
• End Feb Beam pipe and radiation monitor diodes
  installation. Assembly of two MVD halves
• Mar 01 Cosmic ray run with scintillator trigger
  (4 weeks). 2.5 Million events on disk!
• End Mar 01 MVD installation in ZEUS

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System test with cosmic rays

• Extensive tests of detector electronics before
  installation
• At arrival, check response of readout chips after
  programming sequence (fast scope test)
• Proceed with acquisition in random trigger mode
• Noise distributions in all modules and
  calibration files
• Data acquisition with scintillators trigger
• The full final VME read out chain and slow
  control has been assembled and tested before the
  installation
• Test of ADCs acquisition modes (pedestal
  subtraction, zero suppression, clustering)
• High/Low Voltage, humidity, temperature and drip
  sensors, etc.

Faulty full modules 4 of 206
(2 recoverable) Faulty single hybrids 1
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Cosmic test results

• Position reconstruction with a center of gravity
  algorithm
• Require hits in two modules of outer layer
• Kalman fit with straight line

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Cosmic test results
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Test of detector I/V properties

• During the system test we have observed
  increasing leakage currents in some modules.
  Further studies have shown
• At decreasing temperature the relative humidity
  rises and the breakdown voltage decreases
• Relation between leakage current and temperature
  is well known

A careful checking and control of the humidity
is required for the ZEUS MVD!
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Hit reconstruction

• Non linear algorithm h (2 strips)
• where
• Algorithm balance of 3 strips
• where posleft/right represent the centers
  of gravity between the central and lateral
  strips

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Hit reconstruction test beam results
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Radiation Monitoring

• Sources protons, electron, synchrotron radiation
• Three independent measurement systems
• 1 ms 16 PIN diodes in 8 modules (zfwd110,
  zrear-100 cm) ? beam dump
• 30 min 8 Radfets (zfwd200, zrear-160 cm)
• 1 month 6 TLDs (Thermo Luminescent Dosimeters),
  sensitive to g and neutrons

• 1krad absorbed so far (diode measurements,
  confirmed by radfets)
• Max expected dose 50 krad/year
• Final system commissioned

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Final remarks

• Assembly, overall tests and installation of the
  ZEUS MVD have been successfully completed.
• System test data show very good performances
• Detector has run smoothly for 4 weeks under bias
• Only 2 faulty modules. 70 mm track resolution
  already achieved!
• Leakage current of our sensors depends on
  humidity. Need to control air flow in the
  detector
• Analysis of test beam data has shown that a hit
  resolution better then 20 mm can be achieved
  despite the read out pitch of 120 mm
• HERA machine tuning in progress. ZEUS
  contributing with three independent measurements
  of radiation dose
• Luminosity run foreseen January

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OTHER SLIDES
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Half Modules production summary

• Single sensor I/V measurements Yield 99.7
• HM gluing 421 half modules
• Upilex connector gluing 420
• Diode bonding 406
• Long term test 398
• Hybrid gluing 358
• Hybrid bonding 354
• Laser Test 352
• Shipped to NIKHEF 344

Not all Half Modules have been bonded to hybrid
circuits
To ladder production
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HERA II and ZEUS Upgrade

• Increase instantaneous luminosity by a factor 5
• instantaneous expected
• L 7.5 1031cm-2 s-1
• delivered per year 150 pb-1

• General upgrade of the tracking system
• Silicon Microvertex Detector (MVD)
• Straw Tube Tracker (STT)

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Half Module production history
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Beam pipe assembly
Beam pipe shielding installation on MVD
bottom Half (rear side view)
Beam pipe shielding
Tubes for Passive radiation Monitors (TLD)
Beam pipe end switches
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Cooling

• Water cooled
• T water 15 Celsius
• T hybrid 25 Celsius
• Stainless steel tubes
• diameter 2.5 - 2.7 mm
• flow 0.25 l/min
• Material budget
• Total 3 X0 per ladder

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Material in a ladder
3 X0
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Total barrel material
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Physics at HERA

• The lepton-proton interaction proceeds via the
  exchange of a virtual vector boson (g, Z, W)
  which plays the role of a probe.

• The usual variables to describe the scattering
  process are
• Q2 -q2 -(k-k)2
• x Q2 / (2pq)
• y (qp) / (kp)
• Given a certain virtuality Q2 the resolution
  power DR of the probe is given by
• DR ?c / Q 0.197 / Q GeVfm