1. PHOBOS TOF Construction Status
A.B. Hayes, E.B. Johnson,
Robert Pak, R.T.D. Teng,
and F.L.H. Wolfs
University of Rochester
supported by NSF
TAC Review
Brookhaven Nat’l Lab
Nov. 6, 1998
Outline
Detector Configuration:
Baseline
TOF Upgrade
Components & Assembly
Support Structure
Readout Electronics
Summary

2. PHOBOS Baseline Design
Multiplicity Array:
Octagon Barrel
Vertex Detector
Ring Counters
Nearly 4coverage
( < < 5.4 )
Spectrometer Arms:
Detailed measurement
of ptransverse down to
~ 40 MeV/c for pions.

3. TOF System Upgrade Required performance: TOF < 100 ps
Occupancy < 15%

4. Particle ID with PHOBOS
Baseline design relies solely on energy loss
PID based on dE/dx:
/ K : p < 650 MeV/c
K / p : p < 1.2 GeV/c
PID based on TOF (TOF =100 ps):
/ K : p < 1.2 GeV/c
K / p : p < 2.0 GeV/c
1.7 m from interaction point

5. Physics Impact of PHOBOS TOF
Spectral behavior of ptransverse distributions
Extend pt region for and K interferometry
Precise measurement of K/  ratios as a function of pt
Study pt dependence of  meson production

6. Scintillators and Light Guides
BC-404 fast plastic from Bicron
8 x 8 x 200 mm3
Diamond milled surface finish
Light Guides:
BC-800 acrylic dog-leg design
Machined at INP in Krakow

7. Photomultiplier Tubes & Bases
Hamamatsu R M4MOD 12 stage multi-anode PMTs
Minimum gain per any one channel of 2 x at +800 V
Maximum variation in gain (uniformity) is less than 50% per any one tube
Quality assurance done

8. Assembly of components
Gluing of light guides to scintillators is completed
Wrapping in reflective Al foil and first layer of protective tape is finished for all 240 detectors

9. Mounting Fixture
Must precisely align light guides with the face of the PMT
Serve as gluing fixture for PMTs to light guides
Machining at INP in Krakow is completed

10. Magnetic Shields
TOF detectors must operate unaffected by magnetic fringe fields of at least 100 G
Prototype metal shield has been designed and tested in house
Order completed through Perfection Mica

11. LED Calibration System
PIN Diode
Splitter
470 nm (blue) LED from Panasonic (P465)
Duplex fiber optic cables from Thomas & Betts carry pulses to each PMT
Pulse width ~ 10 ns out of PMT (at +8 V) and bright enough to drive multiple PMT’s
Light split between fibers and PIN diode reference
LED
Fiber Bundle
(To PMT’s)

12. LED Calibration System
1 mm dia plastic fiber located in “dead-area” at center of PMT
Upper-right light guide removed to show fiber
NIM to TTL converter
Pulser uses transistor in avalanche
mode to discharge a capacitor
through LED

13. Basic TOF Units
Gluing of PMTs to light guides & fiber optics has begun
Final assembly and testing of basic TOF units progressing well at Rochester (we’re under spec)

14. Benchtest: Crosstalk
Crosstalk in PMT will not be a problem

15. TOF Support Structure
Final design of TOF support structure nearly complete
AutoCAD picture courtesy of our collaborators at INP

16. Readout Electronics
Standard modules were chosen to reduce overhead from development of specialized electronics
LeCroy 1458 HV mainframe with ARCNET card sent to BNL for work on Slow Controls
Order placed with LeCroy for HV cards, FASTBUS ADCs and TDCs, and CAMAC discriminators

17. Cost of PHOBOS TOF Project
Total cost (proposal):
NSF MRI Grant $328,129.00
Cost sharing ,196.00
$573,325.00
Actual current expenditures $475,346.80
Proposed current expenditures ,271.30
$1,075.50

18. Summary
Solid progress has been made on all fronts for the PHOBOS TOF System at Rochester.
The PHOBOS TOF System will be ready on Day 1 of Commissioning Run at RHIC.
Stay tuned: Research/PHOBOS/Phobos.html