THE PHOBOS EXPERIMENT AT RHIC

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THE PHOBOS EXPERIMENT AT RHIC

• Judith Katzy
• for the
• PHOBOS Collaboration

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PHOBOS Collaboration
ARGONNE NATIONAL LABORATORY Birger Back, Russell
Betts, Alan Wuosmaa, Nigel George BROOKHAVEN
NATIONAL LABORATORY Mark D.Baker, Donald Barton,
Alan Carroll, Stephen Gushue, George Heintzelman,
Louis Remsberg, Andrei Sukhanov INSTITUTE OF
NUCLEAR PHYSICS, KRAKOWWojciech Bogucki ,
Andrzej Budzanowski, Tomir Coghen, Kazimierz
Galuszka, Jan Godlewski ,Roman Holynski, Jerzy
Kotula, Marian Lemler, Jerzy Michalowski, Andrzej
Olszewski, Pawel Sawicki Marek Stodulski, Adam
Trzupek, Barbara Wosiek, Krzysztof Wozniak, Pawel
Zychowski JAGELLONIAN UNIVERSITY, KRAKOWAndrzej
Bialas, Wieslaw Czyz, Kacper Zalewski MASSACHUSETT
S INSTITUTE OF TECHNOLOGYWit Busza, Patrick
Decowski, Kristjan Gulbrandsen, P. Haridas, Piotr
Kulinich, Heinz Pernegger, Miro Plesko, Gunther
Roland, Leslie Rosenberg, Pradeep Sarin, Stephen
Steadman, George Stephans, Gerrit van
Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard
Wadsworth, Bolek Wyslouch NATIONAL CENTRAL
UNIVERSITY, TAIWANYuan-Hann Chang, Augustine
Chen, Willis Lin UNIVERSITY OF ROCHESTERAdam
Hayes, Erik Johnson, Steven Manly, Robert Pak,
Inkyu Park, Frank Wolfs UNIVERSITY OF ILLINOIS AT
CHICAGORussell Betts, Clive Halliwell, Burt
Holzman, Judith Katzy, Wojtek Kucewicz, Don
McLeod, Rachid Nouicer, Michael Reuter UNIVERSITY
OF MARYLANDEdmundo Garcia-Solis, Peter Stanskas,
Alice Mignerey
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Physics Goals of PHOBOS
Study QCD Vacuum and Confinement

• Look for Excess Entropy
• Multiplicity Distribution and Fluctuations
• Source Size and Lifetime
• Look for Collective Phenomena over large V
• Low Transverse Momentum
• Look for Unusual Medium Effects
• Phi Mass and Width

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The Phobos detector

• multiplicity array
• h lt5.4, Dh0.1, Dhp/16
• spectrometer
• 0.5lthlt1.5, Df11deg
• vertex detector
• tof
• trigger detectors
• magnet

• first year
• full multiplicity and vertex detector
• 1 spectrometer arm
• 2 TOF elements

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Triggering and data rates
Simple, unbiased trigger paddle scintillators
3.7 ? h ? 4.5 ring cerenkov 4.9 ? h
? 5.3 Rates at nominal Luminosity L 1026 cm2
s1 R(AuAu) 600 Hz (b ? 15
fm) R(AuAu, central) 60 Hz R(BeamGas)
100 Hz R(ee) 10 Hz data
collection volume 18 kb/ event gt 60 Tb raw -
430 Tb total / year
Reduced by vertex timing cut
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Multiplicity array and Vertex detector
Multiplicity measurement octagon and 6 ring
counters acceptance h lt 5.4 0 ? f ? 2p bin
width Dh 0.05 - 0.1, Df p/16
5.0m
2.3m
vertex
1.1m
octagon
ring counter
interaction point
-1.1m
-5.0m
-2.3m
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Vertex reconstruction
11 cm
5.5 cm
z
beam
beam
z
Vertex Resolution
s
60 mm
z
Vertex acceptance -20cm ? z ? 20 cm
Vertex Reconstruction in x,y with tracks
reconstructed in spectrometer
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Multiplicity array
1 ring counter
Part of octagon
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Silicon Detector modules used in the Multiplicity
array
Octagon module
Ring module
6.5 cm
8.5cm
64 pads / sensor Dh0.05 Dfp/32
120 pads / sensor Dh0.05 - 0.1 Dfp/16
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Multiplicity Reconstruction from Energy Loss
Reconstructed multiplicity in Pad i Mi
Edepi / (Eisingle Nitot/Niprim)
Edepi deposited Energy (angle corrected)
Eisingle mean energy loss for one particle
traversing pad
Nitot/Niprim ratio of total/primary tracks
Error on total Multiplicity 2/3

1.5 107 distributions in 1 month at 1 nominal
luminosity
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Event by Event Multiplicity Average over 50
Events
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100 MeV/c
-
p
-
1 GeV/c
p
100 MeV/c

p
Spectrometer and Tracking
Low field region for pattern recognition particl
e id via dE/dx
High B-field
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The Magnet
conventional magnet maximal B-field 2.1 Tesla
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Silicon Detectors mounted on Spectrometer Frame
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Response of Silicon Detector to 285MeV/c Pions
- Data!
without gaussian addition
in collaboration with hephy in Vienna
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Spectrometer Acceptance
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Momentum Resolution
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Track Finding - very low P
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7 Planes, Egt800 keV
Stopping Kaon
f (deg.)
0
-8
q (deg.)
80
20
40
60
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7 Planes, all Hits
f (deg.)
0
-8
q (deg.)
60
20
40
80
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HBT Acceptance for p
Truth Resolution smeared
Source Parameterization C2 1 l exp(-Qi2
Ri2) i L, TO,TS
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HBT Capabilities

• Standard Scenario
• Extrapolate from AGS/Cern Energies

• Exotic Scenario I
• Very Large Source

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• f results after 1 nominal week, 15 central cut,
  Si pid
• 50000 f
• Resolution s(Minv) 1.6 MeV
• Dominated by momentum resolution
• Error on Width 1.0 MeV

f KK-
Phi measurement
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Summary - PHOBOS Highlights

• Coverage for Charged Multiplicity in almost 4 p
• with the Multiplicity Array
• Momentum Measurement and Particle Identification
  
• at Mid-rapidity with Low pt Threshold with the
• Spectrometer
• Unbiased Taking Data Due to High Data Rate
  Capability

READY FOR RHIC START-UP IN NOVEMBER