The PHOBOS Multiplicity and Vertex Detector

1
The PHOBOS Multiplicity and Vertex Detector

• Michael Reuter
• University of Illinois at Chicago
• for the Collaboration
• DNP2000 Williamsburg, VA October 6, 2000

• Describe layout of detector
• Show functionality
• Hint at physics to come

2
Goals for the Detector

• Multiplicity
• Measure 4p multiplicity distribution
• - event-by-event and ensemble
• Fluctuations in multiplicity distribution
• - event-by-event
• Flow
• Vertex
• Find vertices
• Measure multiplicity at mid-rapidity

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The PHOBOS Detector
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Multiplicity and Vertex Detector I
Vertex
30 cm
1 m
Ring
25 cm
Octagon
Multiplicity Detector Octagon 6 Rings
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Multiplicity and Vertex Detector II
Vertex
Ring
Octagon
Multiplicity
Vertex

• Single layer of silicon with large pads
• Can handle large occupancy (gt80)

• Two layers of silicon with
• strip pads
• Low occupancy (20)

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Does it work?
Spec
Spec
0
3
-3
-5.4
5.4
7
Vertex Finding
z
cm
Vertex _at_ Z -0.054 cm
cm
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Silicon Signal Distributions
Vertex
Data
MC
dE (keV)
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Hit Distributions
dE uncorrected for angle (keV)
dE uncorrected for angle (keV)
h
h
Data
MC
Vertex Detector
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On to Physics I
Run 5374 Event 79495
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On to Physics II
Run 5374 Event 79495
h
Octagon
Rings
Rings
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Summary

• The Multiplicity and Vertex Detectors work well!
• Studies underway to understand components for
• various physics topics
• Special thanks to the ERSO Company (Taiwan) and
• the National Central University (Taiwan) for
• producing excellent silicon sensors
• Prospects are bright for physics, so watch this
• space!