Measurement of the
Centrality Dependence of
Charged Particle Pseudorapidity Density
with the PHOBOS Detector

	Michael Reuter
	University of Illinois at Chicago
	for the                         Collaboration
	APS Spring Meeting:  Washington, DC    April 29, 2001

The PHOBOS Detector

The BIG Picture

Selecting Collisions

Determining Centrality

Uncertainty on N_part

	Measurement sensitive to trigger bias
		“Minimum-bias” still has bias
		Affects most peripheral events

Detector Geometry

Vertex Finding

Tracklet Analysis

Tracklet Systematic Error

Measured dN_ch/dh

Centrality Dependence of dN_ch/dh

Comparison to SPS

Summary