Number of Participants Study

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Number of Participants Study

• Mike Miller
• Yale University
• 7/19/01

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Outline

• Motivation
• Optical based Glauber implementation
• Status of current results
• Status of error analysis

Glauber Working Group (7/19/01)
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Motivation

• Compare Central events to peripheral
• Map Nh- to Npart, Ncoll, b
• 2d-Centrality Selection
• ZDC ?
• STAR
• No beam-beam counter (until post AA FY2001), only
  CTB
• ZDCCTB works only for most central bins
• Cannot plot NH- vs. NH-!
• Plot NH- vs. Npart!

Glauber Working Group (7/19/01)
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Year 1 Centrality Selection

• Do not want to select on Et, Ncharge
• STAR Y1 selection valid only at high centrality
• Large improvement in future centrality selection
• Is plotting Ncharge vs Npart shady?

Glauber Working Group (7/19/01)
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General Glauber Theory
All as a function of b!
Glauber Working Group (7/19/01)
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Glauber Results
Npart4/3
Glauber Working Group (7/19/01)
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M.C. Glauber Implementation

• Randomly generate b.
• Look up probability of interaction.
• Use M.C. sampling, decide if interaction takes
  place.

• If interaction, fill histograms with Npart, Nbc

Glauber Working Group (7/19/01)
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Mapping NH- to Npart

• Map means bin-by-bin
• Parameterize (pol2 fit)
• Address Fluctuations later

Avoid peripheral region
Glauber Working Group (7/19/01)
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Particle Production Scaling Model

• Simple assumptions to map b-NH-
• Mean (bin-by-bin)
• Dispersion
• Statistical Model (Gaussian2)
• Parameter a!

Cross section given by integrating over impact
Npart with proper weighting.
Glauber Working Group (7/19/01)
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Optical Glauber Results

• Restricted to 60 or less centrality gt Npart gt
  35
• Use a1.2

Glauber Working Group (7/19/01)
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Error Analysis

1. Sigmapp41-1 mb gt less than 1 effect
2. Npart vs Ncoll MC distribution gt less than 4
   effect
3. Deformation gt less than 1 effect
4. 5 Uncertainty in total cross-section 17 in
   most peripheral bin, .5 in most central bin

Jiggle bin boundaries, calculate change in Npart
Glauber Working Group (7/19/01)
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Results
Centrality () ltNpartgt ltNcollgt
0-5 345-2 (lt1) 1054-7 (lt1)
5-10 286-4 (1) 818-15 (2)
10-20 221-6 (3) 568-21 (4)
20-30 149-7 (5) 338-23 (7)
30-40 97-8 (8) 191-20 (11)
40-50 61-7 (10) 99-17 (17)
50-60 35-6 (17) 46-11 (24)
Glauber Working Group (7/19/01)
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Results
STAR Analysis Meeting (5/01)
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Conclusions

• Pluses
• No scaling hypothesis
• Fluctuations well described with one parameter
• Quote Npart gt 35
• Error on Npart lt 17
• Errors driven by vertex finding inefficiencies,
  trigger inefficiencies, theory estimate on
  cross-section
• Minuses
• Limited to 60 most central bin
• Dependent on Glauber differential cross-section

Glauber Working Group (7/19/01)
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Glauber Working Group (7/19/01)