Centrality Categorization and its Application to Physics Effects in High-Energy d+A Collisions Javier Orjuela-Koop University of Colorado Boulder For the PHENIX Collaboration 30 th Winter Workshop on Nuclear Dynamics Galveston, Texas April 6-12, 2014 ton_entertainment by optictopic CC/BY
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Centrality Categorization and its Application to Physics Effects in High-Energy d+A Collisions
Centrality Categorization and its Application to Physics Effects in High-Energy d+A Collisions. Javier Orjuela-Koop University of Colorado Boulder For the PHENIX Collaboration. gaveston_entertainment by optictopic CC/BY. 30 th Winter Workshop on Nuclear Dynamics Galveston, Texas - PowerPoint PPT Presentation
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Centrality Categorization and its Application to Physics Effects in High-Energy d+A Collisions
Javier Orjuela-KoopUniversity of Colorado Boulder
For the PHENIX Collaboration
30th Winter Workshop on Nuclear DynamicsGalveston, TexasApril 6-12, 2014
gaveston_entertainment by optictopic CC/BY
Motivation
Numerous physics effects can be studied in d+Au collisions.
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30th WWNDJ. Orjuela-Koop
Motivation
Numerous physics effects can be studied in d+Au collisions.
• Modifications of parton distribution functions in nuclei• Gluon saturation• Color neutralization• Collective flow in small systems (!)
2
30th WWNDJ. Orjuela-Koop
Motivation
Numerous physics effects can be studied in d+Au collisions.
• Modifications of parton distribution functions in nuclei• Gluon saturation• Color neutralization• Collective flow in small systems (!)
We need to characterize the event geometry!
2
30th WWNDJ. Orjuela-Koop
Motivation
Numerous physics effects can be studied in d+Au collisions.
• Modifications of parton distribution functions in nuclei• Gluon saturation• Color neutralization• Collective flow in small systems (!)
We need to characterize the event geometry!
b
Au
d
• How to select centrality classes?• How to validate the selection?• Are there any bias effects?• How do they affect ‘the physics’
at the GeV and TeV scales?
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30th WWNDJ. Orjuela-Koop
Experiment 30th WWNDJ. Orjuela-Koop
PHENIX determines centrality by cutting on backward (Au-going) rapidity multiplicity.
SIDE VIEW
3
TOP VIEW
Au
Aud
d
Experiment 30th WWNDJ. Orjuela-Koop
PHENIX determines centrality by cutting on backward (Au-going) rapidity multiplicity.
BBC Range:
BBCs• Vertex pos.• Centrality• Event timing
SIDE VIEW
3
TOP VIEW
Au
Aud
d
Experiment 30th WWNDJ. Orjuela-Koop
PHENIX determines centrality by cutting on backward (Au-going) rapidity multiplicity.
We use Monte Carlo methods to simulate d+Aucollisions by sampling the position of nucleonsfrom a Hulthén wavefunction (d) and a Woods-Saxon distribution (Au). 4
There is recent compelling evidence for collective flow in p+Pb and d+Au.
This is an example of a physics observable where comparison with theoryrequires an understanding of the geometry.
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Collective Flow in 3He+Au 30th WWNDJ. Orjuela-Koop
3He+Au collisions have been proposed as a test system whose intrinsictriangularity can be used to discriminate initial state effects and thosefrom viscous damping.
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Collective Flow in 3He+Au 30th WWNDJ. Orjuela-Koop
3He+Au collisions have been proposed as a test system whose intrinsictriangularity can be used to discriminate initial state effects and thosefrom viscous damping.
18http://arxiv.org/abs/1312.4565
Summary 30th WWNDJ. Orjuela-Koop
• We described the PHENIX methodology for selecting centrality classes.
• The centrality determination method is subject to inherent bias effects thatcan be accounted for.
• Bias correction factors are small for d+Au @ 200 GeV, but large and pT-dependent for p+Pb @ 5.02 TeV.
• There is evidence for collective flow in small systems.
• This is one of many physics analyses that depend on a careful characterizationof the event geometry.
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Thank you!
30th WWNDJ. Orjuela-Koop
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Backup Slides
30th WWNDJ. Orjuela-Koop
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Double-Interaction Study 30th WWNDJ. Orjuela-Koop
Double inelastic interactions result in greater BBC charge deposition.We need to account for this extra charge when categorizing centrality.