Latest Results From PHOBOS

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Latest Results From PHOBOS

• David Hofman
• University of Illinois at Chicago

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PHOBOS Collaboration
Burak Alver, Birger Back, Mark Baker, Maarten
Ballintijn, Donald Barton, Russell Betts, Richard
Bindel, Wit Busza (Spokesperson), Vasundhara
Chetluru, Edmundo García, Tomasz Gburek, Joshua
Hamblen, Conor Henderson, David Hofman, Richard
Hollis, Roman Holynski, Burt Holzman, Aneta
Iordanova, Chia Ming Kuo, Wei Li, Willis Lin,
Constantin Loizides, Steven Manly, Alice
Mignerey, Gerrit van Nieuwenhuizen, Rachid
Nouicer, Andrzej Olszewski, Robert Pak, Corey
Reed, Christof Roland, Gunther Roland, Joe
Sagerer, Peter Steinberg, George Stephans, Andrei
Sukhanov, Marguerite Belt Tonjes, Adam Trzupek,
Sergei Vaurynovich, Robin Verdier, Gábor Veres,
Peter Walters, Edward Wenger, Frank Wolfs,
Barbara Wosiek, Krzysztof Wozniak, Bolek
Wyslouch ARGONNE NATIONAL LABORATORY BROOKHAVEN
NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS
PAN, KRAKOW MASSACHUSETTS INSTITUTE OF
TECHNOLOGY NATIONAL CENTRAL UNIVERSITY,
TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
9 ongoing Ph.D. theses
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PHOBOS Experiment
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Colliding Nuclei at RHIC
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Two snapshots of colliding nuclei at RHIC
nuclei crossing times extremely fast
RHIC 0.13 fm/c SPS 1.6 fm/c AGS 5.3 fm/c
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Well known initial collision geometry matters
Elliptic Flow
Visible in final measured particle azimuthal
angular distributions
Initial overlap eccentricity
ReactionPlane
y0
Impact Parameter
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Well known initial collision geometry matters
Elliptic Flow
Visible in final measured particle azimuthal
angular distributions
Initial overlap eccentricity
ReactionPlane
y0
Impact Parameter
Initial Eccentricity
Final Particle Distributions

• ? To first order initial collision geometry
  drives magnitude of v2
• (of course, the density also matters)

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Is our first RHIC snapshot in focus?
Lets focus on the spatial distribution of the
interaction points of participating nucleons
AuAu
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Is our first RHIC snapshot in focus?
Lets focus on the spatial distribution of the
interaction points of participating nucleons
for the same b, these interaction points will
vary from event-to-event
AuAu
AuAu
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Is our first RHIC snapshot in focus?
Lets focus on the spatial distribution of the
interaction points of participating nucleons
for the same b, these interaction points will
vary from event-to-event
Y0
AuAu
AuAu
Y0
and thus the relevant eccentricity for elliptic
flow also varies event-by-event
From PHOBOS _at_ Quark Matter 2005 ? explored much
further since then
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Does using make a difference?
YES
200 GeV
Increasingly important for smaller systems
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How robust is Glauber MC calculation?
Studied variations in
90 CL bands on calculation
arXivnucl-ex/0610037 Submitted to PRL
In collaboration with Ulrich Heinz
More recent studies have included variations in
individual nucleon density profiles and different
Npart and Ncoll weighting.
calculation from Glauber MC is robust
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How robust is Glauber MC calculation?
Studied variations in
90 CL bands on calculation
arXivnucl-ex/0610037 Submitted to PRL
In collaboration with Ulrich Heinz
More recent studies have included variations in
individual nucleon density profiles and different
Npart and Ncoll weighting.
Bhalerao, Ollitrault PLB641 260,
(2006) Ollitrault private communications
(2006) PHOBOS internal MC
calculation from Glauber MC is robust
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Data average v2 in CuCu and AuAu
CuCu arXivnucl-ex/0610037 submitted PRL
AuAu PRC 72 051901(R)
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Average v2/ in CuCu and AuAu
Standard Eccentricity
200 GeV
CuCu
AuAu
arXivnucl-ex/0610037, submitted to PRL
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Average v2/ in CuCu and AuAu
Participant Eccentricity
Standard Eccentricity
200 GeV
200 GeV
CuCu
CuCu
AuAu
AuAu
arXivnucl-ex/0610037, submitted to PRL
arXivnucl-ex/0610037, submitted to PRL
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Average v2/ in CuCu and AuAu
Participant Eccentricity
Standard Eccentricity
200 GeV
200 GeV
CuCu
CuCu
AuAu
AuAu
arXivnucl-ex/0610037, submitted to PRL
arXivnucl-ex/0610037, submitted to PRL
unifies average v2 in CuCu and AuAu
Related work Miller, Snellings, Zhu, Bleicher,
Stöcker
Voloshin, Poskanzer, PLB 474 27 (2000)
Heiselberg, Levy, PRC 59 2716, (1999)
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Average v2/ in CuCu and AuAu
Participant Eccentricity
Standard Eccentricity
200 GeV
200 GeV
CuCu
CuCu
AuAu
AuAu
arXivnucl-ex/0610037, submitted to PRL
arXivnucl-ex/0610037, submitted to PRL
unifies average v2 in CuCu and AuAu
Related work Miller, Snellings, Zhu, Bleicher,
Stöcker
Voloshin, Poskanzer, PLB 474 27 (2000)
Heiselberg, Levy, PRC 59 2716, (1999)
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New Data pT dependence of v2/
AuAu and CuCu at matched Npart
unifies midrapidity v2(pT) in CuCu and
AuAu
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scaling as a function of h
CuCu and AuAu at matched Npart
The collision geometry controls the dynamical
evolution of heavy ion collisions.
Talk by Rachid Nouicer
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scaling as a function of h
CuCu and AuAu at matched Npart
The collision geometry controls the dynamical
evolution of heavy ion collisions.
Talk by Rachid Nouicer
Consequence this implies that the initial
event-by-event participant collision geometry
appears relevant.
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Fluctuations in participant eccentricity
What magnitude of fluctuations are expected?
Quantify with s(epart)/ltepartgt
Expect large dynamical fluctuation in the
participant eccentricity
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New Analysis event-by-event v2 measurement
200 GeV AuAu

• Utilize Full Phase space coverage of PHOBOS
  (hlt5.4, Df2p).
• Detailed modeling of detector response,
  statistical fluctuations and multiplicity
  dependence.
• Method is described in arXivnucl-ex/0608025
• Measure v2 on an event-by-event basis.
• Take e-by-e result and average to compare to our
  other results.

ltv2gt measured event-by-event is in agreement with
both hit and track based PHOBOS results.
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New Result v2 and epart Fluctuations
s(v2)/ltv2gt in 200 GeV AuAu Collisions
Response of the measurement for MC events with no
dynamical fluctuations
Reminder this analysis corrects for detector and
multiplicity effects as well as statistical
fluctuations
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New Result v2 and epart Fluctuations
s(v2)/ltv2gt in 200 GeV AuAu Collisions
band 90 CL
PHOBOS v2 result
MC with nofluctuations
Observe significant dynamical v2 fluctuations
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New Result v2 and epart Fluctuations
s(v2)/ltv2gt and s(epart)/ltepartgt in 200 GeV AuAu
Collisions
band 90 CL
PHOBOS v2 result
PHOBOS epart prediction
MC with nofluctuations
Magnitude of v2 fluctuations is in agreement with
epart fluctuations
Poster by Burak Alver and talk by Constantin
Loizides
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Expanding Differentially in Phase Space
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New Data global charged particle emission
Midrapidity charged particles
Midrapidity charged particle spectra
Phys.Rev. C74 (2006) 021901 Phys.Rev.Lett. 94
(2005) 082304 Nucl.Phys. A774 (2006) 113-128
Extended longitudinal scaling
Highlights from QM05
Energy/Centrality factorization and scaling
laws in global charged particle production
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New Analysis two particle correlations
PHOBOS Preliminary
PHOBOS Preliminary
CuCu _at_ 200 GeV 0-10 central
pp _at_ 200 GeV
h
h
6
6
-6
-6
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New Analysis two particle correlations
PHOBOS Preliminary
PHOBOS Preliminary
CuCu _at_ 200 GeV 0-10 central
pp _at_ 200 GeV
h
h
6
6
-6
-6
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New Analysis two particle correlations
PHOBOS Preliminary
PHOBOS Preliminary
CuCu _at_ 200 GeV 0-10 central
pp _at_ 200 GeV
h
h
6
6
-6
-6
Study the short-range rapidity correlations
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New Result effective cluster size
Keff effective cluster size
pp
scale error
2
On average, particles tend to be produced in
clusters with a size of 2-3. Interesting
centrality dependence can compare to other
systems
Talk by Wei Li
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New Data antiparticle/particle ratios
200, 62.4 GeV CuCu
200 GeV CuCu and AuAu
Detailed measurement of antiparticle/particle
ratios as function of centrality
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New Publication identified particle spectra
62.4 GeV AuAu
blast-wave fits
arXivnucl-ex/0610001 submitted to PRC
First published identified spectra for 62.4 GeV
AuAu at RHIC (down to very low pT, a unique
PHOBOS measurement)
Talk by Gabor Veres
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PHOBOS Physics for QM06

• New Analyses
• Elliptic flow fluctuations

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PHOBOS Physics for QM06

• New Analyses
• Elliptic flow fluctuations
• Two particle correlations

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PHOBOS Physics for QM06

• New Analyses
• Elliptic flow fluctuations
• Two particle correlations
• Extended Analyses
• Elliptic flow in CuCu

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PHOBOS Physics for QM06

• New Analyses
• Elliptic flow fluctuations
• Two particle correlations
• Extended Analyses
• Elliptic flow in CuCu
• Charged particle multiplicity

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PHOBOS Physics for QM06

• New Analyses
• Elliptic flow fluctuations
• Two particle correlations
• Extended Analyses
• Elliptic flow in CuCu
• Charged particle multiplicity
• Anti-particle/particle ratios

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PHOBOS Physics for QM06

• New Analyses
• Elliptic flow fluctuations
• Two particle correlations
• Extended Analyses
• Elliptic flow in CuCu
• Charged particle multiplicity
• Anti-particle/particle ratios
• QM06 Primary Message PHOBOS has measured large
  dynamical v2 fluctuations in 200 GeV AuAu
  collisions. This suggests that the initial state
  thermalizes very rapidly, taking a detailed
  snapshot, which is propagated by the subsequent
  hydrodynamic evolution.

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Future of PHOBOS Physics

• Rare events, multiplicity fluctuations and
  cluster model poster K. Wozniak
• Continue studies of dynamical flow
  fluctuations
• Two-particle correlations with high-pT
  trigger in spectrometer.
• Identified particles at low pT in 200 GeV
  AuAu as detailed function of centrality
• Spectator breakup in the fragmentation
  region
• Charged particle yields in 200,410 pp
• Phi-meson production

Total Number of Hits

• TALKS Rachid Nouicer - v1 and v2 flow
  (Saturday, 240pm, Parallel 2.4) Constantin
  Loizides - v2 and epart fluctuations (Saturday,
  420pm, Parallel 2.4) Wei Li - Two-particle
  correlations (Sunday, 500pm, Parallel 3.2)
  Gabor Veres - Identified particle spectra and
  ratios (Sunday, 500pm, Parallel 3.4)
• POSTERS Burak Alver Elliptic flow
  fluctuations (Wednesday, 520pm, poster 14)
  Krzysztof Wozniak - Multiplicity fluctuations
  (Wednesday, 520pm, poster 82)