Recent Results from PHOBOS experiment at RHIC

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Recent Results from PHOBOS experiment at RHIC

• VI Simposio Latinoamericano de Física Nuclear
• Iguazú, Argentina Octubre 2005
• Edmundo García, UIC

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PHOBOS Collaboration
Burak Alver, Birger Back, Mark Baker, Maarten
Ballintijn, Donald Barton, Russell Betts, Richard
Bindel, Wit Busza (Spokesperson), Zhengwei Chai,
Vasundhara Chetluru, Edmundo García, Tomasz
Gburek, Kristjan Gulbrandsen, Clive Halliwell,
Joshua Hamblen, Ian Harnarine, Conor Henderson,
David Hofman, Richard Hollis, Roman Holynski,
Burt Holzman, Aneta Iordanova, Jay Kane,Piotr
Kulinich, Chia Ming Kuo, Wei Li, Willis Lin,
Constantin Loizides, Steven Manly, Alice
Mignerey, Gerrit van Nieuwenhuizen, Rachid
Nouicer, Andrzej Olszewski, Robert Pak, Corey
Reed, Eric Richardson, Christof Roland, Gunther
Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith,
Maciej Stankiewicz, Peter Steinberg, George
Stephans, Andrei Sukhanov, Artur Szostak,
Marguerite Belt Tonjes, Adam Trzupek, Sergei
Vaurynovich, Robin Verdier, Gábor Veres, Peter
Walters, Edward Wenger, Donald Willhelm, Frank
Wolfs, Barbara Wosiek, Krzysztof Wozniak, Shaun
Wyngaardt, Bolek Wyslouch ARGONNE NATIONAL
LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITU
TE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS
INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL
UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
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Outline

• Matter phases in Heavy Ion Reactions
• Experimental characterization of RHIC Collisions
• Global observables
• Scaling behaviors
• Limiting fragmentation

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Description of a heavy-ion collision
M. Gyulassy, L. McLerran Nucl. Phys. A 750
(2005)30
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Color Glass Condensate (CGC)
ZEUS data for gluon distribution In partons
Gluon density grows
McLerran, hep-ph/0311028
low x -gt asltlt1 At a given Q(x,A) -gt gluon
density saturation -gt saturation models for heavy
ions
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Saturation Models AuAu
PHOBOS
dN/dhch / (ltNpartgt/2)
PHOBOS 130 GeV
ltNpartgt
Saturation Model (KLN) Phys.Lett.B523 79 (2001)
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Saturation Models d Au
Saturation Model (KLN)
hep-ph/0212316
PHOBOS
PHOBOS
CGC not valid in the Au fragmentation region
Assume dN/dhNpartAu dNpp/dh in the Au
fragmentation region
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Quark Gluon Matter/Plasma
QGM
energy/density
particles
Thermalization
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Estimation of the energy density reached at RHIC
Bearden et al., BRAHMS Collaboration, Nucl.
Phys. A757 (2005) 1-27
Nucleon transparency at RHIC larger than for AGS
and SPS. However the energy density achieved 5
GeV/fm at mid rapidity high energy density
system formed during collisions
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Baryon free medium created at RHIC
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Evidence of thermalization


STAR, Nucl. Phys. A 757 (2005) 102
BRAHMS, Nucl. Phys. A757 (2005) 1-27
Evidence of successful description of data by
hydrodynamics, high energy density system is to
certain degree thermalized. From PHOBOS particle
rations T120 MeV, mB 27.2 MeV
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Another characteristic of the high energy density
matter formed at RHIC Flow
Initial spatial anisotropy
z
z
Reaction plane (YR)
y
f
x
y
y
x
x (defines YR)
dN/d(f -YR ) N0 (1 2v1cos (f-YR)
2v2cos (2(f-YR)) ... )
Final momentum anisotropy
py
px
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Strongly interactive system I
PHOBOS
PHOBOS
centrality
Evidence of large elliptic component of flow
found, the high density system interacts more
like a fluid than like a gas.
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Strongly interacting system II
PHOBOS dAu 200 GeV
41mb (same as for Glauber)
PHOBOS data
From Glauber (HIJING 1.383)
From UA1, using Pythia to go from h lt 2.5 to
0.2 lt h lt 1.4
Suppression of high-pT particles Medium is
highly interactive and parton density is high.
PRL 91, 072302 (2003)
AuAu 200 GeV
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Strongly interacting system II cont.
Suppression of high pt particles
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New on dijet supression Emergence of dijets
with increasing pT(trig)
AuAu, 0-5

• ?? correlations (not background subtracted)
• Hint of narrow back-to-back peak for higher
  pT(trig)
• Jets do exist but they are highly suppressed

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RHIC

• High energy density medium
• Baryon Free medium
• Evidence of Thermalization
• Medium created at RHIC strongly interacts with
  high pt partons.
• What other global observables define RHIC
  collisions so far as measured by PHOBOS?
• Scaling behaviors
• Limiting fragmentation

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Wang,Gulassy Phys. Rev. Lett 86(2001)
Kharzeev,Nardi Phys. Lett. B 501(2001)
Participant Scaling
Npart/2 of participating pairs of
nucleons 1
Npart/2 of participating nucleons N
Collision Scaling
Ncoll of NN collisions 1
Ncoll of NN collisions N4/3
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AuAu centrality dependence allows only about 10
Ncoll scaling at mid rapidity
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dN/dh/(Npart/2)
200 GeV - hlt1
Binary Collision(Ncoll) Scaling
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PHOBOS
pp
AuAu
Participant (Npart) Scaling
0
400
200
0
ltNpartgt
peripheral
central
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All RHIC energies show a similar Npart dependence
Data is normalized by pp value for each energy.
Binary collision scaling
200 GeV
130 GeV
19.6 GeV preliminary
AuAu
PHOBOS
Participant (Npart) scaling
peripheral
central
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Npart scaling for asymmetric collisions
arXivnucl-ex/0403033
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dN/d? in CuCu vs. AuAu
Scaling Laws
PHOBOS
62.4 GeV
200 GeV
CuCu Preliminary 3-6, Npart 96
CuCu Preliminary 3-6, Npart 100
AuAu 35-40,Npart 98
AuAu 35-40, Npart 99
CuCu Preliminary 15-25, Npart 61
CuCu Preliminary 15-25, Npart 60
AuAu 45-55, Npart 56
AuAu 45-50,Npart 62
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Yields vs. Npart, 200 GeV
Scaling Laws
PHOBOS
AuAu PRL 94, 082304 (2005), PLB 578, 297 (2004)
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Limiting Fragmentation
PHOBOS Au Au
0 6 central
UA5, Z.Phys.C33, 1 (1986)
dN/dh
selected systematic errors
35 40 central
PRL 91, 052303 (2003)
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Rest frame of A
Rest frame of p or d
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Elliptic flow
PHOBOS
PRL 91, 052303 (2003)
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Final Notes

• RHIC collisions
• Produce a high energy density medium
• Baryon Free medium
• Evidence of thermalization
• Medium created at RHIC strongly interacts with
  high pt partons.
• Global observables (not clearly understood yet)
  that define RHIC so far
• ltNpartgt scaling behaviors
• Limiting fragmentation
• LHC

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Backup Transparencies
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PHOBOS Experiment
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Triggering on Collisions Centrality

• Coincidence between Paddle counters at Dt 0
  defines a valid collision
• Paddle ZDC timing reject background

Data
DataMC
HIJING GEANT Glauber calculation Model of
paddle trigger
Central
Peripheral
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Energy per Unit Volume Detail
Number of Particles Produced at y0
ltEgt 0.7 GeV
dNch/dh
Therefore total energy released in h lt 1 is
2000GeV
Energy of Collision
Relevant Initial Volume ?R2 ? ( 1 fm) ? 2
Initially released Energy per Unit Volume ? 5
GeV/fm3 Note Energy Density inside Proton 0.5
GeV/fm3
Data from PRL 85, 3100 (2000) PRL 88, 22302
(2002) PRL 91, 052303 (2003)
arXivnucl-ex/0405027
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Strongly interacting system III
?
T 229 MeV for (??-) 293 MeV for (K
K-) 392 MeV for (p pbar)
AuAu at ?sNN 200 GeV
No enhancement in low-pT yields for pions is
observed flattening of (ppbar) spectra down to
very low pT, consistent with strong radial flow
of the systm
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Baryon puzzle at RHIC
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Elliptic Flow in CuCu vs AuAu
Scaling Laws
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Total charged multiplicity scaling with Npart
PHOBOS nucl-ex/0301017
Open symbols are UA5 data at 200 GeV and results
from an interpolation at lower energies
Shaded band is uncertainty on extrapolation
procedure Errors include contributions from Nch
and Npart scaling
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Eccentricity Calculation
Scaling Laws
AuAu
AuAu
CuCu
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Npart scalling of Flow
Participant Eccentricity allows v2 scaling from
CuCu to AuAu
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ltdN/dygt / ltSgt scaling
Standard Eccentricity
CuCu
AuAu
ltdN/dygt / ltSgt scaling STAR, PRC 66 034904
(2002) Voloshin, Poskanzer, PLB 474 27
(2000) Heiselberg, Levy, PRC 59 2716, (1999)
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Emergence of dijets w/ increasing pT(assoc)

• ?? correlations (not background subtracted)

pT(assoc) gt 2 GeV/c
pT(assoc) gt 3 GeV/c
pT(assoc) gt 4 GeV/c
pT(assoc) gt 5 GeV/c
pT(assoc) gt 6 GeV/c
pT(assoc) gt 7 GeV/c
pT(assoc) gt 8 GeV/c

• Narrow peak emerges cleanly above vanishing
  background