Recent Results from PHOBOS experiment at RHIC
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Transcript of Recent Results from PHOBOS experiment at RHIC
Recent Results from PHOBOS experiment at RHIC
VI Simposio Latinoamericano de Física Nuclear
Iguazú, Argentina Octubre 2005
Edmundo García, UIC
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 Hołyński, 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 Woźniak, Shaun Wyngaardt, Bolek Wysłouch
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
PHOBOS Collaboration
Outline
• Matter phases in Heavy Ion Reactions
• Experimental characterization of RHIC Collisions
• Global observables Scaling behaviors Limiting fragmentation
Description of a heavy-ion collision
M. Gyulassy, L. McLerran Nucl. Phys. A 750 (2005)30
McLerran, hep-ph/0311028
ZEUS data for gluon distributionIn partons
Gluon density grows
low x -> s<<1At a given Q(x,A) -> gluon density saturation -> saturation models for heavy ions
Color Glass Condensate (CGC)
Saturation Models Au+Au
Saturation Model (KLN) Phys.Lett.B523 79 (2001)
dN/d c
h /
(<N
part>/
2)
<Npart>
PHOBOS 130 GeV
PHOBOS
centrality
Saturation Models d + Au
PHOBOS
CGC not valid in the Au fragmentation region
Assume dN/d=NpartAu dNpp/d in
the Au fragmentation region
Saturation Model (KLN) hep-ph/0212316
PHOBOS
Quark Gluon Matter/Plasma
particles
QGM
energy/density
Thermalization
Estimation of the energy density reached at RHIC
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
Bearden et al., BRAHMS Collaboration, Nucl. Phys. A757 (2005) 1-27
Baryon free medium created at RHIC
Evidence of thermalization
Evidence of successful description of data by hydrodynamics,high energy density system is to certain degree thermalized. From PHOBOS particle rations T~120 MeV, B~ 27.2 MeV
STAR, Nucl. Phys. A 757 (2005) 102 BRAHMS, Nucl. Phys. A757 (2005) 1-27
Another characteristic of the high energy density matter formed at RHIC: Flow
Reaction plane
(R)
x
z
y
x
x (defines R)
y
zy
Initial spatial anisotropy
px
py
Final momentum anisotropy dN/d(R ) = N0 (1 + 2v1cos (R) +
2v2cos (2(R)) + ... )
Elliptic Flow: v2
Strongly interactive system I
centrality
Evidence of large elliptic component of flow found,the high density system interacts more like a fluid than like a gas.
PHOBOS
PHOBOS
Suppression of high-pT particles: Medium is highly interactive and parton density is high.
AuAu 200 GeV
PHOBOS dAu 200 GeV
PRL 91, 072302 (2003)
From Glauber(HIJING 1.383)
41mb (same as for Glauber)
From UA1, usingPythia to go from|| < 2.5 to 0.2 < < 1.4
PHOBOS data
Strongly interacting system II
Strongly interacting system II cont.
Suppression of high pt particles
New on dijet supression: Emergence of dijets with increasing pT(trig)
Au+Au, 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
pT(trig)
pT(assoc) > 2 GeV/c
preliminary
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?
1. Scaling behaviors
2. Limiting fragmentation
“Participant” Scaling
Ncoll= # of NN collisions: ~N4/3
L~N1/3
Npart/2 = # of participating nucleons: N
“Collision” Scaling
Npart/2 = # of participating
pairs of nucleons: = 1
Ncoll = # of NN collisions: = 1
collpartch Nf
Nf
d
dN 21 2
Wang,Gulassy Phys. Rev. Lett 86(2001) Kharzeev,Nardi Phys. Lett. B 501(2001)
Au+Au centrality dependence allows only about 10% Ncoll scaling at mid rapidity
Au+Au
0 200 4000
10
20dN
/d/
(Np
art/
2)
<Npart>
200 GeV - ||<1
peripheral central
p+p
Binary Collision(Ncoll) Scaling
Participant(Npart) Scaling
PHOBOS
All RHIC energies show a similar Npart dependence
19.6 GeV preliminary
130 GeV200 GeV
Data is normalized by p+p value for each energy.
Au+Au
p + p
peripheral central
Participant (Npart) scaling
Binary collision scaling
PHOBOS
Npart scaling for asymmetric collisions:
arXiv:nucl-ex/0403033
dN/d in Cu+Cu vs. Au+Au Scaling Laws
PHOBOS62.4 GeV 200 GeV
Au+Au35-40%,Npart = 98
Cu+CuPreliminary
3-6%, Npart = 96
Au+Au35-40%, Npart = 99
Cu+CuPreliminary
15-25%, Npart = 61
Au+Au45-50%,Npart = 62
Cu+CuPreliminary
15-25%, Npart = 60
Au+Au45-55%, Npart = 56
Cu+CuPreliminary
3-6%, Npart = 100
Scaling LawsYields vs. Npart, 200 GeV
Au+Au: PRL 94, 082304 (2005), PLB 578, 297 (2004)
Cu+Cupreliminary
Au+Au
PHOBOS
Limiting Fragmentation
UA5, Z.Phys.C33, 1 (1986)
dN
/d
beamy
selected systematic errors
0 – 6 % central
35 – 40 % central
PHOBOS Au + Au
PRL 91, 052303 (2003)
Rest frame of A Rest frame of p or d
Elliptic flow:
PRL 91, 052303 (2003)
PHOBOS
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:
1. <Npart> scaling behaviors2. Limiting fragmentation…• LHC
Backup Transparencies
PHOBOS Experiment
Triggering on Collisions & Centrality
• Coincidence between Paddle counters at t = 0 defines a valid collision
• Paddle + ZDC timing reject background
PP
Negative
Paddles
Positive Paddles
Aux
z
PN
Positive ZDC
Negative ZDC
NegativeCerenkov
PositiveCerenkov
Au
Central Peripheral
HIJING +GEANT Glauber calculation Model of paddle trigger
Data Data+MC
Initially released Energy per Unit Volume 5 GeV/fm3
Note: Energy Density inside
Proton ≈ 0.5 GeV/fm3
11
45
1000~all
d
dN
Therefore total energy released in
|| < 1 is ~2000GeV
Nu
mb
er o
f P
arti
c les
Pro
du
ced
at
y=0
Energy of Collision
“Relevant” Initial Volume ~ R2 ( 1 fm) 2
<E> ~ 0.7 GeV
Data from: PRL 85, 3100 (2000); PRL 88, 22302 (2002); PRL 91, 052303 (2003); arXiv:nucl-ex/0405027
dN
ch/d
Energy per Unit Volume Detail
12
1)/exp(1
21 BET
TT
TmAdydm
Ndm
mT = pT2+mh
2
No enhancement in low-pT yields for pions is observed flattening of (p+pbar) spectra down to very low pT, consistent with strong radial flow of the systm:
T= 229 MeV for (++-) 293 MeV for (K++ K
-)
392 MeV for (p + pbar)
Strongly interacting system III
Au+Au at sNN = 200 GeV
Baryon puzzle at RHIC
Elliptic Flow in Cu+Cu vs Au+AuScaling Laws
preliminary
PHOBOS 200 GeV h±
PHOBOS 200 GeV h±
Statistical errors only
Cu+Cupreliminary
PHOBOS 200 GeV Statistical errors only
Au+Au
0-40% centrality
Total charged multiplicity scaling with Npart
Shaded band is uncertainty on extrapolation procedureErrors include contributions from Nch and Npart scaling
Open symbols are UA5 data at 200 GeV and results from an interpolation at lower energies
PHOBOS: nucl-ex/0301017
Eccentricity CalculationScaling Laws
Standard Eccentricity
x
y Nucleus 2Nucleus 1
ParticipantRegion
b
Au+AuCu+Cu
Au+Au
Nucleus 1
Nucleus 2
Participant Region
x
y
Participant Eccentricity
b
Au+AuCu+Cu
Au+Au
Npart scalling of Flow
Standard Eccentricity
Cu+Cupreliminary
Au+Au
PHOBOS 200 GeV
“Participant Eccentricity” allows v2 scaling from Cu+Cu to Au+Au
Participant Eccentricity PHOBOS 200 GeV
Au+AuCu+Cupreliminary
Standard Eccentricity
Cu+Cu
Au+Au
Participant Eccentricity
Cu+Cu
Au+Au
<dN/dy> / <S> scaling:STAR, PRC 66 034904 (2002)Voloshin, Poskanzer, PLB 474 27 (2000)Heiselberg, Levy, PRC 59 2716, (1999)
<dN/dy> / <S> scaling
Emergence of dijets w/ increasing pT(assoc)
correlations (not background subtracted)
• Narrow peak emerges cleanly above vanishing background
8 < pT(trig) < 15 GeV/c
pT(assoc) > 2 GeV/cpT(assoc) > 3 GeV/cpT(assoc) > 4 GeV/cpT(assoc) > 5 GeV/cpT(assoc) > 6 GeV/cpT(assoc) > 7 GeV/cpT(assoc) > 8 GeV/c