Download - Latest Results from the PHOBOS Experiment
Latest Results from the PHOBOS Experiment
Barbara WosiekThe Henryk Niewodniczański Institute of Nuclear Physics
Polish Academy of Sciences
Kraków, [email protected]
for the Collaboration
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 1
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 Hołyński, 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 Woźniak, 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
9 Ph.D. StudentsBarbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 2
PHOBOS Detector
Unique low-pT measurements
Large acceptance for Nch-5.4 < η < 5.4 (0.5o < θ < 179.5o )
0 < φ < 2π
-5 -3 0 3 5η
2π
φ
RingsN Octagon RingsPVertex+Spec fill the Octagon holes
0
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 3
PHOBOS Research Program
I. Systematic study of charged hadron production inp+p, d+Au, Cu+Cu, Au+Au
II. Comprehensive study of correlations and fluctuations
PHOBOS
Analyses are based on data setscollected during the first 5 RHIC runs,
exploiting the large coverage in η and φ.
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 4
Systematic StudiesThe study of global properties of charged particle production
in different collision systems is essentially completed.arXiv:0709.4008 [nucl-ex]
η-4 -2 0 2 4
η
/dch
dN
0
50
100 22.4 GeV Cu+Cu
η
/dch
dN
50
100
150 62.4 GeV Cu+Cu
η
/dch
dN
50
100
150
200200 GeV Cu+Cu
0- 6%
6-15%
15-25%
25-35%
35-45%
45-55%
PHOBOS ‘fingerprints’:LARGE η coverage
BROAD centrality range
Cu-Cu, 62.4 GeVh±, 0-40%
Cu-Cu, 200 GeV, h± , 0-40%
Phys. Rev. Lett. 98 (2007) 242302
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 5
Systematic Studies: New Results
Charged particle production
arXiv:0709.4008 [nucl-ex]
TotchN
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 6
Poster by Gabor Veres
1 10 210 3100
5
10
15
20
25
30
22.4 GeV (Cu)
19.6 GeV (Au)
200 GeV
62.4 GeV
⟩/2
p
art
N⟨/chT
ot
N
⟩ part
N⟨
d + Au
) + p Inelasticpp(
Cu + Cu
Au + Au
Total charged particle multiplicityscales with Npart
Antiparticle to particle ratiossubmitted
At most weak dependence on system size
Poster by Vasu Chetluru
Systematic Studies: New ResultsUNIQUE PHOBOS measurements on
energy and centrality dependence of the low-pT spectra
[GeV/c]Tp
-110 1
]2/G
eV2
[c
TN
/dyd
p2
d-1 ) Tpπ
(2
1
10
210
310
)-π++π(
)-+K+(K
)p(p+
PHOBOSPHENIX
π K p
Au+Au 200 GeV , 0-6% Au+Au 62.4 GeVPHOBOS
Phys. Rev. C75, 024910 (2007) New data
No anomalous enhancementRadial flow effects breaking mT scaling
Au+Au 200 GeV 0-6% PHOBOS preliminary
Talk by Tomasz GburekBarbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 7
Systematic Studies: Summary
Particle production in HI collisions is controlled by simple scaling rulesNpart scaling of total Nch; extended longitudinal scaling in the nucleus rest frame; factorization of the energy and centrality dependencies
− The collision geometry determines the dynamical evolution of the system
− To date no theory/model can consistently explain the scaling rules
− The observations provide a tool for extrapolating RHIC data to the LHC collisions
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 8
Correlation & Fluctuation Studies
Exploit large η- φ coverage of the PHOBOS detector
PHOBOS Acceptance – by far the largest of all RHIC experiments
-5 -3 0 3 5η
2π
φ
RingsN Octagon RingsPVertex+Spec fill the Octagon holes
0
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 9
Correlation & Fluctuation StudiesInsight into different stages of the system evolution
Initial state Hydrodynamical evolution Freeze-out
Hadronizationtwo-particle correlations
Fluctuations of the
initial source geometry
Elliptic flowfluctuations
Medium response tohigh-pT partons
pT-triggered correlations
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 10
Correlation & Fluctuation Studies
New results from PHOBOS:
Fluctuations of the initial source geometry from the GlauberMonte Carlo model
Elliptic flow fluctuations corrected for non-flow effects
Two-particle correlations with high-pT trigger for Au+Au
Two-particle correlations in (∆η,∆φ) for pp, Cu+Cu, Au+Au
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 11
Initial Source EccentricityMonte Carlo Glauber (MCG) approach
arXiv:0711.3724 to be published in Phys. Rev. C
Robustness of <εpart>:
Cu+CuAu+Au
200 GeV
Phys. Rev. Lett. 98 (2007) 242302
Participant eccentricity
Choice of the MCG parameters• inter-nucleon separation• nuclear radius• nuclear skin depth• σNN
MCG model assumptions• binary collisions vs. participants• local matter distribution(point-like/Gaussian/hard-sphere)
Event-by-Event Fluctuations of εpartCalculation of the higher order cumulants
εpart{2}, εpart{4}
<εpart> is robust
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 12
Poster by Richard Hollis
v2 Fluctuations and Initial Geometry Fluctuations
Quark Matter 2006 Highlight:PHOBOS measured
large dynamical fluctuations of v2
>ε<
εσ≈
><σ
part
part
2
2 )(v
)v(
Quark Matter 2008:- Non-flow contribution determined from data
- Relative v2 fluctuationscorrected for non-flow contribution
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 13
This result was corrected for non-flowcontribution estimated from the HIJING model
(negligible, <2%)
Au+Au 200 GeV nucl-ex/0702036HIJING based non-flow correction
Au+Au 200 GeV PHOBOS preliminaryData based non-flow correction
Determination of the Non-Flow Term δNon-flow term: δ = <cos(2∆φ)>non-flow, ∆φ=φ1-φ2
• Non-flow component is dominated by short-range correlations in ∆η• Flow component depends on η and is present at all ∆η - all particles
are correlated with the reaction planeThis difference and the large PHOBOS acceptance in ηallow us to disentangle the two effects
Au-Au 200GeV, 40-45%22v
η2
η 1
For each η1 and η2 measure the two-particle correlations in ∆φ:
)2cos(),(v2),,(R 212221n φ∆ηη∝φ∆ηη
),()(v)(v),(v 2122122122 ηηδ+η⋅η=ηη
flow component non-flow termflow ⊕ non-flow
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 14
Au-Au 200GeV, 40-45%δ
η2
η 1
Determination of the Non-Flow Term δ• Assume that the non-flow component is small at large ∆η
• Fit at large ∆η (∆η > 2) to find the flow component of
For large ∆η:
• Subtract the flow component from to get δ(η1,η2)
• Average over dN/dη1, dN/dη2<δ>
),(v)(v)(v 21222212 ηη≈η⋅η
• Right-side was corrected for a small non-flow effect at ∆η>2, estimated from HIJING
),(v 2122 ηη
),(v 2122 ηη
non-flow
)(v)(v),(v),( 2212212221 η⋅η−ηη=ηηδ
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 15
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 16
Determination of the Non-Flow Term δ1. Determine v2(η1,η2)2 from the
correlations in (η1,η2,∆φ)
2. Fit v2(η1,η2)2 at ∆η>2 to get theflow component v2(η1)v2(η2)
3. Subtract flow componentfrom v2(η1,η2)2 to get δ(η1,η2)
4. Average over dN/dη1, dN/dη2
flow ⊕ non-flow non-flow
<δ>flow
Au-Au 200GeV, 40-45%22v
η2 η 1
Au-Au 200GeV, 40-45%δ
η2 η 1
η2 η 1
v2(η1)v2(η2)PHOBOS preliminaryAu-Au 200GeV, 40-45%
Au+Au 200GeV
Elliptic Flow Fluctuations
σ(v2) – measured elliptic flow fluctuations(flow ⊕ non-flow)
<δ> – non-flow term determined fromthe data
Contribution from non-flow to σ(v2)σδ(v2) = √<δ>/2 (arXiv:07080800)
Relative flow fluctuations corrected for non flow contribution
and comparedto the eccentricity fluctuations
Within systematic errors the magnitudeof v2 fluctuations
is in agreement with εpart fluctuations
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 17
Au-Au 200GeV
Au+Au 200GeV
Talk by Burak Alver
pT - Triggered Two-Particle Correlations
Au+Au 200 GeV, 0 - 30%PHOBOS preliminary
η∆φ∆ ddNd
N1 ch
2
trig
33cutnop
5.10c/GeV5.2passocassoc
T
trigtrigT
<η<−⋅−
<η<>
Motivation: medium response to high-pT partonstests the presence of long-range ∆η correlationsat near- and away-sides
For pions pT > 35 MeV/c at η~0pT > 4 MeV/c at η~4-5
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 18
pT - Triggered Two-Particle Correlations
Talk by Ed Wenger
Short-range|∆η| <1
Long-range–4< ∆η <–2
Talk by Ed Wenger
Central collisions Peripheral collisions
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 19
-6
6
PHOBOS p+p@200GeV
6
Cu+Cu@200GeV
-6
0-10%
Two-Particle CorrelationsHow are hadrons produced at freeze-out?
Phys. Rev. C75(2007)054913 J. Phys. G34(2007)s1005
New
⎥⎦
⎤⎢⎣
⎡−
φ∆η∆φ∆η∆
−=φ∆η∆ 1),(B),(F)1n(),(R
n
n
Multiplicity independent two-particle correlation function:
6
-6
Au+Au@200GeV0-10%
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 20
Two-Particle Correlations
Au+Au 200 GeV 0-10%
Keff : effective cluster size√2 δ: cluster decay width
After averaging over ∆φ, R(∆η) showsshort-range correlations, which can be
explained in terms of clusters:
p+p
NpartK
effEffective cluster size in Cu+Cu and Au+Au
• Cluster size decreases with centrality• All cluster sizes are larger than extractedfrom models with resonances (~1.7)
• For the same Npart: Au+Au clusters > Cu+Cu clusters
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 21
Two-Particle CorrelationsComparison of Au+Au and Cu+ Cu
for the same fraction of the inelastic cross section σ/σ0
Near- and away-side clusters
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 22
Size of the clusters in Au+Auis similar to that in Cu+Cu
Away-side clusters are smaller and depend more strongly oncentrality than near-side ones.
Kef
f
1-σ/σ0
near-side
away-side
Kef
f
1-σ/σ0
Talk by Wei Li
Correlation & Fluctuation Studies: Conclusions
Fluctuations of the initial sourcegeometry are imprinted inthe final distributions of particles
system thermalizes very rapidly
Ridge effect persists up to ∆η = 4in central Au+Au collisions
Effective cluster size shows intriguing system size dependence
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 23
-4< ∆η <-2
Kef
f
1-σ/σ0
PHOBOS at Quark Matter 2008• TALKS:
Ed Wenger – High-pT triggered correlations in Au+Au collisionsTuesday, parallel session VIII, 16:10
Burak Alver – Measurement of non-flow correlations and elliptic flow fluctuationsin Au+Au collisions at RHICFriday, parallel session XII, 14:00
Tomasz Gburek – Energy and centrality dependence of particle productionat very low pT
Saturday, parallel session XVII, 14:40Wei Li – System size dependence of two-particle correlations in p+p, d+Au,
Cu+Cu and Au+AuSaturday, parallel session XIX, 15:20
• POSTERS (Wednesday) :Gabor Veres – System size, energy, centrality and pseudorapidity dependence of
charged-particle density in Au+Au and Cu+Cu collisions at RHICVasu Chetluru – Antiparticle to particle ratios using the PHOBOS detectorRichard Hollis – The importance of correlations and fluctuations on the initial
source eccentricity in high energy nucleus-nucleus collisions.
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 24
Initial Source EccentricityMonte Carlo Glauber (MCG) approach
arXiv:0711.3724 to be published in Phys. Rev. C
Study of the robustness of <εpart>:
Binary collisions vs. participants Local matter distributions
Number of participants0 50 100 150 200 250 300 350
⟩ pa
rt∈ ⟨
0
0.2
0.4
0.6
0.8
1Binaries (x=1)
Mixture (x=0.13)
Participants (x=0)
Number of participants0 50 100 150 200 250 300 350
1
1.2
1.4
Ratio to Participants
Number of participants0 50 100 150 200 250 300 350
⟩ pa
rt∈ ⟨
0
0.2
0.4
0.6
0.8
1= 0.6fm)
hsHard-sphere (R
= 0.3fm)gσGaussian (
Participants (point-like)
Number of participants0 50 100 150 200 250 300 350
0.7
0.8
0.9
1Ratio to Participants
Au+AuCu+Cu
Au+AuCu+Cu
Participant eccentricity is robust to the Glauber model assumptionsBarbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 26
Fluctuations of the Initial Source EccentricityFull MCG approach: includes spatial correlations among participantsarXiv:0711.3724 to be published in Phys. Rev. C
><= 222 v}EP{v
R0 0.5 1
α
1
1.5
2
= 0bkg
100, f≥ 2N
1≥ bkg
100, f≥ 2N
0 ≥ bkg
= 50, f2N
0≥ bkg
25, f≤ 2N
}EP{vv 2/1
2 =>><< αα
Event Plane Resolution, R
PHOBOS R: 0.13 – 0.55
higher order cumulants
Number of participants0 50 100 150 200 250 300 350
Ecc
entr
icity
0
0.2
0.4
0.6
0.8
1
⟩ part
∈ ⟨{2}part∈{4}part∈
⟩ RP
∈ ⟨s∈
Full MCG
Au+Au
Number of participants0 20 40 60 80 100
Ecc
entr
icity
0
0.2
0.4
0.6
0.8
1
⟩ part
∈ ⟨{2}part∈{4}part∈
⟩ RP
∈ ⟨s∈
Full MCG
Cu+Cu
Poster by Richard HollisBarbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 27
δ as a function of centrality
• Average δ(η1,η2) over all hit pairs
• Non-flow in data islarger than in HIJING• These values are valid for PHOBOS geometry
Au+Au200GeV
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 28
Model Comparison
Au+Au200GeV
• Results are in agreement with both Glauber and CGC calculations within errors
CGC: arXiv:0707.0249
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 29
Comparison to Total Fluctuations
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 30
Comparison to STAR
Error bars go down to 0 for red points
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 31
PYTHIA p+p Reference
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 32
• PHOBOS is limited by statistics in p+p • Compare our Au+Au results to PYTHIA,
which reasonably reproduces STAR p+p data
Ridge Extent in ∆η
0-10% central |∆φ|<1rad
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 33
Comparison to Predictions
0-10% central |∆φ|<1rad
C.Y. Wong, private communication
C.Y. Wong PRC76, 054908 (2007)
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 34
• Cluster size decreases with Npart in A+A, but not monotonically.• Enhancement of cluster from p+p to peripheral A+A.• No strong dependence on Npart for cluster decay width.
p+p p+p
Clusters in Cu+Cu and Au+Au
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 35
K. Eggert et al.,Nucl. Phys. B 86:201, 1975
Cluster Model
R(∆η) = α Γ(∆η)B(∆η)
−1⎡
⎣ ⎢
⎤
⎦ ⎥
Γ(∆η) ∝ exp −(∆η)2
4δ 2
⎛
⎝ ⎜
⎞
⎠ ⎟
Keff = α +1=< k(k −1) >
< k >+1=< k > +
σ k2
< k >
B(∆η)
Decay width: δ
: background distribution
Two-particle rapidity correlation function:
Keff : effective cluster size
2
correlations between particlesfrom one cluster
k: cluster size
Barbara Wosiek for PHOBOS Quark Matter'08 - Jaipur, India, Feb.4 37