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Latest Results From PHOBOS
David HofmanUniversity of Illinois at Chicago
2Shanghai David Hofman - UIC
QM’06 PHOBOSPHOBOS 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 ongoing Ph.D. theses
3Shanghai David Hofman - UIC
QM’06 PHOBOSPHOBOS Experiment
PHOBOS
4Shanghai David Hofman - UIC
QM’06 PHOBOSColliding Nuclei at RHIC
5Shanghai David Hofman - UIC
QM’06 PHOBOSTwo “snapshots” of colliding nuclei at RHIC
nuclei crossing times extremely fast
RHIC: ~0.13 fm/cSPS: ~1.6 fm/cAGS: ~5.3 fm/c
6Shanghai David Hofman - UIC
QM’06 PHOBOSWell known: initial collision geometry matters
Initial overlap eccentricity
Visible in final measured particle azimuthal angular
distributions
Elliptic Flow
ReactionPlane
bImpact
Parameter
0
7Shanghai David Hofman - UIC
QM’06 PHOBOSWell known: initial collision geometry matters
To first order: initial collision geometry drives magnitude of v2
(of course, the density also matters)
Elliptic Flow
Initial Eccentricity
Final ParticleDistributions
Initial overlap eccentricity
Visible in final measured particle azimuthal angular
distributions
bImpact
Parameter
ReactionPlane
0
v2
8Shanghai David Hofman - UIC
QM’06 PHOBOSIs our first RHIC snapshot “in focus”?
Lets focus on: the spatial distribution of the interaction points
of participating nucleons
Au+Au
b
9Shanghai David Hofman - UIC
QM’06 PHOBOSIs our first RHIC snapshot “in focus”?
for the same b, these interaction points will vary from event-to-
event
Lets focus on: the spatial distribution of the interaction points
of participating nucleons
b b
Au+Au Au+Au
10Shanghai David Hofman - UIC
QM’06 PHOBOSIs our first RHIC snapshot “in focus”?
From PHOBOS @ Quark Matter 2005
explored much further since then
and thus the relevant eccentricity for elliptic flow also varies event-
by-event
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
b b
Au+Au Au+Au
0
0
11Shanghai David Hofman - UIC
QM’06 PHOBOSDoes using make a difference?
YES
Increasingly important for smaller systems
<std>“standard” calculation
<part>“participant” nucleonsevent-by-event calculation
200 GeV
12Shanghai David Hofman - UIC
QM’06 PHOBOSHow robust is Glauber MC + calculation?
calculation from Glauber MC is robust
arXiv:nucl-ex/0610037Submitted to PRL
More recent studies have included variations in individual nucleon density profiles and
different Npart and Ncoll weighting.
90% CL bands on calculation
Studied variations in:
In collaboration with Ulrich Heinz
min N-N separation
NN
nuclearradius
skin depth
13Shanghai David Hofman - UIC
QM’06 PHOBOSHow robust is Glauber MC + calculation?
arXiv:nucl-ex/0610037Submitted to PRL
90% CL bands on calculation
Studied variations in:
Bhalerao, Ollitrault – PLB641 260, (2006)Ollitrault – private communications (2006)PHOBOS internal MC
calculation from Glauber MC is robust
More recent studies have included variations in individual nucleon density profiles and
different Npart and Ncoll weighting.
In collaboration with Ulrich Heinz
min N-N separation
NN
nuclearradius
skin depth
14Shanghai David Hofman - UIC
QM’06 PHOBOSData: average v2 in Cu+Cu and Au+Au
Cu+CuarXiv:nucl-ex/0610037
submitted PRL Au+Au: PRC 72 051901(R)
15Shanghai David Hofman - UIC
QM’06 PHOBOSAverage v2/ in Cu+Cu and Au+AuStandard Eccentricity
200 GeV
arXiv:nucl-ex/0610037, submitted to PRL
Cu+Cu
Au+Au
16Shanghai David Hofman - UIC
QM’06 PHOBOSAverage v2/ in Cu+Cu and Au+AuParticipant EccentricityStandard
Eccentricity200 GeV200 GeV
arXiv:nucl-ex/0610037, submitted to PRL
Cu+Cu
Au+Au
arXiv:nucl-ex/0610037, submitted to PRL
Cu+Cu
Au+Au
17Shanghai David Hofman - UIC
QM’06 PHOBOS
Voloshin, Poskanzer, PLB 474 27 (2000); Heiselberg, Levy, PRC 59 2716, (1999)
Average v2/ in Cu+Cu and Au+AuParticipant EccentricityStandard
Eccentricity200 GeV200 GeV
arXiv:nucl-ex/0610037, submitted to PRL arXiv:nucl-ex/0610037, submitted to PRL
unifies average v2 in Cu+Cu and
Au+Au
Related work: Miller, Snellings, Zhu, Bleicher, Stöcker
Cu+Cu
Au+Au
Cu+Cu
Au+Au
18Shanghai David Hofman - UIC
QM’06 PHOBOS
Voloshin, Poskanzer, PLB 474 27 (2000); Heiselberg, Levy, PRC 59 2716, (1999)
Average v2/ in Cu+Cu and Au+AuParticipant EccentricityStandard
Eccentricity200 GeV200 GeV
arXiv:nucl-ex/0610037, submitted to PRL arXiv:nucl-ex/0610037, submitted to PRL
unifies average v2 in Cu+Cu and
Au+Au
Related work: Miller, Snellings, Zhu, Bleicher, Stöcker
Cu+Cu
Au+Au
Cu+Cu
Au+Au
19Shanghai David Hofman - UIC
QM’06 PHOBOS New Data: pT dependence of v2/
Au+Au and Cu+Cu at matched Npart
unifies midrapidity v2(pT) in Cu+Cu and Au+Au
20Shanghai David Hofman - UIC
QM’06 PHOBOS scaling as a function of
The collision geometry controls the dynamical evolution of heavy ion collisions.
Talk by Rachid Nouicer
Cu+Cu and Au+Au at matched Npart
21Shanghai David Hofman - UIC
QM’06 PHOBOS scaling as a function of
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.
Cu+Cu and Au+Au at matched Npart
22Shanghai David Hofman - UIC
QM’06 PHOBOSFluctuations in participant eccentricity
What magnitude of fluctuations are expected?
Expect large dynamical fluctuation in the participant eccentricity
Quantify with (part)/<part>
23Shanghai David Hofman - UIC
QM’06 PHOBOSNew Analysis: event-by-event v2 measurement
• Utilize Full Phase space coverage of PHOBOS (||<5.4, ~2).
• Detailed modeling of detector response, statistical fluctuations and multiplicity dependence.– Method is described in
arXiv:nucl-ex/0608025
• Measure v2 on an event-by-event basis.
• Take e-by-e result and average to compare to our other results.
200 GeV Au+Au
<v2> measured event-by-event is in agreement with both hit and track based PHOBOS results.
24Shanghai David Hofman - UIC
QM’06 PHOBOSNew Result: v2 and part Fluctuations
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
(v2)/<v2> in 200 GeV Au+Au Collisions
25Shanghai David Hofman - UIC
QM’06 PHOBOSNew Result: v2 and part Fluctuations
band: 90% CL
PHOBOS v2 result
MC with nofluctuations
Observe significant dynamical v2 fluctuations
(v2)/<v2> in 200 GeV Au+Au Collisions
26Shanghai David Hofman - UIC
QM’06 PHOBOSNew Result: v2 and part Fluctuations
Poster by Burak Alver and talk by Constantin Loizides
Magnitude of v2 fluctuations is in agreement with part fluctuations
(v2)/<v2> and (part)/<part> in 200 GeV Au+Au Collisions
PHOBOS part prediction
PHOBOS v2 result
MC with nofluctuations
band: 90% CL
Expanding Differentially in Phase Space
28Shanghai David Hofman - UIC
QM’06 PHOBOSNew Data: global charged particle emission
Extended longitudinal scaling
Midrapidity charged particles
Midrapidity charged particle spectra
Highlights from QM05
Energy/Centrality factorization and “scaling laws” in global charged particle production
Phys.Rev. C74 (2006) 021901Phys.Rev.Lett. 94 (2005) 082304Nucl.Phys. A774 (2006) 113-128
29Shanghai David Hofman - UIC
QM’06 PHOBOSNew Analysis: two particle correlations
PHOBOSPreliminary
PHOBOSPreliminary
( , ) ( 1) 1, )
, )
(
(n
n
FR n
B
h±h±
-6
Cu+Cu @ 200 GeV0-10% central
p+p @ 200 GeV
6
-6
6
30Shanghai David Hofman - UIC
QM’06 PHOBOSNew Analysis: two particle correlations
PHOBOSPreliminary
PHOBOSPreliminary
( , ) ( 1) 1, )
, )
(
(n
n
FR n
B
h±h±
-6
Cu+Cu @ 200 GeV0-10% central
6
-6
6
p+p @ 200 GeV
31Shanghai David Hofman - UIC
QM’06 PHOBOSNew Analysis: two particle correlations
Study the short-range rapidity correlations
PHOBOSPreliminary
PHOBOSPreliminary
( , ) ( 1) 1, )
, )
(
(n
n
FR n
B
h±h±
-6
Cu+Cu @ 200 GeV0-10% central
6
-6
6
p+p @ 200 GeV
32Shanghai David Hofman - UIC
QM’06 PHOBOSNew Result: effective cluster size
Talk by Wei Li
On average, particles tend to be produced in clusters with a size of 2-3. Interesting centrality dependence – can compare to
other systems
Keff = effective cluster size
p+p
scale error
2
33Shanghai David Hofman - UIC
QM’06 PHOBOSNew Data: antiparticle/particle ratios200 GeV Cu+Cu and Au+Au
Detailed measurement of antiparticle/particle ratios as function of
centrality
200, 62.4 GeV Cu+Cu
34Shanghai David Hofman - UIC
QM’06 PHOBOSNew Publication: identified particle spectra
Talk by Gabor Veres
First published identified spectra for 62.4 GeV Au+Au at RHIC
(down to very low pT, a unique PHOBOS measurement)
arXiv:nucl-ex/0610001submitted to PRC
blast-wave fits
62.4 GeV Au+Au
35Shanghai David Hofman - UIC
QM’06 PHOBOSPHOBOS Physics for QM06
• New Analyses:– Elliptic flow fluctuations
36Shanghai David Hofman - UIC
QM’06 PHOBOSPHOBOS Physics for QM06
• New Analyses:– Elliptic flow fluctuations– Two particle correlations
37Shanghai David Hofman - UIC
QM’06 PHOBOSPHOBOS Physics for QM06
• New Analyses:– Elliptic flow fluctuations– Two particle correlations
• Extended Analyses:– Elliptic flow in Cu+Cu
38Shanghai David Hofman - UIC
QM’06 PHOBOSPHOBOS Physics for QM06
• New Analyses:– Elliptic flow fluctuations– Two particle correlations
• Extended Analyses:– Elliptic flow in Cu+Cu– Charged particle multiplicity
39Shanghai David Hofman - UIC
QM’06 PHOBOSPHOBOS Physics for QM06
• New Analyses:– Elliptic flow fluctuations– Two particle correlations
• Extended Analyses:– Elliptic flow in Cu+Cu– Charged particle multiplicity– Anti-particle/particle ratios
40Shanghai David Hofman - UIC
QM’06 PHOBOSPHOBOS Physics for QM06
• New Analyses:– Elliptic flow fluctuations– Two particle correlations
• Extended Analyses:– Elliptic flow in Cu+Cu– Charged particle multiplicity– Anti-particle/particle ratios
• QM06 Primary Message:
PHOBOS has measured large dynamical v2 fluctuations in 200 GeV Au+Au collisions. This suggests that the initial state thermalizes very rapidly, taking a detailed snapshot, which is propagated by the subsequent hydrodynamic evolution.
41Shanghai David Hofman - UIC
QM’06 PHOBOSFuture 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 Au+Au as detailed function of centrality• Spectator breakup in the fragmentation region• Charged particle yields in 200,410 p+p• Phi-meson production
• TALKS: Rachid Nouicer - v1 and v2 flow (Saturday, 2:40pm, Parallel 2.4) Constantin Loizides - v2 and part fluctuations (Saturday, 4:20pm, Parallel 2.4) Wei Li - Two-particle correlations (Sunday, 5:00pm, Parallel 3.2) Gabor Veres - Identified particle spectra and ratios (Sunday, 5:00pm, Parallel 3.4)
• POSTERS: Burak Alver – Elliptic flow fluctuations (Wednesday, 5:20pm, poster 14) Krzysztof Wozniak - Multiplicity fluctuations (Wednesday, 5:20pm, poster 82)
Total Number of Hits
Backups
43Shanghai David Hofman - UIC
QM’06 PHOBOSSummary of Backup Slides
• From R. Nouicer’s talk (Flow)– 44 Measuring flow in PHOBOS – 45 Track-based method details
– 46 Moments of part
• From C. Loizides’ talk (v2 fluct.)
– 47 Overview e-by-e v2 meas.
– 48 Methodology– 49 Glauber overview– 50 Glauber Robustness
• From W. Li’s talk (2-part. corr.)From W. Li’s talk (2-part. corr.)– 51 Methodology– 52 Cluster size parameterization
• From G. Veres’ talk (ident. part.)– 53 PHOBOS PID capability– 54 Particle ratios measurement
44
44
44
Rachid Nouicer - BNLPHOBOS QM2006
Measuring Flow in PHOBOS
Hit-based method
Ring counter Vertex detector
Large coverage: || < 5.4
Ring counters
Octagon
Spectrometer
Track-based method PHOBOS: PRC C72, 051901R (2005)PHOBOS: PRL 89, 222301 (2002)
45
45
45
Rachid Nouicer - BNLPHOBOS QM2006
Track-based method: Robustness of Measurements of vTrack-based method: Robustness of Measurements of v22 vs. p vs. pTT The large separation on between the reaction plane subevents and the measured
region reduces the non-flow correlations in track-based (hit-based) method.
Octagonand Rings
RingsOnly
OctagonOnly
1) 2.0 < ||< 3.2 2) 3.0 < ||< 5.4 3) 2.0 < ||< 5.4
• Reaction plane subevents
• v2(pT) measured in 0 < < 1.6
Statistical errors only
Spectrometer
Cu+Cu at 200 GeV
PHOBOS
Preliminary
Track-based method
46
46
46
Rachid Nouicer - BNLPHOBOS QM2006
It has been suggested that v2 may scale as instead of
- Bhalerao, Ollitrault – PLB 641, 260 (2006)- Ollitrault – private communications (2006)
Theorists & PHOBOS since QM2005
• In Collaboration with Ulrich Heinz
2partε partε
PHOBOS MC
47Shanghai David Hofman - UIC
QM’06 PHOBOS
48Shanghai David Hofman - UIC
QM’06 PHOBOS
49Shanghai David Hofman - UIC
QM’06 PHOBOS
50Shanghai David Hofman - UIC
QM’06 PHOBOS
Methodology
Two-particle correlation function:
Background:
Foreground:Event 1
Event 2
( , ) ( 1) 1, )
, )
(
(n
n
FR n
B
4
1 2 1 21 2 1 2
1( , ) ( , , , )
( 1)II n
n nn
dF
n n d d d d
2 2
1 1 2 21 1 2 2
1 1( , ) ( , ) ( , )I I n nn n n
n n
d dB
n d d n d d
~
~
Wei Li, MITQM2006, Shanghai
Parameterize cluster size (multiplicity)
R() ()B()
1
()exp ()2
4 2
Keff 1 k(k 1)
k 1
B()Keff : effective cluster size
Decay width:
: background distribution
Quantitatively understand cluster phenomena
Two-particle rapidity correlation function:
2
correlations between particles from one cluster
k: cluster sizeK. Eggert et al.,
Nucl. Phys. B 86:201, 1975
Wei Li, MITQM2006, Shanghai
53
pT (GeV/c)0.03 0.3 3.0
Stoppingparticles
dE/dx TOF
Particle ID from low to high pT
Eloss (MeV)
PHOBOS PID Capabilities
1 2 3 4 50p (GeV/c)
30
40
50
60
70
1/v
(ps/
cm)p+p
K +K + -
++-
p (GeV/c)
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006
54
Controlling systematic uncertainties
)()( BBpapa
Geometrical acceptance drops out of the ratios:
Ratios measured independently for different:
• bending directions
• spectrometer arms
)()( BBpapa
Z Z
B+B–
h+
h–h+
h+ h+
h–
h–h–
by changing the polarity of the magnetic field
Gábor I. Veres Quark Matter 2006, Shanghai, November 14-20, 2006