latest results from phobos david hofman university of illinois at chicago

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


QM’06 PHOBOSPHOBOS Experiment

PHOBOS


QM’06 PHOBOSColliding Nuclei at RHIC


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


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


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


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



for the same b, these interaction points will vary from event-to-

event



b b

Au+Au Au+Au



From PHOBOS @ Quark Matter 2005

explored much further since then

and thus the relevant eccentricity for elliptic flow also varies event-

by-event



for the same b, these interaction points will vary from event-to-

event

b b

Au+Au Au+Au

0

0


QM’06 PHOBOSDoes using make a difference?

YES

Increasingly important for smaller systems

<std>“standard” calculation

<part>“participant” nucleonsevent-by-event calculation

200 GeV


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


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


QM’06 PHOBOSData: average v2 in Cu+Cu and Au+Au

Cu+CuarXiv:nucl-ex/0610037

submitted PRL Au+Au: PRC 72 051901(R)


QM’06 PHOBOSAverage v2/ in Cu+Cu and Au+AuStandard Eccentricity

200 GeV

arXiv:nucl-ex/0610037, submitted to PRL

Cu+Cu

Au+Au


QM’06 PHOBOSAverage v2/ in Cu+Cu and Au+AuParticipant EccentricityStandard

Eccentricity200 GeV200 GeV


Cu+Cu

Au+Au


Cu+Cu

Au+Au


QM’06 PHOBOS

Voloshin, Poskanzer, PLB 474 27 (2000); Heiselberg, Levy, PRC 59 2716, (1999)

Average v2/ in Cu+Cu and Au+AuParticipant EccentricityStandard


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


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


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


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


QM’06 PHOBOSFluctuations in participant eccentricity

What magnitude of fluctuations are expected?

Expect large dynamical fluctuation in the participant eccentricity

Quantify with (part)/<part>


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.


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



band: 90% CL

PHOBOS v2 result

MC with nofluctuations

Observe significant dynamical v2 fluctuations

(v2)/<v2> in 200 GeV Au+Au Collisions



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


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


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



PHOBOSPreliminary

PHOBOSPreliminary

( , ) ( 1) 1, )

, )

(

(n

n

FR n

B

h±h±

-6


6

-6

6

p+p @ 200 GeV



Study the short-range rapidity correlations

PHOBOSPreliminary

PHOBOSPreliminary

( , ) ( 1) 1, )

, )

(

(n

n

FR n

B

h±h±

-6


6

-6

6

p+p @ 200 GeV


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


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


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


QM’06 PHOBOSPHOBOS Physics for QM06

• New Analyses:– Elliptic flow fluctuations



• New Analyses:– Elliptic flow fluctuations– Two particle correlations




• Extended Analyses:– Elliptic flow in Cu+Cu




• Extended Analyses:– Elliptic flow in Cu+Cu– Charged particle multiplicity




• Extended Analyses:– Elliptic flow in Cu+Cu– Charged particle multiplicity– Anti-particle/particle ratios




• 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.


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


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


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


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


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

latest results from phobos david hofman university of illinois at chicago

Documents

eventlets focus

rhic snapshot

spatial distribution

glauber mc calculation

peter steinberg

richard bindel

christof roland

gunther roland