April 28, 2005Ohio State University, S. Manly1 The Information of Flow at RHIC Not a systematic...

April 28, 2005Ohio State University, S. Manly 1

The Information of The Information of Flow at RHICFlow at RHIC

Not a systematic review of historical/RHIC/PHOBOS results. More a personal tour of what I find

interesting with emphasis on PHOBOS results.

Steven ManlyUniv. of Rochester

Ohio State UniversityApril 28, 2005

[email protected]://hertz.pas.rochester.edu/smanly/


Trying to understand the Trying to understand the different faces of QCD different faces of QCD

Why do we believe in this QCD crap anyway?


q qqq

Quantum Chromodynamics - QCDQuantum Chromodynamics - QCD

Similar to QED … Similar to QED … But ... Gauge field But ... Gauge field carries the chargecarries the charge

q q

distance

energy density, temperature

rel

ativ

e st

ren

gth

asymptotic freedom

qq qq

confinement

qq


A few reasons we believe QCD is a good description of the strong interaction?

Deep inelastic scattering: There are quarks.

From D.H. Perkins, Intro. to High Energy Physics

nucleon

parton

P

Px



No direct observation of quarks: confinement



ee

qqhadronseeR

)(

P. Burrows, SLAC-PUB7434, 1997

R. Marshall, Z. Phys. C43 (1989) 595

Need the “color” degree of freedom



Event shapes

e+e- Zo qq e+e- Zo qqg



Measure the coupling

P. Burrows, SLAC-PUB7434, 1997


Strong interaction is part of our heritage

April 28, 2005Ohio State University, S. Manly 10qqqq

qqqq

qqq

qqq

qqq

qqq

The essence of mass at the quantum levelThe essence of mass at the quantum level(quantum field theory)(quantum field theory)

Strongly interacting particles interact with the vacuum

condensate … which makes them much heavier than the constituent

quark masses.


The view from above


“Flow” = patterns in the energy, momentum, or particle density distributions that we use to ferret out clues as to the nature of the collision/matter

To what extent is the initial geometric

asymmetry mapped into the final state?

View along beamline


Flow as an experimental probeFlow as an experimental probe

Sensitive to interaction strength

Sensitive to very early times and particle velocities since asymmetry disappears with

time With sufficient coverage, it probes longitudinal

uniformity of system

View along beamline


(reaction plane)

Flow quantifiedFlow quantified

dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R) + ... )

View along beamline

Fourier decomposition of the azimuthal multiplicity distribution

Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671

Best estimate event plane

iii

iii

w

w

2cos

2sintan

2

1 12


(reaction plane)


Directed flow

Flow quantifiedFlow quantifiedView from

above

View along beamline


(reaction plane)


Elliptic flow


View along beamline


(reaction plane)


Higher terms


View along beamline


b (reaction plane)

View along beamline

n=2, elliptic flown=2, elliptic flow


Flow at RHIC to date (a few highlights)Flow at RHIC to date (a few highlights)

Elliptic flow is large near =0 (relative to hydro limit)

||<1

(PHOBOS : Normalized Paddle Signal)

Hydrodynamic limit

STAR: PRL86 (2001) 402

PHOBOS preliminary

Hydrodynamic limit

STAR: PRL86 (2001) 402

PHOBOS preliminary

Thanks to M. Kaneta




V2(pT) grows with pT at low pT, consistent with hydro (including fine structure!)

PRL 91 (2003) 182301




V2(pT) grows with pT at low pT, consistent with hydro

V2(pT) saturates at high pT

STAR 130 GeV 4-cumulant


STAR 130 GeV Reaction Plane

5-53% central

Preliminary

PHOBOS 200 GeV0-55% central

pT (GeV/c)

v 2

Preliminary




Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference

Perhaps viscous corrections to elliptic flow grow with pT reducing v2 Teaney Phys. Rev. C 68 (2004) 034913



Xhangbu Xu, Quark Matter 2004nucl-ex/0306007







Elliptic flow falls off sharply as a function of ||

T.Hirano, K.Tsuda, PRC66,054905(2002).








n2 terms observed








n2 terms observed

Strongly interacting

dense matter! Partonic?

Longitudinal structure of the collision not trivially understood

Systematic study of v2(E,) probes the longitudinal dynamics of the collisionRecent work


Flow in PHOBOSFlow in PHOBOS


Large coverage

Data at 19.6, 62.4, 130 and 200 GeV

1m2m

5m

0 1 2 3 4 512345

coverage for vtx at z=0


Subevent technique: correlate event plane in one part of detector to asymmetry in track pattern in other part of detector

Correct for imperfect reaction plane resolution

-2.0 < < -0.1

SubE (a) SubE (b)

na n

b

0.1 < < 2.0

dependence of the multiplicity

Flow: basic methodFlow: basic method


Pixelized detectorPixelized detector

Hit saturation, grows with occupancy

Sensitivity to flow reduced

Can correct using analog energy deposition

–or-

measure of occupied and unoccupied pads in local region assuming Poisson statistics


z

Dilutes the flow signal

Remove Background

Estimate from MC and correct

flow signal

Azimuthally symmetric background

+

Azimuthally symmetric backgroundsAzimuthally symmetric backgrounds


Background suppressionBackground suppression

Works well in Octagon

dE

(keV)cosh

Background!

Technique does not work in rings because angle of incidence is ~90

Beampipe

Detector

Demand energy deposition be consistent with angle


RingsN Octagon RingsP

Spec holes

Vtx holes



Hit-based methodHit-based method

Vertex range -10<z<10

Subevents for reaction plane evaluation


Flow: method continuedFlow: method continued

Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671

Determine event plane in each subevent, 2±






Correlate 2± with hits outside of given subevent to get raw v2




Determine event plane resolution by correlating 2+ and 2

-





Correct raw v2 by resolution (factor of 1.7 to 3 depending on energy and centrality, well understood)

Correction determined from data




Resolution-corrected v2 is further corrected by ~30%

dilution due to azimuthally symmetric background

effects due to residual bias in 2± due to hole filling

Correction derived from Monte Carlo




Have agreement between:

Two hit-based analyses one “holy”, one not

Track-based analysis with NO background



vv2 2 vs. vs. (four energies) (four energies)

(0-40% central Au+Au data)

Bars are 1 “statistical” errors, expect some correlation




Boxes are 90% C.L. systematic errors




Shape is triangular at all four energies, no evidence of plateau




Drop highest || points at 19.6 GeV in following results


Systematic errorsSystematic errors

Hit definition

Beam orbit/alignment

Subevent definition

Transverse vertex position cut

Bins for weighting matrix definition

Dead channel correction algorithm

Poisson occupancy correction algorithm

Hole filling algorithm

Knowledge of azimuthally symmetric background

dN/d shape

Symmetry in


vv2 2 vs. vs. (four energy overlay) (four energy overlay)

Only statistical errors shown

Preliminary

Au+Au data(0-40% central)


ppTT selection important selection important

PHENIX, nucl-ex/0411040


CGC+Hydro

Flat+Gaussian initialization

T. Hirano, RBRC flow workshop, Nov. 2003

T. Hirano, nucl-th/0410017, presented at ISOMD in July 2004


Heinz and Kolb, nucl-th/0403044


M. Csanad, T. Csorgo, B. Lorstad, Nucl.Phys.A742:80-94,2004. [NUCL-TH 0310040]

Buda-Lund hydrodynamic modelBuda-Lund hydrodynamic model


M. Csanad, T. Csorgo, B. Lorstad, Nucl.Phys.A742:80-94,2004.[NUCL-TH 0310040] and M. Csanad et al, private communication and work in preparation.


Evolution of vEvolution of v22 with energy with energy

Preliminary


Note: pT-integrated values


Take out differing beam boosts by going into

approximate frame of reference of target

Look at ’ scaling

Extended longitudinal scalingExtended longitudinal scaling

PHOBOS Au+Au results

PRL 91, 052303 (2003)“limiting fragmentation” energy

independence in ’=||-ybeam


y vs. y vs.

Boost invariant spectra transform as:

)(cosh

cosh

)()(),(

222 TTTT

T

TTT

TTT

TTT

pdydpp

dN

pm

p

pdydpp

dNp

dydpp

dN

d

dyp

ddpp

dN

Jacobian suppresses spectra at low , low pT, and for large mass


y vs. y vs. : effect on multiplicity: effect on multiplicity

dN/ddN/dy

0


y vs. y vs. : effect on multiplicity: effect on multiplicity


y vs. y vs. : effect on v: effect on v22

0

V2()V2(y)

No change in the qualitative features of the result (<20% at =0)


y vs. y vs. : effect on v: effect on v22



Preliminary

Au+Au data

(0-40% central)

Extended longitudinal scaling of vExtended longitudinal scaling of v22


Longitundinal scaling and elliptic flowLongitundinal scaling and elliptic flow


Preliminary


’=||-ybeam


Near future: Near future: finalizing directed flowfinalizing directed flow

Cu-Cu flowCu-Cu flow

Does flow scale with multiplicity and eccentricity? Would be strange given success of hydrodynamics.

Different system with different energy density in the initial state, perhaps we test if falling v2 is due to the highly

viscous late hadronic stage

Heinz, nucl-th/0412094 and Teaney, Lauret, Shuryak, nucl-th/0110037

With all the differential flow data and progress in hydro models, we may be entering a stage where we can probe the

nature of the beast.


ConclusionsConclusions

Interaction length is short - early thermalization likelyInteraction length is short - early thermalization likely

Hydro works well at mid-Hydro works well at mid- … dense, almost ideal fluid … dense, almost ideal fluid

Flow gives evidence for partonic energy loss in medium and Flow gives evidence for partonic energy loss in medium and quark coalescencequark coalescence

Is Hydro/Bjorken/Feynman consistent with multiplicity and Is Hydro/Bjorken/Feynman consistent with multiplicity and elliptic flow data as function of elliptic flow data as function of ηη? Evidence for Landau?? Evidence for Landau?

No indication of sharp change in dynamics of particle No indication of sharp change in dynamics of particle production as function of production as function of or E from 20-200 GeV. But maybe or E from 20-200 GeV. But maybe a smooth evolution as initial energy density decreased and a smooth evolution as initial energy density decreased and viscosity/time spent as hadronic gas increases?viscosity/time spent as hadronic gas increases?

Stay tuned for Cu-Cu results.Stay tuned for Cu-Cu results.


Au-Au event in the PHOBOS detector

Backup slides


Acceptance (phase space) weightingAcceptance (phase space) weighting

Octagonal detector

Require circular symmetry for equal phase space per pixel

Pixel’s azimuthal phase space coverage depends on location

Relative phase space weight in annular rings = <Nocc>-1


Determining the collision pointDetermining the collision point

High Resolution

extrapolate spectrometer tracks

Low Resolution

octagon hit density peaks at vertex z

position



Spec holes

Vtx holes

Detector symmetry issues where SPEC vertex efficiency highest

Most data taken with trigger in place to enhance tracking efficiency



Offset vtx methodOffset vtx method

Limited vertex range along z

Subevents for reaction plane evaluation

Good azimuthal symmetry

Fewer events, no 19.6 GeV data

Technique used for published elliptic flow signal at 130 GeV


Dealing with the holesDealing with the holes


Inner layer of vertex detector fills holes in top and bottom. Must map hits from Si with different pad pattern and radius onto a “virtual” octagon Si layer


Dealing with the holesDealing with the holes


Fill spectrometer holes by extrapolating hit density from adjoining detectors onto a virtual Si layer. (Actual spec layer 1 is much smaller than the hole in the octagon.)



Track-based methodTrack-based method

Vertex range -8<z<10

Subevents for reaction plane

Momentum analysis

200 GeV data

Gap between tracks and subevents large

Little/no background


Elliptic flow vs Elliptic flow vs

width of bin

PHOBOSPreliminary

central 3-15%midcentral 15-25%peripheral 25-50%

Hit-based method

h±

M. Belt-Tonjes, Quark Matter 2004

200 GeV Au+Au


Track-basedHit-based

peripheral25-50%h±

v 2

PHOBOS Preliminary


midcentral15-25%h±

v 2

PHOBOS Preliminary

central3-15%h±


v 2

PHOBOS Preliminary

v2 vs. v2 vs. 200 GeV method comparison 200 GeV method comparison




STAR 130 GeV Reaction Plane5-53% central

Preliminary

PHOBOS 200 GeV0-55% central

pt (GeV/c)

v 2

Elliptic flow vs pElliptic flow vs pTT

Preliminary


Transformation of spectra from to y leads to

suppression of multiplicity at low pt and low ||

This leads to an enhancement of inclusive v2

at mid-

P. Kolb, Proc. of 17th Winter Workshop on Nuclear Dynamics (2001)

T. Hirano, BNL-Riken Workshop on Collective Flow and the QGP (Nov. 2003)

~10%


Poisson occupancy weighting

)1ln(

1),(

unocc

occ

N

N

eOcc


Directed flow as function of ’

Limiting fragmentationLimiting fragmentation

PHOBOS Au+Au results

M. Belt-Tonjes, QM04


Molnar and Voloshin, nucl-th/0302014

Partonic energy loss alone leads drop at very large pT and does not account for meson/baryon differences

Quark coalescence vs. fragmentationQuark coalescence vs. fragmentation

nucl-ex/0306007nucl-ex/0305013


v 1

PHOBOS Preliminary

PHOBOS AuAu √sNN=19.6 GeV

NA49 PbPb √sNN=17.2 GeV

Phys.Rev.C68, 034903, 2003

6-55%

MinimumBias

h±

±

19.6 GeV AuAu & 17.2 GeV PbPb


STAR AuAu 200 GeV 10-70% central

v1 at 200 GeV AuAu:PHOBOS & STARv 1

STAR, PRL 92 (2004) 062301

PHOBOS Preliminary

PHOBOS 6-55% centralh±


() PHOBOS Preliminary v2200

() PHOBOS v2130

Minimum Bias

h±

v2 vs. at 130 and 200 GeV AuAu

() PRL 89, 222301 (2002)

Hit-based method

() Nucl.Phys. A715 (2003) 611-614

April 28, 2005Ohio State University, S. Manly1 The Information of Flow at RHIC Not a systematic...

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