April 28, 2005Ohio State University, S. Manly1 The Information of Flow 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 Manly Univ. of Rochester Ohio State University April 28,

April 28, 2005Ohio State University, S. Manly2 Trying to understand the different faces of QCD Why do we believe in this QCD crap anyway?

April 28, 2005Ohio State University, S. Manly3 q q Quantum Chromodynamics - QCD Similar to QED … But... Gauge field carries the charge q q distance energy density, temperature relative strength asymptotic freedom qq qq confinement qq

April 28, 2005Ohio State University, S. Manly4 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

April 28, 2005Ohio State University, S. Manly5 A few reasons we believe QCD is a good description of the strong interaction? No direct observation of quarks: confinement

April 28, 2005Ohio State University, S. Manly6 A few reasons we believe QCD is a good description of the strong interaction? P. Burrows, SLAC-PUB7434, 1997 R. Marshall, Z. Phys. C43 (1989) 595 Need the “color” degree of freedom

April 28, 2005Ohio State University, S. Manly7 A few reasons we believe QCD is a good description of the strong interaction? Event shapes e + e -  Z o  qqe + e -  Z o  qqg

April 28, 2005Ohio State University, S. Manly8 A few reasons we believe QCD is a good description of the strong interaction? Measure the coupling P. Burrows, SLAC-PUB7434, 1997

April 28, 2005Ohio State University, S. Manly9 Strong interaction is part of our heritage

April 28, 2005Ohio State University, S. Manly10qq qq qqq The essence of mass at the quantum level (quantum field theory) Strongly interacting particles interact with the vacuum condensate … which makes them much heavier than the constituent quark masses.

April 28, 2005Ohio State University, S. Manly11

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April 28, 2005Ohio State University, S. Manly14 The view from above

April 28, 2005Ohio State University, S. Manly15 “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

April 28, 2005Ohio State University, S. Manly16 Flow 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

April 28, 2005Ohio State University, S. Manly17 (reaction plane) Flow quantified dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) View along beamline Fourier decomposition of the azimuthal multiplicity distribution Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Best estimate  event plane

April 28, 2005Ohio State University, S. Manly18 (reaction plane) dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) Directed flow Flow quantified View from above View along beamline

April 28, 2005Ohio State University, S. Manly19 (reaction plane) dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) Elliptic flow Flow quantified View along beamline

April 28, 2005Ohio State University, S. Manly20 (reaction plane) dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) Higher terms Flow quantified View along beamline

April 28, 2005Ohio State University, S. Manly21 b (reaction plane) View along beamline n=2, elliptic flow

April 28, 2005Ohio State University, S. Manly22 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

April 28, 2005Ohio State University, S. Manly23 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro (including fine structure!) PRL 91 (2003)

April 28, 2005Ohio State University, S. Manly24 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T STAR 130 GeV 4-cumulant STAR 130 GeV 2-cumulant STAR 130 GeV Reaction Plane 5-53% central Preliminary PHOBOS 200 GeV 0-55% central p T (GeV/c) v2v2 Preliminary

April 28, 2005Ohio State University, S. Manly25 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference Perhaps viscous corrections to elliptic flow grow with p T reducing v 2 Teaney Phys. Rev. C 68 (2004) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T Xhangbu Xu, Quark Matter 2004 nucl-ex/

April 28, 2005Ohio State University, S. Manly26 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference Elliptic flow falls off sharply as a function of |  | T.Hirano, K.Tsuda, PRC66,054905(2002).

April 28, 2005Ohio State University, S. Manly27 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference Elliptic flow falls off sharply as a function of |  | n  2 terms observed

April 28, 2005Ohio State University, S. Manly28 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference Elliptic flow falls off sharply as a function of |  | n  2 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 collision Recent work 

April 28, 2005Ohio State University, S. Manly29 Flow in PHOBOS

April 28, 2005Ohio State University, S. Manly30 Large  coverage Data at 19.6, 62.4, 130 and 200 GeV 1m 2m 5m  coverage for vtx at z=0

April 28, 2005Ohio State University, S. Manly31  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na nbnb 0.1 <  < 2.0  dependence of the multiplicity Flow: basic method

April 28, 2005Ohio State University, S. Manly32 Pixelized detector Pixelized 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

April 28, 2005Ohio State University, S. Manly33  z Dilutes the flow signal  Remove Background  Estimate from MC and correct flow signal Azimuthally symmetric background + Azimuthally symmetric backgrounds Azimuthally symmetric backgrounds

April 28, 2005Ohio State University, S. Manly34 Background 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

April 28, 2005Ohio State University, S. Manly35   RingsN OctagonRingsP Spec holes Vtx holes

April 28, 2005Ohio State University, S. Manly36   RingsN OctagonRingsP Hit-based method Vertex range -10<z<10 Subevents for reaction plane evaluation

April 28, 2005Ohio State University, S. Manly37 Flow: method continued Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Determine event plane in each subevent,  2 ±   RingsN OctagonRingsP

April 28, 2005Ohio State University, S. Manly38 Flow: method continued   RingsN OctagonRingsP Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Correlate  2 ± with hits outside of given subevent to get raw v 2

April 28, 2005Ohio State University, S. Manly39 Flow: method continued Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Determine event plane resolution by correlating  2 + and  2 -   RingsN OctagonRingsP

April 28, 2005Ohio State University, S. Manly40 Flow: method continued Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Correct raw v 2 by resolution (factor of 1.7 to 3 depending on energy and centrality, well understood) Correction determined from data   RingsN OctagonRingsP

April 28, 2005Ohio State University, S. Manly41 Flow: method continued Resolution-corrected v 2 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   RingsN OctagonRingsP

April 28, 2005Ohio State University, S. Manly42 Flow: method continued Have agreement between:  Two hit-based analyses  one “holy”, one not  Track-based analysis with NO background   RingsN OctagonRingsP

April 28, 2005Ohio State University, S. Manly43 v 2 vs.  (four energies) (0-40% central Au+Au data) Bars are 1  “statistical” errors, expect some correlation

April 28, 2005Ohio State University, S. Manly44 v 2 vs.  (four energies) (0-40% central Au+Au data) Boxes are 90% C.L. systematic errors

April 28, 2005Ohio State University, S. Manly45 v 2 vs.  (four energies) (0-40% central Au+Au data) Shape is triangular at all four energies, no evidence of plateau

April 28, 2005Ohio State University, S. Manly46 v 2 vs.  (four energies) (0-40% central Au+Au data) Drop highest |  | points at 19.6 GeV in following results

April 28, 2005Ohio State University, S. Manly47 Systematic 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 

April 28, 2005Ohio State University, S. Manly48 v 2 vs.  (four energy overlay) Only statistical errors shown Preliminary Au+Au data (0-40% central)

April 28, 2005Ohio State University, S. Manly49 p T selection important PHENIX, nucl-ex/

April 28, 2005Ohio State University, S. Manly50 CGC+Hydro Flat+Gaussian initialization T. Hirano, RBRC flow workshop, Nov T. Hirano, nucl-th/ , presented at ISOMD in July 2004

April 28, 2005Ohio State University, S. Manly51 Heinz and Kolb, nucl-th/

April 28, 2005Ohio State University, S. Manly52 M. Csanad, T. Csorgo, B. Lorstad, Nucl.Phys.A742:80-94,2004. [NUCL-TH ] Buda-Lund hydrodynamic model

April 28, 2005Ohio State University, S. Manly53 M. Csanad, T. Csorgo, B. Lorstad, Nucl.Phys.A742:80-94,2004.[NUCL-TH ] and M. Csanad et al, private communication and work in preparation.

April 28, 2005Ohio State University, S. Manly54 Evolution of v 2 with energy Preliminary Au+Au data (0-40% central) Note: p T -integrated values

April 28, 2005Ohio State University, S. Manly55 Take out differing beam boosts by going into approximate frame of reference of target Look at  ’ scaling Extended longitudinal scaling PHOBOS Au+Au results PRL 91, (2003) “limiting fragmentation”  energy independence in  ’=|  |-y beam

April 28, 2005Ohio State University, S. Manly56 y vs.  Boost invariant spectra transform as: Jacobian suppresses spectra at low , low p T, and for large mass

April 28, 2005Ohio State University, S. Manly57 y vs.  : effect on multiplicity dN/d  dN/dy 0

April 28, 2005Ohio State University, S. Manly58 y vs.  : effect on multiplicity

April 28, 2005Ohio State University, S. Manly59 y vs.  : effect on v 2 0 V2()V2() V 2 (y) No change in the qualitative features of the result (<20% at  =0)

April 28, 2005Ohio State University, S. Manly60 y vs.  : effect on v 2

April 28, 2005Ohio State University, S. Manly61 Only statistical errors shown Preliminary Au+Au data (0-40% central) Extended longitudinal scaling of v 2

April 28, 2005Ohio State University, S. Manly62 Longitundinal scaling and elliptic flow Only statistical errors shown Preliminary Au+Au data (0-40% central)  ’=|  |-ybeam

April 28, 2005Ohio State University, S. Manly63 Near future:  finalizing directed flow  Cu-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 v 2 is due to the highly viscous late hadronic stage Heinz, nucl-th/ and Teaney, Lauret, Shuryak, nucl-th/ 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.

April 28, 2005Ohio State University, S. Manly64 Conclusions  Interaction length is short - early thermalization likely  Hydro works well at mid-  … dense, almost ideal fluid  Flow gives evidence for partonic energy loss in medium and quark coalescence  Is Hydro/Bjorken/Feynman consistent with multiplicity and elliptic flow data as function of η? Evidence for Landau?  No indication of sharp change in dynamics of particle production as function of  or E from GeV. But maybe a smooth evolution as initial energy density decreased and viscosity/time spent as hadronic gas increases?  Stay tuned for Cu-Cu results.

April 28, 2005Ohio State University, S. Manly65

April 28, 2005Ohio State University, S. Manly66 Au-Au event in the PHOBOS detector Backup slides

April 28, 2005Ohio State University, S. Manly67

April 28, 2005Ohio State University, S. Manly68 Acceptance (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 = -1

April 28, 2005Ohio State University, S. Manly69 Determining the collision point High Resolution extrapolate spectrometer tracks Low Resolution octagon hit density peaks at vertex z position

April 28, 2005Ohio State University, S. Manly70   RingsN OctagonRingsP Spec holes Vtx holes Detector symmetry issues where SPEC vertex efficiency highest Most data taken with trigger in place to enhance tracking efficiency

April 28, 2005Ohio State University, S. Manly71   RingsN Octagon RingsP Offset 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

April 28, 2005Ohio State University, S. Manly72 Dealing with the holes   RingsN Octagon RingsP 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

April 28, 2005Ohio State University, S. Manly73 Dealing with the holes   RingsN Octagon RingsP 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.)

April 28, 2005Ohio State University, S. Manly74   RingsN OctagonRingsP Track-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

April 28, 2005Ohio State University, S. Manly75 Elliptic flow vs  width of  bin PHOBOS Preliminary central 3-15% midcentral 15-25% peripheral 25-50% Hit-based method h±h± M. Belt-Tonjes, Quark Matter GeV Au+Au

April 28, 2005Ohio State University, S. Manly76 Track-based Hit-based peripheral 25-50% h ± v2v2  PHOBOS Preliminary Track-based Hit-based midcentral 15-25% h ± v2v2  PHOBOS Preliminary central 3-15% h ± Track-based Hit-based v2v2  PHOBOS Preliminary v2 vs.  200 GeV method comparison

April 28, 2005Ohio State University, S. Manly77 STAR 130 GeV 4-cumulant STAR 130 GeV 2-cumulant STAR 130 GeV Reaction Plane 5-53% central Preliminary PHOBOS 200 GeV 0-55% central p t (GeV/c) v2v2 Elliptic flow vs p T Preliminary

April 28, 2005Ohio State University, S. Manly78 Transformation of spectra from  to y leads to suppression of multiplicity at low p t and low |  | This leads to an enhancement of inclusive v 2 at mid-  P. Kolb, Proc. of 17 th Winter Workshop on Nuclear Dynamics (2001) T. Hirano, BNL-Riken Workshop on Collective Flow and the QGP (Nov. 2003) ~10%

April 28, 2005Ohio State University, S. Manly79 Poisson occupancy weighting

April 28, 2005Ohio State University, S. Manly80 Directed flow as function of  ’ Limiting fragmentation PHOBOS Au+Au results M. Belt-Tonjes, QM04

April 28, 2005Ohio State University, S. Manly81 Molnar and Voloshin, nucl-th/ Partonic energy loss alone leads drop at very large pT and does not account for meson/baryon differences Quark coalescence vs. fragmentation nucl-ex/ nucl-ex/

April 28, 2005Ohio State University, S. Manly82 v1v1 PHOBOS Preliminary PHOBOS AuAu √s NN =19.6 GeV NA49 PbPb √s NN =17.2 GeV Phys.Rev.C68, , % Minimum Bias h±h± ±± 19.6 GeV AuAu & 17.2 GeV PbPb 

April 28, 2005Ohio State University, S. Manly83 STAR AuAu 200 GeV 10-70% central v 1 at 200 GeV AuAu:PHOBOS & STAR v1v1  STAR, PRL 92 (2004) PHOBOS Preliminary PHOBOS 6-55% central h±h±

April 28, 2005Ohio State University, S. Manly84 (  ) PHOBOS Preliminary v (  ) PHOBOS v Minimum Bias h±h± v 2 vs.  at 130 and 200 GeV AuAu (  ) PRL 89, (2002) Hit-based method (  ) Nucl.Phys. A715 (2003)