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Hadronization and chirality in Hadronization and chirality in strongly interacting partonic matter: strongly interacting partonic matter:

the future of the RHIC Heavy Ion the future of the RHIC Heavy Ion ProgramProgram

Rene BellwiedWayne State University

Nuclear Physics Seminar,Kent State University,

Tuesday, March 8th, 2005

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A few introductory remarksA few introductory remarks

We found strongly coupled partonic, collective matter

(sQGP), which is interesting in itself but it will not secure the future of our field.

What defines the relevance of our field in the next two decades ? The QGP paradigm had its time but needs to be updated or replaced.

Where do we go from here ? The connection with cosmology is weakening, the connection with QCD is strengthening.

The 2007 NSAC Long Range Plan needs to set new goals, especially for the U.S. community.

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One goal: Proving asymptotic One goal: Proving asymptotic freedom in the laboratory.freedom in the laboratory.

Measure deconfinement and chiral symmetry restoration under the conditions of maximum particle or energy density.

Gross, Politzer, Wilczek win2004 Nobel Prize in physics for the discovery of asymptotic freedom in the theory of the strong interaction

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The main features of Quantum The main features of Quantum Chromodynamics (QCD)Chromodynamics (QCD)

Confinement– At large distances the effective coupling between quarks is large, resulting

in confinement.– Free quarks are not observed in nature.

Asymptotic freedom– At short distances the effective coupling between quarks decreases

logarithmically.– Under such conditions quarks and gluons appear to be quasi-free.

(Hidden) chiral symmetry– Connected with the quark masses– When confined quarks have a large dynamical mass - constituent mass– In the small coupling limit (some) quarks have small mass - current mass

Lattice QCD predicts that deconfinement and chiral symmetry restoration occur at the same critical parameters (T and )

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The RHIC-I State Of Affairs:The RHIC-I State Of Affairs:Hydrodynamics describes the bulkHydrodynamics describes the bulk

Hydrodynamics =strong coupling,small mean free path,lots of interactionsnot plasma-like

Strong collective flow:elliptic and radial expansion withmass orderingrequires a partonic EoS

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For the first time: ideal liquid behaviorFor the first time: ideal liquid behavior

First time in Heavy-Ion Collisions a system created which, at low pt,is in quantitative agreement with ideal hydrodynamic model. The new phase behaves like an ideal liquid (very low viscosity (D.Teaney)) But are the degrees of freedom partonic ?

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Confirmed consequences of the sQGPConfirmed consequences of the sQGP

The ‘quenching’ of high pt particles due to radiative partonic energy loss.

Energy loss 15 times higher (several GeV/fm3 ) than in cold nuclear matter (compare STAR AA to HERMES eA) ?

The disappearance of the away-side jet in dijet events traversing the opaque medium

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Constituent quark scaling in the sQGP:Constituent quark scaling in the sQGP:Identified particles at intermediate pIdentified particles at intermediate ptt

Grouping according to number of valence quarks for baryons and mesons, which seem to approach each other around 5 GeV/c

coalescence/recombination provides a description ~1.5 - 5 GeV/c constituent quark scaling for hadron production

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Contributions to particle production Contributions to particle production in RHI collisionsin RHI collisions

pT

pQCDHydro

~ 2 GeV/c ~ 6 GeV/c

SoftSoft

Medium Medium modifiedmodifiedfragmentation fragmentation (jet quenching)(jet quenching)

0

pT independence of pbar/p ratio.

p/ and /K ratio increases with pT to > 1 at pT ~ 3-4 GeV/c in central collisions.

Suppression factors of p, different to that of , K0

s in the intermediate pT region.

Parton Parton recombinationrecombination

andandcoalescencecoalescence

Fragmentation Fragmentation

~ 30 GeV/c ?

LHC, RHIC-IISPS, RHIC-I

RHIC-II: pT to 30 GeV/c

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Expression of Interest -Expression of Interest -A Comprehensive New Detector for RHIC IIA Comprehensive New Detector for RHIC II

P. Steinberg, T. Ullrich (Brookhaven National Laboratory)

M. Calderon (Indiana University)

J. Rak (Iowa State University)

S. Margetis, C.Markert (Kent State University)

M.A. Lisa, D. Magestro, B. Petrak (Ohio State University)

R. Lacey (State University of New York, Stony Brook)

G. Paic (UNAM Mexico)

T. Nayak (VECC Calcutta)

R. Bellwied, C. Pruneau, A. Rose, S. Voloshin (Wayne State University)

and

H. Caines, A. Chikanian, E. Finch, J.W. Harris, M.A.C. Lamont,

J. Sandweiss, N. Smirnov (Yale University)

(90 pages, submitted in August 2004)

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The Physics Pillars of R2DThe Physics Pillars of R2D What are the detailed properties of the sQGP and what

are the degrees of freedom at high densities ? What is the mechanism of hadronization and is chiral

symmetry restored in the deconfined medium ?

Is there another state (CGC) of matter at low x, what are its features, and how does it evolve into the QGP ?

What is the structure and dynamics inside the proton (parton spin, L) and what do we learn from parity violation and polarization measurements ?

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Evolution of a strongly interacting systemEvolution of a strongly interacting system Measurements:

Initial conditions ( HBT, low-x physics (CGC))

Composition above Tc

(v2 and jet quenching of partons, constituent quarks,

gluonic bound states, pre-hadrons ?)Parton density and chiral symmetry

(jet tomography, intra-, inter-jet correlations with

resonances)Deconfinement Tc

(Quarkonium melting)

Shuryak QM04 ?

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In and out of a sQGPIn and out of a sQGP

What are the degrees of freedom above TC ?

Is chiral symmetry restored above TC ?

Are chiral symmetry restoration and deconfinement decoupled ? (deconfinement at TC, chiral symmetry restoration well above TC ?).

How does hadronization and spontaneous breaking of chiral symmetry (SBCS) occur ?

Shuryak QM04 ?

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How strong is the sQGP ?How strong is the sQGP ?Lattice QCD :/T4 never reaches theBoltzmann limitNo perturbative QGPNo wQGP

Polyakov Loop QCD :Perturbative QGP (wQGP)is reached at 3Tc

Different initial conditionsat RHIC and LHC !

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The temperature dependent running The temperature dependent running coupling constant coupling constant ss

A.Peshier et al. (quasi-particles) O.Kaczmarek et al. (thermal mass, LQCD) (hep-ph/0502138) (hep-lat/0406036)

1.05 Tc

1.5 Tc

3 Tc

6 Tc12 Tc

in an expanding system: interplay betweendistance and temperature

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The sQGP degrees of freedomThe sQGP degrees of freedom

Models that require chiral symmetry breaking above TC:Recombination models: constituent quark (dressed up valence quarks)

Models that restore chiral symmetry above TC:Zhe Xu (hep-ph/0406278): multi-gluon interactions (e.g.strong 2 to 3)A. Peshier (Hirschegg 05): quasi particles above Tc

E.Shuryak (hep-p/0405066): colored and colorless bound states above Tc

R.Rapp (Hirschegg 05): quasi-resonant heavy states above TC

Let’s learn from traditional plasma physics:M. Thoma (hep-ph/0409213): strongly coupled, non-relativistic plasmas

Measurements : Elliptic flow v2 jet quenching High mass resonance shifts due to partonic bound states (Shuryak)

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What is the relevant scale for QCD ?What is the relevant scale for QCD ?

pQCDHydro

SoftSoft

Medium Medium modifiedmodifiedfragmentation fragmentation (jet quenching)(jet quenching)

pT independence of pbar/p ratio.

p/ and /K ratio increases with pT to > 1 at pT ~ 3-4 GeV/c in central collisions.

Suppression factors of p, different to that of , K0

s in the intermediate pT region.

Parton Parton recombinationrecombination

andandcoalescencecoalescence

Fragmentation Fragmentation

pT~ 2 GeV/c ~ 6 GeV/c 0 ~ 30 GeV/c ?

LHC, RHIC-IISPS, RHIC-I

time thadtf T(MeV) Thad = 170 300 ?Tf = 100 400 ?

deconfin

emen

t

Ch

iral symm

etry restoration

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Recombination is not the only solution Recombination is not the only solution for baryon/meson dependence for baryon/meson dependence

V. Topor-Pop et al. (PRC 70 (2004) 064906)

HIJING with:1.) baryon junction-antijunction loops2.) pt kick to diquarks3.) strong color fields

Describes:1.) baryon/meson difference in AA2.) strangeness yield from pp to AA (incl. multi-strange baryons)

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Short life time [fm/c] K* < *< (1520) < 4 < 6 < 13 < 40

Medium effects on resonances:Mass and width modificationsUse resonances with light decay channels, e.g. to e+e-, to , a1 to

Chiral symmetry restorationChiral symmetry restoration

Measurements: Resonances in jets (Christina Markert, Breckenridge 05)

– Is the leading particle resonance different from the bulk matter resonances (off shell vs on shell, same side vs away side, leading vs. next-to-leading)

Resonances to prove SBCS (Ralf Rapp, Hirschegg 05)– Is off mass shell resonance (e.g. shifting or broadening in mass) visible in chiral

partner pairs ( and a1) or ( and ) via hadronic channels?

VacuumAt Tc: Chiral Restoration

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hadrons

hadrons

leading particle

Jet: A localized collection of hadrons which come from a fragmenting parton

Parton Distribution Functions

Hard-scattering cross-section

Fragmentation Function

a

b

c

dParton Distribution FunctionsHard-scattering cross-sectionFragmentation Function

c

chbbaa

abcdba

T

hpp

z

Dcdab

td

dQxfQxfdxdxK

pdyd

d

0

/222

)(ˆ

),(),(

High pT (> 2.0 GeV/c) hadron production in pp collisions:

~

Hadronization in QCD Hadronization in QCD (the factorization theorem)(the factorization theorem)

“Collinear factorization”

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00 in pp: well described by NLO in pp: well described by NLO

Ingredients (via KKP or Kretzer)– pQCD– Parton distribution functions– Fragmentation functions

p+p->0 + X

hep-ex/0305013 S.S. Adler et al.

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Strange particles in ppStrange particles in pp

This NLO calculation describes K0 reasonably well, but is off for B.Jaffe (MIT): maybe we need to look at fragmentation again

Universality for FF only shown for pions (KKP 2001)

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New NLO calculation based on STAR data New NLO calculation based on STAR data (AKK, hep-ph/0502188)(AKK, hep-ph/0502188)

K0s (V0 vs NLO)

apparent Einc dependence. As of now only tested on light mesons

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Octet baryon fragmentationOctet baryon fragmentationBourrely & Soffer (hep-ph/0305070)Bourrely & Soffer (hep-ph/0305070)

Strong heavy quarkcontribution to parton fragmentation into octet baryons at low fractional momentum in pp !!Intrinsic charm inlight baryons ??Fragmentation isnot universal !!

Is the heavy quark contribution Q-dep.?

What is <Q> at RHIC ?zz

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Intrinsic kT , Cronin Effect

Parton Distribution Functions

Shadowing, EMC Effect

Fragmentation Function leading

particle suppressed

Partonic Energy Loss

c

d

hadrons

a

b

Hard-scattering cross-section

c

ccch

c

c

bbBaaA

ba

bBbaAa

baabcd

baT

hAB

z

QzD

z

zPd

cdabtd

d

QxSQxS

gg

QxfQxf

dddxdxABKpdyd

dN

),(

)(

)(ˆ

),(),(

)()(

),(),(

2*0/

1

0

*

22

2/

2/

222

kk

kk

High pHigh pTT Particle Production in A+A Particle Production in A+A

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Is the fragmentation function Is the fragmentation function modification universal ?modification universal ?

Induced Gluon Radiation ~collinear gluons in cone “Softened” fragmentation

in je

i j t

t

n e

: increases

z : decreases

chn

Modification according to Gyulassy et al. (nucl-th/0302077)

Quite generic (universal) but attributable to radiative rather than collisional energy loss

z z

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Yu.Dokshitzer

Different partons lose different Different partons lose different amounts of energyamounts of energy

Examples:1.) dead cone effect for heavy quarks:For heavy quarks in the vacuum and in the medium the radiation at small angles is suppressed (Dokshitzer & Kharzeev, PLB 519 (2001) 199)

2.) gluon vs. quark energy loss:Gluons should lose more energy and have higher particle multiplicities due to the color factor effect.

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The goal of particle identified The goal of particle identified fragmentation in the mediumfragmentation in the medium

1.) we need to understand fragmentation (hadronization) in

pp collisions

2.) use the medium modified fragmentation functions in AA

collisions

3.) Different flavor contributions to D(z) at different z lose different z in the opaque

medium.

Measure fragmentation functions in pp & modifications in AA.

Study z = phadron/pjet and x dependence :

High pT identified particlesIntra- and inter-jet particle correlationsLarge acceptance for -tagged jets

Essential to understand hadronization

0.2 < z < 1 7 < p < 30 GeV/c 0.1 < x < 0.001 0 < < 3

pq,g > 10 GeV/call

106 particles in AA

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The Measurement Pillars of R2DThe Measurement Pillars of R2D-jets, g-jets & flavor tagged jets

Particle Identification in jet measurements

Detailed onium measurements

Forward (low x) physics

Bulk observables in 4

High rate spin measurements

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Requirements for a complete jet program Requirements for a complete jet program

Broadening in and pT in pp (+jet) and AA

Full coverage in tracking and pid and calorimetryPreferably -jets to determine jet energy unambiguously

R2D rates per RHIC year: 40 GeV di-jets: 120kNChwith pt>5 GeV/c in -jets with E = 20 GeV :

19,000

Need hadronic calorimetry in order to apply isolation cuts for ’s

Glueck et al., PRL 73, 388

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Gluon jet selections at RHIC-IIGluon jet selections at RHIC-II

1.) Large rapidity interval correlations

(Mueller-Navelet Jets)

2.) Three jet events (?)

3.) PT-dependence of -jets (?)

low-x gluon

0.001< xg < 0.1

high-x valence quark

0.3 < xq< 0.7

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Requirements according to RHIC II Requirements according to RHIC II Physics PillarsPhysics Pillars

Detailed properties of sQGP (see John’s talk)

Quarkonium: EMC/HCal Resolution, Acceptance, Rates Jets: PID at high pT and tracking over full acceptance (-jet, jet-jet)

Mechanisms of hadronization PID at High pT, correlations, large acceptance, -tagged jets

Origin of Spin (of Proton) Large acceptance, jets, -jet, PID at high pT , correlations

Low x physics (CGC QGP) PID at high-pT to large Multi-particle correlations over small & large range

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We need high pt PID over large acceptance !We need high pt PID over large acceptance !

-4 -3 -2 -1 0 1 2 3 4

10 GeV

4 GeV

PHENIX

STAR, 4 GeV

R2D, 25 GeV

0

2

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A Heavy Ion ‘Dream Detector’: The best of ALICE, CMS and ATLAS combined

Prohibitively expensive ??(requires the utilization of decommissioned HEP

detector components (from SLAC, FNAL, DESY))Present projected price tag: $100 Million

Main detector is based on SLD magnet and calorimetry

High magnetic field conceptDedicated high momentum detector over full phase space

R2D detector concept: best of both worldsR2D detector concept: best of both worlds

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Alternative: R2D based on CDFAlternative: R2D based on CDF(CDF and CLEO have same field and magnet radius)(CDF and CLEO have same field and magnet radius)

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Do we need RHIC-II in the LHC era ?Do we need RHIC-II in the LHC era ? Is the LHC viewing the sQGP through the distorted lens

of the Color Glass Condensate ? (M. Gyulassy)

Maybe the QGP degrees of freedom change from RHIC to LHC. Does the sQGP get weaker ? Are we in the sQGP sweet spot ?

The conditions will be different. This is a unique situation which allows us to study the QGP from two angles. RHIC-II offers longer running time, higher luminosity, more detailed detector capabilities. LHC offers higher energy and larger cross sections.

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A few thoughts for your way homeA few thoughts for your way home

The fundamental question of parton to hadron conversion can be tackled through systematic studies of particle identified

fragmentation processes inside and outside the produced medium.

This is a fundamental question of physics that complements Elementary Particle Physics studies of the Higgs boson !

It will require systematic studies at the LHC and RHIC-II

From my point of view that in itself is tantalizing, but it does not lead to a larger physics payoff per se.

We have just scratched the surface !!

The evidence for QGP formation, i.e. the creation of strongly interacting, collective partonic matter formation is strong (sQGP).

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The future is brightThe future is brightA three prong approach:

lower energy better facility higher energy

FAIR: Facility for Antiproton & Ion Reseach

                                                    

LHC: Large Hadron Colliderwith ALICE, CMS, ATLAS heavy ion programs

RHIC-II:RHIC upgradewith new detectorR2D

critical point (?) hadronization, chirality pQGP (?)