# Presentation: 738592

## Hadronization mechanisms and degrees of freedom above Tc at RHIC-II

- Hadronization mechanisms and degrees of freedom above Tc at RHIC-II

- Rene Bellwied
- Wayne State University

**21****st**** International Workshop on Nuclear Dynamics,**
**Breckenridge 2005, Colorado, Feb.5****th****-12****th**** **

## A 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. Another press conference will not enhance the relevance of RHI physics.

- 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.

## We measure two predicted QGP signatures

- 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

## Constituent quark scaling in the sQGP:Identified particles at intermediate pt

- 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

## Hydrodynamics describes the data 

- Hydrodynamics:
- strong coupling,
- small mean free path,
- lots of interactions
- NOT plasma-like

- Strong collective flow:
- elliptic and radial
- expansion with
- mass ordering

## For the first time: ideal liquid behavior 

## Charm flow by STAR/PHENIX

- STAR data very preliminary (F. Laue, SQM04)

## How can something so heavy flow with the light quarks ? 

- Many interactions of the
- heavy quark in the partonic phase
- (thermalization ?)
- Ideal hydro - low viscosity, high
- diffusion (D. Teaney, Hirschegg 05)
- mfp = 1 fm, or even smaller (D.Molnar)
- What are the degrees of freedom in the partonic phase?
- Let’s measure v2 for D (through hadron channels), B-mesons (through J/channelsand onium states.

## Contributions to particle production in RHI collisions

- pT

- pQCD

- Hydro

- ~ 2 GeV/c

- ~ 6 GeV/c

- Soft

- Medium modifiedfragmentation (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 , K0s in the intermediate pT region.

- Parton recombinationandcoalescence

- Fragmentation

- ~ 30 GeV/c ?

**RHIC-II: p****T**** to 30 GeV/c**

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

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

- P. Steinberg, T. Ullrich (Brookhaven National Laboratory)
- M. Calderon (Indiana University)
- J. Rak (Iowa State University)
- S. Margetis (Kent State University)
- M.A. Lisa, D. Magestro (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, C. Markert,
- J. Sandweiss, N. Smirnov (Yale University)
- (90 pages, submitted in August 2004)

## The 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 ?

## The Measurement Pillars of R2D

- Particle Identified Jet measurements
- Measurement-jets & flavor tagged jets
- Detailed onium measurements
- Forward (low x) physics
- Bulk observables in 4
- High rate spin measurements

## Evolution 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)

## In 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 ?

## How strong is the sQGP ?

- Lattice QCD :
- /T4 never reaches the
- Boltzmann limit
- No perturbative QGP
- No wQGP

- Polyakov Loop QCD :
- Perturbative QGP  (wQGP)
- is reached at 3Tc
- Different initial conditions
- at RHIC and LHC !

## The sQGP degrees of freedom

**Models that require chiral symmetry breaking above T****C****:**
- Recombination models: constituent quark (dressed up valence quarks)
**Models that restore chiral symmetry above T****C****:**
- Zhe Xu (hep-ph/0406278): multi-gluon interactions (e.g.strong 2 to 3)
- C.Greiner (hep-ph/0412095): high mass resonances near Tc (Hagedorn states)
- 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 v****2**
**jet quenching**
**High mass resonance shifts due to partonic bound states (Shuryak)**

## Chiral symmetry restoration

**Measurements:**
**Resonances in jets ****(Christina Markert, this workshop)**
**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 a****1****) or (******** and ********) via hadronic channels?**

## Particle Production in QCD (the factorization theorem)

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

**Parton Distribution Functions**
**Hard-scattering cross-section**
**Fragmentation Function**

**a**

**b**

**c**

**d**

- Particle Production in QCD (the factorization theorem)

*“**Collinear factorization”*

## 0 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.

## Strange particles in pp

**This NLO calculation describes K****0**** 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)**

## Octet baryon fragmentationBourrely & Soffer (hep-ph/0305070)

**Strong heavy quark**
**contribution to **
**parton fragmentation **
**into octet baryons **
**at low fractional **
**momentum in pp !!**
**Intrinsic charm in**
**light baryons ??**
**Fragmentation is**
**not universal !!**

## Peculiarities in dA

**P.Straub et al., FNAL**

**Is Cronin flavor dependent ?**
**(not reproduced by recombination)**

## High pT Particle Production in A+A

- High pT Particle Production in A+A

## Is the fragmentation function modification universal ?

- Modification according to Gyulassy et al. (nucl-th/0302077)
- Quite generic (universal) but attributable to radiative rather than collisional energy loss

## Different partons lose different amounts 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)**** **

- Derek Teaney (Hirschegg 05):
- Heavy quark energy loss is
- collisional not radiative ??
- Sergey Butsyk (this workshop):
- Significant energy loss for D

## The goal of particle identified fragmentation 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.

## strange-charged hadron correlations in AA

- 0-5%

- 10-30%

- 5-10%

- 30-50%

- 50-70%

**No significant difference for different trigger **
**particle species at intermediate trigger pt.**
**Asymmetry might develop as a function**
**of trigger pt (increased jettiness)**
**But we are statistics limited, **
**we need ********, ********-Anti-********, ********-K to higher pt**
**Anticipated R2D rates:**
**50,000 ******** pairs > 4 GeV/c , 5,000 pp pairs > 10 GeV/c **

- STAR preliminary

- STAR preliminary

******-charged particle**
**correlations as a**
**f(centrality)**

## Requirements according to RHIC II Physics Pillars

**Detailed properties of sQGP ****(see John’s talk)**
**Quarkonium: EMC/HCal Resolution, Acceptance, Rates**
**Jets: ****PID**** ****at high p****T**** and tracking over ****full** acceptance (-jet, jet-jet)

**Mechanisms of hadronization**
**PID at High p****T****, correlations, ****large ******** acceptance****, ********-tagged jets**

**Origin of Spin (of Proton)**
**Large ******** acceptance****, jets, ********-jet, ****PID at high p****T**** , correlations**

**Low x physics (CGC ******** QGP)**
**PID at high-p****T**** to ****large ******
**Multi-particle correlations over small & large ******** range**

## Slide 29

## R2D detector concept

- 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 concept
- Dedicated high momentum detector over full phase space

## 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. **

## A 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).**** **

## The future is bright

**A three prong approach:**
**lower energy  ****	**** better facility****	****      higher energy**

- FAIR:
- Facility for
- Antiproton &
- Ion
- Reseach

- LHC:
- Large Hadron Collider
- with ALICE, CMS,
- ATLAS heavy ion
- programs

- RHIC-II:
- RHIC upgrade
- with new detector
- R2D

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

## Gluon jet selections at RHIC-II

- 1.) Large rapidity interval correlations
-       (Mueller-Navelet Jets)
- 2.) Three jet events (?)
- 3.) PT-dependence of -jets (?)

## RAA and high-pT suppression

- STAR, nucl-ex/0305015

- energy
- loss

- pQCD + Shadowing + Cronin

- pQCD + Shadowing + Cronin + Energy Loss

- RAA and high-pT suppression

- Deduced initial gluon density at  = 0.2 fm/c    dNglue/dy ≈ 800-1200
-  ≈ 15 GeV/fm3, eloss = 15*cold nuclear matter (compared to HERMES eA)                                      (e.g. X.N. Wang nucl-th/0307036)

## Do we understand fragmentation ?

- statistical approach based on measured inclusive cross sections of unpolarized
- octet baryons in e+e- annihilation:
- Du ~ 0.07 Ds ,and Du / Ds ratio about constant as a function of x
- but: de Florian et al., (1998): u,d,s contribution to  is about the same
-        J.J.Yang (2001,2002): Du / Ds drops by factor 5 with increasing X.

**Strong heavy quark**
**contribution to **
**parton fragmentation **
**into octet baryons **
**at low fractional **
**momentum in pp !!**
**Fragmentation is**
**not universal !!**

## Octet baryon fragmentationBourrely & Soffer (hep-ph/0305070)

- Works well...but not for mesons !!

## Requirements for a complete jet program  

- Broadening in  and pT  in pp (+jet) and AA

-  Full coverage in tracking and pid and calorimetry
- Preferably g-jets to determine jet energy unambiguously

- R2D rates per RHIC year: 40 GeV di-jets: 120k
- NChwith 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