# Presentation: 807249

## Exploring QCD with Heavy Ion Physics

**Mark D. Baker**

## The plan of attack - where are we?

- Collide gold nuclei at high energy
- Is it “strongly interacting bulk matter”
- Collective motion
- Temperature, density
- Probe the strong interaction
- What we’ve learned
- Some puzzles
- Confinement, Chiral Symmetry

- Mark D. Baker

## Can we probe the EARLY stages?

**Quark Gluon Plasma?**

**Crude estimate using ********0****~0.2-1 fm/c**

- Mark D. Baker

## Lattice QCD predictions 

**** can be measured using jet dE/dx
**T** can be measured using direct ’s

- Mark D. Baker

**Notes:**
P / T**4  ==  3 pi**2 / 90  as  T -> 0
P/ T**4 == ( 16 + Nf * 21 / 2 ) pi**2 / 90   as T -> infinity

The pressure does reflect the number of degrees of freedom.  These are the ideal gas limits.  Nf is number of flavors and 3 stands for the 3 light pions at low temperature

## High-pT Particles @ RHIC: “Jet Tomography”

**scatterings with large Q****2****.**
**Sensitive  to hot/dense medium: **
**parton energy loss**** ****(“jet quenching”).**
**Compare leading (in p****T****) hadron**
**yields to scaled pp yields**** **
**(“binary scaling”):**
**Production ****yields**** ****calculable**** ****via pQCD + Glauber geometry**

- High-pT Particles @ RHIC: “Jet Tomography”

- Mark D. Baker

## Charged Hadron Spectra

- C. Jorgensen, BRAHMS
- Parallel Saturday

- C. Roland,
- PHOBOS
- Parallel Saturday

- J. Jia, PHENIX
- Parallel Saturday

- J. Klay, STAR
- Parallel Saturday

- 200 GeV results from all experiments

**QM2002 summary talk (Peitzmann)**

- Mark D. Baker

## Comparing AuAu to pp

**L~A****1/3**

**A**

**# of NN collisions ****~A****4/3    ****(formally Glauber T****AA****(b))**
**# of participating nucleons: ****2A**

- Mark D. Baker

## Measuring Hadron Suppression

- 1. Compare Au+Au to nucleon-nucleon cross sections
- 2. Compare Au+Au central/peripheral

- Nuclear
- Modification
- Factor:

- If no “effects”:
-  R < 1 in regime of soft physics
-  R = 1 at high-pT where hard
-            scattering dominates
- Suppression:
- R < 1 at high-pT

**T. Ullrich**

- Mark D. Baker

## Leading Hadrons at CERN-SPS energies

- Any parton energy loss
- effects buried in initial
- state mult. scatt.,
- transverse radial flow,
- etc. ...

- Central Pb+Pb(Au) collisions at SPS

- From compilation of X.N. Wang

- Mark D. Baker

## Caveat: The “Cronin effect”

- Multiple scattering in initial state:

- Mark D. Baker

## Suppression of High pT Hadrons

- AuAu data
- central (0-10%) and
- 	peripheral (60-80%)
- compared  to N-N reference
- peripheral collisions
- described at high pT
- central collision
- suppressed at high pT

**PHENIX**

- Mark D. Baker

## Hadron Suppression: Au+Au at 130 GeV

- Phenix: PRL **88** 022301 (2002)
-  and charged hadrons, central collisions

- STAR: nucl-ex/0206011
- Charged hadrons, centrality dependence

- Clear evidence for high pT hadron suppression in central nuclear collisions

- Mark D. Baker

## yield in AuAu vs. p-p collisions

- 70-80% Peripheral

- Ncoll =12.3 ±4.0

- PHENIX Preliminary

- D. d’Enterria

- Yield ratio s=200/130 GeV
- Consistent at at high pT with
- pQCD predictions (STAR)

- Mark D. Baker

## Hadron Suppression: Au+Au at 200 GeV

- PHENIX preliminary

- 200 GeV preliminary data: suppression of factor 4-5 persists to pT=12 GeV/c

- Phenix peripheral and central over *measured* p+p

- STAR charged hadrons: central/peripheral

- Mark D. Baker

## How much energy loss @ RHIC?

**<dE/dx> = 0.25 GeV/fm naïve**
**                   ****7 GeV/fm when expansion included**

- scaled pp

- energy
- loss

**Still under systematic study, but it’s a large effect.**

**X.N.Wang**

- Mark D. Baker

## Another view:

**Normalize by <N****part****>/2**
**Divide by the value at N****part****=65**

- Mark D. Baker

## Hadron production ~ Npart!

**PHOBOS Preliminary:**

**Au+Au 200 GeV**

**UA1 pp  (200 GeV)**

- Hadron production ~ Npart!

**C. Roland, QM2002**

**PHENIX nucl-ex/0207009**

- Normalize by Npart/2.
- Divide by the value at Npart=65

- Mark D. Baker

## Approximate Npart scaling is MAXIMAL jet quenching! 

- Ncoll * / V ~ Npart4/3 / L ~  Npart

**Only jets produced on the surface survive!**

- PHENIX preliminary

**Npart***

**Ncoll**

**Even for 8 GeV hadrons!**

*** - not drawn by PHENIX**

- Mark D. Baker

**Notes:**
Printed 

## Jets in Heavy Ion Collisions

- ee q q (OPAL@LEP)

- pp jet+jet (STAR@RHIC)

- Au+Au ??? (STAR@RHIC)

- Hopeless task? No, but a bit tricky...

- Mark D. Baker

## Peripheral Au+Au data vs. pp+flow

**Hardtke, QM2002**

- Mark D. Baker

## Central Au+Au data vs. pp+flow

**Hardtke, QM2002**

- Mark D. Baker

##  “Ratio Signal” = (AA-flow)/pp

-  “Ratio Signal” = (AA-flow)/pp

- Mark D. Baker

## Jet suppression @ RHIC!

**Hardtke, QM2002**

- Mark D. Baker

## Is final state “jet quenching” the only explanation?

**Particle Yield/<Npart/2>**

**Particle Yield (spectrum)**

**Initial state parton saturation works too ...**

**Kharzeev, Levin, McLerran **
**hep-ph/0210332**

- Mark D. Baker

## Initial state parton saturation?

**See Iancu, Leonidov, McLerran  hep-ph/0202270**

** ****Gluon density cannot grow indefinitely.**
** ****Non-Abelian diagram gg********g kicks in at****                                            low x or low k********.**

- Mark D. Baker

## “Tau scaling” in DIS

**Statso et al., PRL 86 (2001) 596**

******tot *********p (********b)**

**1**

**10**

**100**

**1000**

**0.1**

******Q************x**********

**1**

**10****3**

**10****-3**

**Fit ********=0.25**

- Mark D. Baker

## Parton Saturation “predicts” AA

- Saturated initial state gives predictions about final state.
-  Nh = c x Ng

- Kharzeev & Levin, nucl-th/0108006

- PRL 87 (2001)

******~0.25 from fits to HERA data: **
**     ****xG(x)~x************scaling**
**Describes dN/d******** shape correctly!**

**Fit PHOBOS data at 130 GeV to set c, Q****s**

- Mark D. Baker

## Saturation Works at 200 GeV

- L. McLerran, DNP 2001

- 

- nucl-ex/0112001

******~0.25 from fits to HERA data: **
**             ****xG(x)~x************scaling**
**Describes dN/d******** energy evolution correctly!**

- Mark D. Baker

## J/

**Energy/Momentum**

- Data consistent with:
- Hadronic comover breakup (Ramona Vogt) w/o QGP
- Limiting suppression via surface emission (C.Y. Wong)
- Dissociation + thermal regeneration (R. Rapp)

- Mark D. Baker

## Charm Does Scale (doesn’t quench)

**Favors quenching interpretation for pions. **

**Gluon radiation**
**suppressed for**
**heavy quarks.**

**Dokshitzer,Kharzeev**
**hep-ph/0106202**

- Mark D. Baker

## High pT v2 reaches geometric surface limit

** ****QM2002 (Voloshin)**

- E. Shuryak, nucl-th/0112042

** ****QM2002 (Filimonov, STAR)**

- Mark D. Baker

## System is “black” to very high pT

- Adler et al., nucl-ex/0206006

- System is “black” to very high pT

- Mark D. Baker

## Summary so far

- Soft physics:
-  System appears to be “hydrodynamic bulk matter”
-  System is opaque and expanding explosively.
-  Naïve energy density much higher than theoretical transition
-  Freezeout along a universal curve near theoretical transition.
- Hard physics:
-  Strong suppression of inclusive yields & back-to-back pairs
-  Azimuthal anisotropy at high pT
-  Open charm remains unsuppressed
-  ****** **large parton energy loss and surface emission?
- Caveats
-  d+Au needed to disentangle initial state effects in jet production
-  The PHENIX & PHOBOS Puzzles...

- Mark D. Baker

## p/

- p/

-  Proton yield is comparable with pions @ 2-4 GeV in central collisions, less in peripheral

- Central

- p/

- Peripheral

- Tatsuya Chujo (PHENIX)

- Mark D. Baker

## Extrapolate soft component using hydrodynamics

**Hydrodynamic flow modifies p****t**** threshold where hard physics starts to dominate**
**physics is soft (thermal) until p****t**** ******** 3 GeV/c**

- Calculate spectra using hydro. parameters
- h+ + h - =   , K, p

- Compare sum to measured
- Charged particle pT spectrum

- J. Burward-Hoy

- Mark D. Baker

## The PHENIX Puzzle:

- T. Sakaguchi, PHENIX Parallel Saturday

- Important baryon and/or kaon contribution out to pT = 8 GeV/c?

- Mark D. Baker

## Baryons at high pT

- Baryons at high pT

- Jia, Sorenson

*Accident? Complex hard/soft interplay?*
*Medium modified jet fragmentation function?*
*Gluons and quarks “quenching” differently?*

- Yields scale with Ncoll near pT = 2 – 3 GeV/c
- Then start to fall

- Mark D. Baker

## The PHOBOS Puzzle

- pQCD e+e- Calculation

**nucl-ex/0211002**

- Mark D. Baker

## Comparison of Nch vs. Energy

- Comparison of Nch vs. Energy

**Different systems converge **
**at high energy.**
**Universality of Nch?**

**From talk by P. Steinberg**

**          ****Central Au+Au**

**Central****       AA**

**pp (pp) data @ ********s****eff**

**e****+****e****-**

**1             10           10****2****          10****3**** **

******s (GeV)**

**nucl-ex/0211002**

- Mark D. Baker

## More detailed comparison of AA, ee

**e****+****e****-**** measures dN/dy****T****(rapidity relative to****“thrust” axis)**

**200 GeV**

- Mark D. Baker

## Universal hadronization/tranistion?

**LEP!**

- Mark D. Baker

## Works vs. energy & centrality 

- Works vs. energy & centrality

**QM2002: nucl-ex/0212009**

**Need dAu data to **_**cleanly**_** isolate initial & final state effects!**

- Mark D. Baker

## Heavy ion collisions in “target frame”

**p + p inel.**** **** **

- UA5, Z.Phys.C33, 1 (1986)

**dN/d******

**Systematic errors not shown**

**19.6 GeV is preliminary**

**PHOBOS Au+Au**

**dN****ch****/d********/<N****part****>**

- 6% central

- Mark D. Baker

## Summary (really!)

- Very interesting state:
-  System appears to be “hydrodynamic bulk matter”
-  Initial , T appear to be above theoretical transition.
-  Freezeout along a universal curve near theoretical transition.
- We are beginning to probe this state:
-  large parton energy loss and surface emission?
-  Caveats and puzzles remain
-  Addressable with more RHIC running & detector upgrades!
- Is it deconfined matter (Quark Gluon Plasma)?:
-  We have not achieved a clear proof yet
-  But Probably! Evidence is building.
-  Stay tuned!!

- Mark D. Baker

## Extras

- Mark D. Baker

## Interlude: Many ways to slice pz

**Rapidity: Generalized velocity**

**Pseudorapidity: ~y: easier to measure**

**Feynman x: scaled p****z**

- Mark D. Baker

## What is ’?

_**Away from mid-rapidity:**_

- Mark D. Baker

## Two “Large” Detectors at RHIC

**Two “Large” Detectors at RHIC**

- Mark D. Baker

## Two “Small” Experiments at RHIC

- Mark D. Baker

## v2 vs pseudorapidity

- PHOBOS:  No boost invariance !

** ****QM2002 summary slide (Voloshin)**

- Mark D. Baker

## Elliptic Flow

**V****2**

**Normalized Multiplicity**** **

**Particle **
**asymmetry**

**dN/d(********R ****) = N****0 ****(1 + 2V****1****cos (********R****) + 2****V****2****cos (2(********R****)) + ... ) **

**midrapidity : |********| < 1.0 **

- Mark D. Baker

## v2 of mesons & baryons

**v****2**** of mesons & baryons**

- v2

- 1) High quality M.B. data!!!
- 2) Consistent between
-      PHENIX and STAR
-  pT < 2 GeV/c
-     v2(light) > v2(heavy)*  *
-  pT > 2.5 GeV/c
-     v2(light) < v2(heavy)*  *
*Model: P.Huovinen, et al., Phys. Lett. *
***            ******B503****, 58 (2001)*

- Mark D. Baker

## What do the data say?

- dNch/d = 640

- G. Roland

- Rises somewhat faster than Npart

- Mark D. Baker

## Excitation function of B

- Nucl. Phy. A697: 902-912 (2002)

- Extrapolation of fit

- Mark D. Baker

## Same analysis @ CERN-SPS

- Mark D. Baker