# Presentation: 651677

## Heavy Flavor 

**Heavy Flavor **
**for the **
**Perfect Java (QGP)**

- Jamie Nagle
- University of Colorado

- _Would you like one or two QGPs with your coffee?_

## Outline

-  Why are the measurements of heavy quarks important for studying a medium dominated by light quarks and gluons?
-  Measurements of open heavy flavor and implications
-  Measurements of closed heavy flavor and implications
-  Putting it all together (or at least starting)

## Charm/Beauty Probes

- Heavy quarks are produced at early times (due to large Q2 requirement) and are potentially separate from the bulk medium, thus we can utilize them as probes of the medium.
- Large charm/beauty mass may allow calibrating this probe via pQCD calculations.
- Non-relativistic velocities will also prove to be a useful feature in some kinematics.

## Open Charm Techniques

- 1.  Non-photonic lepton method
-  	- need to control and subtract
- 	  other lepton contributions
- 	- loss of kinematic information
- 2.  Direct D meson reconstruction
- 	- large combinatoric background 	  without displaced vertex

- This is already after background subtraction!

## Proton Proton Baseline

- _Proton Proton Baseline_

- Non-photonic electrons:  presumed from ce and be.

- 50% charm / 50% beauty contribution at pT ~ 4 GeV.

- FONLL = Fixed-Order plus **Next**-to-Leading-Log

## STAR and PHENIX and FONLL

- _STAR and PHENIX and FONLL_

- 1.  STAR D meson and non-photonic electrons are consistent
-      and are ~ 4x above pQCD FONLL
- 2.  PHENIX non-photonic electrons are ~ 2x above pQCD FONLL
- 3.  Is it surprising that pQCD has a factor of two systematic error
-      (and this is just a scale factor check) !

## pQCD and Charm

- _pQCD and Charm_

- FONLL factor of ~ x2 below the data and significant scale factor dependencies!

## Probing Gold Gold  Medium

- _Probing Gold Gold ____ Medium_

- 1.  Total Charm Production Scales with Nbinary !
-      Hard Process Production (as expected) and no
-      Destruction (as expected).
- 2.  Large Suppression
-      for high pT heavy
-      quark traversing
-      medium (surprise) !

**c**

## Heavy Quark Energy Loss

- _Heavy Quark Energy Loss_

- Radiative energy loss would need a very large color opacity.
- Picture of static scattering centers is “odd” for beauty quarks.

- DVGL:  Djordjevic et al., PLB 632(2006)81
- BDMPS:  Armesto et al., PLB 637(2006)362

- Static Scattering Center

## Heavy Quark Energy Loss

- _Heavy Quark Energy Loss_

- Collisional energy loss adds significantly.
- Still a challenge to include both radiative and collisional consistently (and also for light quarks).

- DVGL:  Djordjevic et al., PLB 632(2006)81
- BDMPS:  Armesto et al., PLB 637(2006)362

- Wicks et al., nucl-th/0512076
- van Hees & Rapp, PRC 73(2006)034913

## Heavy Quark Flow !

- _Heavy Quark Flow !_

- Heavy quarks also show a significant elliptic flow (v2).
- Model calculations require charm quark small relaxation time  or diffusion coefficient *D**HQ*.
- This implies a very low viscosity to entropy density ratio.
- Perfect Liquid?

## ?

- Critical goal to put the QCD data point on this plot with realistic error bars.

- _Near the Viscosity Bound_

## Closed Heavy Flavor (Quarkonia)

-  free energy :  S.Digal et al. Phys.Rev.D64(2001)094015
-  linear comb. of both:  C.Y.Wong hep-ph/0509088
-  internal energy: W.M.Alberico et al. hep-ph/0507084

- _Closed Heavy Flavor (Quarkonia)_

- Quarkonia are a different probe of the medium.
- They have the potential to act as a thermometer of the medium.

**10 trillion degrees Fahrenheit**

## J/ Suppression !

- _J/____ Suppression !_

- Nuclear Suppression Factor

- Ratio **Blue **/ **Red**

- Collision Centrality ( More Central)

- Collision Centrality ( More Central)

## Simple Theory

- If local density (dET/dy or dN/dy) > threshold then no J/.
- Note it does include a Woods-Saxon Density Profile !
- Predictions:
- (1) Much larger J/ suppression at RHIC compared with SPS.
- (2) Larger J/ suppression at mid-rapidity where local density is highest.

- _Simple Theory_

**J/******

## Statistical and Systematic Comparison

- _Statistical and Systematic Comparison_

**PHENIX data at 200 GeV is quite surprisingly compatible with **
**NA50 data at 17.2 GeV !**

**PHENIX data at forward rapidity shows a significantly stronger suppression.**

## Theoretical Explanations

- II. Cancellation of multiple effects (unnaturalness?)

- _Theoretical Explanations_

- * Note that Occam’s razor does not tell you the right answer, but it does give some insight into burden of proof.

## Naturalness (Cold Nuclear Matter)

- Calculation by Qiu, Vary, Zhang (PRL 2002).
- Assumes q2 between c and c pair increases linearly with
- cold nuclear matter path L from multiple scattering.

- _Aside_
- (i) There are no non-monotic changes in derivatives
- (ii) This “second drop” has been acknowledged by NA50 as an experimental artifact.

- _Naturalness (Cold Nuclear Matter)_

- NA50 Experimental Data

## Naturalness (Very Opaque Matter)

- _Naturalness (Very Opaque Matter)_

**q**

- Quark or Gluon has to propagate through the medium.
- Large opacity  surface emission and lack of sensitivity.
- Imagine ccbar propagating through medium, or medium propagating through ccbar.
- If c or cbar scatters, then J/ correlation lost.  Why not similar biased emission and lack of density sensitivity?

**c**

## Example:  MPC Dynamics

-               Molnar Parton Cascade
- Gold-Gold b=8 fm simulation.
- Embed charm into the initial state using PYTHIA kinematics.
- (Upper) Initial position of all charm quarks from slice along z=0.
- (Lower) Initial position of charm quarks that had no collisions through the time evolution.

- x (fm)

- x (fm)

- y (fm)

- y (fm)

- _Example:  MPC Dynamics_

- Work by A. Glenn, D. Molnar, JN

## Similar Trends

- _Similar Trends_

## Charm / Anticharm Correlations

- These pairs have a suppression just like J/, probably due to strong in medium interactions breaking up correlations.

- _Charm / Anticharm Correlations_

## Feed Down Effects

- NA50 at SPS (0<y<1)
- PHENIX at RHIC (|y|<0.35)
- PHENIX at RHIC (1.2<|y|<2.2)

- _Feed Down Effects_

- Cold nuclear matter effect smaller at RHIC, and thus hot nuclear matter effect must be larger to match RAA.

- Need better constraint at RHIC (d-Au running in Run-8 !)

- Perhaps pattern is similar due to C  J/  suppression.
- Slightly larger suppression at RHIC, but masked by different cold nuclear matter effects.

## Cancelling Effects (Recombination)

- R. Rapp *et al.* (for _y=0_) PRL 92, 212301 (2004)
- R. Thews  (for _y=0_)  Eur. Phys. J C43, 97 (2005)
- N. Xu *et al.*  (for _y=0_)  nucl-th/0608010
- Bratkovskaya *et al. *(for _y=0_)  PRC 69, 054903 (2004)
- A. Andronic *et al.* (for _y=0_)  nucl-th/0611023
- And many other calculations....

- Original J/ suppressed.
- Compensated for by recombination of originally uncorrelated
- c and c.

## Open Charm Input

- _Open Charm Input_

**Non-photonic electrons**
**(from heavy flavor decay)**

- Any recombination model must also match the charm distribution.

- Note that J/ get contributions from charm at 1⁄2 J/ pT.
- And charm yields electrons with ~ 0.7 x D meson pT.

- J/

## “Does the Charm Flow at RHIC?”

- _“__Does the Charm Flow at RHIC?”_

- RHIC II White Paper

## My Recombination Prediction

- ’

- J/

- NA38 / NA50

- _My Recombination Prediction_

**Prediction:******
******’ ****Suppression Pattern for RHIC**

- At the CERN-SPS the ’ is suppressed much more than the J/.  This is attributed to the ’ larger physical size and smaller binding energy.

## Forward Rapidity Puzzle?

- x

**Anti**
**Shadowing**

**Shadowing**

- 0 mb

- 3 mb

- RdAu

- _Forward Rapidity Puzzle?_

- Recombination could lead to narrowing of J/ rapidity distribution, though it depends on the flatness of the initial charm rapidity distribution.
- Another explanation may come from nuclear modification of the initial parton distribution functions.

**Low x****2**** ~ 0.003**
**(shadowing region)**

##  Heavy Outlook

- On the experiment side, we must have measurements of multiple states (J/, ’, C, 1s,2s,3s)) !
- We also need clean separation of open charm and open beauty to disentangle energy loss mechanisms and have a quantitative constraint on the “perfect liquid” viscosity.
- Theory needs full dynamical evolution matching both open and closed charm in a consistent picture (good progress here).
- Exciting future with more results from RHIC, RHIC II and LHC !

- _ __Heavy Outlook_

## The Collider Accelerator Division at Brookhaven deserves a cup of the perfect java !  Thanks !

## Back to the Salt Mines !

- _Back to the Salt Mines !_

**RHIC **
**RHIC II**
**LHC**