# Presentation: 004106

## High pT group update

- Kirill Filimonov
- Denes Molnar
- Saskia Mioduszewski
-                      11 November 2005

## Recall main questions from first RHICII Meeting

- #1 What is the nature of the phase transition between nuclear matter and quark matter(...)? How does hadronization work? Is there evidence for deconfinement?
- #2 How does the clearly evident thermodynamic character of a high-energy heavy-ion collision evolve ...? How does the collision thermalize so quickly?
- #3 What are the properties of the strongly-coupled quark-gluon plasma? ...
- #4 Is chiral symmetry restored? ...
- ...
- High-pT measurements relate to #1-3, perhaps #4
**Case for RHIC II based on:**
- - What is unique when at T~2Tc ?
- - Heavy flavor measurements and more correlation studies to understand energy loss
- - Excitation Function

## Lattice QCD at Finite Temperature

**F. Karsch, ****hep-ph/010314**

- Ideal gas (Stefan-Boltzmann limit)

- B=0)

- Deconfinement:

## Observations at RHIC 

- Large (factor 5) suppression of high pT hadrons in central Au+Au collisions
- Absence of such a suppression in d+Au collisions
- Excess of p/ ratio in central Au+Au collisions
- Large v2 saturating at pT~2 GeV/c and > 10% up to higher pT
- Constituent quark scaling of v2
- Suppression of heavy-flavor (c+b decays), significant v2 of heavy-flavor
- Is there a consistent picture?
- Consistent picture is crucial in understanding the matter created at RHIC

## Theoretical Understanding?

- Both
- Au-Au suppression **(I. Vitev and M. Gyulassy, hep-ph/0208108)**
- d-Au enhancement** ****(I. Vitev, nucl-th/0302002** **)**
- understood in an approach that combines multiple scattering with absorption in *a dense partonic medium (15 GeV/fm**3** ~100 x normal nuclear matter)*
- Our high pT probeshave been calibratedand are now being                                                                          used to explore the precise propertiesof the medium

**Au-Au**

**d-Au**

## 0 v2

- Red: Sys. error (abs)

- Large v2 at high pT!

## Recombination

- Recombination (Fries et al, Greco et al, Molnar, Hwa, ...) describes quark-scaling of v2, but what about jet correlations?

## Calculations based on Arnold, Moore, Yaffe (AMY) formalism
JHEP 0305:51 2003
Energy loss only (BDMS++)
High-pT
v2 appears to decrease to energy loss calculation
Low(er)-pT
Something additional going on...  (not just the protons)
While the data appear to approach the energy loss limit at high pT, there is something extra going on in 3-6 GeV/c region

- JHEP 0305:51 2003
- Energy loss only (BDMS++)
- High-pT
- v2 appears to decrease to energy loss calculation
- Low(er)-pT
- Something additional going on...  (not just the protons)
- While the data appear to approach the energy loss limit at high pT, there is something extra going on in 3-6 GeV/c region

- 0 v2 Theory Comparison: AMY (Turbide et al.)

## 0 v2 Theory Comparison: D.Molnar

- Molnar Parton Cascade (MPC)
- nucl-th/0503051
- Contains:
- Energy loss due to interactions
- pT boost due to interactions
- Consistency would suggest:
- QGP?
- sQGP?
- Model shown here is for one set of parameters
- Can larger opacity reproduce the v2?

## What do we learn from RAA(, pT)

- What do we learn from RAA(, pT)

- Constant RAA below 7 GeV/c not “intrinsic”.
- Some additional  physics varying w/ pT.
- That physics must require spatial /flow anisotropy.
- “bump” below 3 GeV/c in all centrality bins ?!
- Extra yield in plane ?

## Conclusions?

- What’s responsible for larger v2 at intermediate pT?
- Flow + recombination (Fries et al, Greco et al, Hwa)?
- Partons pushed to higher pT (à la Molnar)?  Collisional energy loss?
- Other explanations ....
- Larger energy loss crossing the flow field (Wiedemann et al)? ....
- Perhaps heavy flavor can shed more light on the picture....

## Heavy flavor v2 and RAA

- Single electrons from charm and bottom decays
- v2 measurement agrees with calculation assuming thermalization of charm
- RAA is a challenge for energy loss calculations

## Heavy flavor suppression measurements at RHIC

**Heavy flavor suppression measurements at RHIC**

**V. Greene, S. Butsyk, QM2005 talks**

**J. Dunlop, J. Bielcik; QM05 talks**

**Can this be explained by radiative energy loss? **

## RAA for charm and bottom decays

**At pt~5GeV,**** ****R****AA****(e****-****)**** ******** 0.7********0.1**** ****at RHIC. **

- Djordjevic et al.

## Single electron suppression with the elastic energy loss 

**Reasonable agreement with single electron data, even for dN****g****/dy=1000.**

**(S. Wicks, W. Horowitz, M.D. and M. Gyulassy, in preparation.)**

**Include elastic energy loss**

## HQ Langevin Solutions to Hydro + pQCD    

- HQ Langevin Solutions to Hydro + pQCD

**Elliptic Flow**

**[Moore+Teaney ’04]**

-  Charm-pQCD cross sections with variable** ***********s***** **,**  ***********D******=1.5T***** **fix
-  Hydrodynamic bulk evolution with ***T******c******=165MeV, ************ ≈ 9fm/c***

******s**** ,  g**
**  ****1  , 3.5**
**0.5 , 2.5**
**0.25,1.8**

** **correlation: small **R****AA** ↔ large **v****2 **
-  realistic coupling /drag coefficients?** **

**Nuclear Modification**

## Calculation of elastic energy loss for charm and bottom    

**[van Hees,Greco**
**   ****+Rapp ’05]**

-  how to fix level of coalescence ?
-  induced gluon radiation?!

**Elliptic Flow**** **

**Nuclear Modification Factor**

-  Elliptic QGP fireball with **D**-/**B**-resonances, coal./frag. and decay

## Parton Cascade 

- with fixed ******(q,g-c)**, forward/isotropic, coalescence

-  Cross section has moderate effect on v2 of charm
-  no bottom included

**Elliptic Flow**** **

**[MPC,**
** ****Molnar]**

## Summary

- Flat RAA is an “accident” (at least for pT between 3 and 7 GeV/c)
- Large v2 for pT between 3 and 7 GeV/c cannot be described by energy loss alone
- Do hadron yields from soft production extend to 7 GeV/c?  If so, how?
**Recombination + Flow?**
**Interactions “pushing” softer particles to higher p****T****? ****(unique to RHIC?)**
- What is the mechanism for charm thermalization in the medium?
**Recombination + survival of heavy-quark resonances? ****(unique to RHIC?)**
- Is the energy loss resulting in high pT hadron suppression only radiative or also collisional?
- Do we really understand energy loss at RHIC?
- Not completely

## Measurements to do

**A:**
-  – jet  (X.-N. Wang) and   leading hadron –  correlations
- Heavy vs light flavor at high pT
- Charm-triggered dijet correlations
- Medium + jets interplay in correlations (“Mach cones”, jets+v2) – 3-particle correlations
- Multi-dimensional tomography: pT--rp -centrality–flavor
**B:**
- Gluon jets  (J/psi – jet correlations)
- Leading hadron – dilepton correlations; resonances in jets (in near/away-side correlations)

## Rate estimate                              (Kirill Filimonov, Breckenridge 2005)

- Number crunching for run4 data:

**- ****Invariant cross section  at 10 GeV from Pythia: ****5.6x10****-9****  mbGeV****-****2**** ****- ****Invariant yield is ****5.6x10****-9**** mbGeV****-2**** ****divided by ****σ****pp****inel****(****42 mb****)****  =****1.3 x10****-10****GeV****-2**** **
** ****Multiply by <N****binary**** (minbias)>=256, get ****341x10****-10****GeV****-****2**** ****- ****Multiply by 2********p****T********η****=****125****.****6****, get ****4****.****2****x10****-6****/GeV**** ****- ****Assume integrated luminosity of ****250****μ****b****-1****, 6.8 barn AuAu cross section, ****get 1.7x10****^****9 events. **** **
**At 8 GeV, it's about 3 times larger, at 12 GeV, 3 times smaller. **
**Folding in dead time, calorimeter acceptance in run4:**
**~18****00 ****direct photons at 10 GeV**

**dN/dp****T**** is then ****72****00/GeV**** ****@10 GeV in BEMC STAR calorimeter**
**         ****(not counting STAR Endcap calorimeter at 1<****η****<2)**

## Correlation Functions (STAR)

****** ****(radian)**

- 4 < pT trig < 6 GeV/c
- 1 < pTassoc < 2.5 GeV/c

- - large angle gluon radiation: Vitev
- - conical flow: Stoecker,Shuryak,Muller
- - jets deflected by medium flow

- 1/Ntrig dN/d()

- 2.5 < pT trig < 4 GeV/c
- 1 < pTassoc < 2.5 GeV/c

*See talk, J. Ulery *
*(section 3c) and*
*poster, M. Horner (#70)*

- broad away-side correlations.
- consistent with flat.