# Presentation: 623223

## 

Frédéric FLEURET
LLR - École polytechnique, France

X Whorkshop on High Energy                Physics Phenomenology

PHENIX collaboration

**Frédéric FLEURET**
**LLR - École polytechnique, France**
**X Whorkshop on High Energy                Physics Phenomenology**
**PHENIX collaboration**

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Recent RHIC results on photon, dilepton and heavy quarks

- Jan 2 - 13, 2008

## Deconfined matter : Quark Gluon Plasma

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- The phase diagram

- Star collapse
- High density of matter
-         (5 to 10 times standard nuclear density)
- Confined matter  plasma

- high temperature (1012 K)
- 10-6 s. : Plasma  confined matter

- Big Bang

- Core of Neutron stars

## History of experimental facilites

- F. Fleuret - LLR

- QGP : experiment history

**BNL - AGS 4 GeV**

**CERN - SPS 20 GeV**

**BNL - RHIC 200 GeV**

**CERN - LHC 5.5 TeV**

- Fixed target
- Experiments

- Collider
- Experiments

## Experimental facility : RHIC-BNL-NY

| Year | Run | Species | Ldt |
| --- | --- | --- | --- |
| 01/02 | 2 | Au+Au (200 GeV)
p+p (200 GeV) | 24.0 b-1
0.15 pb-1 |
| 02/03 | 3 | d+Au (200 GeV)
p+p (200 GeV) | 2.74 nb-1
0.35 pb-1 |
| 03/04 | 4 | Au+Au (200 GeV)
Au+Au (62 GeV) | 241 b-1
9 b-1 |
| 04/05 | 5 | Cu+Cu (200 GeV)
Cu+Cu (62 GeV)
Cu+Cu (22.5 GeV)
p+p (200 GeV) | 3 nb-1
0.19 nb-1
2.70 b-1
3.8 pb-1 |
| 05/06 | 6 | p+p (200 GeV) | ~10 pb-1 |
| 06/07 | 7 | Au+Au (200 GeV) | ~800 b-1 |
| 07/08 | 8 | d+Au (200 GeV) | running |

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- PHOBOS

- BRAHMS

**PHENIX**

**STAR**

- 2 independent rings with 3.9 km circumference
**Anything from p+p (up to 500 GeV) to Au+Au (up to 200 GeV per nucleon pair)**

- species and (PHENIX) luminosity

- Jan 2 - 13, 2008

**RHIC**

## Experimental facility: PHENIX & STAR

- PHENIX
- Beam counters
- Central rapidity |y|<0.35
- Tracking (DC, PC)
- EM calorimeter
- TOF
- RICH
- Muon spectrometers 1.2<|y|<2.2
- Measures everything

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- STAR
- Large TPC
- Silicon vertex tracker
- EM calorimeter
- Time of flight
- Track ~2000 charges particles in ||<1

## Centrality and Nuclear Modification Factor

***N******part***** **= number of interacting nucleons
***N******coll***** **= number of binary nucleon-nucleon collisions
- small impact parameter *b*  large *N**part*, large *N**coll*
- large impact parameter *b*  small *N**part*, small *N**coll*

- Centrality
- Nuclear Modification Factor

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

- Soft interactions ~ Nparticipants
- Hard interactions ~ Ncollisions

- For hard probes, if no nuclear effects, RAA = 1

## The smoking gun @ RHIC

- Jet quenching

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

**p-p**

- Suppression in central Au+Au due to high density medium

-  back-to-back di-hadron correlations :
-  very similar in p+p and d+Au
-  strongly suppressed in central Au+Au collisions at 200 GeV

## Electromagnetic radiations 

**Why studying electromagnetic radiations ?**
*** ******electromagnetic probes do not interact strongly***
*** ***
**Suffer little or no final state interaction**
**Give access to the hot and dense phase of the reaction**
**Carry information of the system at the time of their production**

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Formation phase (pre-equilibrium)

- thermalisation

- hadronisation

- photons

- Freeze-out

- Jan 2 - 13, 2008

## Electromagnetic radiations

-  I) photons
- Testing pQCD
- Thermal photons
-  II) Low Mass Region
- Vector mesons in medium
-  III) Intermediate Mass Region
- Thermal dileptons
- Heavy quarks continuum : open charm
-  IV) High Mass Region
- Heavy quarks resonances

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## 

pQCD PHOTONS

THERMAL PHOTONS

**pQCD PHOTONS**
**THERMAL PHOTONS**

- Photons

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## Sources of photons

- In p+p collisions
- Direct photons
- Compton scattering
- q + g  q + 
- qq annihilation
- q + q  g + 
- Bremsstrahlung
- Fragmentation photons
- Final state hadron decay (background)
-  0, , K0,...   + 

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

## Sources of photons

- In A+A collisions
- High pT photons (pT> 6 GeV): **non thermal**
-  **Initial parton-parton scattering**: as in p+p
- not affected by Hot and Dense Matter  test the theoretical description of A+A collisions with pQCD
- Low pT photons (pT < 3 GeV) : **thermal**
**Come from the thermalized medium **
- Carry information about the initial temperature of the Quark Gluon Plasma
- Thermal photons are created in the QGP as well as in the hadron gas over the entire lifetime of these phases  test hydro models
- Low and intermediate pT photons (up to 6 GeV)
**Interaction of the quarks and gluons **from the hard scattering processes **with the QGP**
-  qhard + gQGP  q + 
-   get a large fraction of the momentum of qhard

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

## pQCD photons (High pT) in p+p collisions

- Phenix year-3 and year-5 data set
- Reference for Au+Au
**Measured p+p yield compatible with NLO pQCD calculations (tends to be higher by ~20%)**

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

- Run 5

**Phenix Run 3**

- Phys. Rev. Lett. 98, 012002 (2007)

**Phenix Run 5**

## pQCD photons (High pT) in d+Au

- Phenix
- Consistent with NLO pQCD calculation

- Star
- dir = incl – decay
- Plot R = 1 + dir/decay
- Cancel systematic uncertainties
- Signal consistent with pQCD NLO calculation

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## pQCD photons (high pT) in Au+Au

- PHENIX Run 2
- Computing RAA.vs.Npart
- 0 are quenched
- Direct  are not

- PHENIX Run 4
- Reach up to 18 GeV/c (12 GeV for Run 2)
- Qualitatively well described by NLO pQCD calculations

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

## pQCD photons (High pT) in Au+Au

**Au+Au run 4 compared with p+p**
- Computing RAA
-  consistent with Ncoll scaling below ~10 GeV
- Small decrease observed at very high pT
- interpretation
- F. Arleo : JHEP 0609 (2006) 015
- High-pT suppression due to isospin effect, in addition to jet quenching and shadowing.

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

**isospin**

**shadowing**

**shadowing **
**+ **
**energy loss**

## Thermal photons (low pT)

**Central Au+Au run 4**
-  Excess over pQCD observed at pT< 4
****** ****Well described including hydrodynamical predictions for thermal photons (QGP + HG)**
- D. d’Enterria and D. Perressounko : (Eur. Phys. J. C46, 451 – 464 (2006))
- Initial temperature T0 ~ 590 MeV      at 0 = 2R/ ~ 0.15 fm/c
- Precision d+Au data required to confirm...

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

**PHENIX preliminary**

## 

VECTOR MESONS IN MEDIUM
(Low Mass Region)

THERMAL DILEPTONS
(Intermediate Mass Region)

**VECTOR MESONS IN MEDIUM**
**(Low Mass Region)**
**THERMAL DILEPTONS**
**(Intermediate Mass Region)**

- Dileptons

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## Vector meson in medium (Low Mass Region)

- Chiral Symmetry Restoration
- Adding mass term in QCD lagrangian brokes chiral symetry
- Lattice QCD predicts that it is restored at Tc ~ 150 – 200 MeV
- Experimentally expect mass drop and broadening of the -meson
- At SPS-CERN (~20 GeV), low mass excess observed by CERES in Pb+Au and  confirmed by NA60 in In+In.

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Phys. Rev. Lett 96, 162302 (2006)

- Nucl. Phys. A774, 43 (2006)

## Thermal radiations (Intermediate Mass Region)

- QGP thermal radiation
- Expect thermal radiation from hot medium  initial temperature of the QGP
- Experimentally, should be accessible in the Intermediate Mass Region
- At SPS – CERN (~20 GeV):
- Intermediate mass excess observed by NA50 in Pb+Pb
-  NA60 in In+In  not coming from D decays  prompt dileptons

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

- Excess over open charm and Drell-Yan

- Excess compared to the expected Drell-Yan yield

## LMR and IMR at RHIC

**Au+Au 200 GeV (run 4)**
***Measured by PHENIX***
***Measures di-electrons***
-  8.108 Min Bias events
-  large background at low mass (S/B ~ 1/200 @ 0.5 GeV)
-  Background subtracted by event mixing technique
-    checking background subtraction (converter run)
- use a subset of data (5.107 events) taken with additional material around the beam pipe
-  increase background by a factor ~ 2.5
- Results agree within statistical errors

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

## LMR and IMR at RHIC

**Au+Au 200 GeV (run 4) **
***Cocktail plot***
-  low mass region
**Data below 150 MeV/c2 well described by the cocktail**
**Enhancement observed in 150 < m****ee**** < 750 MeV**
-  intermediate mass region
**Absence of excess with cc correlated PYTHIA distribution**
**But medium effect should randomize the cc correlation ******** room for thermal radiation**

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## Low Mass Region at RHIC

**Au+Au 200 GeV (run4)**
***Centrality dependence***
* ****  **(Yield/(N**part**/2)) .vs. N**part*
**Low Mass Region :**
**    ****0 < m****ee**** < 100 MeV/c2 **
*dominated by ****0** decays        *
****** ****follows expected yield**
**    ****150 < m****ee**** < 750 MeV/c2 **
*excess increases with N**part**                                   *
****** ****consistent with  in-medium enhancement from scattering processes like ******** or qq annihilation**

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## Intermediate Mass Region at RHIC

**Au+Au 200 GeV (run4)**
***Centrality dependence***
* ****  **(Yield/N**coll**) .vs. N**part*
**Intermediate Mass Region :**
** ****1.2 < m****ee**** < 2.8 GeV/c2 **
****** ****Consistent with the expectations based on PYTHIA**

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## Closer look at heavy quarks

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Closer look at heavy quarks

- +

**c**

- K-

- l-

- K+

- Direct reconstruction
- Difficult without measure of vertex (c ~120 mm)

- Indirect reconstruction
- Measure contribution of semileptonic decays from Heavy flavor to lepton spectra

## Heavy flavour in p+p

- Precise measurements made by both PHENIX and STAR
- Difference observed between PHENIX and STAR
- PHENIX is ~ a factor 2 larger than FONLL calculations (but agrees within uncertainties)
- STAR is ~ a factor > 2 larger than PHENIX

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- PRL97, 252002 (2006)

- PRL98, 192301 (2007)

## Heavy flavour cross section

- Comparison between STAR and PHENIX
- Same discrepancy observed in Au+Au
- PHENIX is ~ a factor 2 larger than FONLL calculations
- STAR is ~ a factor > 2  larger than PHENIX

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

## Heavy flavour RAA

- RAA comparison
- Consistent RAA observed between PHENIX and STAR
- The difference observed in p+p and Au+Au yields is cancelled out in the ratio.
- At large pT suppression similar to that of light hadrons

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- STAR     : PRL98, 192301 (2007)
- PHENIX : PRL98, 172301 (2007)

## Elliptic flow: v2

**Within a strongly interacting medium**
-  Initial spatial anisotropy converted into momentum anisotropy
-  Efficicency of conversion depends on the properties of the medium
- v2 = 2nd fourier coefficient of momentum anisotropy

- Flow

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- v2>0  flow in the reaction plane
- v2<0  flow out of the reaction plane

- reaction plane

- Jan 2 - 13, 2008

## Charm flows

- Large v2 observed
- Armesto et al. : pQCD calculation with radiative energy loss (curve I)  strongly coupled medium.
- Van Hees et al. : heavy quark transport calculation including elastic scattering (curve II)  diffusion coefficient consistent with estimates obtained in the light quark sector.
- Moore and Teaney : (curve III)  diffusion coefficient similar to II.
- Large energy loss and flow in Au+Au  strong evidence for the coupling of heavy quarks in the medium

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- PHENIX : PRL98, 172301 (2007)

## 

J/ CROSS SECTION

J/ CNM EFFECTS
(Cold Nuclear Matter)

J/ HDM EFFECTS
(Hot and Dense Matter)

OTHER QUARKONIA

**J/******** CROSS SECTION**
**J/******** CNM EFFECTS**
**(Cold Nuclear Matter)**
**J/******** HDM EFFECTS**
**(Hot and Dense Matter)**
**OTHER QUARKONIA**

- Quarkonia

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## Quarkonia

- Theoretical context

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

**Matsui and Satz**** ****first proposed the study of quarkonia as a signature of Quark Gluon Plasma (QGP) **
**Phys. Lett. B 178 (1986) 416**

- « if high energy heavy ion collisions lead to the formation of a hot quark-gluon plasma, then color screening prevents cc binding in the deconfined interior of the interaction region .../... it is concluded that J/ suppression in nuclear collisions should provide an unambigous signature of quark-gluon plasma formation »

## Quarkonia

- Experimental context
**J/******** production in p+A and A+A collisions has been studied at SPS starting 1986.**
**NA38, NA50, NA60**
**Anomalous suppression**** observed in ****Pb+Pb**** (NA50) and ****In+In**** (NA60) ****central collisions**** (high energy density, high temperature).**
**Different models (with or without QGP) describe the data**
**At RHIC, √s up to 200 GeV, 10 x bigger than SPS √s**** **

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

**NA50, Eur. Phys. Journal C39 (2005) 335 **

**central**

**peripheral**

**Mid-central**

## J/ at RHIC

- Production
- Main production process : gluon fusion
- Feed-down:
- 60% from direct production
- 30% c  J/ + 
- 10% ’  J/ + X
- In nuclear matter
- Initial state effects
- Nuclear shadowing		(Cold Nuclear Matter Effect)
- Final state effects
- Absorption in nuclear matter	(Cold Nuclear Matter Effect)
- Anomalous suppression		(Hot and Dense Matter Effect ?)
- Experimentally
- At RHIC : √s up to 200 GeV (<20 GeV at SPS)
- J/ is mainly measured by the PHENIX experiment
- Measure J/ in p+p : used as a reference
- Measure J/ in d+Au : to study Cold Nuclear Effects
- Measure J/ in Au+Au and Cu+Cu to study anomalous suppression.

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## J/ production in p+p

- To be used as a reference for A+A
- pp in agreement with Color Octet Model

- PRL 98, 232002 (2007)

- J/ is a **hard process ** expect in A+A collisions : (J/)AA  **<N****coll****>**(J/)pp

- In the following, we’ll use

**(if no nuclear effect R****AA****=1)**

- PRL98,232002(2007)

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## Cold Nuclear Matter (CNM) effects

- Absorption by nuclear matter
- After its production, charmonium can interact with nucleons from projectile and target
- Introducing L, the « length » of nuclear matter seen by the J/
- J/ survival probability :
- At SPS :
- Expect some absorption at RHIC

- Shadowing
- Nuclear shadowing is an initial-state effect on the parton distributions.
- Gluon distribution function can be different when comparing proton and nucleus.
- Expect some (anti) shadowing at RHIC

***Eskola, Kolhinen, Vogt*** Nucl. Phys. A696 (2001)

-  ***x****  is the momentum fraction of the  nucleon that a parton (quark or gluon) carries.*

**J/******** normal nuclear absorption curve**

- J/

- L

- Projectile

- Target

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## CNM effects @ RHIC – J/ in d+Au

- CNM effects @ RHIC – J/ in d+Au

- PHENIX data compatible with :
- Weak gluon shadowing
- Small absorption :             mb
- Need more precise d+Au data

**S****outh**

**Central**

**Nor****th**

**X****1**** < X****2****(~0.09)**

**J/******** S****outh**
**y < 0**

**X****1**** ~ X****2****(~0.02)**

**J/******** Central**
**y ~ 0**

**X****1**** > X****2****(~0.003)**

**J/******** Nor****th**
**y > 0**

**central**

**peripheral**

**mid-central**

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

- _[arXiv:0711.3917](http://arxiv.org/abs/0711.3917)_

## Au+Au and Cu+Cu @ RHIC

**Suppresssion       at RHIC**
****** ****Similar suppression in Au+Au and Cu+Cu at same centrality      **
****** ****larger  suppression observed at forward rapidity in Au+Au**

- Au+Au PHENIX Final: PRL98, 232301 (2007)
- Cu+Cu PHENIX Preliminary: nucl-ex/0510051

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008

## A+A results - comparison SPS .vs. RHIC

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

**Including CNM effects**
**Lack of precision on CNM effects at RHIC**
-  can’t discriminate between
- Same anomalous suppression at SPS and RHIC
- Different anomalous suppression at SPS and RHIC
****** ****need more precise measurement of CNM effects at RHIC ******** need more d+Au data**

**Comparison with SPS results**
****** ****Suppression at RHIC ******** suppression at SPS (at mid-rapidity).**
-  But cold nuclear matter effects may be different.

## Interpretations

- Models including anomalous suppression only
- Which reproduce SPS data,
- Predict too much suppression
- Color screening + CNM (1 mb)
- Comovers + CNM (1 & 3 mb)
- Direct production + CNM

- Rapidity dependence
- Predict more suppression at central rapidity
- Comover density is higher in central region
- Does not reproduce the data
- Data show more suppression at forward rapidity than at central rapidity

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- PRL98, 232301 (2007)

## Interpretations

- Models including anomalous suppression only
- Which reproduce SPS data,
- Predict too much suppression
- Color screening + CNM (1 mb)
- Comovers + CNM (1 & 3 mb)
- Direct production + CNM

- Adding recombination
- Recombination c+c -> J/ + g
- NJ/  Ncc2
- Compensate direct suppression
- Need better open charm measurement to better constraint recombination
- Measure J/ flow to check recombination

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- PRL98, 232301 (2007)

- PRL 92, 212301 (2004)

- Eur. Phys. J C43, 97 (2005)

-  PRL97, 232301 (2006)

- PRC 69, 054903 (2004)

- NPA789, 334 (2007)

## Futur quarkonia measurements

- Measuring other quarkonia would help to understand J/c’

- Jan 2 - 13, 2008

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- PHENIX
- Run 5 200GeV p+p

## Conclusions

- Electromagnetic radiations provide a large physics potential
- Photon
- Test of pQCD and initial state effects in A+A collisions
- Evidence for thermal radiation at low pT...
- Dileptons
- Enhancement in mass range 150 < mee (MeV/c2) < 750  vector meson modification in medium...
- Heavy quarks
- Heavy quarks suppression at large pT and heavy quarks flow  coupling of heavy quarks in the medium...
- Quarkonia
- J/ suppression similar to SPS results
- Need to better constraint Cold Nuclear Matter effects
- Recombination at play ?
- Futur :
-  run 7 : Au+Au data taken in 2007  currently analysing ...
-  run 8 : d+Au data   currently taking data ...
-  other high-luminosity runs + detector upgrades
- Quark matter 2008
- February 4 – 10, 2008, Jaipur

- F. Fleuret - LLR Ecole Polytechnique, France                                       WHEPP X, Chennai

- Jan 2 - 13, 2008