# Presentation: 080331

##  Experimental ResultsAGS/RHIC Users’ Meeting 19/June/2007

-  **Experimental Results****AGS/RHIC Users’ Meeting 19/June/2007**

- Manuel Calderón de la Barca
- UC Davis

## Interest in Heavy Flavor

- Produced at initial impact
- Large mass: additional knob to probe QGP
- Prediction: reduced energy loss (‘dead cone’ effect)
- Prediction: quarkonium suppression
- Heavy Quark flow: signature of thermalization
- Where are we with this program?

## Charm Yields and Cross sections

## dNNcc/dy from p+p to A+A

**D****0****,**** ****e****±****, and ****μ****±**** combined fit**
**Advantage: Covers ~95% of cross section**
**Mid-rapidity d********NN****cc****/dy vs Nbin **
******NN****cc****follows binary scaling**
**Charm production from initial state (as expected)**
**Higher than FONLL prediction in pp collisions.**

## Checking STAR electrons

- Discrepancy between STAR and PHENIX
- Investigated method to estimate Photonic background.  No issues found.
- Reanalyzed from scratch
- pp results change by ~25%
- dAu results change by ~10%
- AuAu results do not change
- Within systematics
- Still difference btw. STAR & PHENIX
- RAA still slightly below most c+b calculations.
- Future: low material run
- Improve uncertainty on background
- Issue remains: no information on contribution from beauty.

**  ****STAR Au+Au 0-5%**

## RAA of electrons from heavy flavor decays

- RAA of electrons from heavy flavor decays

- PHENIX & STAR: rough agreement
- → disagreement is common to p+p & Au+Au, cancels in the nuclear modification factor RAA

- describing the suppression is difficult for models
- radiative energy loss with typical gluon densities is not enough
- 	(Djordjevic et al., PLB 632(2006)81)
- models involving a very opaque medium agree better
- 	(Armesto et al., PLB 637(2006)362)
- collisional energy loss / resonant elastic scattering
- 	(Wicks et al., nucl-th/0512076,                                       van Hees & Rapp, PRC 73(2006)034913)
- heavy quark fragmentation and dissociation in the medium → strong suppression for charm and bottom
- 	(Adil & Vitev, hep-ph/0611109)

## Can we tell how much beauty?

- Use e-h Correlation
- Large B mass compared to D
- Semileptonic decay: e gets larger kick from B.
- Broadened e-h correlation on near-side.
- Extract B contribution
- Use PYTHIA shapes
- Con: Model dependent
- Pro: Depends on decay kinematics well described
- Fit ratio B/(B+D)

## B contribution to NP electrons vs. pT

**p+p 200 GeV**

- B contribution to NP electrons vs. pT

- Fit e-h correlation with PYTHIA Ds and Bs
**Non-zero B contribution**
- Contribution consistent with FONLL
**Model dependent (PYTHIA)**
**Depends mainly on kinematics of D/B decay (not on Fragmentation).**
- Dominant systematic uncertainty:
- photonic background rejection efficiency
- Additional uncertainties under study

- Beauty !

## RAA and B/(B+D) implication

- If, NPE electrons are suppressed in AA wrt pp
- and B fraction is ~30-40% in pp and also in AA
- then, suppressing only charm contribution NPE does not work:
**Need to suppress B contribution as well! **

## Charm Flow

## Does charm flow?

- strong elliptic flow of electrons from D meson decays → v2D > 0
- v2c of charm quarks?
- recombination Ansatz:                            (Lin & Molnar, PRC 68 (2003) 044901)
- universal v2(pT) for all quarks
- simultaneous fit to , K, e v2(pT)

**a = 1**
**b = 0.96**
******2****/ndf: 21.85/27**

- within recombination model: charm flows as much as light quarks
- implications: thermalization?

## Quarkonium

## J/ suppression: SPS vs. RHIC 

- J/ suppression: SPS vs. RHIC

- RAA versus Npart

- J/ suppression pattern
- Pb+Pb from NA50 (0<y<1)
- Au+Au from PHENIX (|y|<0.35)
- Extremely Similar!!
- Is it a coincidence?
- cold nuclear matter effects: (slightly) larger at SPS than at RHIC
- need more d+Au data
- plus recombination at RHIC?
- ‘sequential dissociation’ at   SPS and RHIC?
- J/ survives well above Tc
- dissociation of ’ and c
- feed down not well constrained (~40 %)
-  c hard to measure

## J/ at RHIC: rapidity dependence 

- RAA: rapidity dependence

- p+p ref. and Au+Au data
-  → rapidity and pT spectra challenge for production models
- more suppression at forward rapidity!
- opposite to trend from co-mover or CNM absorption
- more co-movers at y~0
- suppression not only driven by local particle density
- more regeneration at y~0?
- gluon saturation at forward y?

- models
- no clear picture yet, but important new constraints
- two (or more) ingredients needed to describe suppression pattern
- suppression + regeneration
- sequential dissociation + saturation

**nucl-ex/0611020**

## Sequential Screening(Karsch, Kharzeev, Satz, hep-ph/0512239)

- Sequential screening only of the higher-mass resonances that feed-down to the J/; with the J/ itself still not dissolved?** **
** **supported by recent Lattice calculations that give TJ/ > 2 TC
- gives similar suppression at RHIC & SPS (for mid-rapidity)

- But carefull! Hard to know how to set relative energy density for RHIC vs SPS
-  0 > 1 fm/c @ SPS?
-  1.6 fm/c crossing time
-  0 smaller @ RHIC?

-  Suppression stronger than possible from  ’, C alone?
-  Gluon saturation can lower forward relative to mid-rapidity?

## Sequential Screening Scenario

-  QGP suppression of C, ’
-  + additional forward suppression from gluon saturation (CGC)
- but approx. flat forward/mid above Npart ~ 100 seems inconsistent – forward should drop more for more central collisions as gluon saturation increases

- nucl-ex/0611020

## More Beauty:  signal in p+p

- More Beauty:  signal in p+p

- Large dataset sampled in Run VI
- Luminosity limited trigger
- Analyzed 5.6 pb-1, with corrections.
- Measure (1s+2s+3s) d/dy at y=0

**STAR Preliminary**
**p+p 200 GeV**
**e+e- M****inv**
**Background Subtracted**

**e+e- M****inv**** **
** ****Unlike-Sign Pairs**
** ****Like-Sign Pairs**

**STAR **
**Preliminary**
**p+p 200 GeV**

## Mid-rapidity (1s+2s+3s) Cross section

- Mid-rapidity (1s+2s+3s) Cross section

- Integrate yield at mid-rapidity: |y|<0.5
- (1s+2s+3s) BR * d/dy
**91 ± 28 ****stat**** ± 22 ****syst**** pb****-1**** (Preliminary)**
**Consistent with NLO pQCD calculations at midrapidity.**
**Phenix + STAR Preliminary points:**
**Broader rapidity distribution? **

- STAR Preliminary
- p+p 200 GeV

**y**

**d********/dy (nb)**

**Counts**

## Conclusions and Outlook

**Charm**
- pp, AA, dAu NPE, open charm
- Still difference of ~2 btw STAR and PHENIX.
- STAR Larger than NLO by ~4,
- PHENIX at the top of NLO theoretical uncertainty
- Flow: In recombination model, c quark flows like light quark.
- Future:
- low material run in STAR
- open charm reconstruction in PHENIX and STAR w/ vertex detectors
**Beauty:**
**Non-zero beauty contribution to non-photonic electrons**
**Together with AuAu NPE electron suppression:**
**Beauty suppression in Au+Au at RHIC ?!**
**Future handles to find B fraction via B decay geometry**
**Displaced electron+kaon DCA to primary vertex**
**Azimuthal correlation between electron+kaon **
**Quarkonium**
**J/******** : Larger suppression forward.**
**Need to invoke 2 or more mechanisms**
**Melting of **C, ’ **+ gluon saturation**
**Suppression + Regeneration at midrapidity **
**Explanations don’t match observed behavior vs centrality.**
******(1s+2s+3s) in p+p**:
**Consistent with pQCD at y=0**.
- Maybe wider than pQCD forward?