# Presentation: 521465

## PHENIX results on quarkonia

- Ermias T. ATOMSSA
- École Polytechnique
- Palaiseau, France

- Hard Probes
- 8-15 June, 2008, Illa da Toxa, Galicia-Spain

## Probing QGP with quarkonia

- The start:
- J/ψ anomalously suppressed in heavy ion collisions due to color screening if Quark Gluon Plasma is formed (Matsui & Satz PL B178 (1986) 416 )
- The NA38, NA50 and NA60 experiments at CERN SPS measured J/ψ suppression in a variety of systems

- Anomalous suppression
- ‘measured/expected’ J/ψ yield for light-light and heavy-light type collisions follow a universal scaling as a function of L
- Trend is broken by central heavy-heavy type collisions
- Models with no QGP have reproduced this behavior, so further investigation is needed

- E. T. ATOMSSA, Hard Probes, 06/12/08

## J/ψ detection in PHENIX

- Hadrons, photons, electrons
-  J/ψ→ e+e-
-  |η|<0.35
-  p*e* > 0.2 GeV/c
-  Δφ=π(2 arms x π/2)

- J/ψ detection in PHENIX

- Forward rapidity Arms:
- Muons
-  J/ψ → μ+μ-
-  1.2<|η|<2.2
-  pμ > 1 GeV/c
-   Δφ = 2π

- Global detectors
- Beam-Beam Counter (BBC)
- Zero Degree Calorimeter (ZDC)
- Reaction Plane Detector (RxNP)

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Contributions to J/ψ yield in HICs

- Production (RHIC energies)
- Mainly by gluon fusion (gg → J/ψ)
- Very early in nucleon-nucleon hard scatterings
- Feed down from excited states of charmonia, multiple measurements
- HERA-B : (χc → J/ψX ) ~ 21±5% and (ψ’ → J/ψX) ~ 7±0.4% (*)
- PHENIX prelim.: (χc→ J/ψX) <42%(90% CL) and (ψ’ → J/ψX) ~ 8.6 ± 2.5%
- ...
- Gluon shadowing: modification of PDFs in nuclei
- Suppression
- Breakup by scattering on nucleons from initial heavy ions (J/ψ+N→X)
- Melting in QGP/dissociation by comovers
- Enhancement
- Possible recombination from _uncorrelated_ c and c quarks

- _

- E. T. ATOMSSA, Hard Probes, 06/12/08

## J/ψ measurements in p+p collisions

- Why J/ψ in p+p?
- Constrain J/ψ production models
- Baseline to heavy ion yields
- Compared to a superposition of independent pp collisions

- BRll•tot = 178 ± 3stat ± 53sys ± 18norm nb

- Total cross section:

**Nuclear modification factor**

*B**ll** *is the *J/ψ *dilepton branching ratio (~12%)

- E. T. ATOMSSA, Hard Probes, 06/12/08

**Notes:**
The absolute normalization error (norm) represents the uncertainty in the BBC trigger cross section.

## J/ψ production mechanism

- Constraints from data
- Most color singlet models underestimate total cross section
- A new approach allowing off-shell and non static heavy quarks to form quarkonium reproduces total cross section and polarization
-           (PRL 100, 032006 (2008)  cf. Talk by J-P. Lansberg )
- Color octet model, gets good cross section, but predicts transverse polarization at high pt, not seen yet
- Precision on rapidity dependence is starting to become good enough to bring useful constraint

- E. T. ATOMSSA, Hard Probes, 06/12/08

## J/ψ from ψ’

******’ →****e****+****e****-**

|  | PHENIX | Theory |
| --- | --- | --- |
| J/ψ from ψ’ | 0.086±0.025 | 0.08 Digal et al., Phys. Rev. D 64 (2001) 94015 |

- J/ψ from ψ’

- E. T. ATOMSSA, Hard Probes, 06/12/08

## J/ψ from c

******c**** →J/******** + ******

- R******c**

|  | PHENIX | Theory |
| --- | --- | --- |
| J/ψfromχc | <0.42(90% CL) | 0.30 Digal et al., Phys. Rev. D 64 (2001) 94015 |

- J/ψ from c

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Cold nuclear matter (CNM) effects

- J/ψ suppression in d+Au:
- Study CNM effects
- Shadowing, absorption/breakup

- x2 : Momentum fraction in nucleus

**<x****2****> ~ 0.05-0.2**

**<x****2****> ~ 0.01-0.05**

**<x****2****> ~ 0.002-0.01**

**PRC 77, 024912 (2008)**

**K.J. Eskola et al. Nucl. Phys. B535 (1998) 351**

- Ncoll(dAu) = 7.6 ±0.3

- E. T. ATOMSSA, Hard Probes, 06/12/08

**Notes:**

EKS – determine R(x,Q_0) at some scale Q^2_0 from fits to DIS heavy flavour data(l-A  lf-p) and use DGLAP evolution equations to calculate x dependence
NDGS - ? 
Main point : predictions differ by a factor of 3, data can bring constraint
X2 = 0.5 (-xf + sqrt(xf**2 + 4*(Mjpsi**2/sNN)))

## Breakup cross-section

- Extraction method
- Rapidity dependence of RdAu  calculated (*) assuming a shadowing model EKS (**) or NDSG (#)
- Any additional suppression is accounted for by a single free parameter : break up cross-section (σbreakup)
- EKS => σbreakup =2.8 -1.4+1.7 mb
- NDSG => σbreakup = 2.2-1.5+1.6 mb
- Compatible with SPS (##):
-           σabs = 4.2±0.5 mb
- 	(Anti shadowing effect not taken into account in SPS calculation)

- (*) R. Vogt, PRC, 71 054902 (2005)

- (**) K.J. Eskola et al., Nucl. Phys. A 696, 729 (2001)
- (#) D. deFlorian et al., PRD, 69 074028 (2004)
- (##) B. Alessandro et al., Euro. Phys. J. C48, 329 (2006)

**PRC 77 024912 (2008)**

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Coming up...

- New d+Au from very high luminosity run
- 30x the previously available statistics (80nb-1)
- Will bring a much stronger constraint on CNM

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Au+Au and Cu+Cu collisions

**Bar: stat. + uncorrelated syst. errors**
**Band: correlated syst. Errors**

- Au+Au final: **PRL 98, 232301(2007)**
- Cu+Cu prelim: **nucl-ex/0801.0220**

- RAA summary plot :
- J/ψ suppression measurements in Au+Au and Cu+Cu collisions at √sNN=200GeV
- Curves show the CNM constraint from d+Au data
- Suppression in most central Au+Au goes as far as by a factor of 5 at forward rapidity

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Two surprises

- Comparison to SPS
- RAA (RHIC, (|y|<.35) ≈ RAA (SPS)
- Not what’s expected from
-          εSPS < εRHIC
- Caution:
- Rapidity ranges not same
-              0 < ysps < 1
- Different CNM effects
- Rapidity trend
- RAA (|y|<.35) > RAA (1.2<|y|<2.2)
- Challenge to most “local density” based suppression models
- More matter at mid rapidity, should lead to more suppression there

**Global error = 7%**

**Global error = 12%**

- Scomparin (proc. QM06) : nucl-ex/0703030

**PRL 98, 232301 (2007)**

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Model dependent extrapolation from d+Au

- Shadowing + σbreakup from RdAu fit used to get RAA
- Same theoretical framework as one used for RdAu

- Observations
- Statistically significant suppression observed at forward rapidity in AuAu
- Less clear in other cases
- Forward and mid extrapolation uncertainties correlated
- According to these models, anomalous suppression is higher at forward rapidity in Au+Au

**PRC 77, 024912 (2008)**

**|y|<0.35(Au+Au)**

**|y|<0.35(Cu+Cu)**

**1.2<|y|<2.2(Cu+Cu)**

**1.2<|y|<2.2(Au+Au)**

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Data driven extrapolation from d+Au

- Minimal model dependence
- Modification depends only on local impact parameter
- Glauber model + rapidity symmetrization of d+Au points (*)
- RAA(±y,b) = (1/Ncoll)*ΣiRdA(-y,b1,i)xRdA(+y,b2,i)
- Suppression slightly higher than accountable by CNM effects at least at y=0

**Bar : stat. + uncorrelated syst. errors**
**Box : correlated syst. errors**

- (*) For method cf. R. Granier de Cassagnac, J.Phys.G34:S955-958,2007

- If we want minimal model dependence, RAA/CNM doesn’t exclude the same anomalous suppression at forward and mid rapidities.

**PRC 77, 024912 (2008)**

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Alternate explanation

- Lattice QCD results suggest :
- No J/ψ suppression for T as high as 2.1Tc ( ≳ 10GeV/fm3)
- ψ’and χc  start melting at around 1.1Tc (attained both at RHIC & SPS)
- Suppression seen at RHIC & SPS may be only the feed down part

- Color Glass Condensate
- Charmed meson calculations based on CGC give higher mid rapidity yields (no final prediction for J/ψ)
- If valuable for J/ψ this should partly explain the forward/mid tendency, but is challenged by the saturating Forward/Mid rapidity RAA
- Quantitative prediction for J/ψ in d+Au and Au+Au is indispensable to draw conclusion

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Yet another explanation: regeneration

- Why regeneration explains rapidity trend?
- Uncorrelated c and c quarks coalesce at hadronization
- At mid rapidity, more charm quarks => enhance the direct J/ψ yield
- Just an example below (*), a number of other models do as good a job (**)

- (*) Capella et al.n, arXiv:0712.4331

- _

- (**) Without being exhaustive some of these models are listed below :
- O. Linnyk et. al. arXiv:0801.4282; R. Thews et. al. Eur.Phys. JC43, 97 (2005); Yan et al. PRL 97, 232301 (2006); Andronic et. al. NPA789, 34(2007), Ravagli et al. arXiv:0705:0021; Zhao et. al. arXiv:0712.2450,

- cf. Talks by  R. Thews and K. Tywoniuk

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Testing regeneration with J/ψ flow

- Elliptic flow
- In non central collisions, almond shaped interaction region results in a pressure gradient
- More particles are emitted ‘in plane’ than ‘out of plane’
- Magnitude measured by v2
- J/ψ flow : promising test of regeneration
**Electrons from open c and b semileptonic decays show large nonzero elliptic flow**
- J/ψ regenerated from c quarks should inherit their flow

**Réaction Plane ****ψ****RP**

**Run 4 Final : PRL 98, 172301 (2007)**

**(cf. Talk by A. Dion)**

- E. T. ATOMSSA, Hard Probes, 06/12/08

**Notes:**
Have to explain rapidly what elliptic flow is, add backup on it and add a paper on upgrades especially vtx...

## J/ψ flow results (1/2)

- Preliminary results

**Bar : stat. + uncorrelated syst. errors**
**Band : correlated syst. errors**

**cf. Talk by C. Silvestre**

**New**

- E. T. ATOMSSA, Hard Probes, 06/12/08

## J/ψ flow results (2/2)

- Preliminary results
- This is more of a proof of principle that the measurement is feasible
- Completely independent measurement techniques at forward & mid rapidity
- A slightly negative v2 observed at intermediate pT in both measurements
- Highest pt data points are compatible with zero to maximum flow predictions within errors
- Current precision doesn’t allow to draw strong conclusions. Much larger data sample, expected to be available in future runs, is required.

**cf. Talk by C. Silvestre**

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Summary

- Reviewed PHENIX results on quarkonia
- In p+p collisions, production baseline is measured
- J/ψ feed-down ratios from ψ’ and χc constrained from data
- In d+Au collisions, despite lack of statistics, data is used to extract
- J/ψ CNM σbreakup, comparable within errors to SPS measurement
- Extrapolation to Au+Au and Cu+Cu collisions
- In Au+Au and Cu+Cu measurements:
- Very similar suppression to SPS at mid rapidity
- Higher suppression at forward rapidity than at mid rapidity
- RAA/CNM (abnormal suppression) difference b/n mid and forward not very clear
- Regeneration is a possible scenario to explain rapidity trend
- Many models describe data satisfactorily when regeneration is allowed
- A promising experimental test : J/ψ v2, so far limited by statistics
- Outlook
- New d+Au data set (30x more statistics), better constraint on CNM effect
- Better precision on J/ψ v2 from larger statistics in future runs

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Backup

## Measuring J/ψ flow (central rapidity)

- Measuring J/ψ flow (central rapidity)

- Estimate reaction plane
- New detector for event by event reaction plane determination
- Measure v2
- Nsig*v2,J/ψ= Nfg*v2,fg – Nbg*v2,bg(MJ/ψ)
- v2,fg = <cos(2*(φ-ΨRP))> of unlike sign pairs in J/ψ mass window
- v2,bg at Mj/ψ is interpolated from a polynomial fit outside of J/ψ mass window of like sign v2(m)
- Correct for finite resolution
- v2 = v2,meas / σRP, where

- 24 segment plastic scintillator
-        1 < η < 2.8

- φ-ΨRP

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Centrality classes

- Dividing total cross section according to centrality
- Use BBC charge vs. ZDC energy
- Ncoll : number of binary inelastic N-N collisions
- Npart : number of nucleons that undergo inelastic collisions
- Glauber model + detector response simulation => <Npart> & <Ncoll>

- Most peripheral
- 80 - 92.2%
- < Npart > = 6.3 ± 1.2
- < Ncoll > = 4.9 ± 1.2

- Most central
- 0 - 5 %
- < Npart > = 351.4 ± 2.9
- < Ncoll > = 1065 ± 105

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Indirect comparisons to SPS

- Test with RHIC data models that worked at SPS
- Most models are strongly challenged by the rapidity trend, and less suppression at mid rapidity

**All calculations shown here give predictions at mid rapidity**
** ****Digal, Fortunato, Satz **
** ****hep-ph/0310354**
** ****Capella, Ferreiro**
** ****hep-ph/0505032**
** ****Grandchamp, Rapp, Brown**
** ****hep-ph/0306077**

**Bar : stat. + uncorrelated syst. errors**
**Band : correlated syst. errors**

- E. T. ATOMSSA, Hard Probes, 06/12/08

## Signal extraction

- Invariant mass spectra of μ+μ- and e+e- (J/ψ branching ratio ~ 6% each)
- Combinatorial background subtracted by event mixing
- Fitted with:

- Gaussians for the mass peak
- Exponentials for physical background (heavy flavor decay and/or Drell-Yan)
- Average value of various fits used as J/ψ count
- Dispersion is included in systematic errors.

- E. T. ATOMSSA, Hard Probes, 06/12/08

## PHENIX J/ψ measurements summary

- E. T. ATOMSSA, Hard Probes, 06/12/08

## PHENIX J/’s from Run8

- PHENIX J/’s from Run8

- E. T. ATOMSSA, Hard Probes, 06/12/08

## RHIC

- Heavy ion and polarized proton colliding machine
- 4 species: p+p, d+Au, Au+Au, Cu+Cu
- 6 energies: 9.2 GeV, 19 GeV, 22.5 GeV, 62.4 GeV, 130 GeV, 200 GeV

- Au+Au

- Cu+Cu

- E. T. ATOMSSA, Hard Probes, 06/12/08

## RAA vs. Npart summary

- Au+Au final: **PRL 98, 232301(2007)**
- Cu+Cu prelim: **nucl-ex/0801.0220**

- E. T. ATOMSSA, Hard Probes, 06/12/08