# Presentation: 941828

## Relativistic Heavy Ion  Physics:Heavy Quarks and Quarkonia

- James Nagle

- CTEQ Summer School
- Lecture #2 - June 8, 2002

- Relativistic Heavy Ion  Physics:Heavy Quarks and Quarkonia

- University of Colorado, Boulder

## Studying Quark Deconfinement

- Lattice QCD results show that the confining potential between heavy quarks is screened at high temperature.

- This screening should suppress bound states such as J/.

- r

- V(r)/

- Lattice QCD calculation

## Thermometer

- The** ********’ **and** ********c**** **melt below or at Tc
**   **the** J/******melts above Tc  and
-        eventually the** ******(1s) melts.

- Different states “melt” at different temperatures due to different binding energies.

- hep-ph/0105234 -  “indicate ’ and the c dissociate below the deconfinement point.”

## Drell-Yan Baseline

- At CERN-SPS energies, Drell-Yan dominates the dimuon invariant mass spectrum above the J/ and ‘.
- Drell-Yan provides a good baseline for J/ suppression that should scale with binary collisions since the photon does not interact with the medium.

## Charm Normalization

- At RHIC, Drell-Yan is not easily measured because it is dominated by leptons from open charm above the ’.
- Shadowing of initial state partons means that one must compare J/ production with something that couples directly to the gluons
- (eg. Charm, Beauty).

- RHIC

- SPS

- LHC

## More Charm Interest

- In addition, total charm production may be affected not just in a factorized shadowing picture, but from the saturation of gluons in a Color Glass Condensate.
- Is there thermal or simple secondary scattering charm production after the initial
- parton-parton scattering?

- Could large thermal charm production lead to J/ enhancement via c-cbar coalescence?

## Charm and Jets

- Radiative quark energy loss is qualitatively different for heavy and light quarks.
- More massive charm quarks move slower and this leads to suppression of co-linear gluon emission
- (“dead-cone” effect)
- Suppression of Suppression = NO Suppression
- Predict enhanced **D/****** ratio

- D

- D

-  Y.L.Dokshitzer and D.E. Kharzeev, hep-ph/0106202

## Charm Diagram

- For example:

- Direct reconstruction of open charm is ideal, but difficult.
- Open charm and bottom can be measured through single leptons and lepton pairs.

- K+

- K-

- e+

- e

- -

- 

**D*****0**

********

## Charm via Electrons

- 	High pT single electrons were observed at the ISR in the early 1970’s
-   F. W. Busser et al., PLB 53, 212
-   F.W.Busser et al., NPB 113, 189
- 	These electrons were later interpreted as a signal from semi-leptonic decays of
- 	open charm
- 	    I.Hunchlife and C.H.Llewellyn Smith, PLB 61,472
-    M. Bourquin and J.-M.Gaillard, NPB 114,334

## Direct D Reconstruction

- Direct charm measurement in
- hadron-hadron collisions has proved to be quite challenging.
- Using D* reconstruction and displaced vertex measurements have allowed observations at FNAL and CERN.
- Extrapolation of p-p data at lower energies to RHIC 130 GeV yields
-     cc = 380  120 b
- Systematic error should probably be somewhat larger.

## Measuring Charm

- PHENIX recorded 2 million Au-Au events in Run I, and can thus address charm production via single electrons.

- D0      K-  **e****+** e

- One must account for contributions:
-   0,  Dalitz
-  conversions
- Remaining signal is then from
-   **open charm** and **open beauty**
-   **Drell-Yan**
-   thermal production
-   new physics

- B0      D-  **e****+** e

## PHENIX Pioneering High Energy Ion eXperiment

- Designed to measure electrons, muons, photons and hadrons.
- Complex set of four separate
- particle spectrometers.
- This requires many different types of detector technologies and an integrated electronics readout.

- Yellow beam

- Blue beam

## Electron Needle in a Hadron Haystack

**PHENIX Spectrometer**

- PHENIX is designed to find
- 1 electron out of 10,000 pions !
- Electron identification:
- track reconstructed (momentum p)
- ring found in Ring Imaging Cherenkov Counter
-    (velocity threshold)
- energy cluster found in
-     Electro-magnetic Calorimeter
-     (energy E)

## PHENIX Picture

## Total Electron Yield

-  conversion

**Transverse Momentum (GeV/c)**

**Electron Yield per Event**

- Many electrons are from light hadron decays, and must be subtracted off to see the charm contribution.

## Charm Results

- 	PYTHIA model is tuned to match lower energy charm production data.
- 	PYTHIA shows good agreement with charm production that scales with the number of binary
- 	collisions.

**Transverse Momentum (GeV/c)**

**Electron Yield per Event**

- 	Clear remaining electron signal observed that appears consistent with semi-leptonic decays of charmed D mesons.

## Binary Scaling

- 	Surprisingly good agreement with assumption of binary collision scaling and extrapolated proton-proton charm cross section at 130 GeV.

## Charm Cross Section

**	**We estimate the charm yield by assuming that all single electrons above “background” are from D mesons.
- 	Neglect other possible sources such as thermal dileptons, etc.
- 	By fitting the single electron distribution, we obtain:

- 	Data is consistent with binary scaling (no nuclear or medium effects), but with large uncertainties.
- 	Errors - statistical uncertainty (14%), fitting range (18%), background subtraction (44%), PYTHIA kT (11%), D+/D0 (13%).
- 	Additional uncertainty in the total charm cross section from PDF in the charm rapidity distribution.

**N****binary**

**Centrality**

**d********cc****/dy|****y=0****(********b)**

******cc****(********b)**

**0-10%****	**

**0-92%****	**

**905********64**

**246********16**

**97********13********49**

**107********8********63**

**380********60********200**

**420********33********250**

## Proton-Nucleus Studies

**E769 250 GeV ********± **** PRL **_**70**_**,722 (1993)**

**WA82 340 GeV ********- **** PRB **_**284**_**,453 (1992)**

**Vogt et al., NP **_**383**_**,643 (1992)**

**E769 250 GeV ***********-***** **

**WA78 320 GeV ***********- ******(Beam dump)***** **

- 	D meson production in
- 	proton-Nucleus and -Nucleus collisions at lower energies is consistent with binary collision scaling ( = 1).

## Theoretical Calculation

- Z.Lin, R. Vogt, X-N. Wang PRC 57 (1998)

- Charm =340 b

- Charm w/ dE/dx=-2 GeV/fm

- 	Theoretical prediction for electrons from charm.
- 	Inclusion of energy loss at the same scale as for light quarks.

- Why is the calculation with
- no energy loss different
- from the PYTHIA result?
- Different fragmentation
- function used in calculation.

## D Meson Contributions

- The three types of D mesons that contribute single electrons are:
- _name_    _b.f. D____eX_        _percentage contribution to electrons in PYTHIA_
- D+	   17.2%		21.6%
- D0	    7.7%		66.8%
- D+S	    8.0%		11.6%
- Note that most all excited charm mesons do not decay semi-leptonically, but only contribute via sequential decay
- D*+      D0 +    68.3%
- 	D+ 0    30.6%
- 	D+        1.1%
- D*0      D0 0     61.9%
- 	D0       38.1%
- D+/D0 = 0.32  (PYTHIA) gives an average b.f. DeX of **9.7%**
- PHENIX paper uses D+/D0 = 0.65  0.35 which gives b.f. DeX of **11.0%**
- Theory prediction of Lin, Vogt, Wang uses b.f. DeX of **12.0%**

## Fragmentation Functions

- Lund symmetric fragmentation function (PYTHIA default)

- Quark mass dependence is in the mT

- Bowler modification “since LUND predicts a somewhat
- harder B meson spectrum than observed in data.”

- Other options are:

- Field-Feynman (for light quarks)

- Peterson (for heavy quarks)

## Comparing Functions

- _Light quarks (u,d)_
- blue = Fields-Feynman
- black dash = Lund fragmentation

- z

- dN/dz * z

- _Heavy quarks (c,b)_
- red = Peterson function
- black dash = Lund fragmentation
- Bowler correction not shown
- (1-z) is obvious

- For charm quarks, the Peterson and Lund fragmentation roughly agree and give an average
- <z> ~ 0.8.

## Intrinsic Charm

- Dashed = (1-z) function
- Solid = Peterson function

- For example, in R. Vogt, Brodsky, Hoyer, “Systematics of Charm Production”, Nucl. Phys. B383, 643 (1992), they discuss a model where large xF D mesons are dominantly produced by intrinsic charm pairing with co-moving valence quarks.

- - + A at 250 GeV

- Charm quark is not slowed
- down in combining with
- nearby d quark.  Thus more
- D- than D+ at high xF.

## Electron Inversion

- Going beyond the PHENIX data, one can invert the single electrons to calculate a D meson spectrum.
- 1) Power Law Form
- 2) Guassian Form
- Both forms are agree with limited statistics PHENIX data from Run1.

- Work withSean Kelly

## D/ ?

- 0 x 10

**PYTHIA output**

- PHENIX D/ is a factor of 2-3 larger than from PYTHIA model tuned to lower energy charm data.
- We _must_ replace PYTHIA with PHENIX p-p data
- for  and D with Run 2 data !  Then we will see.

- PHENIX 0 x 10

- p-p with binary scaling

## Hydrodynamics? Or Fragmentation

- If we assume that there is large pressure build up in the partonic phase, charm quarks may participate in hydrodynamic expansion.  This could also happen in the hadronic stage via D meson scattering.

- Simply taking the hydrodynamic model parameters from matching the PHENIX , K, p, one  calculates the D meson pT spectra.
- We then calculate the single electrons and find good agreement.
- Remember there is a free normalization.

- Best hydro parameters
- +/-2 parameters

- Work with Sotiria Batsouli

## Alternate Inversion Method

- One can invert the electrons point by point to a D meson yield integrated above some pT minimum.
- Much greater statistics from Run 2 should help discriminate between these models.

- Distribution of D mesons that contribute to different electron bins.

## Many Lepton Channels

**D****0****      K****-****  ********+**

**D****0****      K****-****  e****+ ********e**

**D****0****      K****-****  ********+ **********

**B****0****      D****-****  ********+**

**B****0****      D****-****  e****+ ********e**

**B****0****      D****-****  ********+ **********

**D****0****D****0****      ********+********-****  K****+**** K****-**** ******************

**D****0****D****0****      e****+****e****-****  K****+**** K****-**** ********e********e**

**D****0****D****0****      ********+****e****-****  K****+**** K****-**** ********e**********

- Future measurements of single leptons at higher momentum will have large contributions from Beauty decays.
- Also correlated leptons provide additional constraints and very different backgrounds.
- Finally, future RHIC upgrades with inner silicon detectors may allow for displaced vertex measurements to tag the heavy meson decays.

## J/ Production

- Quarkonium states are not directly
- produced, but have pre-cursor states.
- Color Octet Model (COM) necessary
- to explain J/ production at high pT
- measured by **CDF** at the Tevatron.

- F. Abe et al., Phys. Rev. Lett. 79, 3867 (1997).
- Kramer, hep-ph/0106120

## Nuclear Absorption

- The octet state can break-up with nucleons in the colliding nuclei with ccg-N~ 6-7 mb and for the singlet state cc-N~2 mb
- After a proper time
- the J/ or ’ state is formed.  After that the break-up cross section for the ’ is larger due to the lower binding energy.
- J/ and ’ should have similar absorption if   ccg > crossing

## Proton-Nucleus Modeling

-  Model includes both octet and
-    singlet state contributions.
-  Require ******8-1**** = 0.02 fm/c**, much
-    smaller than expected !
-  Still shows disagreement with
-   E866 data.
-  Energy dependent breakup
-   and small 8-1 results in
-   matching the large xF
-   observed nuclear suppression.

- Arleo, Gossiaux, Gousset, Aichelin, hep-ph/9907286

## Nucleus-Nucleus Collisions

- We must understand the normal absorption of the J/ or its precursor state in normal nuclear matter.

- (1) break-up by nucleons in the colliding nuclei can be studied
- 	using p-A collisions
- (2) break-up by co-moving hadrons in the produced **fireball**
- 	is calculated to be small, _but calculations vary a lot!_

**before**

**Pre-resonance**
** ****absorption**

**Quarkonium state**
**in bath of hadrons**

## CERN Press Release 2000

- _http://press.web.cern.ch/Press/Release00/PR01.00EQuarkGluonMatter.html_

## NA50 Suppression Result

**“****Strong evidence for the formation    of a transient quark-gluon phase without color confinement is provided by the observed suppression of the charmonium states J/********, ********c****, and ********’.”**
- 	         Maurice Jacob and Ulrich Heinz

- NA50 at the CERN-SPS

**Discontinuity due to **c** melting**
**Drop due to **J/** melting**
**Using Drell-Yan as control*******

## Model Bias

- Mike Bennett and I find good agreement with their data in the
- ET resolution range 55-75% /(ET)

- Easy to create an inflection point exactly
- where they see one.
- No systematic error included by NA50 for energy resolution,
- Glauber model parameters, transverse energy scaling.

- Ratio of 55%/75% calculated
- Nb versus ET

## Charm Enhancement !

- 	Intermediate mass region (IMR) dimuons are thought to have a large open charm contribution.
- 	NA50 observes an enhancement of IMR relative to Drell-Yan, which scales with binary collisions.
- 	This may imply a charm enhancement by x3.5 over binary scaling in central Pb+Pb collisions !

## Future Measure at RHIC

- At RHIC, PHENIX can measure quarkonia in the electron and muon channel.  We have first low statistics data on tape.
- Future running at high luminosity will be required for a definitive measurement.  STAR will also add a measurement in the electron channel at high pT.

## PHENIX Coverage

## Conclusions, so far...

- RHIC appears to be creating a hot, dense and expanding state of deconfined QCD matter
- All results so far consistent (but not conclusive) with this interpretation
-  initial conditions - saturated gluon distributions from       				color glass condensate
-  energy density - exceeds lattice QCD expectations
-  plasma state - large parton scattering for hydrodynamic 				expansion
-  hard probes - parton energy loss from deconfined medium
- RHIC experiments have two orders of magnitude more data in Run II.   More stringent tests required of models.
- Polarized proton-proton data taking just completed.
- Exciting years ahead of physics discovery !

## High Intensity Future Awaits