# Presentation: 535374

## Leptons, Photons, and Heavy Quarks

## Low and Intermediate-Mass Dileptons
open questions
pending answers
Direct Photons
controlling jets
Heavy Flavor
charmonia
news from SPS
preparing the case for RHIC
open charm at RHIC
reference and probe
Summary

**open questions**
**pending answers**
**Direct Photons**
**controlling jets**
**Heavy Flavor**
**charmonia**
**news from SPS**
**preparing the case for RHIC**
**open charm at RHIC**
**reference and probe**
**Summary**

**Outline**

## SPS dilepton experiments: open questions

**dimuon excess observed at                                                                              intermediate masses (NA50)**
**charm enhancement?**
**thermal dimuons?**

**the ******** puzzle**
**discrepancy between NA49 ********K****+****K****-****)                                                                       and ****NA50 **********************
**physics (******** in-medium vs.                                                                                         ******** at freeze-out)?**

**SPS dilepton experiments: open questions**

**low-mass dielectrons**
**excess established by NA45/CERES **
**vector mesons, i.e.********?**
**where are they?**
**medium modifications of                                                                                   yield, mass, width?******

## SPS dilepton experiments: answers?

**SPS dilepton experiments: perspectives!**

**NA45/CERES (talks by A. Marin, A. Cherlin)**
**improved mass resolution (TPC)**
**possibility for********e****+****e****-**** and ********K****+****K****-**** in one experiment**
**work in progress**

**NA60 (talks by P. Sonderegger, A. David)                                                        **
**DESIGNED to answer open questions!**
**high statistics due to selective trigger**
**good mass resolution (~20 MeV for ********)**
**good phase-space coverage                                                                                           (down to zero p****T****)**
**50 ********m secondary vertex resolution                                                                  (prompt ******** vs. ******** from charm decays)**

**Indium+Indium at 158 AGeV (2003)**
**>10****6**** low-mass dimuons!**
**S/B: 1⁄2 - 1 (depending on centrality)**
**>10****5**** **********************
******K****+****K****-**** feasible as well**
**proton reference run forthcoming (2004)**

**NOT YET!**

## PHENIX (talk by R. Seto): resonance measurements         in leptonic and hadronic   channels in ONE experiment
look forward to results from large statistics Au+Au Run04   at RHIC
 
continuum (low and intermediate mass)
RHIC upgrades                                  (talk by A. Drees):
electron identification                Dalitz / Conversion rejection (poster by I. Ravinovich)
Silicon vertex spectrometers     resolve secondary vertices (heavy flavor physics)

**PHENIX (talk by R. Seto): resonance measurements         in leptonic and hadronic   channels in ONE experiment**
**look forward to results from large statistics Au+Au Run04   at RHIC**
****** **
**continuum (low and intermediate mass)**
**RHIC upgrades                                  (talk by A. Drees):**
**electron identification               ******** Dalitz / Conversion rejection (poster by I. Ravinovich)**
**Silicon vertex spectrometers    ******** resolve secondary vertices (heavy flavor physics)**

**posters by C. Maguire, D. Pal,  Y. Tsuchimoto**

## Virtual photons  real photons

**real photon sources in AA collisions **
**“****trivial” ******** background**
**decays of light hadrons (****************)**
**dominant at low / intermediate p****T**** (few GeV/c)**
**“****thermal” ******** black body radiation from hot medium**
**partonic and/or hadronic medium**
**expected at low p****T**** on top of huge background**
**“****direct” ******** photons from initial state hard scattering**
**Compton scattering dominates, i.e. probe for gluon distribution**
**calculable in pQCD**
**no fragmentation of photon!**
**photon “shines through” hot and dense medium!**
**direct photons “calibrate” hard scattering                    processes                                                                                       ******** IDEAL CONTROL EXPERIMENT FOR JET SUPPRESSION!**
**how-to measure direct photons**
**subtraction of “background” photons (WA98 / PHENIX)**
**photon correlations                                                                              (WA98 talk by                                                                                           D. Peressounko)**

## Direct photons from 200 GeV pp collisions

**Direct photons from 200 GeV pp collisions**

********

- PHENIX Preliminary

**evaluation of excess above background: double ratio****   **
**[********]****measured**** / [********background  ********  ********measured****/********background**
**(small) direct photon signal observed!                         (PHENIX talk by J. Frantz,                                                 ****posters by G. David, K. Reygers, T. Sakaguchi****)**

**consistent with NLO pQCD calculation        ****(W. Vogelsang:         JHEP 9903 (1999) 025     & priv. comm.)**

## Direct photons from 200 GeV  AuAu collisions

**Direct photons from 200 GeV  AuAu collisions**

**strong suppression of high p****T**** pions in central AuAu collisions**
**VERY significant background reduction!****   **

## Comparison with NLO pQCD calculation

**Comparison with NLO pQCD calculation**

**nice agreement with ****unsuppressed, binary scaled pp NLO pQCD calculation!****  **

## Direct photons: centrality dependence

**Direct photons: centrality dependence**

**direct photons are not inhibited by hot/dense medium and ****shine through**** consistent with pQCD!**

**thermal photons: reduction of                      systematic uncertainties is essential!!**

## Another hard probe: heavy flavor production

**a (very) complex playground**
**cc production in hard scattering **
**sensitive to PDF**
**propagation**
**hadronization**
**medium modifications**
**modification of PDF in nuclei (shadowing, antishadowing)**
**multiple scattering                        ******** p****T**** broadening**
**initial state parton energy loss**
**charmonia:**
**“****normal” nuclear absorption**
**“****anomalous” suppression (“Debye” screening)**
**enhancement via “coalescence”?**
**additional “thermal” production?**
**energy loss by induced gluon radiation? “Dead-cone effect”?**
**...****.**

**how to disentangle this?**
**measure charmonium states and open charm**
**in pp, pA, AA collisions**
**in various kinematic regions**
**at various energies**
**news from SPS**
**news from RHIC**

## J/ suppression in PbPb at SPS

**J/******** suppression in PbPb at SPS**

**updated analysis of J/******** (and ********’) absorption in cold nuclear matter (NA50 pA run at 400 GeV (2000) + combined fit of ALL data sets) (NA50 talk by G. Borges)**
- J/abs = 4.3 ± 0.3 mb
**J/********suppression with respect                                                                          to this expected “normal”                                                                 nuclear absorption                                                                                  (relative to Drell-Yan):                                                                               ****a familiar pattern**
**what is new? **
******’ ****measurement**
**challenging because of**
**small dimuon cross section**
**small S/B**
**large suppression (weaker                                                                         bound state than J/********)**

## ’ suppression at SPS

******’  ****suppression relative to Drell-Yan and J/******** increases with centrality in PbPb collisions**

******talk by H. Santos**
******’  ****absorption in pA is stronger than J/******** absorption**
**significantly stronger absorption in AA going from peripheral to central collisions**
**no apparent difference in absorption pattern between SU and PbPb collisions**

## Open questions at SPS

**Open questions at SPS**

**what fraction of J/******** comes from ********c**** feed down (********c**** ******** J/******** + ********)?**
**what is the nuclear dependence of ********c**** production/absorption in pA?**
**is open charm enhanced in AA?**
******c**** measurement at HERA-B (huge statistics dilepton data sample from pA collisions at ********s****NN**** = 42 GeV)                                                  (HERA-B talks by J. Spengler, A. Gorisek)**

**will be answered by NA60**

- c/J/from 15 % of available statistics

- m-mJ/

## J/ suppression / enhancement at RHIC?

**PHENIX: preparing the case**

| Year | Ions | sNN | Detectors | J/ |
| --- | --- | --- | --- | --- |
| 2000 | Au-Au | 130 GeV | Central (electrons) | 0 |
| 2001 | Au-Au | 200 GeV | Central | 13 + 0 |
| 2002 | p-p | 200 GeV | + 1 muon arm | 46 + 66 |
| 2002 | d-Au | 200 GeV | Central | 300+800+600 |
| 2003 | p-p | 200 GeV | + 2 muon arms | 100+300+120 |
| 2004 | Au-Au | 200 GeV | ! ready ! | ~400+2x1600 ? |

_**QM2002**_
**  ****first observation**

_**QM2004**_
**         ****first   **
**sizeable**
**pp & dAu**
**samples**

**study J/******** modifications in cold nuclear medium**
**         **

## J/ in dAu collisions at RHIC 

**J/******** in dAu collisions at RHIC **

**J/******** produced by gluon fusion**
**sensitivity to gluon pdf**
**3 rapidity ranges in PHENIX probe different momentum fraction of Au partons**
**South (y < -1.2) : large X****2**** (in gold)**
**Central (y ~ 0) : intermediate**
**North (y > 1.2) : small X****2**** (in gold) **

- From Eskola, Kolhinen, Vogt
- Nucl. Phys. A696 (2001) 729-746.

**Notes:**
ANTISHADOWING – SHADOWING
MOTORCYCLE + TRUCK

## J/ in pp and dAu collisions at RHIC

**J/******** in pp and dAu collisions at RHIC**

**rapidity distributions: improved pp / first dAu measurements**

**PHENIX talk by R. G. de Cassagnac, ****posters: J.M. Burward-Hoy, S. Kametani,     D. Kim, D. Silvermyr**

## J/ dAu/pp versus rapidity at RHIC

**indication for (weak) shadowing and absorption**
**centrality dependence studied as well!**
**more statistics desirable to disentangle nuclear effects (and distinguish models)**

**STAGE IS SET**
** ****Look forward to high statistics AuAu run!**

## Open charm: reference and probe

**physics motivation for open charm measurements**
**reference for J/******** suppression / enhancement**
**production mainly via gluon fusion ******** interesting probe itself**
**sensitive to gluon structure function (and nuclear modification of this)**
** ****heavy quark energy loss**
**induced gluon radiation**
**“****dead cone” effect**
**does charm flow?**
**open charm measurements at RHIC**

_**direct reconstruction**_
**ideal, difficult in HI, doable **
**200 GeV dAu: STAR (mb) **

_**indirect measurements**_
**electrons from semileptonic decays **
**130 GeV AuAu: PHENIX (cent.)                  ****200 GeV pp:      PHENIX & STAR                   200 GeV dAu:   PHENIX (cent.) & STAR (mb) 200 GeV AuAu: PHENIX (cent)**

## First direct charm measurement (STAR)

**reconstruction of D mesons in minimum bias dAu collisions**
**D****0**
**D****±**
**D*******

*STAR preliminary*

-          = 1.12 ± 0.20 ± 0.37 mb from D data
-       (1.36 ± 0.20 ± 0.39 mb with electrons)

**STAR talks by A. Tai, L. Ruan, A. Suaide**

## Open charm in pp: the baseline

**two single electron measurements**

**three methods to subtract  photonic background          (PHENIX talk by S. Kelly)**

**three methods to identify electrons                                (STAR talk by A. Suaide)**

- PHENIX PRELIMINARY

**charm cross sections (barely) agree!**

- =1.36 ± 0.20 ± 0.39 mb

## Consistency between electron data sets

**STAR systematically (slightly) above PHENIX**
**beware: error bars are meant to be taken seriously!**

## Does the PYTHIA extrapolation work?

**PYTHIA tuned to available data (********s****NN ****< 63 GeV) BEFORE RHIC results**

*STAR preliminary*

**spectra are harder than PYTHIA extrapolation from low energies! (hard fragmentation function, charm quark recombination ...?)**
**PYTHIA can’t be used to extract bottom cross section!**
**bottom measurement requires PRECICE D measurement first!**

## Centrality dependence in dAu (PHENIX)

**single electrons from non-photonic sources agree well with pp fit and binary scaling ****(posters: S. Butsyk, X. Li)**

## Centrality dependence in AuAu (PHENIX)

**1/T****AA**

**1/T****AA**

**1/T****AA**

**Centrality dependence in AuAu (PHENIX)**

**uncertainties too large for definite statements regarding (small) deviations from binary scaled pp results ****(poster: T. Hachiya)**

**1/T****AA**

**1/T****AA**

- 1/TABEdN/dp3 [mb GeV-2]

- 1/TABEdN/dp3 [mb GeV-2]

- 1/TABEdN/dp3 [mb GeV-2]

- 1/TABEdN/dp3 [mb GeV-2]

- 1/TABEdN/dp3 [mb GeV-2]

- 1/TABEdN/dp3 [mb GeV-2]

## Binary collision scaling in AuAu (PHENIX)

**Binary collision scaling in AuAu (PHENIX)**

**binary collision scaling of pp result works VERY WELL for non-photonic electrons in AuAu (PHENIX talk by S. Kelly)**
**open charm is a good CONTROL, similar to direct photons!**

## Does charm flow?

- PHENIX PRELIMINARY

**is partonic flow realized?**
**v2 of non-photonic electrons indicates    non-zero charm flow     in AuAu collisions**
**uncertainties are large**
**definite answer:                         AuAu RUN-04 at RHIC!**

**PHENIX poster by S. Sakai**

## Summary

**low and intermediate-mass dileptons**
**looking forward to **
**solutions of SPS puzzles**
**data from RHIC**
**direct photons as jet control measurement**
**pQCD at work**
**charmonia**
**improvements at SPS**
**preparing the reference for RHIC**
**open charm**
**a second player joined the game**
**what next?**
**LUMINOSITY!!**
**back to work**