# Presentation: 865228

## Measurements of Leptonic and Photonic Probes in Au+Au Collisions at PHENIX Run-2

**Takashi Matsumoto **
** ****for the PHENIX collaboration**
** ****at **
** ****RHIC & AGS Annual User’s Meeting**

- PHENIX

## Topics Covered in This Talk

**Part 1**
- What is PHENIX? Overview of experimental setup and  physics.
**Part 2**
- Electron measurements in PHENIX.
- Results : Leptonic probes in Au+Au.
**Part 3**
- Photon measurements in PHENIX in Au+Au.
- Results : Photonic probes.
**Other Topics**** ****from PHENIX **
- Global/hadron -> by Kensuke Homma in next session.
- pp results -> by Xie Wei on Saturday.

## Part 1 

**Overview of experimental setup **
**and physics.**

_**Part 1**_** **

## Physics in PHENIX	

**Search for a new state of matter, quark-gluon plasma (QGP)** .
- what is happening in heavy ion collision at RHIC energy?
**How do we get the information about the earliest stage of the collision and hot/dense phase?**
- Hadrons and global variables.
- Particle production.
- Achieved energy density, etc.
- Leptons and photons.
- Carry the “direct” information without
- 	affected by strong interaction.
- Difficult, but important
**The preliminary results from PHENIX Run2 presented in this talk  focused on leptons and photons.**

## PHENIX Experiment	

**Capability of measuring the photons and leptons  using 2 central arms and 2 muon arms.  **
**Capability to achieve  different kind of measurements at the same time.  **
- e+e-, K+K-
- J/e+e-  , J/+  -
- Photon measurement in 3 different ways.
- 2 direct measurements
**********e**+e-

## PHENIX Setup

**Central arms cover |********|<0.35, d********=90°x 2**
**Measurements of Vertex and Collision timing**
- Beam-Beam Counters (BBC)
- Zero Degree Calorimeters (ZDC)
- Coincidence between BBC and ZDC produce minimum bias trigger
**Tracking **
- Drift Chambers (DC)
- Pad Chambers (PC)
**Electron identification**** **
- Ring Imaging Cherenkov Detectors (RICH)
- Electro-Magnetic Calorimeters (EMCal)
- Lead Scintillator Calorimeters (PbSc)
- Lead Glass Calorimeters (PbGl)
**Photon identification**
- Electro-Magnetic Calorimeters

## Centrality Determination 

**Centrality Determination **

**Event characterization in terms of impact parameter (b) in Au+Au collisions.**
**Large : ****peripheral collision**
**Small : ****central collision**** **
**Coincidence between BBC and ZDC.**
- Determine collision centrality.
- 92 % of inelastic cross section can be seen.
**Extract variables using Glauber Model **
**Number of participants (*****N_part*****).**
- Number of nucleons participate in a collision.
- Represents centrality.
- Related with soft physics.
**Number of binary collisions (*****N_binary*****).**
- Number of Nucleon-Nucleon collisions.
- Related with hard physics.
- Incoherent sum of N-N collisions becomes a baseline for A-A collisions.

**peripheral**

**central**

**b**

**To ZDC**

**To BBC**

**spectator**

## Electron Identification

**Ring Imaging Cherenkov counter**
- Track - Ring association
- 3 PMT hits
- Ring shape cut

**e****+****e****- ****candidate**

**net e****+****e****-**** **

**Electromagnetic Calorimeter**
- Energy – Momentum matching
- Track – Hit position association
- Timing cut

**charged tracks**

**Background**

-  Energy / momentum

## Photon Measurements

**Direct measurement.**
- 2 types of Electromagnetic Calorimeter.
- PbSc calorimeter.
-  covering 3⁄4 acceptance.
- PbGl calorimeter.
-  covering 1⁄4 acceptance.

**Indirect measurement.**
**Measurements of photons through** **their conversion into e****+****e****-**** pairs****.**

_**Photon converter**__ _located
-  around beam pipe

## Results : Leptonic probes 

**Results : Leptonic probes**** **

**Single electron results**
**Dielectron continuum results**
** ******** ****results**
**J/******** results**

## Single Electron(Charm Measurement)

- Direct method:
- Reconstruction of D-meson (e.g. D0Kp).
- Very challenging without
- measurement of displaced  vertex

- +

- Indirect method:
- Measure leptons from semi-leptonic decay of charm.
_**This method is used by PHENIX at RHIC**_

**Motivation **
**Measurements of Heavy flavor (charm and beauty) production through semi-leptonic decay****.**
**-> non-photonic decay.**
**Background: ********0 ****dalitz decay, photon conversion...**

## Single Electron Spectra from Non-photonic Source 

**Spectra (130 and ****200 ****GeV) with binary scaled PYTHIA calculation of electron spectra from semi-leptonic charm decay.**

**Our data are consistent with binary scaling in all centrality classes within current statistical and systematic errors.**

## Discussion of Single Electron Result 

**NA50 has inferred a factor of ~3 charm enhancement at lower energy.  We do not see this large effect at RHIC.**
**PHENIX observes a factor of ~3-5 suppression in high p****T**** ********0**** relative to binary scaling**** **(See Kensuke Homma’s talk)**.  ****We do not see this large effect in the single electrons**.
- Initial state high **p****T** suppression excluded?
- Smaller energy loss for heavy quark ? (dead cone effect)

- NA50 - Eur. Phys. Jour. C14, 443 (2000).

- N part

**Enhancement of Open Charm Yield**

## Dielectron Continuum

**Dielectron Continuum**

**Motivation**
- Is there excess in low and intermediate mass region, due to
- In-medium mass modification of mesons ?
- Contribution from charm ?

**Background subtracted invariant mass spectra of e****+****e****-**** **
**Expected meson decay contributions.**
**PYTHIA charm calculation scaled by number of binary collisions.**
**Black curve is sum of above two contribution.**
**dN/dm (0.3-1.0 GeV/c****2****) **
**      ****= 13.4 ******** 7.2(stat) ****+12.2**** ****–8.4 ****(sys) x10****-5**** **
**dN/dm (1.1-2.5 GeV/c****2****) **
**      ****= 0.38 ******** 2.60(stat) ****+1.40**** ****–0.81 ****(sys)**** ****x10****-5**** **
**PHENIX will measure this as soon as we get statistics.**

## measurement(e+e-, K+K-)

**Motivation**
**Is there medium modification?**
- Restoration of chiral symmetry
- Mass and natural width
**Difference between leptonic (e) and hadronic (K) probe**
- Simultaneous measurements of two probes
**Strangeness production**
- ___e__+ __e__-__ (__AuAu minimum bias)_
**Signal = 101 ******** ****47**
- _____K__+ __K__-__ (__AuAu minimum bias)_
**Signal = 1135 ******** 120**

## dN/dy for 

**dN/dy for ******

**Au +Au minimum bias data. **
**Corrected for vacuum PDG branching fraction.**
- BR e+e- = 2.9 x 10-4
- BR K+ K- = 0.49
**There is no difference of dN/dy between ******** ******** e****+****e****- ****measurements  and ********K****+ ****K****-****  measurements within current errors.**

## J/measurements (J/e+e-)

**Motivation.**
**Screening effect in deconfined matter**
- Melt the J/y produced in the initial collision
- Suppression of the yield above normal nuclear effect will be seen
**N**** ****J/******** is obtained in 3 centrality bin.**
**  ****0-20%           : ****5.9 ******** 2.4(stat) ******** ****0.7(sys)**
**20-40%           : ****4.5 ******** 2.1(stat) ******** ****0.5(sys)**
**40-90%    ****       : ****3.5 ******** 1.9 (stat)******** 0.5(sys)**
**Systematical error of N ****J/******** is estimated  using several kind of fitting models.**

## B dN/dy for J/

**B dN/dy was measured as a function of number of participants**
- 00-20 % : **(3.9 ******** 1.6 ******** 1.0) x 10****-4**
- 20-40 % : **(2.5 ******** 1.2 ******** 0.7) x 10****-4**
- 40-92 % : **(6.9 ******** 3.7 ******** 1.9) x 10****-5**
** ****B dN/dy per binary collision was calculated.**** **
- 00-20 % (Nbinary 791): **(4.9 ******** 2.0 ******** 1.3) x 10****-7**
- 20-40 % (Nbinary 297): **(8.5 ******** 4.0 ******** 2.2) x 10****-7**
- 40-92 % (Nbinary 45)  : **(1.5 ******** 0.8 ******** 0.6) x 10****-6**
**comparison**
-  p - p data from PHENIX run2
- NA50 data
- Absorption measured at other experiment
- 7.1mb NA50 S-U
- 4.4mb NA50 p-A,S-U (from QM2002)
**Statistics are limited. But BdN/dy per binary seems to decrease  in most central collisions**
- Combine with single electron data

**** constraint to model?

## Results : Photonic probes 

**Results : Photonic probes**** **

**photon measurements given by**
**PbGl calorimeter**
**PbSc calorimeter**
**Converter method**

## Question
Is there photon excess compared to hadron decay background?

Sources of photon
Carry the information of
    matter.
Initial collision.
Thermal radiation.
Background.
0 decay, etc.

**Is there photon excess compared to hadron decay background?**
**Sources of photon**
**Carry the information of**
**    ****matter.**
- Initial collision.
- Thermal radiation.
- Background.
- 0 decay, etc.

**Photon Sources**

## Inclusive Photon Measurement

- Inclusive photon spectra for different  centrality (PbGl).

- Comparison of peripheral spectra between PbGl and PbSc . ****  Two analyses are consistent.

- PHENIX preliminary

- PHENIX preliminary

## Inclusive Photon Measurement(e+e-)

**Inclusive photon spectra**** **
**Black bar** and **green band** show **Statistical** and **systematic** uncertainties.
- Study of Systematic error is ongoing.
**Spectrum is consistent to PbGl result within current error bars.**** **

**Pt[GeV/c]**

## Direct Photon Measurements         ((/0)measured / (/0)simulated)

**What was done ?****	**
**Measure the inclusive photon spectrum.**
**Measure the ********0 ****spectrum.**
**Decay photon simulator (input is ********0 ****spectrum) . Assume mT scaling to get  contribution of ********,****...**
**Compare the measured photon and simulated photon from hadron decay. **
**No excess is observed within current error bars****.**

## Summary

**PHENIX  has shown its capability to measure leptonic and photonic probes in Run2.**
**Leptonic probes**
**Single electron from non-photonic source scales to the binary collision within current statistical and systematical errors.**
**We have made first lepton pair measurement. **
**Dielectron continuum.**
******e****+****e****-****, ********K****+****K****-****.    **
**J/******e+e-
**Photonic probes**
**3 different analyses have been done to obtain inclusive photon spectra.**
**There is no excess above hadronic decay background within current errors.**
**Analysis are preliminary and ongoing.**** **
**Another data set of LVL2 triggered event is being analyzed**
**More will come in final form soon!!**

## Back up

## Single electron spectrum from non-photonic source 

**Single electron spectrum from non-photonic source **

## Single electron

**Motivation **
**Measurements of Heavy flavor (charm and beauty) production through semi-leptonic decay.**
- Gluon-gluon fusion in initial stage of collision?
- Charm yield : Baseline of charmonium analysis
**Converter method (Electron from non-photonic source )**
**Shape of Electron spectrum**
**Without converter**
- Photonic +non-photonic
**With converter**
- Photonic source dominate
**Difference can be seen!!**
**Spectrum of electron from non-photonic source**

- _subtraction_

## Invariant Mass Spectrum of e+e- pairs

- _Invariant Mass Spectrum of e+e- pairs_

-  Conversion peak is clearly seen.
-  Combinatorial B.G. can be
-    estimated correctly.
- Due to our tracking algorithm,
- Reconstructed invariant mass of conversion pairs are shifted to higher value.

**Red    : Real**** **
**Black : Combinatorial BG**

- Conversion at MVD outer shell

- Dalitz and Conversion near beam pipe

- Combinatorial BG