Single Electron Measurements at RHIC-PHENIX

T. HachiyaHiroshima University

For the PHENIX Collaboration

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Motivation

• Charm is produced through mainly gluon-gluon fusion in heavy ion collisions

• Sensitive to gluon density in initial stage of the collisions

• Charm is propagated through hot and dense medium created in the collisions

• Energy loss of charms via gluon radiation can be seen. (PHENIX observed high pT suppressions in hadron measurements)

• Charm can be produced thermally at very high temperature

• Sensitive to state of the matter

• Charm measurements bring us an important baseline of J/ measurement

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Charm Measurement

Direct method:Reconstruction of D-meson(e.g. D0K).Very challenging withoutmeasurement of displaced

vertex

Indirect method:Measure leptons from semi-leptonic decay of charm.

This method is used by PHENIX at RHIC

c c

0DK

0D

K

+

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Electron Measurement

All charged tracks

BG

Net e±

e± real.

Electrons are measured by DC→PC1→RICH→EMCal

Electron Identification : Cherenkov light in RICH

Number of Hit PMT Ring shape

Energy – Momentum matching

e+

EM Calorimeter

PC2

Mirror

PC3

RICH

PC1

DC

X

Cherenkov light in RICH

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Photon conversions :

Dalitz decays of 0,,’,,0ee, ee, etc) Kaon decays Conversion of direct photons Di-electron decays of ,, Thermal di-leptons

Most of the background are PHOTONIC

Source of Electrons

Background

Charm decays Beauty decays

Those are Non-PHOTONIC signal

Signal

0 e+e-

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PHENIX Run 2

Amount of data • 20 times larger statistics

All detectors work in Central arm spectrometers• Acceptance is 4 times as large

Special run with a photon converter 1.7 % radiation length of brass and placed around beam pipe The converter can increase electrons only from photonic source by a fixed factor By comparing the data with and without the converter, We can separate electron from non-photonic and photonic source

Complementary to cocktail method

Photon Converter

e+

e-

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Photon Converter Method

Single electron spectra : • data with the converter• data w/o the converter

If all electrons are from photonic source, the ratio is constant.But the data shows that electron yield approach at high pT each other.

It is an evidence for non-photonic electrons

Ne

0

1.1% 1.7%

Dalitz : 0.8% X0 equivalent

0

With converter Conversion in converter

W/O converter Conversion from pipe and MVD

0.8%

Non-photonic

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Electrons from Non-photonic Source

• Back ground subtracted single electron spectra at sNN=200GeV

• 200GeV data is higher than 130GeV data.• Spectral shape at 200GeV is similar to that at 130GeV• The data is in good agreement with PYTHIA calculation

cc(130GeV)=330 b

cc(200GeV)=650 b

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Centrality Dependence

Single electrons in each centrality class are in reasonable agreement with PYTHIA calculation scaled by binary collision

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Observations• Our data is consistent with binary scaling within our current statistical and systematic uncertainties. • NA50 at SPS has inferred a factor of ~3 charm enhancement from intermediate mass di-muon measurement. We do not see this large effect at RHIC.• PHENIX observes a factor of ~3-5 suppression in high pT 0 relative to binary scali

ng. We do not see this large effect in the single electrons. • Initial state high pt suppression excluded?• smaller energy loss for heavy quark ? (dead cone effect)

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

N part

En

ha

nce

me n

t o

f O

pe

n C

har

m Y

ield Binary Scaling

PHENIX Preliminary

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Summary & Outlook

PHENIX measured single electrons from non-photonic source at sNN=130GeV and 200GeV The single electrons are in good agreement with PYTHIA charm calculation using number of binary collision scaling within current statistic and systematic uncertainties

Refine the converter method and cross-check by the cocktail calculation Finalize single electron spectra from non-photonic source Comparison to single electron in p+p and d+Au at sNN=200GeV (RHIC Run2 and Run3)

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Inclusive Electrons at s=130GeV

1.5M M.B. events are analyzed.

The back ground from random association is estimated by event mixing method

Spectra are fully corrected with acceptance and efficiency loss

Back ground electrons fromphotonic source are included

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conversion

0 ee

ee, 30

ee, 0ee

ee, ee

ee

’ ee

Cocktail Calculation

pT distribution of 0 are constrained with PHENIX 0 and measurement

• pT spectra of , ’ and are

estimated with mT scaling pT = sqrt(pT

2 + Mhad2 – M2)

• Hadrons are relatively normalized by 0 at high pT from the other measurement at SPS, FNAL, ISR, RHIC

• Material in acceptance are studied for photon conversion

Signal above cocktail calculation can be seen at high pT

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Data / Background Ratio of Electrons

• conversions and 0 dalitz are ~ 80% of photonic source• is ~ 20%• Contribution from the other hadrons are very small

Top figure shows data/background ratio in M.B event sample.

The data shows excess above background in pT > 0.6[GeV/c].

Most of the systematic uncertainty comes from single electron measurementand cocktail calculation.-> need reference point in run2

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Single Electron Spectra at sNN=130GeV

PYTHIA

direct (J. Alam et al. PRC 63(2001)021901)

b

c

PHENIX: PRL 88(2002)192303• Single electron spectra after background (photonic source) is subtracted for central and M.B collisions at sNN=130GeV

• Electrons from charm and beauty decays calculated by PYTHIA are overlaid -- PYTHIA parameter is tuned to fit low energy data -- scaled to Au+Au using number of binary collision.

• Charm in PYTHIA are in reasonably agreement with data (within relatively large uncertainty)

• The contribution from thermal dileptons and direct is neglected -- We may over-estimate the charm yield.

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Charm Cross Section

• Single electron cross section is compared with ISR data• Charm cross section is compared with fixed target charm data.

• Solid curve : PYTHIA• shaded Band : NLO pQCD

Assuming binary scaling, PHENIX data are consistent with s systematics (within large uncertainties)

By fitting the PYTHIA electron spectrum to the data for pt>0.8[GeV/c], we obtained charm yield Ncc per event. The charm cross section per binary NN collision is obtained as

TAA is nuclear overlap integral ~ NN integrated luminosity per eventTAA(0-10%)=22.6±1.6/mb TAA(0-92%)=6.2±0.4/mb

Charm cross section derived from the single electron

ccAA

ccN

T

1

0 10%cc 380 60 200 b and 0 92%

cc 420 33 250 b

PHENIX

PYTHIA ISR

NLO pQCD (M. Mangano et al., NPB405(1993)507)

PHENIX: PRL 88(2002)192303

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Cocktail Calculation

pT distribution of 0 are constrained with PHENIX 0 and measurement

• pT spectra of , ’ and are

estimated with mT scaling pT = sqrt(pT

2 + Mhad2 – M2)

Systematic uncertainty in cocktail calculation is assigned 50 % in each ratio

PHENIX DATA

Data Systematic errorsRun1 11%Run2 12%

Meson Meson/ pi0 at high pT0.550.251.001.000.40

ηη'ρωφ

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Photon conversions :

Dalitz decays of 0,,’,,0ee, ee, etc) Kaon decays Conversion of direct photons Di-electron decays of ,, Thermal di-leptons

Most of the background are PHOTONIC Charm decays Beauty decays

Those are Non-PHOTONIC signal

Source of Electrons

Background

Signal

0 e+e-

conversion

0 ee

ee, 30

ee, 0ee

ee, ee

ee

’ ee

20

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Outline

Motivation Charm and electron measurements PHENIX experiment: how to measure electrons Run-1: Au + Au @ sNN = 130 GeV

single electrons from charm decays (c D e + X) Run-2: Au + Au @ sNN = 200 GeV

single electrons refined Summary and outlook

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PHENIX Experiment

Two central spectrometers , e and hadrons Coverage:

• || < 0.35• = /2 2

M.B. Trigger and Centrality • Beam Beam Counter• Zero Degree Calorimeter

Collision vertex• Beam Beam Counter

BBC

DC&PC

RICH

EMCAL