RHIC-PHENIX 実験における単電子の測定

T. Hachiya (hachiya@hepl.hiroshima-u.ac.jp)Hiroshima University

For the PHENIX collaboration

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

• Sensitive to gluon density in initial stage of the collisions

• Charm propagates through hot and dense medium created in the collisions

• Energy loss of charms can be tested.(PHENIX observed high pT suppression in hadron measurements)• PHENIX observed single electron in sNN=130GeV Au+Au collisions.

• Consistent with PYTHIA charm assuming binary scaling.• Charm measurements provide an important baseline of J/ measurement

Charm Measurement

• Measure electrons from semi-leptonic decay of charm and beauty. c c

0D

K

Electron measurement at PHENIX

BG

Net e±

e±candidates.

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

RICHPC1

DC

X

Cherenkov light in RICHE/p

Sources of electrons Charm decays Beauty decays Non-PHOTONIC Signal

Photon conversions :

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

Most background is PHOTONIC

Background

0 e+e-

Photon converter method

Reality

pT[GeV/c]

γAu

Au e+e-Converter

Photon Converter 1.7 % radiation length (brass) The converter increase the yield of electrons from photonic sources by a fixed factor By comparing the data with and without the converter, electrons from non-photonic and photonic sources can be separated.

Non-photonic electrons can be extracted from data itself.

Signal ExtractionMininum Bias Au+Au in sNN=200GeV

Inclusive e/photonic eNe

0

1.1% 1.7%

Dalitz : 0.8% X0 equivalent

0

With converter Conversion in converter

W/O converter Conversion from detector

0.8%

Non-photonic

• R(inclusive/photonic) : Non-photonic signal appears above 1.0.• Non-photonic signal is 50 % at pT = 1.0[GeV/c] compared to photonic electrons• Backgrounds (K->eX and ,,ee) are still included.

Non-photonic electrons at sNN=200GeV Au+Au collisions

(e++e–)/2sys. error

Min. bias at Au+Au sNN=200GeV

PHENIX　 (Run 2 final result) • Fully corrected spectrum

– Acceptance & eID efficiencies– 2.5M and 2.2M events analyzed

with and without the converter• Backgrounds from KeX (les

s than 5%) and , , ee (1%) decays subtracted

• Systematic error is 13% at high pT

eID, acc, etc 11.8%K- >eX, VM- >ee 2.0%Signal extraction 5.0%

PHENIX PRELIMINARYNon-photonic electron in pp

PHENIX PRELIMINARY

• Single electron at sNN=200GeV pp collisions is measured by cocktail method. – Reference for Au+Au data

• Data is compared with a PYTHIA charm + beauty.– PYTHIA parameter is tuned by low e

nergy data– Spectrum is harder than PYTHIA cal

culation at higher pT

• Cross section is measured.– Data at lower pT is described by PYT

HIA– Changing normalizations of PYTHIA

charm and beauty to fit spectral shape

Comparison with pp

•Au+Au data is scaled by TAA and compared with pp data.•Au+Au data at lower pT are consistent with p+p data for all centralities•Need more statistics to study higher pT range 50 times larger statistics in run4

PHENIX PHENIX

PHENIX PHENIX PHENIX

(dN/dy) / Ncoll vs. Ncoll

NA Coll 1

• Green and red points shows the (dN/dy) / Ncoll for min. bias and each centrality.

• Yellow band shows 90% CL of

• Data is consistent with number of binary collision scaling.

PHENIX

• Invariant pT distributions of non-photonic electrons are measured in Au+Au collisions at sNN= 200GeV.– Conversion subtraction method is refined

• Systematic error is much reduced.

• Non-photonic electron spectra are consistent with pp data assuming binary collision scaling (TAA scaling)

• The measured yield of non-photonic electrons is consistent with binary scaling. Indicating no strong enhancement or suppression of the total charm yield.– Statistics is too small to limit the energy loss of charm in high pT (pT > 2 [GeV/c]) (RUN4 data)

• Run2 data analysis is completed. To be published soon.

Summary

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

Centrality dependence

(e++e–)/20-10% central

(e++e–)/210-20% central

(e++e–)/220-40% central

(e++e–)/240-60% central

(e++e–)/260-92% central

PHENIX PHENIX PHENIX

PHENIX PHENIX

Systematic uncertaintyList of Systematic error

•BG subtraction (KeX, VM ee)

pT[GeV/c]

• eID and acceptance calculationMC statistics in the correction 2.5%acceptance in real and simulation 5.0%~10% at lowpT2 sigma matching cut 3.0%N0 cut(n0>=3) 3.0%chi2 cut(chi2<10) 5.0%disp cut(disp<5) 3.0%time cut(emcdt<2.0&&ttof<0.2) 2.0%dep cut (dep>- 2.0) 2.0%embedding 7.0%Sub total 11.8%

• Uncertainty on Rsim• amount of Material (4.4%)• diff of acceptance between the converter and the no-converter run (4%)•Eta/pi0 ratio (50% 6% on Rsim)

pT[GeV/c]Total systematic error

pT[GeV/c]

Comparison of electron yields with and without converter in Data and Simulation

Ratio of pT in Real Data to Simulation

pT[GeV/c]

R(c

onv/

noco

nv)

• If there is no non-photonic source, real data should agree with simulation.

• Ratio in simulation increases slightly with pT.

• Data shows opposite trend. • Presence of Non-PHOTONIC

source in dataReal dataSim.Sim. at higher limit Sim. at lower limit

Higher and lower limit is determined by changing 50% of /0 ratio and amount of material between data and simulation

Photonic simulation

data

Extraction of non-photonic electrons

# of electrons in the converter run# of electrons in the non-converter run

# of photonic electrons# of non-photonic electronsRatio of photonic electrons in the converter run and the no converter run

RNNNN

sim

Npe

Pe

NCe

Ce

Raw pT distributionwithout Noconv.with Conv.

Raw pT distributionInclusive(noconv)PhotonicNon-photonic

•The method can separate non-photonic electrons and photonic electrons.

•e from Kaon and ee from VM is still remaining in non-photonic electrons

1

1

RNNRN

RNNN

sim

Ce

NCesimNp

e

sim

NCe

CeP

e

Ent

ries

/Nev

t

Ent

ries

/Nev

t

pT[GeV/c]

NNNNNRN

Npe

Pe

NCe

Npe

Pesim

Ce

pT[GeV/c]

Assumption : thickness of the converter in simulation is same that in real data.

• Mee distribution is normalized by Nevent.• Calculate the Ratio( RM ) of Mee(inner) and

Mee(converter)

• Then, compare RM in real data and simulation.

• Difference between real data and simulation is 0.1%4.4%.

Converter

InnerM= NR N

NConverter : Mee: 60-100[MeV]NInner : Mee: 0-40[MeV]Mee in simulation

Mee [GeV]

Mee in real data

Mee [GeV]

Mee in conv. RunMee in no-conv. run

Conclusion:

Comparison of amount of material in data and simulation