単電子および電子対測定の物理、現状、展望

単電子および電子対測定の物理、現状、展望

蜂谷　崇広島大学 /PHENIX collaboration

2004/11/5 Workshop at RCNP 2

Physics Motivation• Search for the new State of Matter

(quark-gluon-plasma) and study its properties.

Leptonic ObservablesWhy do we want to measure leptonic observable?

• Heavy flavor (Charm): Single Electrons (c D e + X)• Quarkonia: J/ e+e-,

• Light vector mesons: K+K-, e+e- , , also

• Dielectron Continuum: Low and Intermediate Mass Region

• Photons: Direct (prompt and thermal) photons via its conversionsP

air

wis

e ob

serv

able


J/ measurement


Motivation of J/ measurement• Debye color screening will lead to a suppression of

charmonium production in heavy ion collisions.

• one of the earliest probe of the QGP

• Predictions of enhanced J/ production at RHIC energy

from recombination in final state interaction.

• NA50 measured J/

at SPS energy. They found

an anormalous suppression.

• Systematic study is needed to disentangle the compete effect.


PHENIX ExperimentTwo central spectrometers

, e and hadrons || < 0.35, = /2 2

Two fwd spectrometers 1.2 < || < 2.4

BBC

DC&PC

RICH

EMCAL


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

RICHPC1

DC

X

Cherenkov light in RICH

Ring in RICH


J/ in p+p at s = 200 GeV baseline measurement

• good agreement with:– lower s data and phenomenological extrapolation– Run 2 and Run 3 data

p+pJ/+X at s = 200 GeVPHENIX PRL 92, 051802 (2004)

p+pJ/+X at s = 200 GeV (Run 3)PHENIX preliminary


J/ in d+Au Nuclear Effects • Modification of the parton distribution functions:

•Gluon shadowing -> reduction of production at low x.

• 3 rapidity ranges in PHENIX probe different momentum fraction of Au partons

South (y < -1.2) : large X2 (in gold) Central (y ~ 0) : intermediate North (y > 1.2) : small X2 (in gold)

Predicted Gluon Shadowing in d+Au

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


J/production in d+Au is compared in p+pd Au

J/ in pp and dAu collisions at RHIC

ppdAR 1972/


S.B. Klein and R. Vogt, nucl-th/0305046

Low x2

(shadowing)

• indication for (weak) shadowing and absorption• more statistics desirable to disentangle nuclear

effects (and distinguish models)

d Au

J/ d+Au/p+p vs rapidity

1972 ppdA

Rapidity


J/ in Au + Au at sNN=200 GeV (run2)

• Need more statistics– inconsistent with large enhancement scenarios

SPS NA50 normalized to p+p point

Au+AuJ/ee at sNN = 200 GeVPHENIX PRC 69, 014901 (2004)

normal nuclear absorption

0-20 % centralNcoll = 779



PRC 69, 014901 (2004)


Coming attraction of J/ analysis

Au + Au analysis • Run2

25 M (MB) + 25M (LVL2) events

• Run4 •1.6 B events with healthy detector• 20-30 times larger statistics

• Bdn/dy/Nbinary•Accurate study of the centrality dependence

We see the clear J/ signal.

Au + Au


Current Status of J/ • J/ has been measured in p+p, d+Au, Au+Au

• Nuclear effects are studied in d+Au– Weak shadowing – Smaller absorption than expected ( > 0.92)– Statistics is limited---- Need more data.

• We have 1.6B MB data in Run 4 (Au+Au)– Quantitative study of J/ production in Au+Au


Light vector meson measurement


Motivation of light vector meson (LVM) measurement

• Looking for (partial) Chiral symmetry restoration– LVM has Short lifetime ~ few fm/c

Decay inside medium.

– Mass modification of vector mesons is expected.

• Au + Au and d +Au collisions– Distinguish between hot and cold partonic matter

– Probing nuclear effects

Quark mass in vacuummu ~ md ~ 5 MeV/c2

ms ~ 100 MeV/c2

Effective quark massin hadron

mu ~ md ~ 300 MeV/c2

ms ~ 500 MeV/c2

T.Hatsuda and S.Lee

(Phys.Rev.C46-1 1992)


measurement ind+Au at sNN = 200 GeV

• Fit is to relativistic Breit-Wigner convoluted with a Gaussian (detecter)

– N~120 in e+e– mode and N = 207 16 in K+K– mode

– Both measurements are consistent with PDG

Minv (GeV/c2)

CombinatorialBackgroundY

ield

e+e- K+K-

Yie

ld


Minimum-bias mT distribution of

yields in d-Au collisions

in K+K- and e+e– channels

are consistent.

K+K– channel dN/dy = 0.0468 +/- 0.0092(stat) (+0.0095,-0.0092) (syst.) e+e– channel dN/dy=.056.015(stat) 50%(syst)

dN

/dy

K+K–

e+e–

PHENIX Preliminary

dAuKKdAuee

1/2

mT d

N/d

mTd

y (G

eV

/c2)-

2

MT(GeV/c2)

PHENIX Preliminary


measurement inAu+Au at sNN = 200 GeV

• Clear signal in KK channel

• No clear signal in ee channel,

due to small statistics

• Mass centroid and width is consistent with PDG• No-dependence with centrality

Yie

ld

nucl-ex/0410012


,,in near future

• Full statistics available in RUN3 d+Au.– Background subtracted mass spectra– Amount of data is twice

• Large statistics in Run 4 Au+Au dataset ,,signal inMee spectrum can be seen

work in progress

e+e– invariant mass

Yie

ld


Current Status of LVM is measured in both K+K– and e+e– channel in d+Au

yields in d-Au collisions in K+K– and e+e– channels are consistent. Mass centroid and width is consistent with PDG

is measured in K+K– channel in Au+Au– Not so clear signal in e+e– channel

– Mass centroid and width is consistent with PDG– Not depend on centrality

• We have more statistics in both d+Au and Au+Au– In d+Au, data can be twice– In Au+Au, 1.6B min. bias data in run 4 (20M in run2)


Heavy Flavor Measurement using Single Electrons


Motivation of Heavy flavor Measurement

• 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 (dead cone effect?, else…)

• Charm can be produced thermally at very high temperature

• Sensitive to state of the matter

• Charm measurements bring us an important baseline of J/


Heavy flavor in p+p, d+Au and Au+Au• p + p measurement

– Test pQCD calculation – Baseline measurement for d+Au and Au+Au

• d + Au measurement– Normal nuclear effect

• Cronin effect• Gluon shadowing

• Au + Au measurement– Total yield

• Expected to scale with binary collision

– Spectral shape at higher pT

• Study charm energy loss in dense medium

– Charm Flow• V2 measurement Sakai-san’s Talk


Charm Measurement

Direct method:Reconstruction of D-meson(e.g. D0K).• Very challenging without measurement of displaced vertex.

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

This method is used by PHENIX at RHIC

c c

0DK

0D

K

+


Non-PHOTONIC signal Charm decays Bottom decays

Background Photon conversions : 0,,’,, Dalitz decays0ee, ee, etc) Conversion of direct photons

Di-electron decays of ,, Thermal di-leptons Kaon decays (weak decay)

Most of the backgrounds are PHOTONIC

Source of Electrons

All back grounds should besubtracted to extract the signal

All electrons measured in experiment are EM force origin and Weak force origin

PH

OTO

NIC


Extraction of Non-photonic Electrons (Heavy flavor Electrons)

Converter method• Comparison of electron yield with and without the converter allows to separate the photonic and the non-photonic electrons.

Cocktail method•Light hadron cocktail.

• Major source (0) is measured by the PHENIX spectra.

•Other mesons are estimated by mt scaling assumption and asymptotic ratios from lower energy data. •Photon conversion from material in PHENIX acceptance.

Photon Converter


Result (from PHENIX)

p+p (reference for all other system)

d+Au (nuclear effect)

Au+Au (Suppression? Enhancement?)


PHENIX PRELIMINARY

Non-Photonic Electrons in p+p at s = 200 GeV

• 200 GeV pp non-photonic electron spectrum from cocktail subtraction method

• PYTHIA tuned to low energy data

• Data is harder than PYTHIA charm + bottom above pt=1.5 GeV/c


Non-Photonic Electrons in d+Au at sNN=200GeV

• 200 GeV dAu non-photonic single electron spectrum from converter method

• Data divided by TAB

Spectacular agreement within stated errors

• No indication for strong cold-nuclear matter effects

PHENIX PRELIMINARY

1/T A

B 1/T

ABE

dN/d

p3 [m

b G

eV-2]


PHENIX PRELIMINARY

PHENIX PRELIMINARYPHENIX PRELIMINARY

PHENIX PRELIMINARY

1/T A

B1/

T AB

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

Centrality Dependence in d+Au at sNN = 200 GeV


Status in p+p and d + Au• In p + p, the spectra are described by PYTHA at lo

w pT.

– Spectra are “harder” than PYTHIA at pT > 1.5 GeV/c:

• Non-photonic electrons in d+Au agree well with pp fit and binary scaling. – for whole pT range and all centrality bins.

– No indication for strong nuclear effect

• What happened in Au + Au ?


1/T A

A1/

TA

BE

dN/d

p3 [m

b G

eV-2]

Non-photonic Electron in Au+Au at sNN = 200 GeV

• 200 GeV Au+Au non-photonic single electron spectrum from converter method

• Data is divided by TAA and overlaid with

PHENIX pp fit

• At low pt the pp fit is

in good agreement


1/T A

A

1/T A

A

1/T A

A

1/T A

A

1/T A

A

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

Centrality Dependence in Au+Au at sNN = 200 GeV

• Consistent with binary scaling• Small statistics for high pT


Ncollision Scaling in Au+Au

• Quantitative study of binary scaling.• Fit dN/dy (0.8<pT<4.0) = A (Ncoll) =1 complete binary scaling = 0.938 0.0798 (+0.0201 –0.0148) without p+p

= 0.958 0.0351 with p+p

• Non-photonic (charm) electron production is consistent with number of binary collisions scaling.

nucl-ex/0409028

Ncoll


• PHENIX measures cc = 622 57 160 b in Au+Au at 200GeV (MB)• NLO calculation shows cc = 300~450 b• Total cross section is consistent with pQCD calculation

Charm Cross Section


Coming attraction

• Converter vs Cocktail method – The pT distributions are in good agreement.– The converter is good for lower pT, the cocktail is good for higher pT

– Energy loss effect can be studied by cocktail method.

• Systematic study is now proceeding.– p+p at sNN 200GeV in Run2– p+p and d+Au at sNN 200GeV in Run3 (much more statistics)– Au+Au at sNN =62.4GeV and 200GeV (much more statistics)

Converter vs Cocktail

Work in progress

PHENIX Preliminary

p+p and d+Au at sNN=200GeV Au+Au at sNN=62.4GeV


Status in Au + Au• Total non-photonic electron yield in Au+Au agree w

ell with binary scaling. – Total cross section cc = 622 57 160 b

= 0.938 0.0798 (+0.0201 –0.0148) without p+p

– Small statistics for high pT measurement

• Systematic study is now in progross.– Refine Au+Au data by cocktail method.

– P + p, d + Au and Au + Au measurement with higher statistics

• PHENIX detector upgrade – Silicon vertex to reconstruct displaced vertices

• D → K B → J/ K

– Hadron blind detector• High electron identification capability


Summary• PHENIX measured leptonic observables

j/ in p+p, ｄ＋ Au, Au+Au at sNN = 200GeV. Light vector mesons in d+Au and Au+Au.

+ Both K+K–, e+e– are measured in d+Au.

Non-photonic electrons in p+p, d+Au, Au+Au Total charm production in Au+Au is consistent with binary scaliing. no indication for strong enhancement / suppression of charm cross section in nuclear collision.

Systematic study with wide range of system and kinematic now begins

Much more statistics in Run 4 Detector upgrade will provide new opportunity

単電子および電子対測定の物理、現状、展望

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