Dilepton measurement in H.I.C.

Dilepton measurement in Dilepton measurement in H.I.C.H.I.C.

小沢恭一郎小沢恭一郎東大・理東大・理

●　　 Au ＋ Au ●　　 p+pω φ

J/

Lepton pair measurementsLepton pair measurements

9/15/20079/15/2007 Heavy Ion Cafe @ HongoHeavy Ion Cafe @ Hongo 22

Mass[GeV/c2]

pT

[GeV/c]

１ 2 3

１

2

ω φ J/ρ

Thermal

Radiation

Heavy

Flavor

Drell

Yan

As a function of

Energy

Species

Centrality

Rapidity

φφ ・・ ωω


Chiral Symmetry in Hadronic matterChiral Symmetry in Hadronic matter

Mass shiftMass shift and/or and/or modificationmodification of vector of vector mesons are expectedmesons are expected

Lepton decaysLepton decays become good probes become good probes Not interacting “strongly.”Not interacting “strongly.” However, we only see However, we only see integrated informationintegrated information

from all stages of collisions.from all stages of collisions. Energy and Centrality dependenceEnergy and Centrality dependence

QGPHadron gas

AfterFreeze Out

Integrated information

T.Hatsuda and S.Lee

(Phys.Rev.C46-R34-38, 1992)

Line shapeLine shape Direct measurementsDirect measurements

YieldYield Q value of Q value of → → KK is smallKK is small

( )

( )

BR ee

BR KK


hadron and lepton decayshadron and lepton decays

Main issue:

K+K- and e+e-

seem not consistent

Many efforts are on-going to understand the difference btw K and e.

We have to prove that the difference is not made artificially.We have to prove that the difference is not made artificially.

Analysis in d+Au and p+p data is important as baseline. Analysis in d+Au and p+p data is important as baseline.


p+p p+p

d/dy

Extracted by integrationOMEGA:

3.50037 +/- 0.175942 (stat) +/- 0.875 (sys)

4.37554 (upper sys) 2.62521 (lower sys)

PHI:

0.369182 +/- 0.0195987 (stat) +/- 0.0894 (sys)

0.458564 (upper sys) 0.2798 (lower sys)

omega

phi


spectraspectra Spectra of Spectra of meson are measured in several collision meson are measured in several collision

systems.systems.p+p Au+Aud+Au

Results are mainly obtained using hadron decays. Analysis for electron decay mode is underway.

Lepton pair continuumLepton pair continuum(ρ(ρ ？　？　 ThermalThermal ？？ ))


Lepton pair continuumLepton pair continuum

Broadening of Broadening of meson makes meson makes continuum on the invariant continuum on the invariant mass of electron-positron pairmass of electron-positron pair

In addition,In addition, thermal radiation thermal radiation by by the system via quark anti-quark the system via quark anti-quark annihilation also makes annihilation also makes continuum and it carries direct continuum and it carries direct information from the matter.information from the matter. Matter is formedMatter is formed DeconfinementDeconfinement ThermalizedThermalized

Experimentally, Experimentally, combinatorial combinatorial background is very largebackground is very large and and must be subtracted properly.must be subtracted properly.

Also, useful for charm Also, useful for charm measurementsmeasurements

A prediction

R. Rapp, nucl-ex 0204003


@SPS - NA60@SPS - NA60 and and : : fix yields such fix yields such

as to get, after as to get, after subtraction, a subtraction, a smoothsmooth underlying continuumunderlying continuum

: : (()) set upper limit, set upper limit, defined by “defined by “saturatingsaturating” ” the measured yield in the measured yield in the mass region close to the mass region close to 0.2 GeV/c0.2 GeV/c22 ( (lower limit lower limit for excessfor excess).).

(() use yield measured ) use yield measured for pfor pTT > 1.4 GeV/c > 1.4 GeV/c


What’s this?What’s this?

• absolute norm., melting • M>0.9GeV: “4”→and • baryon effects essential

[van Hees+RR ‘06]


@RHIC@RHIC

Clear enhancement is observed Clear enhancement is observed in the mass region below in the mass region below ..

submitted to Phys. Rev. Lett

arXiv:0706.3034


pp pp –– AuAu comparison AuAu comparison

p+p　NORMALIZED　TO　mee<100　MeVp+p　MULTIPLIED　by　Ncoll


Centrality DependenceCentrality Dependence

• 0 production scales with Npart

• If in-medium enhancement from or qq annihilationyield should increase faster than proportional to Npart

LOW MASS

INTERMEDIATE MASS

• 0 production scales with Npart

• charm follows binary scaling yield should increase proportional to Ncoll

photonphoton



Thermal photonThermal photon Direct photonDirect photon

Directly emitted from the Directly emitted from the medium medium

Not from hadron decaysNot from hadron decays Hard photonHard photon

Initial pQCDInitial pQCD Thermal photonThermal photon

Hadron gasHadron gasQGPQGP

Turbide,　Rapp,　Gale,　Phys.　Rev.　C　69　(014903),　2004

Window for thermal photons from QGP in this calculation: Window for thermal photons from QGP in this calculation: ppTT = 1 - 3 GeV/ = 1 - 3 GeV/cc

pQCD calculation should be confirmed in High ppQCD calculation should be confirmed in High pTT region region

After subtraction of large After subtraction of large background from hadron background from hadron decays, decays,


Idea - Idea - ** e e++ee--

Compton

q

g q

0

0

e+

e-

q

g q

e+

e-

Any　　source　of　real　　emits　virtual　　with　very　low　mass

Dalitz decay Use　lepton　pairs　to　measure　virtual　

　and　extrapolate　to　real　　

PHENIX can measure low mass e+e- pairs

hadron decays and

direct photon

*incl.

*directcan be measured.

*In the analysis, Mee distribution for Dalitz and direct photon is calculated theoretically. Therefore, the ratio of Nee in two different mass region is converted to the ratio between direct and inclusive photons. The systematic error is reduced.


**directdirect / / **

inclusiveinclusive

Significant 10% excess of Significant 10% excess of very-low-massvery-low-mass virtual direct photons virtual direct photons

Results agrees well with Results agrees well with Conventional resultConventional result

*incl.

*direct

One can extract the direct photon yield from the inclusive photon yield.

incl.

direct=


Direct photon yieldDirect photon yield

Direct photon yield is calculated from Direct photon yield is calculated from the inclusive photon yield.the inclusive photon yield.


Direct photon yieldDirect photon yield

Direct photon yield is calculated from Direct photon yield is calculated from the inclusive photon yield.the inclusive photon yield.

Compare to NLO pQCD Compare to NLO pQCD L.E.Gordon and W. VogelsangL.E.Gordon and W. Vogelsang

Phys. Rev. D48, 3136 (1993) Phys. Rev. D48, 3136 (1993)

Excess above the calculation

It might include contribution from thermal photons

Reference measurement needed

pp and dAu

Using same analysis method


Comparison of R* btw p+p and Au+Au

PHENIX Preliminary

Au+Au

p+p


SummarySummary

So many interesting analysis topics are on-So many interesting analysis topics are on-going at PHENIXgoing at PHENIX Such as, Heavy flavor measurements, J/Such as, Heavy flavor measurements, J/, , , and , and

lepton pair continuumlepton pair continuum Measurement for chiral symmetry is Measurement for chiral symmetry is

underway.underway. First result will publish soon.First result will publish soon.

Enhancement is observed in eEnhancement is observed in e++ee-- continuum!continuum!

Interesting results in Direct photon Interesting results in Direct photon measurements.measurements.

Dilepton measurement in H.I.C.

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