dilepton measurement in h.i.c
DESCRIPTION
Dilepton measurement in H.I.C. 小沢恭一郎 東大・理. Lepton pair measurements. p T [GeV/ c ]. φ. ω. J/ y. ρ. As a function of Energy Species Centrality Rapidity. 2. Heavy Flavor. Thermal Radiation. 1. Drell Yan. g*. 1. 2. 3. Mass [GeV/ c 2 ]. ● Au + Au ● p+p. J/ y. φ. ω. - PowerPoint PPT PresentationTRANSCRIPT
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
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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
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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
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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.
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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
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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 ?? ))
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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
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@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
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What’s this?What’s this?
• absolute norm., melting • M>0.9GeV: “4”→and • baryon effects essential
[van Hees+RR ‘06]
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@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
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pp pp –– AuAu comparison AuAu comparison
p+p NORMALIZED TO mee<100 MeVp+p MULTIPLIED by Ncoll
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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
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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,
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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.
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**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=
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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.
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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
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Comparison of R* btw p+p and Au+Au
PHENIX Preliminary
Au+Au
p+p
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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.