BY A PEDESTRIAN Related publications direct photon in Au+Au PRL94, 232301 (2005) direct photon in p+p PRL98, 012002 (2007) e+e- in p+p and Au+Au arXiv:0912.0244 (PRC) Direct (virtual) photon in Au+Au arXiv:0804.4168 (PRL) Latest results on direct photon from Phenix 05/02/2010 1 F. Fleuret - LLR Rencontre ions lourds/Heavy Ion Meeting
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BY A PEDESTRIAN Related publications direct photon in Au+Au PRL94, 232301 (2005) direct photon in p+p PRL98, 012002 (2007) e+e- in p+p and Au+Au
Perfect liquid hot enough to be quark soup Hydro fits T ini ~ 300 – 600 MeV (k B T ~ eV K -1 ) T ~ 4 – K 170 MeV Perfect liquid 300 MeV600 MeV free Gas ? 05/02/ F. Fleuret - LLR Rencontre ions lourds/Heavy Ion Meeting (Arxiv: )
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BY A PEDESTRIAN
Related publicationsdirect photon in Au+Au PRL94, 232301 (2005)direct photon in p+p PRL98, 012002 (2007)e+e- in p+p and Au+Au arXiv:0912.0244 (PRC)Direct (virtual) photon in Au+Au arXiv:0804.4168 (PRL)
Latest results on direct photon from Phenix
05/02/2010
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F. Fleuret - LLR Rencontre ions lourds/Heavy Ion Meeting
New findings on Hot Quark Soup
PHENIX
STAR
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Perfect liquid hot enough to be quark soup
Hydro fits Tini ~ 300 – 600 MeV(kBT ~ 8.6 10-5 eV K-1) T ~ 4 – 8 1012 K
170 MeV
Perfect liquid
300 MeV 600 MeVfree Gas ?
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(Arxiv:0804.4168)
How to measure the temperature ?
Looking at photons Hot matter emits thermal radiation Temperature can be measured from the emission spectrum
Hard parton scatteringHard parton scattering High pT photons (> 6 GeV)High pT photons (> 6 GeV)
Hadron gas photonsHadron gas photons Very low pT photons (<2 GeV)Very low pT photons (<2 GeV)
Measuring the photons In p+p : get the baseline In Au+Au : get the temperature
time
hard parton scattering
AuAu
Hadron Gas
freeze-out
quark-gluon plasma
Space
Time
expansio
n
p K
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Sources of photons in A+A In A+A collisions
High pT photons (pT> 6 GeV): non thermal Initial parton-parton scattering: as in p+p not affected by Hot and Dense Matter test the
theoretical description of A+A collisions with pQCD
Low pT photons (pT < 3 GeV) : thermal Come from the thermalized medium Carry information about the initial temperature
of the Quark Gluon Plasma Thermal photons are created in the QGP as well
as in the hadron gas over the entire lifetime of these phases test hydro models
Low and intermediate pT photons (up to 6 GeV) Interaction of the quarks and gluons from
the hard scattering processes with the QGP qhard + gQGP q + get a large fraction of the momentum of
qhard
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Phenix detector
e+e
2 central arms: electrons, photons, hadrons charmonium J/, ’ e+e-
vector meson , , e+e- high pT o+, -
direct photons open charm hadron physics
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|y|<0.35
Direct photons in p+p : the baseline
PRL98, 012002 (2007)
In p+p collisions Direct photons
Compton scattering q + g q +
qq annihilation q + q g +
Bremsstrahlung (intial state)
Fragmentation photons Brem. From final state partons
Final state hadron decay (background) 0, , K0,… +
Measured p+p yield compatible with NLO pQCD calculations
p+p200 GeV
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Thermal photons
thermal
thermal
direct photons are measured as « excess » above hadron decay photons
πγ0
background
From Monte Carlo : take a parametrization of measured 0 as input and propagate the particles through detectorsbackground photons = remaining photons (from 0) after all cuts
background photons
0 from MC
πγ0
measured
Direct photons candidates : obtained after rejecting photons pairs falling within 110<M<170 MeV/c² (0) and 500<M<620 Mev/c² () Direct photons candidates (from data)
0 from data
γγ
Rbackground
measured
π0γ
background
π0γ
measuredγ
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Difficult to measure below pT<3 GeV/c
(the yield of thermal photons is only 1/10 of that of hadron decay photons)
Alternative: « quasi real » virtual photons
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e+e-
Source of real photon should also be able to emit virtual photon
LMR I (Low Mass Region I)(Mee0) pT
ee >> Mee « quasi real » photons
γee dN
M1
3π2α
dMd²N
(When M << E)
γ2
121ee dN
mmlog
3π2αmMmdN
Advantages : 0 decay photons are removed reduce the bkg by ~80% Signal/Background improved by a factor 5
(See arXiv : 0912.0244 (appendix B) for more details)
J/
DD
’
r = fraction of direct photons = direct/inclusive
Measuring lepton (electron) pairs
Remove (dalitz) 0 e+e- Mee > 100 MeV/c²Remove other sources of bkg Mee < 300 MeV/c²
Look at 100<Mee<300 MeV
Several pT bins
0 cut-off 0 cut-off
ftot=(1-r) fc(Mee) + r fdir(Mee)
fdir(Mee) = expected shape from direct photon spectrum normalized to the data for mee<30 MeV/c²
fc(Mee) = cocktail mass distribution normalized to mee<30 MeV/c²
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Cocktail
(Note : identical shape for fdir and fc for mee<30 MeV/c²)