[Brahms-l] Fwd: New PHENIX paper on e+e- continuum pairs in p+p and Au+Au at 200 Gev

FYI

Flemming Videbaek
videbaek @ bnl.gov
Brookhaven National Lab
Physics Department
Bldg 510D
Upton, NY 11973

phone: 631-344-4106
cell     :  631-681-1596





>
> Dear Nu, Wit, Flemming and Steve,
>
>      I am very happy to announce that in one week's time,
> the PHENIX Collaboration will submit a paper to Phys. Rev. C
> on the topic indicated in the subject line.  Please find the
> title and abstract below.
>
> best regards,
> Barbara
>
>
> Title: Detailed measurement of the e+e- pair continuum in p+p
> and Au+Au collisions at sqrt(s_NN)=200 GeV and implications
> for direct photon production
>
> Abstract:
> PHENIX has measured the e^+e^- pair continuum in sqrt(s_NN)=200
> GeV Au+Au and p+p collisions over a wide range of mass and transverse
> momenta.  The e^+e^- yield is compared to the expectations from
> hadronic sources, based on PHENIX measurements.  In the intermediate
> mass region, between the masses of the phi and the J/psi meson, the
> yield is consistent with expectations from correlated c^bar-c  
> production,
> though other mechanisms are not ruled out.  In the low mass region
> (below the phi) the p+p inclusive mass spectrum is well described by
> known contributions from light meson decays.  In contrast, the Au+Au
> minimum bias inclusive mass spectrum in this region shows an
> enhancement by a factor of 4.7+/-0.4(stat)+/-1.5(syst)+/-0.9(model)
> At low mass (m_ee<0.3 GeV/c^2) and high p_T (1<p_T<5 GeV/c) an
> enhanced e^+e^- pair yield is observed that is consistent with  
> production
> of virtual direct photons.  This excess is used to infer the yield  
> of real
> direct photons.  In central Au+Au collisions, the excess of the direct
> photon yield over the p+p is exponential in p_T, with inverse slope
> T=221+/-19(stat)+/-19(syst) MeV.  Hydrodynamical models with initial
> temperatures ranging from T_init ~=300--600 MeV at times of  
> 0.6--0.15 fm/c
> after the collision are in qualitative agreement with the direct  
> photon data
> in Au+Au. For low p_T<1 GeV/c the low mass region shows a further
> significant enhancement that increases with centrality and has an  
> inverse
> slope of T ~=100 MeV.  Theoretical models under predict the low mass,
> low p_T enhancement.

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