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Dilepton mass spectra in p+p collisions at s=200 GeV and the contribution from open charm
PHENIX Collaboration,Adare, A.,Afanasiev, S.,Aidala, C.,Ajitanand, N.N.,Akiba, Y.,Al-Bataineh, H.,Alexander, J.,Aoki, K.,Aphecetche, L.,Armendariz, R.,Aronson, S.H.,Asai, J.,Atomssa, E.T.,Averbeck, R. North-Holland Pub. Co 2009 Physics letters: B Vol.670 No.4
<P>PHENIX has measured the electron-positron pair mass spectrum from 0 to 8 GeV/c(2) in p + p collisions at root s = 200 GeV. The contributions from light meson decays to e(+)e(-) pairs have been determined based on measurements of hadron production cross sections by PHENIX. Within the systematic uncertainty of similar to 20% they account for all e(+)e(-) pairs in the mass region below similar to 1 GeV/c(2). The e(+)e(-) pair yield remaining after subtracting these contributions is dominated by semileptonic decays of charmed hadrons correlated through flavor conservation. Using the spectral shape predicted by PYTHIA, we estimate the charm production cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) pb. which is consistent with QCD calculations and measurements of single leptons by PHENIX. (C) 2008 Elsevier BV. All rights reserved.</P>
PHENIX Collaboration,Afanasiev, S.,Aidala, C.,Ajitanand, N.N.,Akiba, Y.,Alexander, J.,Al-Jamel, A.,Aoki, K.,Aphecetche, L.,Armendariz, R.,Aronson, S.H.,Averbeck, R.,Awes, T.C.,Azmoun, B.,Babintsev, V. North-Holland Pub. Co 2009 Physics letters: B Vol.679 No.4
We present the first measurement of photoproduction of J/ψ and of two-photon production of high-mass e<SUP>+</SUP>e<SUP>-</SUP> pairs in electromagnetic (or ultra-peripheral) nucleus-nucleus interactions, using Au+Au data at s<SUB>NN</SUB>=200 GeV. The events are tagged with forward neutrons emitted following Coulomb excitation of one or both Au<SUP>@</SUP>? nuclei. The event sample consists of 28 events with m<SUB>e<</SUB>SUP><SUB><</SUB>/SUP>+<SUB>e<</SUB>SUP><SUB><</SUB>/SUP>->2 GeV/c<SUP>2</SUP> with zero like-sign background. The measured cross sections at midrapidity of dσ/dy(J/ψ+Xn,y=0)=76+/-33(stat)+/-11(syst) μb and d<SUP>2</SUP>σ/dmdy(e<SUP>+</SUP>e<SUP>-</SUP>+Xn,y=0)=86+/-23(stat)+/-16(syst) μb/(GeV/c<SUP>2</SUP>) for m<SUB>e<</SUB>SUP><SUB><</SUB>/SUP>+<SUB>e<</SUB>SUP><SUB><</SUB>/SUP>-@?[2.0,2.8] GeV/c<SUP>2</SUP> have been compared and found to be consistent with models for photoproduction of J/ψ and QED based calculations of two-photon production of e<SUP>+</SUP>e<SUP>-</SUP> pairs.
PHENIX Collaboration,Lim, S. North Holland Pub. Co 2014 Nuclear physics. A Vol.931 No.-
Charm and bottom quarks are formed predominantly by gluon fusion in the initial hard scatterings at RHIC, making them good probes of the full medium evolution. Previous measurements at RHIC have shown large suppression and azimuthal anisotropy of open heavy-flavor hadrons in Au + Au collisions at s<SUB>NN</SUB>=200 GeV. Explaining the simultaneously large suppression and flow of heavy quarks has been challenging. To further understand the heavy-flavor transport in the hot and dense medium, it is imperative to also measure cold nuclear matter effects which affect the initial distribution of heavy quarks as well as the system size dependence of the final state suppression. In this talk, new measurements by the PHENIX Collaboration of electrons from heavy-flavor decays in p+p, d+Au, and Cu + Cu collisions at s<SUB>NN</SUB>=200 GeV are presented. In particular, a surprising enhancement of intermediate transverse momentum heavy-flavor decay leptons in d+Au at mid and backward rapidity are also seen in mid-central Cu + Cu collisions. This enhancement is much larger than the expectation from anti-shadowing of the parton distributions and is theoretically unexplained.