### Session K16: Sub-Nucleonic Degrees of Freedom I

 Sunday, April 15, 2007 1:15PM - 1:27PM K16.00001: Longitudinal Structure Functions ($F_{L}$) at an Electron-Ion Collider James C. Dunlop Current knowledge of gluon distribution functions in nuclei is extremely limited in range in $x$ and $Q^{2}$, due to the energies available in fixed target experiments performed to date. An electron-ion collider (EIC) would greatly extend this range, into a region in the $x$ and $Q^{2}$ plane where saturation of gluons is expected to become the dominant mechanism determining the properties of nuclear matter. Measurements of longitudinal structure functions ($F_{L}$) directly probe gluon distributions, as $F_{L}$ is directly related to the gluon distribution at tree level. Projections for experimental measurement of $F_{L}$ will be presented, along with considerations driving experimental setups. Sunday, April 15, 2007 1:27PM - 1:39PM K16.00002: Physics Opportunities at a New Electron-Ion Collider David Morrison An electron-ion collider (EIC) offers novel opportunities for the study of partons in nuclei over a broad range in the kinematic variables $x$ and $Q^2$. The EIC will have acceptance ranging from very low $x$ and $Q^2$ where gluon saturation effects are expected to be strong, to high $x$ and $Q^2$ where phenomena such as the EMC effect can be investigated. An overview of the physics accessible at the EIC, as well as some of constraints shaping the design of experiments for the EIC, will be presented. Sunday, April 15, 2007 1:39PM - 1:51PM K16.00003: Prospects of charm measurements at a new electron-ion collider Zhangbu Xu Heavy-flavor quark production in eA collisions is an important tool to study the gluon distribution function in proton and nuclei and the interaction of heavy quarks with nuclear matter. This talk will present a study of charm spectra and statistics in ep and eA collisions as can be obtained from an electron-ion collider (EIC) with high annual luminosity of 5/A fb$^{-1}$. An R{\&}D project on a novel and compact muon detector, which is potentially a cost-effective solution for such environment, will be discussed. Sunday, April 15, 2007 1:51PM - 2:03PM K16.00004: Measuring the gluon helicity distribution at a polarized electron-proton collider Christine Aidala A polarized electron-proton collider would offer the opportunity to probe the spin structure of the proton over a greatly enhanced kinematic range compared to earlier fixed-target polarized deep-inelastic scattering experiments. Such a facility would provide access to the gluon helicity distribution within the proton through scaling violations of the polarized structure function, $g_1$, as well as through certain exclusive channels. Estimates of improved constraints on the gluon helicity distribution that could be obtained with a proposed polarized electron-proton collider will be shown. Sunday, April 15, 2007 2:03PM - 2:15PM K16.00005: Longitudinal Double Spin Asymmetry for inclusive back-to-back dimuons in polarized $p$+$p$ collisions at $\sqrt{s} = 200$ GeV Carlos Munoz Camacho Longitudinal double spin asymmetries, $A_{LL}$, measured for hard inclusive processes (open charm, open beauty) in polarized proton-proton collisions at high energies are sensitive to the gluon polarization, $\Delta g/g$. By measuring large invariant mass muon pairs, $\Delta g/g$ is probed in the interesting region of momentum fraction $0.02\alt x \alt 0.1$, where $\Delta g/g$ is expected to be significant. The PHENIX forward spectrometers have been used to measure back-to-back muon pairs. The status of the analysis of $A_{LL}$ in polarized $p$+$p$ collisions at $\sqrt{s}=200$ GeV at RHIC will be presented. Sunday, April 15, 2007 2:15PM - 2:27PM K16.00006: ABSTRACT WITHDRAWN Sunday, April 15, 2007 2:27PM - 2:39PM K16.00007: Direct photon-hadron correlations in $\sqrt{s} = 200$ GeV p+p collisions with the PHENIX detector Matthew Nguyen The modification of the away-side jet in hadron-hadron correlations indicates that the matter produced in heavy-ion collisions (A+A) is extraordinarily dense. Direct photon-hadron correlations provide a more sensitive probe than hadron-hadron correlations because the photon tracks the energy of the opposing jet more closely and has much less interaction with the medium than hadrons. A method has been developed to separate the direct photon-hadron correlations from the large background of decay photon-hadron correlations. Results will be presented from $\sqrt{s} = 200$ GeV p+p collisions from the run 5 PHENIX data. This data is an important baseline for the A+A data as well as an important check of the method in an environment free from the large background produced in A+A collisions. The results will be compared to predictions from the PYTHIA generator. The status of the A+A data will also be discussed. Sunday, April 15, 2007 2:39PM - 2:51PM K16.00008: $J/\psi$ Production in p+p and Au+Au collisions from the PHENIX Experiment Abigail Bickley Quarkonia provide a sensitive probe of the properties of the hot dense medium created in high energy heavy ion collisions. Hard scattering processes result in the production of heavy quark pairs that interact with the final state medium as it evolves. These in-medium interactions convey information the fundamental properties of the medium itself and can be used to examine the modification of the QCD confining potential in the collision environment. Baseline measurements from p+p and d+Au collision systems are used to distinguish cold nuclear matter effects while measurements from heavy ion collision systems are used to quantify in-medium effects. The PHENIX experiment has the capability of detecting heavy quarkonia at forward rapidity ($1.2<|y|<2.2$) via the $\mu^+\mu^-$ decay channel and at mid-rapidity ($|y|<0.35$) via the $e^+e^-$ decay channel. Recent runs have resulted in the collection of high statistics data sets that allow for further critical evaluation of heavy quarkonia production mechanisms. The latest PHENIX results for the production of the $J/\psi$ in p+p and Au+Au collisions will be presented and the implications of these results on theoretical models will be examined. Sunday, April 15, 2007 2:51PM - 3:03PM K16.00009: Title: Direct measurement of fragmentation photons in p+p collisions at $\sqrt(s_{NN}) = 200$~GeV with the PHENIX experiment Ali Hanks Direct photon production is an important observable in heavy ion collisions as photons are penetrating and therefore largely insensetive to the final state effects that lead to jet quenching. Perturbative QCD calculations predict a significant contribution to the direct photon yield from photons produced through parton fragmentation. In heavy ion collisions this contribution can be modified due to additional stimulated photon bremsstrahlung as well as the energy loss of the partons through gluon radiation prior to fragmentation. This stimulated bremsstrahlung provides direct observation of the scattering of jets in the medium. Thus direct measurements of the fragmentation component to direct photon yields in both p+p and Au+Au collisions will provide both an important test of pQCD predictions and of predictions for the nuclear modification factor. By selecting photons associated with jets on the near side using hadron-photon correlations, bremsstrahlung photons can be measured directly. Most photons correlated with jets come from $\pi^{0}$'s and other hadronic decays and must be tagged and subtracted from the inclusive correlations. Using this method we can obtain a measure of the bremsstrahlung photon contribution to investigate medium-induced modifications to the jet fragmentation function. We present studies of this methodology and its application to recent PHENIX data.