Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session HF: Structure Functions |
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Chair: Misak Sargsian, Florida International University Room: Salon 6 |
Friday, October 27, 2017 8:30AM - 8:42AM |
HF.00001: Nucleon PDFs and TMDs from Continuum QCD Kyle Bednar, Ian Cloet, Peter Tandy The parton structure of the nucleon is investigated in an approach based upon QCD's Dyson-Schwinger equations. The method accommodates a variety of QCD’s dynamical outcomes including: the running mass of quark propagators and formation of non-pointlike di-quark correlations. All needed elements, including the nucleon wave function solution from a Poincar\'e covariant Faddeev equation, are encoded in spectral-type representations in the Nakanishi style to facilitate Feynman integral procedures and allow insight into key underlying mechanisms. Results will be presented for spin-independent PDFs and TMDs arising from a truncation to allow only scalar di-quark correlations. The influence of axial-vector di-quark correlations may be discussed if results are available. [Preview Abstract] |
Friday, October 27, 2017 8:42AM - 8:54AM |
HF.00002: Nonperturbative Transverse Momentum Effects in p$+$p and p$+$A Collisions at PHENIX Michael Skoby Due to the non-Abelian nature of QCD, there is a prediction that quarks can become correlated across colliding protons in hadron production processes sensitive to nonperturbative transverse momentum effects.~ Measuring the evolution of nonperturbative transverse momentum widths as a function of the hard interaction scale can help distinguish these effects from other possibilities.~ Collins-Soper-Sterman evolution comes directly from the proof of transverse-momentum-dependent (TMD) factorization for processes such as Drell-Yan, semi-inclusive deep-inelastic scattering, and e$+$e- annihilation and predicts nonperturbative momentum widths to increase with hard scale.~ Experimental results from proton-proton and proton-nucleus collisions, in which TMD factorization is predicted to be broken, will be presented.~ The results show that these widths decrease with hard scale, suggesting possible effects from TMD factorization breaking. [Preview Abstract] |
Friday, October 27, 2017 8:54AM - 9:06AM |
HF.00003: Double Polarization Asymmetry Measurement of the Electric Form Factor of the Neutron at $Q^2$=1.16 GeV$^2$ Using the Semi-Exclusive Reaction $^3\vec{\textrm{He}}(\vec{e},e'n)pp$ Richard Obrecht The space-like electric form factor of the neutron has been extracted at $Q^2=1.16$ GeV$^2$ via a beam-target helicity asymmetry measurement using the semi-exclusive reaction $^3\vec{\textrm{He}}(\vec{e},e'n)pp$. The Jefferson Lab Hall A experiment E02-013 ran in 2006 utilizing the 6 GeV CEBAF for its high-duty, longitudinally polarized electron beam. The double-arm coincidence experiment detected the quasielastically scattered electrons in a large angular and momentum acceptance spectrometer referred to as BigBite. The recoiling nucleons were detected in a large neutron detector, built out of planes of scintillator arrays interlaced with iron and lead plates to increase the probability of inducing a hadronic shower. The polarized $^3$He target used the novel technique of hybrid spin-exchange optical pumping, resulting in a 10 atm target that could sustain polarizations greater than 50$\%$ at a beam current of 8 $\mu$A. Presented will be the current analysis and a preliminary result for $G_E^n$ at $Q^2$=1.16 GeV$^2$. [Preview Abstract] |
Friday, October 27, 2017 9:06AM - 9:18AM |
HF.00004: Comparison of the F2 Structure Function in Iron as Measured by Charged Lepton and Neutrino Probes Narbe Kalantarians, Eric Christy, Cynthia Keppel World data for the F2 structure function for Iron, as measured by multiple charged lepton and neutrino deep inelastic scattering experiments, are compared. Data obtained from charged lepton and neutrino scattering at larger values of x are in remarkably good agreement with a simple invocation of the 18/5 rule, while a discrepancy in the behavior of the data obtained from the different probes well beyond the data uncertainties is observed in the shadowing/anti-shadowing transition region where the Bjorken scaling variable x is less than 0.15. The data are compared to theoretical calculations. Details and results of the data comparison will be presented, along with future plans. [Preview Abstract] |
Friday, October 27, 2017 9:18AM - 9:30AM |
HF.00005: Transverse Single-Spin Asymmetries of Direct Photons from Proton-Proton Collisions at Forward Rapidity Oleg Eyser Transverse single-spin asymmetries in high energy collisions offer unique ways to study the nucleon structure beyond the conventional leading twist collinear picture in hard QCD processes. While transverse momentum dependent distribution and fragmentation functions require two scales (hard and soft), observables with a single hard scale can be described in a collinear framework with multiparton correlations (twist-3). Both are related when the intrinsic transverse momentum is integrated. Initial and final state effects can contribute to different probes and need to be disentangled. In 2015, the STAR experiment at RHIC has extended the forward calorimeter, 2.5<$\eta$<4.0 with a preshower detector in order to study transverse asymmetries of direct photon production in proton-proton collisions at a center of mass energy of 200 GeV. This measurement will contribute to the universality test of initial state spin-orbit correlations (sign-change between hadronic collisions and deep inelastic scattering) and serve as first input to a proper evolution of higher twist functions as function of momentum transfer. We will present the status of the analysis and discuss implications on the theoretical description. [Preview Abstract] |
Friday, October 27, 2017 9:30AM - 9:42AM |
HF.00006: ABSTRACT WITHDRAWN |
Friday, October 27, 2017 9:42AM - 9:54AM |
HF.00007: Transverse single-spin asymmetries for direct photon and neutral pion production in midrapidity at PHENIX Nicole Lewis Large transverse single spin asymmetries for hadron production in proton-proton collisions were some of the first indicators of significant nonperturbative spin-momentum correlations in the proton. They have been found to persist up to collision energies of 510 GeV, yet their origin remains poorly understood. Measurements of different final-state particles in a wide variety of collision systems over a range of kinematics can help to identify and separate contributions from the proton versus hadronization, and from different parton flavors. Depending on the rapidity pion production can provide access to both initial- and final-state effects for a mix of parton flavors, while direct photons depend only on initial-state effects and are particularly sensitive to gluon dynamics in RHIC kinematics. The status of transverse single spin measurements for neutral pions and direct photons performed for p+p, p+Al, and p+Au collisions at PHENIX will be presented. [Preview Abstract] |
Friday, October 27, 2017 9:54AM - 10:06AM |
HF.00008: Generalized Parton Distributions of the nucleon from exclusive lepto- and photo-production of lepton pairs Sho Uemura, Marie Boer Generalized Parton Distributions (GPDs) contain the correlation between the parton's longitudinal momentum and their transverse distribution. They are accessed through hard exclusive processes such as exclusive Compton processes, where two photons are exchanged with a quark of the nucleon, and at least one of them has a high virtuality. Exclusive Compton processes are considered "golden" channels, as the only non-perturbative part of the process corresponds to the GPDs. Deeply Virtual Compton Scattering (DVCS) corresponds to the lepto-production of a real photon and has been intensively studied in the past decade. We propose to access GPDs with the two other cases of exclusive Compton processes: Timelike Compton Scattering (TCS) corresponds to the photo-production of a lepton pair, and Double Deeply Virtual Compton Scattering (DDVCS) corresponds to the lepto-production of a lepton pair. The study of these two reactions is complementary to DVCS and will bring new constraints on our understanding of the nucleon structure, in particular for a tomographic interpretation of GPDs. We will discuss the interest of TCS and DDVCS in terms of GPD studies, and present the efforts held at Jefferson Lab for new experiments aiming at measuring TCS and DDVCS. [Preview Abstract] |
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