Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session W10: Partonic Structure in Nucleons and Nuclei |
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Sponsoring Units: GHP DNP Chair: John Arrington, Argonne National Laboratory Room: Embassy A |
Tuesday, April 3, 2012 10:45AM - 10:57AM |
W10.00001: How well do we know the neutron structure function? John Arrington, Joshua G. Rubin, Wally Melnitchouk Given a model of the nuclear effects in the deuteron, one can obtain the neutron structure function from a combination of proton and deuteron measurements. Historically, the results have been very sensitive to the details of the extraction, but recent works have shown that this is often the result of inconsistent kinematics between the calculations of nuclear effects and the structure function data. We present a detailed analysis of the uncertainty in the neutron $F_{2n}$ structure function extracted from inclusive deuteron and proton deep-inelastic scattering data, including experimental uncertainties and the model dependence associated with the deuteron wave-function, the different convolution calculations for the deuteron, and the prescription for the off-shell corrections. We find a significantly smaller range of results than earlier comparisons. In addition to improving the extraction of the neutron structure, this also provided an important baseline that will allow future, model-independent extractions of neutron structure to be used to examine nuclear medium effects in the deuteron. [Preview Abstract] |
Tuesday, April 3, 2012 10:57AM - 11:09AM |
W10.00002: Extracting the Proton Longitudinal Structure Function Moments from World Data Peter Monaghan We present an extraction of the lowest three moments of the proton longitudinal structure function $F_L$ from available world data between $Q^2$ = 0.75 and 45.0~(GeV/c)$^2$. This analysis utilizes new data from DESY at low Bjorken $x$ and from Jefferson Lab at high $x$, allowing the moments to be determined relatively free from uncertainties due to extrapolations into unmeasured regions. The moments are compared with several parton distribution function parameterizations, which tend to underestimate the higher order moments. This suggests either the presence of significant higher twist effects in $F_L$ or a larger gluon distribution at high $x$. [Preview Abstract] |
Tuesday, April 3, 2012 11:09AM - 11:21AM |
W10.00003: Nuclear High Momentum Components and Short Range Structure Donal Day, John Arrington, Nadia Fomin High momentum components are generated by the short range features of the NN force and are an expression of short range correlations (SRC) in the ground state. The tail of the momentum distribution for all nuclei share this common origin and the relative strength of these SRC are revealed in the cross section ratios of heavy to light nuclei. Inclusive scattering data from Jefferson Lab have allowed a precise determination of the A-dependence of SRC in nuclei and suggests that, like the EMC effect, it is especially sensitive to the nuclear local density. These new results will be presented and discussed along with the prospects of future experiments. [Preview Abstract] |
Tuesday, April 3, 2012 11:21AM - 11:33AM |
W10.00004: ABSTRACT WITHDRAWN |
Tuesday, April 3, 2012 11:33AM - 11:45AM |
W10.00005: Study of Three-Nucleon Short Range Correlations in $x>2$ regime Zhihong Ye, John Arrington, Donal Day, Douglas Higinbotham Inclusive electron scattering is a powerful tool to study nuclear short range correlations (SRCs). Recent experiments in Jefferson Lab have established their presence of substantial 2N correlations by taking the ratio of the cross sections of heavy to light nuclei in the region of $1 < x < 2$. However the experimental situation is much more uncertain with regard to three nucleon SRCs (3N-SRCs) which may dominate for $x > 2$. Jefferson Lab experiment E08014 experiment ran in April and May of 2011 in Hall-A and was designed to study the onset of 3N-SRCs with better accuracy and, for the first time, to examine the isospin dependence of SRCs in inclusive scattering. The experiment will be briefly described followed by a discussion of the data analysis and the presentation of any preliminary data. [Preview Abstract] |
Tuesday, April 3, 2012 11:45AM - 11:57AM |
W10.00006: ABSTRACT WITHDRAWN |
Tuesday, April 3, 2012 11:57AM - 12:09PM |
W10.00007: Deep Exclusive PI0 and ETA Electroproduction with CLAS at Jefferson Lab Paul Stoler The CLAS collaboration at Jefferson Lab has undertaken a series of measurements of exclusive $\pi^0$ and $\eta$ electroproduction at a beam energy ~ 6 GeV over a large kinematic coverage in $Q^2, t$ and $x_B$. New results of extracted structure functions $\sigma_L+\sigma_T, \sigma_{LT}$ and $\sigma_{TT}$, are presented in the kinematic range $Q^2$ from 1.2 to 3.2 GeV$^2$/c$^2$, $|t|$ from $|t_{min}|$ to 1.2 GeV$^2$/c$^2$ and $x_B$ from 0.1 to 0.6. Recent theoretical work [1,2] indicate that pseudoscalar meson production is uniquely sensitive to quark helicity-flip processes. The new results, together with CLAS measurements of beam spin asymmetries $A_\phi$ [3] and cross section ratios $\sigma(\pi_0)/\sigma(\eta)$ , compared with theoretical calculations [1,2] that are based on the helicity-flip transversity GPDs, provide supporting evidence that pseudoscalar meson production at these kinematics may be dominated by the handbag mechanism and helicity-flip transversity GPDs. \\[4pt] [1] S.V.Goloskokov and P.Kroll, Eur.Phys.J. A47,112 (2011).\\[0pt] [2] G.R. Goldstein,J.O.Gonzalez and S.Liuti, Phys. Rev., D84,034007(2011).\\[0pt] [3] R.DeMasi,et,al.(CLAS Collaboration),Phys.Rev.,C77,042201(2008) [Preview Abstract] |
Tuesday, April 3, 2012 12:09PM - 12:21PM |
W10.00008: Deeply Virtual Compton Scattering off Helium Eric Voutier Deeply Virtual Compton Scattering (DVCS) is privileged tool to access the partonic structure of hadrons encoded via the so-called Generalized Parton Distributions (GPDs). Similarly to the scattering of light by a material, DVCS provides information about the dynamics and the spatial structure of hadrons. Whether the target nucleus remains intact or not after the reaction, DVCS off a nuclear target allows to address the partonic structure of the nucleus as well as the partonic structure of nucleons embedded in the nuclear medium. Adding transverse degrees of freedom to conventional deep inelastic scattering, these exclusive channels are expected to bring sensitive information about the origin of the EMC effect. The eg6 experiment at the Jefferson Laboratory did explore nuclear DVCS off $^4$He. The experimental asymmetry of the DVCS reaction with respect to the electron beam polarization was measured for the coherent and incoherent channels with the CLAS detector, complemented with a small angle electromagnetic calorimeter and a radial time projection chamber. This talk reviews the experimental methods and techniques of the eg6 run, and discusses the preliminary results of DVXS measurements. [Preview Abstract] |
Tuesday, April 3, 2012 12:21PM - 12:33PM |
W10.00009: Kinematic Issue of GPDs in DVCS Chueng-Ryong Ji, Bernard Bakker Generalized Parton Distributions (GPDs) in Deeply Virtual Compton Scattering (DVCS) have been widely recognized and used as a useful tool to explore the quark and gluon structure of the target hadrons. However, we recently pointed out treacherous kinematic issue in analyzing DVCS in terms of GPDs. In this talk, we present our key findings in the simplest possible level of complete amplitude including the lepton current. Implication in the Jefferson Lab experiment of DVCS will also be discussed. [Preview Abstract] |
Tuesday, April 3, 2012 12:33PM - 12:45PM |
W10.00010: Deeply Virtual Compton Scattering at eRHIC Salvatore Fazio, Dieter Mueller The feasibility for a measurement of the exclusive production of a real photon, a process although known as Deeply Virtual Compton Scattering (DVCS), using the future eRHIC machine at BNL has been explored. eRHIC is a machine designed to collide an electron beam with energies ranging from 5 GeV up to 30 GeV with the RHIC hadron beams (protons (100 -250 GeV) and nuclei ($\leq$ 100 GeV)) at varying center-of-mass energies. DVCS is universally believed to be a golden measurement toward the determination of the Generalized Parton Distribution (GPDs) functions. The high luminosity of the machine, expected in the order of 10$^{34}cm^{-2}s^{-1}$ at the highest center-of-mass energies, together with the large rapidity acceptance of a newly designed dedicated detector, will open the opportunity for very high precision measurements of DVCS, providing an important tool toward a $2+1$ dimensional picture of the internal structure of the proton. The huge impact such measurements would have on the determination of GPDs will be discussed. [Preview Abstract] |
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