Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session J12: Mini-Symposium on Nuclear Structure at Short Distances. II |
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Sponsoring Units: DNP Chair: Eliezer Piasetzky, Tel Aviv University Room: Plaza Court 2 |
Sunday, May 3, 2009 1:30PM - 1:42PM |
J12.00001: Short-Range Correlation Studies on $^{12}C$ with 6-9~GeV/c Proton Beams John Watson, Eliezer Piasetzky, Misak Sargsian Reactions at beam momenta and momentum transfers of several GeV/c can probe nuclei on a size scale where nucleon-nucleon short-range correlations (SRCs) are expected to be dominant. We will report on measurements of the $^{12}C(p,2p+n)$ reaction at Brookhaven National Laboratory at beam momenta of 6 to 9~GeV/c. For that experiment, the primary reaction was quasi-elastic knockout of a proton from $^{12}C$, followed by emission of a coincident neutron. For neutron momenta $\ge k_F$~(220 MeV/c), the reconstructed momentum of the knocked-out proton, and the measured momentum of the detected coincident neutron are nearly back-to-back in the laboratory frame of reference, which is a strong kinematic signature of SRCs~[1]. After correction for neutron-detection efficiency, solid angle coverage, and absorption of the incoming and outgoing nucleons, we find that $92\pm 18$\% of nuclear protons with momenta $\ge 275$~MeV/c have correlated neutron partners~[2]. \medskip \medskip \noindent [1] A. Tang et al., Phys. Rev. Lett. 90 042301 (2003). \noindent [2] E. Piasetzky et al., Phys. Rev. Lett. 97 162504 (2006). [Preview Abstract] |
Sunday, May 3, 2009 1:42PM - 1:54PM |
J12.00002: Probing Short-Range Correlations via the (e,e'pN) Reaction Douglas Higinbotham The nucleons in the nucleus can form strongly correlated pairs. A recent 12C(e,e'pN) experiment with high-momentum transfer and high missing momentum has shown that neutron-proton pairs are nearly 20 times as prevalent as proton-proton and, by inference, neutron-neutron pairs. This result, which is due to tensor correlations, has implications for our understanding of nuclear systems from nuclei to neutron stars. The details of this experiment will be discussed along with the upcoming 4He(e,e'pN) experiment which will have higher missing momentum, and thus, shorter distance correlations. [Preview Abstract] |
Sunday, May 3, 2009 1:54PM - 2:06PM |
J12.00003: Recent Studies of Nucleon-Nucleon Short-Range Correlations with A(e,e'p) Reactions. Shalev Gilad, Peter Monaghan The reaction A(e,e'p) has been used extensively to study short-range nucleon-nucleon correlations. ~We shall review recent such studies at high transferred momenta, and will present new results from Hall A at the Jefferson Laboratory at $x_B >1$ kinematics. ~In light of these results, we shall discuss the advantages and limitations of the A(e,e'p) reaction for the purpose of studying short-range two-nucleon correlations. [Preview Abstract] |
Sunday, May 3, 2009 2:06PM - 2:18PM |
J12.00004: Impulse Approximation limitations to the $(e,e'p)$ reaction on $^{208}$Pb: search for long range correlations at high missing momenta Alexandre Camsonne, Juan Carlos Cornejo, Joaquin Lopez Herraiz Experiment E06007 at Jefferson Lab measured cross sections for the $(e,e'p)$ reaction at constant $(\textbf{q},\omega)$ for Q$^2$ = 0.81 GeV$^2$ over a range of missing momenta from 0 to 500 MeV/c. Spectroscopic factors for states near the Fermi level are typically in the range of 0.65-0.70, a feature usually attributable to short range and long range correlations. It has been conjectured that long range correlations should also have a significant effect on the strength of high momentum components of single nucleon states near the fermi level. Cross sections for missing momenta from 300 MeV/c to 500 MeV/c for the $^{208}$Pb(e,e'p) reaction going to the low lying states of $^{207}$Tl will be presented and compared to theoretical predictions using various prescriptions for including correlations. Data from two recent runs will be presented. [Preview Abstract] |
Sunday, May 3, 2009 2:18PM - 2:30PM |
J12.00005: Hard Break-Up of Two-Nucleons and QCD Dynamics of NN Interaction Misak Sargsian, Carlos Granados We investigate hard photodisintegration of two nucleons from $^3He$ nucleus within the framework of hard rescattering model (HRM). In HRM a quark of one nucleon knocked-out by incoming photon rescatters with a quark of the other nucleon leading to the production of two nucleons with high relative momentum. HRM allows to express the amplitude of two-nucleon break-up reaction through the convolution of photon-quark scattering, NN hard scattering amplitude and nuclear spectral function which can be calculated using nonrelativistic $^3He$ wave function. HRM predicts several specific features for hard break-up reaction. First, the cross section will approximately scale as $s^{-11}$. Also one predicts comparable or larger cross section for pp break up as compared to that of pn break-up, which is opposite to what is observed in low energy kinematics. Another result is the prediction of different spectator momentum dependencies of pp and pn break-up cross sections. This is due to the fact that same-helicity pp-component is strongly suppressed in the ground state wave function of $^3He$. Due to this suppression HRM predicts significantly different asymmetries for the cross section of polarization transfer NN break-up reactions for circularly polarized photons. For the pp break-up this asymmetry is predicted to be zero while for the pn it is close to ${2\over 3}$. [Preview Abstract] |
Sunday, May 3, 2009 2:30PM - 2:42PM |
J12.00006: Hard Photo-disintegration of proton pairs in $^3$He E. Piasetzky, I. Pomerantz, R. Gilman Hard deuteron photo-disintegration has been investigated for 20 years [1], as its cross sections follow the constituent counting rules and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions [2]. During the summer of 2007, we measured in Jefferson Lab Hall A [3] hard $pp$-pair disintegration for the first time, in the reaction $\gamma \, ^3 {\rm He} \to pp + n$, using kinematics corresponding to a spectator neutron. The current state of the analysis and preliminary results will be shown. Clues to the underlying physics can be found in the comparison of our measurements with deuteron photo-disintegration, the energy dependence of the cross sections at 90$^{\circ}$ c.m., and the $\alpha_n$ distribution. \newline \textbf{References:} \newline [1] R. Gilman and F. Gross, J. Phys. G 28, R37 (2002). \newline [2] S. J. Brodsky {\it et al.}, Phys. Lett. B 578, 69 (2004). \newline [3] {\sf http://hallaweb.jlab.org/experiment/E03-101/} [Preview Abstract] |
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