Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session Q4: Three-Body Systems |
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Sponsoring Units: GFB Chair: Werner Tornow, Duke University Room: Hyatt Regency Dallas Marsalis A |
Monday, April 24, 2006 1:30PM - 2:06PM |
Q4.00001: Two-Body Photodisintegration of ${^3\rm{He}}$ between 0.4 and 1.5 GeV Invited Speaker: The $\gamma {^3\rm{He}}\rightarrow pd$ reaction was measured with the CLAS detector at Jefferson Lab for photon energies between 0.4 and 1.5 GeV and proton CM angles $\theta^p_{CM}$ between 40$^\circ$ and 140$^\circ$. It is complementary to the three-body breakup of $^3$He with respect to studying three-body mechanisms. At all photon energies for our experiment, the differential cross sections exhibit a very strong forward-to-backward asymmetry --- approximately one order of magnitude. An interesting feature of the differential cross sections is that their slope does not depend on the photon energy and there is a change of slope at $\theta^p_{CM}=120^\circ$ seen at all photon energies. The invariant cross sections fall off with $s$ (where $s$ is the total CM energy) much faster than expected by the quark counting rules $[1]$. The latter predict that in the asymptotic regime $t\rightarrow\infty$ the invariant cross sections should scale as $s^{-17}$, whereas our data scale as $s^{-22}$. A comparison of our preliminary results with the cross sections predicted by Jean-Marc Laget's model $[2]$ shows that the differential cross sections for angles greater than 60$^\circ$ are sensitive to contributions from three-body mechanisms. The relative importance of the latter, with respect to one- and two-body mechanisms, is larger at 0.6 - 0.8 GeV than at higher energies. This has already been observed in our data for $\gamma {^3\rm{He}}\rightarrow ppn$ $[3]$ and seems to be a characteristic of the three-body mechanisms at medium energies. \vspace{6mm} \newline 1. S.J.~Brodsky and G.R.~Farrar, Phys. Rev. Lett. \textbf{31}, 1153 (1973) \\ 2. J-M.~Laget, Phys. Rev. C \textbf{38}, 2993 (1988)\\ 3. S.~Niccolai \textit{et al.}, Phys. Rev. C \textbf{70}, 064003 (2004) [Preview Abstract] |
Monday, April 24, 2006 2:06PM - 2:42PM |
Q4.00002: Probing Short Range Nuclear Properties in Photodisintegration of Few-Nucleon Systems Invited Speaker: High momentum transfer photodisintegration reactions involving few-nucleon systems represent a powerful tools for studying the nuclear dynamics at short space-time separations. We review on several aspects of this research, such us understanding the nature of short range three nucleon correlations, studying the mechanism of three-nucleon forces and probing the dynamics of quark-hadron transition in the nuclear medium. Particular processes we review are the high $Q^2$ three-body break up reactions, $90^0$ center of mass photodisintegration of $pp$ and $pn$ pairs in the $^3He$ as well as production of energetic deuterons in the current fragmentation region of the reaction. We demonstrate how these studies could allow us to extract unique information about properties of strong interaction which are inaccessible in studies of nucleon-nucleon scattering. [Preview Abstract] |
Monday, April 24, 2006 2:42PM - 3:18PM |
Q4.00003: Three-nucleon forces: new developments Invited Speaker: It is well known from microscopic few- and many-body studies that three-nucleon forces are important for quantitative understanding of various phenomena in nuclear physics. Three-nucleon forces that cannot be reduced to pair-wise nucleon-nucleon interactions arise naturally in the context of meson-exchange theory and at the more fundamental level of QCD. Chiral effective field theory provides a powerful and promising approach to determine two-, three- and more-nucleon forces in a systematic way based on the approximate and spontaneously broken chiral symmetry of QCD. Recent developments along these lines will be discussed. Future directions in this field will be outlined. [Preview Abstract] |
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