Bulletin of the American Physical Society
2007 Annual Meeting of the Division of Nuclear Physics
Volume 52, Number 10
Wednesday–Saturday, October 10–13, 2007; Newport News, Virginia
Session BA: Recent Results from Jefferson Lab |
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Chair: Anthony Thomas, Jefferson Lab Room: Newport News Marriott at City Center Grand Salon I |
Thursday, October 11, 2007 2:00PM - 2:36PM |
BA.00001: What's the matter in the Proton? Invited Speaker: It has been over 70 years since the Nobel Prize was awarded to Otto Stern for the discovery that the proton has an anomalously large magnetic moment, nearly three times what one expects from a spin-1/2 object with no internal structure. This was one of the first hints of the spatial extent of protons and neutrons that make up nearly all of the visible matter in the universe. Not long after this discovery, this interior landscape began to be explored in detail through the use of electron scattering, a precision microscope with which one can peer deep inside the nucleon. Recent experiments, using polarized beams, light polarized targets, recoil detection and complementary views via the weak interaction are now changing our traditional textbook view of the nucleon and its lowest-lying excited states. This talk will be a review of the recent experimental results and a summary of near future opportunities. [Preview Abstract] |
Thursday, October 11, 2007 2:36PM - 3:12PM |
BA.00002: Correlations in Nuclei: Recent Progress on an Old Problem Invited Speaker: The two preeminent features of the nucleon-nucleon ($N$$N$) interaction are its short-range repulsion and intermediate- to long-range tensor character. These induce strong spatial-spin-isospin $N$$N$ correlations, which leave their imprint on the structure of ground- and excited-state wave functions. In the present talk I will review how these features influence a variety of nuclear properties---from energy spectra of low-lying states to two-nucleon density distributions to nuclear response functions---as well as the experimental evidence in support of their presence. In particular, I will show [R.\ Schiavilla, R.B.\ Wiringa, S.C.\ Pieper, and J.Carlson, Phys.\ Rev.\ Lett.\ {\bf 98}, 132501 (2007)] how tensor correlations impact the momentum distribution of $n$$p$ pairs in the ground state of nuclei and make it orders of magnitude larger than that of $p$$p$ pairs for values of the relative momentum in the range (300--600) MeV/c and vanishing total momentum. This order-of-magnitude difference is seen in all nuclei considered, and has a universal character originating from the tensor components present in any realistic $N$$N$ interaction. It should be easily observable in two-nucleon knock-out processes. Indeed, a preliminary analysis of $(e,e^\prime np)$ and $(e,e^\prime pp)$ reactions in $^{12}$C finds [R.\ Subedi {\it et al.}, in preparation] that the $p$$p$ cross section is suppressed relative to the $n$$p$ by a factor $\simeq 10$ in kinematics close to back-to-back emission of the two nucleons. [Preview Abstract] |
Thursday, October 11, 2007 3:12PM - 3:48PM |
BA.00003: A Decade of Structure Function Measurements at Jefferson Lab Invited Speaker: With fine precision and extensive kinematic coverage, experimenters at Jefferson Lab have been measuring nucleon and nuclear structure functions, polarized and unpolarized, in the range of momentum transfer $0.01 < Q^2 < 6$ GeV$^2$. These experiments have greatly increased our understanding of parton distributions, higher twists, duality, resonance excitations, non-perturbative QCD, and nucleons in the nuclear medium. Our present ability to determine moments of structure functions makes direct comparisons to QCD calculations and sum rules possible. I will present the state of our art. [Preview Abstract] |
Thursday, October 11, 2007 3:48PM - 4:24PM |
BA.00004: Excited Nucleon Resonance Properties from Lattice QCD Invited Speaker: We review the progress of the Lattice Hadron Physics Collaboration's ongoing efforts to determine the tower of excited nucleon resonances as predicted by QCD. The most common approach to this problem is to consider two-point correlations of interpolating operators calculated using lattice QCD. We show that realistic interpolating operators are essential for accessing the states of interest and describe how such operators can be designed. We outline how a variant of the variational method combined with a systematic fitting approach can be used to extract finite-volume spectra from the Green's functions, and illustrate the efficacy of the approach by showing preliminary results using two-flavors of dynamical fermions. We outline the connection between the finite-volume spectra obtained from the lattice and the continuum resonance states measured in experiment, and conclude with a discussion of current limitations and ongoing improvements. [Preview Abstract] |
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