New measurements of the proton's size and structure using polarized photons

Improved measurements of the proton's structure are now possible thanks to significant technical advances that allow us to probe the proton with polarized photons. These measurements have shown that the proton is not as simple as previously believed: quark orbital angular momentum and relativistic effects play an important role and the spatial distribution of charge and magnetization do not simply mimic the spatial distribution of the quarks. Even more recently, the large scale structure and size of the proton have been examined more carefully, and a significant discrepancy has been observed between the charge radius of the proton as measured in the Lamb shift of muonic hydrogen and measurements using the electron-proton interaction.Comment: 8 pages, 3 figures. Proceedings of plenary talk at CIPANP 2012, St Petersburg, FL, May 28 - June 3, 201

New Measurements of the EMC Effect in Few-Body Nuclei

Measurements of the EMC effect show that the quark distributions in nuclei are not simply the sum of the quark distributions of the constituent nucleons. However, interpretation of the EMC effect is limited by the lack of a reliable baseline calculation of the effects of Fermi motion and nucleon binding. We present preliminary results from JLab experiment E03-103, a precise measurement of the EMC effect in few-body and heavy nuclei. These data emphasize the large-x region, where binding and Fermi motion effects dominate, and thus will provide much better constraints on the effects of binding. These data will also allow for comparisons to calculations for few-body nuclei, where the uncertainty in the nuclear structure is minimized.Comment: Proceedings from talk at the Topical Group on Hadron Physics meeting, Nashville Tennessee, October 22-24, 2006. 9 pages, 6 figure

Comment on "High-Precision Determination of the Electric and Magnetic Form Factors of the Proton"

In a recent Letter, Bernauer, et al. present fits to the proton electromagnetic form factors, GEp(Q^2) and GMp(Q^2), along with extracted proton charge and magnetization radii based on large set of new, high statistical precision (<0.2%) cross section measurements. The Coulomb corrections they apply differ dramatically from more modern and complete calculations, implying significant error in their final results.Comment: To appear as a comment in Physical Review Letter

Do Ordinary Nuclei Contain Exotic States of Matter?

The strongly repulsive core of the short-range nucleon-nucleon interaction leads to the existence of high-momentum nucleons in nuclei. Inclusive electron scattering can be used to probe these high-momentum nucleons and study the nature of the corresponding short-range correlations in nuclei. With recent data from Jefferson Lab we have begun to map out the strength of two-nucleon correlations in nuclei, while upcoming experiments should allow us to isolate the presence of multi-nucleon correlations. In addition to their importance in describing nuclear structure, these configurations of correlated nucleons represent high density 'droplets' of hadronic matter. As the density of hadronic matter increases there should be a weakening of quark confinement, similar to the onset of deconfinement expected at extremely high temperatures. While there have been hints of non-hadronic structure in nuclei, future measurements will allow us to directly probe the quark distributions of high density configurations in nuclei. A modified quark structure in these closely packed nucleons would provide a clear signature of exotic components to the structure of nuclei.Comment: Proceedings for the 19th Winter Workshop on Nuclear Dynamics, Breckenridge, Colorado, March 8-15, 2003, 6 pages, 4 figure

How Well Do We Know the Electromagnetic Form Factors of the Proton?

Recent measurements of recoil polarization in elastic scattering have been used to extract the ratio of the electric to the magnetic proton form factors. These results disagree with Rosenbluth extractions from cross section measurements, indicating either an inconsistency between the two techniques, or a problem with either the polarization transfer or cross section measurements. To obtain precise knowledge of the proton form factors, we must first understand the source of this discrepancy.Comment: 5 pages, 4 figures; Invited talk at Electron-Nucleus Scattering VII, Elba, Italy, June 2002 (to appear in proceedings

Are Recoil Polarization Measurements of GEp/GMpG_E^p/G_M^p Consistent With Rosenbluth Separation Data?

Recent recoil polarization measurements in Hall A at Jefferson Lab show that the ratio of the electric to magnetic form factors for the proton decreases significantly with increasing Q^2. This contradicts previous Rosenbluth measurements which indicate approximate scaling of the form factors. The cross section measurements were reanalyzed to try and understand the source of this discrepancy. We find that the various Rosenbluth measurements are consistent with each other when normalization uncertainties are taken into account and that the discrepancy cannot simply be the result of errors in one or two data sets. If there is a problem in the Rosenbluth data, it must be a systematic, epsilon-dependent uncertainty affecting several experiments.Comment: 4 pages, 1 figure, to appear in the proceedings of the 9th International Conference on the Structure of Baryons, Jefferson Lab, Newport News, VA, USA, Mar 200

Nucleon Momentum Distributions From a Modified Scaling Analysis of Inclusive Electron-Nucleus Scattering

Inclusive electron scattering from nuclei at low momentum transfer (corresponding to x>1) and moderate Q^2 is dominated by quasifree scattering from nucleons. In the impulse approximation, the cross section can be directly connected to the nucleon momentum distribution via the scaling function F(y). The breakdown of the y-scaling assumptions in certain kinematic regions have prevented extraction of nucleon momentum distributions from such a scaling analysis. With a slight modification to the y-scaling assumptions, it is found that scaling functions can be extracted which are consistent with the expectations for the nucleon momentum distributions.Comment: 4 pages, 2 figures, to appear in the proceedings of the 9th International Conference on the Structure of Baryons, Jefferson Lab, Newport News, VA, USA, Mar 200

Searching for flavor dependence in nuclear quark behavior

The observed correlation between the EMC effect and the contribution of short-range correlations (SRCs) in nuclei suggests that the modification of the quark distributions of bound protons and neutrons might occur within SRCs. This raises the possibility that the EMC effect may have an isospin dependence arising from the np dominance of SRCs. We discuss previous attempts to test this possibility and perform a new analysis of existing data. We find no experimental support for the observation of an isospin dependence of the EMC effect.Comment: 5 pages, 4 figures, submitted for publicatio