arXiv subjects

J. Arrington

Publications and source records attributed to J. Arrington.

140 records · Page 8Linked to original sources

arXiv2003

New measurement of G_E/G_M for the proton

Recent polarization transfer measurements of the proton form factors disagree with previous Rosenbluth extractions. In addition to providing insight into the proton structure, the form factors also provide crucial input for the analysis of quasielastic experiments, and this discrepancy could have a significant impact on such experiments at moderate-to-large Q^2 values. In 2002, a new ``SuperRosenbluth'' measurement was performed to help understand this origin of this discrepancy, as well its implications on other experiments. Preliminary results agree with previous Rosenbluth extractions, indicating that the discrepancy must be related to some fundamental flaw in either the Rosenbluth or polarization transfer technique.

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arXiv2003

Implications of the discrepancy between proton form factor measurements

Recent polarization transfer measurements of the proton electromagnetic form factors yield very different results from previous Rosenbluth extractions. This inconsistency implies uncertainties in our knowledge of the form factors and raises questions about how to best combine data from these two techniques. If the discrepancy is due to missing correction to the cross section data, as has been suggested, then different applications will require the use of different form factors. We present two extractions of the form factors: a global fit to the world's cross section data, and a combined extraction from polarization transfer and cross section data. The former provides a parametrization of the elastic electron-proton cross section, while the latter provides a consistent extraction of the underlying form factors, under the assumption that missing terms in the radiative correction explain the difference between the cross section and polarization transfer results.

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arXiv2003

Modeling Neutrino Quasielastic Cross Sections on Nucleons and Nuclei

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arXiv2003

Modeling Quasi-elastic Form Factors for Electron and Neutrino Scattering

We calculate the total and differential quasielastic cross sections for neutrino and antineutrino scattering on nucleons using up to date fits to the nucleon elastic electromagnetic form factors $G_E^p$, $G_E^n$, $G_M^p$, $G_M^n$, and weak and pseudoscalar form factors. We find that using the updated non-zero value of $G_E^n$ has a significant effect on both the total and differential neutrino and antineutrino quasielastic cross sections. Previous extractions of the weak axial form factor from neutrino scattering data are sensitive to the assumptions that were used for the vector form factors. We perform a re-analysis of previous neutrino data using updated form factors and obtain updated value of the axial vector mass.

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arXiv2003

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.

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arXiv2003

How well do we know the electromagnetic form factors of the proton?

Several experiments have extracted proton electromagnetic form factors from elastic cross section measurements using the Rosenbluth technique. Global analyses of these measurements indicate approximate scaling of the electric and magnetic form factors (mu_p*G_E/G_M = 1), in contrast to recent polarization transfer measurements from Jefferson Lab. We present here a global reanalysis of the cross section data aimed at understanding the disagreement between the Rosenbluth extraction and the polarization transfer data. We find that the individual cross section measurements are self-consistent, and that the new global analysis yields results that are still inconsistent with polarization measurements. This discrepancy indicates a fundamental problem in one of the two techniques, or a significant error in polarization transfer or cross section measurements. An error in the polarization data would imply a large error in the extracted electric form factor, while an error in the cross sections implies an uncertainty in the extracted form factors, even if the form factor ratiois measured exactly.

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arXiv2003

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.

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arXiv2002

Hadrons in the Nuclear Medium

Quantum Chromodynamics, the microscopic theory of strong interactions, has not yet been applied to the calculation of nuclear wave functions. However, it certainly provokes a number of specific questions and suggests the existence of novel phenomena in nuclear physics which are not part of the the traditional framework of the meson-nucleon description of nuclei. Many of these phenomena are related to high nuclear densities and the role of color in nucleonic interactions. Quantum fluctuations in the spatial separation between nucleons may lead to local high density configurations of cold nuclear matter in nuclei, up to four times larger than typical nuclear densities. We argue here that experiments utilizing the higher energies available upon completion of the Jefferson Laboratory energy upgrade will be able to probe the quark-gluon structure of such high density configurations and therefore elucidate the fundamental nature of nuclear matter. We review three key experimental programs: quasi-elastic electro-disintegration of light nuclei, deep inelastic scattering from nuclei at $x>1$, and the measurement of tagged structure functions. These interrelated programs are all aimed at the exploration of the quark structure of high density nuclear configurations. The study of the QCD dynamics of elementary hard processes is another important research direction and nuclei provide a unique avenue to explore these dynamics. We argue that the use of nuclear targets and large values of momentum transfer at would allow us to determine whether the physics of the nucleon form factors is dominated by spatially small configurations of three quarks.

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arXiv2002

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.

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arXiv2002

Are Recoil Polarization Measurements of $G_E^p/G_M^p$ 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.

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arXiv2001

x- and xi-scaling of the Nuclear Structure Function at Large x

Inclusive electron scattering data are presented for ^2H and Fe targets at an incident electron energy of 4.045 GeV for a range of momentum transfers from Q^2 = 1 to 7 (GeV/c)^2. Data were taken at Jefferson Laboratory for low values of energy loss, corresponding to values of Bjorken x greater than or near 1. The structure functions do not show scaling in x in this range, where inelastic scattering is not expected to dominate the cross section. The data do show scaling, however, in the Nachtmann variable ξ. This scaling may be the result of Bloom Gilman duality in the nucleon structure function combined with the Fermi motion of the nucleons in the nucleus. The resulting extension of scaling to larger values of ξopens up the possibility of accessing nuclear structure functions in the high-x region at lower values of Q^2 than previously believed.

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arXiv1998

Inclusive Electron-Nucleus Scattering at Large Momentum Transfer

Inclusive electron scattering is measured with 4.045 GeV incident beam energy from C, Fe and Au targets. The measured energy transfers and angles correspond to a kinematic range for Bjorken $x > 1$ and momentum transfers from $Q^2 = 1 - 7 (GeV/c)^2$. When analyzed in terms of the y-scaling function the data show for the first time an approach to scaling for values of the initial nucleon momenta significantly greater than the nuclear matter Fermi-momentum (i.e. $> 0.3$ GeV/c).

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arXiv1996

SAMPLE: Parity Violating Electron Scattering from Hydrogen and Deuterium

Recently, there has been considerable theoretical interest in determining strange quark contributions to hadronic matrix elements. Such matrix elements can be accessed through the nucleon's neutral weak form factors as determined in parity violating electron scattering. The SAMPLE experiment will measure the strange magnetic form factor $G_M^s$ at low momentum transfer. By combining measurements from hydrogen and deuterium the theoretical uncertainties in the measurement can be greatly reduced and the result will be limited by experimental errors only. A summary of recent progress on the SAMPLE experiment is presented.

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arXiv1995

Inclusive Electron Scattering from Nuclei at $x \simeq 1$

The inclusive A(e,e') cross section for $x \simeq 1$ was measured on $^2$H, C, Fe, and Au for momentum transfers $Q^2$ from 1-7 (GeV/c)$^2$. The scaling behavior of the data was examined in the region of transition from y-scaling to x-scaling. Throughout this transitional region, the data exhibit $ξ$-scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.

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