Determination of the pion charge form factor for Q^2=0.60-1.60 GeV^2

The data analysis for the reaction H(e,e' pi^+)n, which was used to determine values for the charged pion form factor Fpi for values of Q^2=0.6-1.6 GeV^2, has been repeated with careful inspection of all steps and special attention to systematic uncertainties. Also the method used to extract Fpi from the measured longitudinal cross section was critically reconsidered. Final values for the separated longitudinal and transverse cross sections and the extracted values of Fpi are presented.Comment: 11 pages, 6 figure

Measurement of the Charged Pion Electromagnetic Form Factor

Separated longitudinal and transverse structure functions for the reaction 1H(e,eprime pi+)n were measured in the momentum transfer region Q2=0.6-1.6 (GeV/c)**2 at a value of the invariant mass W=1.95 GeV. New values for the pion charge form factor were extracted from the longitudinal cross section by using a recently developed Regge model. The results indicate that the pion form factor in this region is larger than previously assumed and is consistent with a monopole parameterization fitted to very low Q2 elastic data.Comment: 5 pages, 3 figure

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).Comment: 5 pages TEX, 5 Postscript figures also available at http://www.krl.caltech.edu/preprints/OAP.htm

Charged pion form factor between Q2Q^2=0.60 and 2.45 GeV2^2. I. Measurements of the cross section for the 1{^1}H(e,e′π+e,e'\pi^+)nn reaction

Cross sections for the reaction ${^1}$H($e,e'\pi^+$)$n$ were measured in Hall C at Thomas Jefferson National Accelerator Facility (JLab) using the CEBAF high-intensity, continous electron beam in order to determine the charged pion form factor. Data were taken for central four-momentum transfers ranging from $Q^2$=0.60 to 2.45 GeV$^2$ at an invariant mass of the virtual photon-nucleon system of $W$=1.95 and 2.22 GeV. The measured cross sections were separated into the four structure functions $\sigma_L$, $\sigma_T$, $\sigma_{LT}$, and $\sigma_{TT}$. The various parts of the experimental setup and the analysis steps are described in detail, including the calibrations and systematic studies, which were needed to obtain high precision results. The different types of systematic uncertainties are also discussed. The results for the separated cross sections as a function of the Mandelstam variable $t$ at the different values of $Q^2$ are presented. Some global features of the data are discussed, and the data are compared with the results of some model calculations for the reaction ${^1}$H($e,e'\pi^+$)$n$.Comment: 26 pages, 23 figure

Separated Response Function Ratios in Exclusive, Forward pi^{+/-} Electroproduction

The study of exclusive $\pi^{\pm}$ electroproduction on the nucleon, including separation of the various structure functions, is of interest for a number of reasons. The ratio $R_L=\sigma_L^{\pi^-}/\sigma_L^{\pi^+}$ is sensitive to isoscalar contamination to the dominant isovector pion exchange amplitude, which is the basis for the determination of the charged pion form factor from electroproduction data. A change in the value of $R_T=\sigma_T^{\pi^-}/\sigma_T^{\pi^+}$ from unity at small $-t$, to 1/4 at large $-t$, would suggest a transition from coupling to a (virtual) pion to coupling to individual quarks. Furthermore, the mentioned ratios may show an earlier approach to pQCD than the individual cross sections. We have performed the first complete separation of the four unpolarized electromagnetic structure functions above the dominant resonances in forward, exclusive $\pi^{\pm}$ electroproduction on the deuteron at central $Q^2$ values of 0.6, 1.0, 1.6 GeV$^2$ at $W$=1.95 GeV, and $Q^2=2.45$ GeV$^2$ at $W$=2.22 GeV. Here, we present the $L$ and $T$ cross sections, with emphasis on $R_L$ and $R_T$, and compare them with theoretical calculations. Results for the separated ratio $R_L$ indicate dominance of the pion-pole diagram at low $-t$, while results for $R_T$ are consistent with a transition between pion knockout and quark knockout mechanisms.Comment: 6 pages, 3 figure

A Study of the Quasi-elastic (e,e'p) Reaction on 12^{12}C, 56^{56}Fe and 97^{97}Au

We report the results from a systematic study of the quasi-elastic (e,e'p) reaction on $^{12}$C, $^{56}$Fe and $^{197}$Au performed at Jefferson Lab. We have measured nuclear transparency and extracted spectral functions (corrected for radiation) over a Q$^2$ range of 0.64 - 3.25 (GeV/c)$^2$ for all three nuclei. In addition we have extracted separated longitudinal and transverse spectral functions at Q$^2$ of 0.64 and 1.8 (GeV/c)$^2$ for these three nuclei (except for $^{197}$Au at the higher Q$^2$). The spectral functions are compared to a number of theoretical calculations. The measured spectral functions differ in detail but not in overall shape from most of the theoretical models. In all three targets the measured spectral functions show considerable excess transverse strength at Q$^2$ = 0.64 (GeV/c)$^2$, which is much reduced at 1.8 (GeV/c)$^2$.Comment: For JLab E91013 Collaboration, 19 pages, 20 figures, 3 table

Charged pion form factor between Q^2=0.60 and 2.45 GeV^2. II. Determination of, and results for, the pion form factor

The charged pion form factor, Fpi(Q^2), is an important quantity which can be used to advance our knowledge of hadronic structure. However, the extraction of Fpi from data requires a model of the 1H(e,e'pi+)n reaction, and thus is inherently model dependent. Therefore, a detailed description of the extraction of the charged pion form factor from electroproduction data obtained recently at Jefferson Lab is presented, with particular focus given to the dominant uncertainties in this procedure. Results for Fpi are presented for Q^2=0.60-2.45 GeV^2. Above Q^2=1.5 GeV^2, the Fpi values are systematically below the monopole parameterization that describes the low Q^2 data used to determine the pion charge radius. The pion form factor can be calculated in a wide variety of theoretical approaches, and the experimental results are compared to a number of calculations. This comparison is helpful in understanding the role of soft versus hard contributions to hadronic structure in the intermediate Q^2 regime.Comment: 18 pages, 11 figure

Measurements of Deuteron Photodisintegration up to 4.0 GeV

The first measurements of the differential cross section for the d(gamma,p)n reaction up to 4.0 GeV were performed at Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. We report the cross sections at the proton center-of-mass angles of 36, 52, 69 and 89 degrees. These results are in reasonable agreement with previous measurements at lower energy. The 89 and 69 degree data show constituent-counting-rule behavior up to 4.0 GeV photon energy. The 36 and 52 degree data disagree with the counting rule behavior. The quantum chromodynamics (QCD) model of nuclear reactions involving reduced amplitudes disagrees with the present data.Comment: 5 pages (REVTeX), 1 figure (postscript