0000000000139476
AUTHOR
K. I. Blomqvist
High Resolution Spectroscopy ofBΛ12by Electroproduction
An experiment measuring electroproduction of hypernuclei has been performed in Hall A at Jefferson Lab on a $^{12}$C target. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A standard equipment. An unprecedented energy resolution of less than 700 keV FWHM has been achieved. Thus, the observed \lam{12}{B} spectrum shows for the first time identifiable strength in the core-excited region between the ground-state {\it s}-wave $\Lambda$ peak and the 11 MeV {\it p}-wave $\Lambda$ peak.
No evidence for medium effects in the12C(e, e'p)11Bg.s. reaction
The12C(e, e'p)11B g.s reaction has been measured in parallel and anti-parallel kinematics over ap m range of −120<p m<120 MeV/c at a centralT p of 90 MeV. In contrast to previous measurements at NIKHEF, both kinematics can be described without enhancement of the transverse form factor of the bound proton (η=0.98(5)). The spectroscopic factor for this transition as determined with the new Mainz data (S α =1.54(5)) is 22% smaller than the NIKHEF value.
Precise pion electroproduction in thep(e, e? ?+)n reaction at W=1125 MeV
The reactione+p →> e+π ++n at c.m. energyW=1125MeV and momentum transfer Q2=0.117GeV2/c2 has been measured. The transverse and longitudinal structure functions have been separated by varying the polarization of the virtual photon (Rosenbluth plot) with a 3 to 4% error. In addition the longitudinal-transverse interference term has been determined measuring the right-left asymmetry with an accuracy of 3%. The experimental data are compared to model calculations, and the sensitivity of the results to the axial and pion formfactors is discussed.
Precise measurements of the neutron magnetic form factor
Abstract The neutron magnetic form factor Gmn has been determined via a measurement of the ratio of cross sections D(e,e′n) and D(e,e′p). The absolute detection efficiency of the neutron detector was measured with high accuracy using tagged neutrons produced from H(n,p)n elastic scattering by means of a high intensity neutron beam. This approach minimizes the model dependence and improves upon the weakest points of previous experiments. Data in the range q2=0.2–0.8 (GeV/c)2 with uncertainties of
Measurement ofN14(γ, π+)C14(g.s.)at 200 MeV: A Test of the Distorted-Wave Impulse Approximation for Charged-Pion Photoproduction below theΔ(1232)Resonance
Differential cross sections for $^{14}\mathrm{N}(\ensuremath{\gamma}, {\ensuremath{\pi}}^{+})^{14}\mathrm{C}(\mathrm{g}.\mathrm{s}.)$ (${0}^{+}$1) have been measured for an incident photon energy ${E}_{\ensuremath{\gamma}}=200$ MeV at laboratory angles of 45\ifmmode^\circ\else\textdegree\fi{}, 60\ifmmode^\circ\else\textdegree\fi{}, 75\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, 120\ifmmode^\circ\else\textdegree\fi{}, and 140\ifmmode^\circ\else\textdegree\fi{}. Momentum-space distorted-wave-impulse-approximation calculations, using a complete treatment of a one-body pion-photoproduction operator, are found to be in excellent agreement with the experimental data…
The photon tagging facility at the Saskatchewan Accelerator Laboratory
Abstract A photon tagging facility has been constructed for use with the c.w. electron beam at the Saskatchewan Accelerator Laboratory (SAL). The facility consists of a “clam-shell” type magnetic spectrometer with a 62 channel plastic scintillator focal plane detector allowing a post-bremsstrahlung electron energy resolution of 1%. Specialized focal plane and coincidence electronics have been designed and constructed at SAL and allows experiments to be performed with average tagged photon rates of greater than 1 × 108/s.
Investigation of short-range nucleon-nucleon correlations using the reaction in close to 4π geometry
Abstract Two-proton correlations were studied in close to 4 π geometry using the reaction 12 C (e,e′pp) . The beam energy was 705 MeV, the energy transfer 225 MeV, and the three-momentum transfer 412 MeV/c. The electrons were observed in a large-acceptance magnetic spectrometer in coincidence with protons observed in a BGO crystal ball. Missing energy and momentum, relative momentum and angular distributions were derived and compared with a factorized two-nucleon emission model. Soft-core correlation functions are favoured by the data.
The three-spectrometer facility at the Mainz microtron MAMI
Abstract A set-up of three high-resolution magnetic spectrometers, for simplicity named A, B and C, has been built as the central facility for the precise determination of double and triple coincidence cross sections of hadron knock-out and meson production through the scattering of electrons at the Mainz microtron MAMI. The spectrometers A and C with point-to-point optics in the dispersive plane and parallel-to-point optics in the non-dispersive plane have a solid angle of 28 msr and a momentum acceptance of 20 and 25%, respectively. They each consist of a quadrupole, a sextupole and two dipole magnets, reaching maximum momenta of 735 and 550 MeV/c, respectively. The spectrometer B has a s…
Model-independent separation of structure functions over an extended kinematical region
A method for the separation of structure functions in (e, e′ p) experiments is proposed, which is an extension of the traditional Rosenbluth-type techniques of [1,2]. In our approach, we use a very flexible Ansatz to describe the structure functions within an extended kinematical regionG and determine its free parameters with a x2 minimization. The procedure is tested by pseudo data (12C(e, e′p)11Bg.s.) in the quasi-free region.
Pion electroproduction in the 3He(e,é π+)3H reaction at intermediate energies
Abstract The differential coincident pion electroproduction cross section in the 3 He(e,e π + ) 3 H reaction has been measured with high resolution with the three-spectrometer set-up at the Mainz Microtron (MAMI) electron accelerator. Measurements were performed at the four incident energies E 0 = 855, 675, 600, and 555 MeV at fixed four-momentum transfer Q 2 = 0.045 GeV 2 , with the pions detected in parallel kinematics. This enables a separation of the measured cross section into the transverse and longitudinal structure functions by means of the Rosenbluth method. The experimental data are compared to model calculations, in which the elementary pion production amplitude includes the stan…
Large recoil momenta in the D(e,e′p)n reaction
Abstract The D(e,e′p)n reaction cross section has been measured for recoil momenta ranging from 17 MeV/c up to 950 MeV/c at momentum transfers between 600 MeV/c and 700 MeV/c. At recoil momenta above 400 MeV/c, the gross features of the cross section are only reproduced if virtual nucleon excitations are included in the calculations.
High-momentum components in the 1p orbitals of 16O
Abstract We have investigated that part of the proton momentum distribution of 16O that is linked through the (e, e′p) reaction to low-lying discrete states in 15N. The MAMI facility with its new generation of 100%-duty-cycle electron accelerator has allowed to cover in this experiment the previously not accessible momentum range of 265
N14(γ,π+)14Cgsat photon energies of 230, 260, and 320 MeV
The pion angular distribution for {sup 14}N({gamma},{pi}{sup +}){sup 14}C{sub g.s.} has been measured at photon energies of 230 and 260 MeV. These data are consistent with the trend of our earlier data at 200 and 320 MeV. Additional forward angle data were obtained at 320 MeV. The results are compared to several calculations based on the distorted-wave impulse approximation and on the delta-hole model. The data are best fit by the calculations of Tiator {ital et} {ital al}. which use the delta-hole model in the resonance channel. These calculations fit the 230 MeV data well and underestimate the 260 and 320 MeV data by about 25%.
Spectroscopy ofLiΛ9by electroproduction
Background: In the absence of accurate data on the free two-body hyperon-nucleon interaction, the spectra of hypernuclei provides information on the details of the effective hyperon-nucleon interaction.Purpose: To obtain a high-resolution binding-energy spectrum for the ${}^{9}\mathrm{Be}(e,{e}^{\ensuremath{'}}{K}^{+})_{\ensuremath{\Lambda}}^{9}\mathrm{Li}$ reaction.Method: Electroproduction of the hypernucleus $_{\ensuremath{\Lambda}}^{9}\mathrm{Li}$ has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a $^{9}\mathrm{Be}$ target. In order to increase the counting rate and to provide unambiguous kaon identification, two superconducting septum magn…
Forward-AngleH3e(e,e′π±)Coincident Electroproduction and the Search forΔ's in the Ground State ofH3e
Forward-angle coincident electroproduction cross sections of charged pions from ${}^{3}\mathrm{He}$ have been measured at electron energies ${E}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}855$, 675, 600, and 555 MeV. The overall features of the data for energy transfers of $\ensuremath{\omega}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}370$ to 430 MeV with pions detected along the momentum transfer axis are reproduced in terms of a microscopic model, including pole terms, final state rescattering and produced and preformed $\ensuremath{\Delta}$ resonances. Separation of the cross section into its longitudinal and transverse parts was performed at ${Q}^{2}\phantom{\rule{0ex…