Lowest- Q2 measurement of the γp → Δ reaction: Probing the pionic contribution

2006

To determine nonspherical angular momentum amplitudes in hadrons at long ranges (low Q^2), data were taken for the p(\vec{e},e'p)\pi^0 reaction in the Delta region at Q^2=0.060 (GeV/c)^2 utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W=1232 MeV are: M_{1+}^{3/2} = (40.33 +/- 0.63_{stat+syst} +/- 0.61_{model}) (10^{-3}/m_{\pi^+}),Re(E_{1+}^{3/2}/M_{1+}^{3/2}) = (-2.28 +/- 0.29_{stat+syst} +/- 0.20_{model})%, and Re(S_{1+}^{3/2}/M_{1+}^{3/2}) = (-4.81 +/- 0.27_{stat+syst} +/- 0.26_{model})%. These disagree with predictions of constituent quark models but are in reaso…

Measurement of the ExclusiveH3e(e,e′p)Reaction Below the Quasielastic Peak

2004

New, high-precision measurements of the 3He(e,ep) reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-ty…

Half-lives, neutron emission probabilities and fission yields of neutron-rich rubidium isotopes in the mass regionA=96 toA=100

1979

Neutron-rich rubidium isotopes were produced by thermal-neutron induced fission of235U and were isolated by surface ionization and mass separation. The new isotope (51 ±17) ms100Rb was identified. The half-lives of the rubidium isotopes with mass numberA=96 toA=100 were measured using neutron multiscaling or gamma multispectrum analysis. Measurements of the delayed-neutron emission probabilityP n of99Rb and of the fission yields of97Rb,98Rb, and99Rb were performed.

Isotope Distributions in the Reaction ofU238withU238

1978

Radiochemically determined cross sections $\ensuremath{\sigma}(Z, A)$ were used to construct charge and mass distributions for the reaction of 1785-MeV $^{238}\mathrm{U}$ ions with thick $^{238}\mathrm{U}$ targets. Fission of the colliding nuclei is found to dominate. For the surviving uraniumlike fragments an enhancement of yields compared to the Kr + U and Xe + U reactions is observed. The formation of heavy actinides is shown to be associated with the low-energy tails of the broad excitation energy distributions in damped collisions.

Measurement of the Recoil Polarization in thep(e→,e′p→)π0Reaction at theΔ(1232)Resonance

2001

The recoil proton polarization has been measured in the $p(\stackrel{\ensuremath{\rightarrow}}{e}{,e}^{\ensuremath{'}}\stackrel{\ensuremath{\rightarrow}}{p}){\ensuremath{\pi}}^{0}$ reaction in parallel kinematics around $W\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1232\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$, ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.121\phantom{\rule{0ex}{0ex}}(\mathrm{GeV}/c{)}^{2}$, and $\ensuremath{\epsilon}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.718$ using the polarized cw electron beam of the Mainz Microtron. All three proton polarization components, ${P}_{x}/{P}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-…

Determination of quadrupole strengths in the γ∗p→Δ(1232) transition at Q2=0.20(GeV/c)2

2007

Abstract We report new precise p ( e → , e ′ p ) π 0 measurements at the peak of the Δ + ( 1232 ) resonance at Q 2 = 0.20 ( GeV / c ) 2 performed at the Mainz Microtron (MAMI). The new data are sensitive to both the electric (E2) and the Coulomb (C2) quadrupole amplitudes of the γ ∗ N → Δ transition. They yield precise quadrupole to dipole amplitude ratios: CMR = ( − 5.09 ± 0.28 stat + sys ± 0.30 model ) % and EMR = ( − 1.96 ± 0.68 stat + sys ± 0.41 model ) % for M 1 + 3 / 2 = ( 39.57 ± 0.75 stat + sys ± 0.40 model ) ( 10 −3 / m π + ) . The new results are in disagreement with Constituent Quark Model predictions and in qualitative agreement with models that account for mesonic contributions…

The horizontal drift chambers for the focal plane proton-polarimeter of the 3-spectrometer setup at MAMI

2002

Abstract Large-area horizontal drift chambers have been built for use in a proton polarimeter. A gas mixture of 20% argon and 80% ethane is used. The left–right assignment is achieved by measuring the difference of the signals induced on neighboring potential wires. A spatial resolution of 300 μm is achieved.

Measurement of GEp/GMp via polarization transfer at Q2 = 0.4 GeV /c2

2001

The polarization transfer from longitudinally polarized electrons to protons in the elastic scattering p( e, e' p) has been measured around Q2 = 0.4 (GeV/c)2 with the three-spectrometer facility at the Mainz microtron MAMI. From this polarization transfer the ratio G Ep/(G Mp/μp) has been determined. The ratio is found to be slightly less than unity in agreement with recent results from other laboratories and from the Rosenbluth separation of cross-sections measured with unpolarized electrons.

Polarization transfer in the 4HeH reaction

2001

Abstract Polarization transfer in the 4He ( e → ,e′ p → ) 3 H reaction at a Q2 of 0.4 (GeV/c)2 was measured at the Mainz Microtron MAMI. The ratio of the transverse to the longitudinal polarization components of the ejected protons was compared with the same ratio for elastic ep scattering. The results are consistent with a recent fully relativistic calculation which includes a predicted medium modification of the proton form factor based on a quark–meson coupling model.

Final State Interaction Effects in 3He(e ,e'p)

2003

Abstract Asymmetries in quasi-elastic 3 He ( e → , e ′ p ) have been measured at a momentum transfer of 0.67 (GeV/ c ) 2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3 He -ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.

Neutral Pion Threshold Production atQ2=0.05GeV2/c2and Chiral Perturbation Theory

2001

New data are presented on the $p({e,e}^{\ensuremath{'}}p){\ensuremath{\pi}}^{0}$ reaction at threshold at a four-momentum transfer of ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.05{\mathrm{GeV}}^{2}{/c}^{2}$. The data were taken with the three-spectrometer setup of the A1 Collaboration at the Mainz Microtron MAMI. The complete center of mass solid angle was covered up to a center of mass energy of 4 MeV above threshold. Combined with measurements at three different values of the virtual photon polarization $\ensuremath{\epsilon}$, the structure functions ${\ensuremath{\sigma}}_{T}$, ${\ensuremath{\sigma}}_{L}$, ${\ensuremath{\sigma}}_{\mathrm{TT}}$, and ${\ensuremath{\sigma…

Abstracts of scientific papers second international symposium on central nervous system monitoring

1990

Measurement of the Beam-Helicity Asymmetry in thep(e→,e′p)π0Reaction at the Energy of theΔ(1232)Resonance

2002

In a p((e) over right arrow, e' p)pi(0) out-of-plane coincidence experiment at the three-spectrometer setup of the Mainz Microtron MAMI, the beam-helicity asymmetry has been precisely measured around the energy of the Delta(1232) resonance and Q(2) = 0.2(GeV/c)(2). The results are in disagreement with three up-to-date model calculations. This is interpreted as a lack of understanding of the nonresonant background, which in dynamical models is related to the pion cloud.

Charge-Asymmetry Equilibration in the Reaction ofXe129,132,136withAu197near the Interaction Barrier

1977

Neutron-proton population ratios for quasielastic and inelastic processes in the reactions of 761-MeV $^{129}\mathrm{Xe}$, 769-MeV $^{132}\mathrm{Xe}$, and 795-MeV $^{136}\mathrm{Xe}$ ions with thick $^{197}\mathrm{Au}$ targets were determined radiochemically. Completely relaxed $\frac{N}{Z}$ ratios are observed for damped collisions involving the transfer of $\ensuremath{\Delta}Zg~1$ charge units. The limiting condition $\ensuremath{\Delta}Z\ensuremath{\approx}1$ corresponds to a characteristic time of the order of ${10}^{\ensuremath{-}22}$ sec which indicates the absence of dissipative forces in the equilibration of the charge-asymmetry mode.

Evidence for narrow Δ0(1232) states in the 12 C(e,e'pπ−}11 C Reaction

1999

The reaction 12C(e,e'Δ0)11C →12C(e,e'pπ−)11C was investigated at the Mainz Microtron MAMI in a triple coincidence measurement using the three spectrometer setup of the A1 Collaboration. The good missing mass resolution of σm= 0.27 MeV/c2 allowed to select the events belonging to the ground state of 11C. Cutting on these events the excitation energy spectra of 12CΔ0 show evidence for two peaks of about 4 MeV width (FWHM) at 282 MeV and 296 MeV with a significance of about 4.5 standard deviations. The peaks are interpreted in a simple weak coupling model as bound Δ0 states in 12CΔ0.

"Table 1" of "Lowest Q**2 measurement of the gamma* p --> delta reaction: Probing the pionic contribution."

2006

Measured value of SIG(C=T) + EPS*SIG(C=L) as a function of the pion angle relative to the virtual photon direction.

"Table 2" of "Polarization transfer in the He-4(e(pol.),e' p(pol.)H-3 reaction."

2004

No description provided.

"Table 5" of "Lowest Q**2 measurement of the gamma* p --> delta reaction: Probing the pionic contribution."

2006

Unpolarized cross sections as a function of the azimuthal pion angle relative to the virtual photon direction from which the extracted results were taken (to be published).

"Table 1" of "Polarization transfer in the He-4(e(pol.),e' p(pol.)H-3 reaction."

2004

No description provided.

"Table 3" of "Lowest Q**2 measurement of the gamma* p --> delta reaction: Probing the pionic contribution."

2006

Measured value of SIG(C=LT) as a function of the pion angle relative to thevirtual photon direction.

"Table 4" of "Lowest Q**2 measurement of the gamma* p --> delta reaction: Probing the pionic contribution."

2006

Measured value of SIG(C=LTP) as a function of the pion angle relative to the virtual photon direction.

"Table 2" of "Lowest Q**2 measurement of the gamma* p --> delta reaction: Probing the pionic contribution."

2006

Measured value of SIG(C=TT) as a function of the pion angle relative to thevirtual photon direction.

"Table 7" of "Lowest Q**2 measurement of the gamma* p --> delta reaction: Probing the pionic contribution."

2006

Unpolarized cross sections as a function of the azimuthal pion angle relative to the virtual photon direction from which the extracted results were taken (to be published).

"Table 6" of "Lowest Q**2 measurement of the gamma* p --> delta reaction: Probing the pionic contribution."

2006

Unpolarized cross sections as a function of the azimuthal pion angle relative to the virtual photon direction from which the extracted results were taken (to be published).