An experimental study of the {sup 16}O(e,e{sup '}K{sup +}){sub L}AMBDA{sup 16}N reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a ...simultaneous measurement of the p(e,e{sup '}K{sup +})LAMBDA,SIGMA{sup 0} exclusive reactions and a precise calibration of the energy scale. A ground-state binding energy of 13.76+-0.16 MeV was obtained for {sub L}AMBDA{sup 16}N with better precision than previous measurements on the mirror hypernucleus {sub L}AMBDA{sup 16}O. Precise energies have been determined for peaks arising from a LAMBDA in s and p orbits coupled to the p{sub 1/2} and p{sub 3/2} hole states of the {sup 15}N core nucleus.
A large data set of charged-pion (pi+/-) electroproduction from both hydrogen and deuterium targets has been obtained spanning the low-energy residual-mass region. These data conclusively show the ...onset of the quark-hadron duality phenomenon, as predicted for high-energy hadron electroproduction. We construct several ratios from these data to exhibit the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark-->pion production mechanisms.
We have studied the quasielastic He-3(e,e(')p)H-2 reaction in perpendicular coplanar kinematics, with the energy and the momentum transferred by the electron fixed at 840 MeV and 1502 MeV/c, ...respectively. The He-3(e,e(')p)H-2 cross section was measured for missing momenta up to 1000 MeV/c, while the A(TL) asymmetry was extracted for missing momenta up to 660 MeV/c. For missing momenta up to 150 MeV/c, the cross section is described by variational calculations using modern He-3 wave functions. For missing momenta from 150 to 750 MeV/c, strong final-state interaction effects are observed. Near 1000 MeV/c, the experimental cross section is more than an order of magnitude larger than predicted by available theories. The A(TL) asymmetry displays characteristic features of broken factorization with a structure that is similar to that generated by available models.
Virtual Compton scattering, i.e. the exclusive reaction
γ
∗p → γ′p′
with
γ
∗
denoting a virtual photon, provides new insights on the internal structure of the proton. Below
π
0 production threshold, ...this experiment measures the generalized polarizabilities of the proton as defined by Guichon
et al 1, 2 and Drechsel
et al 3. These new electromagnetic observables, functions of
Q
2, enlarge the concept of electric (α0 and magnetic (β) polarizabilities in Real Compton Scattering (
Q
2=0) 4.
The first VCS experiment 5 of this kind was measured at the three spectrometer facility at the Mainz Microtron MAMI for
Q
2=0.33 GeV
2 and we present in this paper the preliminary results.
The d(e,e'p) cross section at a momentum transfer of 3.5 (GeV/c)^2 was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a function ...of the neutron recoil angle theta_nq and to extract missing momentum distributions for fixed values of theta_nq up to 0.55 GeV/c. In the region of 35 (deg) <= theta_nq <= 45 (deg) recent calculations, which predict that final state interactions are small, agree reasonably well with the experimental data. Therefore these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electro-disintegration.
Spectroscopy of Li Λ9 by electroproduction Urciuoli, G. M.; Cusanno, F.; Marrone, S. ...
Physical review. C, Nuclear physics,
03/2015, Letnik:
91, Številka:
3
Journal Article
Odprti dostop
Background: In the absence of accurate data on the free two-body hyperon-nucleon interaction, the spectra of hypernuclei can provide information on the details of the effective hyperon-nucleon ...interaction. Purpose: To obtain a high-resolution spectrum for the 9Be(e,e'K+)9ΛLi reaction. Method: Electroproduction of the hypernucleus 9ΛLi has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a 9Be target. In order to increase the counting rate and to provide unambiguous kaon identification, two superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A standard equipment. Results: The cross section to low-lying states of 9ΛLi is concentrated within 3 MeV of the ground state and can be fitted with four peaks. The positions of the doublets agree with theory while a disagreement could exist with respect to the relative strengths of the peaks in the doublets. A Λ separation energy, BΛ, of 8.36±0.08 (stat.) ±0.08 (syst.) MeV was measured, in agreement with an earlier experiment.
Inclusive electron-proton and electron-deuteron inelastic cross sections have been measured at Jefferson Lab (JLab) in the resonance region, at large Bjorken x, up to 0.92, and four-momentum transfer ...squared Q{sup 2} up to 7.5 GeV{sup 2} in the experiment E00-116. These measurements are used to extend to larger x and Q{sup 2} precision, quantitative, studies of the phenomenon of quark-hadron duality. Our analysis confirms, both globally and locally, the apparent 'violation' of quark-hadron duality previously observed at a Q{sup 2} of 3.5 GeV{sup 2} when resonance data are compared to structure function data created from CTEQ6M and MRST2004 parton distribution functions (PDFs). More importantly, our new data show that this discrepancy saturates by Q{sup 2}{approx}4 GeV{sup 2}, becoming Q{sup 2} independent. This suggests only small violations of Q{sup 2} evolution by contributions from the higher-twist terms in the resonance region that is confirmed by our comparisons to ALEKHIN and ALLM97. We conclude that the unconstrained strength of the CTEQ6M and MRST2004 PDFs at large x is the major source of the disagreement between data and these parametrizations in the kinematic regime we study and that, in view of quark-hadron duality, properly averaged resonance region data could be used in global quantum chromodynamics fits to reduce PDF uncertainties at large x.
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