Search results for "Nucleon"
showing 10 items of 1041 documents
Many-body approach to the inclusive (e,e ') reaction from the quasielastic to the Delta excitation region
1997
We have performed a many body calculation of the inclusive (e,e') cross section which runs over the three traditional regions at intermediate energies: the quasielastic peak, the dip region and the delta region. The longitudinal and transverse response functions in the quasielastic peak have also been evaluated. Traditional effects like polarization, meson exchange currents, final state interaction and delta renormalization in the nuclear medium have been included. Meson exchange currents are generated from a model of pion electroproduction on the nucleon which reproduces accurately the experimental data. The inclusive cross section accounts for 1N,2N,3N mechanisms of virtual photon absorpt…
Measurement of the polarization of the Ξ0 (Ξ0¯) hyperon beam by the NA48/1 experiment
2009
Abstract A total of 368 415 Ξ 0 → Λ π 0 and 31 171 Ξ 0 ¯ → Λ ¯ π 0 were selected from data recorded in the NA48/1 experiment during 2002 data taking. From this sample, the polarization of Ξ 0 and Ξ 0 ¯ hyperons was measured to be P Ξ 0 = − 0.102 ± 0.012 (stat) ± 0.008 (syst) and P Ξ 0 ¯ = − 0.01 ± 0.04 (stat) ± 0.008 (syst) . The dependence of P Ξ 0 on the Ξ 0 transverse momentum with respect to the primary proton beam is also presented. With the same data sample, the ratio of Ξ 0 ¯ and Ξ 0 fluxes in proton collisions at 400 GeV / c on a beryllium target was measured.
Theoretical study of incoherent phi photoproduction on a deuteron target
2012
We study the photoproduction of phi mesons in deuteron, paying attention to the modification of the cross section from bound protons to the free ones with the aim of comparing with recent results at LEPS. For this purpose we take into account Fermi motion in single scattering and rescattering of the phi to account for phi absorption on a second nucleon as well as the rescattering of the proton. We find that the contribution of the double scattering is much smaller than the typical cross section of gamma p to phi p in free space, which implies a very small screening of the phi production in deuteron. The contribution from the proton rescattering, on the other hand, is found to be not negligi…
C(,pn) photon asymmetry for Eγ=180–340 MeV
1999
The photon asymmetry (Σ) of the 12C(,pn) reaction has been measured using linearly polarised tagged photons at the Mainz microtron MAMI for Eγ=180–340 MeV. The data have been analysed in separate missing energy (Em) regions corresponding to the ejection of nucleons from (1p)2 and (1p)(1s) shells. The measured Σ values for both Em regions are smaller in magnitude than corresponding 2H data, but the (1p)2 results have a similar Eγ dependence. Calculations of direct two-nucleon emission overestimate the magnitude of Σ at all photon energies.
Probing short-range nucleon-nucleon correlations with virtual photons at MAMI
2000
Abstract Nucleon-nucleon correlations were studied in two (e, e′pp) experiments. The first one, on 12C, was performed in close to 4π geometry at Ebeam = 705 MeV, ω = 225 MeV, and q = 412 MeV/c. The electrons were observed in a large-acceptance magnetic spectrometer in coincidence with protons detected in a BGO crystal ball. Missing energy and momentum, relative momentum and angular distributions were derived and compared with a facorised two-nucleon emision model. A G-matrix correlation function is favoured by the data. The second experiment was a high resolution study of the reaction 16O(e, e′pp)14C in super-parallel kinematics. Three magnetic spectrometers were used in coincidence at Ebea…
Transverse momentum of j/$\psi$ produced in oxygen-uranium collisions at 200 GeV per nucleon
1990
Abstract The study of the J ψ transverse momentum distribution in oxygen-uranium reactions at 200 GeV/nucleon shows that 〈PT〉 and 〈PT2〉 increase with the transverse energy of the reaction. Muon pairs in the mass continuum do not exhibit the same behaviour. The comparison of the J ψ production rates in central and peripheral collisions shows a significant diminution for low PT central events.
Longitudinal double-spin asymmetry A1p and spin-dependent structure function g1p of the proton at small values of x and Q2
2018
Abstract We present a precise measurement of the proton longitudinal double-spin asymmetry A 1 p and the proton spin-dependent structure function g 1 p at photon virtualities 0.006 ( GeV / c ) 2 Q 2 1 ( GeV / c ) 2 in the Bjorken x range of 4 × 10 − 5 x 4 × 10 − 2 . The results are based on data collected by the COMPASS Collaboration at CERN using muon beam energies of 160 GeV and 200 GeV . The statistical precision is more than tenfold better than that of the previous measurement in this region. In the whole range of x , the measured values of A 1 p and g 1 p are found to be positive. It is for the first time that spin effects are found at such low values of x .
He-8 - He-6: a comparative study of electromagnetic fragmentation reactions
2002
14 pages, 1 table, 2 figures.-- PACS nrs.:27.20.+n; 24.70.+.-- Available online Oct 8, 2001.
Finite-size effects and collective vibrations in the inner crust of neutron stars
2010
We study the linear response of the inner crust of neutron stars within the Random Phase Approximation, employing a Skyrme-type interaction as effective interaction. We adopt the Wigner-Seitz approximation, and consider a single unit cell of the Coulomb lattice which constitutes the inner crust, with a nucleus at its center, surrounded by a sea of free neutrons. With the use of an appropriate operator, it is possible to analyze in detail the properties of the vibrations of the surface of the nucleus and their interaction with the modes of the sea of free neutrons, and to investigate the role of shell effects and of resonant states.
The generalized Gerasimov–Drell–Hearn sum rule for deuteron electrodisintegration
2004
The generalized Gerasimov-Drell-Hearn sum rule $I^{GDH}_{\gamma^*d}(Q^2)$ for deuteron electrodisintegration $d(e,e')np$ as function of the squared four-momentum transfer $Q^2$ is evaluated by explicit integration. The calculation is based on a conventional nonrelativistic framework using a realistic $NN$-potential and including contributions from meson exchange currents, isobar configurations and leading order relativistic terms. Good convergence is achieved. The prominent feature is a deep negative minimum, $I_{\gamma^* d}^{GDH}=-9.5$ mb, at low $Q^2\approx 0.2$ fm$^{-2}$ which is almost exclusively driven by the nucleon isovector anomalous magnetic moment contribution to the magnetic dip…