Search results for "momentum transfer"
showing 10 items of 134 documents
Form factors for semileptonic, nonleptonic, and rareB(Bs)meson decays
2012
We provide new values for the model parameters of the covariant constituent quark model (with built–in infrared confinement) in the meson sector by a fit to the leptonic decay constants and a number of electromagnetic decays. We then evaluate, in a parameter-free way, the form factors of the B(Bs) ! P(V ) transitions in the full kinematical region of momentum transfer. As an application of our results we calculate the widths of the nonleptonic Bs-decays into Ds D + , D � s D + s +D s D � + s
Consistent Treatment of Relativistic Effects in Electrodisintegration of the Deuteron
1996
The influence of relativistic contributions to deuteron electrodisintegration is systematically studied in various kinematic regions of energy and momentum transfer. As theoretical framework the equation-of-motion and the unitarily equivalent S-matrix approaches are used. In a (p/M)-expansion, all leading order relativistic $\pi$-exchange contributions consistent with the Bonn OBEPQ model are included. In addition, static heavy meson exchange currents including boost terms, $\gamma\pi\rho/\omega$-currents, and $\Delta$-isobar contributions are considered. Sizeable effects from the various relativistic two-body contributions, mainly from $\pi$-exchange, have been found in inclusive form fact…
Meson exchange currents in theHe3(γ,π+)3H reaction
1996
We generate meson exchange currents mechanisms for the (\ensuremath{\gamma},${\mathrm{\ensuremath{\pi}}}^{+}$) reaction in nuclei starting from the \ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}N amplitude on one nucleon and allowing one of the pions to be produced off shell and be absorbed by a second nucleon. Detailed calculations are presented for the \ensuremath{\gamma} $^{3}\mathrm{\ensuremath{\pi}}^{+3}$H reaction, where we show that the cross section at large momentum transfers is dominated by these mechanisms, helping improve the agreement with experimental data. It is also shown that the meson exchange currents produce important effects in the photon a…
Renormalization of the weak hadronic current in the nuclear medium
2000
The renormalization of the weak charge-changing hadronic current as a function of the reaction energy release is studied at the nucleonic level. We have calculated the average quenching factors for each type of current (vector, axial vector and induced pseudoscalar). The obtained quenching in the axial vector part is, at zero momentum transfer, 19% for the sd shell and 23% in the fp shell. We have extended the calculations also to heavier systems such as $^{56}$Ni and $^{100}$Sn, where we obtain stronger quenchings, 44% and 59%, respectively. Gamow--Teller type transitions are discussed, along with the higher order matrix elements. The quenching factors are constant up to roughly 60 MeV mom…
Meson exchange currents in kaon scattering on the lightest nuclei
1997
The K^+ scattering on the lightest nuclei, d, 3He and 4He is studied in the framework of multiple scattering theory. Effects from MEC tied to the K^+N-->KNpi reaction are evaluated. We found that at momentum transfers Q^2<0.5 (GeV/c)^2 contributions from MEC are much smaller than kaon rescattering corrections. This makes the conventional multiple scattering picture a reliable tool to study these reactions in this kinematical domain and to extract the K^+n scattering amplitude from the K^+d data. At larger transferred momentum MEC can become more relevant.
The first dedicated Virtual Compton Scattering experiment at MAMI
1999
We measured the absolute cross sections for photon electro-production off the proton, ep to ep gamma , with the high resolution spectrometers at MAMI at momentum transfer q=600 MeV/c and photon polarization epsilon =0.62. We covered the momentum range for the outgoing real photon q'=33/111 MeV/c. From the extracted virtual Compton scattering amplitude we deduce values for two structure functions related to the generalized polarizabilities of the proton.
Violation of Siegert's theorem in the electro-excitation of the (1−, T = 0)-level at 7.117 MeV in 16O
1989
Abstract Cross sections are measured for the electro-excitation of the first 1−-level in 16O at extremely small momentum transfer. The model-independent interpretation with a Fourier-Bessel expansion of the transition charge density reveals an incompatibility with the life-time measurement at the photon point, i.e. a violation of Siegert's theorem.
Coherent pion production induced by protons and light ions
1995
Abstract We study coherent pion production by means of the (p,n) and (He,t) reactions on different nuclei and at different energies of the projectile. Energy and angular distributions are calculated. The angular distributions are rather narrow along the direction of the momentum transfer, particularly in heavy nuclei. The reaction is sensitive to the longitudinal part of the elementary NN→NΔ interaction. It also provides a new tool to obtain information on the pion-nuclear interaction, complementary to that offered by reactions with real pions.
Lower bound on the proton charge radius from electron scattering data
2019
The proton charge-radius determinations from the electromagnetic form-factor measurements in electron-proton scattering require an extrapolation to zero momentum transfer ($Q^2=0$) which is prone to model-dependent assumptions. We show that the data at finite momentum transfer can be used to establish a rigorous lower bound on the proton charge radius. Using the available $ep$ data at low $Q^2$, we obtain $R_E > 0.850(1)$ fm as the lower bound on the proton radius. This reaffirms the discrepancy between the $ep$ and muonic-hydrogen values, while bypassing the model-dependent assumptions that go into the fitting and extrapolation of the $ep$ data.
Linear response theory in asymmetric nuclear matter for Skyrme functionals including spin-orbit and tensor terms
2014
The formalism of linear response theory for a Skyrme functional including spin-orbit and tensor terms is generalized to the case of infinite nuclear matter with arbitrary isospin asymmetry. Response functions are obtained by solving an algebraic system of equations, which is explicitly given. Spin-isospin strength functions are analyzed varying the conditions of density, momentum transfer, asymmetry, and temperature. The presence of instabilities, including the spinodal one, is studied by means of the static susceptibility.