Narrow Results

We derive generic formulas for the polarization density matrix of leptons produced in νN and collisions and briefly consider some important particular cases. Next we employ the general formalism in order to include the final lepton mass and spin into the popular model by Rein and Sehgal for single pion neutrinoproduction.

A numerical analysis of the polarization vector of τ's produced through quasielastic ν_τ and interactions with nucleons is given with two models for vector electromagnetic form factors of proton and neutron. The impact of G parity violating axial and vector second-class currents is investigated by applying a simple heuristic model for the induced scalar and tensor form factors.

We review some recent results obtained in the analysis of two-dimensional quantum field theories by means of semiclassical techniques, which generalize methods introduced during the '70s by Dashen, Hasllacher and Neveu and by Goldstone and Jackiw. The approach is best suited to deal with quantum field theories characterized by a nonlinear interaction potential with different degenerate minima, that generates kink excitations of large mass in the small coupling regime. Under these circumstances, although the results obtained are based on a small coupling assumption, they are nevertheless nonperturbative, since the kink backgrounds around which the semiclassical expansion is performed are nonperturbative too. We will discuss the efficacy of the semiclassical method as a tool to control analytically spectrum and finite-size effects in these theories.

Recently an experiment at Jefferson Lab has measured the proton form factor ratio, , down to Q² ~ 0.3 GeV² with unprecedented precision. Based on the results from this experiment, a re-analysis was carried out for the world data on proton form factors, and a new result was extracted for the proton charge radius. The new result is consistent with published CODATA results and is at odds with the new muonic hydrogen measurement at PSI.

We present the results of the new measurement, as well as discuss an upcoming experiment to measure the form factor ratio down to even lower Q².

We study a new contribution, which is a tree-level transition from long-distance dynamics, to K⁺→π⁺ℓ⁺ℓ^- (ℓ = e, μ) decays. It is found that this tree-diagram can be calculated unambiguously and would generate the additional contribution to the vector, axial-vector, scalar and pseudoscalar form factor of the decay. Our analysis shows that these form factors are strongly suppressed and this long-distance contribution is well under control.

We illustrate the powerfulness of Padé approximants (PAs) as a summation method and explore one of their extensions, the so-called quadratic approximant (QAs), to access both space- and (low-energy) time-like (TL) regions. As an introductory and pedagogical exercise, the function $\frac{1}{z}\mathrm{\text{ln}}(1+z)$ is approximated by both kind of approximants. Then, PAs are applied to predict pseudoscalar meson Dalitz decays and to extract $V_{ub}$ from the semileptonic $B\to \pi \ell {\nu }_{\ell }$ decays. Finally, the $\pi$ vector form factor in the TL region is explored using QAs.

The form factors of the rare ${\mathrm{\Lambda }}_b\to n{l}^{+}{l}^{-}$ decays are calculated in the framework of the relativistic quark–diquark picture of baryons with the consistent account of the relativistic effects. Their momentum transfer squared dependence is determined explicitly in the whole accessible kinematical range. The decay branching fractions, forward–backward asymmetries and the fractions of longitudinally polarized dileptons are determined. The branching fraction of the rare ${\mathrm{\Lambda }}_b\to n{\mu }^{+}{\mu }^{-}$ decay are found to be $\mathrm{\text{Br}}({\mathrm{\Lambda }}_b\to n{\mu }^{+}{\mu }^{-})=(3.75\pm 0.38)\times 10^{-8}$ and thus could be measured at the LHC. Prediction for the branching fraction of the rare radiative ${\mathrm{\Lambda }}_b\to n\gamma$ decay is also given.

By using the minimal extension of the standard model and considering the general relativistic effects near the surface of a static neutron star in the presence of quintessence fields, we drive analytical expressions for the cross-section and energy deposition rate of the process (${\nu }_e+{\overline{\nu }}_e\to (W,Z,\gamma )\to e^{-}+e^{+}$). We have also obtained the ratio of energy deposition to total Newtonian energy deposition ($\dot{Q}∕{\dot{Q}}_{\mathrm{\text{Newt}}}$). We have displayed that the contributions of the electron neutrino’s charge radius are more effective than the dipole moment in this process. The obtained solutions indicate that the contribution of the electron neutrino charge radius changes the results approximately (1–5)% depending on the $\frac{R}{M}$ value of the star.

In this paper, we have analyzed the proton form factor data by using a number of phenomenological parametrizations (models) and extracting the proton electric and magnetic radii. To this end, we performed a global fit to all available form factor data, with the virtual photon momentum squared $Q^2$ from $0.0002$ to nearly 10GeV² for electric form factor and from $0.015$ to 31GeV² for magnetic one. Special attention was given to the small structure shown by the form factor data near $Q^2=0.2$GeV². It was found that different models yield different structures with different numbers of minimum at this kinematics. Since the slope of form factor in the limit of $Q^2\to 0$ is influenced by this structure, the extracted proton radii are consequently different for different models. Our finding recommends that future experiments should focus on this kinematics instead of low $Q^2$. Experimental data with accuracies comparable to those of the latest data at low $Q^2$ would clearly help to clarify the effect of this structure on the proton charge radius. Interestingly, most of the extracted proton charge radii were found to be closer to the value obtained from the muonic hydrogen atom spectroscopy.

We look at the mass spectra of the $D^{\pm }$, $D^{\pm \ast }$, $D_s^{\pm \ast }$, $D_s^{\pm }$, $B^{\pm }$, $B^{\pm \ast }$, $B_s^{0\ast }$, $B_s^0$, $B_c^{\pm \ast }$, $B_c^{\pm }$, $\rho$, $\pi$, and $\omega$ mesons using a relativistic square root potential. Before looking at the mass spectra, we have to figure out the model parameters, which are $U_0=-1.115$GeV and $a=0.885$GeV. The calculated result of $D^{\pm }(1.861\mathrm{\text{GeV}})$, $D^{\pm \ast }(2.010\mathrm{\text{GeV}})$, $D_s^{\pm }(1.903\mathrm{\text{GeV}})$, $D_s^{\ast \pm }(2.112\mathrm{\text{GeV}})$, $B^{\pm }(5.264\mathrm{\text{GeV}})$, $B^{\pm \ast }(5.327\mathrm{\text{GeV}})$, $B_s^0(5.345\mathrm{\text{GeV}})$, $B_s^{0\ast }(5.423\mathrm{\text{GeV}})$, $B_C^{\pm }(5.956\mathrm{\text{GeV}})$, $B_C^{\pm \ast }(6.277\mathrm{\text{GeV}})$, findings of this study exhibit a notable concurrence with the experimental observations and pertinent theoretical projections. We estimate the decay constant, leptonic decay width, semileptonic decay width, and branching fractions of pseudoscalar and vector mesons, specifically B and D mesons, while keeping the model parameters unchanged. The pseudoscalar decay constants and partial decay widths of “B and D-mesons” reasonably agree with the theoretical predictions, lattice quantum chromodynamics (LQCD) calculations, and experimental data. Moreover, we have efficiently found the values for these mesons’ leptonic decay width and branching fraction, matching the experimental findings and theoretical forecasts. The calculated values of semileptonic decays are $D^0\to {\pi }^{-}{e}^{+}{\nu }_e(2.892\times 10^{-3})$, $D^{+}\to {\pi }^0{e}^{+}{\nu }_e(3.669\times 10^{-3})$, $D^{+}\to {\rho }^0{e}^{+}{\nu }_e(1.659\times 10^{-3})$ and $D^{+}\to {\eta }^{\prime }{e}^{+}{\nu }_e(3.17\times 10^{-4})$, $D_S^{+}\to \phi e^{+}{\nu }_e(2.599\times {10}^{-2})$, $D_S^{+}\to \eta e^{+}{\nu }_e(2.303\times {10}^{-2})$, the proximity of the observed results to experimental and certain theoretical models is evident.

In this paper, we examine the radially excited states of B-mesons: $B^{\pm },B^{\pm \ast },B_s^{0\ast },B_s^0,B_c^{\pm \ast }$ and $B_c^{\pm }$-mesons. Our investigation uses the relativistic independent quark model, which relies on a flavor-independent average potential expressed in the scalar and vector square root form. We make phenomenological fit the potential model parameters, $a=0.885$ GeV, $U_0=-1.070$ GeV for calculation of 1S state of B-mesons: $B^{\pm }(5.272\mathrm{\text{GeV}}),B^{\pm \ast }$ (5.329GeV), $B_s^0(5.360\mathrm{\text{GeV}}),B_s^{0\ast }(5.429\mathrm{\text{GeV}}),B_C^{\pm }(6.0593\mathrm{\text{GeV}}),$ $B_C^{\pm \ast }(6.2604\mathrm{\text{GeV}})$, which aligns well with theoretical and experimental data. For higher radially excited states (2S, 3S, 4S, 5S), we adjust $U_0=-1.344$ GeV while keeping “a” fixed, yielding results consistent with other theoretical models. With these parameters, we compute the pseudoscalar and vector meson decay constants, magnetic transition rates, non-leptonic decay widths, branching fractions, rare decay widths, and semileptonic decay widths and branching fractions of the B-mesons. Our findings show reasonable agreement with lattice QCD calculations, experimental results and other theoretical predictions. For instance, our predicted radiative decay width for $B_c^{\ast }$ (1S) $\to$ $B_c$(1S)$\gamma$, sensitive to the $B_c^{\ast }$ and $B_c$, mass difference, can aid in experimentally determining the $B_c^{\ast }$, mass. Predicted non-leptonic branching fractions, such as $B^0\to D^{-}{\rho }^{+}(6.393\times {10}^{-3}),$ $B^0\to D^{-}{k}^{+}(2.148\times {10}^{-4})$ and $B_S^0\to D_S^{-}{k}^{+}(2.188\times {10}^{-4})$, align with PDG values of $(7.6\pm 1.2)\times {10}^{-3},(2.05\pm 0.08)\times {10}^{-4}$ and $(2.25\pm 0.12)\times {10}^{-4}$. Additionally, we calculate the dileptonic decays of $B^0\to {\mu }^{+}{\mu }^{-}(2.245\times {10}^{-10})$ and $B_S^0\to {\mu }^{+}{\mu }^{-}(3.506\times {10}^{-9})$, which agrees with CMS, LHCb and PDG results. Our semileptonic decays of $B^0$ and $B_S^0$ mesons are computed and compared with PDG results. Furthermore, the results obtained for mass difference, $\mathrm{\Delta }M(0.509{\mathrm{\text{ps}}}^{-1}$ and $17.699{\mathrm{\text{ps}}}^{-1})$, mixing parameters, $x_q(0.771$ and $26.82)$, ${\chi }_q$ (0.1866 and 0.4993) of $B^0-{\bar{B}}^0$ and $B_S^0-{\bar{B}}_S^0$ oscillations, shows good agreement with PDG data, validating our model.

The Fourier transform of generalized parton distribution functions at ξ = 0 describes the distribution of partons in the transverse plane. The physical significance of these impact parameter dependent parton distribution functions is discussed. In particular, it is shown that they satisfy positivity constraints which justify their physical interpretation as a probability density. The generalized parton distribution H is related to impact parameter distribution of unpolarized quarks for an unpolarized nucleon, is related to the distribution of longitudinally polarized quarks in a longitudinally polarized nucleon, and E is related to the distortion of the unpolarized quark distribution in the transverse plane when the nucleon has transverse polarization. The magnitude of the resulting transverse flavor dipole moment can be related to the anomalous magnetic moment for that flavor in a model independent way.

B meson rare decays ( and B → K* γ) are analyzed in the framework of effective field theory of heavy quarks. The semileptonic and penguin type form factors for these decays are calculated by using the light cone sum rules method at the leading order of 1/m_Q expansion. Four exact relations between the two types of form factors are obtained at the leading order of 1/m_Q expansion. In particular, the relations are found to hold for the whole momentum transfer region. We also investigate the validity of the relations resulting from the large energy effective theory based on the general relations obtained in the present approach. The branching ratios of the rare decays are presented and their potential importance for extracting the CKM matrix elements and probing new physics is emphasized.

We suggest a unified description of baryon form factors in terms of a two-component model with an intrinsic q³ structure and a meson cloud, parameterized in terms of vector mesons. We use this model to study the N-Δ form factors. The results are in excellent agreement with data. The N-Δ transition appears to be dominated by coupling to the ρ meson.

JUPITER (Jlab Unified Program to Investigate nuclear Targets and Electroproduction of Resonances) is a new collaboration between the Nuclear Physics electron scattering and High Energy Physics neutrino scattering communities to investigate the structure of nucleons and nuclei with electron and neutrino Beams. The first phase of JUPITER is Hall C experiment E04-001 on Inclusive Electron Scattering from Nuclear Targets. First data run of E04-001 is currently scheduled for January of 2005.

QCD instantons generate non-perturbative spin- and flavor- dependent correlations between light quarks. We report on the results of a series of studies on the contribution of instantons to the electro-weak structure of light hadrons. We show that the Instanton Liquid Model can reproduce the available data on proton and pion form factors at large momentum transfer, and explain the delay of the onset of the perturbative regime in some exclusive reactions. We provide unambiguous evidence that instantons lead to the formation of a deeply bound scalar, color anti-triplet diquark, with a mass of about 450 MeV. The strong attraction in the , scalar diquark channel leads to a quantitative description of non-leptonic decays of hyperons and provides a microscopic dynamical explanation of the Δ I = 1/2 rule.

A systematic calculation for the transition form factors of heavy to light mesons (B, B_s, D, D_s → π, K, η, ρ, K*, ω, ϕ) is carried out by using light-cone sum rules in the framework of heavy quark effective field theory. The heavy quark symmetry at the leading order of 1/m_Q expansion enables us to reduce the independent wave functions and establish interesting relations among form factors. Some relations hold for the whole region of momentum transfer. The meson distribution amplitudes up to twist-4 including the contributions from higher conformal spin partial waves and light meson mass corrections are considered. The CKM matrix elements |V_ub|, |V_cs| and |V_cd| are extracted from some relatively well-measured decay channels. A detailed prediction for the branching ratios of heavy to light meson decays is then presented. The resulting predictions for the semileptonic and radiative decay rates of heavy to light mesons (B, B_s, D, D_s → π, K, η, ρ, K*, ω, ϕ) are found to be compatible with the current experimental data and can be tested by more precise experiments at B-factory, LHCb, BEPCII and CLEOc.

Semileptonic B(B_s, B_c) decays are investigated systematically in the light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on weak form factors with an adequate chiral current correlator, which turns out to be particularly effective to control the pollution by higher twist components of spectator mesons. The result for each channel depends on the distribution amplitude of the the producing meson. The leading twist distribution amplitudes of the related heavy mesons and charmonium are worked out by a model approach in the reasonable way. A practical scenario is suggested to understand the behavior of weak form factors in the whole kinematically accessible ranges. The decay widths and branching ratios are estimated for several B(B_c) decay modes of current interest.

We have performed the tree-level calculations of the eta meson photoproduction on proton for photon laboratory energies between 714 and 1500 MeV. The resonances N(1535), N(1710), N(1650), N(1440) and N(1520) were assumed. The form factors were introduced in the hadron vertices to involve the structure of hadrons. The influence of various form factor recipes was investigated. In order to keep gauge invariance, the appropriate contact term was introduced. The parameters of our model (coupling constants, cutoffs) were fitted to recent experimental data of the cross sections and some polarization observables.

The slope and curvature of Isgur–Wise function for B_c meson is computed in a QCD potential model in two different approaches of choosing the perturbative term of the Cornell potential. Based on heavy quark effective theory the exclusive semileptonic decay rates of B_c meson into the states are exploited. Spin symmetry breaking effects are ignored up to a particular point and the form factors are connected with Isgur–Wise function for other kinematic point since the recoil momentum of from B_c is small due to its heavy mass.