arXiv subjects

I. L. Grach

Publications and source records attributed to I. L. Grach.

9 recordsLinked to original sources

arXiv2008

Heavy baryon spectroscopy in the QCD string model

QCD string model formulated in the framework of the Field Correlator Method (FCM) in QCD is employed to calculate the masses of $Σ_c$, $Ξ_c$ and recently observed at Tevatron $Σ_b$, $Ξ_b$ baryons and their orbital excitations. The auxiliary field formalism allows one to write a simple local form of the effective Hamiltonian for the three quark system, which comprises both confinement and relativistic effects, and contains only universal parameters: the string tension $σ$, the strong coupling constant $α_s$, and the bare (current) quark masses $m_i$. We calculate the hyperfine splitting with account of the both perturbative and non--perturbative spin-spin forces between quarks in a baryon. For the orbital excitations we estimate the string correction for the confinement potential - the leading correction to the contribution of the proper inertia of the rotating string. This correction lowers the masses of the P-states by 50 MeV. We find our numerical results to be in good agreement with experimental data.

hep-ph↗

arXiv2001

The bound state corrections to the semileptonic decays of the B meson. The light-front approach versus ACM model

A generalization of the parton-like formula is used for the first time to find the differential distributions in the inclusive semileptonic weak decays of the B meson. The main features of this new approach are the treatment of the b-quark as an on-mass-shell particle and the inclusion of the effects arising from the b-quark transverse motion in the B-meson. Using the b-quark light-front (LF) distribution function related to the equal time momentum wave function taken from the ACM model we compute the electron energy spectra and the total semileptonic widths of the B meson. We find an impressive agreement between the electron energy spectra calculated in the LF approach and the ones obtained in the ACM model, provided the b quark mass is identified with the average of the floating b quark mass in the ACM model. In spite of the simplicity of the model we obtain a fair good description of the CLEO data for V_{cb}=0.042.

hep-ph↗

arXiv1997

Exclusive and inclusive weak decays of the B-meson

A relativistic quark model is applied to the description of semileptonic and non-leptonic charmed decays of the B-meson. The exclusive semileptonic modes B -> D l νand B -> D* l νare described through the universal Isgur-Wise form factor, which is calculated in terms of a constituent quark model wave function for the B-meson. Different approximations for the latter, either based on a phenomenological ansatz or derived from analyses of the meson spectra, are adopted. In particular, two wave functions, constructed via the Hamiltonian light-front formalism using a relativized and a non-relativistic constituent quark model, are considered, obtaining a link between standard spectroscopic quark models and the B-meson decay physics. The inclusive semileptonic and non-leptonic branching ratios are calculated within a convolution approach, inspired by the partonic model and involving the same B-meson wave function used for the evaluation of the exclusive semileptonic modes. Our results for the major branching ratios are consistent with available experimental data and the sum of all the calculated branching ratios turns out to be close to unity. In particular, we found that: i) a remarkable fraction (~ 35%) of semileptonic decay modes occur in non-D, non-D* final states; ii) non-perturbative effects enhance the inclusive b -> c \bar{u} d decay channels, with a sizable contribution provided by internal decays into heavy mesons and baryon-antibaryon pairs; the resulting reduction of the semileptonic branching ratio brings the theoretical prediction in agreement with the experimental value without increasing at the same time the charm counting.

hep-ph↗

arXiv1996

Charmed decays of the B-meson in the quark model

Exclusive and inclusive, semileptonic and non-leptonic, charmed decays of the B-meson are investigated in the context of a phenomenological quark model. Bound-state effects are taken care of by adopting a single (model-dependent) non-perturbative wave function, describing the motion of the light spectator quark in the B-meson. A nice reproduction of both exclusive and inclusive semileptonic data is obtained. Our predictions for the electron spectrum are presented and compared with those of the Isgur-Scora-Grinstein-Wise quark model. Finally, our approach is applied to the calculation of inclusive non-leptonic widths, obtaining a remarkable agreement with experimental findings.

hep-ph↗

arXiv1996

Weak Decay Form Factors of Heavy Pseudoscalar Mesons within a Light-Front Constituent Quark Model

The transition form factors describing the semileptonic decays of heavy pseudoscalar mesons are investigated within a relativistic constituent quark model formulated on the light-front. For the first time, the form factors are calculated in the whole accessible kinematical region, adopting meson wave functions derived from various effective $q \bar{q}$ interactions able to describe the meson mass spectra. It is shown that the decay rates of the $B \to D \ell ν_{\ell}$, $D \to K \ell ν_{\ell}$ and $D \to π\ell ν_{\ell}$ weak decays are mainly governed by the effects of the confinement scale, whereas the $B \to π\ell ν_{\ell}$ decay rate is sensitive to the high-momentum components generated in the meson wave functions by the effective one-gluon-exchange interaction. Our results are consistent with available experimental data and predictions of lattice $QCD$ calculations and $QCD$ sum rules.

hep-ph↗

arXiv1996

Heavy-to-heavy and heavy-to-light weak decay form factors in the light-front approach: the exclusive $ 0^- $ to $ 0^- $ case

Weak transition form factors among heavy pseudoscalar mesons are investigated within a relativistic quark model formulated on the light-front. It is shown that the light-front result derived in the time-like region for the matrix elements of the plus component of the weak vector current coincides with the spectator pole term of the quark triangle diagram. For the first time, the dependence of the form factors on the squared four-momentum transfer $q^2$ is calculated in the whole accessible kinematical region $0 \leq q^2 \leq q^2_{max}$. For the numerical investigations of the semileptonic $B \to D \ell ν_{\ell}$, $B \to π\ell ν_{\ell}$, $D \to K \ell ν_{\ell}$ and $D \to π\ell ν_{\ell}$, the equal-time wave functions corresponding to the updated version of the ISGW model are adopted. Our results for the form factors and the decay rates are presented and compared with available experimental data and predictions of different approaches. Moreover, the $K^0_L \to π^{\pm} ~ e^{\mp} ~ ν_e$ decay is briefly discussed. Our approach is consistent with experimental data.

hep-ph↗

arXiv1995

Electromagnetic Structure of Mesons in a Light-Front Constituent Quark Model

The elastic and transition electromagnetic form factors of mesons are investigated within a light-front constituent quark model. The general formulae for the space-like matrix elements of the one-body component of the electromagnetic current, including both Dirac and Pauli form factors of the constituent quarks, are presented. Our results for the pion charge form factor and the $πρ$ transition form factor are reported and compared with those obtained within various relativistic approaches in a range of values of the four-momentum transfer accessible to $CEBAF$.

nucl-th↗

arXiv1995

Electromagnetic form factors of the $ρ$ meson in a light-front constituent quark model

The electromagnetic form factors of the $ρ$ meson are evaluated adopting a relativistic constituent quark model based on the light-front formalism, and using a meson wave function with the high-momentum tail generated by the one-gluon-exchange interaction. The breakdown of the rotational covariance for the one-body component of the current operator is investigated and the sensitivity of the ratio of the $ρ$-meson form factors to the pion (charge) form factor to the spin-dependent component of the effective $q \bar{q}$ interaction is illustrated.

hep-ph↗

arXiv1994

Hard Constituent Quarks and Electroweak Properties of Pseudoscalar Mesons

The high momentum components generated in the wave function of pseudoscalar mes* by the one-gluon-exchange interaction are investigated within a relativistic constituent quark model. Adopting the light-cone formalism, the sensitivity of the weak decay constant and the charge form factor to hard constituent quarks is illustrated.

nucl-th↗