Baryon Semileptonic Decays Research Articles

Some aspects of large- Nc heavy baryon chiral perturbation theory

Large-Nc chiral perturbation theory is a calculational scheme for baryons that simultaneously exhibits both the mq and 1/Nc expansions, where Nc is the number of colors of quarks. In this work an outline of the calculation of one-loop corrections to the leading baryon axial-vector and vector form factors in baryon semileptonic decays to order O(p2) in the chiral expansion is provided in order to show how the expansion works.

Test of SU(3) Symmetry in Hyperon Semileptonic Decays

Existing analyzes of baryon semileptonic decays indicate the presence of a small SU(3) symmetry breaking in hyperon semileptonic decays, but to provide evidence for SU(3) symmetry breaking, one would need a relation similar to the Gell-Mann–Okubo (GMO) baryon mass formula which is satisfied to a few percents, showing evidence for a small SU(3) symmetry breaking effect in the GMO mass formula. In this talk, I would like to present a similar GMO relation obtained in a recent work for hyperon semileptonic decay axial vector current matrix elements. Using these generalized GMO relations for the measured axial vector current to vector current form factor ratios, it is shown that SU(3) symmetry breaking in hyperon semileptonic decays is of 5–11% and confirms the validity of the Cabibbo model for hyperon semi-leptonic decays.

Test ofSU(3)symmetry in hyperon semileptonic decays

Existing analyzes of baryon semileptonic decays indicate the presence of a small SU(3) symmetry breaking in hyperon semileptonic decays, but to provide evidence for SU(3) symmetry breaking, one would need a relation similar to the Gell-Mann Okubo(GMO) baryon mass formula which is satisfied to a few percents, showing evidence for SU(3) symmetry breaking in the divergence of the vector current matrix element. In this paper, we shall present a similar GMO relation for the hyperon semileptonic decay axial vector form factors. Using these relations and the measured axial vector current to vector current form factor ratios, we show that SU(3) symmetry breaking in hyperon semileptonic decays is of 5-11%.

Renormalization of the baryon axial vector current in large-Ncchiral perturbation theory: Effects of the decuplet-octet mass difference and flavor symmetry breaking

The baryon axial vector current is computed at one-loop order in large-N_c baryon chiral perturbation theory, where N_c is the number of colors. Loop graphs with octet and decuplet intermediate states are systematically incorporated into the analysis and the effects of the decuplet-octet mass difference and SU(3) flavor symmetry breaking are accounted for. As expected, large-N_c cancellations between different one-loop graphs are observed as a consequence of the large-N_c spin-flavor symmetry of QCD baryons. Fitting our analytical formulas against experimental data on baryon semileptonic decays and the strong decays of decuplet baryons, a detailed numerical analysis regarding the determination of the basic parameters of large-N_c baryon chiral perturbation theory as well as the extraction of the baryon axial vector couplings is performed. The large-N_c baryon chiral perturbation theory predictions are in very good agreement both with the expectations from the 1/N_c expansion and with the experimental data.

Ratios of heavy hadron semileptonic decay rates

Ratios of charmed meson and baryon semileptonic decay rates appear to be satisfactorily described by considering only the lowest-lying (S-wave) hadronic final states and assuming the kinematic factor describing phase space suppression is the same as that for free quarks. For example, the rate for ${D}_{s}$ semileptonic decay is known to be $(17.0\ifmmode\pm\else\textpm\fi{}5.3)%$ lower than those for ${D}^{0}$ or ${D}^{+}$, and the model accounts for this difference. When applied to hadrons containing $b$ quarks, this method implies that the ${B}_{s}$ semileptonic decay rate is about 1% higher than that of the nonstrange $B$ mesons. This small difference thus suggests surprisingly good local quark-hadron duality for $B$ semileptonic decays, complementing the expectation based on inclusive quark-hadron duality that these differences in rates should not exceed a few tenths of a percent. For ${\ensuremath{\Lambda}}_{b}$ semileptonic decay, however, the inclusive rate is predicted to be about 13% greater than that of the nonstrange $B$ mesons. This value, representing a considerable departure from a calculation using a heavy-quark expansion, is close to the corresponding experimental ratio $\ensuremath{\Gamma}({\ensuremath{\Lambda}}_{b})/\overline{\ensuremath{\Gamma}}(B)=1.13\ifmmode\pm\else\textpm\fi{}0.03$ of total decay rates.

Radiative corrections to the three-body region of the Dalitz plot of baryon semileptonic decays with angular correlation between polarized emitted baryons and charged leptons: The initial-baryon rest frame case

We complement the results for the radiative corrections to the ${\stackrel{^}{\mathbf{s}}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{^}{\mathbit{l}}$ angular correlation of baryon semileptonic decays of Neri et al. [Phys. Rev. D 78, 054018 (2008)] with the final results in the rest frame of the decaying baryon. In addition, we present an analytical result which was not possible to obtain in Neri et al.'s work.

Radiative corrections to the three-body region of the Dalitz plot of baryon semileptonic decays with angular correlation between polarized emitted baryons and charged leptons

We have calculated the radiative corrections to the Dalitz plot of baryon semileptonic decays with angular correlation between polarized emitted baryons and charged leptons. This work covers both charged and neutral decaying baryons and is restricted to the so-called three-body region of the Dalitz plot. Also it is specialized at the center-of-mass frame of the emitted baryon. We have considered terms up to order $(\ensuremath{\alpha}/\ensuremath{\pi})(q/{M}_{1}{)}^{0}$, where $q$ is the momentum transfer and ${M}_{1}$ is the mass of the decaying baryon, and neglected terms of order $(\ensuremath{\alpha}/\ensuremath{\pi})(q/{M}_{1}{)}^{n}$ for $n\ensuremath{\ge}1$. The expressions displayed are ready to obtain numerical results, suitable for model-independent experimental analyses.

Heavy quark symmetry constraints on semileptonic form factors and decay widths of doubly heavy baryons

We show how heavy quark symmetry constraints on doubly heavy baryon semileptonic decay widths can be used to test the validity of different quark model calculations. The large discrepancies in the results observed between different quark model approaches can be understood in terms of a severe violation of heavy quark spin symmetry constraints by some of those models.

FandDvalues with explicit flavor symmetry breaking andΔscontents of nucleons

We propose a new model for describing baryon semileptonic decays for estimating $F$ and $D$ values with explicit breaking effects of both SU(3) and SU(2) flavor symmetry, where all possible SU(3) and SU(2) breaking effects are induced from an effective interaction. An overall fit including the weak magnetism form factor yields $F=0.477\ifmmode\pm\else\textpm\fi{}0.001$, $D=0.835\ifmmode\pm\else\textpm\fi{}0.001$, ${V}_{ud}=0.975\ifmmode\pm\else\textpm\fi{}0.002$, and ${V}_{us}=0.221\ifmmode\pm\else\textpm\fi{}0.002$ with ${\ensuremath{\chi}}^{2}=4.43/5\text{ }\text{ }\mathrm{d}.\mathrm{o}.\mathrm{f}.$. The spin content of strange quarks $\ensuremath{\Delta}s$ is estimated from the obtained values $F$ and $D$, and the nucleon spin problem is reexamined. Furthermore, the unmeasured values of $({g}_{1}/{f}_{1})$ and $({g}_{1})$ for other hyperon semileptonic decays are predicted from this new formula.

Precision radiative corrections to the semileptonic Dalitz plot with angular correlation between polarized decaying baryon and emitted charged lepton: Effects of the four-body region

Analytical radiative corrections of order $(\ensuremath{\alpha}/\ensuremath{\pi})(q/{M}_{1})$ are calculated for the four-body region of the Dalitz plot of baryon semileptonic decays when the ${\stackrel{^}{\mathbf{s}}}_{1}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{^}{\mathbit{l}}$ correlation is present. Once the final result is available, it is possible to exhibit it in terms of the corresponding final result of the three-body region following a set of simple changes in the latter, except for a few exceptions. We cover two cases, a charged and a neutral polarized decaying baryon.

Erratum: Numerical precision radiative corrections to the Dalitz plot of baryon semileptonic decays including the spin-momentum correlation of the decaying and emitted baryons [Phys. Rev. D70, 093012 (2004)

We calculate the radiative corrections to the angular correlation between the polarization of the decaying and the direction of the emitted spin one-half baryons in the semileptonic decay mode. The final results are presented, first, with the triple integration of the bremsstrahlung photon ready to be performed numerically and, second, in an analytical form. A third presentation of our results in the form of numerical arrays of coefficients to be multiplied by the quadratic products of form factors is discussed. This latter may be the most practical one to use in Monte Carlo simulations. A series of crosschecks is performed. Previous results to order (alpha/pi)(q/M_1) for the decays of unpolarized baryons are reviewed, too, where q is the momentum transfer and M_1 is the mass of the decaying baryon. This paper is self-contained and organized to make it accessible and reliable in the analysis of the Dalitz plot of precision experiments involving heavy quarks and is not compromised to fixing the form factors at predetermined values. It is assumed that the real photons are kinematically discriminated. Otherwise, our results have a general model-independent applicability.

Erratum: Precision radiative corrections to the Dalitz plot of baryon semileptonic decays including the spin-momentum correlation of the decaying baryon and the emitted charged lepton [Phys. Rev. D72, 057503 (2005)

We calculate the radiative corrections to the angular correlation between the polarization of the decaying baryon and the direction of the emitted charged lepton in the semileptonic decays of spin one-half baryons to order (\alpha/\pi)(q/M_1). The final results are presented, first, with the triple integration of the bremsstrahlung photon ready to be performed numerically and, second, in an analytical form. A third presentation of our results in the form of numerical arrays of coefficients to be multiplied on the quadratic products of form factors is discussed. This latter may be the most practical one to use in Monte Carlo simulations. A series of crosschecks is performed. The results are useful in the analysis of the Dalitz plot of precision experiments involving light and heavy quarks and is not compromised to fixing the form factors at predetermined values. It is assumed that the real photons are kinematically discriminated. Otherwise, our results have a general model-independent applicability.

Precision radiative corrections to the Dalitz plot of baryon semileptonic decays including the spin-momentum correlation of the decaying baryon and the emitted charged lepton

We calculate the radiative corrections to the angular correlation s{sub 1}{center_dot}l to order ({alpha}/{pi})(q/M{sub 1}). The final results are presented with the triple integration of the bremsstrahlung photon to be performed numerically and in an analytical form. The results are useful in the analysis of precision experiments involving light and heavy quarks. It is assumed that the real photons are kinematically discriminated. Our results are model-independent.

Numerical precision radiative corrections to the Dalitz plot of light and heavy quark unpolarized baryon semileptonic decays: The casesΞ0→Σ+eν¯andΛc+→Λe+ν

We propose and discuss a numerical use for our previous precision results for the radiative corrections to unpolarized spin one-half baryon semileptonic decays, which is not compromised to fixing the form factors at prescribed values. We present various cross-checks and comparisons with other results available in the literature of such analytical radiative corrections. Our analysis, however, is general and applies to all charge assignments to the baryons allowed by heavy quarks. The procedure is exemplified with the processes ${\ensuremath{\Xi}}^{0}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}^{+}e\overline{\ensuremath{\nu}}$ and ${\ensuremath{\Lambda}}_{c}^{+}\ensuremath{\rightarrow}\ensuremath{\Lambda}{e}^{+}\ensuremath{\nu}$.

Numerical precision radiative corrections to the Dalitz plot of baryon semileptonic decays including the spin-momentum correlation of the decaying and emitted baryons

We calculate the radiative corrections to the angular correlation between the polarization of the decaying and the direction of the emitted spin one-half baryons in the semileptonic decay mode to order $(\ensuremath{\alpha}/\ensuremath{\pi})(q/{M}_{1})$, where $q$ is the momentum transfer and ${M}_{1}$ is the mass of the decaying baryon. The final results are presented, first, with the triple integration of the bremsstrahlung photon ready to be performed numerically and, second, in an analytical form. A third presentation of our results in the form of numerical arrays of coefficients to be multiplied by the quadratic products of form factors is discussed. This latter may be the most practical one to use in Monte Carlo simulations. A series of cross-checks is performed. This paper is organized to make it accessible and reliable in the analysis of the Dalitz plot of precision experiments involving heavy quarks and is not compromised to fixing the form factors at predetermined values. It is assumed that the real photons are kinematically discriminated. Otherwise, our results have a general model-independent applicability.

Radiative corrections to all charge assignments of heavy quark baryon semileptonic decays

In semileptonic decays of spin-1/2 baryons containing heavy quarks up to six charge assignments for the baryons and lepton are possible. We show that the radiative corrections to four of these possibilities can be directly obtained from the final results of the two possibilities previously studied. There is no need to recalculate integrals over virtual or real photon momentum or any traces.

Semileptonic decay constants of octet baryons in the chiral quark-soliton model

Based on the recent study of the magnetic moments and axial constants within the framework of the chiral quark-soliton model, we investigate the baryon semileptonic decay constants $(f_1,f_2)$ and $(g_1, g_2)$. Employing the relations between the diagonal transition matrix elements and off-diagonal ones in the vector and axial-vector channels, we obtain the ratios of baryon semileptonic decay constants $f_2/f_1$ and $g_1/f_1$. The $F/D$ ratio is also discussed and found that the value predicted by the present model naturally lies between that of the Skyrme model and that of the nonrelativistic quark model. The singlet axial constant $g^{(0)}_A$ can be expressed in terms of the $F/D$ ratio and $g^{(3)}_A$ in the present model and turns out to be small. The results are compared with available experimental data and found to be in good agreement with them. In addition, the induced pseudotensor coupling constants $g_2/f_1$ are calculated, the SU(3) symmetry breaking being considered. The results indicate that the effect of SU(3) symmetry breaking might play an important role for some decay modes in hyperon semileptonic decay.

General analysis of weak decay form factors in heavy to heavy and heavy to light baryon transitions

We present a complete analysis of the heavy to heavy and heavy to light baryon semi-leptonic decays in the heavy quark effective theory within the framework of a Bethe-Salpeter (BS) approach and demonstrate the equivalence of this approach to other work in the field. We present in a compact form the baryon BS amplitudes which incorporate the symmetries manifest in the heavy quark limit and which also show clearly the light quark dynamics. A similar form of the BS amplitude is presented for light baryons. Using the BS amplitudes, the heavy to heavy and heavy to light semi-leptonic baryon decays are considered. As expected there is a dramatic reduction in the number of form factors. An advantage of our BS approach is demonstrated where the form factors are written as loop integrals which in principle can be calculated.

SU(3)-symmetry breaking and configuration mixing in baryon semileptonic decays.

We discuss small contributions to baryon semileptonic decays which provide corrections to the simplest SU(3)-symmetric formulas. In particular, we consider (1) SU(3)-symmetry breaking resulting from the wave-function deformations due to the $s\ensuremath{-}u$, $d$ quark mass difference and (2) the effects of the configuration mixing of $^{2}S_{M}$ and $^{2}S_{S}$ states, originating from QCD hyperfine interactions. Both effects are treated in combination with the form-factor suppression effect which is operative if the three-momentum transfer between the initial and final hadron is nonzero. Our estimates are performed in the framework of the harmonic-oscillator quark model. While the inclusion of the $s\ensuremath{-}u$, $d$ quark mass difference leads to an unacceptable $\frac{{g}_{A}}{{g}_{V}}$ ratio for $\ensuremath{\Lambda}\ensuremath{\rightarrow}p{e}^{\ensuremath{-}}\ensuremath{\nu}$ semileptonic decay, the corrections due to configuration mixing do not lead to disagreement with the data. Better measurements of the $\ensuremath{\Xi}\ensuremath{\rightarrow}n{e}^{\ensuremath{-}}\ensuremath{\nu}$ and $\ensuremath{\Xi}\ensuremath{\rightarrow}\ensuremath{\Lambda}{e}^{\ensuremath{-}}\ensuremath{\nu}$ decays are needed if a choice is to be made between the standard SU(3)-symmetric parametrization and the pattern of SU(3) breaking resulting from configuration mixing.

The second EMC effect, semileptonic baryon decays and the chiral bag

TheU(1) anomaly gives a massiveη0 in the chiralSU(3) limit. We show in this limit how a chiral bag model givesboth theF andD amplitudes consistent with all baryon semileptonic decays,and the integral over the spin structure function measured by the EMC collaboration.