arXiv subjects
Publications and source records attributed to Changhao Jin.
The determinations of |V_{cb}| and |V_{ub}| from inclusive semileptonic B decays are reviewed. A comparison of the light-cone approach with the heavy quark expansion approach is made. The perspective for further improvement of the |V_{cb}| and |V_{ub}| determinations is discussed.
We calculate the total and differential decay rates for the semi-inclusive nonleptonic decays $B\to D_s^{(*)} X_q$ ($q=c$ or $u$) under the factorization hypothesis. The initial bound state effect is treated using the light-cone expansion and the heavy quark effective theory. We investigate the contribution of the penguin amplitude for the decay mode $B\to D_s^{(*)} X_c$ and find that it is small but non-negligible. The resulting decay rates for $B\to D_s^{(*)} X_c$ agree with the measurements. The use of the decay mode $B\to D_s^{(*)} X_u$ to determine $|V_{ub}|$ is discussed.
The sum rule for charmless inclusive semileptonic B-meson decays allows a theoretically clean and experimentally efficient determination of |V_{ub}|. The leading twist contribution to the sum rule is known in QCD. We compute higher twist corrections to the sum rule using the heavy quark effective theory.
We discuss an improved theoretical description of the semi-inclusive B meson decays $B\to K(K^*)X$. The decay distributions are calculated. Their branching ratios are found to be appreciable. The CP asymmetries in the neutral B modes $\bar{B^0}\to K^-(K^{*-})X$ are sizable. An observation of direct CP violation and a measurement of $γ$ may come from these neutral B modes.
The effects of initial $b$ quark bound state for the semi-inclusive decays $B\to K(K^*) X$ are studied using light cone expansion and heavy quark effective theory methods. We find that the initial bound state effects on the branching ratios and CP asymmetries are small. In the light cone expansion approach, the CP-averaged branching ratios are increased by about 2% with respect to the free $b$-quark decay. For $\bar B^0 \to K^- (K^{*-}) X$, the CP-averaged branching ratios are sensitive to the phase $γ$ and the CP asymmetry can be as large as 7% (14%), whereas for $B^-\to \bar K^0 (\bar K^{*0})X$ the CP-averaged branching ratios are not sensitive to $γ$ and the CP asymmetries are small ($< 1%$). The CP-averaged branching ratios are predicted to be in the ranges $(0.53 \sim 1.5)\times 10^{-4}$ [$(0.25 \sim 2.0)\times 10^{-4}$] for $\bar B^0 \to K^- (K^{*-})X$ and $(0.77 \sim 0.84)\times 10^{-4}$ [$(0.67 \sim 0.74)\times 10^{-4}$] for $B^-\to \bar K^0 (\bar K^{*0}) X$, depending on the value of the CP violating phase $γ$. In the heavy quark effective theory approach, we find that the branching ratios are decreased by about 10% and the CP asymmetries are not affected. These predictions can be tested in the near future.
Unitarity of the Cabibbo-Kobayashi-Maskawa matrix gives rise to nine new unitarity triangles in the standard model.
The governing role of light-cone dynamics in inclusive heavy hadron decay processes is demonstrated. Nonperturbative QCD effects on the processes can be systematically calculated using light-cone expansion and heavy quark effective theory. The applications of the light-cone approach to studying electroweak and strong interactions and hadron structure with semileptonic and radiative decays of beauty hadrons are briefly reviewed.
A precise determination of |V_{ub}| can be obtained exploiting the sum rule for inclusive charmless semileptonic B-meson decays. The sum rule is derived on the basis of light-cone expansion and b-flavored quantum number conservation. The sum rule does not receive any perturbative QCD correction. In this determination of |V_{ub}|, there is no perturbative QCD uncertainty, while the dominant hadronic uncertainty is avoided. Moreover, this method is not only theoretically quite clean, but experimentally also very efficient in the discrimination between B\to X_u\ellνsignal and B\to X_c\ellνbackground. The sum rule requires measuring the lepton pair spectrum. We analyze the lepton pair spectrum, including the leading perturbative and nonperturbative QCD corrections.
The decay distribution of the kinematic variable ξ_u in inclusive charmless semileptonic decays of B mesons is unique. The novel method for a model-independent determination of |V_{ub}| is described.
Some theoretical results on V_ub and V_cb determinations from inclusive decays of b hadrons are highlighted.
Methods are described in the framework of light-cone expansion which allow one to determine the Cabibbo-Kobayashi-Maskawa matrix elements |V_ub| and |V_cb| from measurements of the differential decay rates as a function of the scaling variables in the inclusive semileptonic decays of B mesons. By these model-independent methods the dominant hadronic uncertainties can be avoided and the B -> X_u\ellνdecay can be very efficiently differentiated from the B -> X_c\ellνdecay, which may lead to precise determinations of |V_ub| and |V_cb|.
We compute long distance effects on the photon energy spectrum in inclusive radiative decays of $B$ mesons using light-cone expansion and heavy quark effective theory. We show that for sufficiently high photon energy the leading nonperturbative QCD contribution is attributed to the distribution function. The distribution function is found to be universal in the sense that the same distribution function also encodes the leading nonperturbative contribution to inclusive semileptonic decays of $B$ mesons at large momentum transfer. Some basic properties of the distribution function are deduced in QCD. Ways of extracting the distribution function directly from experiment and their implications are discussed. The theoretically clean methods for the determination of $|V_{ts}|$ are described.
We calculate the inclusive charmless semileptonic decay width of the B meson using a QCD-based approach. This approach is able to account for both dynamic and kinematic effects of nonperturbative QCD. The charmless semileptonic decay width is found to be enhanced by long-distance strong interactions by +(7\pm 5)% with respect to the free quark decay width. Using the resulting theoretical value for the charmless semileptonic decay width, an extraction of $|V_{ub}|$ is made from the measured lifetime and inclusive charmless semileptonic branching ratio of b hadrons.
The study of inclusive semileptonic decays of $B$ mesons is analyzed from the viewpoint of probing hadron structure and strong interactions. General formulas for the differential decay rates are given in terms of the structure functions in arbitrary frame of reference, taking into account the finite charged lepton mass. These formulas can be used for structure function measurements. The behavior of the structure functions is shown to contain information on the constitution of the $B$ meson and the dynamics of strong interactions. Measurements of the structure functions would reveal the existence of a point-like $b$ quark in the $B$ meson, establish the spin 1/2 nature of the $b$ quark, and identify the $b$ quantum number of the $B$ meson. These measurements would determine the $b$ quark distribution function, and allow new insight into the nature of confinement. The $b$ quark distribution function can also be extracted directly through the measurements of the decay distributions with respect to the scaling variable $ξ_+$.
We make an analysis of the hadronic invariant mass spectrum in inclusive charmless semileptonic B meson decays in a QCD-based approach. The decay width is studied as a function of the invariant mass cut. We examine their sensitivities to the parameters of the theory. The theoretical uncertainties in the determination of $|V_{ub}|$ from the hadronic invariant mass spectrum are investigated. A strategy for improving the theoretical accuracy in the value of $|V_{ub}|$ is described.
We extend the approach based on the light-cone expansion and the heavy quark effective theory to the inclusive semileptonic decay of an unpolarized $b$-flavored hadron. It is applied to calculate the semileptonic decay width of the $Λ_b$ baryon and its ratio to that of the B meson. We obtain $Γ_{SL}(Λ_b)= 51\pm 9 |V_{cb}|^2{ps}^{-1}$ and $Γ_{SL}(Λ_b)/Γ_{SL}(B)= 1.052\pm 0.006$. From the latter, the semileptonic branching fraction for $Λ_b$ is predicted to be $(8.7\pm 0.7)%$.
Nonperturbative QCD contributions to the inclusive semileptonic decay of the B meson consist of the dynamic and kinematic components. We calculate the decay width in an approach based on the light-cone expansion and the heavy quark effective theory, which is able to include both components of nonperturbative QCD contributions. The kinematic component results in the phase-space extension and is shown to be quantitatively crucial, which could increase the decay width significantly. We find that the semileptonic decay width is enhanced by long-distance strong interactions by +(9\pm 6)%. This analysis is used to determine the CKM matrix element |V_{cb}| with a controlled theoretical error. Implications of the phase-space effects for the nonleptonic decay widths of b hadrons are briefly discussed. The experimental evidence for the phase-space effects is pointed out.
We show how radiative QCD corrections calculated in terms of quarks can be incorporated at the hadron level in inclusive semileptonic B-meson decays. The bound state effects are described by a momentum distribution function of the $b$ quark. The summation over the final states and the averaging over the momentum distribution of the decaying quark render the radiative corrections finite. With this coherent formalism we investigate the shape of the electron spectra for $b\to u$ and $b\to c$ decays as a function of the parameters of the theory. The resultant $b\to c$ electron energy spectrum is in agreement with the experimental data.