[Show abstract][Hide abstract] ABSTRACT: We calculate next-to-leading-order (NLO) correction to the pion
electromagnetic form factor at leading twist in the $k_T$ factorization
theorem. Partons off-shell by $k_T^2$ are considered in both quark diagrams and
effective diagrams for the transverse-momentum-dependent (TMD) pion wave
function. The light-cone singularities in the TMD pion wave function are
regularized by rotating the Wilson lines away from the light cone. The soft
divergences from gluon exchanges among initial- and final-state partons cancel
exactly. We derive the infrared-finite $k_T$-dependent NLO hard kernel for the
pion electromagnetic form factor by taking the difference of the above two sets
of diagrams. Varying the renormalization and factorization scales, we find that
the NLO correction is smaller, when both the scales are set to the invariant
masses of internal particles: it becomes lower than 40% of the leading-order
(LO) contribution for momentum transfer squared $Q^2>7$ GeV$^2$. It is observed
that the NLO leading-twist correction does not play an essential role in
explaining the experimental data, but the LO higher-twist contribution does.
[Show abstract][Hide abstract] ABSTRACT: Although the two-body charmed decays B_{(s)} \rightarrow \bar{D}_{(s)}^{(*)}P and \bar{D}_{(s)}^{(*)}V , where P (V) denotes a light pseudoscalar (vector) meson, are Cabbibo-Kobayashi-Maskawa (CKM) suppressed compared with the B(s) --> D(*)(s)P and D(*)(s)V decays, they are important in the CKM angle gamma = phi3 extraction method. We investigated these decays in the perturbative QCD approach to the leading order of mD/mB and LambdaQCD/mD expansion. We find that the nonfactorizable emission diagrams and the annihilation diagrams are not negligible in many of these channels. The numerical results show that most channels have branching ratios with an order of 10-6 or 10-7. The ratio needed for the CKM angle gamma extraction is estimated as r = \frac{|A(B^- \rightarrow \bar{D}^0 K^-)|}{|A(B^- \rightarrow D^0 K^-)|} = 0.092_{-0.003-0.003}^{+0.012+0.003}, which is too small for the experiments. Some of the B_{(s)}\rightarrow \bar{D}_{(s)}^*V decays have a very large transversely polarized contribution that can reach 80%.
Journal of Physics G Nuclear and Particle Physics 01/2010; 37(1). DOI:10.1088/0954-3899/37/1/015002 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We calculate the CP-averaged branching ratios and CP-violating asymmetries for the two-body charmless hadronic decays Λb→pπ, pK in the perturbative QCD (pQCD) approach to lowest order in αs. The baryon distribution amplitudes involved in the factorization formulas are considered to the leading twist accuracy, and the distribution amplitudes of the proton are expanded to the next-to-leading conformal spin (i.e., “P” waves), the moments of which are determined from QCD sum rules. Our work shows that the contributions from the factorizable diagrams in Λb→pπ, pK decays are much smaller compared to the nonfactorizable diagrams in the conventional pQCD approach. We argue that this reflects the estimates of the Λb→p transition form factors in the kT factorization approach, which are found to be typically an order of magnitude smaller than those estimated in the light-cone sum rules and in the nonrelativistic quark model. As an alternative, we adopt a hybrid pQCD approach, in which we compute the factorizable contributions with the Λb→p form factors taken from the light-cone QCD sum rules. The nonfactorizable diagrams are evaluated utilizing the conventional pQCD formalism, which is free from the endpoint singularities. The predictions worked out here are confronted with the recently available data from the CDF Collaboration on the branching ratios and the direct CP asymmetries for the decays Λb→pπ and Λb→pK. The asymmetry parameter α relevant for the anisotropic angular distribution of the emitted proton in the polarized Λb baryon decays is also calculated for the two decay modes.
[Show abstract][Hide abstract] ABSTRACT: In this work, we calculate the form factors for $J/\psi\to \bar{D}^{(*)0}$ induced by the flavor changing neutral currents (FCNC) in terms of the QCD sum rules. Making use of these form factors, we further calculate the branching fractions of semileptonic decays $J/\psi \to \bar{D}^{(*)0} l ^+ l^-$ ($l=e, \mu$). In particular, we formulate the matrix element $<J/\psi|T_{\mu\nu}| \bar{D}^{*0}>$ with $T_{\mu\nu}$ being a tensor current, which was not fully discussed in previous literature. Our analysis indicates that if only the standard model (SM) applies, the production of single charmed mesons at the present electron-positron colliders is too small to be observed even the resonance effects are included, therefore if an anomalous production rates are observed, it would be a hint of new physics beyond SM. Even though the predicted branching ratios are beyond the reach of present facilities which can be seen from a rough order estimate, the more accurate formulation of the three point correlation function derived in this work has theoretical significance and the technique can also be applied to other places. In analog to some complicated theoretical derivations which do not have immediate phenomenological application yet, if the future experiments can provide sufficient luminosity and accuracy, the results would be helpful. Comment: 27 pages, 7 figures
Journal of Physics G Nuclear and Particle Physics 10/2008; 36(10). DOI:10.1088/0954-3899/36/10/105002 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Two-body charmed decays B(s)→D(s)P, D(s)*P, D(s)V, and D(s)*V, where P and V denote the light pseudoscalar meson and vector meson, respectively, are analyzed in the perturbative QCD (pQCD) approach. Using the experimental data of six B→DP channels, we test the D meson wave function by χ2 fit. We give the branching ratios of all the charmed B decay channels, most of which agree with experiments amazingly well. The predicted Bs decays can be confronted with the future experimental data. By straightforward calculations, our pQCD approach gives the right relative strong phase of a2/a1 that agrees with experiments. We also predict the percentage of transverse polarizations in B(s)→D*V decay channels.
Physical Review D 07/2008; 78(1). DOI:10.1103/PhysRevD.78.014018 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In our previous study, we calculated the transition form factors of J/ψ→D(*)
(s) using the QCD sum rules. Based on the factorization approximation, the form factors obtained can be applied to evaluate the
weak non-leptonic decay rates of J/ψ→D(*)
(s)+M, where M stands for a light pseudoscalar or vector meson. We predict that the branching ratio for inclusive non-leptonic
two-body weak decays of J/ψ, which are realized via the spectator mechanism, can be as large as 1.3×10-8; in particular, the branching ratio of J/ψ→D*±
s+ρ∓ can reach 5.3×10-9. Such values will be marginally accessed by the ability of BESIII, which will begin running very soon.
European Physical Journal C 06/2008; 55(4):607-613. DOI:10.1140/epjc/s10052-008-0619-1 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Within the standard model, we investigate the semi-leptonic weak decays of J/ψ. The various form factors of J/ψ making the
transition to a single charmed meson (D(*)
(d,s)) are studied in the framework of QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays
of J/ψ and provide valuable information on non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic
weak decay mode J/ψ→D(*)-
s+e++νe is at the order of 10-10.
European Physical Journal C 02/2008; 54(1):107-121. DOI:10.1140/epjc/s10052-007-0498-x · 5.08 Impact Factor