472 research outputs found

    Study of Bc --> J/psi pi, etac pi decays with perturbative QCD approach

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    The Bc --> J/psi pi, etac pi decays are studied with the perturbative QCD approach. It is found that form factors and branching ratios are sensitive to the parameters w, v, f_J/psi and f_etac, where w and v are the parameters of the charmonium wave functions for Coulomb potential and harmonic oscillator potential, respectively, f_J/psi and f_etac are the decay constants of the J/psi and etac mesons, respectively. The large branching ratios and the clear signals of the final states make the Bc --> J/psi pi, etac pi decays to be the prospective channels for measurements at the hadron collidersComment: 21 pages, revtex

    Relativistic effects in electromagnetic nuclear responses in the quasi-elastic delta region

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    A new non-relativistic expansion in terms of the nucleon's momentum inside nuclear matter of the current for isobar electro-excitation from the nucleon is performed. Being exact with respect to the transferred energy and momentum, this yields new current operators which retain important aspects of relativity not taken into account in the traditional non-relativistic reductions. The transition current thus obtained differs from the leading order of the traditional expansion by simple multiplicative factors. These depend on the momentum and energy transfer and can be easily included together with relativistic kinematics in non-relativistic, many-body models of isobar electro-excitation in nuclei. The merits of the new current are tested by comparing with the unexpanded electromagnetic nuclear responses in the isobar peak computed in a relativistic Fermi gas framework. The sensitivity of the relativistic responses to the isobar's magnetic, electric and Coulomb form factors and the finite width of the isobar is analyzed.Comment: 26 pages plus 6 figure

    Final state interaction and BKKB\to KK decays in perturbative QCD

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    We predict branching ratios and CP asymmetries of the BKKB\to KK decays using perturbative QCD factorization theorem, in which tree, penguin, and annihilation contributions, including both factorizable and nonfactorizable ones, are expressed as convolutions of hard six-quark amplitudes with universal meson wave functions. The unitarity angle ϕ3=90o\phi_3= 90^o and the BB and KK meson wave functions extracted from experimental data of the BKπB\to K\pi and ππ\pi\pi decays are employed. Since the BKKB\to KK decays are sensitive to final-state-interaction effects, the comparision of our predictions with future data can test the neglect of these effects in the above formalism. The CP asymmetry in the B±K±K0B^\pm\to K^\pm K^0 modes and the Bd0K±KB_d^0\to K^\pm K^\mp branching ratios depend on annihilation and nonfactorizable amplitudes. The BKKB\to KK data can also verify the evaluation of these contributions.Comment: 13 pages in latex file, 7 figures in ps file

    Role of 2p-2h MEC excitations in superscaling

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    Following recent studies of inclusive electron scattering from nuclei at high energies which focused on two-nucleon emission mediated by meson-exchange currents, in this work the superscaling behavior of such contributions is investigated. Comparisons are made with existing data below the quasielastic peak where at high momentum transfers scaling of the second kind is known to be excellent and scaling of the first kind is good, in the proximity of the peak where both 1p-1h and 2p-2h contributions come into play, and above the peak where inelasticity becomes important and one finds scaling violations of the two kinds.Comment: 27 pages, 12 figures; references adde

    Applicability of perturbative QCD to ΛbΛc\Lambda_b \to \Lambda_c decays

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    We develop perturbative QCD factorization theorem for the semileptonic heavy baryon decay ΛbΛclνˉ\Lambda_b \to \Lambda_c l\bar{\nu}, whose form factors are expressed as the convolutions of hard bb quark decay amplitudes with universal Λb\Lambda_b and Λc\Lambda_c baryon wave functions. Large logarithmic corrections are organized to all orders by the Sudakov resummation, which renders perturbative expansions more reliable. It is observed that perturbative QCD is applicable to ΛbΛc\Lambda_b \to \Lambda_c decays for velocity transfer greater than 1.2. Under requirement of heavy quark symmetry, we predict the branching ratio B(ΛbΛclνˉ)2B(\Lambda_b \to \Lambda_c l{\bar\nu})\sim 2%, and determine the Λb\Lambda_b and Λc\Lambda_c baryon wave functions.Comment: 12 pages in Latex file, 3 figures in postscript files, some results are changed, but the conclusion is the sam

    Final-state interaction and s-quark helicity conservation in B -> J/psi K*

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    The Section of charm quark spin conservation is deleted since it involves more dynamical assumptions than previously stated. A few comments are added in view of new experimental results.Comment: To replace the earlier version of hep-ph/0106354. Minor additions and one deletion with no change in the main argument nor the conclusio

    Nonfactorizable contributions to BD()MB \to D^{(*)} M decays

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    While the factorization assumption works well for many two-body nonleptonic BB meson decay modes, the recent measurement of BˉD()0M0\bar B\to D^{(*)0}M^0 with M=πM=\pi, ρ\rho and ω\omega shows large deviation from this assumption. We analyze the BD()MB\to D^{(*)}M decays in the perturbative QCD approach based on kTk_T factorization theorem, in which both factorizable and nonfactorizable contributions can be calculated in the same framework. Our predictions for the Bauer-Stech-Wirbel parameters, a2/a1=0.43±0.04|a_2/a_1|= 0.43\pm 0.04 and Arg(a2/a1)42Arg(a_2/a_1)\sim -42^\circ and a2/a1=0.47±0.05|a_2/a_1|= 0.47\pm 0.05 and Arg(a2/a1)41Arg(a_2/a_1)\sim -41^\circ, are consistent with the observed BDπB\to D\pi and BDπB\to D^*\pi branching ratios, respectively. It is found that the large magnitude a2|a_2| and the large relative phase between a2a_2 and a1a_1 come from color-suppressed nonfactorizable amplitudes. Our predictions for the Bˉ0D()0ρ0{\bar B}^0\to D^{(*)0}\rho^0, D()0ωD^{(*)0}\omega branching ratios can be confronted with future experimental data.Comment: 25 pages with Latex, axodraw.sty, 6 figures and 5 tables, Version published in PRD, Added new section 5 and reference

    Implications of Recent Measurements of Hadronic Charmless B Decays

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    Implications of recent CLEO measurements of hadronic charmless B decays are discussed. (i) Employing the Bauer-Stech-Wirbel (BSW) model for form factors as a benchmark, the Bπ+πB\to\pi^+\pi^- data indicate that the form factor F0Bπ(0)F_0^{B\pi}(0) is smaller than that predicted by the BSW model, whereas the data of Bωπ,KηB\to\omega\pi, K^*\eta imply that the form factors A0Bω(0),A0BK(0)A_0^{B\omega}(0), A_0^{BK^*}(0) are greater than the BSW model's values. (ii) The tree-dominated modes Bπ+π,ρ0π±,ωπ±B\to\pi^+\pi^-, \rho^0\pi^\pm, \omega\pi^\pm imply that the effective number of colors N_c(LL) for (V-A)(V-A) operators is preferred to be smaller, while the current limit on BϕKB\to\phi K shows that N_c(LR)>3. The data of BKηB\to K\eta' and KηK^*\eta clearly indicate that Nc(LR)Nc(LL)N_c(LR)\gg N_c(LL). (iii) In order to understand the observed suppression of π+π\pi^+\pi^- and non-suppression of KπK\pi modes, both being governed by the form factor F0BπF_0^{B\pi}, the unitarity angle γ\gamma is preferred to be greater than 9090^\circ. By contrast, the new measurement of B±ρ0π±B^\pm\to\rho^0\pi^\pm no longer strongly favors cosγ<0\cos\gamma<0. (iv) The observed pattern K^-\pi^+\sim \ov K^0\pi^-\sim {2\over 3}K^-\pi^0 is consistent with the theoretical expectation: The constructive interference between electroweak and QCD penguin diagrams in the Kπ0K^-\pi^0 mode explains why {\cal B}(B^-\to K^-\pi^0)>{1\over 2}{\cal B}(\ov B^0\to K^-\pi^+). (v) The observation \nc(LL)<3<\nc(LR) and our preference for \nc(LL)\sim 2 and \nc(LR)\sim 6 are justified by a recent perturbative QCD calculation of hadronic rare B decays in the heavy quark limit.Comment: 21 pages; CLEO measurements of several charmless B decay modes are updated. Discussion of the unitarity angle gamma in the \rho\pi mode is revise

    Shapes, contact angles, and line tensions of droplets on cylinders

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    Using an interface displacement model we calculate the shapes of nanometer-size liquid droplets on homogeneous cylindrical surfaces. We determine effective contact angles and line tensions, the latter defined as excess free energies per unit length associated with the two contact lines at the ends of the droplet. The dependences of these quantities on the cylinder radius and on the volume of the droplets are analyzed.Comment: 26 pages, RevTeX, 10 Figure

    Wetting films on chemically heterogeneous substrates

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    Based on a microscopic density functional theory we investigate the morphology of thin liquidlike wetting films adsorbed on substrates endowed with well-defined chemical heterogeneities. As paradigmatic cases we focus on a single chemical step and on a single stripe. In view of applications in microfluidics the accuracy of guiding liquids by chemical microchannels is discussed. Finally we give a general prescription of how to investigate theoretically the wetting properties of substrates with arbitrary chemical structures.Comment: 56 pages, RevTeX, 20 Figure
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