Improved η′\eta^\prime-Meson Distribution Amplitudes from Inclusive Υ(1S)→η′X\Upsilon (1S) \to \eta^\prime X Decay

We calculate the $\eta^\prime$-meson energy spectrum in the $\Upsilon (1S) \to \eta^\prime g g g \to \eta^\prime X$ decay in the leading-order perturbative QCD in the static-quark limit for the orthoquarkonium.Our principal result is the extraction of parameters of the $\eta^\prime g^* g$ effective vertex function (EVF) involving a virtual and a real gluon from the available data on the hard part of the $\eta^\prime$-meson energy spectrum. The perturbative-QCD based framework provides a good description of the available CLEO data, allowing one to constrain the lowest Gegenbauer coefficients $B^{(q)}_2$ and $B^{(g)}_2$ of the quark-antiquark and gluonic distribution amplitudes of the $\eta^\prime$-meson. The resulting constraints are combined with the existing ones on these coefficients from an analysis of the $\eta^\prime - \gamma$ transition form factor and the requirement of positivity of the EVF, yielding $B^{(q)}_2 (\mu_0^2) = -0.008 \pm 0.054$ and $B^{(g)}_2 (\mu_0^2) = 4.6 \pm 2.5$ for $\mu_0^2 = 2 GeV^2$. This reduces significantly the current uncertainty on these coefficients.Comment: 4 pages, 4 figures, use svjour.cls and svepj.clo; talk given at the International Europhysics Conference on High-Energy Physics (HEP 2003), 17-23 July 2003, Aachen, Germany. Title change

Branching Ratios for B→K∗γB \to K^* \gamma and B→ργB \to \rho \gamma Decays in Next-to-Leading Order in the Large Eneregy Effective Theory

We calculate the so-called hard spectator corrections in ${\cal O} (\alpha_s)$ in the leading-twist approximation to the decay widths for $B \to K^{*} \gamma$ and $B \to \rho \gamma$ decays and their charge conjugates, using the Large Energy Effective Theory (LEET) techniques. Combined with the hard vertex and annihilation contributions, they are used to compute the branching ratios for these decays in the next-to-leading order (NLO) in the strong coupling $\alpha_s$ and in leading power in $\Lambda_{\rm QCD}/M_B$. These corrections are found to be large, leading to the inference that the theoretical branching ratios for the decays $B \to K^* \gamma$ in the LEET approach can be reconciled with current data only for significantly lower values of the form factors than their estimates in the QCD sum rule and Lattice QCD approaches. However, the form factor related uncertainties mostly cancel in the ratios ${\cal B}(B \to \rho \gamma)/{\cal B}(B \to K^* \gamma)$ and $\Delta = (\Delta^{+0}+ \Delta^{-0})/2$, where $\Delta^{\pm 0} = \Gamma (B^\pm \to \rho^\pm \gamma)/ [2 \Gamma (B^0 (\bar B^0)\to \rho^0 \gamma)] - 1$, and hence their measurements will provide quantitative information on the standard model parameters, in particular the ratio of the CKM matrix elements $| V_{td}/V_{ts}|$ and the inner angle $\alpha$ of the CKM-unitarity triangle. We also calculate direct CP asymmetries for the decays $B^\pm \to \rho^\pm \gamma$ and $B^0/\bar B^0 \to \rho^0 \gamma$ and find, in conformity with the observations made in the existing literature, that the hard spectator contributions significantly reduce the asymmetries arising from the vertex corrections.Comment: 45 pages, 18 figures (requires amssymb and epsf); replaced with the revised versio

Implication of the B→(ρ,ω)γB \to (\rho, \omega) \gamma Branching Ratios for the CKM Phenomenology

We study the implication of the recent measurement by the BELLE collaboration of the averaged branching fraction $\bar B_{exp} [B \to (\rho, \omega) \gamma] = (1.8^{+0.6}_{-0.5} \pm 0.1) \times 10^{-6}$ for the CKM phenomenology. Combined with the averaged branching fraction $\bar B_{exp} (B \to K^* \gamma) = (4.06 \pm 0.26) \times 10^{-5}$ measured earlier, this yields $\bar R_{exp} [(\rho, \omega) \gamma/K^* \gamma] = (4.2 \pm 1.3)$ for the ratio of the two branching fractions. Updating earlier theoretical analysis of these decays based on the QCD factorization framework, and constraining the CKM-Wolfenstein parameters from the unitarity fits, our results yield $\bar B_{th} [B \to (\rho, \omega) \gamma] = (1.38 \pm 0.42) \times 10^{-6}$ and $\bar R_{th} [(\rho, \omega) \gamma/K^* \gamma] = (3.3 \pm 1.0)$, in agreement with the BELLE data. Leaving instead the CKM-Wolfenstein parameters free, our analysis gives (at 68% C.L.) $0.16\leq |V_{td}/V_{ts}| \leq 0.29$, which is in agreement with but less precise than the indirect CKM-unitarity fit of the same, $0.18 \leq |V_{td}/V_{ts}| \leq 0.22$. The isospin-violating ratio in the $B \to \rho \gamma$ decays and the SU(3)-violating ratio in the $B_d^0 \to (\rho^0, \omega) \gamma$ decays are presented together with estimates of the direct and mixing-induced CP-asymmetries in the $B \to (\rho,\omega) \gamma$ decays within the SM. Their measurements will overconstrain the angle $\alpha$ of the CKM-unitarity triangle.Comment: 21 pages, 3 figures. Included a discussion of model-dependent estimates of the long-distance/rescattering contributions in radiative B-decays; added a reference. Version accepted for publication in Physics Letters

Spin current injection by intersubband transitions in quantum wells

We show that a pure spin current can be injected in quantum wells by the absorption of linearly polarized infrared radiation, leading to transitions between subbands. The magnitude and the direction of the spin current depend on the Dresselhaus and Rashba spin-orbit coupling constants and light frequency and, therefore, can be manipulated by changing the light frequency and/or applying an external bias across the quantum well. The injected spin current should be observable either as a voltage generated via the anomalous spin-Hall effect, or by spatially resolved pump-probe optical spectroscopy.Comment: minor changes, short version publishe

Branching Fraction of the Decay B+→π+τ+τ−B^+ \to \pi^+ \tau^+ \tau^- and Lepton Flavor Universality Test via the Ratio Rπ(τ/μ)R_\pi (\tau/\mu)

Among (semi)leptonic rare $B$-decays induced by the $b \to d$ flavor changing neutral current, the decay $B^+ \to \pi^+ \mu^+ \mu^-$ is the only one observed so far experimentally. Related decays involving the $e^+e^-$ and $\tau^+ \tau^-$ pairs are the targets for the ongoing experiments at the LHC, in particular LHCb, and Belle II. The muonic and electronic semileptonic decays have almost identical branching fractions in the Standard Model (SM). However, the tauonic decay $B^+ \to \pi^+ \tau^+ \tau^-$ differs from the other two due to the higher reaction threshold which lies slightly below the $\psi (2S)$-resonance. We present calculations of the ditauon ($\tau^+ \tau^-$) invariant-mass distribution and the branching fraction ${\rm Br} (B^+ \to \pi^+ \tau^+ \tau^-)$ in the SM based on the Effective Electroweak Hamiltonian approach, taking into account also the so-called long-distance contributions. The largest theoretical uncertainty in the short-distance part of the decay rates is due to the $B \to \pi$ form factors, which we quantify using three popular parametrizations. The long-distance contribution can be minimized by a cut on the ditauon mass $m_{\tau^+ \tau^-} > M_{\psi (2S)}$. Once available, the branching fractions in the tauonic and muonic (and electronic) modes provide stringent test of the lepton flavor universality in the $b \to d$ transitions. We illustrate this by calculating the ratio $R_\pi (\tau/\mu) \equiv {\rm Br} (B^+ \to \pi^+ \tau^+ \tau^-)/{\rm Br} (B^+ \to \pi^+ \mu^+ \mu^-)$ in the SM for the total and binned ratios of the branching fractions.Comment: 11 pages, 5 figures, 11 table

The η′g∗g(∗)\eta^\prime g^* g^{(*)} Vertex Including the η′\eta^\prime-Meson Mass

The $\eta^\prime g^* g^{(*)}$ effective vertex function is calculated in the QCD hard-scattering approach, taking into account the $\eta^\prime$-meson mass. We work in the approximation in which only one non-leading Gegenbauer moment for both the quark-antiquark and the gluonic light-cone distribution amplitudes for the $\eta^\prime$-meson is kept. The vertex function with one off-shell gluon is shown to have the form (valid for $| q_1^2 | > m_{\eta^\prime}^2$) $F_{\eta^\prime g^* g} (q_1^2, 0, m_{\eta^\prime}^2) = m_{\eta^\prime}^2 H(q_1^2)/(q_1^2 - m_{\eta^\prime}^2)$, where $H(q_1^2)$ is a slowly varying function, derived analytically in this paper. The resulting vertex function is in agreement with the phenomenologically inferred form of this vertex obtained from an analysis of the CLEO data on the $\eta^\prime$-meson energy spectrum in the decay $\Upsilon(1S) \to \eta^\prime X$. We also present an interpolating formula for the vertex function $F_{\eta^\prime g^* g} (q_1^2, 0, m_{\eta^\prime}^2)$ for the space-like region of the virtuality $q_1^2$, which satisfies the QCD anomaly normalization for on-shell gluons and the perturbative-QCD result for the gluon virtuality $| q_1^2| \gtrsim 2$ GeV$^2$.Comment: 26 pages, 6 figures; use epsfig.sty; submitted to the European Physical Journal

An Analysis of the Inclusive Decay Υ(1S)→η′X\Upsilon (1S) \to \eta^\prime X and Constraints on the η′\eta^\prime-Meson Distribution Amplitudes

We calculate the $\eta^\prime$-meson energy spectrum in the decay $\Upsilon (1S) \to \eta^\prime g g g \to \eta^\prime X$ in the leading-order perturbative QCD in the static quark limit for the Orthoquarkonium. Our principal result is the extraction of parameters of the $\eta^\prime g^* g$ effective vertex function (EVF) involving a virtual and a real gluon from the available data on the hard part of the $\eta^\prime$-meson energy spectrum. The perturbative QCD based framework provides a good description of the available CLEO data, allowing to constrain the lowest Gegenbauer coefficients $B^{(q)}_2$ and $B^{(g)}_2$ of the quark-antiquark and gluonic distribution amplitudes of the $\eta^\prime$-meson. The resulting constraints are combined with the existing ones on these coefficients from an analysis of the $\eta-\gamma$ and $\eta^\prime-\gamma$ transition form factors and the requirement of positivity of the EVF, yielding $B^{(q)}_2(\mu_0^2) = -0.008 \pm 0.054$ and $B^{(g)}_2(\mu_0^2) = 4.6 \pm 2.5$ for $\mu_0^2 = 2$ GeV$^2$. This reduces significantly the current uncertainty on these coefficients. The resulting EFV $F_{\eta^\prime g^* g} (p^2, 0, m_{\eta^\prime}^2)$, including the $\eta^\prime$-meson mass effects, is presented.Comment: 23 pages, 8 figures; use epsfig.sty; Typos corrected, numerical analysis further refined; added an equation; to appear in the European Physical Journal

A New Look at the YY Tetraquarks and Ωc\Omega_c Baryons in the Diquark Model

We analyze the hidden charm $P$-wave tetraquarks in the diquark model, using an effective Hamiltonian incorporating the dominant spin-spin, spin-orbit and tensor interactions. We compare with other $P$-wave system such as $P$-wave charmonia and the newly discovered $\Omega_c$ baryons, analysed recently in this framework. Given the uncertain experimental situation on the $Y$ states, we allow for different spectra and discuss the related parameters in the diquark model. In addition to the presently observed ones, we expect many more states in the supermultiplet of $L=1$ diquarkonia, whose $J^{PC}$ quantum numbers and masses are worked out, using the parameters from the currently preferred $Y$-states pattern. The existence of these new resonances would be a decisive footprint of the underlying diquark dynamics.Comment: Revised and extended to accommodate referee comments. Added a table and references. Accepted for publication in the EPJ