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Register a new userQuarkonium radiative decays from the hadronic Paschen-Back effect
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We study the radiative (E1 and M1) decays of P-wave quarkonia in a strong magnetic field based on the Lagrangian of potential nonrelativistic QCD. To investigate their properties, we implement a polarized wave function basis justified in the Paschen-Back limit. In a magnetic field stronger than the spin-orbit coupling, the wave functions of the P-wave quarkonia are drastically deformed by the Hadronic Paschen-Back effect. Such deformation leads to the anisotropy of the direction of decays from the P-wave quarkonia. The analytic formulas for the radiative decay widths in the nonrelativistic limit are shown, and the qualitative decay properties are discussed.
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Recently CLEO has studied the radiative decay of $Upsilon$ into $eta$ and an upper limit for the decay has been determined. Confronting with this upper limit,most of theoretical predictions for the decay fails. After briefly reviewing these predictions we re-examine the decay by separating nonperturbative effect related to the quarkonium and that related to $eta$ or $eta$, in which the later is parameterized by distribution amplitudes of gluons in $eta$. With this factorization approach we obtain theoretical predictions which are in agreement with experiment. Uncertainties in our predictions are discussed. The possibly largest uncertainties are from relativistic corrections for $J/Psi$ and the value of the charm quark mass. We argue that the effect of these uncertainties can be reduced by using quarkonium masses instead of using quark masses. An example of the reduction is shown with an attempt to explain the violation of the famous 14% rule in radiative decays of charmonia.
Recently, the Belle collaboration measured the ratios of the branching fractions of the newly observed $Omega(2012)$ excited state. They did not observe significant signals for the $Omega(2012) to bar{K} Xi^*(1530) to bar{K} pi Xi$ decay, and reported an upper limit for the ratio of the three body decay to the two body decay mode of $Omega(2012) to bar{K} Xi$. In this work, we revisit the newly observed $Omega(2012)$ from the molecular perspective where this resonance appears to be a dynamically generated state with spin-parity $3/2^-$ from the coupled channels interactions of the $bar{K} Xi^*(1530)$ and $eta Omega$ in $s$-wave and $bar{K} Xi$ in $d$-wave. With the model parameters for the $d$-wave interaction, we show that the ratio of these decay fractions reported recently by the Belle collaboration can be easily accommodated.
We propose a new theory framework to study the electroweak radiative corrections in $K_{l3}$ decays by combining the classic current algebra approach with the modern effective field theory. Under this framework, the most important $mathcal{O}(G_Falpha)$ radiative corrections are described by a single tensor $T^{mu u}$ involving the time-ordered product between the charged weak current and the electromagnetic current, and all remaining pieces are calculable order-by-order in Chiral Perturbation Theory. We further point out a special advantage in the $K_{l3}^{0}$ channel that it suffers the least impact from the poorly-constrained low-energy constants. This finding may serve as a basis for a more precise extraction of the matrix element $V_{us}$ in the future.
We show that the large corrections due to final state interactions (FSI) in the D^+to pi^-pi^+pi^+, D^+_sto pi^-pi^+pi^+, and D^+to K^-pi^+pi^+ decays can be accounted for by invoking scattering amplitudes in agreement with those derived from phase shifts studies. In this way, broad/overlapping resonances in S-waves are properly treated and the phase motions of the transition amplitudes are driven by the corresponding scattering matrix elements determined in many other experiments. This is an important step forward in resolving the puzzle of the FSI in these decays. We also discuss why the sigma and kappa resonances, hardly visible in scattering experiments, are much more prominent and clearly visible in these decays without destroying the agreement with the experimental pipi and Kpi low energy S-wave phase shifts.
We summarise the perspectives on heavy-quarkonium production at the LHC, both for proton-proton and heavy-ion runs, as emanating from the round table held at the HLPW 2008 Conference. The main topics are: present experimental and theoretical knowledge, experimental capabilities, open questions, recent theoretical advances and potentialities linked to some new observables.
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