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Register a new userIsospin violation in mixing and decays of rho- and omega-mesons
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Authors
Ya. I. Azimov
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Influence of the isospin-violating (rho^0, omega)-mixing is discussed for any pair of decays of rho^0, omega into the same final state. It is demonstrated, in analogy to the CP-violation in neutral kaon decays, that isospin violation can manifest itself in various forms: direct violation in amplitudes and/or violation due to mixing. In addition to the known decays (rho^0, omega)topi^+pi^- and (rho^0, omega)topi^0gamma, the pair of decays to e^+e^- and the whole set of radiative decays with participation of rho^0, omega (in initial or final states) are shown to be also useful and perspective for studies. Existing data on these decays agree with the universal character of the mixing parameter and indirectly support enhancement of rho^0topi^0gamma in respect to rho^{pm}topi^{pm}gamma. Future precise measurements will allow to separate different forms of isospin violation and elucidate their mechanisms.
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Isospin violating mixing of rho- and omega-mesons is reconsidered in terms of propagators. Its influence on various pairs of (rho^0,omega)-decays to the same final states is demonstrated. Some of them, (rho^0,omega)topi^+pi^- and (rho^0,omega)topi^0gamma, have been earlier discussed in the literature, others (e.g., (rho^0,omega)toetagamma and (rho^0,omega)to e^+e^-) are new in this context. Changes in partial widths for all the decay pairs are shown to be correlated. The set of present experimental data, though yet inconclusive, provides some limits for the direct (rhoomega)-coupling and indirectly supports enhancement of rho^0topi^0gamma in comparison with rho^{pm}topi^{pm}gamma, though not so large as in some previous estimates.
The strong and electromagnetic corrections to $rho-omega$ mixing are calculated using a SU(2) version of resonance chiral theory up to next-to-leading orders in $1/N_C$ expansion, respectively. Up to our accuracy, the effect of the momentum dependence of $rho-omega$ mixing is incorporated due to the inclusion of loop contributions. We analyze the impact of $rho-omega$ mixing on the pion vector form factor by performing numerical fit to the data extracted from $e^+e^-rightarrow pi^+pi^-$ and $taurightarrow u_{tau}2pi$, while the decay width of $omegarightarrow pi^+pi^-$ is taken into account as a constraint. It is found that the momentum dependence is significant in a good description of the experimental data. In addition, based on the fitted values of the involved parameters, we analyze the decay width of $omega rightarrow pi^+pi^-$, which turns out to be highly dominated by the $rho-omega$ mixing effect.
The problem of $rho$- and $omega$- mesons contributions to the background for $eta to pi^0 e^+e^-$ decay and to the asymmetries in the decays $eta to pi^+pi^-pi^0$ and $eta to pi^+pi^-gamma$ is considered.
The phenomenon of mixing in neutral meson systems has now been observed in all flavours, but only in the past year in the D0 system. The standard model anticipated that, for the charm sector, the mixing rate would be small, and also that CP violation, either in mixing or in direct decay, would be below the present levels of observability. It is hoped that further study of these phenomena might reveal signs of new physics. A review of recently available, experimental results is given.
The approximate symmetry of the strong interactions under isospin transformations is among the most precise tools available to control hadronic matrix elements. It is crucial in extracting fundamental parameters, but also provides avenues for the search of phenomena beyond the Standard Model. The precision of the resulting predictions requires special care when determining the quantities they are to be tested with. Specifically, in the extraction of branching ratios often isospin symmetry is assumed at one point or another implicitly, implying a significant bias for precision analyses. We extract a bias-free value for the production asymmetry between charged and neutral $B$ meson pairs at $B$ factories and discuss its consequences for the determination of branching fractions generally, and isospin-violating observables like the rate asymmetries in B -> J/psi K or B -> K* gamma decays specifically.
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