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Register a new userThe Eta decay into three neutral pions is mainly electromagnetic
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A. Nehme
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In the framework of Chiral Perturbation Theory including photons, we found that the contribution of the photon exchange between two intermediate charged Kaons to the slope parameter of the decay (etarightarrow 3pi^{0}) amounts to (-0.0221pm 0.0034). When compared with the experimental value, (alpha =-0.0317pm 0.0016), on the one hand, and with the contribution of the up and down quark mass difference, (+0.013pm 0.032), on the other hand, our result leads to the direct conclusion: textit{The} (etarightarrow 3pi^{0}) textit{decay uline{cannot} be used to determine} (m_{d}-m_{u}).
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Sutherlands theorem dictates that the contribution of the electromagnetic interaction to the decay process (etarightarrow 3pi^{0}) is neglected with respect to the one coming from the difference between the up and down quark masses. In the framework of chiral perturbation theory including virtual photons, we calculated the main diagram concerning the exchange of a virtual photon between two intermediate charged pions. The correction induced by this diagram on the slope parameter amounts to (17%) of the correction induced by the pure strong interaction at one-loop level. If this result is maintained when considering all the diagrams at the chiral order we are working, we can say without any doubt that Sutherlands theorem is strongly violated. As a direct consequence, any determination of light quark masses from the present decay textit{should} take into account the electromagnetic interaction.
A search for dinucleon decay into pions with the Super-Kamiokande detector has been performed with an exposure of 282.1 kiloton-years. Dinucleon decay is a process that violates baryon number by two units. We present the first search for dinucleon decay to pions in a large water Cherenkov detector. The modes $^{16}$O$(pp) rightarrow$ $^{14}$C$pi^{+}pi^{+}$, $^{16}$O$(pn) rightarrow$ $^{14}$N$pi^{+}pi^{0}$, and $^{16}$O$(nn) rightarrow$ $^{14}$O$pi^{0}pi^{0}$ are investigated. No significant excess in the Super-Kamiokande data has been found, so a lower limit on the lifetime of the process per oxygen nucleus is determined. These limits are: $tau_{pprightarrowpi^{+}pi^{+}} > 7.22 times 10^{31}$ years, $tau_{pnrightarrowpi^{+}pi^{0}} > 1.70 times 10^{32}$ years, and $tau_{nnrightarrowpi^{0}pi^{0}} > 4.04 times 10^{32}$ years. The lower limits on each mode are about two orders of magnitude better than previous limits from searches for dinucleon decay in iron.
We compute branching ratios and invariant mass distributions of the tau decays into four pions. The hadronic matrix elements are obtained by starting from the structure of the hadronic current in chiral limit and then implementing low-lying resonances in the different channels. Reasonable agreement with experiment is obtained both for the $tau to u_{tau} + (4 pi ) $ decay rates and the $e^+e^- to (4 pi ) $ cross sections. Furthermore we supply an interface to use our matrix elements within the Tauola Monte-Carlo program.
In this work, we calculate the branching ratios for the $eta(eta)rightarrowbar{ell}ell$ decays, where $ell = e,mu$. These processes have tiny rates in the standard model due to spin flip, loop, and electromagnetic suppression, for what they could be sensitive to New Physics effects. In order to provide a reliable input for the Standard Model, we exploit the general analytical properties of the amplitude. For that purpose, we invoke the machinery of Canterbury approximants, which provides a systematic description of the underlying hadronic physics in a data-driven fashion. Given the current experimental discrepancies, we discuss in detail the role of the resonant region and comment on the reliability of $chi$PT calculations. Finally, we discuss the kind of new physics which we think would be relevant to account for them.
A search for forbidden and exotic Z boson decays in the diphoton mass spectrum is presented for the first time in hadron collisions, based on data corresponding to 10.0 fb^-1 of integrated luminosity from proton-antiproton collisions at sqrt(s) = 1.96 TeV collected by the CDF experiment. No evidence of signal is observed, and 95% credibility level Bayesian upper limits are set on the branching ratios of decays of the Z boson to a photon and neutral pion (which is detected as a photon), a pair of photons, and a pair of neutral pions. The observed branching ratio limits are 2.01 x 10^-5 for Z to pi^0gamma, 1.46 x 10^-5 for Z to gammagamma, and 1.52 x 10^-5 for Z to pi^0pi^0. The Z to pi^0gamma and Z to gammagamma limits improve by factors of 2.6 and 3.6, respectively, the most stringent results from other experiments. The Z to pi^0pi^0 branching ratio limit is the first experimental result on this decay.
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