Phenomenological applications of η and η’ mesons

Student thesis: Doctoral thesis


The present PhD thesis entitled "Application of phenomenological months η and η' " focuses on studying various physical processes involving these mesons.

The physical η i η’ are the result of rotating the mathematical states η8 i η0 that appear in the Lagrangian of Chiral Perturbation Theory once the number of colors is considered as an expansion parameter together with the momenta and quark masses. Therefore, to deal with these mesons is more involved that working with the other pseudoscalar mesons of the theory i.e. pion and kaons. Currently, there are several experiments, such as Belle-II or BESIII among other, which have the phenomenology involving η and η’ mesons among one of their main objectives, whose understanding requires from solid theoretical models. This thesis has been mainly devoted to employ different models to describe and to understand the processes I detail in the following.

·) The first part of the thesis, is dedicated to study different hadronic decays of the tau lepton. In particular the processes τ→K−ηντ , τ→K−η’ντ , τ→Ksπ−ντ ,τ→π−ηντ i τ→ π−η’ντ have been analasyed or predicted in the framework of Chiral Perturbation Theory including resonances as explicit degrees of freedom, making use of dispersion relations for parameterizng the participant form factors and hence ensuring analiticity and unitarity. As a remarkable results, from the combined analysis of the experimental data on the decay spectra of the τ→K−ηντ and τ→Ksπ−ντ decays released by the Belle collaboration, we have obtained the resonance parameters, mass and width, of the vector Κ∗(1410) resonance with a substancial improved precision respect previous analyses. Regarding the τ→π−ηντ and τ→ π−η’ντ decays, which have not seen in Nature so far, our main purpose has been to study in detail the corresponding form factors in order to provide predictions on the branching ratios which might serve to guide the experimental collaborations to mesure them.

·) The second part of the thesis has been devoted to the study of transition form factors through Padé approximants. Concretely, we have analysed the existent data on the π0 ,η and η’ transition form factors extracted from the reaction e+e-→e+e-P , where P=π0 ,η , η’ , in order to predict the Dalitz decays η(’)→l+l−γ and η(’)→l+l−l+l− (l=e, μ). This has served us to test these form factors in the time-like region. Our predictions are in accordance with those processes that have already been measured while, again, we hope them to serve as a guide to the respective experimental collaborations to measure both the transition form factors and the corresponding decays. Finally, we have performed a combined analysis of the η’ transition form factor from both the space-and time-like energy regions, where we have addressed the reason why Padé approximants work so well in describing these processes. From this last analysis we have also managed to extract the η i η’ mixing angle with improved precision.

In summary, the physics related with the η i η’ mesons is of great interest at current hadron facilities. Because of that, studies like pursued in this thesis might contribute to complete, to understand and to have a better description of the theory of strong interactions at low-energies.
Date of Award22 Jul 2016
Original languageEnglish
SupervisorRafel Escribano Carrascosa (Director)

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