Garchinger Maier-Leibnitz-Kolloquium: Partial-Wave Analysis of the tau^- -> pi^- pi^- pi^+ nu_tau Decay at Belle

by Dr Andrei Rabusov (Physik Department E18, TUM)

Thursday 8 Feb 2024, 16:15 → 17:15 Europe/Berlin

Lecture Hall, ground floor (west) (LMU building, Am Coulombwall 1, campus Garching)

Searches for new particles and interactions that are not part of the Standard Model require knowledge of various hadronic form-factors. The parameters of the axial-vector form-factor are not well known. The tau-lepton, a heavier analog of the electron, which can decay into hadrons, provides a clean laboratory to study these parameters for a low energy range where the a_1(1260) resonance dominates the tau^- --> pi^- pi^- pi^+ nu_tau decay. To know how the a_1(1260) and its possible excited states affect the decay, we disentangle possible intermediate states. We use the data collected with the Belle detector at the KEKB e^+ e^- collider. We observe an a_1(1420)-like signal in the 1^+[f_0(980) pi]_P wave for the first time in tau-lepton decays. Also, we find a significant signal of the 1^-[omega(782) pi]_P wave driven by the rare decay of omega(782) --> pi^+ pi^- which violates G-parity. I will present a validation of our findings using a model-independent approach. These results will improve the modeling in simulation studies necessary for measuring the tau electric and magnetic dipole moments and its Michel parameters.

kolloquium-08-02-24.pdf