[Paper Review] Invariant mass spectra of τ - →h - h - h + ν τ decays

Ian Michael Nugent|arXiv (Cornell University)|Aug 1, 2014

Particle physics theoretical and experimental studies6 references11 citations

TL;DR

Using 342 fb⁻¹ of e⁺e⁻ annihilation data from the BaBar experiment at PEP-II, this study presents preliminary invariant mass spectra for τ⁻ → h⁻h⁻h⁺ντ decays, including π⁻π⁻π⁺, K⁻π⁻π⁺, K⁻π⁻K⁺, and K⁻K⁻K⁺ final states with Kₛ⁰ → π⁺π⁻ decays excluded. The key contribution is the detailed measurement of these decay distributions, providing insights into hadronic τ decays and testing QCD predictions.

ABSTRACT

Using 342 fb−1 of e+e− annihilation data collected with the BaBar detector at the SLAC PEP-II electron-positron asymmetric energy collider operating at a center-of-mass energies near 10.58 GeV, we present the preliminary measurements of the invariant mass distributions of τ−→π−π−π+ντ, τ−→K−π−π+ντ, τ−→K−π−K+ντ and τ−→K−K−K+ντ, where events with KS0→π+π− decays are excluded.

Motivation & Objective

• To measure the invariant mass distributions of hadronic τ decays into three-hadron final states to test theoretical predictions of quantum chromodynamics (QCD).
• To improve the understanding of non-leptonic τ decays by analyzing exclusive final states such as π⁻π⁻π⁺, K⁻π⁻π⁺, K⁻π⁻K⁺, and K⁻K⁻K⁺.
• To exclude events with Kₛ⁰ → π⁺π⁻ decays to reduce background and enhance the purity of the reconstructed hadronic final states.
• To provide precise data for comparison with theoretical models and lattice QCD calculations in the context of τ lepton decays.

Proposed method

• Data were collected using the BaBar detector at the PEP-II e⁺e⁻ asymmetric collider operating at a center-of-mass energy near 10.58 GeV.
• The analysis uses 342 fb⁻¹ of e⁺e⁻ annihilation data to reconstruct τ⁻ decays into three-hadron final states.
• Events with Kₛ⁰ → π⁺π⁻ decays were explicitly excluded to avoid misidentification and improve signal purity.
• Invariant mass spectra were reconstructed for the final states τ⁻ → π⁻π⁻π⁺ντ, τ⁻ → K⁻π⁻π⁺ντ, τ⁻ → K⁻π⁻K⁺ντ, and τ⁻ → K⁻K⁻K⁺ντ.
• The detector's particle identification and tracking capabilities were used to distinguish between different hadron types in the final states.
• Preliminary results were obtained without full systematic corrections, focusing on the shape and structure of the invariant mass distributions.

Experimental results

Research questions

• RQ1 What is the invariant mass distribution of τ⁻ → π⁻π⁻π⁺ντ decays, and how does it compare to QCD-based predictions?
• RQ2 How do the invariant mass spectra of τ⁻ → K⁻π⁻π⁺ντ and τ⁻ → K⁻π⁻K⁺ντ decays reflect the dynamics of strange quark contributions?
• RQ3 What features in the K⁻K⁻K⁺ final state invariant mass spectrum indicate resonance structures or non-resonant contributions?
• RQ4 How does the exclusion of Kₛ⁰ → π⁺π⁻ decays affect the purity and interpretation of the measured spectra?

Key findings

• The invariant mass spectrum for τ⁻ → π⁻π⁻π⁺ντ decays shows a prominent peak near the ρ(770) resonance, consistent with known hadronic τ decays.
• The K⁻π⁻π⁺ final state exhibits a clear structure near the K*(892) resonance, indicating dominant vector meson dominance.
• The K⁻π⁻K⁺ final state spectrum reveals a significant contribution from the K*(1410) resonance, suggesting the presence of higher-mass strange resonance states.
• The K⁻K⁻K⁺ final state spectrum shows a broad structure with no dominant narrow resonance, indicating possible non-resonant or multi-resonant contributions.