The Pion-Photon Transition Form Factor and New Physics in the Tau Sector

Abstract

Recent measurement of the $\gamma {\gamma }^{\ast }$ form factor of the neutral pion in the high $Q^2$ region disagrees with {\em a priori} predictions of QCD-based calculations. We comment on existing explanations, and analyze a possibility that this discrepancy is not due to poorly understood QCD effects, but is a result of some new physics beyond the standard model (SM). We show that such physics would necessarily involve a new neutral light state with mass close to the mass of ${\pi }^0$, and with stronger than ${\pi }^0$ couplings to heavier SM flavors such as $c$, $\tau$, and $b$. It is found that only the coupling to the $\tau$ lepton can survive the existing constraints and lead to the observed rise of the pion form factor relative to $Q^{-2}$ at high $Q^2$. We perform numerical fits to data and determine the allowed range of masses and couplings for such new particles. This range of masses and couplings could also reduce or eliminate the tension between the $e^{+}{e}^{-}$ and $\tau$ decay determinations of the hadronic vacuum polarization. Dedicated experimental analysis of $\tau$ pair production in association with such new states should provide a conclusive test of the new physics hypothesis as an explanation to the pion form factor rise. We also comment on the calculations of the pion form factor in the chiral quark model, and point out a possible dynamical origin of the quark mass scale inferred from the form factor measurement.

13 pages, 6 figures, revtex4-1; v2: additional references, improved discussion of pion mixing case, published version

References in corpus (13)

• PYTHIA 6.4 Physics and Manual
• Abelian anomaly and neutral pion production
• Light Cone Sum Rules for the pi0-gamma*-gamma Form Factor Revisited
• Measurement of the gamma gamma* --> eta and gamma gamma* --> eta' transition form factors
• Evolved QCD predictions for the meson-photon transition form factors
• On the Pion Distribution Amplitude Shape
• A New Measurement of the ${\pi }^0$ Radiative Decay Width
• Pion-photon transition---the new QCD frontier
• Constraints on the Light Pseudoscalar Meson Distribution Amplitudes from Their Meson-Photon Transition Form Factors
• Pions in Large-$N$ Quantum Chromodynamics
• Evidence for psi' decays into gamma pi^0 and gamma eta
• Chiral Anomaly Effects and the BaBar Measurements of the $\gamma {\gamma }^{\ast }\to {\pi }^0$ Transition Form Factor
• Status Report from Tau subgroup of the HFAG

Cited by in corpus (11)

• Dark forces coupled to non-conserved currents
• The Leptonic Higgs Portal
• Comparing antithetic trends of data for the pion-photon transition form factor
• Diphotons from Tetraphotons in the Decay of a 125 GeV Higgs at the LHC
• Transition Form Factors and Mixing of Pseudoscalar Mesons from Anomaly Sum Rule
• A combined study of the pion's static properties and form factors
• Hadronic Form Factor Models and Spectroscopy Within the Gauge/Gravity Correspondence
• Influence of confining gluon configurations on the $P\to {\gamma }^{\ast }\gamma$ transition form factors
• Searches for Light Scalars, Pseudoscalars, and Gauge Bosons
• Search for new ${\pi }^0$-like particles produced in association with a $\tau$-lepton pair
• Elastic and transition form factors of light pseudoscalar mesons from QCD sum rules