Measurement of the $\phi \to \pi^0 e^+e^-$ transition form factor with the KLOE detector

TL;DR

This paper reports the first measurement of the transition form factor and an improved branching ratio for the decay $\,phi o \,pi^0 e^+e^-$ using data from the KLOE detector, aligning with theoretical expectations.

Contribution

It provides the first measurement of the transition form factor and a more precise branching ratio for the decay, enhancing previous experimental results.

Findings

Measured the transition form factor $|F_{\,phi \,pi^0}(q^2)|$ for the first time.

Determined the branching ratio $\,BR(\phi o \,pi^0 e^+e^-)$ as $(1.35 \,\pm 0.05^{+0.05}_{-0.10}) \times 10^{-5}$.

Results agree with theoretical predictions.

Abstract

A measurement of the vector to pseudoscalar conversion decay $\phi \to \pi^0 e^+e^-$ with the KLOE experiment is presented. A sample of $\sim 9500$ signal events was selected from a data set of 1.7 fb$^{-1}$ of $e^+e^-$ collisions at $\sqrt{s} \sim m_{\phi}$ collected at the DA$\Phi$NE $e^+e^-$ collider. These events were used to obtain the first measurement of the transition form factor $| F_{\phi \pi^0}(q^2) |$ and a new measurement of the branching ratio of the decay: $\rm{BR}\,(\phi \to \pi^0 e^+e^-) = (\,1.35 \pm 0.05^{\,\,+0.05}_{\,\,-0.10}\,) \times 10 ^{-5}$. The result improves significantly on previous measurements and is in agreement with theoretical predictions.