Speaker
Giuseppe Mandaglio
(University of Messina)
Description
KLOE and KLOE-2 data (almost 8 fb$^{-1}$) constitute the largest sample ever collected at an electron-positron collider operating at the $\phi$ peak resonance.
In total it corresponds to the production of about 24 billion of $\phi$ mesons whose decays include about 8 billion pairs of neutral K mesons and about 300 million $\eta$ mesons.
A wide hadron physics program, investigating rare meson decays, $\gamma-\gamma$ interaction, dark forces and hadronic cross section, is thus carried out by the KLOE-2 Collaboration.
The $\eta \to \pi^0 \gamma \gamma$ decay is a test bench for various models and effective theories like VMD (Vector Meson Dominance) or ChPT (Chiral
Perturbation Theory) which predict BR far from experimental value. KLOE-2, with its highly pure $\eta$ sample produced
in $\phi \to \eta \gamma$ process, has a new preliminary measurement of this branching ratio.
Following the many contributions KLOE and KLOE-2 has done to Dark Matter searches, an alternative model, where the Dark Force mediator is an hypothetical leptophobic B boson, is investigated in the $\phi \to \eta B\to \eta \pi^0\gamma\,, \eta \to \gamma \gamma$ channel.
A KLOE-2 distinctive feature is also the the possibility to investigate $\pi^0$ production from $\gamma \gamma$ scattering by
tagging final-state leptons from $e^+e^- \to \gamma^{\ast}\gamma^{\ast}e^+e^-\to \pi^0 e^+e^-$ in coincidence with the $\pi^0$ in the barrel calorimeter. KLOE-2 aims to use this process to precisely measure the $\pi^0$ decay width into $ \gamma\gamma$ to test low-energy QCD dynamics. Progresses made on the $\gamma^{\ast}\gamma^{\ast}\to \pi^0$ event counting will be reported.
A search for the P and CP violating decay $\eta\rightarrow\pi^+\pi^-$ has been recently published by KLOE-2 using 1.6~fb$^{-1}$ of KLOE data.
No signal is observed in the $\pi^+\pi^-$ invariant mass spectrum, and the
upper limit on the branching fraction at 90\% confidence level is B($\eta\rightarrow\pi^+\pi^-$)$< 4.9 \times 10^{−6}$, which is
three times lower than previous KLOE result. A combination of the two KLOE limits will be presented.
Moreover, the search for the double suppressed $\phi\rightarrow \eta\, \pi^+ \pi^- $ and the conversion
$\phi\rightarrow \eta\, \mu^+ \mu^- $ decays are performed at KLOE-2 with both $\eta \to \gamma \gamma$ and $\eta \to 3\pi^0$ final states. Clear signals are seen for the first time.
Finally, preliminary and promising results on the $\omega$ cross section measurement in the $e^+ e^- \to \pi^+ \pi^- \pi^0 \gamma_{\rm ISR}$ channel using the Initial State Radiation (ISR) method will be also presented.
Primary author
Giuseppe Mandaglio
(University of Messina)
