### Speaker

### Description

Studying electron-positron annihilation into $K_SK\pi$ and $K_SK\pi\pi^0$ with the CMD-3 detector

*A. A. Uskov.
Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences.*

We studied the process $e^+e^- → KK\pi$ with the СMD-3 detector at the electron-positron collider VEPP-2000. The statistics collected by the СMD-3 detector in the energy range of $1.2-2$ GeV during the 2011, 2012, 2017, 2019 runs, with a total luminosity integral of $\sim120pb^{-1}$, was used for the analysis.

The measured cross-section is crucial for the physics of light hadrons from $u, d, s$ quarks, clarifying the hadronic contribution to the anomalous magnetic moment of the muon $(g-2)_\mu$, and independently measuring the resonance parameters of both $\phi(1680)$, $\rho(1450)$. The intermediate dynamics of this process is also of interest, allowing us to check the isotopic relations and prove the dominance of the neutral $K^*(892)$ channel.

We developed a novel methodology for selecting signal events. Including multi-staged kinematic reconstruction. By adding the second stage, we reduced the background $\sim5$ more times. This stage depends on a rigorous study of the background. Since we identified - the main physical background to be the process $e^+e^- → 4\pi$.

The outline of the designed steps:

- Kinematic reconstruction with $4$ charged tracks.
- Track combination, to distinguish the $K_S$ meson by invariant mass and decay vertex.
- Restriction on the energy of $\gamma$ not bound to tracks.
- Final selection of signal events based on analysis of 2D-distribution of four-track events by energy imbalance $\Delta E$ and momentum vector sum modulus of all four particles $\Delta p$.
- Simulation to find efficiency $\varepsilon$ and estimate systematic errors.

So, as a result of this work we not only designed a new selection algorithm, but also studied the theoretical aspect of the cross-section in the Vector Meson Dominance Framework. Therefore, we improved the world precision of $\phi(1680)$, $\rho(1450)$ and measured the cross-section of $e^+e^- → KK\pi$ with the best accuracy.