Angular analysis of the $e^+ e^- \to D^{(*) \pm} D^{* \mp}$ process near the open charm threshold using initial-state radiation

TL;DR

This paper presents precise measurements of the cross sections for the process e+ e- to D(*)± D*∓ near the open charm threshold, including the first angular analysis of the D* helicity components, using initial-state radiation data from Belle.

Contribution

It provides the most accurate cross section measurements to date and introduces the first angular analysis of the D* helicity states in this process.

Findings

Cross section measurements are twice as precise as previous Belle results.

First angular decomposition of the e+ e- to D*+ D*- process into helicity components.

Observation of the energy dependence of the cross sections near the open charm threshold.

Abstract

We report a new measurement of the exclusive $e^+ e^- \to D^{(*) \pm} D^{*\mp}$ cross sections as a function of the center-of-mass energy from the $D^{(*) \pm} D^{* \mp}$ threshold through $\sqrt{s}=6.0$ GeV with initial-state radiation. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of $951$ fb$^{-1}$. The accuracy of the cross section measurement is increased by a factor of two over the first Belle study. We perform the first angular analysis of the $e^+ e^- \to D^{* \pm} D^{* \mp}$ process and decompose this exclusive cross section into three components corresponding to the $D^*$ helicities.