Production of the excited charm mesons D_1 and D^*_2 at HERA

TL;DR

This paper reports measurements of excited charm mesons D_1 and D^*_2 at HERA, including their masses, widths, decay properties, and production rates, providing insights into charm quark hadronization and meson decay dynamics.

Contribution

It presents the first detailed measurements of D_1 and D^*_2 production and decay parameters in ep collisions, comparing them with previous e^+ e^- results and theoretical models.

Findings

Masses and widths of D_1 and D^*_2 measured.

Helicity parameter of D_1^{0} determined, indicating possible decay wave mixing.

Production fractions of charm quarks into D_1 and D^*_2 consistent with e^+ e^- data.

Abstract

The production of the excited charm mesons D_1(2420) and D^*_2(2460) in ep collisions has been measured with the ZEUS detector at HERA using an integrated luminosity of 373 pb^{-1}. The masses of the neutral and charged states, the widths of the neutral states, and the helicity parameter of D_1(2420)^{0} were determined and compared with other measurements and with theoretical expectations. The measured helicity parameter of the D^0_1 allows for some mixing of S- and D-waves in its decay to D^{*\pm}\pi^{\mp}. The result is also consistent with a pure D-wave decay. Ratios of branching fractions of the two decay modes of the D^*_2(2460)^0 and D^*_2(2460)^{\pm} states were measured and compared with previous measurements. The fractions of charm quarks hadronising into D_1 and D^{*}_2 were measured and are consistent with those obtained in e^+ e^- annihilations.