Production of the excited charm mesons D1 and D*2 at HERA

Abstract

The production of the excited charm mesons D1(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 D1(2420)0 were determined and compared with other measurements and with theoretical expectations. The measured helicity parameter of the D0 1 allows for some mixing of S- and D-waves in its decay to D ∗± π ∓. 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) ± states were measured and compared with previous measurements. The fractions of charm quarks hadronising into D1 and D ∗ 2 were measured and are consistent with those obtained in e + e − annihilations.