First observation of a narrow charm-strange meson DsJ(2632) -> Ds eta and D0 K+

TL;DR

This paper reports the first observation of a narrow charm-strange meson, DsJ(2632), detected in two decay modes with significant statistical evidence, highlighting its unusual decay pattern and narrow width.

Contribution

The discovery of the DsJ(2632) meson in two decay channels with detailed measurements of its mass, width, and decay ratios is a novel experimental result in charm meson spectroscopy.

Findings

Observed DsJ(2632) at 2632.6 MeV/c^2 with high significance

Measured decay modes: Ds eta and D0 K+ with specific event counts

Determined decay width <17 MeV/c^2 and unusual decay pattern

Abstract

We report the first observation of a charm-strange meson DsJ(2632) at a mass of 2632.6+/-1.6 MeV/c^2 in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, Ds eta and D0 K+. In the Ds eta decay mode we observe an excess of 49.3 events with a significance of 7.2sigma at a mass of 2635.9+/-2.9 MeV/c^2. There is a corresponding peak of 14 events with a significance of 5.3sigma at 2631.5+/-1.9 MeV/c^2 in the decay mode D0 K+. The decay width of this state is <17 MeV/c^2 at 90% confidence level. The relative branching ratio Gamma(D0K+)/Gamma(Dseta) is 0.16+/-0.06. The mechanism which keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the Ds eta decay mode.