Paper detail

Measurement of mass and width of the excited charmed meson states $D_1^0$ and $D_2^{*0}$

This paper describes a measurement of the mass and of the width of two neutral narrow resonances $D_10$ and $D_2^{0*}$, both composed of a charm quark and an up antiquark. The difference with respect to the well-known resonance $D0$, also neutral and with the same quark composition, is that the two quarks have an orbital momentum 1, which increases their binding energy. Therefore the mass is larger than that of the $D0$. Since the relative orientation of the spin is the same, in the limit of very large charm mass, the masses of these resonances should be the same; their small difference is predicted by theory and therefore important to measurement to distinguish the different models. These states have been observed in their decay into a kaon and three pions; two of these particles are required to originate from a displaced vertex with respect to the primary interaction vertex, to account for the longer lifetime of the charmed mesons. The resonances parameters have been extracted using a fitting procedure accounting for the expected resonance shape, including effects from detector resolution and background, providing a new best single measurement of the $D_10$ and $D_2^{0*}$ masses and a competitive measurement of their widths.