Studies of Charm Decays

In fig.49 the various $D$-meson states are shown.

Figure: Overview of the known $D$-Meson states. The three columns show the states with $\bar{u}$, $\bar{d}$ and $\bar{s}$ for angular momenta $J=0,1,2$, respectively. The circles indicate those states which have been studied so far at HERA.

ZEUS has reconstructed the resonances $D^0_1$ and $D^{*0}_2$ in the decays into $D^{*\pm}\pi^{\mp}$ (fig.50a) [49]. The fraction of $D^{*\pm}$ mesons produced in decays from $D^0_1$ and $D^{*0}_2$ was determined to be at the level of 3.4 and 1.4%, respectively. In the same analysis, the production rate of $D^{*'\pm}$ mesons in charm fragmentation was determined to be less than 0.7% (95%C.L.).

Figure: The distributions of a-c) $M(D^*\pi )$ and d) of $\Delta M^{ext} + M(D^{*+})_{PDG} + M(K^0)_{PDG}$. Here, $M^{ext}=M(K\pi \pi _s\pi _3\pi _4)-M(K\pi \pi _s)-M(\pi _3\pi _4)$ and $M(D^{*+})_{PDG}$ and $M(K^0)_{PDG}$ are the nominal masses of the $D^{*+}$ and $K_S^0$, respectively.

ZEUS also measured the production of the excited charm-strange meson $D_{s1}^{\pm}(2536)$ using its decays into the final state $D^{*\pm} K_S^0$ [50]. In fig.50b the invariant mass distribution of $D^{*\pm} K_S^0$ candidates is shown. The fraction of $c$ quarks hadronizing as $D_{s1}^{\pm}$ mesons was determined to be $f(c\rightarrow D_{s1}^{+})=1.24 \pm 0.18 (stat.) ^{+0.08}_{-0.06}(syst.) \pm 0.14(BR)$.