Scaled momentum distributions for the strange hadrons K0s and Lambda/bar Lambda were measured in deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 330 pb-1. The evolution of these distributions with the photon virtuality, Q2, was studied in the kinematic region 10<Q2<40000 GeV2 and 0.001<x<0.75, where x is the Bjorken scaling variable. Clear scaling violations are observed. Predictions based on different approaches to fragmentation were compared to the measurements. Leading-logarithm parton-shower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Next-to-leading-order QCD calculations based on fragmentation functions, FFs, extracted from e+e- data alone, fail to describe the measurements. The calculations based on FFs extracted from a global analysis including e+e-, ep and pp data give an improved description. The measurements presented in this paper have the potential to further constrain the FFs of quarks, anti-quarks and gluons yielding K0s and Lambda/bar Lambda strange hadrons.
The measured scaled momentum distributions for K0S production as a function of Q^2 in three XP regions.
The measured scaled momentum distributions for K0S production as a function of Q^2 in six XP regions.
The measured scaled momentum distributions for K0S production as a function of Q^2 in three XP regions.
Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^{-1}. Charm has been tagged by reconstructing D^{*+}, D^0, D^{+} and D_s^+ (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range p_T(D^{*+},D^0,D^{+}) > 3 GeV, p_T(D_s^+)>2 GeV and |\eta(D)| < 1.6 for 1.5 < Q^2 < 1000 GeV^2 and 0.02 < y < 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising into a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in p_T(D) and \eta(D) in order to determine the open-charm contribution, F_2^{c\bar{c}}(x,Q^2), to the proton structure function F_2.
Production cross section for all D0 mesons, those not originating fom D* decays and those originating from D* decays.
Production cross section for additional D* mesons (not decaying to D0) and all D* mesons.
Production cross section for D+ mesons.
We report the first observation of $K^{\star}(892)^{0}\to\pi K$ in relativistic heavy ion collisions. The transverse momentum spectrum of $(K^{\star0}+\bar{K}^{\star0})/2$ from central Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV is presented. The ratios of the $K^{\star0}$ yield derived from these data to the yields of negative hadrons, charged kaons, and $\phi$ mesons have been measured in central and minimum bias collisions and compared with model predictions and comparable $e^{+}e^{-}$, $pp$, and $\bar{p}p$ results. The data indicate no dramatic reduction of $K^{\star0}$ production in relativistic heavy ion collisions despite expected losses due to rescattering effects.
Transverse mass spectrum of K*0 with YRAP = -0.5 to 0.5 for the 14 PCT most central interactions. Numerical values requested from the authors.
K*0 to negative hadron ratio using hadron data from Adler et al PRL 87,112303(2001).
K*0 to kaon ratio using STAR kaon data.
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