Speaker
Description
A search for a narrow baryonic state in the $pK_S^0$ and $\bar{p}K_S^0$ system has been performed in $ep$ collisions at HERA with the ZEUS detector using an integrated luminosity of 358 pb$^{−1}$ taken in 2003-2007. The search was performed with deep inelastic scattering (DIS) events at an $ep$ centre-of-mass energy of 318 GeV for exchanged photon virtuality, $Q^2$, between 20 and 100 GeV$^2$. Contrary to evidence presented for such a state around 1.52 GeV in a previous ZEUS analysis using a sample of 121 pb$^{−1}$, taken in 1995–2000, no resonance peak is found in the $p(\bar{p})K_S^0$ invariant-mass distribution in the range 1.45–1.7 GeV. Upper limits on the production cross section are set for different assumptions on the width of the resonance.
The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 2 < Q2 < 80 GeV2, 30 < W < 210 GeV and |t| < 1 GeV2, where Q2 is the photon virtuality, W is the photon--proton centre-of-mass energy and t is the squared four-momentum transfer at the
proton vertex. The data for 2 < Q2 < 5 GeV2 were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb−1. The data for 5 < Q2 < 80 GeV2 are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb−1. The decay modes analysed were μ+μ− and J/ψ(1S)π+π− for the ψ(2S) and μ+μ− for the J/ψ(1S). The cross-section ratio σ(ψ(2S))/σ(J/ψ(1S)) has been measured as a function of Q2, W, and t. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.
| Experimental Collaboration | ZEUS |
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