Prof Roman Walczak

Abstract:

We present the results from the laserwire system at the Accelerator Test Facility 2 (ATF2) during recent operation after relocation to the virtual image point of the ATF2 final focus. The characterisation of the 150 mJ, 77 ps long laser pulses at a scaled virtual interaction point is used to deconvolve the transverse laserwire profile demonstrating a 1.16 ± 0.06 μm vertical electron beam profile. Horizontal laserwire scans were used in combination with the vertical scans to measure the electron beam size using a full overlap integral model due to the problems presented by a large aspect ratio electron beam. Copyright © 2013 by JACoW.

Abstract:

The laserwire system at the Accelerator Test Facility 2 (ATF2) is a transverse beam profile measurement system capable of measuring a micrometre-size electron beam. We present recent results demonstrating a measured vertical size of 1.16 ± 0.06 μm and a horizontal size of 110.1 ± 3.8 μ m. Due to the high aspect ratio of the electron beam, the natural divergence of the tightly focussed laser beam across the electron beam width requires the use of the full overlap integral to deconvolve the scans. For this to be done accurately, the propagation of the 150 mJ, 167 ps long laser pulses was precisely measured at a scaled virtual interaction point.

Abstract:

The production of D 0, D *+, D +, Ds+ and Λc+ charm hadrons and their antiparticles in ep scattering at HERA has been studied with the ZEUS detector, using a total integrated luminosity of 372 pb-1. The fractions of charm quarks hadronising into a particular charm hadron were derived. In addition, the ratio of neutral to charged D-meson production rates, the fraction of charged D mesons produced in a vector state, and the stangeness-suppression factor have been determined. The measurements have been performed in the photoproduction regime. The charm hadrons were reconstructed in the range of transverse momentum p T > 3.8 GeV and pseudorapidity |η| < 1.6. The charm fragmentation fractions are compared to previous results from HERA and from e + e - experiments. The data support the hypothesis that fragmentation is independent of the production process. © 2013 SISSA.

Abstract:

Charm production in deep inelastic ep scattering was measured with the ZEUS detector using an integrated luminosity of 354 pb-1. Charm quarks were identified by reconstructing D± mesons in the D ± → K∓π±π ± decay channel. Lifetime information was used to reduce combinatorial background substantially. Differential cross sections were measured in the kinematic region 5 < Q 2 < 1000 GeV 2, 0.02 < y < 0.7, 1.5 < p T (D ±) < 15 GeV and |η(D ±)| < 1.6, where Q 2 is the photon virtuality, y is the inelasticity, and p T (D ±) and η(D ±) are the transverse momentum and the pseudorapidity of the D ± meson, respectively. Next-to-leading-order QCD predictions are compared to the data. The charm contribution, F2cc̄, to the proton structure-function F 2 was extracted. © 2013 SISSA.