ZEUS Microvertex Detector Research Articles

Measurement of D ± and D 0 production in deep inelastic scattering using a lifetime tag at HERA

The production of D+- and D0 mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb-1. The measurements cover the kinematic range 5 < Q^2 < 1000 GeV^2, 0.02 < y < 0.7, 1.5 < p_T^D < 15 GeV and eta^D < 1.6. Combinatorial background to the D meson signals is reduced by using the ZEUS microvertex detector to reconstruct displaced secondary vertices. Production cross sections are compared with the predictions of next-to-leading-order QCD which is found to describe the data well. Measurements are extrapolated to the full kinematic phase space in order to obtain the open-charm contribution, F2^ccbar, to the proton structure function, F2.

Beauty production at HERA using the ZEUS experiment

Beauty quark production in ep collisions is being studied with the ZEUS detector at HERA. The latest measurements of beauty production in deep inelastic scattering and photoproduction regime are presented. The first measurement exploits the potential of the ZEUS microvertex detector to identify beauty in photoproduction dijet events with a muon in the final state. The second is based on statistical methods to determine the fraction of beauty in photoproduction dijet events with an electron in the final state. Finally, the first measurement by ZEUS of the beauty contribution to the proton structure function, F2bb, in deep inelastic scattering is presented. The three measurements are compared with QCD predictions as well as with previous results. All the results presented here are preliminary.

Charm Particle Finders With the ZEUS Micro-Vertex Detector

The ZEUS micro-vertex detector (MVD) has been installed during a luminosity upgrade in 2000-01 the proton electron storage ring HERA. It has been reliably operated in the HERA-II run period from the year 2002 to 2007. The design of the MVD is described briefly. The tagging capability for charmed particles, obtained exploiting this detector is presented in this paper. The MVD is particularly important for resolving two shortly displaced vertices which are typical for decays of charm particles. Different charm particle decay topologies and the corresponding vertex finder techniques adopted are discussed.

The optical alignment system of the ZEUS microvertex detector

The laser alignment system of the ZEUS microvertex detector is described. The detector was installed in 2001 as part of an upgrade programme in preparation for the second phase of electron–proton physics at the HERA collider. The alignment system monitors the position of the vertex detector support structure with respect to the central tracking detector using semi-transparent amorphous-silicon sensors and diode lasers. The system is fully integrated into the general environmental monitoring of the ZEUS detector and data has been collected over a period of 5 years. The primary aim of defining periods of stability for track-based alignment has been achieved and the system is able to measure movements of the support structure to a precision around 10 μ m .

Performance of the ZEUS Micro-Vertex Detector

The ZEUS Micro-Vertex Detector (MVD) was installed in 2001 and the ZEUS experiment has started the HERA-II data taking since 2003. An integrated luminosity of 190 pb - 1 has been recorded at HERA-II which already exceeds the total integrated luminosity at HERA-I. The operational experience with the MVD and the performance of the new ZEUS tracking system are presented.

Alignment of the ZEUS micro-vertex detector using cosmic tracks

ZEUS Micro-Vertex Detector (MVD) was installed in ZEUS after the HERA upgrade in 2000. MVD is a precise position detector consisting of 712 single-sided silicon strip detectors. The alignment of the barrel MVD has been performed in units of ladders using cosmic tracks. The procedure used is an iterative χ 2 minimization, where χ 2 is defined locally for each ladder. The procedure is numerically stable since it only requires an inversion of 30 6 × 6 matrices and reasonably fast in spite of the iterative approach.

The ZEUS microvertex detector

The ZEUS microvertex detector (MVD) was installed in 2001 and commissioned in 2002/03. Doses of up to 1.2 kGy were observed from synchrotron radiation and beam–gas interactions. Detector operation is stable. Hit efficiencies are around 98%. Alignment accuracies of around 40–60 μm have been reached.

Test of silicon strip detectors for the ZEUS microvertex detector

Results of tests on silicon strip detectors which will be used for the ZEUS Microvertex detector are presented. The sensors use capacitive charge division with a readout pitch of 120 μm with five intermediate strips equally spaced. The design criteria and the performance of the detectors have been studied in electrical and testbeam measurements for unirradiated and irradiated detectors.