86 research outputs found
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 m.Comment: 38 pages; 17 figure
Cortical oscillations implement a backbone for sampling-based computation in spiking neural networks
Brains need to deal with an uncertain world. Often, this requires visiting
multiple interpretations of the available information or multiple solutions to
an encountered problem. This gives rise to the so-called mixing problem: since
all of these "valid" states represent powerful attractors, but between
themselves can be very dissimilar, switching between such states can be
difficult. We propose that cortical oscillations can be effectively used to
overcome this challenge. By acting as an effective temperature, background
spiking activity modulates exploration. Rhythmic changes induced by cortical
oscillations can then be interpreted as a form of simulated tempering. We
provide a rigorous mathematical discussion of this link and study some of its
phenomenological implications in computer simulations. This identifies a new
computational role of cortical oscillations and connects them to various
phenomena in the brain, such as sampling-based probabilistic inference, memory
replay, multisensory cue combination and place cell flickering.Comment: 30 pages, 11 figure
Phenomenological modeling of diverse and heterogeneous synaptic dynamics at natural density
This chapter sheds light on the synaptic organization of the brain from the
perspective of computational neuroscience. It provides an introductory overview
on how to account for empirical data in mathematical models, implement them in
software, and perform simulations reflecting experiments. This path is
demonstrated with respect to four key aspects of synaptic signaling: the
connectivity of brain networks, synaptic transmission, synaptic plasticity, and
the heterogeneity across synapses. Each step and aspect of the modeling and
simulation workflow comes with its own challenges and pitfalls, which are
highlighted and addressed in detail.Comment: 35 pages, 3 figure
Measurement of (anti)deuteron and (anti)proton production in DIS at HERA
The first observation of (anti)deuterons in deep inelastic scattering at HERA
has been made with the ZEUS detector at a centre-of-mass energy of 300--318 GeV
using an integrated luminosity of 120 pb-1. The measurement was performed in
the central rapidity region for transverse momentum per unit of mass in the
range 0.3<p_T/M<0.7. The particle rates have been extracted and interpreted in
terms of the coalescence model. The (anti)deuteron production yield is smaller
than the (anti)proton yield by approximately three orders of magnitude,
consistent with the world measurements.Comment: 26 pages, 9 figures, 5 tables, submitted to Nucl. Phys.
High-E_T dijet photoproduction at HERA
The cross section for high-E_T dijet production in photoproduction has been
measured with the ZEUS detector at HERA using an integrated luminosity of 81.8
pb-1. The events were required to have a virtuality of the incoming photon,
Q^2, of less than 1 GeV^2 and a photon-proton centre-of-mass energy in the
range 142 < W < 293 GeV. Events were selected if at least two jets satisfied
the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV
and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of
the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to
the parton distributions in the photon and proton and effects beyond
next-to-leading order in QCD. Hence these data can be used to constrain further
the parton densities in the proton and photon.Comment: 36 pages, 13 figures, 20 tables, including minor revisions from
referees. Accepted by Phys. Rev.
Inclusive jet cross sections and dijet correlations in photoproduction at HERA
Inclusive jet cross sections in photoproduction for events containing a
meson have been measured with the ZEUS detector at HERA using an integrated
luminosity of . The events were required to have a
virtuality of the incoming photon, , of less than 1 GeV, and a
photon-proton centre-of-mass energy in the range . The measurements are compared with next-to-leading-order (NLO) QCD
calculations. Good agreement is found with the NLO calculations over most of
the measured kinematic region. Requiring a second jet in the event allowed a
more detailed comparison with QCD calculations. The measured dijet cross
sections are also compared to Monte Carlo (MC) models which incorporate
leading-order matrix elements followed by parton showers and hadronisation. The
NLO QCD predictions are in general agreement with the data although differences
have been isolated to regions where contributions from higher orders are
expected to be significant. The MC models give a better description than the
NLO predictions of the shape of the measured cross sections.Comment: 43 pages, 12 figures, charm jets ZEU
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