91 research outputs found
Measurement of the Luminosity in the ZEUS Experiment at HERA II
The luminosity in the ZEUS detector was measured using photons from electron
bremsstrahlung. In 2001 the HERA collider was upgraded for operation at higher
luminosity. At the same time the luminosity-measuring system of the ZEUS
experiment was modified to tackle the expected higher photon rate and
synchrotron radiation. The existing lead-scintillator calorimeter was equipped
with radiation hard scintillator tiles and shielded against synchrotron
radiation. In addition, a magnetic spectrometer was installed to measure the
luminosity independently using photons converted in the beam-pipe exit window.
The redundancy provided a reliable and robust luminosity determination with a
systematic uncertainty of 1.7%. The experimental setup, the techniques used for
luminosity determination and the estimate of the systematic uncertainty are
reported.Comment: 25 pages, 11 figure
First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength
We present the first observation of Self-Amplified Spontaneous Emission
(SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109
nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and
the radiation characteristics, such as dependency on bunch charge, angular
distribution, spectral width and intensity fluctuations all corroborate the
existing models for SASE FELs.Comment: 6 pages including 6 figures; e-mail: [email protected]
TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider
The TESLA Technical Design Report Part III: Physics at an e+e- Linear
ColliderComment: 192 pages, 131 figures. Some figures have reduced quality. Full
quality figures can be obtained from http://tesla.desy.de/tdr. Editors -
R.-D. Heuer, D.J. Miller, F. Richard, P.M. Zerwa
VUV/EUV ionising radiation and atoms and ions: dual laser plasma investigations
The interaction of ionising radiation with atoms and ions is a key fundamental process. This report concentrates on studies of photoexcitation/photoionisation using laser-produced plasmas as continuum sources and synchronised laser plasma plumes to provide the absorbing atom or ion species. Examples from studies of the interaction of ionising radiation with atoms and ions ranging from few-electron atomic and ionic systems to the many-electron high atomic number actinides are reviewed and illustrate the advantages and limitations of the Dual Laser Plasma technique
Trends in autoionization of Rydberg states converging to the 4s threshold in the Kr-Rb⁺-Sr²⁺ isoelectonic sequence: theory and experiment
We have measured the photoabsorption spectra of the Kr-like ions Rb+ and Sr2+ at photon energies corresponding to the excitation of 4s-np resonances using, the dual laser plasma photoabsorption technique. Dramatic changes in the line profiles, with increasing ionization and also proceeding along the Rydberg series of each ion, are observed and explained by the trends in 4s-transition amplitudes computed within a framework of configuration-interaction Pauli-Fock calculations. Total photoionization cross sections show very good agreement with relative absorption data extracted from the measured spectra
Exclusive electroproduction of J/psi mesons at HERA
The exclusive electroproduction of J/psi mesons, ep->epJ/psi, has been
studied with the ZEUS detector at HERA for virtualities of the exchanged photon
in the ranges 0.15<Q^2<0.8 GeV^2 and 2<Q^2<100 GeV^2 using integrated
luminosities of 69 pb^-1 and 83 pb^-1, respectively.The photon-proton
centre-of-mass energy was in the range 30<W<220 GeV and the squared
four-momentum transfer at the proton vertex |t|<1.The cross sections and decay
angular distributions are presented as functions of Q^2, W and t. The effective
parameters of the Pomeron trajectory are in agreement with those found in J/psi
photoproduction. The spin-density matrix elements, calculated from the decay
angular distributions, are consistent with the hypothesis of s-channel helicity
conservation. The ratio of the longitudinal to transverse cross sections,
sigma_L/sigma_T, grows with Q^2, whilst no dependence on W or t is observed.
The results are in agreement with perturbative QCD calculations and exhibit a
strong sensitivity to the gluon distribution in the proton.Comment: 33 pages, 10 figures. Submitted to Nuclear Physics
Association between increased blood interleukin-6 levels on emergency department arrival and prolonged length of intensive care unit stay for blunt trauma
Traumatic injuries among adult obese patients in southern Taiwan: a cross-sectional study based on a trauma registry system
Measurement of beauty and charm production in deep inelastic scattering at HERA and measurement of the beauty-quark mass
The ZEUS collaborationThe production of beauty and charm quarks in ep interactions has been studied with
the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q^2 < 1000 GeV^2
using an integrated luminosity of 354 pb^{−1}. The beauty and charm content in events
with at least one jet have been extracted using the invariant mass of charged tracks
associated with secondary vertices and the decay-length significance of these vertices.
Differential cross sections as a function of Q^2, Bjorken x, jet trans- verse energy
and pseudorapidity were measured and compared with next-to-leading-order QCD
calculations. The beauty and charm contributions to the proton structure functions
were extracted from the double-differential cross section as a function of x and Q^2.
The running beauty-quark mass, m_b at the scale m_b , was determined from a QCD fit
at next-to-leading order to HERA data for the first time and found to be
m_b(m_b) = 4.07 ± 0.14(fit)_{−0.07}^{+0.01}(mod.)_{−0.00}^{+0.05}(param.)_{−0.05}^{+0.08}(theo.)GeV.We appreciate the contributions to the construction, maintenance and operation of the
ZEUS detector of many people who are not listed as authors. The HERA machine group
and the DESY computing staff are especially acknowledged for their success in providing
excellent operation of the collider and the data-analysis environment. We thank the DESY
directorate for their strong support and encouragement. It is a pleasure to thank the
ABKM, CTEQ, JR and MSTW groups that provided the predictions for F_2^{b\overline{b}} shown in figure
12. We gratefully acknowledge the advice from S. Alekhin and R. Plačakytė concerning
the appropriate usage of OPENQCDRAD and HERAFitter. Article funded by SCOAP
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