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Register a new userA Luminosity Spectrometer for the Zeus Experiment at HERA
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Authors
S. D. Paganis
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The HERA luminosity upgrade is expected to generate two major problems in the current method of luminosity determination which is based on counting brehmsstrahlung photons: damage of the calorimeter monitor due to high primary synchrotron radiation and large multiple event (pile-up) corrections. The luminosity spectrometer presented in this talk, is a novel method that reduces the impact of these problems in the luminosity measurement and is expected to yield a total systematic uncertainty of 1.4%. The spectrometer counts brehmsstrahlung photon
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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.
The forward proton spectrometer is part of the H1 detector at the HERA collider. Protons with energies above 500 GeV and polar angles below 1 mrad can be detected by this spectrometer. The main detector components are scintillating fiber detectors read out by position-sensitive photo-multipliers. These detectors are housed in so-called Roman Pots which allow them to be moved close to the circulating proton beam. Four Roman Pot stations are located at distances between 60 m and 90 m from the interaction point.
The photoproduction of isolated photons has been measured in diffractive events recorded by the ZEUS detector at HERA. Cross sections are evaluated in the photon-proton transverse-energy and pseudorapidity ranges 5<ET(gamma)<15 GeV and -0.7<eta(gamma)<0.9 inclusively and also with a jet with transverse energy and pseudorapidity in the range 4<ET(jet)<35 GeV and -1.5<eta(jet)<1.8, using a total integrated electron-proton luminosity of 374 pb-1. A number of kinematic variables were studied and compared to predictions from the RAPGAP Monte Carlo model. An excess of data is observed above the RAPGAP predictions for z|P(meas)>0.9, where z|P(meas) is the fraction of the longitudinal momentum of the colourless Pomeron exchange that is transferred to the photon-jet final state, giving evidence for direct Pomeron interactions.
The reduced cross sections for $e^{+}p$ deep inelastic scattering have been measured with the ZEUS detector at HERA at three different centre-of-mass energies, $318$, $251$ and $225$ GeV. The cross sections, measured double differentially in Bjorken $x$ and the virtuality, $Q^2$, were obtained in the region $0.13 leq y leq 0.75$, where $y$ denotes the inelasticity and $5 leq Q^2 leq 110$ GeV$^2$. The proton structure functions $F_2$ and $F_L$ were extracted from the measured cross sections.
A measurement of the longitudinal polarization of the electron beam at HERA utilizing coherent interactions of high energy photons in crystals is proposed. Modification of existing facilities would allow an independent polarization measurement and a verification of birefringence phenomena in crystals for 20--30~GeV photons. Relevant experimental issues and systematic uncertainties are also presented.
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