Department of Hadron Structure 133 the luminosity photon conversion spectrometer and two electron taggers at 6 m and 40 m from the interaction point (1p). The Krak6w group, which was responsible for the luminosity monitor, built and tested the pho- ton calorimeter, the active filter and the position detector placed inside the photon calorimeter. In addition, the group prepared the read-out electronics for all the mentioned detectors We have been also working on the modifications and adjustment of the MC programs simulating the ZEUS detector and in particular the new luminosity system. Luminosity Monitor Upgrade PLO300093 J. Chwastowski, A. Eskreys, J. Figiel, K. Klimek, K. Olkiewicz, M. Przybyciefl, P. Stopa, and L. Zawiejski, J. Andruszk6w W Daniluk, P. Jurkiewiez, A. Kotarba, J. Ligocki, K. Ohwa, W. Ruchlewicz, W. Wierba, W. Ostrowicz, and B. Dqbrowski To meet the consequences of the HERA collider upgrade (increase of flux and hardness of the synchrotron radiation and increase of the bremsstrahlung photon rates), the new luminosity monitor consisting of the active filter (2XO carbon absorber - aerogel Cerenkov counter - 2XO carbon absorber - aerogel Cerenkov counter) and the sandwich lead-scintillator calorimeter together with position detector was proposed. In 2001 all these components were built and tested and in Fig. these detectors are shown installed in the HERA tunnel. In Fig. 2 we show the bremsstrahlung photon rate as a function of time and its horizontal and vertical distributions observed during the first run after HERA upgrade. The tests of the luminosity monitor were performed using DESY electron test beam Alexander Fig. 1: The componets of the new LUMI monitor: - three parts of carbon filters: (0.2XO Cu + 0.5Xo C), (1.5Xo C) and (1.8XO C), aerogel coun- ters and photon calorimeter - after installation in te HERA tunnel. H.,V-10 B- Hdk Fig. 2 The first luminosity run (ep collisions) after HERA upgrade, (November 2001), 18:42 ICA) 101.14 I" Ime observed on the new LUMI display. The bremsstrahlung Beams displaced -no collisions rate and the beam position Collisions -first luminosity! as observed in photon position detector are shown. of energy I - 6 GeV/c. The photon calorimeter energy resolution was found to be 14%IVE and the light collection efficiency in aerogel counters reached about 40%. The test data were well reproduced by standalone EANT simulation. 3These activities were carried out in collaboration with the aculty of Physics ad Nuclear Techniques of the University of Mining and Metallurgy. 134 Department of Hadron Structure The electronics of the read-out and control system for three detectors: calorimeter, spectrometer and 6 m tagger, was finally mounted and put into operation. The final electronics system consists two main modules connected via transmission cables. In the first one there are several crates containing front-end electronics and slow control boards located next to particular detectors. The second module includes fast analog to digital converter (FADC) and data acquisition (DAQ) crates and is located in the ZEUS hall. The new luminosity DAQ system was synchronized with the ZEUS DAQ system and the connections to the first and second levels of the ZEUS trigger system GFLT, GSLT) and Event Builder were partially established. As far as software is concerned, the procedure for online and offline luminosity measurements after HERA uprage, was improved and extented. The simulation of electron and proton beam line from IP up to the luminosity monitor, as required for the ZEUS detector simulation in program MOZART, has been started. Measurement of the Total Photoproduction Cross Section UTOT CY) J. Chwastowski 0 0 co0 In 1952, Heisenberg predicted rise of the total cross section with energy. A similar predicton put 0 forward by Regge and ribov was based on the analytical properties of the scattering amplitude. Experimentally, this effect was confirmed in proton - proton collisions at CERN. With the advent of HERA it was possible to study high energy behaviour of the photoproduction total cross section. The ZEUS Collaboration found the photoproduction total cross section, at the average photon-proton center-of-mass energy of 209 GeV, to be: u7 (W 209 GeV) = 174 ± I stat. ± 13(syst.) mb . This measurement is shown in Fig. 1. together with an earlier result of the H Collaboration and the lower energy data [1]. The curves shown, labeled DL98 and ZEUS fit, are the model predictions -190 -ZEUS...'' 0 ZEUS 1996 OH[ 1994 low-energy experiments ...... DL99 ZEUS fit 160 Fig. 1: The photon-proton total cross section as a 130 - function of photon-proton center-of-mass energy. The present measurement is shown as the filled square. Also shown are the published HI value (open square), the low-energy data (filled circles), 100 I 10L 100 the DL98 parameterization (dot-dashed curve) and WV (GeV) the ZEUS fit (solid curve). based on the Regge - Gribov theory. In particular these models predict the same energy dependence of the total cross sections for the photon - proton, proton - proton and anti-proton - proton cross sections. Reference: 1. ZEUS Collaboration, "Measurement of the Photon-Proton Total Cross Section at a Center-of-Mass Energy of 209 GeV at HERA", DESY-01-216, December 2001, submitted to Nuclear Physics B..