DEPARTMENT OF HIGH ENERGY PHYSICS 115

The new analysis performed in Warsaw on the DELPHI preliminary basis of the full data from LEP1 should allow the I ' ' ' I ! • ' I ' ' ' I I I I ' ' ' I ' ' ' I ' ' ' I ' measurements of the inclusive b —> s(d)g branching 77 -> K+K~ •• DELPHI «lV>=91CiV Brodxkj xnd Lcpxge ratio with better precision. Icostf'l < 0.6 -— Niiic ° • TrC/Two-Gjiniiia 3. Exclusive and kaon pair production in gamma - gamma collisions at LEP The cross-sections for the two- production of charged pion and kaon pairs have been measured in Warsaw using the data collected by the DELPHI experiment at e+ e centre-of-mass energies 4s =91 GeV and 4s - 183 GeV. The cross-section for high invariant masses (above 1.7 GeV) is compared to leading order and next-to-leading order QCD predictions in Fig.3. These are the first results coming from LEP, concerning exclusive two-photon production of kaons and at high-invariant masses. This part of analysis was done in collaboration with University of Warsaw. Fig. 3 Cross-section for two-photon production of charged kaon pairs as a function of K+K" invariant mass W for I cos 0* 1 < 0.6 and yS =91 GeV. The error bars represent statistical errors.

6.2 The ZEUS Experiment at DESY by M.Adamus and T.Gadaj PL0001533

The ZEUS experiment [1] was designed to investigate results of 920 (820) GeV collisions JL< PROGRAMMABLE P0L3ER with 27.6 GeV electrons (). HERA . ISD -M HVCHLOl accelerator delivers colliding beams. Main scopes of SCIHIILE2TCK research are: structure functions and electroweak COUNT SRS

physics VDI3CHIMIHAI0H3 - hadronic final states - diffraction and vector mesons ~t— uamsuaxs - heavy flavour physics - exotics and rare phenomena The Warsaw ZEUS group participated in experiment since the very beginning and took part in the designing, assembling, maintenance and upgrade of the detector. The main field of group activity is the VETO WALL component (fig.l).

Fig. 2. Control systems of VW electronics.

The VETO WALL (VW) detector is situated about 7.5 m upstream of interaction point near the Fig. 1 VETO WALL component of ZEUS detector. tunnel exit. Its main purpose is to protect the central detector against particles from the beam halo accompanying bunches. It helps to absorb the background particles and to veto events produced by