Dissociation of virtual photons in events with a leading proton at HERA

The ZEUS detector has been used to study dissociation of virtual photons in events with a leading proton, gamma^* p -> X p, in e^+p collisions at HERA. The data cover photon virtualities in two ranges, 0.03<Q^2<0.60 GeV^2 and 2<Q^2<100 GeV^2, with M_X>1.5 GeV, where M_X is the mass of the hadronic final state, X. Events were required to have a leading proton, detected in the ZEUS leading proton spectrometer, carrying at least 90% of the incoming proton energy. The cross section is presented as a function of t, the squared four-momentum transfer at the proton vertex, Phi, the azimuthal angle between the positron scattering plane and the proton scattering plane, and Q^2. The data are presented in terms of the diffractive structure function, F_2^D(3). A next-to-leading-order QCD fit to the higher-Q^2 data set and to previously published diffractive charm production data is presented

New Results Of Kaon Rare Decays From Na48 I.-A. Pellmann

iagrams 1 (Figure 1a). The expected branching ratio was Br(KL ! ) = 6:8 10 with a characteristic two photon invariant mass distribution. The rst measurements demonstrated that the two photon mass distribution favours the shape p, h p g p g p g g p g 0 0 0 0 0 * K p r,w,f p 0 0 * g r,w,f p Figure 1: a) 1-loop diagrams to calculate KL ! in chiral perturbation theory (O(p )). b) Vector meson exchange contribution to the decay KL ! . given by the meson loop contribution, but gave a branching ratio larger than predicted by chiral perturbation theory ((1:70:3) 10 by NA31 2 ; 3 and (1:860:6) 10 by E731 , respectively). Because of this discrepancy the calculations have been extended to the next to leading order of (p 5; 6; 7; 8 . The two dominant mechanisms at this order are the two pion intermediate state and the vector meson exchange (Figure 1b). For non-vanishing vector meson exchange the two photon invariant mass spectrum di

New Results On Kaon Decays From Na48 R. Wanke

Introduction The NA48 experiment has originally been designed to precisely measure direct CP violation in the decay of neutral kaons to two pions. It is a typical xed target experiment: Neutral kaons and hyperons are produced by protons interacting with two targets and decay in a roughly 100 m long decay region (Fig. 1). One target (far target) is located 126 m before the begin of the decay region, a distance large enough that all K S mesons and neutral hyperons have decayed before reaching the nal collimator. The other target (near target) is located only 6 m before the decay region. Decays observed from this target therefore are predominantly K S and and neutral hyperon (, ) decays, but may also be K L decays. In both neutral beams charged particles are deected from the beam line by sweeping magnets. During the CP violation measurement, both targets were used simultaneously, producing two almost collinear beams of neutral kaons. Apart from the CP violation measurement, severa

Albert--Ludwig--Universit

collected between 1996 and 1998 with the OPAL detector at LEP2. A sample of 92 events is selected in the data, for a Monte Carlo prediction of (87.6 3.7) events. The selected events are used to measure the parameters describing the triple gauge boson vertex #W W - : # # = 1.15 and # # = where the errors include both statistical and systematic uncertainties and each parameter is determined setting the other to its Standard Model value. The cross section # for the qq # e - # e process proceeding through t--channel diagrams is measured in the kinematic region m qq # &gt; 40 GeV/c at # s = 189 GeV to be # = (615 60) fb, where the first error is statistical and the second systematic. All measurements are consistent with the Standard Model predictions