Beam Spot Position Measurement at the LEP Collider

A precise knowledge of the beam spot position is required for many physics topics at LEP2. The movement of the beam spot is studied at LEP1 using beam orbit monitors close to the interaction points and compared with measurements from tracks produced in e+e- collisions. The beam orbit monitors are found to follow the beam spot position well, particularly when corrected for movements of nearby quadrupole magnets. Data from the LEP high energy run of November 1995 are also analysed, and projections made for the prospects at LEP2

A quark model framework for the study of nuclear medium effects

A quark-model framework for studying nuclear medium effects on nucleon resonances is described and applied here to pion photoproduction on the deuteron, which is the simplest composite nucleon system and serves as a first test case. Pion photoproduction on nuclei is discussed within a chiral constituent quark model in which the quark degrees of freedom are explicitly introduced through an effective chiral Lagrangian for the quark-pseudoscalar-meson coupling. The advantage of this model is that a complete set of nucleon resonances can be systematically included with a limited number of parameters. Also, the systematic description of the nucleon and its resonances at quark level allows us to self-consistently relate the nuclear medium's influence on the baryon properties to the intrinsic dynamic aspects of the baryons. As the simplest composite nucleus, the deuteron represents the first application of this effective theory for meson photoproduction on light nuclei. The influence of the medium on the transition operators for a free nucleon is investigated in the Delta resonance region. No evidence is found for a change of the Delta properties in the pion photoproduction reaction on the deuteron since the nuclear medium here involves just one other nucleon and the low binding energy implies low nuclear density. However, we show that the reaction mechanism is in principle sensitive to changes of Delta properties that would be produced by the denser nuclear medium of heavier nuclei through the modification of the quark model parameters.Comment: Revtex, 8 pages, 4 figure

Radiation background at the LHCb detector from proton-proton interactions-a first look

97-03 First results from Monte Carlo simulations of hadron and electron background particles to the LHC-B muon system are presented. The MARS code and DTUJET source code have been used. An Fe shield of 10 to 17 cm thickness, placed around the last 6 m of a conical vacuum chamber, reduces hadron and electron rates to well below 10'3 particles/cm2/s for a luminosity of 2 x 1O'32 cm-2 s-1 in IP8

Radiation background at the LHCb detector from p-p interactions II

97-010 The results of the second stage of the background calculations for the LHC-B detector using the MARS program are reported. For these simulations the muon filters are retracted around a 10 mrad polar angle cone and no bottom shielding is used. Different vacuum chamber layouts are tested under these conditions. As to be expected, the most favorable solution is the largest vacuum chamber with a 10 mrad cone angle. The obtained rates of charged hadrons and electrons at three muon chambers are compared with previous results of calculations for the original LHC-B layout from the LOI, including bottom shielding