115464633
Do We Understand the Luminosity Imbalance
56048929
The BOM 1000 Turn Display : a Tool to Visualize the Transverse Phase-Space Topology at LEP
The LEP BOM 1000 Turn facility enables the User to acquire the position of the beam at each beam position monitor over a number of consecutive turns. By kicking the beam and acquiring the first 1000 turns after the kick, the dynamic behavior of the beam in such a condition can be studied. In particular, by selecting a position monitor and plotting the position of the beam at a given turn against the position shifted by one (or n) turn(s), the evolution of the beam in the phase-space can be observed. Fixed points in the phase-space can be put in evidence, as well as the beam behavior in their neighbourhood. Quantities like the beam damping, or the beam detuning as function of the position amplitude can also be studied in this way. Significant examples from real life will be shown.
12798237
Overview of LEP operation in 1998
After the installation of 32 additional RF cavities in the 1997-1998 shutdown LEP was operated at a beam energy of 94.5 GeV. The total integrated luminosity for the year 1998 clearly surpassed its target and reached 198 pb/sup -1/. Vertical beam-beam tuneshifts of more than 0.07 were obtained. The performance did not seem to be beam-beam limited, but the total beam current was limited by power dissipation problems to around 6 mA. A high phase advance optics (102/spl deg/, 90/spl deg/), with a smaller natural emittance, was used for regular operation in 1998. This contributed to the excellent performance of LEP, together with the further reduction of both the horizontal and vertical beta function at the interaction points. No dynamic aperture problems were encountered.
62825805
THE CLIC MACHINE PROTECTION
INTRODUCTION The proposed Compact Linear Collider (CLIC) [1, 2] is based on a two-beam acceleration scheme. The energy of two high-intensity, low-energy drive beams is extracted and transferred to the two low-intensity, high-energy main beams. The machine protection has to cope with a wide variety of failures, from real-time failures (RF breakdowns, kicker misfiring), to slow equipment failures, to beam instabilities (caused by e.g. temperature drifts, slow ground motions). Due to the many different types of accelerator components and the beams of various characteristics throughout the entire complex, the CLIC machine protection is an extensive subject. The machine protection has the mission to protect the various machine components from damage caused by ill controlled beams. The severity of the damage is given by the financial impact of the damage and the reduction in the operational availability of the facility. The risk equivalent is given by the product of the fault rate and the impact of the fault (i.e. in statistical terms: risk is the expectation value of the fault impact). This concept is illustrated by some examples for downtime in Table 1.
55091650
Betatron function measurement at LEP using the BOM 1000 turns facility
A new method for measuring the beta function around LEP is presented. The method uses phase difference measurements between three adjacent beam position monitors to obtain the value for the beta function at the monitors and in their neighbourhood, e.g. at interaction points, electrostatic separators etc. The phase differences are obtained from measuring coherent betatron oscillations for 1024 turns at the 504 beam position monitors. After a discussion of the accuracy of the method the measured values for the beta function are compared with the theoretical values for different lattices. In regular parts of the lattice (e.g. arcs) the beating of the beta function measured using this method agrees well with the beating obtained by another method using a fit of the phase over 15 monitors.<<ETX>>
119009661
Determination of coupled-lattice properties using turn-by-turn data
A formalism for extracting coupled betatron parameters from multiturn, shock excited, beam position monitor data is described. The most important results are nonperturbative in that they do not rely on the underlying ideal lattice model. Except for damping, which is assumed to be exponential and small enough to be removed empirically, the description is symplectic. As well as simplifying the description, this leads to self-consistency checks that are applied to the data. The most important of these is a {open_quotes}magic ratio{close_quotes} of Fourier coefficients that is required to be a lattice invariant, the same at every beam position monitor. All formulas are applied to both real and simulated data. The real data was acquired June, 1992 at LEP as part of decoupling studies, using the LEP beam orbit measurement system. Simulated data, obtained by numerical tracking (TEAPOT) in the same (except for unknown errors) lattice, agrees well with real data when subjected to identical analysis. For both datasets, deviations between extracted and design parameters and deviations from self-consistency can be accounted for by noise and signal processing limitations. This investigation demonstrates that the LEP beam position system yields reliable local coupling measurements. It can be conservatively assumed that systems of similar design at the SSC and LHC will provide the measurements needed for local decoupling.
123242166
The magnetic levitation electrometer and its use in the search for fractionally charged particles
Abstract The operation of the magnetic levitation electrometer both in the static and in the resonance version is described in detail. The sensitivity of the instrument in the resonance version allows measurements of charge to a precision often better than 1 20 e in grains of matter (graphite) having a mass of the order of 5×10 −7 g. On a total amount of 3.4 × 10 −6 g of pyrolitic graphite explored, corresponding to ≈2 × 10 18 nucleons, no fractionally charged quark has been found.
115473197
Pion exchange contribution to baryon magnetic moments in QCD:an apparent paradox and its solution
122993504
A short guide to the quark model
121541770
SCALING OF THE NUCLEON E.M. ELASTIC FORM FACTORS: A GENERAL DERIVATION
Abstract The scaling of the elastic e.m. form factors of the nucleon ( p charge form factor and magnetic form factors of p and n ) has been discussed so far mainly in the non relativistic quark model. We ask: Can the scaling be derived in a model independent way from general properties of QCD? Using the QCD general parametrization we show that: (1) The magnetic form factors of p and n are expected to scale in QCD to a few percent; (2) As to the p electric and magnetic form factors, their scaling, in general, is not guaranteed. The most likely explanation of its empirical validity is that only the “valence quarks” determine the expectation values of both the local charge and magnetization density; the effects of “sea” quarks and antiquarks cancel locally, on the average, as far as the p form factors are concerned.
122238217
A relation between the charge radii of π+,K+,K0 derived by the general QCD parametrization
We derive, using the general QCD parametrization, the approximate relation r2(π+) − r2(K+) − r2(K0) where the r's are the charge radii. The relation is satisfied but the experimental errors are still sizeable. The derivation is similar to (but even simpler than) that for r2(p) − r2(n) r2(Δ+) (Phys. Lett. B, 448 (1999) 107).