<正>项目概况建筑师:Marbod Fritsch材料多种材料时间:2007年这是一个被置于康斯坦茨湖(Lake Constance)的道闸。康斯坦茨湖位于瑞士、奥地利和德国三国交界处,由三国共同管理,湖区景色优美,风景迷人。

The ATLAS collaboration has recently started the construction of its detector for the LHC at CERN. An essential part of its Muon Spectrometer is based on Monitored Drift Tube (MDT) technology. It consists of about 1200 large muon drift chambers that will be built at 13 institutes spread all over the world. The MDT chambers require an exceptional mechanical construction accuracy of better than 20 mum. The construction quality of the chambers is controlled using X-ray tomography. A dedicated X-ray tomograph has been developed at CERN since 1996. This instrument measures the chamber wire positions with a 2 mum statistical and 2 mum systematic uncertainty over the full tomograph working area of 2.2 x 0.6 m(2). During the four-year construction phase of the MDT chambers, the X-ray tomograph will be the key tool for ensuring consistent chamber production quality with a sampling rate of similar to15%. To achieve this program efficiently, an effort for complete automation of the tomograph operation is underway. Since mid-2000, first modules from 11 of the construction sites have been measured. Results from this site certification process have demonstrated the essential role of the X-ray tomograph in assessing the validity of the various construction steps.

A gigantic detector, the ATLAS project, is under construction at CERN for particle physics research at the Large Hadron Collider which is to be ready by 2006. An X-ray tomograph has been developed, designed and constructed at CERN in order to control the mechanical quality of the ATLAS muon chambers. We reached a measurement accuracy of 2μm systematic and 2μm statistical uncertainties in the horizontal and vertical directions in the working area 220cm (horizontal)×60cm (vertical). Here we describe in detail the fundamental approach of the basic principle chosen to achieve such good accuracy. In order to crosscheck our precision, key results of measurements are presented.

An essential part of the Muon Spectrometer of the ATLAS experiment is based on the Monitored Drift Tube (MDT) technology. About 1200 muon drift chambers are being built at 13 institutes all over the world. The MDT chambers require an exceptional mechanical construction accuracy of better than 20 /spl mu/m. A dedicated X-ray tomograph has been developed at CERN since 1996 to control the mechanical quality of the chambers. The chamber wire positions are measured with a statistical error of 2 /spl mu/m and a systematic error of 2 /spl mu/m over a working area of 2.2 m /spl times/ 0.6 m. During the construction phase of the MDT chambers, from middle 2000 to mid 2005, the X-ray tomograph is the key tool for ensuring consistent chamber production with a sampling rate of /spl sim/15%. To achieve this program efficiently, an effort for complete automation of the tomograph operation has been underway. Until September 2003, 79 chambers out of 739 chambers produced at 11 of the construction sites have been measured. The X-ray tomograph has proved to be an essential and powerful tool in assessing the validity of the various construction steps.

For the Large Hadron Collider (LHC), ATLAS, a large general-purpose detector for physics experiment, is under construction. The muon spectrometer of ATLAS is on the scale of a very large industrial project: 1200 large monitored drift tubes (MDT) chambers will be built aiming at an exceptional quality in terms of mechanical accuracy, material reliability, assembly, and monitoring. For Quality Control, an X-ray tomograph, monitored by a set of interferometers, has been developed and built at CERN. The tomograph provides an accuracy below 10μm in the determination of the position of each MDT drift tube. First, results have been obtained on MDT prototypes.

Purpose of this note is to propose a search for typical signatures produced by charginos, neutralinos and sleptons on the basis of two supergravity model predictions, at the highest e+ e− energy which will be available with LEP-II. The typical signatures are of two main classes: i) «pure leptonic» states; ii) «mixed lepton-jets» states. The «pure leptonic» states consist of acoplanardi-leptons with «leading» and «non-leading» leptonic components plusmulti-di-lepton states. All with at least two missing momenta. The «mixed lepton-jets» states contain at least two jets and one or three leptons plus missing momenta. All these final states represent clear signatures for SUSY. Cross-sections and branching ratios are computed using two «local» supersymmetry models:i.e. the minimalSU(5) supergravity and theSU(5)×U(1) supergravity. The corresponding numbers of «pure leptonic» and of «mixed lepton-jets» final states are computed. We also discuss the upgrading needed in an experimental set-up at LEP-II especially suited for the detection of the supersymmetry signals expected on the basis of the two supergravity models quoted. These models are at present the most reliable in terms of physically sound assumptions.

A search for free quarks liberated via neutrino-quark coupling using the highest possible available energy was performed at CERN (WA-44 experiment) in the neutrino wide-band beam. The neutrino interactions take place in a 23 ton lead target. A forward large avalanche chamber is triggered when one or more charged particles from the neutrino (antineutrino) interactions cross two sets of counter hodoscopes. Ionization measurements in the avalanche chamber have been performed using two measuring machines: HPD in Bologna and PERPR in Frascati. The 6% expected statistical fluctuations in the ionization measurements have been obtained on one metre long tracks. This allowed an accurate analysis of the data to search in the 1/3 and even in the 2/3 charge regions. About 3.7·105 tracks were observed in the chamber, from about 105 neutrino (antineutrino) interactions. The analysis of the digitized data has selected 20 candidates for fractional charges. After a detailed analysis of both pictures and measurements, and a complete investigation of all possible instrumental effects, one event remains as a fractional charge (+1/3) candidate. This candidate has a small probability to be an edge effect in the apparatus. However this event is at the expected level of candidate events from the rejection power of our detector. Upper limits (90% c.l.) on the flux of quarks produced in both neutrino and antineutrino interactions are at the level of a few 10−5.

The problem of detecting electrons in the 0.5–4.0 GeV energy range, in the presence of a high pion background, has been studied using a new type of electromagnetic shower detector. Its structural properties and the main parameters are given, together with the basic results in terms of energy resolution and of rejection power against pion background. The optimization of this new instrument gives a pion rejection power of ∼ 6 × 10−4 for energy ≳ 1.2 GeV.

In this paper, we review briefly the main hypotheses and extrapolations used to predict the observability of new heavy flavours at the CERN (pp) collider. Some results from this study are compared with the first experimental data on the production of high-p T electrons accompained by hadronic « jets » at the (pp) collider, as observed by the UA1 collaboration. These events could, in fact, be the signature of the semi-leptonic decay of a very massive new heavy-flavoured state. Its « downlike » or « uplike » nature cannot be established in a direct and unambiguous way. More sophisticated measurements are needed as discussed in detail in a previous paper.

Evidence is reported for the same two-particle correlations in rapidity space in soft, high-energy (pp) collisions and (e+e-) annihilation when the leading baryons’ effects are taken into account.