The two-photon collision reaction e+e~ e+e~/+/~ has been studied at y/s ~ 91 GeV using the L3 detector at LEP for / = e, (i, r. We have analysed untagged configurations where the two photons are quasi-real. Good agreement is found between our measurements and the ö ( a 4) QED expectation. © 1997 Elsevier Science B.V.

We present a study of the inclusive co and r¡f production based on 3,1 million hadronic Z decays recorded with the L3 detector at LEP during 1991-1994. The production rates per hadronic Z decay have been measured to be 1.17 ± 0.17 co mesons and 0.25 ± 0.04 r)' mesons. The production rates and the differential cross sections have been compared with predictions of the JETSET and the HERWIG Monte Carlo models. We have observed that the differential cross sections can be described by an analytical quantum chromodynamics calculation.

We have measured the time integrated B°-B° mixing parameter and the forward-backward asymmetry in the process e+e~ 4bb using hadronic events containing muons or electrons. The data sample corresponds to 1,044,000 hadronic decays of the Z. From a fit to the momentum and transverse momentum distributions for single lepton and dilepton events, we have determined the Bu-B° mixing parameter to be XB = 0.123 ± 0.012 (stat.) ± 0.008 (sys.), and the bb forward-backward asymmetry at the effective center-of-mass energy \/s = 91.30GeV to be A b5 = 0.087_± 0.011 (stat.) ±0.004 (sys.) This measurement corresponds to a value of the effective electroweak mixing angle of sin20w = 0.2335 ± 0.0021. Dedicated to the memory of Professor Salvatore Lanzano

We present a study of the structure of hadronic events recorded by the L3 detector at LEP at the center of mass energies of 161 and 172 GeV. The data sample corresponds to an integrated luminosity of 21.25 pb“ 1 collected during the high energy runs of 1996. The distributions of event shape variables and the energy dependence of their mean values are well reproduced by QCD models. From a comparison of the data with resummed QCD calculations, we determine the strong coupling constant at the two energies. Combining this with our earlier measurements we find that the strong coupling constant decreases with increasing energy as expected in QCD. © 1997 Published by Elsevier Science B.V. ..... ......................................................................................................................................................................................................................................................................................................................... .................. ................................................................................................................................ ...................—

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We have analyzed one-prong r decays with neutral kaons using the information from a fine-grained hadron calorimeter. The data sample consists of 43 500 Z 7-V~(y) events collected by the L3 detector at LEP in 1991, 1992 and 1993. The following branching fractions are measured: B(t~~ —+ iy7r“ K°) = 0.0095 ± 0.0015(stat) ± 0.0006(syst); B ( t —> vrir " 7r°K°) = 0.0041 ± 0.0012(stat) ± 0.0003(syst) and 2?(r' -> pTir~K°K°) = 0.0031 ± 0.0012(stat) ± 0.0004(syst).

A search for exclusive decays of B[] and mesons has been performed in the channels ̂ J77, Bj —+ J77, Bj —» J7r° and Bs —► J7t°. The data sample consisted of more than three and half million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1995. No candidate events have been observed for any of the modes thus determining upper limits at 90% confidence level: 3.2 x 10~4 on Br(B^ -► J7r°) and the first experimental limits: Br(B° -+ J77) < 1.2 x 10\ Br(Bs -> J77) < 3.8 x 10“ 3, Br(B° -> h r°) < 1.2 x 10-3 .

A banana shaped closed design MSGC detector module was tested together with silicon detectors and other MSGCs in a 100 GeV muon beam. Despite of an undesirable geometry of the test setup, a spatial resolution below 40 m was reached. The efficiency of the module, defined by track reconstruction, showed to be 95.6%.

For the application of MSGCs at CMS it is of special importance to optimize the time resolution of these detectors which is determined by the signal developement in the detector and its processing by the front-end electronics. In this paper we study the timing properties of MSGCs operated in combination with the PreMux128 front-end chip, performing double correlated sampling. The results are compared to calculations from a simulation program. Using this program the method of the weighted sum — an alternative sampling scheme to double correlated sampling — is investigated and optimized.

We present evidence for soft gluon interference, as required by QCD. This interference is expected to manifest itself in an angular ordering of the gluons radiated within a jet. Using hadronic decays of the Z boson in the L3 detector at LEP, we compare variables sensitive to such an angular ordering, namely the energy-energy correlation asymmetry and the newly introduced particle-particle correlation asymmetry, with the predictions of various parton shower models. Only those models which incorporate the expected interference agree with the data.

The vertex drift chamber of the L3 Experiment at LEP, based on the time expansion principle, was in operation from the start-up of LEP in 1989 until the shutdown of LEP in 2000. The gas mixture used was 80% CO2 and 20% i-C4H10 at a pressure of 1200mbar. We present the design of the chamber, the infrastructure and the performance during the 11 years of operation. The total radiation received on the anode wires was ∼10−4C/cm. No degradation of the anode pulse amplitude, wire efficiencies and resolution was observed for the whole running period.

The design and construction of the silicon strip microvertex detector (SMD) of the L3 experiment at LEP are described. We present the sensors, readout electronics, data acquisition system, mechanical assembly and support, displacement monitoring systems and radiation monitoring system of the recently installed double-sided, double-layered SMD. This detector utilizes novel and sophisticated techniques for its readout. At the beginning of 1991, the radius of the LEP beam pipe at its four interaction points was reduced from 8.0 cm to 5.5 cm . L3 decided to take advantage of this newly acquired space by installing a silicon microstrip detector (SMD) to upgrade its central tracking capability . The intention was to design, build and install the SMD in a period of just two years so that this new detector would be taking data by 1993 . Consequently, our general design philosophy was to use existing technology as much as possible to guide our choices for such key items as sensor design, readout electronics, data acquisition system, cooling techniques and displacement monitoring systems. The advantages of placing a tracking system with a coordinate resolution of 10 lam close to the beam pipe are well known [1]. For L3, the SMD will significantly improve transverse momentum and impact parameter resolution for studying W-pair production physics at LEP200 (rs 200 GeV), and to provide enhanced b-quark tagging capability to aid a potential Higgs detection in this energy regime . Installation during LEP100 (~s_ mz) facilitates detector debugging due to the large reaction cross section at the Z resonance. 29° SMD two-layer coverage ' ~220 SMD one-layer coverage Fig . 1 . The top view shows the SMD positioned inside the L3 central tracking system . The bottom view shows a transverse view of the SMD's two radial planes.

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Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible.

In order to check the system aspects of the forward–backward MSGC tracker designed for the future CMS experiment at LHC, 38 trapezoidal MSGC counters assembled in six multi-substrates detector modules were built and exposed to a muon beam at the CERN SPS. Results on the gain uniformity along the wedge-shaped strip pattern and across the detector modules are shown together with measurements of the detection efficiency and the spatial resolution.

Inside the CMS detector(1) charged particles are measured precisely with layers of low-occupancy silicon detectors and Micro Strip Gas Chambers (MSGCs) with pitches of 50 and 200 mu m, respectively. Low occupancy is achieved by a high granularity of 3 x 10(6) channels for silicon detectors and 11 x 10(6) for MSGCs. For the CMS forward tracker we tested a closed MSGC module with wedge-shaped strip patterns on 300 mu m DESAG263(2) glass substrates produced by OPTIMASK. Using a 100 GeV mu-beam at CERN we investigated the behaviour of this MSGC module foreseen for four wedge-shaped substrates, 512 strips each. (C) 1998 Elsevier Science B.V. All rights reserved.