The measurement of scintillation light from the lead tungstate crystals of the Compact Muon Solenoid (CMS) electromagnetic calorimeter (ECAL) poses a substantial technical challenge, particularly in ...the endcap regions, where the radiation levels are highest. The photodetectors must be fast, sensitive, radiation-hard, and operate with significant internal gain in a magnetic field of 4 Tesla. The measured performance characteristics of the first batches of series production vacuum phototriodes (VPT), developed to satisfy the needs of CMS, will be described.
A new generation of vacuum phototriodes (VPTs) has been developed for application in the end-cap sub-system of the crystal electromagnetic calorimeter (ECAL) for the CMS experiment at the CERN Large ...Hadron Collider (LHC). These VPTs must operate with high reliability for at least 10 years in an extremely hostile environment. Results are presented from an extensive programme of tests, demonstrating that the required properties of significant gain in a 4
T magnetic field, resistance to ionising radiation, and stable operation with large photocurrents can all be satisfied in a robust, compact, inexpensive device.
The performance of prototype vacuum phototriodes is presented from the first full sized supercrystal array for the CMS ECAL endcaps. The array was exposed to high-energy electrons and tested in ...magnetic fields of up to 3T, in the CERN North area, in July and August 1999. The mean VPT electron yield, normalised to a naked crystal light yield of 8photoelectrons/MeV into an HPMT, was found to be 25electrons/MeV at 3T for devices from Research Institute Electron, 35electrons/MeV for devices from Hamamatsu and 18/23electrons/MeV from Electron Tubes.
The endcap electromagnetic calorimeter of the compact muon solenoid detects particles with the dense fast scintillator lead tungstate (PbWO4). Due to the low light yield of this scintillator, ...photodetectors with internal gain are required. Silicon avalanche photodiodes cannot be used in the endcap region due to the intense neutron flux. Following an extensive R&D programme, 26mm diameter single-stage photomultipliers (vacuum phototriodes) have been chosen as the photodetector in the endcap region. The first 1400 production devices are currently being evaluated following recent tests of a pre-production batch of 500 tubes. Tubes passing our acceptance tests have responses, averaged over the angular acceptance of the endcap calorimeter, corresponding to the range 20–55electrons/MeV deposited in PbWO4. These phototriodes operate, with a typical gain of 10, in magnetic fields up to 4T.
Tests of a prototype for the electromagnetic calorimeter (ECAL) of the compact muon solenoid experiment (CMS) at the large hadron collider are described. The basic unit for the endcap ECAL in CMS is ...a “supercrystal” of 25 lead tungstate crystals. Results are presented from tests of the first full-sized supercrystal in electron beams and in a 3
T magnetic field. The supercrystal was exposed to electron beams with energies from 25 to 180
GeV. An energy resolution (
σ
E/
E) of (0.48±0.01)% was measured at 180
GeV.
The properties of heavy metal fluoride glasses have been investigated to assess the potential for using these materials to construct electromagnetic calorimeters for particle physics. We report here ...on measurements of scintillation yield, transmission and decay time, on large blocks of CeF
3-doped HfF
4-based glasses. The effects of sample temperature, the addition of Ce and In, ZrF
4 concentrations, and different HfF
4 feedstocks, have also been studied. The samples were excited by a high energy proton beam and the associated scintillation yield and time structure was measured. The optical transmission of the samples was measured. It was observed that by comparing the time dependence of scintillation yield with optical transmission, the relative contributions of quenching and absorption in reducing optical yield could be separated. It was concluded that variations in HfF
4 feedstock purity can be a dominant factor in determining affective scintillation yield of large glass samples.
Gluon jets are identified in hadronic Z decays as all the particles in a hemisphere opposite to a hemisphere containing two tagged quark jets. Gluon jets defined in this manner are equivalent to ...gluon jets produced from a color singlet point source and thus correspond to the definition employed for most theoretical calculations. In a separate stage of the analysis, we select quark jets in a manner to correspond to calculations, as the particles in hemispheres of flavor tagged light quark (uds) events. We present the distributions of rapidity, scaled energy, the logarithm of the momentum, and transverse momentum with respect to the jet axes, for charged particles in these gluon and quark jets. We also examine the charged particle multiplicity distributions of the jets in restricted intervals of rapidity. For soft particles at large , we observe the charged particle multiplicity ratio of gluon to quark jets to be , in agreement with the prediction that this ratio should approximately equal the ratio of QCD color factors, . The intervals used to define soft particles and large for this result, GeV/ and GeV/, are motivated by the predictions of the Herwig Monte Carlo multihadronic event generator. Additionally, our gluon jet data allow a sensitive test of the phenomenon of non-leading QCD terms known as color reconnection. We test the model of color reconnection implemented in the Ariadne Monte Carlo multihadronic event generator and find it to be disfavored by our data.
Cross-sections for hadronic, and lepton pair final states in collisions at =183 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. ...Forward-backward asymmetries for the leptonic final states have also been measured. Cross-sections and asymmetries are also presented for data recorded in 1997 at =130 and 136 GeV. The results are used to measure the energy dependence of the electromagnetic coupling constant , and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a leptoquark, or of a squark or sneutrino in supersymmetric theories with R-parity violation.
The inclusive production rates and differential cross-sections of photons and mesons with a final state containing photons have been measured with the OPAL detector at LEP. The light mesons covered ...by the measurements are the , , , , and a. The particle multiplicities per hadronic Zdecay, extrapolated to the full energy range, are: where the first errors are statistical and the second systematic. In general, the results are in agreement with the predictions of the JETSET and HERWIG Monte Carlo models.
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