121350221
Evidence forΨ production by neutrinos via neutral currents
Abstract Experimental evidence for the diffractive production of Ψ mesons in weak neutral current reactions is reported. The spectrum-averaged cross section for this process is σ diff = (4.2±1.5) × 10 −41 cm 2 /nucleon, in agreement with gluonfusion models, but at variance with vector dominance calculations.
122041721
Production of excited beauty states inZ decays
AbstractA data sample of about 3.0 million hadronicZ decays collected by the ALEPH experiment at LEP in the years 1991 through 1994 is used to make an inclusive selection of B hadron events. In this event sample 4227±140±252B* mesons in the decayB*→Bγ and 1944±108±161B**u,d mesons decaying into a B meson and a charged pion are reconstructed. Here and in the followingB**u,d denotes the eightL=1(bū) and (bd) states and their charge conjugate.For the well establishedB* meson the following quantities are obtained:ΔM=MB*−MB=(45.30±0.35±0.87) MeV/c2 andNB*/(NB+NB*)=(77.1±2.6±7.0)%. The angular distribution of the photons in theB* rest frame is used to measure the relative contribution of longitudinalB* polarization states to beσL/(σL+σT)=(33±6±5)%.In theM(Bπ)−M(B) mass difference resonance structure is observed at (424±4±10) MeV/c2, for which the shape and position is consistent with the expectation forB**u,d states decaying intoB(*)π±. The relative production rate is determined to be
$$\begin{gathered} \frac{{BR(Z \to b \to B_{u,d}^{ * * } )}}{{BR(Z \to b \to B_{u,d} )}} \hfill \\ = [27.9 \pm 1.6(stat) \pm 5.9(syst) {}_{ - 5.6}^{ + 3.9} (model)]\% \hfill \\ \end{gathered} $$
 where the third error reflects the uncertainty due to different production and decay models for the broadB**u,d states.
123101518
Studies of quantum chromodynamics with the ALEPH detector
Abstract Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented. The unprecedented statistics allows detailed studies of both perturbative and non-perturbative aspects of strong interactions to be carried out using hadronic Z and tau decays. The studies presented include precise determinations of the strong coupling constant, tests of its flavour independence, tests of the SU(3) gauge structure of QCD, study of coherence effects, and measurements of single-particle inclusive distributions and two-particle correlations for many identified baryons and mesons.
122204997
First measurement of the quark-to-photon fragmentation function
Earlier measurements at LEP of isolated hard photons in hadronic Z decays, attributed to radiation from primary quark pairs, have been extended in the ALEPH experiment to include hard photon productioninside hadron jets. Events are selected where all particles combine democratically to form hadron jets, one of which contains a photon with a fractional energyz≥0.7. After statistical subtraction of non-prompt photons, the quark-to-photon fragmentation function,D(z), is extracted directly from the measured 2-jet rate. By taking into account the perturbative contributions toD(z) obtained from anO(ααs) QCD calculation, the unknown non-perturbative component ofD(z) is then determined at highz. Provided due account is taken of hadronization effects nearz=1, a good description of the other event topologies is then found.
122188618
Charged particle pair production associated with a lepton pair in Z decays. indication of an excess in the tau channel
In a sample of 200 000 Z decays, events with two leptons and an additional pair of charged particles are studied. The 35 events found show a possible excess in the tau channel compared with the expectation from electroweak processes. The features of the events are consistent with radiation of virtual photons.
122230572
A measurement of the ratio of longitudinal and transverse structure functions in neutrino interactions between 30 and 200 GeV
Abstract A new measurement of the ratio R = σ L / σ T of longitudinal and transverse structure functions in neutrino interactions on iron between 30 and 190 GeV neutrino energy is reported. The result is given as a function of the scale parameter x and the inelasticity ν of the interaction. The average value is R = 0.10 ± 0.07 around ν ≈ 50 GeV and is in accordance with a prediction from the QCD theory.
138732815
MICROSCOPIC INVESTIGATION OF FIELD EMITTERS LOCATED BY THERMOMETRY IN 1.5 GHz SUPERCONDUCTING NIOBIUM CAVITIES
A new high resolution, high speed thermometry system has been built to permit the study of eld emitters in 1.5 GHz superconducting niobium cavities. Following a cavity test, the cavity is dissected for examination of the emitters in an electron microscope. Presented below is a survey of the topographical characterstics and composition of various defects found so far. A correlation between the current characteristics of emitters and their ability to process away was observed. It has been found that plasma production in the vicinity of an emitter is of importance in determining how much heat an emitter deposits on the rf surface as the electric eld in the cavity is increased. In particular, this plasma plays a pivotal role in the extinction of emitters.
8322223
Flux trapping in niobium cavities during breakdown events ∗
We report on the discovery of increased residual losses in niobium cavities following rapid quenches, in particular after thermal breakdown and multipacting. Increases of the residual resistance in the breakdown affected region by more than a factor of 10 have been recorded in some instances. It is believed that magnetic flux, generated by thermocurrents during breakdown, is trapped as the cavity reverts to the superconducting state, resulting in the enhanced losses. A thermal cycle to above the critical temperature of niobium is required to restore the initial low-loss state.
27779267
Microscopic examination of defects located by thermometry in 1.5 GHz superconducting niobium cavities
A new high resolution, high speed thermometry system has been built at Cornell to permit the study of anomalous loss regions in 1.5 GHz superconducting Nb cavities in superfluid He. Following a cavity test, the cavity is dissected for examination of these regions in an electron microscope. Presented is a survey of the topographical and elemental characteristics of various defects found so far. Included are field emitters which were known to be active at the end of a cavity test, as well as those which processed.
110231148
Industrial production of turn key superconducting accelerator modules for high current storage rings
During the past decade Cornell has developed and built superconducting 500 MHz accelerator RF (SRF) modules for the upgrade of their e/sup +/e/sup -/-storage ring CESR. ACCEL has agreed with Cornell on a transfer of the technology, with the goal to offer such modules for light sources or other high current e/sup +/e/sup -/-storage rings. Currently 6 SRF modules are under production, 2 for the Taiwan Light Source, 2 for Cornell University and 2 for the Canadian Light Source. The SRF modules will be delivered ready for turn key operation, including state-of-the-art cavity preparation and performance guarantees. First cavity test results as well as the production status will be presented.
15240610
Field Emission and Thermal Breakdown in Superconducting Niobium Cavities for Accelerators
Field emission and thermal breakdown are the main mechanisms limiting the accelerating gradient of niobium radio-frequency cavities. Diagnostic tools to study these mechanisms include quality measurements, thermometry, and microscopy. Results presented here demonstrate that micron-size, conducting particles are the source of field emission. Thermal breakdown is caused by a variety of defects such as inclusions, pits, and submillimeter-size particles. Techniques developed to minimize field emission and thermal breakdown include clean-room assembly, high-power processing (to avoid field emission) and the use of high-purity niobium (to avoid thermal breakdown). With these techniques, accelerating gradients of 20–30 MV/m can be achieved in