120582474
Study of inclusive neutral current interactions of neutrinos and antineutrinos
Abstract We report on results from a study of hadron-energy distributions for ν and ν inclusive neutral current interactions. There is no significant variation of the neutral to charged current total cross-section ratios R ν and R ν with neutrino energy. The space-time structure of neutral currents is dominated by V − A , with a significant admixture of V + A . The Weinberg-Salam model is in agreement with all data if sin 2 θ w =0.24±0.02.
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.
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.
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.
73548820
Microscopic investigation of RF surfaces of 3 GHz niobium accelerator cavities following RF processing
RF processing of superconducting accelerating cavities is achieved through a change in the electron field emission (FE) characteristics of the RF surface. We have examined the RF surfaces of several single-cell 3 GHz cavities, following RF processing, in a scanning electron microscope (SEM). The RF processing sessions included both high peak power (P/spl les/50 kW) pulsed processing, and low power (/spl les/20 W) continuous wave processing. The experimental apparatus also included a thermometer array on the cavity outer wall, allowing temperature maps to characterize the emission before and after RF processing gains. Multiple sites have been located in cavities which showed improvements in cavity behavior due to RF processing. Several SEM-located sites can be correlated with changes in thermometer signals, indicating a direct relationship between the surface site and emission reduction due to RF processing. Information gained from the SEM investigations and thermometry are used to enhance the theoretical model of RF processing.<<ETX>>
49389571
CHARACTERIZATION OF THE PIEZO BLADE TUNER FOR SUPERCONDUCTING RF CAVITIES
Cavity tuners are mechanical devices designed to precisely match the resonant frequency of a superconducting (SC) cavity to the RF frequency synchronous with the beam. The blade tuner is mounted coaxially to the cavity and changes the resonator frequency by varying its length. A high tuning range is desired together with small mechanical hysteresis, to allow for easy and reproducible resonator setup operations. A high stiffness of the tuner system is also necessary both to ensure mechanical stability and to mitigate the frequency instabilities induced by perturbations. In high gradient SC resonators, the main sources of resonant frequency instability are the Lorentz Force Detuning (LFD) under pulsed mode operation, and the microphonic noise, in continuous wave (CW) with high loaded quality factors. Piezoelectric ceramic (piezo) elements add a dynamic tuning capability to the system, allowing fast compensation of these instabilities with the help of feedforward and feedback loops. The piezo blade tuner has been extensively tested assembled on a TESLA type cavity in its final configuration. Tests were done both at room temperature and under cryogenic conditions. This paper presents the summary of the complete characterization tests.
124174586
INTERPRETATION OF DARK CURRENT EXPERIMENTAL RESULTS IN HZB SC RF GUN
The experimental dark current measurement results are obtained on HZB SC RF gun. The field emitters are considered to be random defects on the back wall of the cavity. Conducting wires with 1 micron length, blobs of 200 micron diameter and ”tip on tip” combination of them are taken as dark current emitters in the cavity. RF fields were calculated with CLANS program. The dynamic simulation of dark currents from these emitters fit experimental data. The emitter heating power by RF induced current is four orders of magnitude larger than by the field emitted dark current. The RF induced emitter temperature is proportional to ω 1/2 which explains the accelerating gradient limit of a cavity like Kilpatrik law. The RF processing by high order modes seems to be promising.
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.
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.