118315524
A Search for New Quarks and Leptons From $\Z^0$ Decay
A search for Z0 decays into pairs of possible new heavy quarks (t and b′), new heavy charged leptons (L±), stable heavy neutral leptons (νL) and unstable heavy neutral leptons (L0) is performed on data collected by the ALEPH detector corresponding to 11 550 events of Z0→hadrons. The limits on the masses of the heavy quarks are Mt > 45.8 GeV and Mb′ > 46.0 GeV, allowing for both charged-current and flavor-changing neutral-current decays of the b′. If an L± decays into a stable νL, then for MνL MνL. Finally, while the mass of the stable νL is excluded up to 42.7 GeV, the mass of the unstable L0 is excluded up to 45.7 GeV with the mixing parameters |UlL0|2 down to 10−13 at this mass. For 25.0 GeV < ML0 < 42.7 GeV, all values of |UlL0|2 are excluded. All limits are given at 95% CL.
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Abstract Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented.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.
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.
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.
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.
36916632
Basic Concepts of Measurements Made on Superconducting RF Cavities
Presented here is an introduction to some of the concepts used in the tests performed on superconducting RF cavities in the SRF group at Cornell. It is intended for the 'novice' to this field and by no means attempts a rigorous derivation. Assumed is some previous exposure to the physics of waveguides and cavities. Explained is the concept of the Quality (Q) of a cavity, the coupling parameters and how these quantities are determined by experiment. Furthermore a short overview of the results obtained for a typical cell is presented.
121092553
Detailed characterization of electron sources yielding first demonstration of European X-ray Free-Electron Laser beam quality
The photoinjector test facility at DESY, Zeuthen site (PITZ), was built to develop and optimize photoelectron sources for superconducting linacs for high-brilliance, short-wavelength free-electron laser (FEL) applications like the free-electron laser in Hamburg (FLASH) and the European x-ray free-electron laser (XFEL). In this paper, the detailed characterization of two laser-driven rf guns with different operating conditions is described. One experimental optimization of the beam parameters was performed at an accelerating gradient of about 43 MV=m at the photocathode and the other at about 60 MV=m. In both cases, electron beams with very high phase-space density have been demonstrated at a bunch charge of 1 nC and are compared with corresponding simulations. The rf gun optimized for the lower gradient has surpassed all the FLASH requirements on beam quality and rf parameters (gradient, rf pulse length, repetition rate) and serves as a spare gun for this facility. The rf gun studied with increased accelerating gradient at the cathode produced beams with even higher brightness, yielding the first demonstration of the beam quality required for driving the European XFEL: The geometric mean of the normalized projected rms emittance in the two transverse directions was measured to be 1:26 ` 0:13 mm mrad for a 1-nC electron bunch. When a 10% charge cut is applied excluding electrons from those phase-space regions where the measured phase-space density is below a certain level and which are not expected to contribute to the lasing process, the normalized projected rms emittance is about 0.9 mm mrad.
121377634
RF superconductivity for accelerators
BASICS Introductory Overview Cavity Fundamentals and Cavity Fields Superconductivity Essentials Electrodynamics of Normal and Superconductors Maximum Surface Fields PERFORMANCE OF SUPERCONDUCTING CAVITIES Cavity Fabrication and Preparation Multicell Field "Flatness" Tuning Cavity Testing Residual Resistance Multipacting Thermal Breakdown Field Emission The Quest for High Gradients Alternate Materials to Solid Niobium COUPLERS AND TUNERS Mode Excitation and Its Consequences Higher Order Mode Couplers Coupling Power to the Beam Input Power Couplers and Windows Tuners and Frequency Related Issues FRONTIER ACCELERATORS High-Current Accelerators High-Energy Accelerators Problems References Index
73624195
MICROPHONICS MEASUREMENTS IN A CW-DRIVEN TESLA-TYPE CAVITY ∗
Superconducting cavities with a high quality factor exhibit a very low bandwidth in their resonant frequency, which makes their operation very sensitive to mechanical oscillations. In CW mode of operation, as it is intended for the BESSY-FEL Linac, microphonics are therefore the dominant error source for field stability. In order to compensate the detuning, it is necessary to properly characterize amplitude and frequency with respect to all involved mechanical and electrical components. Such measurements have been performed at the HoBiCaT test facility at BESSY and will be described in detail.
31537972
First Considerations Concerning an Optimized Cavity Design for the Main Linac of BERLinPro
The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW linac technology and expertise required to drive next-generation Energy Recovery Linacs. Strongly HOM-damped multicell 1.3 GHz cavities are required for the main linac. The optimization of the cavities presented here is primarily based on the CEBAF 1.5 GHz 5-cell high-current cavity design, including HOM waveguide couplers. The cavity was scaled to 1.3 GHz and extended to 7 cells. Modifications to the end group design have also been studied. An effort was also made to reduce the ratio Epk/Eacc while still permitting HOMs to propagate.