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.
118144238
Measurements of |V(cb)|, form-factors and branching fractions in the decays anti-B0 ---> D*+ lepton- anti-lepton-neutrino and anti-B0 ---> D+ lepton- anti-lepton-neutrino
Two samples of exclusive semileptonic decays, 579 events and 261 events, are selected from approximately 3.9 million hadronic Z decays collected by the ALEPH detector at LEP. From the reconstructed differential decay rate of each sample, the product of the hadronic form factor (ω) at zero recoil of the D(∗)+ meson and the CKM matrix element |Vcb| are measured to be , FD+(1)|Vcb| = (27.8 ± 6.8stat ± 6.5syst) × 10−3. The ratio of the form factors FD+(1) and is measured to be . A value of |Vcb| is extracted from the two samples, using theoretical constraints on the slope and curvature of the hadronic form factors and their normalization at zero recoil, with the result |Vcb| = (34.4 ± 1.6stat ± 2.3syst ± 1.4th) × 10−3. The branching fractions are measured from the two integrated spectra to be %, %.
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.
119085485
Heavy quark tagging with leptons in the ALEPH detector
This paper deals with sustainable development policies in the French South-Eastern Alps region (Digne-les-Bains). It aims to delineate the influence of communication and mediation practices which are used to implement such principles in a largely reluctant area. This approach combines the point of views of two sciences, media and communication on the one hand, geography , on the other hand
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.
122314436
Comparison of moments from the valence structure function with QCD predictions
Abstract We present moments (both ordinary and Nachtmann) of the nucleon valence structure function measured in high Q 2 ν FE scattering, supplemented by data from deep inelastic eD scattering. These data seem to agree with QCD predictions for vector gluons. The QCD parameter Λ is found to be of the order 0.5 GeV.
55994461
FIRST CHARACTERIZATION OF A FULLY SUPERCONDUCTING RF PHOTOINJECTOR CAVITY
As a first step towards a high brightness, high average current electron source for the BERLinPro ERL a fully superconducting photo-injector was developed by HZB in collaboration with JLab, DESY and the A. Soltan Institute. This cavity-injector ensemble is made up of a 1.6-cell superconducting cavity with a superconducting lead cathode deposited on the half-cell backwall. A superconducting solenoid is used for emittance compensation. This system, including a diagnostics beamline, has been installed in the HoBiCaT facility to serve as a testbed for beam dynamics studies and to test the combination SRF cavity and superconducting solenoid. This paper summarizes the characterization of the cavity in this configuration including Q measurements, dark current tests and field-stability analyses.
122656487
Microscopic investigation of high gradient superconducting cavities after reduction of field emission
Abstract In the previous companion paper we showed that high power RF processing (HPP) is an effective technique to reduce field emission in superconducting cavities, so higher accelerating gradients can be reached. In this work we show improved understanding of the mechanisms at work when field emitters process. Thermometry measurements of the outer wall of single-cell cavities reveal the field emission from localized sites and also the reduction in field emission by processing. Subsequent scanning electron microscope (SEM) examination of the RF surface at the emission/processed sites reveals 5–10 μm sized molten craters, micron sized molten particles of foreign elements, and sub-mm sized spots shaped like starbursts. These features indicate that processing occurs through a violent melting/vaporization phenomenon. A “model” for RF processing is presented based upon the experimental evidence, both from this study and from others.
45678107
Investigation of voltage breakdown caused by microparticles
Degradation of RF accelerating cavities caused by field emission currently limits the design of future linear accelerators. When field emission is the problem, foreign particles often deserve the blame, but they can be "processed" away if the cavity electric field is high enough to initiate voltage breakdown near the particle site, in which case the troublesome particle vaporizes, leaving behind a crater surrounded by a starburst-shaped feature. Severe cratering, however, erodes cavity surfaces to the point of significantly diminished acceleration capability. Breakdown events producing craters and starbursts. similar to those seen in RF cavities can also be incited by a DC electric field. After intentionally contaminating niobium and copper cathodes with different kinds of micron-sized particles, we used scanning electron microscopes with EDX and AES capabilities to obtain "before" and "after" pictures of particles that vaporized under DC electric fields between 30 and 150 MV/m.
55555181
STATUS OF THE BERLINPRO OPTICS DESIGN
Following the funding approval late 2010, HelmholtzZentrum Berlin officially started the realization of the Berlin Energy Recovery Linac Project BERLinPro in January 2011. The goal of this compact ERL is to develop the accelerator physics and technology required to accelerate a high-current (100 mA) and low emittance (1 mm·mrad normalized) beam, as desired by future large scale facilities based on ERLs, e.g ERL-based synchrotron light sources. Using the flexibility ERLs provides, a short bunch operation mode will also be investigated. A modified optics is presented and different non-linear issues are addressed.
18885837
Beam test of a superconducting cavity for the CESR luminosity upgrade
The prototype superconducting cavity system for CESR-Phase III was tested in CESR in August 1994. The performance of the system was very gratifying. The cavity operated gradients of 4.5-6 MV/m and accelerated beam currents up to 220 mA. This current is a factor of 3 above the world record 67 mA for SRF[1]. The high circulating beam current did not increase the heat load or present any danger to the cavity. No instability attributable to the SRF cavity was encountered. A maximum of 155 kW of rf power was transferred to a 120 mA beam. The window was subjected to 125 kW reflected power and processed easily. In the travelling wave mode, vacuum bursts and are trips prevented us from going above 165 kW. The maximum HOM power extracted was 2 kW. Beam stability studies were conducted for a variety of bunch configurations. In other tests a 120 mA beam was bumped horizontally and vertically by /spl plusmn/10 mm. While supporting a 100 mA beam, the cavity was axially deformed with the tuner by 0.4 mm to sweep the HOM frequencies across dangerous revolution harmonics. In all such tests, no resonant excitation of HOMs or beam instabilities were observed, which confirms that the potentially dangerous modes were damped strongly enough to be rendered harmless.