26322213
A study of Bose-Einstein correlations ine+e− annihilation at 91 GeV
This paper describes a study of Bose-Einstein correlations made using the ALEPH detector at LEP. The correlations are found to enhance the two particle differential cross section for pairs of identical pions by a factor which can be roughly parametrized byR(Q)=1+λ exp(-Q2σ2), whereQ is the difference in the 3-momenta of the two pions in their centre of mass frame, λ=0.51±0.04±0.11 and σ=3.3±0.2±0.8 GeV−1, which corresponds to a source size of 0.65±0.04±0.16 fm. The large systematic errors on these results reflect their strong dependence on the choice of the reference sample used in the analysis. This problem is believed to occur primarily because of uncertainties in the rates of resonance production and a lack of knowledge about the pion-pion strong interaction. No significant correlations are seen amongst like-charged pion-kaon pairs.
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.
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.
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
111052021
SUPERCONDUCTING ACCELERATOR MODULES FOR STORAGE RINGS AND SYNCHROTRONS
We report on the production status of 6 superconducting 500 MHz accelerating modules (2 for Cornell University for upgrading CESR, 2 for the Taiwan Light Source and two for the Canadian Light Source). We focus on the test results on cavities and RF windows. The superconducting 500 MHz cavities fully prepared and assembled at ACCEL reached 12 MV/m accelerating gradient during cold vertical RF test on a regular basis. The assembly of the first module is almost completed. The cold RF test of this first module at Cornell is scheduled for June this year.[1]
40909893
Enhanced susceptibility of Nb cavity equator welds to the hydrogen related Q-virus ∗
Thermometric studies of chemically treated niobium cavities have demonstrated that preferential niobium-hydride precipitation takes place along the electron-beam-welded equator (“Q-virus”). High residual losses are recorded as a result of the hydride in this region. Such precipitation can take place even when the cavity is rapidly cooled from 300 K to 4.2 K, a procedure that is known to be effective at preventing the Q-virus in bulk niobium.
32138968
Performance of Tesla Cavities after Fabrication and Preparation in Industry
In order to demonstrate cw operation of TESLA cavities in a linear accelerator driven FEL application, two TESLA cavities were manufactured for BESSY. After production, both cavities were prepared for vertical test at ACCEL’s premises using state of the art chemical polishing and high pressure water rinsing techniques. The cavities were tested in DESY’s vertical RF test installation. Accelerating gradients close to 25 MV/m were reached. One cavity was completed with helium vessel modified for cw operation, prepared with chemical polishing and high pressure water rinsing and assembled with the required high power coupler at ACCEL. The fully dressed cavity was then shipped under vacuum to BESSY and is currently under test in the horizontal cryostat HoBiCaT.
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.
59036810
First Demonstration of Electron Beam Generation and Characterization with an All Superconducting Radio-frequency (SRF) Photoinjector
In preparation for a high brightness, high average current electron source for the energy recovery linac BERLinPro an all superconducting radio-frequency (SRF) photoinjector is now in operation at Helmholtz-Zentrum Berlin. The aim of this experiment is beam demonstration with a high brightness electron source able to generate short, few ps long pulse length electron bunches from a superconducting (SC) cathode film made of Pb coated on the backplane of a Nb SRF cavity. This paper describes the setup of the experiment, first results from beam measurements and capabilities of the source derived from beam dynamics considerations. In April 2011 the photoinjector generated and accelerated for the first time electron beam. This result marks the highlight of the project running for two years starting with project approval in May 2009.