125914955
Electroproduction in a Streamer Chamber: Multiplicities, Inclusive Cross-Sections and Production of $\rho^0$ and $\omega$ Mesons
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Abstract Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented.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.
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.
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.
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.
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]
124968181
THE BESSY 2 nd -GENERATION SOFT X-RAY FEL USER FACILITY ∗
VUV-to-soft-X-ray FEL facilities promise to open fundamentally new frontiers for the synchrotron user community. So-called 2nd generation FELs, which use seeded schemes rather than SASE, an deliver reproducible ultrashort photon pulses in the GW range. BESSY has been designing a high-gain-harmonic-generation (HGHG) based FEL with a 2.3 GeV CW superconducting driver linac that covers photon energies from 24 eV to 1 keV. The design presented here provides full tuneability of photon energy, variable beam polarization and complete synchronization to external lasers—all essential for future femtosecond, time-resolved pump-probe experiments. In addition, CW operation offers the flexibility to tune the repetition rate and pulse pattern to the users’ needs.
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.
24618282
CW Operation of the TTF-III Input Coupler
Several newly proposed superconducting linacs are designed to use TESLA technology operating CW rather than pulsed for which the system was developed. It must therefore be demonstrated that CW operation is feasible. Here we describe a series of CW tests with the TTF-III power coupler to determine the average power limit. These tests were performed on a coupler test stand both at room temperature at the FZ Rossendorf and under cryogenic operating conditions in BESSY’s HOBICAT[1] facility. An extrapolation of the measurements suggests that the coupler can handle 5 kW CW standing wave. It was also demonstrated that even higher power levels are feasible if the cooling of the inner conductor is modified.
58910854
RF CONTROL OF THE SUPERCONDUCTING LINAC FOR THE BESSY FEL
For the BESSY-FEL superconducting linac, precise RF control of the cavities’ voltage is imperative to maintain a bunch-to-bunch time jitter of less than 50 fs for synchronization in the HGHG section. Noise, in particular microphonic detuning, strongly impact the achievable level of control. Presented here are simulations of the cavityfeedback system, taking into account beam loading and noise sources such as measurement noise, microphonics and injection jitter. These simulations are used to estimate the resultant time and energy jitter of the bunches as they enter the HGHG section of the BESSY-FEL. It will be shown, that under the given assumptions these requirements can be fulfilled.