118829325
Search for CP violation in Z ---> tau tau
Using the 18.8 pb−1 of data accumulated at LEP in 1990 and 1991 with the ALEPH detector, a direct test of neutral current CP-invariance is performed by a search for CP-odd correlations in Z decays to τ pairs where both τ decay modes are identified. No evidence for CP-violation is observed. The weak dipole moment of the τ has been measured to be dτ(mZ) = (1.3 ± 1.4 ± 0.1) × 10−17e·cm which results in an upper limit on the weak dipole moment of |dτ(mZ)| ⩽ 3.7 × 10−17e·cm with 95% confidence level.
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.
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Abstract Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented.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.
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.
121749411
Beam breakup instability suppression in multicell superconducting rf guns
Helmholtz-Zentrum, Berlin, Germany(Received 28 November 2009; revised manuscript received 28 November 2010; published 19 May 2011)In this paper, we provide an analytical description for transverse coupling impedances with dipole highorder modes (HOMs) and beam breakup (BBU) instability suppression of relativistic, high-current beamsundergoing strong acceleration, such as those typically produced by rf photoinjectors. The model adoptedis based on the accepted theory of coupling impedances extended to the case of beams characterized by afast transition due to strong acceleration, from the nonrelativistic to the relativistic regime in whicha bunch trajectory may not be rigidly directed parallel to the axis of the electric ﬁeld. The trajectoryoscillations in a dipole HOM ﬁeld in the transverse plane are effective in perturbing the bunch energy,which causes an increase of the coupling impedance up to the BBU instability. This BBU instabilityanalysis is based on equations obtained by Volkov [Phys. Rev. ST Accel. Beams 12, 011301 (2009)]inwhich external focusing due to both the applied transverse electric (TE) HOM and the acceleratingfundamental mode as well as dipole HOM damping by external loads are investigated. This analysis isvalid in the limit in which the weak nonlinearity of applied ﬁelds near the axis may be neglected. Thesolution suggests a means of enhancing the BBU threshold current. The possibility of obtaining BBUinstability suppression in a long, integrated photoinjector and linac structure, such as the superconductingrf source at Forschungs Zentrum Dresden (FZD), are numerically examined. New designs of photo-injectors that provide BBU instability suppression of all dipole HOMs to enhance the threshold currentsare suggested.
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.
56307984
FIRST RF TESTS IN THE HOBICAT SUPERCONDUCTING TEST FACILITY AT BESSY
In preparation for the construction of the BESSY-FEL User Facility, BESSY recently completed the installation of the HoBiCaT cryogenic test facility for superconducting RF (SRF) TESLA cavity units [1], including all ancillary devices (helium tank, input coupler, tuner, magnetic shielding). It is designed to house two such units in a configuration similar to that envisaged for the superconducting CW linac of the BESSY FEL. Commissioning of the facility is now complete and the first TTF-III RF coupler and cavity unit has been tested. In particular, the complete production, cleaning and assembly of the cavity unit was carried out by industry. These tests thus serve as a first step at qualifying industrial partners for series production of such systems, which will be essential for the future construction of SRF based light sources.
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.
46074015
Dark current measurements on a superconducting cavity using a cryogenic current comparator.
This paper presents nondestructive dark current measurements of tera electron volt energy superconducting linear accelerator cavities. The measurements were carried out in an extremely noisy accelerator environment using a low temperature dc superconducting quantum interference device based cryogenic current comparator. The overall current sensitivity under these rough conditions was measured to be 0.2 nA/Hz(1/2), which enables the detection of dark currents of 5 nA.