125230629
Measurement of electroweak parameters fromZ decays into fermion pairs
We report on the properties of theZ resonance from 62 500Z decays into fermion pairs collected with the ALEPH detector at LEP, the Large Electron-Positron storage ring at CERN. We findMZ=(91.193±0.016exp±0.030LEP) GeV, ΓZ=(2497±31) MeV, σhad0=(41.86±0.66)nb, and for the partial widths Γinv=(489±24) MeV, Γhad(1754±27) MeV, Γee=(85.0±1.6)MeV, Γμμ=(80.0±2.5) MeV, and Γττ=(81.3±2.5) MeV, all in good agreement with the Standard Model. Assuming lepton universality and using a lepton sample without distinction of the final state we measure Γu=(84.3±1.3) MeV. The forward-backward asymmetry in leptonic decays is used to determine the vector and axial-vector weak coupling constants of leptors,gv2(MZ2)=(0.12±0.12)×10−2 andgA2(MZ2)=0.2528±0.0040. The number of light neutrino species isNν=2.91±0.13; the electroweak mixing angle is sin2θW(MZ2)=0.2291±0.0040.
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Abstract Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented.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.
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.
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.
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.
648097
Adapting TESLA technology for future cw light sources using HoBiCaT.
The HoBiCaT facility has been set up and operated at the Helmholtz-Zentrum-Berlin and BESSY since 2005. Its purpose is testing superconducting cavities in cw mode of operation and it was successfully demonstrated that TESLA pulsed technology can be used for cw mode of operation with only minor changes. Issues that were addressed comprise of elevated dynamic thermal losses in the cavity walls, necessary modifications in the cryogenics and the cavity processing, the optimum choice of operational parameters such as cavity temperature or bandwidth, the characterization of higher order modes in the cavity, and the usability of existing tuners and couplers for cw.
37292985
FABRICATION , TREATMENT AND TESTING OF A 1 . 6 CELL PHOTO- INJECTOR CAVITY FOR HZB
As an amendment to a CRADA (Cooperative Research and Development Agreement) between Forschungszentrum Dresden (FZD) and JLab we have fabricated and tested after appropriate surface treatment a 1.6 cell, 1300 MHz RRR niobium photo-injector cavity to be used in a demonstration test at HZB. Following a baseline test at JLab, the cavity received a lead spot coating of ~8 mm diameter deposited with a cathode arc at the Soltan Institute on the endplate made from large grain niobium. It had been demonstrated in earlier tests with a DESY built 1.6 cell cavity – the original design – that a lead spot of this size can be a good electron source, when irradiated with a laser light of 213 nm. In the initial test with the lead spot we could measure a peak surface electric field of ~29 MV/m; after a second surface treatment, carried out to improve the cavity performance, but which was not done with sufficient precaution, the lead spot was destroyed and the cavity had to be coated a second time. This contribution reports about the experiences and results obtained with this cavity.
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.
11679008
MIRCO-STRUCTURES OF RF SURFACES IN THE ELECTRON-BEAM-WELD REGIONS OF NIOBIUM
Micro-structures of RF surfaces in the electron-beam-weld (EBW) regions of niobium samples were studied. These surfaces were polished with different techniques,namely buffered chemical polish (1:1:2 BCP) and electrolytic polish (EP). It was found that there are three distinctively different regions near the EBW, characterized by different grain sizes, shapes, and orientations. Strikingly, we found grain boundaries within the EBW are nicely lined up so that they form an angle of about 60 degree with respect to the weld seam. Upon being polished with BCP, these grain boundaries evolve into micro-steps with sharp edges, due to preferential etching of different crystallographic planes. There is evidence that the step height increases up to possibly more than 30 microns with repeated chemical polish. In contrast to the result with BCP, dimensions of surface irregularities were reduced with EP and sharp edges were rounded off.These observations have important implications in explanations of the high-field-Q-drop of niobium superconducting cavities.
202037513
SIMULTANEOUS LONG AND SHORT ELECTRON BUNCHES IN THE BESSY II STORAGE RING
We present first ideas of a scheme to develop BESSY II into a variable electron pulse length storage ring. The final goal is, to fill BESSY II with short bunches of 1.5 ps length (rms) and long bunches of 15 ps length simultaneously in the presently applied user optics. All insertion devices are operated as usual, i.e. the helical undulators and 7 T-field insertions. Long bunches of 1.5 mA current per bunch, twice the value of the present user optics, are filled in each second bucket. The other buckets can be filled with short bunches of up to 0.8 mA. The lower current value is required to avoid increase in the bunch length and bunch energy spread, predicted by scaling laws. The total current is e.g. limited by the HOM damping capabilities of the sccavities and the machine impedances. This scheme is achievable with recent developments in sc-rf cavity technology driven by requirements of high current cw applications like for the energy recovering linacs (ERLs). These developments seem to make it feasible to install high gradient HOM damped multi-cell cavities in electron storage rings. With an appropriate choice of the cavity resonance frequencies a beating of the effective longitudinal focusing voltage at the stable fixed points can be introduced and leads to different zero current bunch lengths. Basic parameters of this scheme are presented.