i Present address: Lockheed Missiles and Space Co., Sunnyvale, CA 94086, USA. 2 Present address: Stanford Linear Accelerator Center, Stanford, CA 94305, USA. 3 Present address: Bell Laboratories, Naperville, IL60566, USA. 4 Present address: SRI International, Menlo Park, CA 94025, USA. 5 Present address: State University of New York at Stony Brook, Stony Brook, LI, NY 11794, USA. 6 Present address: Brandeis University, Waltham, MA 02254, USA.

Cross sections are presented for the inclusive production of Λ hyperons in electron-positron annihilations at s=29 GeV based on the full 291-pb−1 sample of data taken in the High Resolution Spectrometer experiment at the SLAC e+e− storage ring PEP. These results, and the associated correlation analyses, are consistent with the Lund model predictions with the strange diquark suppression ratio δ fixed at 0.59±0.10±0.18, as compared to the standard Lund value of 0.32. The Λ multiplicity has been found to be 0.182±0.020 per event. The opposite-strangeness multiplicity 〈nΛΛ¯〉 has been measured to be 0.046±0.020, whereas the like-strangeness multiplicity 〈nΛΛ+Λ¯Λ¯〉 is 0.009±0.028. A strong correlation is found between Λ's and Λ¯'s; when one is found in an event, the other is found in the same event with a probability that exceeds 50%.Received 8 July 1991DOI:https://doi.org/10.1103/PhysRevD.45.3949©1992 American Physical Society

We report a study of electron proton collisions at very low Q2, corresponding to virtual photoproduction at centre of mass energies in the range 100–295 GeV. The distribution in transverse energy of the observed hadrons is much harder than can be explained by soft processes. Some of the events show back-to-back two-jet production at the rate and with the characteristics expected from hard two-body scattering. A subset of the two-jet events have energy in the electron direction consistent with that expected from the photon remnant in resolved photon processes.

The ZEUS barrel calorimeter consists of 32 wedge-shaped modules constructed using alternate layers of depleted uranium and scintillator with one radiation length sampling. In this paper we summarize tests made on 22 of these modules by measuring their response to hardened cosmic rays. We describe the cosmic ray facility, the data taking, the track reconstruction, the data analysis, and the module testing. These tests include the uniformity, both tower-to-tower and module-to-module, in the response to minimum ionizing particles, the mapping of this response as a function of lateral position of the particles inside a given tower, and the measurement of the number of photoelectrons produced by a minimum ionizing particle. In addition, we present data on the stability of the current in the photomultiplier tube generated by the natural radioactivity of the uranium.

Cross sections are presented for the inclusive production of A hyperons in electron-positron annihilations at square-root s=29 GeV based on the full 291-pb-1 sample of data taken in the High Resolution Spectrometer experiment at the SLAC e+e- storage ring PEP. These results, and the associated correlation analyses, are consistent with the Lund model predictions with the strange diquark suppression ratio-delta fixed at 0.59+/-0.10+/-0.18, as compared to the standard Lund value of 0.32. The LAMBDA multiplicity has been found to be 0. 182+/-0.020 per event. The opposite-strangeness multiplicity [n(LAMBDA-LAMBDABAR)] has been measured to be 0.046+/-0.020, whereas the like-strangeness multiplicity [n(LAMBDA-LAMBDA+LAMBDABAR-LAMBDABAR)] is 0.009+/-0.028. A strong correlation is found between LAMBDA's and LAMBDABAR's; when one is found in an event, the other is found in the same event with a probability that exceeds 50%.

The total photoproduction cross section is determined from a measurement of electroproduction with the ZEUS detector at HERA. The Q2 values of the virtual photons are in the range 10−7<Q2<2×10−2 GeV2. The γp total cross section in the γp centre of mass energy range 186–233 GeV is 154 ± 16 (stat.) ± 32 (syst.) μb.

We describe an inexpensive system for mixing argon and ethane gas for drift chambers which was used for an experiment at Fermilab. This system is based on the idea of intermittent mixing of gases with fixed mixing flow rates. A dual-action pressure switch senses the pressure in a mixed gas reservoir tank and operates solenoid valves to control mixing action and regulate reservoir pressure. This system has the advantages that simple controls accurately regulate the mixing ratio and that the mixing ratio is nearly flow-rate independent without readjustments. We also report the results of the gas analysis of various samplings, and the reliability of the system in long-term running.

We present the mechanical design and construction techniques used in building the barrel calorimeter for the ZEUS detector. The latter is currently under construction for use at the HERA electron-proton colliding beam facility. The calorimeter consists of 32 wedge shaped modules with approximate dimensions of 3×0.5×1.7 m3. The modules use alternate layers of depleted uranium and scintillator with one radiation length sampling. The light is collected via wavelength shifter plates placed on the sloping sides of the modules and read out by photomultiplier tubes located at the outer radius. The unit cell dimensions result in a ratio eh = 1 which yields an optimal energy resolution for hadronic jets. The placing of the structural components and the arrangement of the cracks between modules were chosen to maximize the uniformity of the response. Details of the construction and assembly effort needed to realize the total calorimeter are given. We finally describe the procedures used for transporting the completed modules to DESY and to install them on ZEUS.

Total and dift'erential K cross sections are presented from e+e collisions at &s =29 GeV in the High Resolution Spectrometer detector.K and charged-particle distributions are compared in a study of the hadronization of quarks of known flavor.Events of the reaction e e ~cc are tagged by identifying D*'s while uu, dd, or ss events are tagged through the identification of a charged par- ticle with fractional momentum near 1.Parton-shower models with cluster and string fragmenta- tion are compared with these data.Also, certain particle scaling tests are performed using the quark-flavor tags.In addition, K production in two-and three-jet events is compared to these models.

The intermittency and fractal behavior in e{sup +}e{sup {minus}} annihilations has been studied using the HRS detector at PEP ({radical}s = 29 GeV). The factorial moments F{sub i}(i = 2 {approximately} 5) in small rapidity intervals show stronger intermittency slopes than those for the {pi}p, {bar p}p, and AA reactions. This direct measurement confirms our previous data derived from the k-values in the negative binomial fits to the multiplicity distributions in various central rapidity windows. The fractal moments G{sub q} have been measured for the first time in e{sup +}e{sup {minus}} annihilations. The Legendre transform f({alpha}) derived from the fractal moments show a self-similar behavior which is consistent with the jet cascading mechanism. 95 refs., 46 figs., 2 tabs.

This paper reports a new measurement of the branching ratio for the decay ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{e}{\ensuremath{\nu}}_{\ensuremath{\tau}}$. The data were taken with the High Resolution Spectrometer at the SLAC ${e}^{+}{e}^{\ensuremath{-}}$ colliding-beam facility PEP, operating at $\sqrt{s}=29$ GeV. The result $B({\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{e}{\ensuremath{\nu}}_{\ensuremath{\tau}})=(17.0\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\pm\else\textpm\fi{}0.6)%$, together with our measurements of the lifetime and the topological branching fractions of the $\ensuremath{\tau}$ lepton are compared with theoretical expectations.

We report measurements of the lifetimes of the D0, D+, and Ds+ (F+) mesons produced in e+e− collisions at a center-of-mass energy of 29 GeV. The decay vertex distributions in the processes D0→K−π+, D+→K−π+π+, and Ds+→φπ+ were made using a vertex chamber installed in the High Resolution Spectrometer at the SLAC storage ring PEP. The measured lifetimes are & =(4.4±1.0±0.6)×10−13 s, &=(9.2−1.3+1.7± 1.6)×10−13 s, and &=(3.1−2.0+2.4±0.5) ×10−13 s. In addition the lifetime of the B0 meson is determined assuming that only the B0 and not the B− decays to a D*+ meson. The B0 is not directly observed. The lifetime & is estimated indirectly to be (8.2−3.7+5.7±2.7) ×10−13 s.Received 31 May 1988DOI:https://doi.org/10.1103/PhysRevD.39.123©1989 American Physical Society

We report a new measurement of the branching ratio for the decay τ − →e − v e v τ . The data were taken with the High Resolution Spectrometer at the PEP e + e − colliding beam facility operating at √ s = 29 GeV. The result is B(τ − →e − v = (17.0±0.5±0.6)% .