The design and performance of the ZEUS global tracking trigger

The Global Tracking Trigger (GTT) of the ZEUS experiment is described. The GTT is data driven at the ZEUS first level trigger rate of and performs event-based track finding on data from the experiment's Central Tracking Detector (CTD), silicon Micro Vertex Detector (MVD) and Straw Tube Tracker (STT) forward detectors. The resulting track-based trigger quantities calculated (track multiplicity, vertices, vector meson masses, background event probabilities, etc.) are available within and are used in the experiment's second level trigger to improve the selection of physics events. Detector information is pushed to the PC farm of the GTT using PowerPC VME board computers which are either embedded within the detector's frontend readout system (MVD) or are parasitically attached to them via multiple serial transputer links (CTD and STT). Data flow and control is performed via point-to-point Fast and Giga ethernet switched network connections using the TCP protocol. The principal design challenges were: integrating new and interfacing to existing frontend systems, providing a useful trigger result, satisfying the rate and latency requirements and not interfering with ongoing data taking during commissioning. These aims have been achieved. The GTT has been actively used in the ZEUS trigger since 2004 when an initial CTD-only algorithm was used; in 2005 this was upgraded to use MVD information which significantly improves track and primary vertex resolutions. Commissioning problems delayed the STT implementation and its use in the GTT has only been tested.     

Molecular alignment structure of dimeric liquid crystals

While an antiferroelectric liquid crystal (AFLC) with dimeric molecules which take a bent molecular structure may show the phase transition from the isotropic liquid to the chiral smectic-C AFLC () phase via the nematic (N) phase, it has not been obvious yet why the and N phases may coexist in the phase sequence of the dimeric AFLC medium. In this study, the molecular alignment structures of the N and the SmC_A phases of an achiral dimeric LC were researched in detail with a polarized Fourier transform infrared spectroscopy (FT-IR). The domain structure with two orientational directions is formed both in the SmC_A and N phase, and the occupation ratio of two types of domain does not change in the phase transition. Since their alignment structures are basically same except for the existence of layer structure, their phases may coexist in the phase sequence of the dimeric AFLC.     

Liquid-filled ionization chamber temperature dependence

Temperature and pressure corrections of the read-out signal of ionization chambers have a crucial importance in order to perform high-precision absolute dose measurements. In the present work the temperature and pressure dependences of a sealed liquid isooctane filled ionization chamber (previously developed by the authors) for radiotherapy applications have been studied.

We have analyzed the thermal response of the liquid ionization chamber in a interval around room temperature. The temperature dependence of the signal can be considered linear, with a slope that depends on the chamber collection electric field. For example, a relative signal slope of for an operation electric field of has been measured in our detector. On the other hand, ambient pressure dependence has been found negligible, as expected for liquid-filled chambers.

The thermal dependence of the liquid ionization chamber signal can be parametrized within the Onsager theory on initial recombination. Considering that changes with temperature of the detector response are due to variations in the free ion yield, a parametrization of this dependence has been obtained. There is a good agreement between the experimental data and the theoretical model from the Onsager framework.     

GABRIELA: A new detector array for -ray and conversion electron spectroscopy of transfermium elements

With the aid of the Geant4 Monte Carlo simulation package a new detection system has been designed for the focal plane of the recoil separator VASSILISSA situated at the Flerov Laboratory of Nuclear Reactions, JINR, Dubna. GABRIELA (Gamma Alpha Beta Recoil Investigations with the ELectromagnetic Analyser VASSILISSA) has been optimised to detect the arrival of reaction products and their subsequent radioactive decays involving the emission of - and β-particles, fission fragments, γ- and X-rays and conversion electrons. The new detector system is described and the results of the first commissioning experiments are presented.     

Position sensitivity of the TIGRESS 32-fold segmented HPGe clover detector

Sensitivity to the locations of γ-ray interactions within a 32-fold segmented clover-type HPGe detector has been investigated through 90 Compton scattering of -rays from a collimated source. A mean position sensitivity of 0.44 mm at an energy of 373 keV is deduced by comparing the average pulse shapes for net charge collecting signals, as well as transient induced signals in neighbouring contacts, from 1007 pairs of three-dimensionally localized interaction points. The reconstruction of individual event locations based on a χ² comparison with the measured set of basis waveforms is presented.     

The I-meter, a distributor unit for the OPERA RPC HV system

The OPERA RPC HV system has been implemented using custom current measurement/distribution systems developed by the LNF Electronics Workshop.

Each system features eight inputs and 24 outputs (1–3 modularity). The current on each channel is measured with 100 pA sensitivity and 3% accuracy in the 1 nA– range.

In the paper we describe the measurement circuit as well as the results of the tests we have carried out to qualify the system.     

Study on the electronic structures and absorption spectra for sheelite- and the sheelite-like structures lead tungstate crystal

The electronic structures and absorption spectra of perfect crystals and crystals containing lead vacancy for both sheelite(PbWO₄) and sheelite-like(Pb_7.5W₈O₃₂) structures have been calculated using density functional theory with the lattice structure optimized. The optical properties of lead tungstate exhibit anisotropy. Numerical calculation shows that the absorption spectra of the sheelite structure crystal containing exhibit additional absorption bands in the visible and near ultra-violet ranges. However, this is not the case for other structures of the PWO crystals such as the sheelite structure crystal without lead vacancy and the sheelite-like structure crystal with or without lead vacancy.     

Performance optimisation of the micro pixel chamber

A thorough performance analysis of large-area μ-PIC detectors has been made. Through systematic simulations and comparison with test results of the two detector versions, μ-PIC1 and μ-PIC3, we have identified that low primary electron collection was responsible for the degradation of measured gas gain of the μ-PIC3 device. The test of a new detector, μ-PIC5, fabricated with a narrower inter-cathode gap and anodes raised above the insulator surface, shows a threefold increase in gas gain reaching 10⁴ in argon 80%–ethane 20% gas mixture, which agrees with simulations. The new detector demonstrates a stable long-term operation at high gains, above 6000 measured during more than 70 h with an X-ray source, with a moderate 6% gain increase due to dielectric polarisation.     

The time-of-flight technique for the HERMES experiment

This paper describes the use of the time-of-flight (TOF) technique as a particle identification method for the HERMES experiment. The TOF is measured by two scintillation hodoscopes that initially were designed only for the first-level trigger. However, the suitable time structure of the HERA electron beam allows an extension of their functions to also measure the TOF for low momentum hadron identification. Using only these conventional hodoscopes, good particle identification was achieved for protons and pions in the momentum range up to and for kaons up to .     

A new analogue sampling readout system for the COMPASS RICH-1 detector

A new electronic readout for CsI-coated multiwire proportional chambers (MWPC), used as photon detectors in the COMPASS ring imaging Cherenkov (RICH) detector, is described. A prototype system comprising more than 5000 channels has been built and tested in high-intensity beam conditions. It is based on the APV25-S1 analogue sampling chip, and replaces the GASSIPLEX chip readout used previously. The APV25 chip, although originally designed for Silicon microstrip detectors, is shown to perform well even with “slow” signals from an MWPC, maintaining a signal-to-noise ratio (SNR) of 9. For every trigger the system reads out three consecutive amplitudes in time, thus allowing to extract information on both the signal amplitude and its timing. This information is used to reduce pile-up events in a high-rate environment. Prototype tests of the new readout electronics on a central RICH photocathode in nominal COMPASS beam conditions showed that the effective time window is reduced from more than for the GASSIPLEX to less than for the APV25 chip. This leads to a significant improvement of the signal-to-background ratio (SBR) with respect to the original readout. A gain by a factor of 5–6 was experimentally verified in the very forward region of phase space, where pile-up due to the muon beam halo is most significant. Owing to its pipelined architecture, the new readout system also considerably reduces the dead time per event, thus allowing to make use of trigger rates exceeding .     

GRAPES-3—A high-density air shower array for studies on the structure in the cosmic-ray energy spectrum near the knee

The change in the spectral index from about -2.7 to -3.1 at 3×10¹⁵ eV in the all-particle energy spectrum of primary cosmic rays is very significant for learning about the nature of cosmic sources of ultra-high energy particles and their acceleration and propagation in the galactic disk. Any observation of a fine structure in the spectrum would be important for improving our understanding of these physical processes. The GRAPES-3 air shower array has been designed to achieve higher precision in determination of various shower parameters to enable observation of any fine structure in the energy spectrum, if it exists. The details of the shower detectors, shower trigger and the data acquisition system are presented here along with estimates of trigger efficiencies from Monte Carlo simulations for primary photons (γ-rays) and several nuclei.     

Coupled simulation of microstructural formation and deformation behavior of ferrite–pearlite steel by phase-field method and homogenization method

A coupled simulation by the phase-field (PF) method and the finite element method based on the homogenization theory (FEH) is developed to predict the microstructure formations and mechanical properties of ferrite–pearlite steels. The formation of the phase during the isothermal transformation is simulated by the PF method. Furthermore, the FEH analysis is performed to clarify the effects of the predicted microstructure on the deformation behavior of the steels. In order to link to the FEH analysis, the microstructure in the steel is described by the representative volume element (RVE) based on the results of the PF simulation. The results reveal that although the macroscopic stress–strain relationship is mainly characterized by the volume fraction of the constituent phase, the localization of plastic strain is reduced due to the fine-grained phase. This numerical model provides a systematic way of predicting the mechanical properties of steel depending on the microstructure.     

Development of gas electron multiplier foils with a laser etching technique

Fine-pitch gas electron multiplier (GEM) foils have been produced for cosmic X-ray polarimeters using a carbon dioxide laser etching technique. The finest hole pitch of the foil which can be produced repeatedly is and the smallest hole diameter is . The electron amplification factor was measured as a function of applied voltage. The behavior of the factor is almost the same as the -pitch standard foil fabricated by CERN. Our GEMs had no rate-dependent gain instability, which is expected of the GEMs having holes of good cylindrical geometry. The amplification factor of the foil in a mixture of 70% argon and 30% carbon dioxide reaches about 5000 without any micro-discharge at a voltage of 570 V between foil electrodes.     

Differential die-away analysis system response modeling and detector design

Differential die-away-analysis (DDAA) is a sensitive technique to detect presence of fissile materials such as and . DDAA uses a high-energy (14 MeV) pulsed neutron generator to interrogate a shipping container. The signature is a fast neutron signal hundreds of microseconds after the cessation of the neutron pulse. This fast neutron signal has decay time identical to the thermal neutron diffusion decay time of the inspected cargo. The theoretical aspects of a cargo inspection system based on the differential die-away technique are explored. A detailed mathematical model of the system is developed, and experimental results validating this model are presented.     

A NaI activation method for the measurement of the weak thermal neutron field around the MEG experiment

A precise measurement of the thermal neutron flux (and an approximate measurement of the non-thermal neutron flux), associated with the high intensity stopping μ⁺ beam (≈) of the MEG experiment, was studied by measuring the delayed radioactivity of an activated NaI detector. This passive method provides a high sensitivity and allows the neutron flux determination at all locations, even in regions of high magnetic field. We present and discuss the results.     

A parametric study of a pressurized blister test for an elastic–plastic film-rigid substrate system

A finite element simulation of a blister test of an elastic–plastic film, bonded to a substrate and subject to plane strain conditions, is performed. A traction-separation law models the fracture process ahead of the crack tip at the interface between the thin film and the substrate. Only two parameters are significant in describing the traction-separation law: adhesion energy, Γ₀ and interface strength, . The dependences of the pressure, P, and the product of the pressure with the central deflection, PH, on the adhesion properties (Γ₀ and ), the geometry and material properties of the film are studied. The latter quantity (PH) has the same unit as the adhesion energy, Γ₀, and is “conceptually” appropriate for the analysis. We suggest a method to extract the adhesion energy, Γ₀ and the interface strength, , independently from the total energy dissipated.     

A 5 ps TOF-counter with an MCP–PMT

We measured the timing resolution of TOF counters by means of Cherenkov-light detection with a Micro-Channel Plate Photo-Multiplier Tube, and attained using pion-beams with a readout electronics of 4.1 ps resolution. The optimum radiator thickness was examined and the detectable number of photo-electrons was analyzed.     

Composite detector for mixed radiations based on CsI(Tl) and dispersions of small ZnSe(Te) crystals

A new large area detector of high-energy X-ray and β-radiation has been designed and studied. A composite material based on small-crystalline ZnSe(Te) was applied onto the wide surface of a light guide. An experimental specimen has been prepared, which showed β-sensitivity . The spectrograms of a ⁹⁰Sr+⁹⁰Y β-source obtained with the specimen under study make it possible to evaluate the age of the source by the ratio of low- and high-energy regions of the spectrum.

The combined detector (CD) comprises a single crystalline plate of ZnSe(Te) placed onto the output window of a scintillating transparent light guide made of CsI(Tl) in the shape of a truncated pyramid. The CsI(Tl) light guide is used to create an additional channel for detection of γ-radiation, as well as for protecting the photodiode from the penetrating radiation. It is shown that introduction of the light guide does not worsen the energy resolution characteristics of ZnSe(Te). Separate detection of - and γ-radiation has been achieved under simultaneous excitation by ²³⁹Pu (ZnSe(Te), R=6%) and ²⁴¹Am (CsI(Tl), R_γ=20%). The use of selective optical filters allows separation of the peaks of total absorption (p.t.a.) in the case of their superposition.     

ILC beam energy measurement based on synchrotron radiation from a magnetic spectrometer

We propose to measure, on a bunch-to-bunch basis, the beam energy at the International Linear e⁺e^- Collider by recording synchrotron radiation (SR) light emitted in the magnets of an energy spectrometer based on beam position monitors. Measuring the width of the horizontal SR fan permits to determine the relative beam energy with a precision better than 10^-4. There are two different measuring schemes possible. The first one is based on edge measurements of the direct SR fan, while the second option includes mirrors to deflect soft SR light to detectors located sufficiently off the beamline. Three possibilities for high-spatial resolution detectors are considered: a standard silicon strip detector, a novel-type Si detector and a gas amplification detector, both with exceptional position resolution. The main issue of the first scheme is the high radiation dose expected in the direct SR fan. If mirrors are used this dose is strongly reduced and allows application of any of the three detectors proposed.     

Production of a low-energy radioactive nuclear beam with high purity using JAERI-RMS

Low-energy (1–2 MeV/nucleon) radioactive nuclear beams (RNBs) of ⁸Li, ¹²B and ¹⁶N have been produced through nuclear transfer reactions using a recoil mass separator (RMS) at Japan Atomic Energy Research Institute (JAERI). The contamination of the primary beam to the RNB was investigated quantitatively and was well suppressed. The typical beam intensities of ⁸Li-, ¹²B- and ¹⁶N-RNB were 1.4×10⁴, 7.8×10³ and , respectively. Their purities were 99%, 98% and 98.5%, respectively.