Medium Energy Physics Research Articles

Quark Hadron Duality in Unpolarized Structure Functions

Quark hadron duality establishes an intriguing connection between medium and high energy physics by identifying, in certain cases, dual descriptions of observables either in terms of explicit quark degrees of freedom or as averages over hadronic variables. Duality has been studied extensively in inclusive electron scattering experiments at Jefferson Lab. The present talk is an overview of these results for unpolarized structure functions for proton, neutron, and nuclei.

Signal characteristics of a resistive-strip micromegas detector with an integrated two-dimensional readout

In recent years, micropattern gaseous detectors, which comprise a two-dimensional readout structure within one PCB layer, received significant attention in the development of precision and cost-effective tracking detectors in medium and high energy physics experiments. In this paper, we present for the first time a systematic performance study of the signal characteristics of a resistive strip micromegas detector with a two-dimensional readout, based on test-beam and X-ray measurements. In particular, comparisons of the response of the two independent readout layers regarding their signal shapes and signal reconstruction efficiencies are presented.

Polarized 3He targets in medium energy physics at MAMI

Experiments with polarized 3He targets at the Mainz Microtron (MAMI) involve double polarized photoabsorption or the extraction of the electric form factor of the neutron Ge,n via electron scattering, respectively. Polarized 3He with an initial polarization of up to 70% at the experimental areas is provided by a polarizer based on the principle of metastability exchange optical pumping (MEOP). In this article both target setups for the photon- and the electron beamlines will be described and a status of the data analysis will be given.

From nuclei to hypernuclei: a retrospective view of medium energy physics at Brookhaven

A new frontier in physics originated with programs at two Brookhaven National Laboratory facilities--the Cosmotron and the Alternating Gradient Synchrotron. The development of this frontier over a half century is described, as it turned from conventional nuclear physics to the hypernuclei and the study of strange matter.

Tight Budget Could Shut Down MIT Accelerator

Unless the U.S. government finds more money for medium-energy physics research, the Siberian Snake may never slither into the Massachusetts Institute of Technology9s (MIT9s) Bates Linear Accelerator. Last week, a government advisory panel recommended that the MIT accelerator be shut down in 2 years and that other nuclear physics experiments elsewhere be abandoned if the Department of Energy (DOE) and the National Science Foundation do not boost funding for the field. DOE officials plan to use the report to convince the Administration to do exactly that in its upcoming 2000 budget.

Cooler synchrotron COSY

COSY Jülich is a cooler synchrotron and storage ring delivering high precision beams with at present up to 5·10 10 protons with momenta between 600 MeV/c and 3.3 GeV/c for medium energy physics. Two cooling systems are used to accomplish this goal. An electron-cooling system that reaches up to a momentum of 645 MeV/c and a stochastic cooling system that covers the upper momentum range from 1500 to 3300 MeV/c. Since its inauguration in April 1993 substantial progress in developing beams for internal and external experiments has been achieved and the physics program is now running. At the beginning of 1996 a polarized proton beam could be successfully accelerated up to 820 MeV/c for the first time.

Cooler synchrotron COSY — Performance and perspectives

COSY is a cooler synchrotron and storage ring delivering protons with momenta between 300 MeV/c and 3300 GeV/c for experiments in medium energy physics. It contains two cooling systems to shrink the beam phase space. An electron-cooling system reaches up to a momentum of 600 MeV/c and is complemented by a stochastic cooling system that covers the upper range from 1500 to 3300 MeV/c. Beam extraction is accomplished by the conventional resonant extraction mechanism as well as with the stochastic extraction method. Proton beams are being delivered routinely to three internal and three external experimental areas.

A plastic-BaF/sub 2/ phoswich telescope for charged/neutral particle and photon detection

BaF/sub 2/ has become a very versatile scintillator for particle and photon detection commonly applied in medium and high energy physics experiments. The intrinsic properties allow particle identification via time-of-flight, /spl Delta/E-E and pulse-shape techniques. A new NE102A-BaF/sub 2/ phoswich detector using the standard TAPS crystals has been tested at relativistic energies. The drastically improved particle identification and first results obtained with a large annular forward wall consisting of 120 phoswich modules with 15 mm NE102A attached to the BaF/sub 2/-crystal will be discussed in detail.

The cooler synchrotron COSY in Jülich

COSY Jülich is a cooler synchrotron and storage ring with a proton momentum range from 270 to 3300 MeV/ c. It has been conceived to deliver high precision beams for medium energy physics. To accomplish this goal two cooling systems are foreseen: an electron cooling system for the momentum range up to 645 MeV/ c and a stochastic cooling system which covers the upper momentum range from 1500 to 3300 MeV/ c. Proton beams in a wide momentum range have been delivered to internal as well as external experiments. The beam properties measured by these experiments and the main parameters of COSY are presented.

ACQU a data acquisition and analysis system for medium energy physics experiments

The ACQU system, which has been developed for data acquisition and analysis in medium energy electron and photonuclear experiments is described. This system comprises a front-end component, whose task is to control and read out the experimental hardware, and a data storage and sorting part, which is used to perform on-line or off-line analysis of the experimental information. The hardware capabilities and real-time performance of the system are outlined, as is the structure of both the front-end and analysis software.

Particle discrimination in medium energy physics with an aerogel Cherenkov detector

A new threshold Cherenkov detector to discriminate pions from kaons in the momentum range from 1.2 GeV/ c to 1.73 GeV/ c is discussed. Silica aerogel is used as radiator. A method for developing such detectors by the aid of Monte Carlo simulations is presented. A rejection rate for π + of 99.8±0.2% has been reached. The production of fast secondary electrons by subthreshold particles is considered.

Development of vectorized Monte Carlo particle transport programs

Special developments of vectorized Monte Carlo simulation codes for particle interaction with matter were performed for applications in medium and high energy physics, namely simulation of particle shower development in particle detectors. Particle showers in such large pieces of matter comprise particle energies from the energy of the incident high energy particle down to thermal energies. Due to high multiplicity of cascade particles with low energy, the Monte Carlo programs for low energy particle transport (mainly neutrons and photons) are the most time consuming ones. Therefore, we developed a vectorized geometry package for use with Monte Carlo programs, since it was found that in many cases this part of the codes is the most time consuming one at all. The question how to gather vectors in Monte Carlo programs was solved by a scheme of particle parallel processing by the code. Recently we developed vectorized versions of a nuclear event generator and a routine for tracking of neutral particles in material. The nuclear event generator code uses tabulated partial cross sections for all reactions of interest and simulates single nuclear collision events in the CM system, conserving energy and momentum in each. The tracking routine and the nuclear event generator together with the geometry package form the main parts of a particle transport MC program. Thus, we were able to assemble such a program for neutral particles with most of the inner loops vectorized. A series of test runs was performed, which showed CPU time gains of about 4.

Hadron sampling calorimetry, a puzzle of physics

The physics involved in hadron sampling calorimetry covers the wide energy range between high energy, medium energy, nuclear and atomic physics. All the processes contributing to energy depositions are discussed as well as illustrated by model calculations. The sampling fraction which determines the fraction of incident energy, which becomes visible in the detector layers, turns out to be strongly affected by the type of energy flow and the atomic number Z of the materials used. Normalized to mips, such fractions might range in the examples discussed between 0 and 2. Model calculations have been based on the HERMES scheme, which makes use of improved versions of the HET, the MORSE and the new developed DYMO code. The results allow to evaluate the degree of compensation and to predict e/h ratios. Such predictions agree quite well with the experimental results. In case of depleted uranium/scintillator sampling structures, compensation can be tuned by means of layer thicknesses. Finally, first results are presented for the investigation of fluctuations and correlations from model calculations evaluated event-by-event.

Pion Physics at the Meson Factories

Pions are excellent probes of the structure of the nucleus and are useful in a variety of particle physics experiments of fundamental significance. For the past 15 years, physicists have been producing copious beams of these mesons by directing intense proton beams into targets. Three “meson factories” are now in operation: TRIUMF, in Vancouver, British Columbia; SIN, in Villigen, Switzerland; and LAMPF, in Los Alamos, New Mexico. A fourth is under construction in the Soviet Union, at Troitsk, south of Moscow. This article surveys the scientific achievements that have come out of pion experiments at the meson factories since they came into operation and explains how the availability of pions has caused medium-energy physics to burgeon.

A fast timing light pulser for scintillation detectors

We report on the development of a compact, inexpensive and fast light pulser system designed to set up the timing of scintillators in a medium energy physics spectrometer.

Capabilities of the Los Alamos National Laboratory in nuclear target technology

Targets are made at Los Alamos for experiments at the Ion Beam Facility (Van de Graaff), the Medium Energy Physics Facility (LAMPF), and for experiments conducted at many other accelerators in the US and Europe. Thin, isotopic targets are made by sputtering and evaporation. Versatile, large-scale facilities exists for ceramics and plastics fabrication, electroplating, powder metallurgy, fabrication by pressing, casting and rolling, chemical and physical vapor deposition, and sputtering. Special developments include ultra-precision machining, cryogenic targets, and shaped-foil targets.

A high speed driftchamber readout system: “Tirus”

TIRUS (Time Interval Readout Using Scalers) is a fast and accurate, digitalwire chamber readout system which is capable of operating under high background and high real count rate conditions. The system can be configured for a variety of experiments in medium energy physics, including multiple arm spectrometer setups. Drift time is measured directly by a 500 MHz counter for each wire. Timing resolution is 1 ns, readout speed is 30 to 60 ns per event and relative channel efficiency variation is less than 3%. No delay adjustments are necessary. Current results from a 28 wire prototype are presented.

The cloudy bag model

We review recent developments in the bag model, in which the constraints of chiral symmetry are explicitly included. The model has profound implications for nuclear, medium energy and high energy physics.

Baryonic excitations and meson exchange currents in nuclei

The rôle of mesonic and isobar degrees of freedom in nuclei and their effect on electron scattering and photonuclear reactions for low and medium energy physics are discussed. Specifically, two- and three-body systems are considered, where cleanest evidence for exchange current effects exists. Furthermore, exchange contributions to the two-photon amplitude for photon scattering are studied and results for deuterium are presented.

Possible uses of the FASTBUS in medium energy physics

The FASTBUS is a high-speed data-acquisition bus currently being developed by the NIM-CAMAC Committee of the National Bureau of Standards. The major features of the FASTBUS will be reviewed and evaluated with respect to possible uses in medium-energy physics experiments.