Large Acceptance Spectrometer Research Articles

Coulomb dissociation of 8B: determination of the E2 component

The 7Be(p, γ) 8B reaction has been studied at GSI via the Coulomb Dissociation of 8B at 254 A MeV, using the large acceptance spectrometer KAOS to detect the outgoing fragments. We have studied experimentally the E2 contribution to the Coulomb Dissociation by measuring the angular correlations of the breakup fragments. The resulting astrophysical S 17 factor is compared to the results of other direct and indirect measurements.

The CEBAF large acceptance spectrometer (CLAS)

Abstract The CEBAF large acceptance spectrometer (CLAS) is used to study photo- and electro-induced nuclear and hadronic reactions by providing efficient detection of neutral and charged particles over a good fraction of the full solid angle. A collaboration of about 30 institutions has designed, assembled, and commissioned CLAS in Hall B at the Thomas Jefferson National Accelerator Facility. The CLAS detector is based on a novel six-coil toroidal magnet which provides a largely azimuthal field distribution. Trajectory reconstruction using drift chambers results in a momentum resolution of 0.5% at forward angles. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 10 34 nucleon cm −2 s −1 . These capabilities are being used in a broad experimental program to study the structure and interactions of mesons, nucleons, and nuclei using polarized and unpolarized electron and photon beams and targets. This paper is a comprehensive and general description of the design, construction and performance of CLAS.

Coupling a CLOVER detector array with the PRISMA magnetic spectrometer

Following the commissioning of the PRISMA large-acceptance spectrometer, installed at the Laboratori Nazionali di Legnaro (LNL), an international nuclear-structure collaboration has started to develop a large $\gamma$ -ray setup to be installed in the target position of the spectrometer. The array is based on the EUROBALL composite CLOVER detectors. In this contribution the CLOVER detector array is described and its expected performance figures discussed. This new setup, by using the high-intensity heavy-ion beams provided by the LNL ALPI linac, will push the study of nuclear structure towards moderately neutron-rich nuclei by means of quasi-elastic and deep inelastic reactions.

PHOTOREACTIONS ON 3He AND 4He UP TO 1.6 GEV AT JEFFERSON LAB

We have measured photoreactions on 3 He and 4 He in Hall B at Jefferson Lab, using real photons from the Photon Tagger and the CEBAF Large-Acceptance Spectrometer (CLAS). We obtained data over the full range of the Tagger — 0.33 to 1.56 GeV with an incident electron-beam energy of 1.645 GeV. Tagged, circularly polarized photons, produced by the 70% longitudinally polarized electrons, were incident on 1.2-g/cm2 liquid-helium targets positioned at the center of the CLAS. We were able to collect data at rates exceeding 3 kHz, and succeeded in collecting approximately 1.2 billion events for 3 He and 0.8 billion for 4 He . Over 5 Tb of data were obtained. The data show very good stability throughout the experimental run. Preliminary results from the analysis of several reaction channels are given here.

A polarized target for the CLAS detector

Abstract We describe the design, construction, and performance of a polarized solid target for use in electron scattering experiments with the CEBAF Large Acceptance Spectrometer. Protons and deuterons are continuously polarized by microwave-induced spin–flip transitions at 1 K and 5 T . The target operated successfully during two cycles in 1998 and 2000, providing proton and deuteron polarizations as high as 96% and 46%, respectively. The unique features of the target which permit its use inside a 4π spectrometer are stressed. Comparison is made between the target polarization measured by the traditional method of NMR and by electron elastic scattering.

On the determination of polarization observables in proton-induced reactions using large-acceptance magnetic spectrometers

For proton-induced reactions, a formalism is presented to determine polarization observables using a focal-plane polarimeter in combination with a large-acceptance spectrometer, where also the effect of the scattering in the non-dispersive plane of the spectrometer is taken into account. The inclusive proton-carbon analyzing power needed for the determination of spin observables was studied over a wide angular range and a new parameterization for this quantity was deduced.

Numerical computation of arbitrary order transfer maps and reconstructive correction of aberrations in the large acceptance spectrometer MAGNEX

Abstract The large angular (∼50 msr) and momentum (∼20%) acceptance spectrometer MAGNEX is under construction at the South National Laboratories INFN. In the spectrometer, positions of ions in two planes near the focal plane and their vertical positions near the target are measured. The energy resolution of about 1000 is achieved due to the use of the reconstruction of trajectories and reconstructive correction of aberrations. Main features of the spectrometer ion optics are considered. A numerical method of calculation of an arbitrary order transfer map is proposed. In this method, a transfer map is calculated using, as input, initial and final coordinates of a set of rays in an ion-optical system. The rays start at the nods of a regular multi-dimensional mesh in the particle phase space. Rays of the set are chosen automatically according to the order and dimension of the map to be calculated. Final coordinates of the rays are calculated with a regular numerical integration. The proposed is, in fact, a general (ray tracing based) method of calculation of a transfer map, of any order and dimension, for an arbitrary ion-optical system. The method has been used for numerical simulations of the reconstructive correction of aberrations in the MAGNEX spectrometer. Simulation results are considered. A C++ class library has been developed to realize the proposed transfer map calculation method. Elementary operations with vectors and maps, both being C++ objects, are realized as C++ operator functions. The map order is defined by a user at the moment of initialization of the corresponding map object. Its maximum value is limited only by an available computer memory. Computational aspects of the method are discussed in brief.

A low-pressure gas detector for heavy-ion tracking and particle identification

A low-pressure gas tracker for heavy ions is described. It is based on a drift chamber with four series of multiplying wires for energy loss measurement and underlying strips for position and angle determination. Results of tests with an α-source and with low-energy heavy-ion beams are presented. They indicate the suitability of such a detector in a wide range of experiments with heavy ions where a low energy threshold, a large solid angle, together with a precise measurement of ion trajectories and identification is needed. In particular, the application as a prototype of the focal plane detector for the large-acceptance spectrometer MAGNEX is discussed.

Intermediate energy nuclear physics at MIT-Bates

The MIT-Bates Linear Accelerator Center is a university-based laboratory carrying out frontier research in nuclear physics. The research program is focussed on the flavor structure, charge distribution, shape, size and polarizability of the nucleon; the spin and electromagnetic structure of light nuclei; and the origin of the elements. The Bates research program has three central thrusts: the SAMPLE experiments to probe the flavor structure of the proton using parity-violating electron scattering at back angles; the OOPS (Out-Of-plane Spectrometer System) program which uses out-of-plane detection to probe nucleon and few-body nuclear structure; and the BLAST (Bates Large Acceptance Spectrometer Toroid) program which will use a new spectrometer under construction to measure electron scattering from internal gas targets in the South Hall Ring.

The BLAST project at MIT-Bates

The Bates Large Acceptance Spectrometer Toroid (BLAST) is a detector designed to study the spin-dependent electromagnetic response of few-body nuclei at momentum transfers up to 1 (GeV/c)2 at the MIT/Bates Linear Accelerator Center's South Hall Ring (SHR). The BLAST detector consists of an eight-sector copper coil array producing a toroidal magnetic field, instrumented with two opposing wedge-shaped sectors of wire chambers, scintillation detectors, Cerenkov counters, neutron detectors, a lead-glass forward calorimeter, and recoil detectors. A status of the project is presented as well as highlights of the scientific program.

Design study of the superconducting magnet for a large acceptance spectrometer

New generation of experiments in Nuclear Physics is requiring large spectrometers with typical width and height at entrance /spl sim/0.36 /spl times/ 0.32 m and /spl sim/1.2 /spl times/ 0.6 m at exit and field integral /spl sim/4.8 Tm. Very low fringe field is requested, especially upstream from the beam. The innovative design of the superconducting magnet for such spectrometers has been extensively studied on the base of active shielding method. The designed magnet is the combination of several tilted and graded racetrack-type trapezoidal windings for creating both main and shielding fields. This requires high mechanical rigidity by use of aluminum containers where windings will be encased. Indirect cooling with thermosiphon is suggested. The internal protection method is discussed. In the paper the details of the magnet design, magnetic field shape, cooling and protection are presented.

The [formula omitted] program with CLAS at Jefferson Laboratory

The study of the baryon spectrum is a fundamental part of the scientific program in Hall B at Jefferson Laboratory. The so called N* program indeed concerns the measurement of the electromagnetic production of exclusive baryon excited states. CLAS, the CEBAF Large Acceptance Spectrometer, is explicitly designed for conducting a broad experimental program in hadronic physics, using the continuous electron beam provided by the laboratory. Some selected issues in the N* CLAS experimental program will be outlined, then the beam and detector performance will be discussed and finally some relevant new experimental results will be reported.

Corrected Article: Exclusive electroproduction of φ mesons at 4.2 GeV [Phys. Rev. C63, 065205 (2001)

We studied the exclusive reaction $e\stackrel{\ensuremath{\rightarrow}}{p}{e}^{\ensuremath{'}}{p}^{\ensuremath{'}}\ensuremath{\varphi}$ using the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\varphi}}{K}^{+}{K}^{\ensuremath{-}}$ decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in ${Q}^{2}$ from 0.7 to 2.2 ${\mathrm{GeV}}^{2},$ and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of $\ensuremath{\varphi}$ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time $c\ensuremath{\Delta}\ensuremath{\tau}$ below 2 fm. At $〈c\ensuremath{\Delta}\ensuremath{\tau}〉=0.6$ fm, we measure ${b}_{\ensuremath{\varphi}}=2.27\ifmmode\pm\else\textpm\fi{}0.42$ ${\mathrm{GeV}}^{\ensuremath{-}2}.$ The cross section dependence on W as ${W}^{0.2\ifmmode\pm\else\textpm\fi{}0.1}$ at ${Q}^{2}=1.3$ ${\mathrm{GeV}}^{2}$ was determined by comparison with $\ensuremath{\varphi}$ production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction.

Low-energy measurement of the 7Be(p,gamma)8B cross section.

We have measured the cross section of the 7Be(p,gamma)8B reaction for E(c.m.) = 185.8, 134.7, and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta+ and alpha particles from 8B and 8Be* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5+/-2.4 eV b and a weighted mean value of 18.8+/-1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies.

The CLAS forward electromagnetic calorimeter

The CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab utilizes six iron-free superconducting coils to provide an approximately toroidal magnetic field. The six sectors are instrumented individually to form six independent spectrometers. The forward region (8°< θ<45°) of each sector is equipped with a lead–scintillator electromagnetic sampling calorimeter (EC), 16 radiation lengths thick, using a novel triangular geometry with stereo readout. With its good energy and position resolution, the EC is used to provide the primary electron trigger for CLAS. It is also used to reject pions, reconstruct π° and η decays and detect neutrons. This paper treats the design, construction and performance of the calorimeter.

Overview of the status and strangeness capabilities of STAR

STAR is a large-acceptance spectrometer capable of precisionmeasurements of a wide variety of strange particles. We discuss the STARdetector, its configuration during the first two years of RHIC operation,and its initial performance for Au + Au collisions. The expectedperformance for strangeness physics and initial data on strange particlereconstruction in Au + Au collisions are presented.

JINR participation in COMPASS project

A new fixed target experiment to study hadron structure and hadron spectroscopy has been approved at CERN as the CERN experiment NA58—COMPASS. An appropriate two-stage large acceptance spectrometer, with particle identification and calorimetry in both stages, using either polarized muon (100–200 GeV) or hadron (up to 300 GeV) beams and polarized as well as unpolarized targets is being constructed at CERN. The beams for the COMPASS were provided in the years 1999–2000 and physics measurements will start in the year 2001.

Status of the BLAST project

The Bates Large Acceptance Spectrometer Toroid (BLAST) is a detector designed to study the spin-dependent electromagnetic response of few-body nuclei at momentum transfers up to 1 (GeV/c)2 at the MIT/Bates Linear Accelerator Center's South Hall Ring (SHR). The BLAST detector consists of an eight-sector copper coil array producing a toroidal magnetic field, instrumented with two opposing wedge-shaped sectors of wire chambers, scintillation detectors, Cerenkov counters, neutron detectors, a lead-glass fo ward calorimeter, and recoil detectors. Presently, BLAST is under construction and it is on schedule to be done in summer 2001. A status of the project is presented as well as highlights of the scientific program.

The CLAS drift chamber system

Experimental Hall B at Jefferson Laboratory houses the CEBAF Large Acceptance Spectrometer, the magnetic field of which is produced by a superconducting toroid. The six coils of this toroid divide the detector azimuthally into six sectors, each of which contains three large multi-layer drift chambers for tracking charged particles produced from a fixed target on the toroidal axis. Within the 18 drift chambers are a total of 35,148 individually instrumented hexagonal drift cells. The novel geometry of these chambers provides for good tracking resolution and efficiency, along with large acceptance. The design and construction challenges posed by these large-scale detectors are described, and detailed results are presented from in-beam measurements.

The MIT-Bates out-of-plane and polarized internal target programs

The OOPS and BLAST projects are the main thrusts to the research program at MIT-Bates for the next few years. The OOPS system is a unique facility of multiple magnetic spectrometers specifically designed for accurate extraction of the five response functions accessible through the (e,e′p) reaction with polarized beam. Results from the initial round of experiments are presented as well as a brief out-look into the upcoming measurements. The Bates Large Acceptance Spectrometer Toroid (BLAST) is a detector designed to study in a comprehensive and precise way the spin dependent electromagnetic response of few-body nuclei. At present BLAST is under construction and a brief status is presented as well as projected results for some of the key experiments.