Detector Acceptance Research Articles

Two-body photodisintegration of the deuteron from 100 to 800 MeV

Abstract The total and the differential cross sections for the D(γ,p)n reaction have been measured over the photon energy range 100-800 MeV at the 855 MeV MAMI Microtron in Mainz. Using the large acceptance detector DAPHNE in conjunction with the Glasgow tagging spectrometer, high precision results with small systematic errors were obtained. The data are presented in the form of thirty-five angular distributions at c.m. proton angles between 30°–160° in 10° intervals and at photon energies in steps of 20 MeV. Previous experimental work is reassessed in the light of the present results and comparison with some recent theoretical calculations.

Front end electronics for the STAR TPC

The Solenoidal Tracker at RHIC (STAR) is a large acceptance detector now being built to study high energy heavy ion collisions. It detects charged particles with a large time projection chamber. The 136,600 TPC pads are instrumented with waveform digitizers, implemented in custom low noise preamplifier/shaper and switched capacitor array/ADCs ICs. The system is highly integrated with all analog functions mounted on small cards that plug into the TPC. Detector mounted readout boards multiplex data from 1152 channels onto a 1.5 Gbit/sec fiber optic link to the data acquisition system.

A Large Acceptance Detector System (LADS) for studies of pion absorption

Abstract A Large Acceptance Detector System (LADS) has been designed and built at the Paul Scherrer Institute to study multiparticle final states following pion-nucleus absorption. It consists of a 28-sector cylinder of plastic scintillators of 1.6 m active length and 1.4 m diameter, two cylindrical wire chambers, and two 14-sector plastic scintillator end-caps which close each end. The nearly 4π solid angle coverage of this detector minimizes uncertainties associated with extrapolations over unmeasured regions of phase space. The design and the performance of the LADS detector are presented.

An approach to a B-spline description of experimental distributions

A method to estimate continuous distributions obtained from an experiment in the form of a linear combination of cubic B -splines is considered. An algorithm to choose the optimal number of splines, their coefficients and errors is proposed. The method can also be applied to detector resolution functions and acceptance (obtained by Monte Carlo methods) smoothing when solving the unfolding problem.

Reaction mechanisms in 12C( gamma,pp) near 200 MeV.

Inclusive $^{12}\mathrm{C}(\ensuremath{\gamma}, pp)$ cross sections have been measured with tagged photons in the range ${E}_{\ensuremath{\gamma}}=187\ensuremath{-}227$ MeV using the Saskatchewan-Alberta Large Acceptance Detector (SALAD). The large angular acceptance allowed the measurement of noncoplanar $\mathrm{pp}$ emission. The cross sections were compared to a Monte Carlo intranuclear cascade calculation. Agreement was reasonable for the shapes of the cross sections but the calculated total cross section was 3.9 times larger than the data.

Direct measurement of the branching ratio for the decay of the eta meson into two photons.

The first direct, precision measurement of the branching ratio for the decay of the \ensuremath{\eta} meson into two photons, B(\ensuremath{\eta}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})\ensuremath{\equiv}\ensuremath{\Gamma}(\ensuremath{\eta}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})/${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{tot}}$(\ensuremath{\eta}), is presented. The systematic undertainties are quite different than in previous indirect measurements. Using the SATURNE II proton beam and a liquid-deuterium target, the \ensuremath{\eta} mesons were produced in the reaction pd${\ensuremath{\rightarrow}}^{3}$He \ensuremath{\eta} at 1.5 MeV above threshold, and tagged by the detection of the recoil $^{3}\mathrm{He}$ in the magnetic spectrometer SPES2. The two decay photons were detected in two BGO electromagnetic calorimeters located at 65\ifmmode^\circ\else\textdegree\fi{} left and right of the beam axis. A lead collimator placed in front of the right calorimeter defined the detector acceptance. The analysis yielded B(\ensuremath{\eta}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})=0.3949\ifmmode\pm\else\textpm\fi{}0.0017(stat)\ifmmode\pm\else\textpm\fi{}0.0030(syst). \textcopyright{} 1995 The American Physical Society.

Total photoabsorption cross sections for 1H, 2H, and 3He from 200 to 800 MeV.

The total photoabsorption cross sections for $^{1}\mathrm{H}$, $^{2}\mathrm{H}$, and $^{3}\mathrm{He}$ have been measured for incident photon energies ranging from 200 to 800 MeV. The $^{3}\mathrm{He}$ data are the first for this nucleus. By using the large acceptance detector DAPHNE in conjunction with the tagged photon beam facility of the MAMI accelerator in Mainz, cross sections of high precision have been obtained. The results show clearly the changes in the nucleon resonances in going from $^{1}\mathrm{H}$ to $^{3}\mathrm{He}$. In particular, for the ${\mathit{D}}_{13}$ region the behavior for $^{3}\mathrm{He}$ is intermediate between that for $^{1}\mathrm{H}$, $^{2}\mathrm{H}$, and heavier nuclei. This will provide a strong constraint to the theories that are presently being developed with a view to explaining the apparent ``damping'' of higher resonances in heavy nuclei. \textcopyright{} 1996 The American Physical Society.

Nuclear transparencies for nucleons, knocked-out under various semi-inclusive conditions.

Using hadron dynamics we calculate nuclear transparencies for protons, knocked-out in high-$Q^2$, semi-inclusive reactions. Predicted transparencies are, roughly half a standard deviation above the NE18 data. The latter contain the effects of binned proton missing momenta and mass, and of finite detector acceptances. In order to test sensitivity we compare computed transparencies without restrictions and the same with maximal cuts for missing momenta and the electron energy loss. We find hardly any variation, enabling a meaningful comparison with data and predictions based on hadron dynamics. Should discrepancies persist in high-statistics data, the above may with greater confidence be attributed to exotic components in the description of the outgoing proton.

Dijet cross sections in photoproduction at HERA

Dijet production by almost real photons has been studied at HERA with the ZEUS detector. Jets have been identified using the cone algorithm. A cut on x γ OBS, the fraction of the photon energy participating in the production of the two jets of highest transverse energy, is used to define cross sections sensitive to the parton distributions in the proton and in the photon. The dependence of the dijet cross sections on pseudorapidity has been measured for x γ OBS ⩾ 0.75 and x γ OBS < 0.75. The former is sensitive to the gluon momentum density in the proton. The latter is sensitive to the ginon in the photon. The cross sections are corrected for detector acceptance and compared to leading order QCD calculations.

Comparison of energy flows in deep inelastic scattering events with and without a large rapidity gap

Energy flows in deep inelastic electron-proton scattering are investigated at a centre-of-mass energy of 269 GeV for the range Q 2 ≥ 10 GeV 2 using the ZEUS detector. A comparison is made between events with and without a large rapidity gap between the hadronic system and the proton direction. The energy flows, corrected for detector acceptance and resolution, are shown for these two classes of events in both the HERA laboratory frame and the Breit frame. From the differences in the shapes of these energy flows we conclude that QCD radiation is suppressed in the large-rapidity-gap eents compared to the events without a large rapidity gap.

Two-body photodisintegration of 3He between 200 and 800 MeV

Differential cross sections for the 3He(γ,pd) reaction at photon energies between 200 and 800 MeV at all proton c.m. angles between 35° and 145° have been measured using the tagged photon beam facility of the 855 MeV MAMI accelerator in Mainz. Reaction products were detected using the large acceptance detector DAPHNE. The results confirm the rapid decrease of forward-angle cross sections with increasing E γ whilst at backward angles, aided by the high precision of the measurement, we can see a clear enhancement in the angular distribution which is a possible signature of three-body mechanisms.

Large-solid-angle study of pion absorption on 3He.

Measurements have been made of pi+ absorption on He3 at T_pi+ = 118, 162, and 239 MeV using the Large Acceptance Detector System (LADS). The nearly 4pi solid angle coverage of this detector minimizes uncertainties associated with extrapolations over unmeasured regions of phase space. The total absorption cross section is reported. In addition, the total cross section is divided into components in which only two or all three nucleons play a significant role in the process. These are the first direct measurements of the total and three nucleon absorption cross sections.

The influence of target composition on the specific energy loss measured in transmission geometry

At low projectile velocities, stopping cross section measurements by transmission methods with high directional correlation between incoming beam and detected projectiles and with a detector acceptance appreciably smaller than 4 π, may suffer from experimental artifacts. Thickness inhomogeneities make the measured specific energy loss appear angle dependent. The influence of the target areal density may be traced to the impact parameter dependence of both, the elastic and the inelastic stopping cross section. In this contribution we deal with a mixture of gases. A “true” deviation from Bragg's rule may be due to charge changing processes. Here, we discuss an additional but only apparent violation of Bragg's rule in gas mixtures: due to impact parameter selection by the experimental geometry, target atoms with different atomic numbers may contribute differently to the measured specific energy loss. Our arguments are based on experimental results and on Monte Carlo simulations.

A versatile, software configurable multichannel STEM detector for angle-resolved imaging

A new type of STEM detector has been developed and tested. This detector consists of 30 rings which are split in quadrants (= 120 channels) and it allows further advantage to be taken of the image formation principle of STEM: the scattered electrons can be recorded separately according to their scattering angles and eight images can be acquired in parallel. Because of its electron counting capability, this detector is very well suited to analytical and quantitative applications of STEM (e.g. absolute mass determination and Z-contrast). The various channels of the detector can be combined by software in order to obtain images with the desired detector acceptance angles. The minimal time per pixel ( t/ pixel≥4 μs) is approximately as short as in the case of conventional single-channel detectors.

3He( gamma,pd) cross sections with tagged photons below the Delta resonance.

The reaction cross section for $^{3}\mathrm{He}$(\ensuremath{\gamma},pd) has been measured using the Saskatchewan-Alberta Large Acceptance Detector (SALAD) with tagged photons in the energy range from 166 to 213 MeV. The energy and angle of the proton and the deuteron were measured with SALAD while the tagger determined the photon energy. Differential cross sections have been determined for 40\ifmmode^\circ\else\textdegree\fi{}${\mathrm{\ensuremath{\theta}}}_{\mathit{p}}^{\mathrm{*}}$150\ifmmode^\circ\else\textdegree\fi{}. The results are in agreement with the Bonn and Saclay photodisintegration measurements. The most recent photodisintegration measurement performed at Bates is higher by a factor of 1.3, which is just within the combined errors of the experiments. The proton capture results differ by a factor of 1.7 from the present experiment. Comparisons are made with microscopic calculations of the cross sections.

Gamma gamma physics at relativistic heavy-ion colliders.

Relativistic heavy-ion colliders like the Brookhaven Relativistic Heavy Ion Collider or CERN Large Hadron Collider open up the possibilities for \ensuremath{\gamma}\ensuremath{\gamma} physics. This provides tests of the standard model, possible extensions and especially QCD in the resonance and the continuum regime. The model independent quantity to study these processes is the \ensuremath{\gamma}\ensuremath{\gamma} luminosity function due to the experimentally limited detector acceptance. Due to irreducible \ensuremath{\gamma}-hadron interactions, there are serious background problems at such colliders. We discuss this background due to \ensuremath{\gamma}A and especially \ensuremath{\gamma}g reactions.

About resonance signal extraction from multiparticle data: combinatorics and event mixing methods

The question of the resonance signal extraction from the invariant mass distribution of two particles is examined for the experimental situation of multiparticle events measured in a large acceptance detector. The different contributions to the distribution are calculated. Their magnitude is related to the particle pair combinatorics. The consequences for the resonance extraction methods based on event mixing are given. The situation is investigated in the framework of a simulation for relativistic heavy ion collisions. Finally, the formalism developed for one kind of resonance decaying in two different particles is generalized to other cases.

Study of polarization of laser radiation scattered 90 deg

A qualitative experimental study was undertaken of the effects of spherical particle scattering on the polarization of linearly polarized He-Ne laser beams. Four concentrations of particles (either 0.22- or 0.494-^im diam) were suspended in filtered, distilled water to serve as the scattering centers. Data representing the effects of volumetric particle concentration, detector acceptance angle, cylindrical scattering volume container diameter, and detector depth are investigated. In general, large diameter particles and high particle concentrations depolarize the incident beam the most. Also, increasing the length of the path traversed by the scattered beam greatly increases the depolarization of the beam.

Coherent pions in charge-exchange reactions

Data are presented on the 12 C( 3 He, tπ +) reaction at 2 GeV bombarding energy. In coincidence with forward scattered tritons, pions are momentum-analysed in a large acceptance detector. For events where the target is left in its g.s. or low-lying states, the angular correlation between the momentum transfer vector and the momentum of the pion is sharply peaked at small relative angles.

DESTRUCTION OF PEAK SWITCHING IN STRONG-FIELD AUTOIONIZATION PHOTOELECTRON SPECTRA

In this paper, the effect of the spatial inhomogeneity of the laser field and the size of detector acceptance angle or aperture on strong-field autoionization photoelectron spectra is investigated. It is shown that the photoelectron spectra are drastically affected by the above factors , for small detector acceptance angle or aperture size, peak switching appears in the photoelectron spectra, but for large detector acceptance angle or aperture size, peak switching is destroyed completely.