A combined photon-hadron hodoscope calorimeter

The energy and spatial resolution and other characteristics of a combined detector permitting simultaneous detection of a large number of photons and hadrons has been studied in a 200 GeV/c hadron beam at the CERN SPS. The detector consists of the GAMS-4000 spectrometer (4096 lead-glass cells) and a modular hadron calorimeter MHC-200 located behind it (240 total-absorption sandwich counters). A new method for adding the signals from the two calorimeters, which takes into account the difference in the development of hadron showers in photon and hadron calorimeters, has been developed. It permits substantial improvement of the energy resolution of the combined detector. The hadron coordinates are defined with a precision of several millimeters and the energy resolution is typical for steel-scintillator sandwiches with a wavelength-shifter readout. The effect of the gap between the photon and the hadron calorimeters has also been studied.     

The e/h ratio and energy resolution of hadron calorimeters

The e/h ratio and the energy resolution for a variety of experimental test setups are compared with Monte Carlo calculations, using the GHEISHA/EGS hadronic and electromagnetic cascade code. The compensation mechanism in uranium calorimeters is discussed. The dependence of the e/h ratio and the energy resolution on the absorber and detector material, on the sampling thickness and the thickness of the detector material is studied in detail. Solutions for uranium calorimeters with equal response to electrons and hadrons are investigated for different readout techniques.     

快速闪烁晶体在未来高能物理实验中的应用

简要综述了快速闪烁晶体在未来高能物理实验中的应用和目前研究进展.在未来高亮度强子对撞机（HL LHC）上通过采用高亮度、快速和高抗辐照强度的LYSO晶体为CMS的量能器升级,可以建成具有良好E/γ能量分辨率的稳定的精密电磁量能器.通过读取PbF2,PbFCl和BSO晶体中的切伦科夫光和闪烁光,可以为未来的轻子对撞机建立具有良好的喷注能量分辨率的均匀强子量能器.有亚纳秒衰变时间的BaF2晶体将为未来的高能物理强度前沿实验建立在速率及时间分辨率提高超过10倍的晶体量热器.对新型快闪烁晶体如PbFCl,YAP:Yb,ZnO:Ga和CuI的研究可能为今后高能物理实验发挥重要作用.     

Measurement of the resolution of a combined hodoscope calorimeter at 18 GeV and 38 GeV

The energy and spatial resolution of a combined detector consisting of the Cherenkov photon calorimeter GAMS-2000 and the modular hadron calorimeter MHC-100 has been studied at 18.5 and 38 GeV incident pion energies at the IHEP accelerator. The energy resolution of the combined setup is substantially improved by applying a correction based on the analysis of the lateral development of hadron showers in GAMS and MHC. It is shown that the parameters of the correction depend only weakly on the hadron energy. The influence of the gap between both photon and hadron calorimeters on the combined detector characteristics is of less importance with increasing energy.     

Test of a prototype of the ZEUS backing calorimeter

We have studied the performance of a high resolution uranium-scintillator calorimeter followed by a much coarser backing calorimeter, made out of iron plates interleaved with planes of limited streamer tubes. The test results, obtained at the CERN-SPS hadron beam, show that the backing calorimeter can be used either to veto events with significant energy leakage from the uranium calorimeter or to correct for the energy. In both cases the energy resolution of the combined calorimeters improves significantly compared to the uranium calorimeter alone.     

Performance of a BGO calorimeter with photodiode readout and with photomultiplier readout at energies up to 10 GeV

Bismuth germanate (BGO) calorimeter arrays, consisting of up to 12 elements of 30 × 30 × 200 mm³ have been tested at the CERN PS with pions and electrons of up to 10 GeV/c momentum, and at SIN with pions, electrons and protons up to 450 MeV/c. Both photomultiplier (PM) and photodiode (PD) readouts were used. Accurate calibration in the 100 MeV energy range was achieved with stopping protons, stopping pions and minimum ionizing pions. With 212 MeV electrons and PM readout, a time resolution of the BGO signal of 640 ps fwhm has been measured. The energy resolution for electrons above 1 GeV (PD readout) was found to be roughly constant at σ/E ～ 1%. This is consistent with a negligible intrinsic resolution for BGO at these energies, after taking into account shower leakage and PD noise. For electrons of 92 and 200 MeV, we obtained (PM readout) energy resolutions close to the theoretical limit given by photon statistics and shower leakage. The electron/hadron separation was better than 1:500 over the energy range of 0.5 to 10 GeV, and improved to better than 1:1000 after a simple pattern cut. The energy deposition of the e.m. showers, both laterally and longitudinally (rear leakage), was found to be in agreement at the 0.1% level with Monte Carlo calculations using the SLAC-EGS program.     

Experimental validation of Direct Simulation Monte Carlo (DSMC) model of vapour jets from high temperature sources

A 3-D Direct Simulation Monte Carlo (DSMC) code has been developed to study the vapour characteristics of atomic species. This model needs to be verified with experimental results. Experiments have been conducted with free jet of copper using electron beam source and the flux distribution data have been obtained under different experimental conditions. For better statistics, the Direct Simulation Monte Carlo (DSMC) code was parallelised to run on parallel system. The experimental results from circular and a slit source (Kn varies from 0.47 to 0.083) have been compared with Direct Simulation Monte Carlo (DSMC) results. The results have shown excellent agreement. From the trend of the flux distribution curves, it is clear that with lower Kn, more uniform coating can be expected.     

Monte Carlo Simulation of Massive Absorbers for Cryogenic Calorimeters

There is a growing interest in cryogenic calorimeters with macroscopic absorbers for applications such as dark matter direct detection and rare event search experiments. The physics of energy transport in calorimeters with absorber masses exceeding several grams is made complex by the anisotropic nature of the absorber crystals as well as the changing mean free paths as phonons decay to progressively lower energies. We present a Monte Carlo model capable of simulating anisotropic phonon transport in cryogenic crystals. We have initiated the validation process and discuss the level of agreement between our simulation and experimental results reported in the literature, focusing on heat pulse propagation in germanium. The simulation framework is implemented using Geant4, a toolkit originally developed for high-energy physics Monte Carlo simulations. Geant4 has also been used for nuclear and accelerator physics, and applications in medical and space sciences. We believe that our current work may open up new avenues for applications in material science and condensed matter physics.     

Effects of light guides and optical filters for a high density lead glass counter

Effects of various light guides on energy resolution, position dependence of the output pulse and the hadron suppression factor were studied for a high density lead glass counter with particles of energies between 1 GeV and 16 GeV. The best hadron suppression factor was obtained for a configuration with a plastic light guide and a short wave cutoff filter at little expense to energy resolution. The energy resolution is worse at high energy and is dependent on the hit position of an incident particle for a BK7 light guide.     

Pion muon identification in the ALEPH detector using the discriminant analysis

This paper illustrates the application of Discriminant Analysis to the separation between π's and μ's through the energy measurement and tracking capability of a hadron calorimeter followed by a system of chambers. For data taken in a test run with π and μ beams of 5–10–20 GeV, Discriminant Analysis provides an identification level of about 99.5%, very close to the physical limit corresponding to sail-through pions. The extension of the method to the case of the whole ALEPH detector and Z⁰ events is also discussed, with the aid of a Monte Carlo program.     

Hadron cascades induced by electron and photon beams in the GeV energy range

We consider the calculation of high energy hadron cascades induced by electron and photon beams in the GeV energy range. The most important source of high energy hadrons is the hadronic interaction of photons from the primary electron-photon shower. The hadronic interaction of high energy photons is described by the vector meson dominance model and by a Monte Carlo version of the dual multistring fragmentation model. The results of the calculation are compared to experimental data on hadron production in photon-proton collisions and on the hadron production by electron beams on targets. The electron beam induced hadron cascade is calculated in extended materials.     

Electron-pion separation in a highly segmented electromagnetic calorimeter designed for the ALEPH experiment

In this paper, we will emphasize the advantage we can take of highly segmented electromagnetic calorimeters in both transverse and longitudinal directions. Such calorimeters lead particularly to powerful methods of hadron rejection and electron identification.     

Application of position-sensitive semiconductor detectors in a magnetic beta-spectrometer

The possibility to use continuous position-sensitive semiconductor detectors for a magnetic beta-spectrometer of the π√2 type is shown. The momentum resolution of the spectrometer for the electron energy region of 300–1000 keV is Δp/p = 0.2–0.3%. Monte Carlo calculations of electron multiple scattering in silicon are made and its influence on position resolution is shown.     

An experimental study of the contribution of nuclear fission to the signal of uranium hadron calorimeters

We determined the number of fissions that occur in the development of a hadron shower in a ²³⁸U calorimeter, using a method based on the analysis of induced radioactivity. Measurements were done at 300 GeV (π⁻, and at 591 MeV (protons). The number of fissions turns out to be much smaller (∼ 10 fissions per GeV) than usually assumed, and is very sensitive to the calorimeter configuration. For example, in massive ²³⁸U the number of neutron-induced fissions is 25% larger than in a fine-sampling uranium/scintillator device. The results for calorimeters with a high-Z readout are similar to the massive U case. A significant fraction (10–15%) of the fissions are caused by fast charged particles rather than by slow neutrons. We also determined the total neutron production in the proton beam. It turns out that less than 25% of the neutrons produced in the shower development cause fission. The insertion of low-Z readout layers decisively determines how fast and by which mechanisms the neutrons lose their kinetic energy. The neutron flux in lead is about 40% of that in uranium, but the neutrons are on an average faster. We measured that 4.1 ± 0.4 fisions per GeV are on an average induced in the shower development of an incoming 300 GeV π. An attempt is made to explain these data.The consequences for calorimetric measurements of the hadron energy are discussed.     

A background rejection efficiency calculation for a proposed gaseous xenon TPC in a double beta decay experiment

A detailed calculation of the double beta (ββ) decay distribution and probability are presented, together with the results of a Monte Carlo simulation. The expected background rejection efficiency and achievable neutrinoless ββ decay half-life for a proposed high pressure (5–10 atm) gaseous xenon time projection chamber are calculated. The half-life is comparable to or longer than the present limit (∼ 10²³yr). It is found that ∼ 4π sr active shielding with NaI scintillator is effective in rejecting e^-e⁺ events when the energy resolution is 2% or better at 2.5 MeV. Monte Carlo calculations of electron tracks from neutrinoless ββ decay events show that a magnetic field can be used to distinguish ββ decay events from e^-e⁺ events when the energy resolution is ≥ 2%.     

Monte Carlo investigations of aspects of liquid argon calorimeters

Using the EGS3 Monte Carlo program we have examined the response of liquid argon sampling calorimeters for different absorber materials. In particular, the response to electrons (compared to muons) has been studied as a function of the width of the argon gap. Effects due to cladding of absorber plates have also been investigated.     

Solid Phase of Krypton on the Exterior of Individual Single-Walled Carbon Nanotubes

We have computed the adsorption of Krypton in a closed single-walled carbon nanotube using the method of Grand Canonical Monte Carlo. Our results indicate evidence of an incommensurate solid formed at high pressure and low temperature (T<85 K), before the formation of a second layer. The solid melts above that temperature. Our simulations are in good agreement with novel experimental results for adsorption in individual carbon nanotubes.     

Monte Carlo modeling of optical coherence tomography imaging through turbid media

We combine a Monte Carlo technique with Mie theory to develop a method for simulating optical coherence tomography (OCT) imaging through homogeneous turbid media. In our model the propagating light is represented by a plane wavelet; its line propagation direction and path length in the turbid medium are determined by the Monte Carlo technique, and the process of scattering by small particles is computed according to Mie theory. Incorporated into the model is the numerical phase function obtained with Mie theory. The effect of phase function on simulation is also illustrated. Based on this improved Monte Carlo technique, OCT imaging is directly simulated and phase information is recorded. Speckles, resolution, and coherence gating are discussed. The simulation results show that axial and transversal resolutions decrease as probing depth increases. Adapting a light source with a low coherence improves the resolution. The selection of an appropriate coherence length involves a trade-off between intensity and resolution.     

Pulse shape simulation for drift chambers with long drift paths

A detailed Monte Carlo program for the simulation of drift chamber pulse shapes is described. It has been applied to the case of a jet chamber with drift paths up to 24 cm. Results on pulse shapes and corresponding spatial and double hit resolution are discussed and compared to recent measurements of the OPAL central detector jet chamber full size prototype and to measurements of a small 20-wire prototype, which was designed to study the pulse shapes generated by tracks in a magnetic field. Simulated pulse shapes and spatial resolutions agree well with the experimental data. Clustering, saturation and wire crosstalk are shown to be necessary ingredients in the simulation. A deterioration in resolution due to the influence of crosstalk signals is correctly reproduced, as well as the cancellation of this effect by a hardwired first and second neighbour crosstalk compensation. The simulation correctly describes the asymmetry in spatial resolution observed for tracks with positive or negative inclination against the wire plane when a magnetic field is present. The effect of saturation on double hit resolution is found to be small. The magnetic field is predicted to improve the double hit resolution.     

Adaptive mesh refinement applied to the scalar transported PDF equation in a turbulent jet

This paper describes a novel solution method for the transported probability density function (PDF) equation for scalars (compositions). In contrast to conventional solution methods based on the Monte Carlo approach, we use a finite‐volume method combined with adaptive mesh refinement (AMR) applied in both physical and compositional space. The obvious advantage of this over a uniform grid is that fine meshes are only used where the solution requires high resolution. The efficiency of the method is demonstrated by a number of tests involving a turbulent jet flow with up to two scalars (both reacting and non‐reacting). We find that the AMR calculation can be at a fraction of the computer cost of a uniform grid calculation with the same accuracy. Copyright © 2010 John Wiley & Sons, Ltd.