Energy Resolution Of Calorimeters Research Articles

Correlated fluctuations between luminescence and ionization in liquid xenon

The ionization of liquefied noble gases by radiation is known to be accompanied by fluctuations much larger than predicted by Poisson statistics. We have studied the fluctuations of both scintillation and ionization in liquid xenon and have measured, for the first time, a strong anti-correlation between the two at a microscopic level, with coefficient -0.80 < {rho}{sub ep} < -0.60. This provides direct experimental evidence that electron-ion recombination is partially responsible for the anomalously large fluctuations and at the same time allows substantial improvement of calorimetric energy resolution.

Crystal conditioning for high-energy physics detectors

In homogeneous high-resolution calorimetry for particle physics, scintillating crystals can now be considered as a mature technique. In the past decades, several large high-energy experiments have included crystal calorimeters from which a considerable harvest of physics results could be made. To extract the ultimate precision from such calorimeters, great care must be taken in the crystal conditioning, i.e. machining and wrapping or coating. These operations have a strong influence on some key crystal properties for the calorimeter energy resolution, such as light yield and light collection uniformity. In this note, some aspects of machining and of the techniques for uniformizing light collection will be discussed in the light of a recent experiment: L3 at LEP collider, using bismuth germanate crystals and an experiment in construction: CMS for LHC collider, using lead tungstate. To illustrate these techniques, results obtained on medium-scale crystal productions will be shown.

Performance of the NuTeV Fe-scintillator sampling calorimeter and implications for thin calorimeters

NuTeV is a neutrino-nucleon deep inelastic scattering experiment at Fermilab. The NuTeV detector is a traditional heavy target neutrino detector which consists of an iron/liquid scintillator sampling calorimeter followed by a muon spectrometer. The calorimeter response to hadrons, muons and electrons has been measured in an in situ calibration beam over the energy range from 4.5 to 190 GeV. The small non-linearity of the response to hadrons is compared to the expectation from the measured ratio of responses between electrons and hadrons combined with the energy dependence of the fractional electromagnetic energy deposition in the form of neutral pions in hadronic showers f π 0 ( E π ). The predictions use f π 0 ( E π ) from the Monte Carlo simulations by GHEISHA, GFLUKA and GCALOR and also from the parameterizations of Wigmans and Groom. In addition, a study based on the NuTeV hadron calibration data of the effectiveness of a thin calorimeter is presented. The results of this study have important consequences for the energy resolution of calorimeters used in other applications; for example, measuring the cosmic ray flux in space or with balloon-based experiments.

Beam energy measurement at LEP2 using Møller scattering

A detailed study has been made of the feasibility of Møller scattering as a method for continuous monitoring of the LEP beam energy at high energies where the currently used resonant depolarisation technique may be unusable. Two methods, based on Møller scattering, to measure the energy with different dominant systematic errors are discussed. Monte Carlo studies of the effect on the energy measurement of radiative corrections, target binding effects, beam parameters and calorimetric energy resolution have been made. It is shown how the beam parameters necessary to control the systematic error may be deduced from the Møller scattering events, and the crucial target-detector distance monitored using ep scattering events. The beam energy precision is expected to be a few MeV at 90 GeV. The reduction of the systematic error on the W-mass measurement can be appreciable, and for a fixed total error on the W-mass may provide a considerable economy in running time at LEP2. The method is also applicable to precise energy measurement at high-energy electron linear colliders.

Effect of nonuniformity on the energy resolution of EM sampling calorimeters

The response of a sampling tile electromagnetic calorimeter was simulated for incident electrons in the 10–500 GeV energy range. The influence of tile to tile nonuniformity on the a and b coefficients of the calorimeter energy resolution parametrisation formula was investigated in detail. An energy resolution deterioration due to nonuniformity was observed, but it was shown that by calibrating the towers individually one can reduce this undesirable effect to reasonable limits. An explicit a and b coefficients dependence on σ non, the tile response nonuniformity standard deviation, was found. Our previous results on this dependence obtained by analytical methods using the electromagnetic shower mean profile universal parametrisation and the present results obtained by Monte Carlo simulation are compared and found to be in good agreement.

Searches for new particles using cone and cluster jet algorithms: a comparative study

We discuss the reconstruction of the hadronic decays of heavy particles using jet algorithms. The ability to reconstruct the mass of the decaying particles is compared between a traditional cone-type algorithm and a recently proposed cluster-type algorithm. The specific examples considered are the semileptonic decays of a heavy Higgs boson at $$\sqrt s = 16$$ TeV, and of top quark-antiquark pairs at $$\sqrt s = 1.8$$ TeV. We find that the cluster algorithm offers considerable advantages in the former case, and a slight advantage in the latter. We briefly discuss the effects of calorimeter energy resolution, and show that a typical resolution dilutes these advantages, but does not remove them entirely.

Modeling and scanning of lightguides for Pb/SCIFI calorimeters

Calorimeters containing embedded arrays of scintillating fibers often require uniform-acceptance lightguides to gather, mix and transport light from the end face of the module to a photo-sensitive detector. To optimize such devices, we have built a flexible lightguide scanning station which imitates the distribution of light coming from an array of scintillating fibers. This system has been used to map the photocathode response of photomultiplier tubes, the transmission uniformity of lightguides and the performance of detector-lightguide combinations. Additionally, we have developed a ray-trace modeling program which accurately reproduces the experimental results. These tools are described in the context of our own application-specific examples, while their general nature makes them attractive in other situations where lightguides are involved. Finally, the effect of lightguide non-uniformity is evaluated in order to estimate the systematic contribution to the calorimeter energy resolution description.

Dependence of hadron calorimeter energy resolution on the properties of a wavelength shifter

An analytical expression which describes the dependence of a hadron calorimeter energy resolution on the main properties of a wavelength shifter is presented. The above mentioned properties are the light attenuation, the length and the degree of light reflection at the free end of the wavelength shifter. The expression obtained is compared with experimental data.

Improving energy resolution of calorimeters using a covariance matrix approach

Abstract A covariance matric technique is used to improve energy resolution of electromagnetic and hadronic showers produced in a uranium/liquid argon calorimeter. An event of unknown energy is compared with parametrized energy depositions through a χ 2 minimization procedure, thereby providing an estimate of the true energy of the shower. The method is effective for calorimeters that have large amounts of uninstrumented material.

The response of an aluminum-scintillator calorimeter to electrons near the critical energy from 50 to 150 MeV and comparisons with the EGS4 program predictions

We measured electron shower transport through a finely granulated calorimeter composed of alternating layers of aluminum and plastic scintillator for electron energies of 53, 108 and 144 MeV. These data were in the transition region near to the critical energies for both aluminum and carbon. Previous measurements in this region suggested deviations from the predicted calorimeter energy resolution; however, our data were in agreement with resolutions calculated using the EGS4 computer program. We made detailed measurements of the penetration depth of electrons and their electromagnetic showers into the calorimeter, as well as the size of gaps where the energy was transported by neutral particles. These measurements were also found to be in general agreement with the EGS4 predictions. However, there was one significant discrepancy, the data showed significantly deeper shower penetration into the calorimeter than predicted by the program.

On the energy resolution of electromagnetic sampling calorimeters

We investigate the energy resolution of electromagnetic sampling calorimeters using the Monte Carlo program EGS. We study how the energy resolution depends on the shower energy, on the thickness of the absorber and detector layers, and on the charge number and density of the materials used to construct the calorimeter. Finally we compare our Monte Carlo results with experimental data.

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.

On the energy resolution of uranium and other hadron calorimeters

The various components that contribute to the signal from a hadron calorimeter, and the factors that affect the energy resolution with which hadrons can be detected, are examined in detail. The role of the electromagnetic to hadronic signal ratio e h is crucial in this respect. Its value is determined by the Z of the absorber material, the thickness of the passive and active layers, the signal integration time of the detector, and the properties of the readout material, in particular the free proton content and the saturation or recombination properties for few-MeV proton detection. Readout media that contain free protons offer the possibility to tune the e h ratio to the desired value (1.0) through the sampling fraction. Signal equalization ( e h = 1.0) does not seem to be a property unique to 238U, but can also be achieved for lead and even iron calorimeters. The calculations show, on the other hand, that e h values are larger than 1.0 for any calorimeter using liquid-argon readout. The intrinsic energy resolution for hadron detection is largely dominated by fluctuations in the binding energy losses that occur in the nuclear reactions. Efficient neutron detection can considerably reduce these effects provided that energy loss through recoil protons dominates. Calorimeters using 238U, Pb or Fe absorbers, and plastic scintillator, liquid-argon, silicon or TMP readout were investigated. Experimental results on e h values and energy resolution, which are often considered confusing, are nicely reproduced and explained.

Monte Carlo study of the light yield, uniformity and energy resolution of electromagnetic calorimeters with a fiber readout system

We perform a Monte Carlo simulation in order to evaluate the light yield and uniformity of the response of an electromagnetic calorimeter with a fiber readout system. We show how these quantities depend on the fiber density, the attenuation length and the reflectivity of the scintillator plate. Finally, we calculate the effect of the nonuniform response on the energy resolution.