Accurate Energy Measurements Research Articles

Enhancement of hadron–electron discrimination in calorimeters by detection of the neutron component

In many physics experiments where calorimeters are employed, the requirement of an accurate energy measurement is accompanied by the requirement of very high hadron–electron discrimination power. Normally the latter requirement is achieved by designing a high-granularity detector with sufficient depth so that the showers can fully develop. This method has many drawbacks ranging from the high number of electronic channels to the high mass of the detector itself. Some of these drawbacks may in fact severely limit the deployment of such a detector in many experiments, most notably in space-based ones. Another method, proposed by our group and currently under investigation, relies on the use of scintillation detectors which are sensitive to the neutron component of the hadron showers. Here a review of the current status will be presented starting with the simulations performed both with GEANT4 and FLUKA. A small prototype detector has been built and has been tested in a high-energy pion/electron beam behind a “shallow” calorimeter. Results are encouraging and indicate that it is possible to enhance the discrimination power of an existing calorimeter by the addition of a small-mass neutron detector, thus paving the way for better performing astroparticle experiments.

In situ Study of Cracking and Buckling of Chromium Films on PET Substrates

Chromium (Cr) films are widely used as interlayers to promote the adhesion of copper or gold to substrates. However, the Cr interlayer usually fractures at lower strains than the ductile metal films. In this paper, the cracking and buckling behavior of Cr films on polyethylene terephthalate (PET) substrates were studied in situ under tensile loading with the Atomic Force Microscope (AFM) and optical microscope imaging. Cr films with three nominal thicknesses of 15, 70 and 140 nm were studied. The depth and width of the cracks, as well as the height and width of the buckles, were measured from AFM images acquired at incremental loading steps. The buckle shapes at different strain levels were carefully examined using AFM line profile. It was found that at large strain levels the measured buckle shapes usually deviated from the elastic buckling mode shapes. Further in situ AFM imaging of the buckles at a smaller scan area revealed that in some cases the buckles were cracked at the apex. These in situ nanoscale measurements provided experimental observations and data for further model development and more accurate measurement of the interfacial fracture energy at the Cr-PET interface.

Testing the engineering sample of the NUCLEON setup on a pion beam

Results from testing the sample of the setup for the NUCLEON experiment aimed at studying the energy spectra and the charge composition of cosmic rays in the energy range of 1012–1015 eV are presented. The sample has been made approach the actual setup to the maximum degree. Charged particle beams with energies of 200–350 GeV have been used for testing. The problem of selecting high-energy events and the accuracy of energy measurements using the method being developed are discussed. This method is based on measuring the spatial flux density of secondary particles that are produced in the first act of inelastic nuclear interaction inside the target of the setup and pass through a thin converter layer in which the electromagnetic component is multiplied. The event selection efficiency is shown to be rather high. The precision in determining the energy (90–80%) using this method is in good agreement with simulation results (∼100-80%). The results of the study fully comply with the requirements of the NUCLEON experiment.

Likelihood-based Technique for measuring the Energy of Hadronically Decaying Tau Leptons

We present a new technique for accurate energy measurement of hadronically decaying tau leptons at the collider experiments. The technique employs a particle flow algorithm complemented with a likelihood-based method for separating contributions of overlapping energy depositions of spatially close particles. The technique was tested at CDF experiment at the Tevatron. In addition to superior energy resolution provided by the method and better measurement of other ID variables such as invariant mass of the jet, this technique provides a direct estimate of the uncertainty in the energy measurement of each individual tau candidate. While important in itself, this latter feature can serve as a powerful identification tool in distinguishing hadronically decaying tau leptons from jet and light lepton backgrounds. This new technique is expected to provide significant improvements in sensitivity of the H → τ τ search at the Tevatron and can be further extended to the case of generic (quark or gluon) jets.

Doppler-tuned Bragg spectroscopy of excited levels in He-like uranium: A discussion of the uncertainty contributions

We present the uncertainty discussion of a recent experiment performed at the GSI storage ring ESR for the accurate energy measurement of the He-like uranium 1s2p3P2→ 1s2s3S1 intra-shell transition. For this propose we used a Johann-type Bragg spectrometer that enables to obtain a relative energy measurement between the He-like uranium transition, about 4.51 keV, and a calibration x-ray source. As reference, we used the Kα fluorescence lines of zinc and the Li-like uranium 1s22p2P3/2 → 1 s22s 2S1/2 intra-shell transition from fast ions stored in the ESR. A comparison of the two different references, i.e., stationary and moving x-ray source, and a discussion of the experimental uncertainties is presented.

Studies of the CMS electromagnetic calorimeter performance in the electron test beam

The Compact Muon Solenoid (CMS) is a general purpose detector for LHC. The electromagnetic calorimeter (ECAL), comprising about 76,000 PbWO4 scintillating crystals, will allow a very accurate energy measurement of electrons and photons. The 36 supermodules (units of 1700 crystals) of the barrel have been successfully integrated inside the CMS solenoid. In 2006 nine supermodules with the final mechanics, cooling and electronics were exposed to electron test beams in order to perform precise inter-calibration and comprehensive studies of the detector response. A survey of results from these tests are here presented, with emphasis given to the energy resolution and linearity achieved.

Calibration & measurement facilities for AC high current & high voltage ratio standards at NPL

Regular calibration of the Instrument Transformers (ITs) is very essential for the accurate measurement of power and energy at high voltages. ITs are also used in the measurement of high currents & high voltages at power frequencies. The nominal transformation of an IT depends only on the number of turns of its windings but due to various losses there are always errors in the Instrument Transformers’ ratios. The correct knowledge of their errors requires calibrations of the ITs. In this paper the methods used in calibrating the Current Transformers (CTs) & Potential Transformers (PTs) and the required accuracy have been discussed.

Commissioning run of the CRESST-II dark matter search

The CRESST cryogenic direct dark matter search at Gran Sasso, searching for WIMPs via nuclear recoil, has been upgraded to CRESST-II by several changes and improvements. The upgrade includes a new detector support structure capable of accommodating 33 modules, the associated multichannel readout with 66 SQUID channels, a neutron shield, a calibration source lift, and the installation of a muon veto. We present the results of a commissioning run carried out in 2007. The basic element of CRESST-II is a detector module consisting of a large ( ∼ 300 g ) CaWO 4 crystal and a very sensitive smaller ( ∼ 2 g ) light detector to detect the scintillation light from the CaWO 4 . The large crystal gives an accurate total energy measurement. The light detector permits a determination of the light yield for an event, allowing an effective separation of nuclear recoils from electron–photon backgrounds. Furthermore, information from light-quenching factor studies allows the definition of a region of the energy-light yield plane which corresponds to tungsten recoils. A neutron test is reported which supports the principle of using the light yield to identify the recoiling nucleus. Data obtained with two detector modules for a total exposure of 48 kg-days are presented. Judging by the rate of events in the “all nuclear recoils” acceptance region the apparatus shows a factor ∼10 improvement with respect to previous results, which we attribute principally to the presence of the neutron shield. In the “tungsten recoils” acceptance region three events are found, corresponding to a rate of 0.063 per kg-day. Standard assumptions on the dark matter flux, coherent or spin independent interactions, then yield a limit for WIMP-nucleon scattering of 4.8 × 10 - 7 pb , at M WIMP ∼ 50 GeV .

Development of a highway noise prediction model using an Leq20 s measure of basic vehicular noise

The objective of the study reported here was to build a highway traffic noise simulation model for free-flow traffic conditions in Thailand employing a technique utilizing individual vehicular noise modelling based on the equivalent sound level over 20 s ( L eq20 s). This L eq20 s technique provides a more accurate measurement of noise energy from each type of vehicle under real running conditions. The coefficient of propagation and ground effect for this model was then estimated using a trial-and-error method, and applied to the highway traffic noise simulation model. This newly developed highway traffic noise model was tested for its goodness-of-fit to field observations. The test shows that this new model provides good predictions for highway noise conditions in Thailand. The concepts and techniques that are modeled and tested in this study can also be applied for prediction of traffic noise for local conditions in other countries.

Vibronic emission spectra of jet-cooled 2,3-difluorobenzyl radical in a corona excited supersonic expansion

We report the spectroscopic observation of difluorobenzyl radical in a corona excited supersonic expansion using a pinhole-type glass nozzle. A jet-cooled 2,3-difluorobenzyl radical was generated and vibronically excited from 2,3-difluorotoluene seeded in a large amount of inert carrier gas He. The vibronic emission spectra of the jet-cooled 2,3-difluorobenzyl radical were recorded for the first time in the visible region and analyzed to obtain an accurate measurement of the vibronic transition energy between the D 1 and D 0 electronic states. The vibrational mode frequencies in the ground electronic state were determined by comparison with those from an ab initio calculation as well as those of 2,6-difluorobenzyl radical and 1,2,3-trimethylbenzene.

Pulsed laser ablation and deposition of complex oxides

The pulsed laser ablation and deposition (PLD) processes of SrTiO3 were studied as a model system for developing a technique for the growth of structurally bulk-equivalent epitaxial thin films of typical complex oxides. Deposition rate vs. laser fluence measurements showed that there is a second critical fluence value above the ablation threshold. Below the critical value, both the ablation and deposition rates are linear functions of the fluence and independent of the ablation spot area. Above the critical value, the deposition rate per unit ablation area depends strongly on the ablation spot area. Homoepitaxial SrTiO3 films possessed the exact bulk lattice constant value only when the films were grown at the critical fluence, whereas larger lattice constants were obtained if the fluence was either higher or lower. Composition analysis revealed that the enlargement of the lattice constant was related to cationic unbalance. This critical laser fluence is essential for the growth of bulk-equivalent epitaxial films, and therefore accurate measurement of laser energy and ablation area is vital for reproducible film growth.

A new AMS setup for nuclear astrophysics experiments

The Nuclear Structure Laboratory (NSL) at the University of Notre Dame installed its Browne–Buechner spectrograph in the early 1970s for highly accurate energy measurements of nuclear reactions. Current renovation and upgrading of this spectrograph will enable operation of the magnet in a gas-filled mode, in particular for the study of nuclear reactions with low cross-sections of interest in nuclear astrophysics. One of the principle issues shared by measurements of extremely low abundances in Accelerator Mass Spectrometry (AMS) and nuclear astrophysics is the discrimination between the nuclei of interest and often very intense isobaric background. Recently the AMS technique of the gas-filled magnet has very successfully been used at Argonne National Laboratory (ANL) to overcome this in the study of both environmental noble gas traces (39Ar) and the measurement of cross-sections of interest in stellar nucleosynthesis i.e. the 62Ni(n,γ)63Ni reaction. We hope to extend these techniques further to the observations of astrophysically important reactions such as 40Ca(α,γ)44Ti and 78Kr(α,γ)82Sr.

Muon Detector Description as built and its Simulation for the ATLAS experiment

The ATLAS detector is designed to exploit the full potential of the LHC, identifying and providing highly accurate energy and momentum measurements of particles emerging from the LHC proton–proton collisions. High-momentum final-state muons are among the most promising signatures at the LHC, thanks to a high-resolution Muon Spectrometer with standalone triggering and momentum measurement. The Muon Spectrometer is a large and complex system of gaseous detectors, requiring a detailed simulation to exploit its full capabilities. Over the last few years these systems have been described in terms of a set of geometrical primitives known as GeoModel. This description is now used in the GEANT4-based simulation program, which is fully operational and integrated into the ATLAS common analysis framework.

Observation of vibronic emission spectrum of jet-cooled 2,4-difluorobenzyl radical in a corona excitation

The jet-cooled 2,4-difluorobenzyl radical was generated and vibronically excited in a corona excited supersonic expansion from 2,4-difluorotoluene seeded in a large amount of inert carrier-gas helium. The well-resolved vibronic emission spectrum of the jet-cooled 2,4-difluorobenzyl radical was recorded in the visible region with a long-path monochromator and analyzed to obtain an accurate measurement of the electronic energy of the D 1 → D 0 transition and vibrational-mode frequencies in the ground electronic state by comparison with those of 2,4-difluorotoluene as well as those from an ab initio calculation.

Energy properties of an EMI-Im ionic liquid ion source

The identity and the energy distributions of positive and negative ions electrostatically extracted from the liquid phase in an ionic liquid ion source (ILIS) are analysed with a time-of-flight mass spectrometer and a multi-grid retarding potential analyzer. Accurate energy measurements using ionic liquids in an externally wetted configuration are reported for the first time. Droplet-free beams are produced using the ionic liquid 1-ethyl-3-methylimidazolium bis(triflouromethylsulfonyl)amide (EMI-Im) in which the solvated ions (EMI-Im)nEMI+ and (EMI-Im)nIm− with n = 0,1,2 are observed. The small ion source size and the energy distribution widths and deficits of a few electronvolts are quite similar to those of liquid metal ion sources, confirming that ILIS can be used in applications requiring highly focusable beams, e.g. sub-micron ion lithography. Measurements also suggest that solvated ions with n ⩾ 1 exhibit post-extraction fragmentation into lighter species at a rate increasing with their original degree of solvation. About 10% of the total beam current is carried away by metastable species that break up almost immediately after extraction while inside the emitter accelerating region.

Proton CT setup at CV-28 of IEN/CNEN

Although the idea of proton Computed Tomography (pCT) is not new, it is currently not available. It is still unknown if the image quality of pCT is sufficient for localizing tumors and if the accuracy of proton range calculations surpass that of X-ray CT based range calculations without significantly increasing the patient exposure. The spatial resolution of pCT is limited mainly by multiple Coulomb scattering, while the contrast resolution is affected principally by the statistical nature of the proton energy loss mechanism. Both effects are more pronounced and thus easier to study at the low proton energies available at CV-28. An experimental setup for pCT at CV-28 was elaborated by our team. The first-generation CT scheme was assumed as the most adequate for the existing CV-28 proton "pencil" beam. All equipment, which includes the collimators for the initial and outgoing proton beam, the tomographic turntable, and the ORTEC L-035-025-5 proton detector, was assembled onto the support bar of the ORTEC vacuum chamber. A water-filled glass tube of 5 mm external diameter with a 1 mm diameter polyethylene rod on the central axis was chosen as the first sample to be studied. Later, the water will be substituted by tissue-equivalent solutions of different densities to study the contrast resolution. A Monte Carlo simulation of the experiment, assuming 25 MeV monochromatic proton beam, was made using the SRIM-2003.20 code. The simulation permitted to choose the critical parameters for the setup, such as the beam collimation, the steps of translation and rotation of the turntable, and the required statistics for an accurate measurement of proton energy.

Measurements of Energy of Cosmic-Ray Nuclei by Specific Energy Release at the Hadron Cascade Maximum

A method of measuring the particle energy in the range higher than 1 TeV based on detection of the maximum specific energy release in hadron cascades that develop in dense media is proposed and studied. This method makes it possible to improve the accuracy of energy measurements carried out with partial-absorption ionization calorimeters in the high-altitude studies of energy spectra of high-energy cosmic rays. The attainable accuracies of energy measurements are considered for light, intermediate, and heavy nuclei in iron and lead absorbers. The results of modeling are compared with the data of an experiment onboard the Kosmos-1713 satellite.

The readout of the LHC beam luminosity monitor: accurate shower energy measurements at a [formula omitted] repetition rate

The LHC beam luminosity monitor is based on the following principle. The neutrals that originate in LHC at every PP interaction develop showers of minimum ionizing particles in the absorbers placed in front of the separation dipoles. The shower energy, measured by suitable detectors in the absorbers is proportional to the number of neutral particles and, therefore, to the luminosity. The principle lends itself to a luminosity measurement on a bunch-by-bunch basis. However, to make such a measurement feasible, the system must comply with extremely stringent requirements. Its speed of operation must match the 40 MHz bunch repetition rate of LHC. Besides, the detector must stand extremely high radiation doses. This paper discusses the solutions adopted to comply with these requirements.

X-ray spectral measurements and collisional radiative modeling of Ni- to Kr-like Au ions in electron beam ion trap plasmas.

The line emission of n=7-->3, 6-->3, 5-->3, and 4-->3 transitions in Ni- to Kr-like gold ions produced in the Livermore electron beam ion traps EBIT-I and EBIT-II has been recorded with an x-ray crystal spectrometer and a photometrically calibrated microcalorimeter. The plasmas had either monoenergetic electron beams with E(beam)=2.66, 3.53, or 4.54 keV or an experimentally simulated thermal electron distributions with T(e)=2.5 keV. The electron densities were approximately 10(12)cm(-3). The measured spectra have been compared to atomic structure calculations and synthetic spectra provided by the Hebrew University Lawrence Livermore Atomic Code atomic data package. Line identifications and accurate photon energy measurements have been made for many collisionally excited transitions. Approximately 140 lines have been identified in nine charge states. Agreement within 20-30 % exists between the measured and modeled line intensities for most lines excited by the monoenergetic electron beam plasmas, although some larger discrepancies can be found for some weaker features.

Measurement of energy of medium-mass and heavy cosmic-ray nuclei by a specific energy deposition at the maximum of hadron showers in dense matter

The possibility of measuring the energy of cosmic-ray nuclei (for energies higher than 1 TeV) by means of recording the greatest specific energy deposition in hadron showers generated in dense matter is investigated. This method makes it possible to improve the accuracy of energy measurements by thin calorimeters in studying high-energy cosmic rays at high altitudes. Attainable accuracies in measuring energy are considered for the cases of light and heavy nuclei. The results of a relevant simulation are compared with data from the Kosmos-1713 satellite-borne experiment.