Elias Sideras-Haddad
University of the Witwatersrand, School of Physics, Faculty Member
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We summarise high-resolution, high-precision spectroscopy experiment where caesium-133 atoms in a vapour cell are excited directly with a femtosecond laser frequency comb. In this experiment the laser beam is sent counter-propagating by... more
We summarise high-resolution, high-precision spectroscopy experiment where caesium-133 atoms in a vapour cell are excited directly with a femtosecond laser frequency comb. In this experiment the laser beam is sent counter-propagating by the beam-splitting cube, focussed to a reasonable waist in the interaction region in the vapour cell, thereby exciting a multitude of low lying transitions allowing the measurement of transition energies and hyperfine coupling coefficients for the 8S1/2, 9S1/2 and 7D3/2,5/2 states.
Charged-particle fragmentation functions for jets azimuthally balanced by a high-transverse-momentum, prompt, isolated photon are measured in $25$ pb$^{-1}$ of $pp$ and $0.49$ nb$^{-1}$ of Pb+Pb collision data at $5.02$ TeV per nucleon... more
Charged-particle fragmentation functions for jets azimuthally balanced by a high-transverse-momentum, prompt, isolated photon are measured in $25$ pb$^{-1}$ of $pp$ and $0.49$ nb$^{-1}$ of Pb+Pb collision data at $5.02$ TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The measurements are compared to predictions of Monte Carlo generators and to measurements of inclusively selected jets. In $pp$ collisions, a different jet fragmentation function in photon-tagged events from that in inclusive jet events arises from the difference in fragmentation between light quarks and gluons. The ratios of the fragmentation functions in Pb+Pb events to that in $pp$ events are used to explore the parton color-charge dependence of jet quenching in the hot medium. In relatively peripheral collisions, fragmentation functions exhibit a similar modification pattern for photon-tagged and inclusive jets. However, photon-tagged jets are observed to be modified in a differe...
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The first measurement of longitudinal decorrelations of harmonic flow amplitudes v_{n} for n=2-4 in Xe+Xe collisions at sqrt[s_{NN}]=5.44 TeV is obtained using 3 μb^{-1} of data with the ATLAS detector at the LHC. The decorrelation... more
The first measurement of longitudinal decorrelations of harmonic flow amplitudes v_{n} for n=2-4 in Xe+Xe collisions at sqrt[s_{NN}]=5.44 TeV is obtained using 3 μb^{-1} of data with the ATLAS detector at the LHC. The decorrelation signal for v_{3} and v_{4} is found to be nearly independent of collision centrality and transverse momentum (p_{T}) requirements on final-state particles, but for v_{2} a strong centrality and p_{T} dependence is seen. When compared with the results from Pb+Pb collisions at sqrt[s_{NN}]=5.02 TeV, the longitudinal decorrelation signal in midcentral Xe+Xe collisions is found to be larger for v_{2}, but smaller for v_{3}. Current hydrodynamic models reproduce the ratios of the v_{n} measured in Xe+Xe collisions to those in Pb+Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe+Xe and Pb+Pb. The results on the system-size dependence provide new insights and an important lever arm to sep...
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Electroweak symmetry breaking explains the origin of the masses of elementary particles via their interactions with the Higgs field. Besides the measurements of the Higgs boson properties, the study of the scattering of massive vector... more
Electroweak symmetry breaking explains the origin of the masses of elementary particles via their interactions with the Higgs field. Besides the measurements of the Higgs boson properties, the study of the scattering of massive vector bosons (with spin one) at the Large Hadron Collider allows to probe the nature of electroweak symmetry breaking with an unprecedented sensitivity. Among all processes related to vector-boson scattering, the electroweak production of two jets and a $Z$-boson pair is a rare and important one. This article reports on the first observation of this process using proton-proton collision data corresponding to an integrated luminosity of 139 fb$^{-1}$ recorded at a centre-of-mass energy of 13 TeV by the ATLAS detector. Two different final states originating from the decays of the $Z$-boson pair, one containing four charged leptons and the other containing two charged leptons and two neutrinos, are considered. The hypothesis of no electroweak production is reje...
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The ATLAS experiment at the Large Hadron Collider employs a two-level trigger system to record data at an average rate of 1 kHz from physics collisions, starting from an initial bunch crossing rate of 40 MHz. During the LHC Run 2... more
The ATLAS experiment at the Large Hadron Collider employs a two-level trigger system to record data at an average rate of 1 kHz from physics collisions, starting from an initial bunch crossing rate of 40 MHz. During the LHC Run 2 (2015-2018), the ATLAS trigger system operated successfully with excellent performance and flexibility by adapting to the various run conditions encountered and has been vital for the ATLAS Run-2 physics programme. For proton-proton running, approximately 1500 individual event selections were included in a trigger menu which specified the physics signatures and selection algorithms used for the data-taking, and the allocated event rate and bandwidth. The trigger menu must reflect the physics goals for a given data collection period, taking into account the instantaneous luminosity of the LHC and limitations from the ATLAS detector readout, online processing farm, and offline storage. This document discusses the operation of the ATLAS trigger system during the nominal proton-proton data collection in Run 2 with examples of special data-taking runs. Aspects of software validation, evolution of the trigger selection algorithms during Run 2, monitoring of the trigger system and data quality as well as trigger configuration are presented.
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High-resolution inelastic electron (performed at the S-DALINAC) and proton (performed at iThemba LABS) scattering experiments on 92Zr and 94Mo with emphasis on E2 transitions are presented The measured form factors and angular... more
High-resolution inelastic electron (performed at the S-DALINAC) and proton (performed at iThemba LABS) scattering experiments on 92Zr and 94Mo with emphasis on E2 transitions are presented The measured form factors and angular distributions provide a measure for the F-spin purity, respectively the isovector nature, of the proposed one-phonon mixed symmetry states and furthermore provide a sensitive test of a possible
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Digital thermal neutron imaging (radiography and tomography) is a powerful non-destructive analytical tool and h as demonstrated its importance in industrial and res earch application world-wide. However, standards throu gh test samples,... more
Digital thermal neutron imaging (radiography and tomography) is a powerful non-destructive analytical tool and h as demonstrated its importance in industrial and res earch application world-wide. However, standards throu gh test samples, methods and procedures, which are essential when t he technique is to be ap plied in the nati onal and i nternational industrial and research environment, do not exist yet. This contribution provides proposed w ork intended at contri buting towards the establishment of national and i nternational standards for di gital thermal neutron imaging. This entails a con tribution towards the establ ishment, evaluation, validation and i mprovement of quanti tative measurements and practice utilizing digital thermal neutron radiography.
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Nuclear Instruments and Methods in Physics Research A271 (1988) 383-386 North-Holland, Amsterdam 383 A POSITRON SOURCE PRODUCED BY A TANDEM VAN DE GRAAFF ACCELERATOR FOR USE IN A RELATIVISTIC ENERGY SPECTROMETER DESIGNED FOR SYMMETRICAL... more
Nuclear Instruments and Methods in Physics Research A271 (1988) 383-386 North-Holland, Amsterdam 383 A POSITRON SOURCE PRODUCED BY A TANDEM VAN DE GRAAFF ACCELERATOR FOR USE IN A RELATIVISTIC ENERGY SPECTROMETER DESIGNED FOR SYMMETRICAL MASS SYSTEMS U. VON WIMMERSPERG *, SH CONNELL, RFA HOERNLE, E. SIDERAS-HADDAD and JPF SELLSCHOP Wits -CSIR Schonland Research Centre for Nuclear Sciences, University of the Witwatersrand, PO Wits 2050, JohannesburgSouth Africa Received 11 February ...
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The Schonland Scanning Proton Microprobe has been used over several years to investigate various types of geological materials in order to understand the evolution of these materials in the earth. This paper represents an overview of some... more
The Schonland Scanning Proton Microprobe has been used over several years to investigate various types of geological materials in order to understand the evolution of these materials in the earth. This paper represents an overview of some selected studies.
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A Fe and Mn heterogeneity effect was observed in microscopic garnet inclusion in diamond using micro-PIXE. Results are presented and the implications of these disequilibrium element distributions during growth of garnets are discussed.... more
A Fe and Mn heterogeneity effect was observed in microscopic garnet inclusion in diamond using micro-PIXE. Results are presented and the implications of these disequilibrium element distributions during growth of garnets are discussed. The occurrence of zoning or any type of chemical inhomogeneity within inclusions encapsulated within diamond has implications on the age of formation of the inclusion and the diamond. It is believed that the age of the inclusion is that of the diamond formation itself, with subsequent isolation of the ...
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High-resolution inelastic electron (performed at the S-DALINAC) and proton (performed at iThemba LABS) scattering experiments on 92Zr and 94Mo with emphasis on E2 transitions are presented The measured form factors and angular... more
High-resolution inelastic electron (performed at the S-DALINAC) and proton (performed at iThemba LABS) scattering experiments on 92Zr and 94Mo with emphasis on E2 transitions are presented The measured form factors and angular distributions provide a measure for the F-spin purity, respectively the isovector nature, of the proposed one-phonon mixed symmetry states and furthermore provide a sensitive test of a possible
Research Interests:
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High-resolution inelastic electron scattering experiments at the S-DALINAC and proton scattering experiments at iThemba LABS permit a thorough test of the nature of proposed one- and two-phonon symmetric and mixed-symmetric 2+ states of... more
High-resolution inelastic electron scattering experiments at the S-DALINAC and proton scattering experiments at iThemba LABS permit a thorough test of the nature of proposed one- and two-phonon symmetric and mixed-symmetric 2+ states of the nucleus 94Mo. The combined analysis reveals the one-phonon content of the mixed-symmetry state and its isovector character suggested by microscopic calculations. The purity of two-phonon 2+
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Research Interests: Geochemistry, Chemistry, Analytical Chemistry, Accelerator Mass Spectrometry, Sample Preparation, and 9 moreCost effectiveness, Inductively Coupled Plasma Mass Spectrometry, Very high throughput, Interdisciplinary Engineering, Mass Spectroscopy, Certified Reference Material, High Sensitivity, Reference Value, and Mass Spectrometer
A fast-imaging technique for the total elemental hydrogen concentration distribution is described, which is helpful in the study of its chemistry and dynamics in the diamond system. The micro-scanned Heavy-Ion Elastic Recoil Detection... more
A fast-imaging technique for the total elemental hydrogen concentration distribution is described, which is helpful in the study of its chemistry and dynamics in the diamond system. The micro-scanned Heavy-Ion Elastic Recoil Detection Analysis (HI-ERDA) technique can deliver information on hydrogen distributions in three dimensions. In our system, the count rate is enhanced by use of a 2-D position and energy sensitive detector for the hydrogen recoils. Software geometry collimation and recoil energy rebinning ensure that the ...
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ABSTRACT The ubiquitous use of ion implantation and the simultaneous interest in the emplacement of selected impurities in the matrix of choice bring added emphasis to the need for a quantitative understanding of the residence sites... more
ABSTRACT The ubiquitous use of ion implantation and the simultaneous interest in the emplacement of selected impurities in the matrix of choice bring added emphasis to the need for a quantitative understanding of the residence sites adopted by such imputities. The time-dependent perturbed angular distribution technique has been used to study the case of fluorine implanted in diamond. Careful examination is presented of the dependence of the perturbation parameters on the characteristics of the implant sites. These comprehensive investigations reveal the power of the technique in the richness of detail exposed and make possible the theoretical modelling of the data.
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Studies into the effect of hydrogen and oxygen on the growth of CVD diamonds have been in progress for a number of years. Surface oxygen studies on natural diamond using Rutherford backscattering spectrometry have yielded partial... more
Studies into the effect of hydrogen and oxygen on the growth of CVD diamonds have been in progress for a number of years. Surface oxygen studies on natural diamond using Rutherford backscattering spectrometry have yielded partial monolayer coverage on low index planes. To increase the sensitivity of the measurements, elastic scattering using the 16O (α, α) 16O resonance at 3.045 MeV has been performed. This resonance can enhance, by up to 30 times, the Rutherford cross-section. The samples are natural diamonds with ...
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ABSTRACT We report conductance fluctuation in VO2 nano-ribbons of 10 nm thickness at moderate temperatures. Synthesis of these nano-ribbons was reported elsewhere [1-4]. The fluctuations are periodic at room temperature up to the VO2... more
ABSTRACT We report conductance fluctuation in VO2 nano-ribbons of 10 nm thickness at moderate temperatures. Synthesis of these nano-ribbons was reported elsewhere [1-4]. The fluctuations are periodic at room temperature up to the VO2 transition temperature of 70 oC. These are surprising results since dc currents are producing a.c. potential difference values in i-v characteristics of the nano-ribbons of VO2 contrary to those of normal bulk materials. Three main theories were considered in order to explain these findings (1) The LRC equivalent circuit theory (2) the Gunn effect [5] and (3) the Universal Conductance Fluctuations theories [6-15]. The first two theories failed to explain our experimental data. We have explained this anomalous behaviour by the third theory which is a manifestation of the wave nature of electrons. The wave nature of electrons has been demonstrated in many instances including the Nobel–prize–winning Davisson & Germer experiment on electron diffraction. In electronic circuits, quantum interference in metallic wires [6-8], the so-called ‘weak localization’ [9,10] and universal conductance fluctuations (UCF) [11-13] are all manifestations of this wave nature. Fluctuations originate from coherence effects for electronic wave–functions and thus the phase–coherence length, lf needs to be smaller than the momentum relaxation length lm. UCF is more profound when electrical transport is in the weak localization regime lf < lc ="M" g0="2e2/h">
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Carvedilol (Coreg) is a nonselective β-adrenergic blocking agent with vasodilating activity. It is used for the treatment of congestive heart failure and hypertension. During the bulk synthesis of carvedilol, we have observed six... more
Carvedilol (Coreg) is a nonselective β-adrenergic blocking agent with vasodilating activity. It is used for the treatment of congestive heart failure and hypertension. During the bulk synthesis of carvedilol, we have observed six impurities: Imp-I, Imp-II, Imp-III, Imp-IV, Imp-V, and Imp-VI. The present work describes the synthesis and characterization of these impurities.
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The use of heavy-ion microprobes has significant advantages over the commonly used microprobes with proton and alpha beams. Heavy ions due to their higher atomic and mass numbers they induce atomic and nuclear interactions which provide... more
The use of heavy-ion microprobes has significant advantages over the commonly used microprobes with proton and alpha beams. Heavy ions due to their higher atomic and mass numbers they induce atomic and nuclear interactions which provide unique features for ion beam analysis. The Elastic Recoil Detection Analysis technique (ERDA) is often applied to the detection of light elements and benefits from larger scattering cross section, better sensitivity and depth resolution when using heavy ions as projectiles. ERDA has ...
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Nuclear Instruments and Methods in Physics Research A271 (1988) 383-386 North-Holland, Amsterdam 383 A POSITRON SOURCE PRODUCED BY A TANDEM VAN DE GRAAFF ACCELERATOR FOR USE IN A RELATIVISTIC ENERGY SPECTROMETER DESIGNED FOR SYMMETRICAL... more
Nuclear Instruments and Methods in Physics Research A271 (1988) 383-386 North-Holland, Amsterdam 383 A POSITRON SOURCE PRODUCED BY A TANDEM VAN DE GRAAFF ACCELERATOR FOR USE IN A RELATIVISTIC ENERGY SPECTROMETER DESIGNED FOR SYMMETRICAL MASS SYSTEMS U. VON WIMMERSPERG *, SH CONNELL, RFA HOERNLE, E. SIDERAS-HADDAD and JPF SELLSCHOP Wits -CSIR Schonland Research Centre for Nuclear Sciences, University of the Witwatersrand, PO Wits 2050, JohannesburgSouth Africa Received 11 February ...
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A Fe and Mn heterogeneity effect was observed in microscopic garnet inclusion in diamond using micro-PIXE. Results are presented and the implications of these disequilibrium element distributions during growth of garnets are discussed.... more
A Fe and Mn heterogeneity effect was observed in microscopic garnet inclusion in diamond using micro-PIXE. Results are presented and the implications of these disequilibrium element distributions during growth of garnets are discussed. The occurrence of zoning or any type of chemical inhomogeneity within inclusions encapsulated within diamond has implications on the age of formation of the inclusion and the diamond. It is believed that the age of the inclusion is that of the diamond formation itself, with subsequent isolation of the ...