Papers by WGD Dharmaratna
HAL (Le Centre pour la Communication Scientifique Directe), Jul 4, 2023
HAL (Le Centre pour la Communication Scientifique Directe), Jul 25, 2023
A search for the production of pairs of heavy Majorana neutrinos (N ℓ) from the decays of Z ′ bos... more A search for the production of pairs of heavy Majorana neutrinos (N ℓ) from the decays of Z ′ bosons is performed using the CMS detector at the LHC. The data were collected in proton-proton collisions at a center-of-mass energy of √ s = 13 TeV, with an integrated luminosity of 138 fb −1. The signature for the search is an excess in the invariant mass distribution of the final-state objects, two same-flavor leptons (e or µ) and at least two jets. No significant excess of events beyond the expected background is observed. Upper limits at 95% confidence level are set on the product of the Z ′ production cross section and its branching fraction to a pair of N ℓ , as functions of N ℓ and Z ′ boson masses (m N ℓ and m Z ′ , respectively) for m Z ′ from 0.4 to 4.6 TeV and m N ℓ from 0.1 TeV to m Z ′ /2. In the theoretical framework of a left-right symmetric model, exclusion bounds in the m N ℓ-m Z ′ plane are presented in both the electron and muon channels. The observed upper limit on m Z ′ reaches up to 4.42 TeV. These are the most restrictive limits to date on the mass of N ℓ as a function of the Z ′ boson mass.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 8, 2023
HAL (Le Centre pour la Communication Scientifique Directe), Aug 16, 2023
HAL (Le Centre pour la Communication Scientifique Directe), Apr 20, 2023
Physical Review Letters, 2020
Physical Review D, Particles and fields, 2019
Results are presented for an extraction of the top quark Yukawa coupling from top quark-antiquark... more Results are presented for an extraction of the top quark Yukawa coupling from top quark-antiquark (tt¯) kinematic distributions in the lepton plus jets final state in proton-proton collisions, based on data collected by the CMS experiment at the LHC at s=13 TeV, corresponding to an integrated luminosity of 35.8 fb-1. Corrections from weak boson exchange, including Higgs bosons, between the top quarks can produce large distortions of differential distributions near the energy threshold of tt¯ production. Therefore, precise measurements of these distributions are sensitive to the Yukawa coupling. Top quark events are reconstructed with at least three jets in the final state, and a novel technique is introduced to reconstruct the tt¯ system for events with one missing jet. This technique enhances the experimental sensitivity in the low invariant mass region, Mtt¯. The data yields in Mtt¯, the rapidity difference |yt-yt¯|, and the number of reconstructed jets are compared with distribut...
2011 7th Asia-Pacific International Conference on Lightning, 2011
ABSTRACT Thunder waves generated by lightning ground and cloud flashes are considered to be one o... more ABSTRACT Thunder waves generated by lightning ground and cloud flashes are considered to be one of strong natural sound source. Even though the strongest thunder signatures are generated at the return stroke stage, thunder signals generated at other events also can be strong enough to record using a sensitive system. In this study, it was attempted to construct the channel geometry of cloud and ground flashes by locating the temporal and spatial variation of thunder sources. The system was consisted of 3 Bruel & Kjaer type 4198 prepolarized, free field 1/2' microphones placed at difference locations. A mathematical model using the time of arrival method was developed to calculate the location of thunder sources. Five lightning flashes were reconstructed using the recorded thunder signatures. Possible effects that can cause by atmospheric conditions were neglected. However, numerical calculations suggest that the possible error on the location due to miscalculations of time is less than 2%. Accuracy of the calculations can be improved by increasing the number of microphones. Therefore, we suggests that the thunder signal generated by lightning ground and cloud flashes could be used to study the channel geometry of lightning.
2014 International Conference on Lightning Protection (ICLP), 2014
Journal of the Chemical Society, Faraday Transactions 2, 1982
A study of the conductivity characteristics of ferric tungstate indicates that this material unde... more A study of the conductivity characteristics of ferric tungstate indicates that this material undergoes a semiconductor-to-metal transition at ca. 182 °C.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1993
The two End Calorimeter Electromagnetic (ECEM) modules of the Do liquid argon calorimeter system ... more The two End Calorimeter Electromagnetic (ECEM) modules of the Do liquid argon calorimeter system have been constructed as monolithic units of 1 m radius to provide full azimuthal coverage in the forward and backward regions (1 .4 < 1 77 1 < 4.0) for the study of pp collisions at the Fermilab Tevatron Collider. An ECEM module consists of 18 layers of absorber disks (mostly 4 mm thick uranium) with interleaved signal disks that have readout pads m semi-projective towers. The mechanical design and construction of the ECEM modules is described in detail. The performance of one ECEM module has been studied in beam tests with electrons. Results are given for the linearity and uniformity of response, the energy and position resolutions, and pion rejection.
Journal of Atmospheric and Solar-Terrestrial Physics, 2013
ABSTRACT Thunder is generated as a result of a shock wave created by sudden expansion of air in t... more ABSTRACT Thunder is generated as a result of a shock wave created by sudden expansion of air in the lightning channel due to high temperature variations. Even though the highest amplitudes of thunder signatures are generated at the return stroke stage, thunder signals generated at other events such as preliminary breakdown pulses also can be of amplitudes which are large enough to record using a sensitive system. In this study, it was attempted to reconstruct the lightning channel geometry of cloud and ground flashes by locating the temporal and spatial variations of thunder sources. Six lightning flashes were reconstructed using the recorded thunder signatures. Possible effects due to atmospheric conditions were neglected. Numerical calculations suggest that the time resolution of the recorded signal and 10 ms−1error in speed of sound leads to 2% and 3% errors, respectively, in the calculated coordinates. Reconstructed channel geometries for cloud and ground flashes agreed with the visual observations. Results suggest that the lightning channel can be successfully reconstructed using this technique.
Zeitschrift für Physik C Particles and Fields, 1989
It is well known that single polarization asymmetries vanish in QCD at momenta that are high rela... more It is well known that single polarization asymmetries vanish in QCD at momenta that are high relative to quark masses, due to chirality conservation. However, the particular form of those asymmetries for non-zero masses has not been explored. We have calculated the fourth order contributions to massive quark polarization in quark-quark and quark-gluon scattering. The dependence on the non-abelian character of the theory is emphasized and a comparison is made with the Mott scattering limit. Unusual momentum dependence and large polarizations are noted for some regions of parameter space. The relation to polarized hyperon production is explored.
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Papers by WGD Dharmaratna