Density functional theory calculation of the optical properties of graphene quantum dots

Graphene quantum dots (GQDs) are class of nanoparticles exhibiting unique and tunable electronic, optical, chemical and structural properties owing to their small size and quantum confinement and edge effects. GQDs most prominent characteristics are high photoluminescence, photostability, excellent photobleaching resistance, low citotoxicity, good biocompatibility, exceptional electrochemical activity and physicochemical stability, making them suitable for a wide range of applications, from biosensing and fluorescence bioimaging usage, photodynamic therapy, to optoelectronic, susteanable agricultural and environmental applications. Using density functional theory (DFT) we demonstrate that the optical properties of the GQDs can be sensitively tuned by its size, shape, edge configuration, attached chemical functionalities.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi

Ab Initio Study of Structural, Electronic and Optical Properties of Edge-Functionalized Graphene Quantum Dots

Graphene quantum dots (GQD) are nano-particles small enough to exhibit unique electronic and optical properties that results from quantum confinement and edge effects. Unlike graphene they exhibit opening of the HOMO-LUMO band gap responsible for their unique optoelectronic properties high photoluminescence (PL) quantum yield, excellent photobleaching resistance and photostability, low citotoxicity, good biocompatibility, high solubility in various solvents, exceptional electrochemical activity and physicochemical stability. These characterisics of the GQDs make them suitable for a wide range of applications from biomedical applications such as diagnostics and therapy, to susteanable agricultural and environmental appications. In this respect carbon-based quantum dots such as GQDs, present promising candidates for usage in biosensing and fluorescence bioimaging applications, allowing a fast, more sensitive and more selectable detection and diagnosis. As biocompatible nanoparticles, they also have the potential to revolutionize the prospects of photodynamic therapy (PDT) in clinical treatments of cancer [1] and other diseases, antibacterial [2] and preventive antivirus PDT [3], being applied as photosensitizer agents. In a meanwhile comprehensive biomedical studies should pave the way for safe and efficient use of carbon-based quantum dots in clinical applications. In the present work, we investigate the effects of size and shape variation, as well as edge-functionalization on the structural and optical properties of GQDs, using the first-principles study based on the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). We investigate edge-functionalized GQDs, with oxygen-containing –OH and –COOH groups, different shapes, such as hexagonal, triangular and rectangular and zigzag/armchair edge configuration, as well as variation of size, in tailoring the optoelectronic properties and photoluminescence behaviour of GQDs leading to a wide variety of applications.29th International Symposium on Analytical and Environmental Problems : Proceedings; November 13-14, 2023; Szeged, Hungary

Study of ordered hadron chains with the ATLAS detector

The analysis of the momentum difference between charged hadrons in high-energy proton-proton collisions is performed in order to study coherent particle production. The observed correlation pattern agrees with a model of a helical QCD string fragmenting into a chain of ground-state hadrons. A threshold momentum difference in the production of adjacent pairs of charged hadrons is observed, in agreement with model predictions. The presence of low-mass hadron chains also explains the emergence of charge-combination-dependent two-particle correlations commonly attributed to Bose-Einstein interference. The data sample consists of 190 mu b(-1) of minimum-bias events collected with proton-proton collisions at a center-of-mass energy root s = 7 TeV in the early low-luminosity data taking with the ATLAS detector at the LHC

Integrated luminosity measurement at CEPC

The very forward region is one of the most challenging regions to instrument at a future $e^+e^-$ collider. At CEPC, machine-detector interface includes, among others, a calorimeter dedicated for precision measurement of the integrated luminosity at a permille level or better. Here we review a feasibility of such precision, from the point of view of luminometer mechanical precision and positioning, beam-related requirements and physics background.A method of the effective center-of-mass determination from $e^+e^- \to \mu^+\mu^-$, initially proposed for FCC, is also discussed for the CEPC beams.Comment: Talk presented at the International Workshop on Future Linear Colliders (LCWS2021), 15-18 March 2021. C21-03-15.1. arXiv admin note: text overlap with arXiv:2010.15061, arXiv:2002.0366

Measurement of the Higgs Branching Ration BR(H→γγH\rightarrow\gamma\gamma) at 3 TeV CLIC

In this paper we address the potential of a 3 TeV center-of-mass energy Compact Linear Collider (CLIC) to measure the Standard Model (SM) Higgs boson decay to two photons. Since photons are massless, they are not coupled to the Higgs boson at the tree level, but they are created in a loop exchange of heavy particles either from the Standard Model or beyond. Any deviation of the effective $H\rightarrow\gamma\gamma$ branching ratio and consequently of the Higgs to photon coupling may indicate New Physics. The Higgs decay to two photons is thus an interesting probe of the Higgs sector, both at the running and future experiments. A similar study has been performed by C. Grefe at 1.4 TeV CLIC, where the statistical uncertainty is determined to be 15\% for an integrated luminosity of 1.5 $ab^{-1}$ with unpolarized beams. \noindent This study is performed using a full simulation of the detector for CLIC and by considering all relevant physics and beam-induced processes in a full reconstruction chain. The measurement is simulated on 5000 samples of pseudo-experiments and the relative statistical uncertainty is extracted from the pull distribution. It is shown that the Higgs production cross-section in $W^+W^-$ fusion times the branching ratio BR($H\rightarrow\gamma\gamma$) can be measured with a relative statistical accuracy of 8.2\%, assuming an integrated luminosity of 5 $ab^{-1}$ with unpolarized beams

CP violation in the Higgs sector at ILC

CP violation is one of Sakharov's condition for the matter-antimatter asymmetry of the Universe. The experimentally observed size of CP violation is insufficient to account for this. Is CP violated in the Higgs sector? Could the SM-like Higgs boson be a mixture of CP even and CP odd states of an extended Higgs sector? With what precision could such effects be measured at future electron-positron colliders? These questions will be discussed in the light of the latest studies at ILC

Search for new phenomena in high-mass final states with a photon and a jet from pp collisions at √s = 13 TeV with the ATLAS detector

A search is performed for new phenomena in events having a photon with high transverse momentum and a jet collected in 36.7fb-1 of proton–proton collisions at a centre-of-mass energy of s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The invariant mass distribution of the leading photon and jet is examined to look for the resonant production of new particles or the presence of new high-mass states beyond the Standard Model. No significant deviation from the background-only hypothesis is observed and cross-section limits for generic Gaussian-shaped resonances are extracted. Excited quarks hypothesized in quark compositeness models and high-mass states predicted in quantum black hole models with extra dimensions are also examined in the analysis. The observed data exclude, at 95% confidence level, the mass range below 5.3 TeV for excited quarks and 7.1 TeV (4.4 TeV) for quantum black holes in the Arkani-Hamed–Dimopoulos–Dvali (Randall–Sundrum) model with six (one) extra dimensions

Search for new phenomena in dijet events using 37 fb−1 of pp collision data collected at √s=13 TeV with the ATLAS detector

Dijet events are studied in the proton-proton collision data set recorded at s=13 TeV with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to integrated luminosities of 3.5 fb-1 and 33.5 fb-1 respectively. Invariant mass and angular distributions are compared to background predictions and no significant deviation is observed. For resonance searches, a new method for fitting the background component of the invariant mass distribution is employed. The data set is then used to set upper limits at a 95% confidence level on a range of new physics scenarios. Excited quarks with masses below 6.0 TeV are excluded, and limits are set on quantum black holes, heavy W′ bosons, W∗ bosons, and a range of masses and couplings in a Z′ dark matter mediator model. Model-independent limits on signals with a Gaussian shape are also set, using a new approach allowing factorization of physics and detector effects. From the angular distributions, a scale of new physics in contact interaction models is excluded for scenarios with either constructive or destructive interference. These results represent a substantial improvement over those obtained previously with lower integrated luminosity

Search for supersymmetry in final states with missing transverse momentum and multiple b-jets in proton-proton collisions at √s=13 TeV with the ATLAS detector

A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino χ˜10 $$\left({\tilde{\chi}}_1^0\right)$$ is reported. It uses LHC proton-proton collision data at a centre-of-mass energy s=13 $$\sqrt{s}=13$$ TeV with an integrated luminosity of 36.1 fb−1 collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from b-quarks. To increase the sensitivity, the sample is divided into subsamples based on the presence or absence of electrons or muons. No excess is found above the predicted background. For χ˜10 $${\tilde{\chi}}_1^0$$ masses below approximately 300 GeV, gluino masses of less than 1.97 (1.92) TeV are excluded at 95% confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided. These results improve upon the exclusion limits obtained with the 3.2 fb−1 of data collected in 2015