arXiv subjects

A. Kumar

Publications and source records attributed to A. Kumar.

At least 73 records · Page 4Linked to original sources

arXiv2024

Integrated modeling of RF-Induced Tungsten Erosion at ICRH Antenna Structures in the WEST Tokamak

This paper introduces STRIPE (Simulated Transport of RF Impurity Production and Emission), an advanced modeling framework designed to analyze material erosion and the global transport of eroded impurities originating from radio-frequency (RF) antenna structures in magnetic confinement fusion devices. STRIPE integrates multiple computational tools, each addressing different levels of physics fidelity: SolEdge3x for scrape-off-layer plasma profiles, COMSOL for 3D RF rectified voltage fields, RustBCA code for erosion yields and surface interactions, and GITR for 3D ion energy-angle distributions and global impurity transport. The framework is applied to an ion cyclotron RF heated, L-mode discharge #57877 in the WEST Tokamak, where it predicts a tenfold increase in tungsten erosion at RF antenna limiters under RF-sheath rectification conditions, compared to cases with only a thermal sheath. Highly charged oxygen ions (O6+ and higher) emerge as dominant contributors to tungsten sputtering at the antenna limiters. To verify model accuracy, a synthetic diagnostic tool based on inverse photon efficiency or S/XB coefficients from the ColRadPy-collisional radiative model enables direct comparisons between simulation results and experimental spectroscopic data. Model predictions, assuming plasma composition of 1% oxygen and 99% deuterium, align closely with measured neutral tungsten (W-I) spectroscopic data for the discharge #57877, validating the framework's accuracy. Currently, the STRIPE framework is being extended to investigate plasma-material interactions in other RF-heated linear and toroidal devices, offering valuable insights for RF antenna design, impurity control, and performance optimization in future fusion reactors.

physics.plasm-ph↗

arXiv2024

Enhancing multiscale simulations for spark plasma sintering with a novel Direct FE$^2$ framework

The spark plasma sintering (SPS) process, a key technology for advanced material manufacturing, demands accurate and efficient simulation tools to capture the complex electro-thermal-mechanical interactions inherent in powder materials. This paper introduces a novel concurrent multiscale framework employing the Direct FE$^2$ method, designed for fully coupled electro-thermal-mechanical simulations in SPS. The model integrates microscale powder characteristics into a macroscopic analysis through multi-point constraints within a 3D finite element (FE) solver. This approach enables, for the first time, a direct and seamless coupling of micro- and macroscale physical phenomena, enhancing both accuracy and computational efficiency by capturing interactions across scales. The proposed method achieves a temperature and displacement error margin below 1% compared to full FE analysis while reducing computational degrees of freedom by a factor of 8, resulting in a 70-fold acceleration in simulation time. Additionally, the methodology provides robust flexibility in accommodating diverse powder morphologies without compromising precision, enabling degree-of-freedom reductions of up to 44 times. This combination of enhanced efficiency and accuracy establishes the proposed Direct FE$^2$ approach as a highly effective tool for realistic and scalable simulations of the SPS process.

physics.comp-ph↗

arXiv2024

Uncertainty propagation and covariance analysis of 181Ta(n,γ)182Ta nuclear reaction

The neutron capture cross-section for the $^{181}$Ta(n,$γ$)$^{182}$Ta reaction has been experimentally measured at the neutron energies 0.53 and 1.05 MeV using off-line $γ$-ray spectrometry. $^{115}$In(n,n'$γ$)$^{115m}$In is used as a reference monitor reaction cross-section. The neutron was produced via the $^{7}$Li(p,n)$^{7}$Be reaction. The present study measures the cross-sections with their uncertainties and correlation matrix. The self-attenuation process, $γ$-ray correction factor, and low background neutron energy contribution have been calculated. The measured neutron spectrum averaged cross-sections of $^{181}$Ta(n,$γ$)$^{182}$Ta are discussed and compared with the existing data from the EXFOR database and also with the ENDF/B-VIII.0, TENDL-2019, JENDL-5, JEFF-3.3 evaluated data libraries.

nucl-ex↗

arXiv2024

Search for $CP$-Violating Neutrino Nonstandard Interactions with the NOvA Experiment

This Letter reports a search for charge-parity ($CP$) symmetry violating nonstandard interactions (NSI) of neutrinos with matter using the NOvA Experiment, and examines their effects on the determination of the standard oscillation parameters. Data from $ν_μ(\barν_μ)\rightarrowν_μ(\barν_μ)$ and $ν_μ(\barν_μ)\rightarrowν_{e}(\barν_{e})$ oscillation channels are used to measure the effect of the NSI parameters $\varepsilon_{eμ}$ and $\varepsilon_{eτ}$. With 90% CL the magnitudes of the NSI couplings are constrained to be $|\varepsilon_{eμ}| \, \lesssim 0.3$ and $|\varepsilon_{eτ}| \, \lesssim 0.4$. A degeneracy at $|\varepsilon_{eτ}| \, \approx 1.8$ is reported, and we observe that the presence of NSI limits sensitivity to the standard $CP$ phase $δ_{\tiny\text{CP}}$.

hep-ex↗

arXiv2024

Measurement of the double-differential cross section of muon-neutrino charged-current interactions with low hadronic energy in the NOvA Near Detector

The NOvA collaboration reports cross-section measurements for $ν_μ$ charged-current interactions with low hadronic energy (maximum kinetic energy of 250 MeV for protons and 175 MeV for pions) in the NOvA Near Detector. The results are presented as a double-differential cross section as a function of the direct observables of the final-state muon kinematics. Results are also presented as a single-differential cross section as a function of the derived square of the four-momentum transfer, $Q^{2}$, and as a function of the derived neutrino energy. The data correspond to an accumulated 8.09$\times10^{20}$ protons-on-target (POT) in the neutrino mode of the NuMI beam, with a narrow band of neutrino energies peaked at 1.8 GeV. The analysis provides a sample of neutrino-nucleus interactions with an enhanced fraction of quasi-elastic and two-particle-two-hole (2p2h) interactions. This enhancement allows quantitative comparisons with various nuclear models. We find strong disagreement between data and theory-based models in various regions of the muon kinematic phase space, especially in the forward muon direction.

hep-ex↗

arXiv2024

Hard jet substructure in a multistage approach

We present predictions and postdictions for a wide variety of hard jet-substructure observables using a multistage model within the JETSCAPE framework. The details of the multistage model and the various parameter choices are described in [A. Kumar et al., arXiv:2204.01163]. A novel feature of this model is the presence of two stages of jet modification: a high virtuality phase [modeled using the modular all twist transverse-scattering elastic-drag and radiation model (MATTER)], where modified coherence effects diminish medium-induced radiation, and a lower virtuality phase [modeled using the linear Boltzmann transport model (LBT)], where parton splits are fully resolved by the medium as they endure multiple scattering induced energy loss. Energy-loss calculations are carried out on event-by-event viscous fluid dynamic backgrounds constrained by experimental data. The uniform and consistent descriptions of multiple experimental observables demonstrate the essential role of modified coherence effects and the multistage modeling of jet evolution. Using the best choice of parameters from [A. Kumar et al., arXiv:2204.01163], and with no further tuning, we present calculations for the medium modified jet fragmentation function, the groomed jet momentum fraction $z_g$ and angular separation $r_g$ distributions, as well as the nuclear modification factor of groomed jets. These calculations provide accurate descriptions of published data from experiments at the Large Hadron Collider. Furthermore, we provide predictions from the multistage model for future measurements at the BNL Relativistic Heavy Ion Collider.

hep-ph↗

arXiv2024

SN 2023tsz: A helium-interaction driven supernova in a very low-mass galaxy

SN 2023tsz is a Type Ibn supernova (SNe Ibn) discovered in an extremely low-mass host. SNe Ibn are an uncommon subtype of stripped-envelope core-collapse SNe. They are characterised by narrow helium emission lines in their spectra and are believed to originate from the collapse of massive Wolf-Rayet (WR) stars, though their progenitor systems still remain poorly understood. In terms of energetics and spectrophotometric evolution, SN 2023tsz is largely a typical example of the class, although line profile asymmetries in the nebular phase are seen, which may indicate the presence of dust formation or unshocked circumstellar material. Intriguingly, SN 2023tsz is located in an extraordinarily low-mass host galaxy that is in the 2nd percentile for SESN host masses and star formation rates (SFR). The host has a radius of 1.0 kpc, a $g$-band absolute magnitude of $-12.73$, and an estimated metallicity of $\log(Z_{*}/Z_{\odot}$) = $-1.56$. The SFR and metallicity of the host galaxy raise questions about the progenitor of SN 2023tsz. The low SFR suggests that a star with sufficient mass to evolve into a WR would be uncommon in this galaxy. Further, the very low-metallicity is a challenge for single stellar evolution to enable H and He stripping of the progenitor and produce a SN Ibn explosion. The host galaxy of SN 2023tsz adds another piece to the ongoing puzzle of SNe Ibn progenitors, and demonstrates that they can occur in hosts too faint to be observed in contemporary sky surveys at a more typical SN Ibn redshift.

astro-ph.HE↗

arXiv2024

Unravelling the asphericities in the explosion and multi-faceted circumstellar matter of SN 2023ixf

We present a detailed investigation of photometric, spectroscopic, and polarimetric observations of the Type II SN 2023ixf. Earlier studies have provided compelling evidence for a delayed shock breakout from a confined dense circumstellar matter (CSM) enveloping the progenitor star. The temporal evolution of polarization in SN~2023ixf revealed three distinct peaks in polarization evolution at 1.4 d, 6.4 d, and 79.2 d, indicating an asymmetric dense CSM, an aspherical shock front and clumpiness in the low-density extended CSM, and an aspherical inner ejecta/He-core. SN 2023ixf displayed two dominant axes, one along the CSM-outer ejecta and the other along the inner ejecta/He-core, showcasing the independent origin of asymmetry in the early and late evolution. The argument for an aspherical shock front is further strengthened by the presence of a high-velocity broad absorption feature in the blue wing of the Balmer features in addition to the P-Cygni absorption post 16 d. Hydrodynamical light curve modeling indicated a progenitor of 10 solar mass with a radius of 470 solar radii and explosion energy of 2e51 erg, along with 0.06 solar mass of 56-Ni, though these properties are not unique due to modeling degeneracies. The modeling also indicated a two-zone CSM: a confined dense CSM extending up to 5e14 cm, with a mass-loss rate of 1e-2 solar mass per year, and an extended CSM spanning from 5e14 cm to at least 1e16cm with a mass-loss rate of 1e-4 solar mass per year, both assuming a wind-velocity of 10 km/s. The early nebular phase observations display an axisymmetric line profile of [OI], red-ward attenuation of the emission of Halpha post 125 days, and flattening in the Ks-band, marking the onset of dust formation.

astro-ph.HE↗

arXiv2024

Bayesian Inference analysis of jet quenching using inclusive jet and hadron suppression measurements

The JETSCAPE Collaboration reports a new determination of the jet transport parameter $\hat{q}$ in the Quark-Gluon Plasma (QGP) using Bayesian Inference, incorporating all available inclusive hadron and jet yield suppression data measured in heavy-ion collisions at RHIC and the LHC. This multi-observable analysis extends the previously published JETSCAPE Bayesian Inference determination of $\hat{q}$, which was based solely on a selection of inclusive hadron suppression data. JETSCAPE is a modular framework incorporating detailed dynamical models of QGP formation and evolution, and jet propagation and interaction in the QGP. Virtuality-dependent partonic energy loss in the QGP is modeled as a thermalized weakly-coupled plasma, with parameters determined from Bayesian calibration using soft-sector observables. This Bayesian calibration of $\hat{q}$ utilizes Active Learning, a machine--learning approach, for efficient exploitation of computing resources. The experimental data included in this analysis span a broad range in collision energy and centrality, and in transverse momentum. In order to explore the systematic dependence of the extracted parameter posterior distributions, several different calibrations are reported, based on combined jet and hadron data; on jet or hadron data separately; and on restricted kinematic or centrality ranges of the jet and hadron data. Tension is observed in comparison of these variations, providing new insights into the physics of jet transport in the QGP and its theoretical formulation.

hep-ph↗

arXiv2024

Successive ferroelectric orders and magnetoelectric coupling without long-range magnetic order in highly frustrated pyrochlore compounds: Sm$_2$Ti$_{2-x}$V$_x$O$_7$

Sm$_2$Ti$_2$O$_7$, a member of rare-earth titanate pyrochlores, exhibits dipolar-octupolar antiferromagnetism below $T_N$ = 0.35 K. We observed two ferroelectric transitions at 182 ($T_{FE1}$) and 52 K ($T_{FE2}$), significantly higher than $T_N$ for Sm$_2$Ti$_{2-x}$V$_x$O$_7$ ($x$ = 0, 0.1). Although the ferroelectric transition temperatures remain unchanged, the polarization value decreases considerably with V doping. A structural transition to a polar $R3m$ rhombohedral phase from the cubic $Fd\bar{3}m$ structure occurs at $T_{FE1}$, involving a distortion in the pyochlore lattice. Remarkably, significant linear magnetoelectric coupling is observed in both compounds, with further enhancement of magnetoelectric coupling due to magnetic V doping. The existence of magnetoelectric coupling without long-range magnetic order in a frustrated pyrochlore system could enable the tailoring of magnetoelectric coupling properties, which can be further fine-tuned through V doping. The emergence of ferroelectricity in a frustrated magnetic system introduces an intriguing aspect to these compounds and paves the way for developing ferroelectric order driven by the alleviation of magnetic frustration in pyrochlore systems.

cond-mat.mtrl-sci↗

arXiv2024

$\textit{Kilonova Seekers}$: the GOTO project for real-time citizen science in time-domain astrophysics

Time-domain astrophysics continues to grow rapidly, with the inception of new surveys drastically increasing data volumes. Democratised, distributed approaches to training sets for machine learning classifiers are crucial to make the most of this torrent of discovery -- with citizen science approaches proving effective at meeting these requirements. In this paper, we describe the creation of and the initial results from the $\textit{Kilonova Seekers}$ citizen science project, built to find transient phenomena from the GOTO telescopes in near real-time. $\textit{Kilonova Seekers}$ launched in July 2023 and received over 600,000 classifications from approximately 2,000 volunteers over the course of the LIGO-Virgo-KAGRA O4a observing run. During this time, the project has yielded 20 discoveries, generated a `gold-standard' training set of 17,682 detections for augmenting deep-learned classifiers, and measured the performance and biases of Zooniverse volunteers on real-bogus classification. This project will continue throughout the lifetime of GOTO, pushing candidates at ever-greater cadence, and directly facilitate the next-generation classification algorithms currently in development.

astro-ph.IM↗

arXiv2024

A soft-hard framework with exact four momentum conservation for small systems

A new framework, called x-scape, for the combined study of both hard and soft transverse momentum sectors in high energy proton-proton ($p$-$p$) and proton-nucleus ($p$-$A$) collisions is set up. A dynamical initial state is set up using the 3d-Glauber model with transverse locations of hotspots within each incoming nucleon. A hard scattering that emanates from two colliding hotspots is carried out using the Pythia generator. Initial state radiation from the incoming hard partons is carried out in a new module called I-matter, which includes the longitudinal location of initial splits. The energy-momentum of both the initial hard partons and their associated beam remnants is removed from the hot spots, depleting the energy-momentum available for the formation of the bulk medium. Outgoing showers are simulated using the matter generator, and results are presented for both cases, allowing for and not allowing for energy loss. First comparisons between this hard-soft model and single inclusive hadron and jet data from $p$-$p$ and minimum bias $p$-$Pb$ collisions are presented. Single hadron spectra in $p$-$p$ are used to carry out a limited (in number of parameters) Bayesian calibration of the model. Fair comparisons with data are indicative of the utility of this new framework. Theoretical studies of the correlation between jet $p_T$ and event activity at mid and forward rapidity are carried out.

hep-ph↗

arXiv2024

The Belle II Detector Upgrades Framework Conceptual Design Report

We describe the planned near-term and potential longer-term upgrades of the Belle II detector at the SuperKEKB electron-positron collider operating at the KEK laboratory in Tsukuba, Japan. These upgrades will allow increasingly sensitive searches for possible new physics beyond the Standard Model in flavor, tau, electroweak and dark sector physics that are both complementary to and competitive with the LHC and other experiments.

hep-ex↗

arXiv2024

Optical heterodyne microscopy of operating spin Hall nano-oscillator arrays

Optical heterodyne detection is a powerful technique for characterizing a wide range of physical excitations. Here, we use two types of optical heterodyne detection techniques (fundamental and parametric pumping) to microscopically characterize the high-frequency auto-oscillations of single and multiple nano-constriction spin Hall nano-oscillators (SHNOs). To validate the technique and demonstrate its robustness, we study SHNOs made from two different material stacks, NiFe/Pt and W/CoFeB/MgO, and investigate the influence of both the RF injection power and the laser power on the measurements, comparing the optical results to conventional electrical measurements. To demonstrate the key features of direct, non-invasive, submicron, spatial, and phase-resolved characterization of the SHNO magnetodynamics, we map out the auto-oscillation magnitude and phase of two phase-binarized SHNOs used in Ising Machines. This proof-of-concept platform establishes a strong foundation for further extensions, contributing to the ongoing development of crucial characterization techniques for emerging computing technologies based on spintronics devices

cond-mat.mes-hall↗

arXiv2024

Dark Matter Influence on Quarkyonic Stars: A Relativistic Mean Field Analysis

The formulation of quarkyonic matter consists of treating both quarks and nucleons as quasi-particles, where a cross-over transition occurs between the two phases. This work is based upon some of the early ideas of quark matter. It can satisfy the different observational constraints on the neutron star (NS), such as its maximum mass and the canonical radius. In addition, we put an extra component inside the NS known as Dark Matter (DM) because it is trapped due to its immense gravitational potential. In this work, we explore the impact of fermionic DM on the structure of the NS. The equation of state (EOS) is derived for the NS with the quarkyonic matter by assuming that nucleons and quarks are in equilibrium, followed by the relativistic mean-field (RMF) formalism. The recently modeled two parameterizations, such as G3 and IOPB-I, are taken to calculate the various macroscopic properties of the NS. The three unknown parameters such as the transition density ($n_t$), the QCD confinement scale ($Λ_{\rm sc}$), and the DM Fermi momentum ($k_f^{\rm DM}$) are varied to obtain the NS properties. The quarkyonic matter stiffens the EOS while DM softens it. The mutual combination provides us with good theoretical predictions for the magnitude of macroscopic properties consistent with the different observational results. Also, one can estimate the parameters of the DM admixed quarkyonic star with different statistical analyses, which can be further used to explore the other properties of the quarkyonic star.

astro-ph.HE↗

arXiv2024

Expanding neutrino oscillation parameter measurements in NOvA using a Bayesian approach

NOvA is a long-baseline neutrino oscillation experiment that measures oscillations in charged-current $ν_μ \rightarrow ν_μ$ (disappearance) and $ν_μ \rightarrow ν_{e}$ (appearance) channels, and their antineutrino counterparts, using neutrinos of energies around 2 GeV over a distance of 810 km. In this work we reanalyze the dataset first examined in our previous paper [Phys. Rev. D 106, 032004 (2022)] using an alternative statistical approach based on Bayesian Markov Chain Monte Carlo. We measure oscillation parameters consistent with the previous results. We also extend our inferences to include the first NOvA measurements of the reactor mixing angle $θ_{13}$ and the Jarlskog invariant. We use these results to quantify the strength of our inferences about CP violation, as well as to examine the effects of constraints from short-baseline measurements of $θ_{13}$ using antineutrinos from nuclear reactors when making NOvA measurements of $θ_{23}$. Our long-baseline measurement of $θ_{13}$ is also shown to be consistent with the reactor measurements, supporting the general applicability and robustness of the PMNS framework for neutrino oscillations.

hep-ex↗

arXiv2024

Investigation of reaction and $α$ production cross sections with $^9$Be projectile

In order to investigate the contribution of $α$ production in the reaction cross sections, measurements of elastic scattering and inclusive $α$ particle angular distributions have been carried out with the $^9$Be projectile on $^{89}$Y, $^{124}$Sn, $^{159}$Tb, $^{198}$Pt, and $^{209}$Bi targets over a wide angular range at energies near the Coulomb barrier. The measured elastic scattering angular distributions were fitted with optical model calculations, and reaction cross sections were extracted. The same data were also analysed using both global optical model potentials (Global OMP) and microscopic S$\tilde{a}$o Paulo potentials (SPP), to obtain the reaction cross sections. The data available in the literature for $^9$Be projectile includes the elastic scattering angular distributions, $α$ production cross sections, and complete fusion cross sections on these and other targets at several energies are also utilised for comparative studies. The reaction cross section extracted from the three potentials (Best Fit, Global OMP and SPP) are in reasonable agreement for all the targets except for the energies below the barrier where the results from SPP deviate by 30-50 \%. Inclusive $α$ particle production cross sections were also extracted by integrating the $α$ particle angular distributions. The present data and data available from literature of reaction and $α$-particle production cross sections were utilised to make systematic studies. Systematics of reaction and $α$-particle production cross sections revealed their universal behaviour.

nucl-ex↗

arXiv2024

Photon-triggered jets as probes of multi-stage jet modification

Prompt photons are created in the early stages of heavy ion collisions and traverse the QGP medium without any interaction. Therefore, photon-triggered jets can be used to study the jet quenching in the QGP medium. In this work, photon-triggered jets are studied through different jet and jet substructure observables for different collision systems and energies using the JETSCAPE framework. Since the multistage evolution used in the JETSCAPE framework is adequate to describe a wide range of experimental observables simultaneously using the same parameter tune, we use the same parameters tuned for jet and leading hadron studies. The same isolation criteria used in the experimental analysis are used to identify prompt photons for better comparison. For the first time, high-accuracy JETSCAPE results are compared with multi-energy LHC and RHIC measurements to better understand the deviations observed in prior studies. This study highlights the importance of multistage evolution for the simultaneous description of experimental observables through different collision systems and energies using a single parameter tune.

nucl-th↗