Hard Interactions Research Articles

N -jettiness subtractions for gg→H at subleading power

$N$-jettiness subtractions provide a general approach for performing fully-differential next-to-next-to-leading order (NNLO) calculations. Since they are based on the physical resolution variable $N$-jettiness, $\mathcal{T}_N$, subleading power corrections in $\tau=\mathcal{T}_N/Q$, with $Q$ a hard interaction scale, can also be systematically computed. We study the structure of power corrections for $0$-jettiness, $\mathcal{T}_0$, for the $gg\to H$ process. Using the soft-collinear effective theory we analytically compute the leading power corrections $\alpha_s \tau \ln\tau$ and $\alpha_s^2 \tau \ln^3\tau$ (finding partial agreement with a previous result in the literature), and perform a detailed numerical study of the power corrections in the $gg$, $gq$, and $q\bar q$ channels. This includes a numerical extraction of the $\alpha_s\tau$ and $\alpha_s^2 \tau \ln^2\tau$ corrections, and a study of the dependence on the $\mathcal{T}_0$ definition. Including such power suppressed logarithms significantly reduces the size of missing power corrections, and hence improves the numerical efficiency of the subtraction method. Having a more detailed understanding of the power corrections for both $q\bar q$ and $gg$ initiated processes also provides insight into their universality, and hence their behavior in more complicated processes where they have not yet been analytically calculated.

Three-body correlations and conditional forces in suspensions of active hard disks.

Self-propelled Brownian particles show rich out-of-equilibrium physics, for instance, the motility-induced phase separation (MIPS). While decades of studying the structure of liquids have established a deep understanding of passive systems, not much is known about correlations in active suspensions. In this work we derive an approximate analytic theory for three-body correlations and forces in systems of active Brownian disks starting from the many-body Smoluchowski equation. We use our theory to predict the conditional forces that act on a tagged particle and their dependence on the propulsion speed of self-propelled disks. We identify preferred directions of these forces in relation to the direction of propulsion and the positions of the surrounding particles. We further relate our theory to the effective swimming speed of the active disks, which is relevant for the physics of MIPS. To test and validate our theory, we additionally run particle-resolved computer simulations, for which we explicitly calculate the three-body forces. In this context, we discuss the modeling of active Brownian swimmers with nearly hard interaction potentials. We find very good agreement between our simulations and numerical solutions of our theory, especially for the nonequilibrium pair-distribution function. For our analytical results, we carefully discuss their range of validity in the context of the different levels of approximation we applied. This discussion allows us to study the individual contribution of particles to three-body forces and to the emerging structure. Thus, our work sheds light on the collective behavior, provides the basis for further studies of correlations in active suspensions, and makes a step towards an emerging liquid state theory.

An investigation of tool and hard particle interaction in nanoscale cutting of copper beryllium

The present study adopts molecular dynamics simulation to analyze tool and hard particle interaction in the nano-cutting of copper beryllium (CuBe). The presence of hard particles in workpiece materials affects the cutting process in terms of surface generation, material deformation, and tool wear mechanisms. Therefore, in this simulation study, three cases are considered based on the distinct size and location of hard particle in the base material. Results show that Be particle, when encountered by a diamond tool at the cutting plane, is suppressed and subsequently is projected from the generated surface with a dig left behind the particle. Furthermore, particle removal or suppression depends on its size and location with respect to the cutting plane. Shockley partial dislocations are noticed to be dominant in plastically deforming the workpiece material. Moreover, it is not only the workpiece surface which gets affected; hard particle also deteriorates the tool by causing wear to its cutting edge. The cutting process – in terms of surface generation, material deformation, and tool edge condition – is found to be dependent on the crystallographic planes of the base material.

Sequestering Ability of Oligophosphate Ligands toward Al3+ in Aqueous Solution

The interactions between Al3+ and ortho-phosphate (PO43–), pyro-phosphate (P2O74–, PP), tripolyphosphate (P3O105–, TPP) and hexa-metaphosphate (P6O186–, HMP) in aqueous solution have been studied. Formation constants, speciation models, and possible structures for the complexes formed are discussed on the basis of potentiometric, calorimetric, 31P–{1H} NMR, laser desorption mass spectrometric (LD MS) and MS/MS results. 31P–{1H} NMR experiments for Al3+–TPP system are in agreement with the speciation model drawn from analysis of potentiometric titration data, suggesting that TPP binds to Al3+ with two adjacent phosphate oxygen atoms, forming a six-membered ring. LD MS has provided identification and structural information for Al3+–PP, −TPP, and −HMP complexes which supports the reliability of speciation models proposed on the basis of the potentiometric data. Moreover, MS/MS spectra obtained from [ML]+ precursor ion show that the ion species involve linear HMP isomers and that two adjacent terminal phosphate groups probably bind Al3+. Standard enthalpy change values were obtained by titration calorimetry; all are endothermic, as is typical for hard–hard interactions. The dependence of formation constants on ionic strength over the range I = 0.1–1 mol kg–1 is also reported. The sequestering ability of all the ligands under study toward Al3+ was also evaluated by the empirical parameter pL0.5.

Can the triple-parton scattering be observed in open charm meson production at the LHC?

We investigate whether the triple-parton scattering effects can be observed in open charm production in proton–proton collisions at the LHC. We use so-called factorized Ansatz for calculations of hard multiple-parton interactions. The numerical results for each parton interaction are obtained within the kT-factorization approach. Predictions for one, two and three cc¯ pairs production are given for s=7 TeV and s=13 TeV. Quite large cross sections, of the order of milibarns, for the triple-parton scattering mechanism are obtained. We suggest a measurement of three D0 or three D0¯ mesons by the LHCb Collaboration. Confronting our results with recent LHCb experimental data for single and double D0 (or D0¯) meson production we present our predictions for triple meson final state: D0D0D0 or D0¯D0¯D0¯. We present cross sections for the LHCb fiducial volume as well as distributions for D0 meson transverse momentum and three-D0 meson invariant mass. The predicted visible cross sections, including the detector acceptance, hadronization effects and c→D0 branching fraction, is of the order of a few nanobarns. The counting rates including D0→K−π+ branching fractions are given for known or expected integrated luminosities.

Anomalous transport in heterogeneous media

The diffusion dynamics of particles in heterogeneous media is studied using particle-based simulation techniques. A special focus is placed on systems where the transport of particles at long times exhibits anomalies such as subdiffusive or superdiffusive behavior. First, a two-dimensional model system is considered containing gas particles (tracers) that diffuse through a random arrangement of pinned, disk-shaped particles. This system is similar to a classical Lorentz gas. However, different from the original Lorentz model, soft instead of hard interactions are considered and we also discuss the case where the tracer particles interact with each other. We show that the modification from hard to soft interactions strongly affects anomalous-diffusive transport at high obstacle densities. Second, non-linear active micro-rheology in a glass-forming binary Yukawa mixture is investigated, pulling single particles through a deeply supercooled state by applying a constant force. Here, we observe superdiffusion in force direction and analyze its origin. Finally, we consider the Brownian dynamics of a particle which is pulled through a two-dimensional random force field. We discuss the similarities of this model with the Lorentz gas as well as active micro-rheology in glass-forming systems.

Explicit Incorporation of Hard and Soft Protein-Protein Interactions into Models for Crowding Effects in Protein Mixtures. 2. Effects of Varying Hard and Soft Interactions upon Prototypical Chemical Equilibria.

Previously derived approximate analytical relations for the activity coefficient of each solute in a mixture of up to three spherical solutes in a highly nonideal solution interacting via square well potentials of mean force (Hoppe, T.; Minton, A. P. J Phys Chem B. 2016, 120, 11866-11872) were used to explore the effect of heterogeneity in volume occupancy and intermolecular interactions upon prototypical schemes representing solubility, partitioning, conformational isomerization, and self-association in crowded solutions. Results generally indicate that all of the equilibria explored are exquisitely sensitive to variations in both volume occupancy and intermolecular interaction and have important implications for the design and execution of more detailed simulations of complex media.

Subleading power corrections for N -jettiness subtractions

The $N$-jettiness observable $\mathcal{T}_N$ provides a way of describing the leading singular behavior of the $N$-jet cross section in the $\tau =\mathcal{T}_N/Q \to 0$ limit, where $Q$ is a hard interaction scale. We consider subleading power corrections in the $\tau \ll 1$ expansion, and employ soft-collinear effective theory to obtain analytic results for the dominant $\alpha_s \tau \ln\tau$ and $\alpha_s^2 \tau\ln^3\tau$ subleading terms for thrust in $e^+e^-$ collisions and $0$-jettiness for $q\bar q$-initiated Drell-Yan-like processes at hadron colliders. These results can be used to significantly improve the numerical accuracy and stability of the $N$-jettiness subtraction technique for performing fixed-order calculations at NLO and NNLO. They reduce the size of missing power corrections in the subtractions by an order of magnitude. We also point out that the precise definition of $N$-jettiness has an important impact on the size of the power corrections and thus the numerical accuracy of the subtractions. The sometimes employed definition of $N$-jettiness in the hadronic center-of-mass frame suffers from power corrections that grow exponentially with rapidity, causing the power expansion to deteriorate away from central rapidity. This degradation does not occur for the original $N$-jettiness definition, which explicitly accounts for the boost of the Born process relative to the frame of the hadronic collision, and has a well-behaved power expansion throughout the entire phase space. Integrated over rapidity, using this $N$-jettiness definition in the subtractions yields another order of magnitude improvement compared to employing the hadronic-frame definition.

Decision making of university teacher: motivating and inspiring students versus too high criticality and demands of teacher

Profession of a university teacher is extremely difficult and responsible. On the one hand, teachers are faced with a sense of high social responsibility for their work, and on the other hand, they need a high motivation for their work, often associated with a great deal of altruism and a sense of belonging with their colleagues and students. Based on the questionnaire survey, conducted on a sample of 357 students of University of Žilina, students deemed the skills to motivate and inspire students as essential attribute of a great university teacher. On the contrary, excessive criticism and demands of teachers in relation to students (which basically represents the mirror – reflection – of the teacher’s perceived responsibility) is considered by students as inappropriate, undesirable attribute of teacher. Based on analysis, synthesis, comparison and generalization of theoretical knowledge and evaluation of the survey results, the aim of paper is to focus attention on two academic top- attributes of teacher: (a) the effort to instill in students a high responsibility for their own decisions/outcomes; (b) the skills to motivate and inspire students to expected results. To master a harmonized mixture of these two elements represents a difficult decision problem of many university teachers. Therefore, conclusion of the paper gives a simple qualitative model of decision-making that can simplify teacher’s decision-making regarding the efforts to be popular among the students for easy tasks and/versus be respected in motivating-and-inspiring approach based on precise and hard work and interaction of both the student and the teacher.Â

The cage effect in systems of hard spheres.

The cage effect is generally invoked when discussing the delay in the decay of time correlation functions of dense fluids. In an attempt to examine the role of caging more closely, we consider the spread of the displacement distributions of Brownian particles. These distributions are necessarily biased by the presence of neighbouring particles. Accommodation of this bias by those neighbours conserves the displacement distribution locally and presents a collective mechanism for exploring configuration space that is more efficient than the intrinsic Brownian motion. Caging of some particles incurs, through the impost of global conservation of the displacement distribution, a delayed, non-local collective process. This non-locality compromises the efficiency with which configuration space is explored. Both collective mechanisms incur delay or stretching of time correlation functions, in particular the particle number and flux densities. This paper identifies and distinguishes these mechanisms in existing data from experiments and computer simulations on systems of particles with hard sphere interactions.

Monte Carlo updates on color coherence at 7 TeV

An important feature of quantum chromodynamics (QCD) is the effects of color coherence. Color coherence manifests as a color connection between the outgoing partons produced in hard interactions, leading to a suppression of particle radiation between the two leading jets of a three-jet event. The angular distribution of the third jet around the second jet was measured in e−e+ and pp collisions. The latest result for the color coherence effect is from the Compact Muon Solenoid (CMS) experiment with a center-of-mass energy of 7 TeV. At the time, none of the Monte Carlo (MC) models was shown to be able to describe the data successfully. This study shows the results of the latest MC models describing the color coherence effect and compares them to the CMS 7 TeV data. The latest MC models are able to describe the CMS data much more satisfactorily.

Wall depletion length of a channel-confined polymer.

Numerous experiments have taken advantage of DNA as a model system to test theories for a channel-confined polymer. A tacit assumption in analyzing these data is the existence of a well-defined depletion length characterizing DNA-wall interactions such that the experimental system (a polyelectrolyte in a channel with charged walls) can be mapped to the theoretical model (a neutral polymer with hard walls). We test this assumption using pruned-enriched Rosenbluth method (PERM) simulations of a DNA-like semiflexible polymer confined in a tube. The polymer-wall interactions are modeled by augmenting a hard wall interaction with an exponentially decaying, repulsive soft potential. The free energy, mean span, and variance in the mean span obtained in the presence of a soft wall potential are compared to equivalent simulations in the absence of the soft wall potential to determine the depletion length. We find that the mean span and variance about the mean span have the same depletion length for all soft potentials we tested. In contrast, the depletion length for the confinement free energy approaches that for the mean span only when depletion length no longer depends on channel size. The results have implications for the interpretation of DNA confinement experiments under low ionic strengths.

Use of Two-Body Correlated Basis Functions with van der Waals Interaction to Study the Shape-Independent Approximation for a Large Number of Trapped Interacting Bosons

We study the ground state and the low-lying excitations of a trapped Bose gas in an isotropic harmonic potential for very small ($\sim 3$) to very large ($\sim 10^7$) particle numbers. We use the correlated two-body basis functions and the shape-dependent van der Waals interaction in our many-body calculations. We present an exhaustive study of the effect of inter-atomic correlations and the accuracy of the mean-field equations considering a wide range of particle numbers. We calculate the ground state energy and the one-body density for different values of the van der Waals parameter $C_{6}$. We compare our results with those of the modified Gross-Pitaevskii results, the correlated Hartree hypernetted-chain equations (which also utilize the two-body correlated basis functions), as well as of the Diffusion Monte Carlo for hard sphere interactions. We observe the effect of the attractive tail of the van der Waals potential in the calculations of the one-body density over the truly repulsive zero-range potential as used in the Gross-Pitaevskii equation and discuss the finite-size effects. We also present the low-lying collective excitations which are well described by a hydrodynamic model in the large particle limit.

Does the configurational entropy of polydisperse particles exist?

Classical particle systems characterized by continuous size polydispersity, such as colloidal materials, are not straightforwardly described using statistical mechanics, since fundamental issues may arise from particle distinguishability. Because the mixing entropy in such systems is divergent in the thermodynamic limit, we show that the configurational entropy estimated from standard computational approaches to characterize glassy states also diverges. This reasoning would suggest that polydisperse materials cannot undergo a glass transition, in contradiction to experiments. We explain that this argument stems from the confusion between configurations in phase space and states defined by free energy minima, and propose a simple method to compute a finite and physically meaningful configurational entropy in continuously polydisperse systems. Physically, the proposed approach relies on an effective description of the system as an M*-component system with a finite M*, for which finite mixing and configurational entropies are obtained. We show how to directly determine M* from computer simulations in a range of glass-forming models with different size polydispersities, characterized by hard and soft interparticle interactions, and by additive and non-additive interactions. Our approach provides consistent results in all cases and demonstrates that the configurational entropy of polydisperse system exists, is finite, and can be quantitatively estimated.

Dimer crystallization of chiral proteoids.

Proteins can self-assemble into a variety of exquisitely organized structures through hierarchical reaction pathways. To examine how different core shapes of proteins and entropy combine to influence self-assembly, we create systems of lithographically fabricated proteomimetic colloids, or 'proteoids', and explore how Brownian monolayers of mobile proteoids, which have hard interactions, self-assemble as they are slowly crowded. Remarkably, chiral C-shaped proteoids having circular heads on only one side form enantiopure lock-and-key chiral dimers; these dimers have corrugated, shape-complementary perimeters, so they, in turn, form lock-and-key arrangements into chiral dimer crystals. Time-lapse video microscopy reveals the expulsion of monomers from the growing dimer crystals through tautomerization translocation reactions which expedite the crystallization kinetics. By lithographically mutating proteoids, we also tune the types and structures of the resulting dimer crystals. Thus, rational design of sub-particle features in hard-core colloidal shapes can be used to sterically select desired self-assembly pathways without introducing any site-specific attractions, thereby generating a striking degree of hierarchical self-ordering, reminiscent of protein crystallization.

Determination of the local density of polydisperse nanoparticle assemblies.

Quantitative characterization of the average structure of dense nanoparticle assemblies and aggregates is a common problem in nanoscience. Small-angle scattering is a suitable technique, but it is usually limited to not too big assemblies due to the limited experimental range, low concentrations to avoid interactions, and monodispersity to keep calculations tractable. In the present paper, a straightforward analysis of the generally available scattered intensity - even for large assemblies, at high concentrations - is detailed, providing information on the local volume fraction of polydisperse particles with hard sphere interactions. It is based on the identical local structure of infinite homogeneous nanoparticle assemblies and their subsets forming finite-sized clusters. This approach is extended to polydispersity, using Monte-Carlo simulations of hard and moderately sticky hard spheres. As a result, a simple relationship between the observed structure factor minimum - termed the correlation hole - and the average local volume fraction κ on the scale of neighboring particles is proposed and validated through independent aggregate simulations. This relationship shall be useful as an efficient tool for the structural analysis of arbitrarily aggregated colloidal systems.

Tuning the phase diagram of colloid-polymer mixtures via Yukawa interactions.

Theory that predicts the phase behavior of interacting Yukawa spheres in a solution containing nonadsorbing polymer is presented. Our approach accounts for multiple overlap of depletion zones. It is found that additional Yukawa interactions beyond hard core interactions strongly affect the location and presence of coexistence regions and phase states. The theoretical phase diagrams are compared with Monte Carlo simulations. The agreement between the two approaches supports the validity of the theoretical approximations made and confirms that, by choosing the parameters of the interaction potentials, tuning of the binodals is possible. The critical end point characterizes the phase diagram topology. It is demonstrated how an additional Yukawa interaction shifts this point with respect to the hard sphere case. Provided a certain depletant-to-colloid size ratio for which a stable colloidal gas-liquid phase coexistence takes place for hard spheres, added direct interactions turn this into a metastable gas-liquid equilibrium. The opposite case, the induction of a stable gas-liquid coexistence where only fluid-solid was present for hard spheres, is also reported.

Probing heterogeneous dynamics from spatial density correlation in glass-forming liquids.

We numerically investigate the connection between spatial density correlation and dynamical heterogeneity in glass-forming liquids. We demonstrate that the cluster size defined by the spatial aggregation of densely packed particles (DPPs) can better capture the difference between the dynamics of the Lennard-Jones glass model and the Weeks-Chandler-Andersen truncation model than the commonly used pair correlation functions. More interestingly, we compare the mobility of DPPs and loosely packed particles, and we find that high local density correlates well with slow dynamics in systems with relatively hard repulsive interactions but links to mobile ones in the system with soft repulsive interactions at one relaxation time scale. Our results show clear evidence that the above model dependence behavior stems from the hopping motion of DPPs at the end of the caging stage due to the compressive nature of soft repulsive spheres, which activates the dynamics of DPPs in the α relaxation stage.

Healthcare service quality model

Purpose The purpose of this paper is to develop and test a multi-level healthcare service quality (HSQ) model in Jakarta, Indonesia. Design/methodology/approach The research used a quantitative research method. Data were collected via a survey with questionnaire. The respondents are 154 patients of a healthcare institution in Jakarta, Indonesia. Findings The research result shows a multi-level HSQ model. The HSQ model consists of three primary dimensions, namely, healthcare service outcome, healthcare service interaction, and healthcare service environment. Healthcare service outcome has three subdimensions, i.e. waiting time, medicine, and effectiveness. Healthcare service interaction has three dimensions, namely, soft interaction, medical personnel expertise, and hard interaction. Healthcare service environment has two dimensions, which are equipment condition and ambient condition. Research limitations/implications This research was only conducted in one healthcare institution in Jakarta, Indonesia. The data collection using convenience sampling method as well as the use of small sample size caused the limitation of the research results in representing across the customer of the healthcare institution. This study can be replicated with larger sample size and involving more healthcare institutions in order to examine the stability of the HSQ model. Practical implications Healthcare institution’s managers can use the HSQ model to monitor, measure, and improve their service quality. Originality/value There is a lack of research that develops and tests HSQ model based on multi-level approach in the context of developing country. This paper has fulfilled the gap.

Recent heavy flavor measurements from PHENIX at RHIC

Heavy flavor quarks are an important probe of the initial state of the Quark Gluon Plasma formed in heavy-ion collisions. Bottom and charm quarks are primarily produced through hard interactions, early in the collision and experience the full time evolution of the medium. Measuring their production in p + p collisions can also give a baseline reference to study larger collision systems, including asymmetric systems and can directly test pQCD calculations. At PHENIX open heavy flavor states can be measured through leptonic decay channels. Some measurements have utilized silicon vertex detectors to determine meson decay lengths in order to separate D mesons from B mesons. Recent measurements have been made at √sNN = 200 and 500 GeV, with a variety of collision species, in both forward/backward and central rapidities.A review of the recent heavy flavor measurements from PHENIX will be presented in this proceeding.