Effect Of Collisions Research Articles

Influence of globally spin-aligned vector mesons to the measurements of the chiral magnetic effect in heavy-ion collisions

The chiral magnetic effect (CME) in high-energy heavy-ion collisions arises from the interplay between the chirality imbalance and the intense magnetic field and will cause a charge separation along the magnetic field direction. While the CME search is still ongoing in experiments, the non-CME contributions need to be excluded from the CME observables. In this work, we examine the influence of globally spin-aligned ρ mesons on the γ112 correlator, the RΨ2(ΔS) correlator, and the signed balance functions, via a toy model and a multiphase transport model (AMPT). We find that the CME observables are sensitive to the 00-component of the spin density matrix, ρ00: they receive positive (negative) contributions when ρ00 is larger (smaller) than 1/3.

Novel fully-heterogeneous GNN designs for track reconstruction at the HL-LHC

Data from the LHC detectors are not easily represented using regular data structures. These detectors are comprised of several species of subdetectors and therefore produce heterogeneous data. LHC detectors are highly granular by design so that nearby particles may be distinguished. As a consequence, LHC data are sparse, in that many detector channels are not active during a given collision event. Graphs offer a flexible and efficient alternative to rectilinear data structures for representing LHC data. Accordingly, graph-based machine learning algorithms are becoming increasingly popular for a large number of LHC physics tasks [1, 2]. This popularity, and the corresponding potential for substantial increase in physics output, are illustrated on the cover of a recent issue [3] of the CERN Courier magazine. The graphs used in almost all practical applications at the LHC so far are homogeneous, i.e. each node is assigned the same features, and each edge is assigned the same features. In other words, the power of graphs to represent sparse data has been exploited in applications for the LHC, but the potential of graphs to represent heterogeneous data has not. The pink graph on the cover of the CERN Courier [3] can be seen as an illustration of this limitation: all nodes are pink, regardless of their position in the detector. We present novel fully-heterogeneous GNN designs and apply them to simulated data from a tracking detector that resembles the trackers that will be used at the HL-LHC. It contains a pixel subsystem that provides 3D hits and a strip subsystem that provides 2D hits. We present a new design which solves the degraded performance observed in the strip detector in the first GNNbased tracking studies presented by the ATLAS Collaboration [4].

Suppressing Beam Background and Fake Photons at Belle II using Machine Learning

The Belle II experiment situated at the SuperKEKB energyasymmetric e+ e− collider began operation in 2019. It has since recorded half of the data collected by its predecessor, and reached a world record instantaneous luminosity of 4.7 × 1034 cm-2s-1. For distinguishing decays with missing energy from background events at Belle II, the residual calorimeter energy measured by the electromagnetic calorimeter is an important quantity. Ideally, calorimeter clusters due to beam backgrounds and fake photons should be excluded when the residual calorimeter energy is calculated, so identifying them during the analysis process is key. We present two new boosted decision tree classifiers that have been trained to identify such clusters at Belle II and distinguish them from real photons originating from collision events at the interaction point. We provide results from their application to the B → D*ℓν decay mode, and show that the distribution of residual calorimeter energy for signal events is significantly improved.

GPS tracking reveals the timing of collisions with powerlines and fences of three threatened steppe bird species

Summary Collision with powerlines is a major cause of mortality for many bird species, including bustards and sandgrouse. In this work, we used GPS tracking data to identify the hour of collision of three threatened steppe birds, i.e. Little Bustard Tetrax tetrax, Black-bellied Sandgrouse Pterocles orientalis, and Pin-tailed Sandgrouse Pterocles alchata. Out of a data set of 160 GPS-tracked individuals collected over a 13-year period, we detected eight collision events with powerlines or fences. Of these, we were able to determine the timing of 87.5% of the collision events with a resolution accurate to within two hours. Our results reveal that collisions occurred throughout the year and at different hours of the day, presenting a challenge for implementing effective mitigation strategies. The use of dynamic and reflective or luminescent devices may therefore be appropriate to prevent collision of steppe birds with powerlines during the day and night. Overall, this study adds evidence to the utility of using tracking data to better understand anthropogenic mortality in birds.

Tying up loose ends together: Cetaceans, maritime traffic and spatial management tools in the Strait of Gibraltar

Abstract The transboundary area of the Strait of Gibraltar is home to seven protected cetacean species that are threatened by high intensity of maritime traffic. More comprehensive knowledge of cetaceans and maritime traffic is required, together with analyses of legislations, strategies and policies. This study quantitatively investigates cetacean distribution and maritime traffic intensity and, for the species of community interest bottlenose dolphin, habitat suitability. Results are qualitatively discussed considering the overlap of cetacean hot spots with different maritime activities and the consistency of spatial conservation management measures in force. The Fixed Line Transect Mediterranean Monitoring Network protocols were followed for 59 visual surveys using ferries as observation platforms for monitoring cetaceans and maritime traffic. Surveys were carried out along the transects between Algeciras and Ceuta and between Algeciras and Tanger‐Med, in 2018 and 2019. 264 cetacean sightings, including seven different species and four near‐miss collision events (involving pilot, sperm and fin whales), were reported. Monitoring cetaceans from ferries in the Strait provided insights into cetacean distribution and maritime traffic, enabling the identification of cetacean hot spots, suitable habitats and maritime traffic high‐risk zones. A transboundary management effort is required, together with an adaptive approach for protecting highly mobile species such as cetaceans. Proposals include a long‐term cetacean monitoring program carried out by dedicated observers on board ferries as a cost‐effective methodology and mandatory training for crew members, to increase cetacean knowledge and reduce collision risk. The designation of an international temporal or, in some zones, permanent speed reduction area (i.e., Cetacean Critical Navigation Zone, with a maximum speed of 13 knots) and of a micro‐sanctuary with a seasonal no‐take zone in the Bay between Algeciras and Gibraltar, together with international surveillance, are recommended measures for the enhancement of conservation efforts in the Strait.

Assessment of the risk of a dangerous event of a human collision with a remote-controlled robot

This study assesses the risk of a collision between a human and the “Robot Arm” during remote control, using a 6DoIt Mobile Robot Arm with six degrees of freedom. The bow-tie approach, combined with EN ISO 12100 standards, was employed to evaluate the risk of such a dangerous event, considering physical, organizational, psychosocial, and informational factors. The proposed risk assessment method is based on the bow-tie model, emphasizing the importance of determining the possibility of avoiding hazards as per EN ISO 12100. A three-level protective system – physical, psychological, and informational – is suggested to mitigate the risk, interconnected to enhance safety by reducing the severity of potential consequences. The approach has been refined to better determine the severity of outcomes, focusing on the ability to avoid danger. Additionally, recommendations for enhancing robotics safety management were developed, aiming to improve the effectiveness of measures to reduce collision risks during the operation of the “Robot Arm”.

Sphaleron damping and effects on normal and anomalous charge transport in high-temperature QCD plasmas

We modify the hydrodynamic equations of a relativistic chiral plasma to account for dissipative effects due to QCD sphaleron transitions. By analyzing the linearized hydrodynamic equations, we show that sphaleron transitions lead to nontrivial effects on vector and axial charge transport phenomena in the presence of a magnetic field. Notably, dissipative effects of sphaleron transitions lead to the emergence of a wavenumber threshold that characterizes the onset of Chiral Magnetic Waves. Sphaleron damping also significantly impacts the time evolution of both vector and axial charge perturbations in the presence of a magnetic field. We further investigate the dependence of charge separation on the rate of sphaleron transitions, which may have implications for the experimental search for the Chiral Magnetic Effect in heavy ion collisions.

Initial-state and final-state effects on hadron production in small collision systems

Heavy meson production in reactions with nuclei is an active new frontier to understand QCD dynamics and the process of hadronization in nuclear matter. Measurements in various colliding systems at RHIC and LHC, including Pb-Pb, Xe-Xe, O-O, p-Pb, and p-O, enable precision tests of the medium-size, temperature, and mass dependencies of the in-medium parton propagation and shower formation. We employ a coupled DGLAP evolution framework that takes advantage of splitting functions recently obtained in softcollinear effective theory with Glauber gluons (SCETG) and hard thermal loop (HTL) motivated collisional energy loss effects. With jet quenching effects constrained to the nuclear modification factor of charged hadrons in Pb-Pb collisions at 5.02 TeV, we present predictions for light and heavy-meson in Xe-Xe, O-O and p-Pb collisions at the LHC.We find that the nuclear modification scales non-trivially with the quark mass and medium properties. In particular, there can be sizeable collision-induced attenuation of heavy mesons in small systems such as oxygen-oxygen and high-multiplicity p-Pb events. Finally, we analyze the impact of different models of initial-state parton dynamics on the search for QGP signatures in small colliding systems.

Elucidating the chemical dynamics of the elementary reactions of the 1-propynyl radical (CH3CC; X2A1) with 2-methylpropene ((CH3)2CCH2; X1A1).

Exploiting the crossed molecular beam technique, we studied the reaction of the 1-propynyl radical (CH3CC; X2A1) with 2-methylpropene (isobutylene; (CH3)2CCH2; X1A1) at a collision energy of 38 ± 3 kJ mol-1. The experimental results along with ab initio and statistical calculations revealed that the reaction has no entrance barrier and proceeds via indirect scattering dynamics involving C7H11 intermediates with lifetimes longer than their rotation period(s). The reaction is initiated by the addition of the 1-propynyl radical with its radical center to the π-electron density at the C1 and/or C2 position in 2-methylpropene. Further, the C7H11 intermediate formed from the C1 addition either emits atomic hydrogen or undergoes isomerization via [1,2-H] shift from the CH3 or CH2 group prior to atomic hydrogen loss preferentially leading to 1,2,4-trimethylvinylacetylene (2-methylhex-2-en-4-yne) as the dominant product. The molecular structures of the collisional complexes promote hydrogen atom loss channels. RRKM results show that hydrogen elimination channels dominate in this reaction, with a branching ratio exceeding 70%. Since the reaction of the 1-propynyl radical with 2-methylpropene has no entrance barrier, is exoergic, and all transition states involved are located below the energy of the separated reactants, bimolecular collisions are feasible to form trimethylsubstituted 1,3-enyne (p1) via a single collision event even at temperatures as low as 10 K prevailing in cold molecular clouds such as G+0.693. The formation of trimethylsubstituted vinylacetylene could serve as the starting point of fundamental molecular mass growth processes leading to di- and trimethylsubstituted naphthalenes via the HAVA mechanism.

Integrating the Rivet analysis tool into EPOS 4

Integrating the Rivet analysis tool into EPOS 4

Holographic transport coefficients and jet energy loss for the hot and dense quark-gluon plasma

We employ an Einstein-Maxwell-dilaton model, based on the gauge/gravity correspondence, to obtain the thermodynamics and transport properties for the hot and dense quark-gluon plasma. The model, which is constrained to reproduce lattice QCD thermodynamics at zero density, predicts a critical point and a first order line at finite temperature and density, is used to quantify jet energy loss through simulations of high-energy collision events.

Wrapping a Craton: A Review of Neoproterozoic Fold Belts Surrounding the São Francisco Craton, Eastern Brazil

A synthesis of the evolution of the Neoproterozoic belts or orogens surrounding the São Francisco craton (SFC) in northeastern and southeastern Brazil is presented. Emphasis is placed on recognizing the superposition of sedimentary basins, from rift to passive margin to retroarc and foreland, as well as identifying three diachronic continental collisions in the formation of the SFC. The Tonian passive margin occurs in the southern Brasília Belt with the Vazante, Canastra, and Araxá Groups. During the Tonian, island magmatic arcs and basins developed in front and behind these arcs (fore- and back-arcs). Subsequently, in the Cryogenian–Ediacaran, a retroarc foreland basin developed with part of the Araxá Group and the Ibiá Group, and finally, a foreland basin developed, which was filled by the Bambuí Group. A tectonic structure of superimposed nappes, with subhorizontal S1–2 foliation, formed between 650 and 610 Ma, is striking. In the northern Brasília Belt, there is the Stenian passive margin of the Paranoá Group, the Tonian intrusion of the Mafic–Ultramafic Complexes, and the Mara Rosa Island magmatic arc, active since the Tonian, with limited volcanic–sedimentary basins associated with the arc. A thrust–fold belt structure is prominent, with S1 foliation and late transcurrent, transpressive tectonics characterized by the Transbrasiliano (TB) lineament. The Cryogenian–Ediacaran collision between the Paranapanema and São Francisco cratons is the first collisional orogenic event to the west. In the Rio Preto belt, on the northwestern margin of the São Francisco craton, the Cryogenian–Ediacaran Canabravinha rift basin is prominent, with gravitational sediments that represent the intracontinental termination of the passive margin that occurs further northeast. The rift basin was intensely deformed at the Ediacaran–Cambrian boundary, as was the Bambuí Group. On the northern and northeastern margins of the São Francisco craton, the Riacho do Pontal and Sergipano orogens stand out, showing a comparable evolution with Tonian and Cryogenian rifts (Brejo Seco, Miaba, and Canindé); Cryogenian–Ediacaran passive margin, where the Monte Orebe ophiolite is located; and Cordilleran magmatic arcs, which developed between 620 and 610 Ma. In the Sergipano fold belt, with a better-preserved outer domain, gravitational sedimentation occurs with glacial influence. A continental collision between the SFC and the PEAL (Pernambuco-Alagoas Massif) occurred between 610 and 540 Ma, with intense deformation of nappes and thrusts, with vergence to the south and accommodation by dextral transcurrent shear zones, such as the Pernambuco Lineament (PE). The Araçuaí belt or orogen was formed at the southeastern limit of the SFC by a Tonian intracontinental rift, later superimposed by a Cryogenian–Ediacaran rift–passive margin of the Macaúbas Group, with gravitational sedimentation and glacial influence, and distally by oceanic crust. It is overlain by a retroarc basin with syn-orogenic sedimentation of the Salinas Formation, partly derived from the Rio Doce cordilleran magmatic arc and associated basins, such as the Rio Doce and Nova Venécia Groups. A third continental collision event (SF and Congo cratons), at the end of the Ediacaran (580–530 Ma), developed a thrust–fold belt that deforms the sediments of the Araçuaí Belt and penetrates the Paramirim Corridor, transitioning to the south to a dextral strike-slip shear zone that characterizes the Ribeira Belt.

The effect of multiple collisions on the electronic stopping losses

The paper considers the question of the dependence of electronic stopping dE/dx on the measurement technique. Usually, when using the transmission geometry, the value of electron stopping is defined as the ratio of the energy loss of the particle after passing through the film to the thickness of the film d. It is shown that this procedure provides overestimated results at low collision energies. Using the computer simulation, the dependence of the ratio of the particle mean trajectory length L in the film to its thickness d on the particle energy E has been obtained. Experimental values of inelastic loss dE/dx for transmission geometry were corrected for the L/d ratio and compared with the results of the “backscattering geometry” experiments. A good agreement of the corrected “transmission” data with the “backscattering” data has been demonstrated for the H-Cu, H-Ag and H-Au systems. The incident particle energies E0 ranged from 0.5 to 20 keV.

Future physics prospects with CEPC and HL-LHC synergy

After constructing the Circular Electron Positron Collider (CEPC) and the High-Luminosity Large Hadron Collider (HL-LHC), particle physics experiments will reach a new mass region with more incredible energy. Both types of colliders have the unique duty of searching for new particles or estimating the coupling constants of the reactions based on their different structures, providing a different focus. This presentation will discuss and cover the regions of CEPC and HL-LHC to show their complementary functions. The CEPC can answer the Higgs particle, whether it is a composite particle, how it contributes to the dark matter mass, and whether its field provides enough matter mass for the universe. It can generally provide detections below 10 TeV, leading to possible new theories. For the HL-LHC, the upgraded HL-LHC has a higher luminosity and data acquisition capability, ten times higher than predicted. It is expected to produce 15 million Higgs particles annually, five times more than the LHC. The large number of collision events provides more opportunities to measure the characteristics of the Higgs particles.

Modelling dense particle streams during free-fall electrostatic separation

Electrostatic particle separation is an attractive option for dry processing in the resource and recycling industries. Free-fall electrostatic separators are particularly simple and versatile member of this family of technologies. This paper presents numerical simulations of the movement of particles with different charges and masses within a stream of other particles in an electric field. The modelled system comprises much larger numbers and higher spatial densities of particles than previous models, and allows a realistic assessment of the effect of interparticle electrostatic forces and collisions. The effect of an angled feed with both co- and counter-directional fields is investigated, and the results translated to grade-recovery curves for different configurations. Among the important results were the degradation of separation performance with particle feed rate, the potential importance of Coulombic interparticle reactions in dense particle streams, and the benefits of an angled feed with a counter-directional electric field.

Single-Impact Electrochemistry for Bacterial Sensing

The main objective in the detection and analysis of bio-entities such as bacteria is a low detection limit, a short assay time and a high selectivity in identification, ideally combined with easy-handling and cheap instrumentation. In this way, the development of innovative analytical methods in terms of high sensitivity and spatial-temporal resolution allowing both qualitative and quantitative analysis at single-cell and subcellular levels is becoming a technological requirement. The main advantage of electrochemistry in biosensing applications is to combine high sensitivity and ease of use with the possibility of miniaturization at low cost. Especially, new electrochemical techniques and various types of electrodes have been recently developed offering the feasibility of analysis at the single-cell level with high sensitivity and selectivity. Nano-electrochemistry has been widely extended to various applications such as biosensing thanks to the continuous improvement of the instrumentation sensitivity, especially for individual entity electrochemical detection. Single-impact electrochemistry provides a low limit of detection (in principle, one single species) inherent to this electro-analytical method and the ability to study single entities (cells, viruses, bacteria, nanoparticles...) in real-time through a dynamic measurement [1]. The electrochemical nano-impacts method or discrete collisions technique (stochastic events) consists in detecting single impacts of various entities such as nanoparticles, cells, bacteria, vesicles, viruses, proteins in solution at a polarized ultramicroelectrode (UME) [2]. For each collision event, a specific signal is recorded in the chronoamperometry curve (current as a function of time) corresponding to an “impact” of the entity onto the UME surface. Crucial information can be reached from the analysis of the electrochemical impact event in the amperometry measurement, such as the concentration and the size of the colliding entity.Electrochemical nano-impacts (or collisions) of single bacteria are usually detected by recording a chronoamperometry measurement (i–t curve) at a UME biased at a redox potential of an electroactive species in an aqueous electrolyte containing between 106 and 109 bacteria per milliliter [1, 3]. Since 2015, most of the reports in this area concern Escherichia coli (E. coli) as a model bacterium but this sensitive electro-analytical technique has not proved to be efficient for selective detection yet, except for the discrimination between Gram-positive and Gram-negative bacteria. In order to develop single-impact electrochemistry toward the identification of bacterial cells, several studies deal with the use of redox mediators for probing the electrochemical activity of the bacterium. Also, an original and recent approach is to detect the virulence factors released by pathogenic bacteria rather than the cells themselves, based on redox liposomes single-impact electrochemistry [2, 4].

Arc magmatism associated with continental convergence in the SE segment of the UDMA, Iran: Insights from zircon geochronology and Hf–Sr–Nd–Fe isotopes

Magmatic suites provide the keys to evaluate the growth and reworking of continental crust. Late Cretaceous to Pleistocene convergence in the Urumieh–Dokhtar magmatic arc (UDMA) of Iran produced continental-arc magmatism that traces the transition from subduction to collision. The extent and origin of some magmatic segments in the SE UDMA remain poorly understood. The Oligocene (31 to 25 Ma) Jiroft plutonic rocks here investigated encompass the compositional spectrum from gabbro to granodiorite. Zircon εHf(t) (−1.3 to +8.1), whole rock εNd(t) (+0.8 to +3) and δ56Fe (0.07‰ to 0.16‰) are intermediate between values of depleted mantle and arc-related magmas, and indicate low degrees of oxidization of metasomatized mantle. Modelling indicates that the trace element patterns of Jiroft parental melts can be closely replicated by 4% partial melting (i.e., F = 4%) of a mantle source which was metasomatized by 2% of sediment melt. The parental melt fits well with a model pattern of ∼97% batch melt (i.e., 98% DM + 2% sediment at F = 4%) and contaminated with ∼3% upper crustal components. The 31–25 Ma magmas of the SE UDMA formed before the main collision event (< 20 Ma) between Arabia and Iran, in conjunction with changing tectonic regime from extensional to compressional. Compilation of the Cenozoic magmatic front (i.e., UDMA) and rear-arc (NE Iran and Alborz–Azerbaijan) data reveals variable degrees of crustal cannibalization during the flare-up episodes. We find that individual segments of the UDMA experienced different geodynamics conditions, further documenting the diachronous collision and correspondingly non-uniform crustal thickening across the UDMA.

One Collision-Two Substituents: Gas-Phase Preparation of Xylenes under Single-Collision Conditions.

The fundamental reaction pathways to the simplest dialkylsubstituted aromatics-xylenes (C6 H4 (CH3 )2 )-in high-temperature combustion flames and in low-temperature extraterrestrial environments are still unknown, but critical to understand the chemistry and molecular mass growth processes in these extreme environments. Exploiting crossed molecular beam experiments augmented by state-of-the-art electronic structure and statistical calculations, this study uncovers a previously elusive, facile gas-phase synthesis of xylenes through an isomer-selective reaction of 1-propynyl (methylethynyl, CH3 CC) with 2-methyl-1,3-butadiene (isoprene, C5 H8 ). The reaction dynamics are driven by a barrierless addition of the radical to the diene moiety of 2-methyl-1,3-butadiene followed by extensive isomerization (hydrogen shifts, cyclization) prior to unimolecular decomposition accompanied by aromatization via atomic hydrogen loss. This overall exoergic reaction affords a preparation of xylenes not only in high-temperature environments such as in combustion flames and around circumstellar envelopes of carbon-rich Asymptotic Giant Branch (AGB) stars, but also in low-temperature cold molecular clouds (10 K) and in hydrocarbon-rich atmospheres of planets and their moons such as Triton and Titan. Our study established a hitherto unknown gas-phase route to xylenes and potentially more complex, disubstituted benzenes via a single collision event highlighting the significance of an alkyl-substituted ethynyl-mediated preparation of aromatic molecules in our Universe.

One Collision—Two Substituents: Gas‐Phase Preparation of Xylenes under Single‐Collision Conditions

AbstractThe fundamental reaction pathways to the simplest dialkylsubstituted aromatics—xylenes (C6H4(CH3)2)—in high‐temperature combustion flames and in low‐temperature extraterrestrial environments are still unknown, but critical to understand the chemistry and molecular mass growth processes in these extreme environments. Exploiting crossed molecular beam experiments augmented by state‐of‐the‐art electronic structure and statistical calculations, this study uncovers a previously elusive, facile gas‐phase synthesis of xylenes through an isomer‐selective reaction of 1‐propynyl (methylethynyl, CH3CC) with 2‐methyl‐1,3‐butadiene (isoprene, C5H8). The reaction dynamics are driven by a barrierless addition of the radical to the diene moiety of 2‐methyl‐1,3‐butadiene followed by extensive isomerization (hydrogen shifts, cyclization) prior to unimolecular decomposition accompanied by aromatization via atomic hydrogen loss. This overall exoergic reaction affords a preparation of xylenes not only in high‐temperature environments such as in combustion flames and around circumstellar envelopes of carbon‐rich Asymptotic Giant Branch (AGB) stars, but also in low‐temperature cold molecular clouds (10 K) and in hydrocarbon‐rich atmospheres of planets and their moons such as Triton and Titan. Our study established a hitherto unknown gas‐phase route to xylenes and potentially more complex, disubstituted benzenes via a single collision event highlighting the significance of an alkyl‐substituted ethynyl‐mediated preparation of aromatic molecules in our Universe.

Wavelet transform-based multi-scale analysis of ring-like and jet-like events in relativistic heavy-ion collisions

Wavelet transform-based multi-scale analysis of ring-like and jet-like events in relativistic heavy-ion collisions