Energetic Jets Research Articles

Modeling Light Curves of Bipolar Core Collapse Supernovae from the Equatorial Plane

Abstract We use the two-components bipolar toy model of core collapse supernova (CCSN) ejecta to fit the rapid decline from maximum luminosity in the light curve of the type IIb CCSN SN 2018gk (ASASSN-18am). In this toy model we use a template light curve from a different CCSN that is similar to SN 2018gk, but that has no rapid drop in its light curve. The bipolar morphology that we model with a polar ejecta and an equatorial ejecta increases the maximum luminosity and causes a steeper decline for an equatorial observer, relative to a similar spherical explosion. The total energy and mass of our toy model for SN 2018gk are E SN = 5 × 10 51 erg and M SN = 2.7 M ⊙ . This explosion energy is more than what a neutrino driven explosion mechanism can supply, implying that jets exploded SN 2018gk. These energetic jets likely shaped the ejecta to a bipolar morphology, as our toy model requires. We crudely estimate that f ≈ 2%–5% of all CCSNe show this behavior, most being hydrogen deficient (stripped-envelope) CCSNe, as we observe them from the equatorial plane. We estimate the overall fraction of CCSNe that have a pronounced bipolar morphology to be f bip ≈ 5%–15% of all CCSNe.

Identifying Black Hole Central Engines in Gamma-Ray Bursts

Abstract The nature of the gamma-ray burst (GRB) central engine still remains an enigma. Entities widely believed to be capable of powering the extreme jets are magnetars and black holes. The maximum rotational energy that is available in a millisecond magnetar to form a jet is ∼1052 erg. We identify eight long GRBs whose jet-opening angle-corrected energetics of the prompt emission episode are >1052 erg with high confidence level and, therefore, their central engines are expected to be black holes. The majority of these GRBs present significant emission in the sub-GeV energy range. The X-ray afterglow light curves of these bursts do not show any shallow decay behavior such as a plateau; however, a few cases exhibit flares and multiple breaks instead of a single power-law decay. For a minimum mass of the black hole (∼2 M ⊙), we find the efficiency of producing a jet from its rotational energy to range between 2% and 270%. Highly energetic jets requiring high efficiencies implies that either the mass of these black holes are much larger or there are, in addition, other sources of energy that power the jet. By considering the Blandford–Znajek mechanism of jet formation, we estimate the masses of these black holes to range between ∼2 and 60 M ⊙. Some of the lighter black holes formed in these catastrophic events are likely candidates to lie in the mass-gap region (2–5 M ⊙).

Zonal jets at the laboratory scale: hysteresis and Rossby waves resonance

Abstract

Distributed Gas Ignition Using Injection Strategy for High Efficiency and Clean Combustion Under Lean Condition

Jet ignition is an efficient way to achieve lean burn of the engine and a promising strategy to meet the stringent emission regulations in the future. This paper presents a distributed gas ignition (DGI) combustion concept and realizes a DGI combustion mode using a newly designed DGI igniter. The igniter integrates a fuel injector and a spark plug to achieve minimum volume and easy installation. As the mixture preparation within the jet chamber is essential for the performance of the igniter, different jet chamber injection strategies were tested with varying excess air–fuel ratio ranging from 1.4 to 2.0. By addressing the dual injection strategy, the ignition delay and combustion duration were improved evidently. Compared with the single injection strategy, dual injection strategy improves the flexibility when preparing the mixture inside the jet chamber and therefore retains more fuel. The increased energy density of the jet chamber helps to generate more energetic jets under dual injection strategy, resulting in the improvement of ignition and combustion performance with lean burn. A higher thermal efficiency and a leaner limit of the engine are attained with dual injection than that with single injection. Dual injection exhibits its potential in reducing CO and THC emissions to an acceptable level with leaner mixture. Based on dual injection strategy, the maximum indicated thermal efficiency of 45% is achieved.

Probing stops in the coannihilation region at the HL-LHC: A comparative study of different processes

In the minimal supersymmetric model, the coannihilation of the lighter stop t˜1 and bino-like dark matter χ provides a feasible way to accommodate the correct dark matter relic abundance. In this scenario, due to the compressed masses, t˜1 merely appears as missing energy at the LHC and thus the pair production of t˜1 can only be probed by requiring an associated energetic jet. Meanwhile, since t˜2 and b˜1 are correlated in mass and mixing with t˜1, the production of t˜2t˜2⁎ or b˜1b˜1⁎, each of which dominantly decays into t˜1 plus Z, h or W boson, may serve as a complementary probe. We examine all these processes at the HL-LHC and find that the 2σ sensitivity to χ mass can be as large as about 570 GeV, 600 GeV for mt˜2≲1100 GeV and 1.1 TeV for mb˜1≲1375 GeV from the production process of t˜1t˜1⁎+jet, t˜2t˜2⁎ and b˜1b˜1⁎, respectively.

The global geometrical property of jet events in high-energy nuclear collisions

We present the first theoretical study of medium modifications of the global geometrical pattern, i.e., transverse sphericity (S_{perp }) distribution of jet events with parton energy loss in relativistic heavy-ion collisions. In our investigation, POWHEG + PYTHIA is employed to make an accurate description of transverse sphericity in the p + p baseline, which combines the next-to-leading order (NLO) pQCD calculations with the matched parton shower (PS). The Linear Boltzmann Transport (LBT) model of the parton energy loss is implemented to simulate the in-medium evolution of jets. We calculate the event normalized transverse sphericity distribution in central Pb + Pb collisions at the LHC, and give its medium modifications. An enhancement of transverse sphericity distribution at small S_{perp } region but a suppression at large S_{perp } region are observed in A + A collisions as compared to their p + p references, which indicates that in overall the geometry of jet events in Pb + Pb becomes more pencil-like. We demonstrate that for events with 2 jets in the final-state of heavy-ion collisions, the jet quenching makes the geometry more sphere-like with medium-induced gluon radiation. However, for events with ge 3 jets, parton energy loss in the QCD medium leads to the events more pencil-like due to jet number reduction, where less energetic jets may lose their energies and then fall off the jet selection kinematic cut. These two effects offset each other and in the end result in more jetty events in heavy-ion collisions relative to that in p + p.

Study of the Impact Energy Releasing Characteristics of Al/PTFE/W Energetic Jets

Compared with traditional jets, energetic jets have more efficient damage effects. To study the reaction characteristics of polytetrafluoroethylene- (PTFE-) based energetic jets under impact loading, the static mechanical properties of Al/PTFE/W composite energetic materials are studied by using a universal testing machine at a strain rate of 0.01 s−1, and the dynamic mechanical properties are tested on a slip Hopkinson pressure bar (SHPB) system at a strain rate of 1000∼5500 s−1. A dynamic energy acquisition system is established to quantify the energy generated by the response of the Al/PTFE/W energetic jets to impact targets. The effects of the material proportion and impact energy on the mechanical and energy release properties of the Al/PTFE/W energetic jets are analyzed. The results show that the Al/PTFE/W composite has an obvious strain rate effect. As the W content in the composite increases, the yield strength and compressive strength of the material increase gradually, but the strain at break decreases. When the W content is 45%, the peak pressure, total release energy, pressure platform duration, and total pressure duration of the Al/PTFE/W energetic jets are the highest. As the impact energy increases, the pressure peak and energy release values of the energetic jets increase. At an impact energy threshold of 106.1 MJ/m2, the chemical reaction of the Al/PTFE/W (45%) energetic jets is saturated. The results provide a theoretical and experimental basis for the application of energetic jets.

Can we observe jet PT-broadening in heavy-ion collisions at the LHC?

We investigate the effect of PT-broadening on jet substructure observables in heavy-ion collisions at the LHC. As an example, we focus on the opening angle of the two branches that satisfy the soft drop grooming condition in a highly energetic jet. The medium modification of the angular distribution can provide important information on the jet transport properties of hot QCD matter. In addition, we take into account a change of the overall fraction of quark and gluon jets in heavy-ion collisions. We comment on the comparison to a recent measurement from the ALICE Collaboration.

Jet-driven AGN feedback in galaxy formation before black hole formation

We propose a scenario where during galaxy formation an active galactic nucleus (AGN) feedback mechanism starts before the formation of a supermassive black hole (SMBH). The supermassive star (SMS) progenitor of the SMBH accretes mass as it grows and launches jets. We simulate the evolution of SMSs and show that the escape velocity from their surface is ≈several×103kms−1, with large uncertainties. We could not converge with the parameters of the evolutionary numerical code MESA to resolve the uncertainties for SMS evolution. Under the assumption that the jets carry about ten percent of the mass of the SMS, we show that the energy in the jets is a substantial fraction of the binding energy of the gas in the galaxy/bulge. Therefore, the jets that the SMS progenitor of the SMBH launches carry sufficient energy to establish a feedback cycle with the gas in the inner zone of the galaxy/bulge, and hence, set a relation between the total stellar mass and the mass of the SMS. As the SMS collapses to form the SMBH at the center, there is already a relation (correlation) between the newly born SMBH mass and the stellar mass of the galaxy/bulge. During the formation of the SMBH it rapidly accretes mass from the collapsing SMS and launches very energetic jets that might unbind most of the gas in the galaxy/bulge.

Dynamic analysis of the primary breakup of an annular energetic liquid jet injecting into a confined space

The Large Eddy Simulation (LES) with the Volume of Fluid (VOF) method was carried out to investigate the primary breakup dynamic mechanism of an annular energetic liquid jet injecting into a confined space. The gas vortex structure and the liquid jet formation were visualized by tracking the evolution of the phase velocity and the interface location, and hence the coalescence process of the goblet-shaped liquid jet from the annular liquid jet was reproduced. Simulation results indicate that the first coalescence is caused by the Rayleigh-Taylor instability, which is generated by the interaction between the liquid jet head and the gas in the confined space. Two kinds of large-scale vortex structure expedite the secondary coalescence and the final goblet-shaped liquid jet form. Cavities are observed on the dense liquid jet column as a result of the coalescence on the upstream. Consequently, the droplet breakup occurs more frequently on the downstream liquid jet under the gas phase disturbance. The viscous shear is created by the aerodynamic interaction, and the regular fish-scale structure is presented under the Kelvin-Helmholtz instability, which promotes the bulge surface to break into droplets. The research reveals the dynamic mechanism of the annular energetic liquid jet structural destabilization observed in the previous experiments. The combination of the structural instability and the surface instability facilitate the primary breakup of the annular energetic liquid jet, which is beneficial to improve the atomization and the combustion performance.

Performance of the ALICE electromagnetic calorimeters in LHC Runs 1 and 2 and upgrade projects

ALICE (A Large Ion Collider Experiment) at the LHC is designed for studies of nuclear matter at extreme temperatures and energy densities, the so-called Quark-Gluon Plasma (QGP). Two detectors for measurements of electromagnetic signals, high-granularity photon spectrometer PHOS and large acceptance electromagnetic calorimeter EMCal/DCal, are incorporated into the ALICE detector. In order to enhance the data sample of the high-energy part of the spectra, dedicated triggers on high energetic photons or jets are used. High precision measurements of neutral mesons require fine energy and timing calibrations. Photon signal purity is improved using dedicated photon PID criteria based on cluster shape and anti-track matching with the ALICE central tracking system, as well as a special detector located in front of PHOS called CPV. PHOS and EMCal participated in LHC Run 1 (2009-2013) and Run 2 (2015-2018) during data taking periods of pp, p-Pb and Pb-Pb collisions. We give an overview of their performance in Runs 1 and 2 in low and high multiplicity environments as well as the upgrade plans for future LHC runs.

Search for Supersymmetry with a Compressed Mass Spectrum in Events with a Soft τ Lepton, a Highly Energetic Jet, and Large Missing Transverse Momentum in Proton-Proton Collisions at sqrt[s]=13 TeV.

The first search for supersymmetry in events with an experimental signature of one soft, hadronically decaying τ lepton, one energetic jet from initial-state radiation, and large transverse momentum imbalance is presented. These event signatures are consistent with direct or indirect production of scalar τ leptons (τ[over ˜]) in supersymmetric models that exhibit coannihilation between the τ[over ˜] and the lightest neutralino (χ[over ˜]_{1}^{0}), and that could generate the observed relic density of dark matter. The data correspond to an integrated luminosity of 77.2 fb^{-1} of proton-proton collisions at sqrt[s]=13 TeV collected with the CMS detector at the LHC in 2016 and 2017. The results are interpreted in a supersymmetric scenario with a small mass difference (Δm) between the chargino (χ[over ˜]_{1}^{±}) or next-to-lightest neutralino (χ[over ˜]_{2}^{0}), and the χ[over ˜]_{1}^{0}. The mass of the τ[over ˜] is assumed to be the average of the χ[over ˜]_{1}^{±} and χ[over ˜]_{1}^{0} masses. The data are consistent with standard model background predictions. Upper limits at 95%confidence level are set on the sum of the χ[over ˜]_{1}^{±}, χ[over ˜]_{2}^{0}, and τ[over ˜] production cross sections for Δm(χ[over ˜]_{1}^{±},χ[over ˜]_{1}^{0})=50 GeV, resulting in a lower limit of 290GeV on the mass of the χ[over ˜]_{1}^{±}, which is the most stringent to date and surpasses the bounds from the LEP experiments.

Exclusive displaced hadronic signatures in the LHC forward region

The LHCb detector provides accurate vertex reconstruction and hadronic particle identification, which make the experiment an ideal place to look for light long-lived particles (LLP) decaying into Standard Model (SM) hadrons. In contrast with the typical search strategy relying on energetic jets and a high multiplicity of tracks from the LLP decay, LHCb can identify LLPs in exclusive, specific hadronic final states. To illustrate the idea, we study the sensitivity of LHCb to an exotic Higgs decay h → SS, followed by the displaced decay of GeV-scale scalars into charged kaons S → K+K−. We show that the reconstruction of kaon vertices in narrow invariant mass windows can efficiently eliminate the combinatorial backgrounds from B-meson decays. While the same signal is extremely difficult to probe in the existing displaced jet searches at ATLAS/CMS, the LHCb search we propose can probe the branching ratio BR(h → SS) down to 0.1% (0.02%) level with 15 (300) fb−1 of data. We also apply this projected bound to two scenarios with Higgs portal couplings, where the scalar mediator S either couples to a) the SM quarks only, or b) to both quarks and leptons in the minimal flavor violation paradigm. In both scenarios we compare the reach of our proposed search with the expected constraints from ATLAS and CMS on the invisible Higgs width and with the constraints from rare B-decays studies at LHCb. We find that for 1 GeV < mS< 2 GeV and 0.5 mm ≲ cτ ≲ 10 mm our proposed search will be competitive with the ATLAS and CMS projections, while at the same time providing crucial information of the hadronic interactions of S, which can not be obtained from the indirect measurement of the Higgs invisible width.

Connecting particle physics and cosmology: Measuring the dark matter relic density in compressed supersymmetry models at the LHC

Abstract The identity of Dark Matter (DM) is one of the relevant topics in particle physics today. The R-parity conserving Minimal Supersymmetric Standard Model (MSSM), which naturally provides a DM candidate in the form of the lightest neutralino ( χ 1 0 ), is used as a benchmark scenario to show that a measurement of the DM relic density, Ω χ 1 0 h 2 , can be achieved from measurements at the CERN Large Hadron Collider. Focus is placed on compressed mass spectra regions, where the mass difference Δ m between the χ 1 0 and the supersymmetric partner of the tau lepton ( τ 1 ) is small and where the τ 1 - χ 1 0 coannihilation (CA) mechanism of the early Universe plays an important role. The technique for measuring Ω χ 1 0 h 2 relies on two proposed searches for compressed Supersymmetry (SUSY): (1) production via Vector Boson Fusion (VBF) processes; and (2) production with associated energetic jets from initial state radiation (ISR). These approaches allow for the determination of the relic abundance at the LHC for any model where CA is an important DM reduction mechanism in the early Universe. Thus, it is possible to confirm that the DM we observe today corresponds to χ 1 0 ’s created in the early Universe. We show that from measurements in the VBF and ISR SUSY searches at the LHC, the mass gap Δ m and the dark matter relic density can be measured with an uncertainty of 4.5% and 25%, respectively, assuming 13 TeV proton–proton data from the high-luminosity LHC. The precise measurement of a small Δ m value would also confirm the existence of τ 1 - χ 1 0 CA.

Study of the Impact Energy Release Characteristics of Fine‐Grained Fe−Al Energetic Jets

AbstractFine‐grained Fe−Al energetic materials have high reaction enthalpies, and the release energy of the iron phase and a large portion of the active aluminium phase in sintered materials enables the replacement of conventional materials in new types of weapons. To study the energy release characteristics of fine‐grained Fe−Al energetic jets under impact loading, a dynamic energy acquisition system is established to quantify the energy generated by the response of fine‐grained Fe−Al energetic jets to impact targets. The pressure‐time curves of fine‐grained Fe−Al energetic jets with different ratios under different impact conditions are obtained, and a method for calculating the pressure differential value is proposed to quantitatively determine the energy release values of fine‐grained Fe−Al energetic jets. The energy release mechanism of the Fe−Al energetic jet is analysed at the micro‐level by recovering the reaction products. The results show that there is an optimal Fe−Al ratio that attains the greatest energy release effect from fine‐grained Fe−Al energetic jets. With increasing impact energy, the energy released by energetic jets tends to increase, and an impact energy threshold that saturates the chemical reaction of energetic materials in the jets exists. The relationship between the impact conditions and the energy release value of fine‐grained Fe−Al energetic jets is established.

Performance of Capillary Plasma Source With Combustible Materials

Application of an energetic material (EM) in a liquid or gaseous form to electrothermal (ET) plasma discharge systems can provide an energetic plasma jet that has desirable parameters for launching applications. In this energetic ET concept, the EM is basically injected into the plasma source that is operated in an ablation-free regime. The discharge and EM combustion processes have been simulated using the ETFlowCom code, which is an in-house developed energetic ET plasma model. In this article, the ETFlowCom code is used to predict the energetic plasma jet parameters such as temperature, pressure, heat flux, and exit velocity. Different computational case studies have been conducted using a variety of EM mixtures. The simulation results show that the generated energetic plasma jet has the density on the order of 10271/m3, kinetic pressure on the order of hundreds of MPa, and an exit velocity that can reach up to 6 km/s. These parameters are found to be functions of the EM type and the mixing ratio as well. The jet parameters show strong potential for launching applicability.

Measurement of the top-quark mass in toverline{t} + 1-jet events collected with the ATLAS detector in pp collisions at sqrt{s} = 8 TeV

A determination of the top-quark mass is presented using 20.2 fb−1 of 8 TeV proton-proton collision data produced by the Large Hadron Collider and collected by the ATLAS experiment. The normalised differential cross section of top-quark pair production in association with an energetic jet is measured in the lepton+jets final state and unfolded to parton and particle levels. The unfolded distribution at parton level can be described using next-to-leading-order QCD predictions in terms of either the top-quark pole mass or the running mass as defined in the (modified) minimal subtraction scheme. A comparison between the experimental distribution and the theoretical prediction allows the top-quark mass to be extracted in the two schemes. The value obtained for the pole-mass scheme is:mtpole=171.1±0.4stat±0.9syst−0.3+0.7theoGeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_t^{\\mathrm{pole}}=171.1\\pm 0.4\\left(\\mathrm{stat}\\right)\\pm 0.9{\\left(\\mathrm{syst}\\right)}_{-0.3}^{+0.7}\\left(\\mathrm{theo}\\right)\\;\\mathrm{GeV} $$\\end{document}The extracted value in the running-mass scheme is:mtmt=162.9±0.5stat±1.0syst−1.2+2.1theoGeV.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_t\\left({m}_t\\right)=162.9\\pm 0.5\\left(\\mathrm{stat}\\right)\\pm 1.0{\\left(\\mathrm{syst}\\right)}_{-1.2}^{+2.1}\\left(\\mathrm{theo}\\right)\\kern0.33em \\mathrm{GeV}. $$\\end{document}The results for the top-quark mass using the two schemes are consistent, when translated from one scheme to the other.

Experimental Study on the Energy-Release Characteristics of Fine-Grained Fe/Al Energetic Jets under Impact Loading.

The energy released by the active metal phase in fine-grained Fe/Al energetic materials enables the replacement of conventional materials in new types of weapons. This paper describes an experiment designed to study the energy-release characteristics of fine-grained Fe/Al energetic jets under impact loading. By means of dynamic mechanical properties analysis, the physical and chemical properties of Fe/Al energetic materials with specific content are studied, and the preparation process is determined. The energy-release properties of fine-grained Fe/Al jets subject to different impact conditions are studied based on experimental data, and energy-release differences are discussed. The results show that for fine-grained Fe/Al energetic materials to remain active and exhibit high strength, the highest sintering temperature is 550 °C. With increasing impact energy, the energy release of fine-grained Fe/Al energetic jets increases. At an impact-energy threshold of 121.1 J/mm2, the chemical reaction of the fine-grained Fe/Al energetic jets is saturated. The experimental data and microscopic analysis show that when the impact energy reaches the threshold, the energy efficiency ratio of Fe/Al energetic jets can reach 95.3%.

Probing the charm Yukawa coupling at future e−p and e+e− colliders

Large Hadron Collider (LHC) has provided direct evidence of Yukawa couplings between the third generation charged fermions and the 125 GeV Higgs boson. Whether the first two generation charged fermions arise from exactly the same mechanism becomes the next interesting question. Therefore, direct measurements of charm or muon Yukawa couplings will be crucial to answering this puzzle. The charm Yukawa measurement at the LHC suffers from severe QCD background and it is extremely difficult to reach the sensitivity. In this paper, we compare the potential of probing charm Yukawa coupling at the two proposed future "Higgs Factory" experiments, the Large Hadron electron Collider (LHeC) and Circular electron positron collider (CEPC). At the LHeC, Higgs bosons will be produced via weak boson fusion and the energetic forward jet may suppress the background significantly. However, due to huge $\gamma-g$ scattering background, the potential of LHeC search is still limited. With $-80\%$ polarized electron beam of 60 GeV, the signal significance can only reach $2\sigma$ for $ \kappa_{c}\simeq 1$ with a 3 ab$^{-1}$ integrated luminosity. In comparison, measurement at the CEPC can then reach $8.0\sigma$ for $\kappa_{c}\simeq 1$ with a 2 ab$^{-1}$ of data.

Search for invisible Higgs boson decays in vector boson fusion at [formula omitted] with the ATLAS detector

We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1)TeV and O(100)GeV missing transverse momentum. The analysis uses 36.1fb−1 of pp collision data at s=13TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set bounds on the wimp–nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3TeV for which the upper limits on the cross section times branching fraction are in the range of 0.3–1.7pb.