Jet Topology Research Articles

Anomaly Awareness

We present a new algorithm for anomaly detection called Anomaly Awareness. The algorithm learns about normal events while being made aware of the anomalies through a modification of the cost function. We show how this method works in different Particle Physics situations and in standard Computer Vision tasks. For example, we apply the method to images from a Fat Jet topology generated by Standard Model Top and QCD events, and test it against an array of new physics scenarios, including Higgs production with EFT effects and resonances decaying into two, three or four subjets. We find that the algorithm is effective identifying anomalies not seen before, and becomes robust as we make it aware of a varied-enough set of anomalies.

Evaporation and clustering of ammonia droplets in a hot environment

Liquid ammonia has been under investigation as a possible substitute of the current carbon-based fuels. However, its thermodynamical properties are responsible for a strong cooling effect of the surrounding environment and peculiar dispersion patterns that can affect the efficiency of a combustor. Through this computational study, it is highlighted how the rapid environmental cooling and change of carrier mixture make ammonia droplets condense, despite the ambient temperature being considerably higher than the saturation one, affecting the jet topology as well.

Characteristics of a dielectric barrier discharge plasma actuator driven by pulsed-DC high voltage

Dielectric barrier discharge using pulsed-DC high voltage (pulsed-DC DBD) have been proven to be capable of effectively reducing skin friction drag in turbulent boundary layers with limited power consumption, thus producing significant net power savings. In this work, the characteristics of pulsed-DC DBD, including power consumption, induced flow structure, thermal effect, and body force, are investigated sequentially. Both the power consumption and pressure waves produced by pulsed-DC DBD are similar to that of DBD using nanosecond pulses (ns-DBD), whereas the wall-bounded jet structure resembles that of DBD using sinusoidal high voltage (ac-DBD). A curved wall jet is induced at a small pulse width, which turns into a straight one due to the combined effect of momentum and thermal addition when the pulse width increases. With increasing pulse width, the induced body force goes up while the thermal effect weakens. Although pulse frequency has no impact on the wall-bounded jet topology, the body force increases with pulse frequency because of the enhanced energy entrainment. With these results, four parameters that affect the performance of pulsed-DC DBD are extracted, including the pulse leading edge, pulse width, frequency, and amplitude, which lays the foundation for the optimization of pulsed-DC DBD.

Contribution to the physical description of supercritical cold flow injection: The case of nitrogen

While increased pressure and temperature contribute to an overall efficiency gain in the mixing of propellants and oxidizers, characteristic of conditions in the combustion chambers of liquid rocket engines, they also propel mixtures to trans- and supercritical conditions. In these conditions, the engine flow exhibits a gas jet-like behavior that may be described using an approach developed for variable density incompressible flows. The present study focuses on an approach using the Reynolds-averaged Navier–Stokes equations to evaluate the jet topology for different injectors’ conditions. Based on the so-called ’thermal breakup mechanism concept’ proposed in the literature, the axial density decay in supercritical nitrogen jets is predicted for a wide range of conditions. The results show the influence of thermal breakup, providing a better insight of the available experimental data.

Flow topology and heat transfer analysis of slotted and axisymmetric synthetic impinging jets

This work is focused on exploring the flow and heat transfer capabilities for slotted and axisymmetric cavity configurations for synthetic impinging jets; the jet is enclosed between two isothermal parallel plates, impinging into the top hot plate. Numerical simulations using the Arbitrary Lagrangian-Eulerian formulation of the Navier-Stokes equations are performed for Reynolds numbers of 50, 300 and 500 and a jet formation criteria of 3. The pattern of the flow from both configurations differ, which result in different impinging behaviors. The slotted jet is wider than the axisymmetric one, showing an increased turbulent mixing and a lower velocity deficit. On the other hand, the narrower jet of the axisymmetric configuration results in less mixing and more penetration, with a higher velocity deficit. This leads to a higher heat transfer peak in the axisymmetric configuration with a faster decay when moving away from the jet centerline than observed for the slotted configuration.

Looking for minimal inverse seesaw scenarios at the LHC with jet substructure techniques

Simple extensions of the standard model (SM) with additional right handed neutrinos (RHNs) can elegantly explain the existence of small neutrino masses and their flavor mixings. Collider searches for sterile neutrinos are being actively pursued currently. Heavy RHNs may dominantly decay into after being produced at the LHC. In this paper, we consider collider signatures of heavy pseudo-Dirac neutrinos in the context of the inverse seesaw scenario, with a sizable mixing with the SM neutrinos under two different flavor structures, viz. flavor diagonal and flavor non-diagonal (FND) scenarios. For the latter scenario we use a general parametrization for the model parameters by introducing an arbitrary orthogonal matrix and nonzero Dirac and Majorana phases. We then perform a parameter scan to identify allowed parameter regions which satisfy all experimental constraints. As an alternative channel to the traditional trilepton signature, we propose the opposite-sign di-lepton signature in the final state, in association with a fat jet from the hadronic decay of the boosted . We specifically consider a fat jet topology and explore the required enhancements from exploiting the characteristics of the jet substructure techniques. We perform a comprehensive collider analysis to demonstrate the effectiveness of this channel in both of the scenarios, significantly enhancing the bounds on the RHN mass and mixing angles at the 13 TeV LHC. Interestingly the FND scenario can reach up to a 5-σ limit under the presence of the general parametrization at the high luminosity LHC.

Effects of equations of state and constitutive models on simulating copper shaped charge jets in ALEGRA

We investigate the effects of copper equations of state and constitutive models on simulations of shaped charge jets using the Sandia National Laboratories’ multiphysics hydrocode, ALEGRA. Specifically, we compare (1) the 3320, 3325, 3331, and 3337 SESAME copper equations of state (EOS), and (2) Johnson–Cook, Zerilli–Armstrong, Preston–Tonks–Wallace, Steinberg–Guinan–Lund, and Mechanical Threshold Stress constitutive models. Several of these cases are also compared against photon Doppler velocimetry measurements of the tip velocity. Lagrangian tracer particles are used to follow a part of the jet's evolution in state space for the various models. We monitored the jet topology and found that the various EOS produce similar results, although the 3325 model generates a cavity near the jet tip whose size decreases with increasing mesh resolution. Constitutive models generated more noticeable differences. We found the SGL and PTW models produced higher temperatures while the MTS and JC models returned very similar results at lower temperatures. The SGL model was the only strength model that reported a liquid region along the axis of the jet. For all material models, we found similar results for the velocity history of the jet tip as measured against experiment using photon Doppler velocimetry.

Azimuthal separation in nearly back-to-back jet topologies in inclusive 2- and 3-jet events in {text {p}} {text {p}} collisions at sqrt{s}=13,text {Te}text {V}

A measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, varDelta phi _{12}, is presented. The measurement considers events where the two leading jets are nearly collinear (“back-to-back”) in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13,text {Te}text {V} and corresponding to an integrated luminosity of 35.9{,text {fb}^{-1}} are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log parton showers and hadronization are generally in agreement with the measurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region 177^circ< varDelta phi _{12} < 180^circ . The 2- and 3-jet measurements are not simultaneously described by any of models.

Evolution of elliptic synthetic jets at low Reynolds number

The influence of the nozzle aspect ratio ($AR=1$, 2 and 4), stroke length ($L_{0}=1.85$, 3.7 and 5.55) and Reynolds number ($Re=79$, 158, 316 and 632) on the behaviour of elliptic synthetic jets is studied experimentally. Laser-induced fluorescence and two-dimensional and stereoscopic particle image velocimetry are used to analyse the vortex dynamics and evolution mechanism. It is found that the fluid elements around the major axis of an elliptic vortex ring move downstream faster and tend to approach the centreline, while the fluid elements around the minor axis move downstream at a slower speed and away from the centreline, thereby resulting in the occurrence of the well-known axis-switching phenomenon for elliptic synthetic jets. During this process, a pair of arc-like vortices forms ahead of the primary vortex ring, and they are constituted by streamwise vortices in the leg part and spanwise vortices in the head part; two pairs of streamwise vortices form from the inside of the primary vortex ring and develop in the tails. The streamwise vortices are pushed away progressively from the centreline by the synthetic jet vortex rings that are formed during the subsequent periods. These additional vortical structures for non-circular synthetic jets show regular and periodic characteristics, which are quite different from the previous findings for non-circular jets. Their mutual interaction with the vortex ring causes significant changes in the topology of elliptic synthetic jets, which further results in the variation of the statistical characteristics. Increasing the aspect ratio, stroke length and Reynolds number will make the evolution of the synthetic jet become more unstable and complex. In addition, the entrainment rate of an elliptical synthetic jet is larger than that of a circular synthetic jet and it increases with the nozzle aspect ratio ($AR\leqslant 4$) and Reynolds number. It is indicated that the formation of streamwise vortices could enhance the entrainment rate. This finding provides substantial evidence for the potential application of elliptic synthetic jets for effective flow control.

Direct Photon Production at Next-to-Next-to-Leading Order.

We present the first calculation of direct photon production at next-to-next-to-leading order (NNLO) accuracy in QCD. For this process, although the final-state cuts mandate only the presence of a single electroweak boson, the underlying kinematics resembles that of a generic vector boson plus jet topology. In order to regulate the infrared singularities present at this order, we use the N-jettiness slicing procedure, applied for the first time to a final state that at the Born level includes colored partons but no required jet. We compare our predictions to ATLAS 8TeV data and find that the inclusion of the NNLO terms in the perturbative expansion, supplemented by electroweak corrections, provides an excellent description of the data with greatly reduced theoretical uncertainties.

The topology of gas jets injected beneath a surface and subject to liquid cross-flow

Gas injection into a liquid cross-flow is examined for the case where the gas is injected beneath a horizontal flat surface. For moderate Froude numbers, the gas pocket that is formed will rise toward the flow boundary under the action of buoyancy, a condition that is conducive to the formation of gas layers for friction-drag reduction on the surface. At the location of gas injection, a plume whose geometry is related to the mass and momentum flux of the injected gas and liquid cross-flow is formed, and the influence of buoyancy is minimal. However, as the gas pocket convects downstream, buoyancy brings the gas back upward to the flow boundary, and leads to the bifurcation of the pocket into two distinct branches, forming a stable ‘V’-shape. Under some conditions, the flow between the two gas branches is almost entirely liquid, while for others there exists a bubbly flow or a continuous sheet of gas between the branches. The sweep angle and cross-sectional geometry of the gas branches are related to free-stream speed and boundary-layer thickness of the liquid cross-flow, the mass-injection rate of the gas, the diameter of the injection orifice and the gas outlet mean velocity and gas–jet angle. Data for a range of experimental conditions are used to scale the flow and results are compared to numerical computations of the flow, and these data are used to illustrate the underlying flow processes responsible leading to the formation the stable and straight gas branches. A simple model based on the balance of forces around a stable gas branch is presented and used to scale the observed data, and we use the results of this analysis and the computations to discuss how the process of gas injection may interact with the formation of the stable gas pockets farther downstream.

THE TOPOLOGY OF CANONICAL FLUX TUBES IN FLARED JET GEOMETRY

ABSTRACT Magnetized plasma jets are generally modeled as magnetic flux tubes filled with flowing plasma governed by magnetohydrodynamics (MHD). We outline here a more fundamental approach based on flux tubes of canonical vorticity, where canonical vorticity is defined as the circulation of the species’ canonical momentum. This approach extends the concept of magnetic flux tube evolution to include the effects of finite particle momentum and enables visualization of the topology of plasma jets in regimes beyond MHD. A flared, current-carrying magnetic flux tube in an ion-electron plasma with finite ion momentum is thus equivalent to either a pair of electron and ion flow flux tubes, a pair of electron and ion canonical momentum flux tubes, or a pair of electron and ion canonical vorticity flux tubes. We examine the morphology of all these flux tubes for increasing electrical currents, different radial current profiles, different electron Mach numbers, and a fixed, flared, axisymmetric magnetic geometry. Calculations of gauge-invariant relative canonical helicities track the evolution of magnetic, cross, and kinetic helicities in the system, and show that ion flow fields can unwind to compensate for an increasing magnetic twist. The results demonstrate that including a species’ finite momentum can result in a very long collimated canonical vorticity flux tube even if the magnetic flux tube is flared. With finite momentum, particle density gradients must be normal to canonical vorticities, not to magnetic fields, so observations of collimated astrophysical jets could be images of canonical vorticity flux tubes instead of magnetic flux tubes.

DNS analysis of incipient drop impact dynamics using an accurate level set method

A series of 2D direct numerical simulations were performed with an accurate level set method for single drop impacts. The adopted ACLS method was validated to be efficient with perfect mass conservation in both normal and oblique impacts. A square-root correction for neck bases was modified in accuracy as well as scope of applications. In addition, process of jet formation and evolution was studied to reveal internal dynamics in drop impacts. It's found that pressure gradient and vortex are coexisting and completive reasons for jet topology while the inclined angle has a significant effect on them. Mechanisms of jet formation and evolution are different in the front and back necks. With the help of PDF distribution and correction calculation, a compromise in the competition is observed. This work lays a solid foundation for further studies of dynamics in gas–liquid flows.

Third generation in cascade decays

In supersymmetric models with gluinos around 1000-2000 GeV, new physics searches based on cascade decay products of the gluino are viable at the next run of the LHC. We investigate a scenario where the light stop is lighter than the gluino and both are lighter than all other squarks, and show that its signal can be established using multi b-jet, multi W and/or multi lepton final state topologies. We then utilize both boosted and conventional jet topologies in the final state in conjunction with di-tau production as a probe of the stau-neutralino co-annihilation region responsible for the model's dark matter content. This study is performed in the specific context of one such phenomenologically viable model named No-Scale F-SU(5).

Single Top Quark Measurements at the Tevatron

This paper reports the measurement of electroweak production of single top quarks in lepton plus jets final state by the DØ and CDF collaborations. At Fermilab's 1.96 TeV proton-antiproton collider, events are selected from several inverse femtobarns of data in the W+jets topology consistent with the signature of an isolated charged lepton (electron or muon), large missing transverse energy from the W boson decay and two or more jets, at least one of them is required to be identified as originating from a bottom quark. Sophisticated multivariate analysis techniques are employed to separate the small single top quark signal from background. Both experiments measure the single top production cross section in s-channel, t-channel and s + t-channel. The data is also used to extract limits on the CKM matrix element |Vtb|.

Jets and photons.

This Letter applies the concept of "jets," as constructed from calorimeter cell four-vectors, to jets composed (primarily) of photons (or leptons). Thus jets become a superset of both traditional objects such as QCD jets, photons, and electrons, and more unconventional objects such as photon jets and electron jets, defined as collinear photons and electrons, respectively. Since standard objects such as single photons become a subset of jets in this approach, standard jet substructure techniques are incorporated into the photon finder toolbox. Using a (reasonably) realistic calorimeter model we demonstrate that, for a single photon identification efficiency of 80% or above, the use of jet substructure techniques reduces the number of QCD jets faking photons by factors of 2.5 to 4. Depending on the topology of the photon jets, the substructure variables reduce the number of photon jets faking single photons by factors of 10 to 10(3) at a single photon identification efficiency of 80%.

Noise Characteristics of Twin-Square Slot Jets

Acoustic measurements have been undertaken on two different twin square jet topologies. OASPL, spectra, directivity measurement and shock-cell visualization have been conducted to evaluate twin square jets in different edge-vertex orientations. The results indicate that twin square jets effectively suppress noise up to 4 dB in terms of OASPL and 6 dB in terms of screech tonal SPL compared to an equivalent single circular jet. The study promises that twin-jet topology could serve as an effective tool for noise suppression.

Measurement of the top quark mass in the [formula omitted] channel using the lepton transverse momentum

This Letter reports a measurement of the top quark mass, Mtop, in data from pp¯ collisions at s=1.96 TeV corresponding to 2.7 fb−1 of integrated luminosity at the Fermilab Tevatron using the CDF II detector. Events with the lepton+jets topology are selected. An unbinned likelihood is constructed based on the dependence of the lepton transverse momentum, PT, on Mtop. A maximum likelihood fit to the data yields a measured mass Mtop=176.9±8.0stat±2.7syst GeV/c2. In this measurement, the contribution by the jet energy scale uncertainty to the systematic error is negligible. The result provides an important consistency test for other Mtop measurements where explicit use of the jet energy is made for deriving the top quark mass.

Observation of single top quark production and measurement of |Vtb|with CDF

We report the observation of electroweak single top quark production in 3.2 fb-1 of ppbar collision data collected by the Collider Detector at Fermilab at sqrt{s}=1.96 TeV. Candidate events in the W+jets topology with a leptonically decaying W boson are classified as signal-like by four parallel analyses based on likelihood functions, matrix elements, neural networks, and boosted decision trees. These results are combined using a super discriminant analysis based on genetically evolved neural networks in order to improve the sensitivity. This combined result is further combined with that of a search for a single top quark signal in an orthogonal sample of events with missing transverse energy plus jets and no charged lepton. We observe a signal consistent with the standard model prediction but inconsistent with the background-only model by 5.0 standard deviations, with a median expected sensitivity in excess of 5.9 standard deviations. We measure a production cross section of 2.3+0.6-0.5(stat+sys) pb, extract the CKM matrix element value |Vtb|=0.91+0.11-0.11 (stat+sys)+-0.07(theory), and set a lower limit |Vtb|>0.71 at the 95% confidence level, assuming m_t=175 GeVc^2.

Measurement oftt¯production in theτ+jetstopology usingpp¯collisions ats=1.96 TeV

We present a measurement of the ttbar production cross section multiplied by the branching ratio to tau lepton decaying semihadronically plus jets, at a center of mass energy sqrt{s}=1.96 TeV using 1 fb^(-1) of integrated luminosity collected with the D0 detector. Assuming a top quark mass of 170 GeV, we measure sigma_ttb * BR=0.60^{+0.23}_{-0.22} (stat) ^{+0.15}_{-0.14} (syst) +/- 0.04\;(lumi) pb. In addition, we extract the ttbar production cross section using the ttbar->tau+jets topology, with the result sigma_ttbar = 6.9_{-1.2}^{+1.2} (stat)_{-0.7}^{+0.8} (syst) \pm 0.4 (lumi) pb. These findings are in good agreement with standard model predictions and measurements performed using other top quark decay channels.