Jet Clustering Research Articles

The LAMP instrument at the Linac Coherent Light Source free-electron laser.

The Laser Applications in Materials Processing (LAMP) instrument is a new end-station for soft X-ray imaging, high-field physics, and ultrafast X-ray science experiments that is available to users at the Linac Coherent Light Source (LCLS) free-electron laser. While the instrument resides in the Atomic, Molecular and Optical science hutch, its components can be used at any LCLS beamline. The end-station has a modular design that provides high flexibility in order to meet user-defined experimental requirements and specifications. The ultra-high-vacuum environment supports different sample delivery systems, including pulsed and continuous atomic, molecular, and cluster jets; liquid and aerosols jets; and effusive metal vapor beams. It also houses movable, large-format, high-speed pnCCD X-ray detectors for detecting scattered and fluorescent photons. Multiple charged-particle spectrometer options are compatible with the LAMP chamber, including a double-sided spectrometer for simultaneous and even coincident measurements of electrons, ions, and photons produced by the interaction of the high-intensity X-ray beam with the various samples. Here we describe the design and capabilities of the spectrometers along with some general aspects of the LAMP chamber and show some results from the initial instrument commissioning.

Jittering Jets in Cooling Flow Clusters

I put forth a scenario of jet-driven jittering-jets in cooling flows in galaxies and clusters of galaxies. By uplifting cool gas from the center of the cluster jets and the bubbles they inflate cause the direction of later jets to substantially change. Some uplifted cool clumps fall back to feed the active galactic nucleus, in what is termed the cold feedback mechanism, but with an average angular momentum that is largely inclined to that of the original jets. The proposed jittering jets scenario allows, over the cooling time of the intracluster medium (ICM), the heating by the mixing of hot jet-inflated bubble gas with the ICM to operate in all directions. The proposed scenario further supports the heating by mixing mechanism of the ICM. The feedback heating mechanism of the ICM chiefly refers to the energy cycle. The cold feedback mechanism introduces mass as another ingredient of the feedback cycle, as the mass accretion of future activity cycles is determined by the formation of perturbations by the present activity cycle. The jittering jets scenario that I propose here brings angular momentum to be another ingredient of the feedback cycle.

Enhancement of high-order harmonics in a plasma waveguide formed in clustered Ar gas.

Generation of high-order harmonics (HHs) is intensified by using a plasma waveguide created by a laser in a clustered gas jet. The formation of a plasma waveguide and the guiding of a laser beam are also demonstrated. Compared to the case without a waveguide, harmonics were strengthened up to nine times, and blue-shifted. Numerical simulation by solving the time-dependent Schrödinger equation in strong field approximation agreed well with experimental results. This result reveals that the strengthening is the result of improved phase matching and that the blue shift is a result of change in fundamental laser frequency due to self-phase modulation (SPM).

Linking high-energy cosmic particles by black-hole jets embedded in large-scale structures

The origin of ultrahigh-energy cosmic rays (UHECRs) is a half-century old enigma (Linsley 1963). The mystery has been deepened by an intriguing coincidence: over ten orders of magnitude in energy, the energy generation rates of UHECRs, PeV neutrinos, and isotropic sub-TeV gamma rays are comparable, which hints at a grand-unified picture (Murase and Waxman 2016). Here we report that powerful black hole jets in aggregates of galaxies can supply the common origin of all of these phenomena. Once accelerated by a jet, low-energy cosmic rays confined in the radio lobe are adiabatically cooled; higher-energy cosmic rays leaving the source interact with the magnetized cluster environment and produce neutrinos and gamma rays; the highest-energy particles escape from the host cluster and contribute to the observed cosmic rays above 100 PeV. The model is consistent with the spectrum, composition, and isotropy of the observed UHECRs, and also explains the IceCube neutrinos and the non-blazar component of the Fermi gamma-ray background, assuming a reasonable energy output from black hole jets in clusters.

Measurements of Durham, anti-kt and SIScone jet rates at LEP with the OPAL detector

We study jet production in e+e− annihilation to hadrons with data recorded by the OPAL experiment at LEP at centre-of-mass energies between 91 GeV and 209 GeV. The jet production rates were measured with Durham and for the first time with the anti-kt and SISCone jet clustering algorithms. We compare the data with predictions by modern Monte Carlo event generators.

The electron beam diagnostic of the clustered supersonic nitrogen jets

Axial and radial distributions of the rotational temperature and density of N2 molecules in supersonic nitrogen jets formed with conic nozzles (critical diameters dcr of 0.17 and 0.21 mm) were studied using the electron beam fluorescence technique at stagnation pressures P0 of 0.1-0.6 MPa. A rotational temperature Tr, equaling a gas temperature Tg owing to fast RT relaxation, was obtained using the rotational line relative intensity distribution in (0-1) vibrational band of the N2 first negative system. Gas density profiles in the jets were obtained using the integral intensity of the band. It is found, Tr at the nozzle outlet is of the order of a few tens of Kelvin and at further expansion Tr drops up to 15-20K at distance of (100-200) dcr. The gas temperature and density distributions in the studied supersonic nitrogen jets are not similar to the isentropic distributions. It is shown that the lower is the stagnation pressure the faster the gas density and temperature decrease with distance from the nozzle. Increase in P0 leads to elevating Tg in the jets. A reason for this effect may be cluster formation in the jets. Estimations of cluster mean sizes in the jets using Hagena’s parameter show presence of large clusters (M≥200) at P0 = 0.4-0.6 MPa.

Features of molecular-beam mass spectrometry registration of clusters in underexpanded supersonic jets

The structure of clustered supersonic underexpanded jets of molecular nitrogen and argon was measured by the method of molecular beam mass-spectrometry. Peculiarities of application of the molecular beam methods for recording the supersonic rarefied gas jets under the conditions of weak and developed condensation (i.e., in the presence of small and large clusters in jets) have been discovered, identified, and studied. An unusual shape of longitudinal and transverse cross sections of the clustered supersonic jets was revealed and explained when scanning with a molecular-beam system. It has been determined that small clusters and monomers are the sources of double-ionized monomers available near the flow axis, and dimer ions at the early stages of condensation, whereas another mechanism of such ion formation dominates, when large clusters area available in the flow. A marker for fixing the stage of formation of small clusters in a supersonic flow is proposed.

Measurement of the inclusive jet cross-sections in proton-proton collisions at sqrt{s}=8 TeV with the ATLAS detector

Inclusive jet production cross-sections are measured in proton-proton collisions at a centre-of-mass energy of sqrt{s}=8 TeV recorded by the ATLAS experiment at the Large Hadron Collider at CERN. The total integrated luminosity of the analysed data set amounts to 20.2 fb−1. Double-differential cross-sections are measured for jets defined by the anti-kt jet clustering algorithm with radius parameters of R = 0.4 and R = 0.6 and are presented as a function of the jet transverse momentum, in the range between 70 GeV and 2.5 TeV and in six bins of the absolute jet rapidity, between 0 and 3.0. The measured cross-sections are compared to predictions of quantum chromodynamics, calculated at next-to-leading order in perturbation theory, and corrected for non-perturbative and electroweak effects. The level of agreement with predictions, using a selection of different parton distribution functions for the proton, is quantified. Tensions between the data and the theory predictions are observed.

Cluster size dependence of high-order harmonic generation

We investigate high-order harmonic generation (HHG) from noble gas clusters in a supersonic gas jet. To identify the contribution of harmonic generation from clusters versus that from gas monomers, we measure the high-order harmonic output over a broad range of the total atomic number density in the jet (from 3×1016 to 3 × 1018 ) at two different reservoir temperatures (303 and 363 K). For the first time in the evaluation of the harmonic yield in such measurements, the variation of the liquid mass fraction, g, versus pressure and temperature is taken into consideration, which we determine, reliably and consistently, to be below 20% within our range of experimental parameters. By comparing the measured harmonic yield from a thin jet with the calculated corresponding yield from monomers alone, we find an increased emission of the harmonics when the average cluster size is less than 3000. Using g, under the assumption that the emission from monomers and clusters add up coherently, we calculate the ratio of the average single-atom response of an atom within a cluster to that of a monomer and find an enhancement of around 100 for very small average cluster size (∼200). We do not find any dependence of the cut-off frequency on the composition of the cluster jet. This implies that HHG in clusters is based on electrons that return to their parent ions and not to neighboring ions in the cluster. To fully employ the enhanced average single-atom response found for small average cluster sizes (∼200), the nozzle producing the cluster jet must provide a large liquid mass fraction at these small cluster sizes for increasing the harmonic yield. Moreover, cluster jets may allow for quasi-phase matching, as the higher mass of clusters allows for a higher density contrast in spatially structuring the nonlinear medium.

Parallel ktjet clustering algorithm

AbstractThe numerical simulation allows to study the high energy particle physics. It plays important of role in the reconstruction and analyze of these experimental and theoretical researches. This requires a computer background with a large capacity. Jet physics is an intensively researched area, where the factorization process can be solved by algorithmic solutions. We studied parallelization of the ktcluster algorithms. This method allows to know the development of particles due to the collision of highenergy nucleus-nucleus. The Alice offline library contains the required modules to simulate the ALICE detector that is a dedicated Pb-Pb detector. Using this simulation we can generate input particles, that we can further analyzed by clustering them, reconstructing their jet structure. The FastJet toolkit is an efficient C++ implementation of the most widely used jet clustering algorithms, among them the ktclustering. Parallelizing the standard non-optimized version of this algorithm utilizing the available CPU architecture a 1:6 times faster runtime was achieved, paving the way to drastic performance increase using many-core architectures.

Ion pinhole imaging diagnostics on fast ion source in femtosecond laser plasma of cluster targets.

The spatial configuration of the ion source generated under femtosecond laser interaction with clusters is investigated. While intense laser pulses (36 fs, 60 mJ, intensity of 4 × 1017 W/cm2) propagated in CO2 cluster (~0.22 μm in diameter) media, the shape of the obtained plasma ion source was registered for the first time by means of pinhole imaging method. The remarkable decrease in fast ion yield in the vicinity of the assumed best laser focus near the gas cluster jet axis is observed. Such observed anisotropy of the ion source is suggested to originate from the influence of the laser prepulse destroying clusters in advance to the arrival of the main pulse. The assumption is confirmed by optical shadowgraphy images of the plasma channel and is important for further development of an efficient laser-plasma-based fast ion source. Following the observed geometry of the ion source, the laser intensity limit allowing to accelerate ions to ~100 keV energy range was estimated.

Jet clustering dependence of Higgs boson production in vector-boson fusion

Precise predictions for Higgs production via vector-boson fusion play an important role when testing the properties of the Higgs boson and probing new-physics effects. While the inclusive cross section changes little when including NNLO and N3LO QCD corrections, a differential NNLO calculation with typical VBF cuts shows large corrections of up to 10% in distributions. In this article, we investigate the dependence of the differential NNLO QCD calculation on the jet definition. Starting from the known results at a fixed jet clustering choice, we use the electroweak H+3 jets production cross section at NLO precision to derive NNLO results for H+2 jets production for other jet definitions. We find that larger clustering radii significantly reduce the impact of NNLO corrections. The sizable NNLO corrections for distributions are largely caused by the broader energy flow inside jets at NNLO and are to be expected generally for processes with jets at LO.

Condensable Supersonic Jet Facility for Analyses of Transient Low-Temperature Gas Kinetics and Plasma Chemistry of Hydrocarbons

LEMPUS-2 facility is designed and built to study processes of cluster formation and plasma-chemical reactions that include atoms, molecules, and clusters, in supersonic jets. The facility is equipped with modern diagnostics tools and molecular-beam, electron-beam, mass-spectrometer, spectrometer, and laser systems for testing and fine-tuning technological processes in a laboratory environment. One of the key advantages of the discussed facility is that in a single system and a single experiment, it combines the tools for the activation of transient and steady-state supersonic flow with self-sustaining or nonself-sustaining discharge, and flow analysis using electron-beam spectroscopy and molecular-beam mass spectroscopy. Dry roughing and high-vacuum pumps enable accurate diagnostics of chemically reacting processes in virtually any gas mixture, including hydrocarbons. A pulsed flow regime controlled by developed in-house fast valves provides an efficient way to examine quasi-stationary flows at fairly high flow rates, with significant material and energy savings. The facility serves a number of purposes, from cluster-surface interaction studies with thin film and surface structure formation, to high-pressure jet expansions that emulate spacecraft nozzles at high altitudes, to technological process development, primarily focused on hydrocarbons. Details of key applications of the facility are presented that include the gas dynamics of cluster jets, the formation of heterogeneous clusters, the study of plasma-chemistry of hydrocarbons, and the thin film deposition.

X-ray laser near 13.5 and 11.3 nm in Xe26+ driven by an intense pump laser interacting with xenon cluster jet as a promising radiation source for nanolithography

The model of highly efficient (yield ~0.1–1% of pumping energy) monochromatic radiation sources near λ = 13.5 and 11.3 nm, intended for commercial nanolithography is presented. The sources are based on x-ray lasers on four transitions: 3p53d104l–3p53d104l′ (λ near 13.5 nm) and self photo-pumped 3d 94f (J = 1)–3d 94d (J = 1) (λ ~ 11.3 nm) transition of Ni-like xenon (Xe26+). New inversion mechanisms are discussed. A sufficiently intensive pumping pulse interacting with xenon cluster jet forms plasma. Optimal plasma parameters and quantum yields are predicted for each x-ray laser line. At pump intensities ⩾1018 W cm−2, immediately after the interaction, plasma is formed in the state with dominating Xe26+ ions. This condition is absolutely necessary for the short-lived lasing at 11.3 nm and for the wavelengths of laser transition measurements.

Temporal model for quasi-phase matching in high-order harmonic generation.

We present a model for quasi-phase matching (QPM) in high-order harmonic generation (HHG). Using a one-dimensional description, we analyze the time-dependent, ultrafast wave-vector balance to calculate the on-axis harmonic output versus time, from which we obtain the output pulse energy. Considering, as an example, periodically patterned argon gas, as may be provided with a grid in a cluster jet, we calculate the harmonic output during different time intervals within the drive laser pulse duration. We find that identifying a suitable single spatial period is not straightforward due to the complex and ultrafast plasma dynamics that underlies HHG at increased intensities. The maximum on-axis harmonic pulse energy is obtained when choosing the QPM period to phase match HHG at the leading edge of the drive laser pulse.

Higher Order Corrections in the CoLoRFulNNLO Framework

We discuss the CoLoRFulNNLO method for computing higher order radiative corrections to jet cross sections in perturbative QCD. We apply our method to the calculation of event shapes and jet rates in three-jet production in electron-positron annihilation. We validate our code by comparing our predictions to previous results in the literature and present the jet cone energy fraction distribution at NNLO accuracy. We also present preliminary NNLO results for the three-jet rate using the Durham jet clustering algorithm matched to resummed predictions at NLL accuracy, and a comparison to LEP data.

Measurements of jet rates with the anti-ktand SISCone algorithms at LEP with the OPAL detector

We study jet production in e + e − annihilation to hadrons with data recorded by the OPAL experiment at LEP at centre-of-mass energies between 90 GeV and 207 GeV. The jet production rates were measured for the first time with the anti-k t and SISCone jet clustering algorithms. We compare the data with predictions by modern Monte Carlo event generators.

Influence of Xe and Kr impurities on x-ray yield from debris-free plasma x-ray sources with an Ar supersonic gas jet irradiated by femtosecond near-infrared-wavelength laser pulses.

Many aspects of physical phenomena occurring when an intense laser pulse with subpicosecond duration and an intensity of 10^{18}-10^{19}W/cm^{2} heats an underdense plasma in a supersonic clustered gas jet are studied to determine the relative contribution of thermal and nonthermal processes to soft- and hard-x-ray emission from debris-free plasmas. Experiments were performed at the University of Nevada, Reno (UNR) Leopard laser operated with a 15-J, 350-fs pulse and different pulse contrasts (10^{7} or 10^{5}). The supersonic linear (elongated) nozzle generated Xe cluster-monomer gas jets as well as jets with Kr-Ar or Xe-Kr-Ar mixtures with densities of 10^{18}-10^{19}cm^{-3}. Prior to laser heating experiments, all jets were probed with optical interferometry and Rayleigh scattering to measure jet density and cluster distribution parameters. The supersonic linear jet provides the capability to study the anisotropy of x-ray yield from laser plasma and also laser beam self-focusing in plasma, which leads to efficient x-ray generation. Plasma diagnostics included x-ray diodes, pinhole cameras, and spectrometers. Jet signatures of x-ray emission from pure Xe gas, as well as from a mixture with Ar and Kr, was found to be very different. The most intense x-ray emission in the 1-9 KeV spectral region was observed from gas mixtures rather than pure Xe. Also, this x-ray emission was strongly anisotropic with respect to the direction of laser beam polarization. Non-local thermodynamic equilibrium (Non-LTE) models have been implemented to analyze the x-ray spectra to determine the plasma temperature and election density. Evidence of electron beam generation in the supersonic jet plasma was found. The influence of the subpicosecond laser pulse contrast (a ratio between the laser peak intensity and pedestal pulse intensity) on the jets' x-ray emission characteristics is discussed. Surprisingly, it was found that the x-ray yield was not sensitive to the prepulse contrast ratio.

A new tagger for hadronically decaying heavy particles at the LHC

A new algorithm for the identification of boosted, hadronically decaying, heavy particles at the LHC is presented. The algorithm is based on the known procedure of jet clustering with variable distance parameter $R$ and adapts the jet size to its transverse momentum $p_T$. Subjets are found using a mass jump condition. The resulting algorithm - called Heavy Object Tagger with Variable $R$ (HOTVR) - features little algorithmic complexity and combines jet clustering, subjet finding and rejection of soft clusters in one sequence. While the HOTVR algorithm can be used for the identification of any heavy object decaying hadronically, e.g. W, Z, H, t, or possible new heavy resonances, this paper targets specifically the tagging of boosted top quarks. The studies presented here demonstrate a stable performance of the HOTVR algorithm in a wide range of top quark $p_T$, from low $p_T$, where the decay products can be resolved, to the region of boosted decays at high $p_T$.

A method for identifying and characterising particle clusters in a two-phase turbulent jet

A novel technique for identifying and characterising clusters of particles from measurements within a densely seeded two-phase flow is reported. This technique involves the smoothing of normalised instantaneous planar images of particle concentration followed by the application of a robust and unambiguous dynamic threshold to identify particle clusters. Also reported is a method to extract quantitative cluster data including cluster length, width and number of branches. The method employs an algorithm to morphologically skeletonize images of clusters, and subsequently, prune skeleton branches to select those which most strongly represent the shape of the cluster. Together, these techniques have been shown to identify and characterise two-dimensional slices of three-dimensional particle clusters of complex shapes, including those that are bent, wrinkled and branched, with an uncertainty of ≈4% relative to the manually determined values. This method was applied to planar measurements of particles in a heavily seeded turbulent jet with an exit Stokes number of SkD=1.4 and Reynolds number of ReD=10,000, based on the pipe diameter, D. The results show that particle clusters are already present at the exit plane and have a characteristic width that is narrowly distributed around an average value of ≈0.17D. This implies that particle clusters are generated inside the pipe at this preferred length scale. The results also show that the average cluster length at the pipe exit is ≈1.0D, which, together with the observation that the clusters are oriented at oblique angles to the axis of the jet, suggests that the length of these clusters within the pipe is limited by the pipe diameter. The aspect ratio of the cluster slices was found to be typically AR≈6−7, consistent with the observations that the clusters form long, thin, filament-like structures.