Polar Angle Distributions Research Articles

Product rotational angular momentum polarization in the N + NH (v = 0, j = 0, 3, 6, 9)→N2 + H reaction

Based on the ground state HN2(12A′) potential energy surface (PES), the effects of collision energy and the rotational excitation of the reagent on the product alignment and the orientation for the title reaction are investigated by using quasi-classical trajectory (QCT) method. The distribution of polar angle P(θr) at collision energies 2–40kcal/mol with v=0 and j=0 level has been presented. The three angle distribution functions P(θr), P(ϕr), P(θr,ϕr) and four generalized polarization dependent differential cross sections (PDDCSs) at collision energy of 10kcal/mol with different rotational excitation are plotted. The results show that the product rotational angular momentum j′ is not only aligned, but also oriented along the direction perpendicular to the scattering plane. It has been found that the three angle distributions are sensitive to initially rotational excitation. The HHL mass combination and the property of the PES are used to explain the found results.

An experimental and theoretical view of energetic C60 cluster bombardment onto molecular solids.

Recent experimental measurements and calculations performed by molecular dynamics computer simulations indicate, for highly energetic C60 primary ions bombarding molecular solids, the emission of intact molecules is unique. An energy- and angle-resolved neutral mass spectrometer coupled with laser photoionization techniques was used to measure the polar angle distribution of neutral benzo[a]pyrene molecules desorbed by 20-keV [Formula: see text] primary ions and observed to peak at off-normal angles integrated over all possible emission energies. Similarly, computer simulations of 20-keV C60 projectiles bombarding a coarse-grained benzene system resulted in calculations of nearly identical polar angle distributions. Upon resolving the measured and calculated polar angle distributions, sputtered molecules with high kinetic energies are the primary contributors to the off-normal peak. Molecules with low kinetic energies were measured and calculated to desorb broadly peaked about the surface normal. The computer simulations suggest the fast deposition of energy from the C60 impact promotes the molecular emission by fluid-flow and effusive-type motions. The signature of off-normal emission angles is unique for molecules because fragmentation processes remove molecules that would otherwise eject near normal to the surface. Experimental measurements from a Ni {001} single crystal bombarded by 20-keV [Formula: see text] demonstrate the absence of this unique signature.

Ultra‐low frequency wave coupling in the ionospheric Alfvén resonator: Characteristics and implications for the interpretation of ground magnetic fields

In cold magnetospheric plasmas, ultra‐low frequency (ULF) waves occur in either the Alfvén or magnetosonic mode. Owing to the strong inhomogeneity of the near‐Earth plasma, these waves can produce cavity‐like or waveguide‐like eigenmodes which are mutually coupled by wave‐driven ionospheric currents and perpendicular plasma inhomogeneity. Here we present results from a numerical study of the ionospheric Alfvén resonator (IAR) and the ULF waves generated by wave‐driven field‐aligned currents (FACs) in the ionosphere. We demonstrate the excitation of cavity and waveguide eigenmodes of the IAR by a localized field‐aligned current, and examine the polarization patterns of the resultant ground magnetic fields. We find that the distribution of ellipticity reflects the configuration of the magnetospheric source while the distribution of polarization angles depends primarily on the localization of the signal. The pattern of magnetosonic waves generated by ionospheric Hall currents is generally isotropic, but its configuration is representative of the structure of the incident FAC. Apparent preferences for wave propagation eastward and to lower latitudes are identified, and implications for the interpretation of ground magnetic signatures are discussed.

J/ψPolarization inppCollisions ats=7 TeV

The ALICE Collaboration has studied J/ψ production in pp collisions at √s=7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/ψ polarization parameters λ(θ) and λ(φ) were obtained. The study was performed in the kinematic region 2.5<y<4, 2<p(t)<8 GeV/c, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties.

Analysis of the rotation of the polarisation direction in a cylindrical liquid crystal lens where the direction of the incident linear polarisation is not parallel to the axis of the cylindrical lens

A liquid crystal (LC) lens is used to change the propagating direction of the incident light at the lens-shaped boundary of two different media and shows strong dependence on the polarisation direction of the incident light. The performance of the cylindrical LC lens is investigated in the situation that the directions of the incident linear polarisation and the axis of the cylindrical lens are not parallel. Two LC cell configurations were considered where LC directors aligned twisted or homogeneously. In case of the twisted LC configuration, the polarisation direction of the propagating light follows the twist of the LC directors if the directions of the incident linear polarisation and the LC alignment on the side of the lower substrate are parallel. For these two configurations, the LC lens can control the propagating light in the LENS-ON state. In case of homogeneously aligned LC configuration, polar angle distributions of LC directors are not uniform due to the lens-shaped boundary. So in the LENS-OFF state where LC directors rotate under the driving voltage, a LC domain boundary may occur in some cases.

Two jets and missing E T signature to determine the spins of new particles

We consider the spin determination of new colored particles in the missing energy plus jets channel at the early stage of the discovery. We use a three site moose model to describe the low energy Lagrangian of all same spin partner (LHT or UED like) models and check the gauge invariance of the amplitude. For the benchmark production and decay channel pp → U (R) U (R) → uuB H B H , in contrast to those in supersymmetric models, there are spin correlations which affect the polar and azimuthal angle distributions of the quarks from the heavy partner U (R) decay. We show such effects would be visible in the E Tmiss /M eff distribution and the reconstructed azimuthal angle correlation using MAOS reconstruction.

Disorder-induced exciton localization and violation of optical selection rules in supramolecular nanotubes

Using numerical simulations, we study the effect of disorder on the optical properties of cylindrical aggregates of molecules with strong excitation transfer interactions. The exciton states and the energy transport properties of such molecular nanotubes attract considerable interest for application in artificial light-harvesting systems and energy transport wires. In the absence of disorder, such nanotubes exhibit two optical absorption peaks, resulting from three super-radiant exciton states, one polarized along the axis of the cylinder, the other two (degenerate) polarized perpendicular to this axis. These selection rules, imposed by the cylindrical symmetry, break down in the presence of disorder in the molecular transition energies, due to the fact that the exciton states localize and no longer wrap completely around the tube. We show that the important parameter is the ratio of the exciton localization length and the tube's circumference. When this ratio decreases, the distribution of polarization angles of the exciton states changes from a two-peak structure (at zero and ninety degrees) to a single peak determined by the orientation of individual molecules within the tube. This is also reflected in a qualitative change of the absorption spectrum. The latter agrees with recent experimental findings.

Dynamics of pion production in heavy-ion collisions around1A GeV energies

Within the framework of the improved isospin-dependent quantum molecular dynamics model, the dynamics of pion emission in heavy-ion collisions in the region of $1$$A$ GeV energies as a probe of nuclear symmetry energy at suprasaturation densities is investigated systematically. The total pion multiplicities and the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ yields are calculated for selected Skyrme parameters SkP, SLy6, Ska, and SIII and also for the cases of different stiffness of symmetry energy with the parameter SLy6. The influence of Coulomb potential, symmetry energy, and in-medium pion potential on the pion production is investigated and compared to each other by analyzing the distributions of transverse momentum and longitudinal rapidity and also the excitation functions of the total pion and the ${\ensuremath{\pi}}^{\ensuremath{-}}/{\ensuremath{\pi}}^{+}$ ratio. The directed flow, elliptic flow, and polar-angle distributions are calculated for the cases of different collision centralities and also the various stiffnesses of the symmetry energies. A comparison of the calculations with the available experimental data is performed.

Next-to-leading order QCD corrections to a heavy resonance production and decay into top quark pair at the LHC

We present a complete next-to-leading order (NLO) QCD calculation to a heavy resonance production and decay into a top quark pair at the LHC, where the resonance could be either a Randall-Sundrum (RS) Kaluza-Klein (KK) graviton $G$ or an extra gauge boson $Z'$. The complete NLO QCD corrections can enhance the total cross sections by about $80\%- 100\%$ and $20\%- 40\%$ for the $G$ and the $Z'$, respectively, depending on the resonance mass. We also explore in detail the NLO corrections to the polar angle distributions of the top quark, and our results show that the shapes of the NLO distributions can be different from the leading order (LO) ones for the KK graviton. Moreover, we study the NLO corrections to the spin correlations of the top quark pair production via the above process, and find that the corrections are small.

Determination of polar anchoring energy of dye-doped liquid crystals by measuring capacitance

Polar anchoring energy of a dye-doped liquid crystal (DDLC) cell is determined based on capacity measurements. Experimental results indicate that under the illumination of a pump beam, the polar anchoring energy (7.90×10−6 J/m2) includes the adsorption-induced anchoring energy (5.74×10−6 J/m2) and the preexisting-dye-induced anchoring energy (2.16×10−6 J/m2). The latter is attributed to the torque, which is induced by the dye molecules on the boundary surface even before illumination. After the illumination, the adsorption-induced anchoring energy remains and the preexisting-dye-induced anchoring energy disappears, with the former revealing that weak anchoring affects the decay time and threshold voltage of the DDLC cell. Moreover, plotting the polar angle distributions in the DDLC cell reveals its correlation with variations in the capacitance of the DDLC cell.

A Monte Carlo simulation study of Nitrogen on LiF(0 0 1)

The adsorption of N 2 gas on the LiF(0 0 1) surface is studied by canonical Monte Carlo (CMC) computer simulation. These results show that N 2 forms an ordered structure where the molecules are arranged in a unit cell of p ( 2 2 × 2 ) R 45 ° symmetry at temperatures below 23 K with 50% coverage. The nitrogen molecules are tilted by 53° from the surface normal and have the same azimuthal orientation along diagonals, with diagonals alternating their orientation. Beyond 23 K, the molecules become azimuthally disordered but with residual short-range order. No change in the position of the peak of the polar (tilt) angle distribution was observed above the transition temperature. This transition is purely of the order–disorder type.

Anisotropy of secondary ion emission from a Ni4Mo single crystal

The azimuthal and polar angle distribution of Ni+ and Mo+ ions emitted from an ordered Ni4 Mo single crystal irradiated with 10-keV Ar+ ions was studied. Different azimuthal distributions for Ni+ and Mo+ ions emitted from the (001) Ni4Mo face were detected; emission maxima were observed in 〈 011 〉 and 〈 001 〉 directions for Ni+ and Mo+ ions, respectively. It was shown that polar distributions of nickel’s secondary ions vary with its energy. The observed systematic features were explained by correlated collisions in the upper layers of a Ni4Mo single crystal.

φ production in In–In collisions at 158 A GeV

The NA60 experiment has measured muon pair production in In–In collisions at 158 AGeV at the CERN SPS. This paper presents a high statistics measurement of φ→μ μ meson production. Differential spectra, yields, mass and width are measured as a function of centrality and compared to previous measurements in other colliding systems at the same energy. The width of the rapidity distribution is found to be constant as a function of centrality, compatible with previous results. The decay muon polar angle distribution is measured in several reference frames. No evidence of polarization is found as a function of transverse momentum and centrality. The analysis of the p T spectra shows that the φ has a small radial flow, implying a weak coupling to the medium. The T eff parameter measured in In–In collisions suggests that the high value observed in Pb–Pb in the kaon channel is difficult to reconcile with radial flow alone. The absolute yield is compared to results in Pb–Pb collisions: though significantly smaller than measured by NA50 in the muon channel, it is found to exceed the NA49 and CERES data in the kaon channel at any centrality. The mass and width are found to be compatible with the PDG values at any centrality and at any p T : no evidence for in-medium modifications is observed.

Angular distribution for the electron recoil in pair production by linearly polarized [formula omitted]- rays on electrons

In this work we study the angular distribution of electron recoil in pair production by linearly polarized gamma rays in the electron electric field. We also present a new algorithm for the simulation of this cross-section for the polar and azimuthal angle distributions for the recoil electron obtained from the cross section calculated using the Borsellino diagrams in the high energy limit ( [1] E.A. Vinokurov, E.A. Kurae, Sov. Phys. JETP 36 (1973) 602). Although this process has a lower probability than the pair production in the nucleus field ( ∼ 1 / Z ) , it is nevertheless interesting since the azimuthal distribution of the recoil electron is highly sensitive to the polarization of the incoming gamma radiation. This process is also interesting for the fact that in the range of Born approximation, the distribution of the polar and azimuthal angles of the electron recoil momentum does not depend explicitly on photon energy. This is important in astrophysics since the astrophysical sources are in general non-monochromatic. We insert the algorithm into the Geant4 toolkit and made simple simulation to test the method.

Electron attenuation anisotropy at crystal surfaces from LEED

Dynamical theory of electron scattering is used to describe the electron transport in the surface regions of crystals. The angle resolved attenuation length of electrons is derived from the transmitted LEED electron current decay. Electron attenuation length energy dependence and anisotropy in polar angle are found for crystalline Cu(1 1 1) for two high symmetry azimuths. Pronounced anisotropy in polar angle distributions of attenuation lengths is found to be in qualitative agreement with the results obtained from the photoelectron diffraction. Comparison with the attenuation lengths obtained from semiclassical simulations for amorphous copper is given. This comparison demonstrates that simple transfers of the smoothly behaving surface sensitivity from amorphous materials oversimplifies the electron attenuation process and can lead to incorrect results in quantitative analyses of crystalline surfaces.

Orientation ordering of N2 molecules in vertically aligned CN x nanotubes

Arrays of vertically aligned nitrogen-doped carbon (CNx) nanotubes have been synthesized by decomposition of aerosol mixture of acetonitrile and ferrocene at 850°C. Nitrogen concentration in the outer shells of the CNx nanotubes was found from X-ray photoelectron spectroscopy (XPS) data to reach ∼6%. The XPS N 1s spectra and N 1s near-edge X-ray absorption fine structure (NEXAFS) spectra identified three chemical forms of nitrogen in the CNx nanotube arrays: pyridine-like, graphitic, and molecular nitrogen. The π* resonance of molecular nitrogen showed clear polarization dependence that indicates predominant orientation of N2 molecules along the nanotubes axis. The estimated range of the polar angle distribution of the N2 molecules orientation in the CNx nanotube array amounts to 15°.

High-resolution radio continuum survey of M 33

Aims. We study the magnetic field structure, strength, and energy density in the Scd galaxy M 33. Methods. Using the linearly polarized intensity and polarization angle data at 3.6, 6.2 and 20 cm, we determine variations of Faraday rotation and depolarization across M 33. We fit a 3D model of the regular magnetic field to the observed azimuthal distribution of polarization angles. We also analyze the spatial variation of depolarization across the galaxy. Results. Faraday rotation, measured between 3.6 and 6.2 cm at an angular resolution of 3 � (0.7 kpc), shows more variation in the south than in the north of the galaxy. About 10% of the nonthermal emission from M 33 at 3.6 cm is polarized. High degrees of polarization of the synchrotron emission (>20%) and strong regular magnetic fields in the sky plane (� 6.6 μG) exist in-between two northern spiral arms. We estimate the average total and regular magnetic field strengths in M 33 as � 6.4 and 2.5 μG, respectively. Under the assumption that the disk of M 33 is flat, the regular magnetic field consists of horizontal and vertical components: however the inferred vertical field may be partly due to a galactic warp. The horizontal field is represented by an axisymmetric (m = 0) mode from 1 to 3 kpc radius and a superposition of axisymmetric and bisymmetric (m = 0 + 1) modes from 3 to 5 kpc radius. Conclusions. An excess of differential Faraday rotation in the southern half together with strong Faraday dispersion in the southern spiral arms seem to be responsible for the north-south asymmetry in the observed wavelength dependent depolarization. The presence of an axisymmetric m = 0 mode of the regular magnetic field in each ring suggests that a galactic dynamo is operating in M 33. The pitch angles of the spiral regular magnetic field are generally smaller than the pitch angles of the optical spiral arms but are twice as big as simple estimates based on the mean-field dynamo theory and M 33’s rotation curve. Generation of interstellar magnetic fields from turbulent gas motion in M 33 is indicated by the equipartition of turbulent and magnetic energy densities.

Comparison of Geant4 hadron generation with data from the interactions with beryllium nuclei of +8.9 GeV/c protons and pions and −8.0 GeV/c pions

Hadron generation in the Geant4 simulation tool kit is compared with inclusive spectra of secondary protons and pions from the interactions with beryllium nuclei of +8.9 GeV/c protons and pions, and of −8.0 GeV/c pions. The data were taken in 2002 at the CERN Proton Synchrotron with the HARP spectrometer. We report on significant disagreements between data and Monte Carlo simulation especially in the polar-angle distributions of secondary protons and pions.

Polar exit angle distributions of slow H+ ions, related to the presence of a regular domain structure, calculated within the diffuse scattering approximation upon interaction of ions with the sample surface

The angular distributions of slow H ions scattered from the surface of a magnetic film with a stripe domain structure have been calculated. The calculations were performed within the models of specular and diffuse scattering upon collisions of ions with surface. It is shown that the magnetic fields of the stripe domain structure block the ions scattered at small exit angles. It is established that, within the more adequate model of diffuse scattering, the anisotropy of interaction of ions with the magnetic field of the stripe structure manifests itself in a wider angular range.

Polar PWI and CEPPAD observations of chorus emissions and radiation belt electron acceleration: Four case studies

We investigated the role of whistler-mode chorus in accelerating outer radiation belt electrons during four moderate geomagnetic storms when data from the Polar Plasma Wave Investigation (PWI) were available. The storm time periods we examined included two storms associated with coronal mass ejections (CMEs), the well-studied January 10–13, 1997 International Solar Terrestrial Physics event and the May 12–15, 1997 event. We compared these two storms with two geomagnetically active periods that were not associated with CMEs. Although strong chorus emissions were observed during all four events, the association of electron acceleration with chorus emissions is not clear. During all four events, the Polar Comprehensive Energetic Particle and Pitch Angle Distribution (CEPPAD) experiment observed increases in the fluxes of energetic electrons (0.8< E<6.4 MeV). The two events associated with CMEs featured a sudden increase in the electron fluxes above 0.8 MeV that may have been related to the impact of the CME shock wave upon the magnetosphere. The other two events featured more gradual increases in the electron fluxes over a period of several days. The data from these events indicate that the role played by resonant interactions with chorus in accelerating electrons may depend on the upstream solar wind conditions driving the storm.