Azimuthal Modulation Research Articles

FRAGMENTATION FUNCTIONS AT BABAR

Inclusive hadron production cross section in e+e- annihilation shed light on fundamental questions of hadronization and fragmentation processes. We present measurements of inclusive spectra of charged pions, kaons, and protons (antiprotons) produced in e+e- collisions at the center-of-mass energy of 10.54 GeV, and tests of QCD predictions and hadronization models. We also report the results on the measurement of the azimuthal modulation induced by the Collins effect in inclusive production of charged pion pairs e+e- → ππX, where the two pions are produced in opposite hemispheres. These data allows the determination of the polarized Collins fragmentation functions.

Transverse spin and transverse momentum structure of the nucleon from the COMPASS experiment

COMPASS is a fixed target experiment at the CERN SPS M2 beam line, taking data since year 2002. Part of the physics programme is dedicated to the study of the transverse spin and transverse momentum structure of the nucleon, by means of semi-inclusive deeply inelastic lepton scattering (SIDIS). For these measurements, data have been collected using transversely polarised proton (NH 3 ) and deuteron ( 6 LiD) targets. A selection of the results on the azimuthal asymmetries measured is presented, with particular focus on the most recent measurements from the data collected in 2007 and 2010 with the proton target. These results exhibit clear signals for the Collins asymmetry, interpreted as a convolution of a non-zero transversity PDF and Collins fragmentation function, and for the Sivers asymmetry which is related to the Sivers function, the most famous and discussed of the TMD PDFs. The data collected with the 6 LiD target, have also been recently analysed to search for the azimuthal modulations in the production of hadrons which are expected to be present in the unpolarised part of the SIDIS cross-section. The azimuthal hadron asymmetries, which are related to the Boer-Mulders TMD PDF, show strong and somewhat puzzling kinematical dependencies.

Considerations for Ku-Band Scatterometer Calibration Using the Dry-Snow Zone of the Greenland Ice Sheet

Postlaunch calibration of satellite-borne scatterometers using backscatter data from natural land targets helps to maintain scatterometer accuracy. Due to its temporal stability, the dry-snow zone of the Greenland ice sheet has been proposed in previous studies as a calibration target. Using QuikSCAT data, this letter examines the backscatter properties of the dry-snow zone that are relevant to Ku-band scatterometer calibration including temporal and spatial variabilities, and azimuth-angle and polarization and incidence-angle dependences. The backscatter is found to seasonally vary throughout the dry-snow zone by 0.4 dB on average. Small interannual variations (less than 1.5 dB over a nine year period) in the backscatter are also present in some regions. Azimuth modulation is generally less than 0.4 dB in magnitude and is not significant in some regions of the dry-snow zone. Melting and refreezing appear to cause the quasi-polarization ratio to temporarily decrease. Spatially consistent and relatively temporally stable regions that are well within the interior of the dry-snow zone are best suited as calibration sites.

Overview of recent results from the HERMES experiment

HERMES has taken a wealth of deep-inelastic scattering (DIS) data using the 27.6 GeV polarized lepton beam at HERA and various pure gas targets, both unpolarized and polarized, which opened the door to several unique results. Among them are the first evidences for the naive-T-odd Sivers and Collins effects but also the recent first measurements of azimuthal modulations in the unpolarized semi-inclusive DIS cross section for charged kaons and pions and of beam-helicity asymmetries in exclusive leptoproduction of real photons using recoil-proton detection. An overview of HERMES results is given with emphasis on the exploration of the three-dimensional structure of the nucleon.

Azimuthal temperature modulations of Saturn’s A ring caused by self-gravity wakes

The physical temperatures of the Saturn’s A ring measured by the Cassini Composite Infrared Spectrometer (CIRS) show quadrupole azimuthal modulations besides temperature drops in Saturn’s shadow. These azimuthal modulations are likely to be caused by self-gravity wakes. In this paper, we develop a new thermal model in which wakes are modeled as elliptical cylinders ignoring inter-wake particles. All the heat fluxes are calculated explicitly taking into account inter-wake shadowing and heating. We apply our model to azimuthal scans of the A ring obtained by CIRS. It is found that the azimuthal modulation of the ring temperature is primarily caused by the azimuthal variation of the geometric filling factor of the ring seen from the Sun. The thermal inertia estimated from the eclipse data (data only inside and near Saturn’s shadow) of the low phase scans is ∼10Jm−2K−1s−1/2. With this value of the thermal inertia, the amplitude of the azimuthal temperature modulation is overestimated in our model as compared with those observed. This is likely to be because our model ignores inter-wake particles. The bolometric reflectance of wakes is estimated to be 0.35–0.40 although lower values are required to reproduce temperatures at low solar phase angles. This apparent phase dependence of the reflectance indicates that roughness on the wake surfaces is necessary.

Resonance solitons produced by azimuthal modulation in self-focusing and self-defocusing materials

We demonstrate azimuthally modulated resonance scalar and vector solitons in self-focusing and self-defocusing materials. They are constructed by selecting appropriately self-consistency and reso- nance conditions in a coupled system of multicompo- nent nonlinear Schrodinger equations. In the case with zero modulation depth, it was found that the larger the topological charge, the smaller the intensity of the soliton in the self-focusing material, while in the self- defocusing material the opposite holds. For the soli- tons with the same parameters, the ones in the self- focusing material possess larger optical intensity than the ones in the self-defocusing material. The stabil- ity of resonance solitons is examined by direct nu- merical simulation, which demonstrated that a new class of stable scalar fundamental soliton states with m = 0 and low-order vector vortex soliton states with m = 1 can be supported by self-focusing and self- defocusing materials. Higher-order solitons are found unstable, however, displaying quasi-stable propaga- tion over prolonged distances.

Measurements of Jet Suppression with ATLAS

Abstract Measurements of inclusive jet suppression in Pb + Pb collions at s N N = 2.76 TeV with the ATLAS detector are reported. The centrality, p T and jet size dependence of the central-to-peripheral ratio, R CP , is presented. The results indicate that jets are suppressed by approximately a factor of two in the most central collisions, and a significant dependence on the jet size is observed. The path length dependence of jet quenching is studied through measurements of inclusive jet suppression as a function of angle with respect to the event plane. The azimuthal modulation of the jet yield is quantified by its second Fourier coefficent, ν 2 , which is significant in all p T and centrality ranges presented.

An analysis of the influence of background subtraction and quenching on jet observables in heavy-ion collisions

Abstract Subtraction of the large background in reconstruction is a key ingredient in jet studies in high-energy heavy-ion collisions at RHIC and the LHC. Here we address the question to which extent the most commonly used subtraction techniques are able to eliminate the effects of the background on the most commonly discussed observables at present: single inclusive jet distributions, dijet asymmetry and azimuthal distributions. We consider two different background subtraction methods, an area-based one implemented through the FastJet package and a pedestal subtraction method, that resemble the ones used by the experimental collaborations at the LHC. We also analyze different ways of defining the optimal parameters in the second method. We use a toy model that easily allows variations of the background characteristics: average background level and fluctuations and azimuthal structure, but cross-checks are also done with a Monte Carlo simulator. Furthermore, we consider the influence of quenching using Q-PYTHIA on the dijet observables with the different background subtraction methods and, additionally, we examine the missing momentum of particles. The average background level and fluctuations affect both single inclusive spectra and dijet asymmetries, although differently for different subtraction setups. A large azimuthal modulation of the background has a visible effect on the azimuthal dijet distributions. Quenching, as implemented in Q-PYTHIA, substantially affects the di-jet asymmetry but little the azimuthal dijet distributions. Besides, the missing momentum characteristics observed in the experiment are qualitatively reproduced by Q-PYTHIA.

AN EXTENDED FREQUENCY SCALING ALGORITHM FOR HIGH SQUINT SPOTLIGHT AIRBORNE SAR

In high squint spotlight mode SAR, the coupling of the range and azimuth is very serious, which brings challenges to the imaging. In this paper, an extended frequency scaling algorithm is proposed, in which the range migration correction is divided into two steps. Firstly the range walk correction is implemented in 2D time domain. In the second step, the residual range migration is corrected by the frequency scaling and bulk shift operations. Though the second range compression does not consider the range space variance, the range compression is precise. In the azimuth compression, because of the range walk correction, the azimuth modulation frequency rate becomes dependent on the azimuth position. In order to equalize the azimuth modulation frequency rate, the azimuth nonlinear chirp scaling method is involved to remove the dependence. The simulation experiments verify the validity of the proposed algorithm. The comparison of the imaging quality among traditional frequency scaling algorithm, nonlinear frequency scaling algorithm and the proposed method indicates the proposed method is more suitable for the high squint spotlight SAR.

EXCITATION OF AZIMUTHAL EIGEN MODES BY MODULATED ANNULAR ELECTRON BEAM

Excitation of extraordinarily polarized azimuthal eigen modes by modulated annular electron beam is shown to be characterized by the increase of instability growth rates compared with the case of non-modulated electron beam. Interaction between the modulated beam and azimuthal eigen modes happens in the range of electron cyclotron frequency in waveguides with metal walls, which are partially fllled with cold magneto-active plasma. Non- linear set of difierential equations, which describs excitation of these azimuthal modes by an annular electron beam is derived and analyzed numerically. Difierent scenarios of the beam-plasma interaction depending on relation between azimuthal mode number of the exited waves and periodicity of azimuthal modulation of the beam density, degree and manner of the beams' modulation are studied numerically.

Two-dimensional accessible solitons in PT-symmetric potentials

Two-dimensional parity-time (PT) symmetric potentials are introduced, which allow the existence of spatial solitons in the model of the strongly nonlocal nonlinear Schrodinger equation. Two-dimensional accessible solitons are found in the form of solutions separating the radial amplitude, given in terms of Laguerre polynomials, a phase function involving quadratic, linear, and constant phase shifts, and a specific azimuthal modulation function. Shape-preserving solitons are constructed from Laguerre–Gaussian functions containing the self-similar variable and an exponential form of the azimuthal modulation, containing sine and cosine functions, when a suitable PT-symmetric potential is chosen. Interesting soliton profiles and the corresponding PT-symmetric potentials are displayed for different values of the parameters.

KINEMATICS OF THE CO GAS IN THE INNER REGIONS OF THE TW Hya DISK

We present a detailed analysis of the spatially and spectrally resolved 12CO J=2-1 and J=3-2 emission lines from the TW Hya circumstellar disk, based on science verification data from the Atacama Large Millimeter/Submillimeter Array (ALMA). These lines exhibit substantial emission in their high-velocity wings (with projected velocities out to 2.1 km/s, corresponding to intrinsic orbital velocities >20 km/s) that trace molecular gas as close as 2 AU from the central star. However, we are not able to reproduce the intensity of these wings and the general spatio-kinematic pattern of the lines with simple models for the disk structure and kinematics. Using three-dimensional non-local thermodynamic equilibrium molecular excitation and radiative transfer calculations, we construct some alternative models that successfully account for these features by modifying either (1) the temperature structure of the inner disk (inside the dust-depleted disk cavity; r < 4 AU); (2) the intrinsic (Keplerian) disk velocity field; or (3) the distribution of disk inclination angles (a warp). The latter approach is particularly compelling because a representative warped disk model qualitatively reproduces the observed azimuthal modulation of optical light scattered off the disk surface. In any model scenario, the ALMA data clearly require a substantial molecular gas reservoir located inside the region where dust optical depths are known to be substantially diminished in the TW Hya disk, in agreement with previous studies based on infrared spectroscopy. The results from these updated model prescriptions are discussed in terms of their potential physical origins, which might include dynamical perturbations from a low-mass companion with an orbital separation of a few AU.

Topological light bullets supported by spatiotemporal gain

We reveal that the competition between diffraction, cubic nonlinearity, two-photon absorption, and gain localized in both space and time results in arrest of collapse, suppression of azimuthal modula-tion instabilities for spatiotemporal wavepackets, and formation of stable three-dimensional light bul-lets. We show that Gaussian spatiotemporal gain landscapes support bright, fundamental light bullets, while gain landscapes featuring a ring-like spatial and a Gaussian temporal shapes may support stable vortex bullets carrying topological phase dislocations.

Azimuthal vortex clusters in Bose-Einstein condensates

We describe, analytically and numerically, topologically nontrivial stationary states with azimuthal modulation of density in a repulsive Bose-Einstein condensate (BEC) confined in a harmonic trap. We show that, depending on the number of density peaks and total topological charge, these states can have a sophisticated phase texture associated with a vortex cluster. For a given topological charge, the form of density distribution and the structure of phase singularities are uniquely linked, thus simultaneous phase and density modulation enforces the formation of a vortex cluster both in rotating and in nonrotating BEC clouds.

Domain-shape-based modulation of Čerenkov second-harmonic generation in multidomain strontium barium niobate

We study experimentally and numerically the second-harmonic Čerenkov emission with two different characteristic azimuthal intensity distributions in strontium barium niobate with a random structure of χ2 nonlinearity. We monitor in situ the Čerenkov emission during domain switching and show that a change of domain size and shape results in a fourfold azimuthal modulation of the Čerenkov cone.

Diffraction characteristics of optical elements designed as phase layers with cosine-profiled periodicity in the azimuthal direction

The article concerns an investigation of the Fresnel diffraction characteristics of two types of phase optical elements under Gaussian laser beam illumination. Both elements provide an azimuthal periodicity of the phase retardation. The first element possesses azimuthal cosine-profiled phase changes deposited on a plane base. The second element is a combination of the first element and a thin phase axicon. The cosine profile of the phase retardation of both diffractive elements produces an azimuthal cosine-profiled modulation on their diffractograms. It destroys the vortex characteristics of their diffraction fields.

The effect of the geomagnetic field on cosmic ray energy estimates and large scale anisotropy searches on data from the Pierre Auger Observatory

We present a comprehensive study of the influence of the geomagnetic field on the energy estimation of extensive air showers with a zenithangle smaller than 60°, detected at the Pierre Auger Observatory.The geomagnetic field induces an azimuthal modulation of the estimated energy of cosmic rays up to the ∼ 2% level at large zenith angles.We present a method to account for this modulation of the reconstructed energy. We analyse the effect of the modulation on large scale anisotropy searches in the arrival direction distributions of cosmic rays. At a given energy, the geomagnetic effect is shown to induce a pseudo-dipolar pattern at the percent level in the declination distribution that needs to be accounted for.

Localized nonlinear wavepackets with radial–azimuthal modulated nonlinearity and an external potential

We analytically investigated two-dimensional localized nonlinear waves in Kerr media with radial and azimuthal modulation of the nonlinearity and in the presence of an external potential. The solutions have been derived through the similarity transformation. We demonstrate that the properties of nonlinear waves are determined by two parameters: a whole number n (the index of the Jacobi elliptical waves) and an integer m (the topological charge). Our results indicate that the dynamic evolution, including cnoidal and snoidal waves, can be strongly affected by these two parameters, providing an approach to controlling nonlinear waves by an appropriate radial–azimuthal modulation of the nonlinearity, with an appropriate external potential.

Self-focusing of femtosecond diffraction-resistant vortex beams in water

We report experiments on self-focusing of femtosecond diffraction-resistant vortex beams in water. These beams are higher-order Bessel beams with weak azimuthal modulation of the transverse intensity patterns. The modulation overrides the self-focusing dynamics and results in the formation of regular bottlelike filament distributions. The peak-power thresholds for filamentation, at a particular distance, are relatively accurately estimated by the adaptation of the Marburger formula derived earlier for Gaussian beams. The nonlinear conversion of the incident conical waves into the localized spatial wave packets propagating near the beam axis is observed.

Partonic transverse motion in unpolarized semi-inclusive deep inelastic scattering processes

We analyze the role of partonic transverse motion in unpolarized semi-inclusive deep inelastic scattering processes. Imposing appropriate kinematical conditions, we find some constraints which fix an upper limit to the range of allowed ${k}_{\ensuremath{\perp}}$ values. We show that, applying these additional requirements on the partonic kinematics, we obtain different results with respect to the usual phenomenological approach based on the Gaussian smearing with analytical integration over an unlimited range of ${k}_{\ensuremath{\perp}}$ values. These variations are particularly interesting for some observables, like the $⟨\mathrm{cos}{\ensuremath{\phi}}_{h}⟩$ azimuthal modulation of the unpolarized semi-inclusive deep inelastic scattering cross section or the average transverse momentum of the final, detected hadron.