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Absorptive corrections, which are known to suppress proton-neutron transitions with a large fractional momentum z → 1 in p p collisions, become dramatically strong on a nuclear target, and they push the partial cross sections of leading neutron production to the very periphery of the nucleus. The mechanism of the pion π and axial vector meson a 1 interference, which successfully explains the observed single-spin asymmetry in a polarized p p → n X , is extended to the collisions of polarized protons with nuclei. When corrected for nuclear effects, it explains the observed single-spin azimuthal asymmetry of neutrons that is produced in inelastic events, which is where the nucleus violently breaks up. This single-spin asymmetry is found to be negative and nearly atomic mass number A-independent. [ABSTRACT FROM AUTHOR]

Absorptive corrections, which are known to suppress proton-neutron transitions with a large fractional momentum z→1 in pp collisions, become dramatically strong on a nuclear target, and they push the partial cross sections of leading neutron production to the very periphery of the nucleus. The mechanism of the pion π and axial vector meson a1 interference, which successfully explains the observed single-spin asymmetry in a polarized pp→nX, is extended to the collisions of polarized protons with nuclei. When corrected for nuclear effects, it explains the observed single-spin azimuthal asymmetry of neutrons that is produced in inelastic events, which is where the nucleus violently breaks up. This single-spin asymmetry is found to be negative and nearly atomic mass number A-independent.

When tunneling events induced by nontrivial configurations of the quantum chromodynamics gauge fields are taken into consideration, parity violating quantities emerge. Based on this consideration, parity-odd fragmentation functions can be introduced in the high energy reactions. In this paper, we calculate the differential cross-section in terms of both the parity-even and parity-odd fragmentation functions in semi-inclusive electron positron annihilation process. Semi-inclusive implies that not only a vector meson in one jet but also the back-to-back jet is measured in this reaction. According to the differential cross-section, we further calculate the azimuthal asymmetries and hadron polarizations in terms of fragmentation functions. A method of measuring the parity violating effects in the semi-inclusive annihilation process is suggested. [ABSTRACT FROM AUTHOR]

The radiation losses of a relativistic charge moving in vacuum near a dielectric radiator in which Vavilov – Cherenkov radiation is generated are estimated. For a charge moving near the flat surface of an infinite radiator (along the charge path), the radiation losses are calculated based on the existing theory. For a finite radiator of length L along the charge trajectory (that is, for the radiator with input and output planar faces perpendicular to the charge propagation path that give rise the edge effects), we have developed a model for calculating the radiation characteristics by the polarization current method. For this model, the radiation losses are calculated, and it is shown that with allowance for the edge effects, the losses in the finite radiator on Vavilov–Cherenkov radiation are higher by 2–3 orders of magnitude compared to the losses of the infinite radiator. [ABSTRACT FROM AUTHOR]

We present the QCD predictions for the azimuthal cos⁡2φ asymmetry in charm leptoproduction for the kinematics of the COMPASS experiment at CERN. The asymmetry is predicted to be large, about 15%. The radiative corrections to the QCD predictions for the cos⁡2φ distribution are estimated to be small, less than 10%. Our calculations show that the azimuthal asymmetry in charm production is well defined in pQCD: it is stable both perturbatively and parametrically, and practically insensitive to theoretical uncertainties in the input parameters. We analyze the nonperturbative contributions to the cos⁡2φ distribution due to the gluon transverse motion in the target and the c-quark fragmentation. Because of the c-quark low mass, the nonperturbative contributions are expected to be sizable, about (30–40)%. We conclude that extraction of the azimuthal asymmetries from available COMPASS data will provide valuable information about the transverse momentum dependent distribution of the gluon in the proton and the c-quark hadronization mechanism. Finally, we discuss the cos⁡2φ asymmetry as a probe of the gluonic analogue of the Boer–Mulders function, h1⊥g, describing the linear polarization of gluons inside unpolarized proton.

We present the complete azimuthal asymmetries at leading twist in terms of fragmentation functions in dihadron production semi-inclusive electron–positron annihilation process. When the nontrivial 𝜃 vacuum is taken into consideration, the parity symmetry of quantum chromodynamics is violated. As a consequence of the l o c a l 𝒫 -odd effects, 𝒫 -odd fragmentation functions would contribute to the azimuthal asymmetries. Azimuthal asymmetry coming from two interference terms with opposite signs vanishes when sum over many events. This symmetry only survives on the event-by-event basis. Azimuthal asymmetry coming from two interference terms with same signs survives and can be measured to extract the 𝒫 -odd fragmentation functions. We also present the hadron polarizations. [ABSTRACT FROM AUTHOR]

Abstract Modern accelerator technologies may provide electron beams consisting of ultrashort bunches with transverse sizes, which are much larger than longitudinal sizes. The spectral-angular characteristics of coherent Cherenkov radiation (CChR) produced by such bunches have thus been considered. We simulated the characteristics of CChR and those from a single charge on the basis of the polarization current model, which allowed us to consider finite sizes for the Cherenkov radiator. We calculated the angular distribution of the CChR from a bunch tilted by angle ψ , with respect to the velocity direction, with the assumption of a 3-D Gaussian charge distribution in the bunch. Contrary to the azimuthally symmetrical distribution of conventional ChR, a strong azimuthal asymmetry was observed in the CChR from the tilted bunch. The maximal yield of the CChR may be achieved if the tilt angle ψ coincides with the Cherenkov angle Θ ch = arccos ⁡ (1 / n β) , βc is the charge velocity and n is the refraction index. Highlights • The coherent Cherenkov radiation from tilted electron bunches has been investigated. • The coherent Cherenkov radiation produced from such a bunch possesses the strong azimuthal asymmetry. • The direction of the maximal radiation yield is defined by the plane containing a bunch axes and its velocity. [ABSTRACT FROM AUTHOR]

We present the QCD predictions for the azimuthal cos ⁡ 2 φ asymmetry in charm leptoproduction for the kinematics of the COMPASS experiment at CERN. The asymmetry is predicted to be large, about 15%. The radiative corrections to the QCD predictions for the cos ⁡ 2 φ distribution are estimated to be small, less than 10%. Our calculations show that the azimuthal asymmetry in charm production is well defined in pQCD: it is stable both perturbatively and parametrically, and practically insensitive to theoretical uncertainties in the input parameters. We analyze the nonperturbative contributions to the cos ⁡ 2 φ distribution due to the gluon transverse motion in the target and the c -quark fragmentation. Because of the c -quark low mass, the nonperturbative contributions are expected to be sizable, about (30–40)%. We conclude that extraction of the azimuthal asymmetries from available COMPASS data will provide valuable information about the transverse momentum dependent distribution of the gluon in the proton and the c -quark hadronization mechanism. Finally, we discuss the cos ⁡ 2 φ asymmetry as a probe of the gluonic analogue of the Boer–Mulders function, h 1 ⊥ g , describing the linear polarization of gluons inside unpolarized proton. [ABSTRACT FROM AUTHOR]

Elliptic jet mixing influenced by triangular tabs is demonstrated in this work. Mixing modification of a Mach 2 jet from a convergent-divergent elliptic nozzle of aspect ratio 2, in the presence of two triangular tabs along the major and minor axis at the nozzle exit, at different levels of nozzle expansion has been studied. The results show that the mixing caused by tabs along the minor axis is impressive compared to the uncontrolled jet at all the pressure ratios. But for tabs along the major axis, mixing enhancement is significant only for nozzle pressure ratios above 5. Tabs along the minor axis cause better mixing than tabs along the major axis. The iso-pitot pressure contours reveal that the tabs along the minor axis enhance the mixing by bifurcating the jet. Shadowgraphs show that the tabs render the waves in the jet weaker. The present study demonstrates the superior mixing promotion caused by triangular tab than rectangular tab, studied by Aravindh Kumar and Rathakrishnan (2015). [ABSTRACT FROM AUTHOR]

Comparative mixing of a Mach 2 elliptical free jet from a convergent-divergent elliptic nozzle with an aspect ratio of 2:1 in the presence of adverse and marginally favourable pressure gradients has been studied experimentally. It is found that the mixing of the elliptical jet is higher than that for the equivalent circular jet at all the levels of expansion. The decay of elliptic jet is significantly higher than the equivalent circular jet in all three zones of the jet field – the core, characteristic decay and fully developed regions. The reason for the faster decay of the elliptic jet is found to be the continuous variation in the size of the mixing-promoting vortices shed from the nozzle exit owing to its azimuthal asymmetry. The evolution of the jet and its axis-switching phenomenon has been studied using iso-pitot pressure contours taken at different axial locations in the plane normal to the jet axis. As expected, the elliptic jet spreads faster along the minor axis plane than the major axis plane, leading to axis-switching at all the levels of expansion studied. The axis-switching of the elliptic jet shifts upstream with increase in nozzle pressure ratio (NPR) from 4 to 5; from 5 to 7, it shifts downstream. But at marginally under-expanded condition of NPR 8, the axis-switching is found to shift slightly upstream. The occurrence of axis-switching in the elliptic jet indicates enhanced near-field mixing, compared to the equivalent circular jet. The shadowgraph pictures of the jet reveal that the waves prevailing in the elliptic jet are significantly weaker than those in the circular jet. [ABSTRACT FROM AUTHOR]

We study two experimental ways to measure the heavy-quark content of the proton: using the Callan-Gross ratio R( x,Q) = F/ F = and/or azimuthal cos(2φ) -asymmetry in deep inelastic lepton-nucleon scattering. Our approach is based on the perturbative stability of the QCD predictions for these two quantities. We resume the mass logarithms of the type αln( Q/ m) and conclude that heavy-quark densities in the nucleon can, in principle, be determined from data on the Callan-Gross ratio and/or azimuthal asymmetry. In particular, the charm content of the proton can be measured in future studies at the proposed Large Hadron-Electron (LHeC) and Electron-Ion (EIC) Colliders. [ABSTRACT FROM AUTHOR]

Abstract: In this note I report and discuss the physical scheme and the main approximations used by the event generator code DY_AB. This Monte Carlo code is aimed at preliminary simulation, during the stage of apparatus planning, of Drell–Yan events characterized by azimuthal asymmetries, in experiments with moderate center of mass energy . [Copyright &y& Elsevier]

Abstract: The azimuthal elliptic asymmetry v2 observed in heavy ion collisions, is usually associated with properties of the medium created in the final state. We compute the azimuthal asymmetry which is due to multiple interactions of partons at the initial stage of nuclear collisions, and which is also present in pA collisions. In our approach the main source of azimuthal asymmetry is the combination of parton multiple interactions with the steep variation of the nuclear density at the edge of nuclei. We apply the light-cone dipole formalism to compute the azimuthal asymmetry of prompt photons yield from parton–nucleus, proton–nucleus and nucleus–nucleus collisions at the RHIC energy. [Copyright &y& Elsevier]

Abstract: Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter F and elliptic asymmetry coefficient , for proton–neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive F and negative of direct photons are illustrated and they seem to be anti-correlated to the corresponding free proton''s flow. [Copyright &y& Elsevier]

Abstract: We show that measuring the angular dependence in unpolarized Drell–Yan processes with beams colliding on proton and deuteron targets can determine the ratio of the Boer–Mulders functions for d and u quarks inside the proton , which is still lack of theoretical constraint. The comparison of the asymmetries measured in unpolarized and Drell–Yan processes, which are accessible at CERN by the COMPASS Collaboration, can help to discriminate whether effects or QCD vacuum effects are preferred by data. [Copyright &y& Elsevier]

Abstract: Taking into account the effect of final-state interaction, we calculate the non-zero (naïve) T-odd transverse momentum dependent distribution of the pion in a quark-spectator-antiquark model with effective pion-quark-antiquark coupling as a dipole form factor. Using the model result we estimate the asymmetries in the unpolarized Drell–Yan process which can be expressed as . We find that the resulting has the advantage to reproduce the asymmetry that agrees with the experimental data measured by NA10 Collaboration. We estimate the asymmetries averaged over the kinematics of NA10 experiments for 140, 194 and 286 GeV beam and compare them with relevant experimental data. [Copyright &y& Elsevier]

In this paper, we present a numerical study of the axisymmetric Richtmyer–Meshkov instability in converging spherical geometry by the front tracking method for the first time. The front tracking method has been successfully used in solving fluid instability problems in both rectangular and curved geometry.(1–6) The central issue for axisymmetric flows is the absence of the rotational symmetry in the ( r, z) plane, although the perturbed shape of the initial contact interface appears to have it. The cause of the asymmetry is somewhat obvious. The sinusoidal perturbations appear symmetric only in the cross-sectional view; in actuality they are not symmetric because they represent rings around the z-axis and hence the perturbed mass at the equator, for example, is different from the perturbed mass at the pole. The first purpose of this paper is to quantify the effect of this inherited asymmetry on the growth of the spherical mixing. We find this asymmetry drives the original structure to some degree so that the mixing radius at the north pole is noticeably larger than at the equator during the evolution of chaotic mixing. We also study quantitatively the azimuthal dependence of the mixing statistics, such as the mixing edges, the growth rate and volume fraction. Richtmyer–Meshkov (RM) instabilities in spherical geometry have been a challenge due to the inherent difficulty of their accurate simulation. Our second purpose is to demonstrate that our Front Tracking method can describe the Richtmyer–Meshkov instability growth in a complex flow involving multiple reshocks. We have successfully displayed the converging geometry, reshock process, asymmetry phenomenon through the density and pressure color plots. The quantitative growth rate analysis is also presented. [ABSTRACT FROM AUTHOR]