Influence of quantum fluctuations on the motion of relativistic protons in crystals

The influence of multiple scattering and quantum fluctuations in the transverse coordinate, momentum, and energy on the channeling of relativistic protons in a silicon crystal have been studied by computer simulation.     

Transverse momentum in semi-inclusive deep inelastic scattering

Within the framework of perturbative quantum chromodynamics we derive the evolution equations for transverse momentum dependent distributions and apply them to the case of semi-inclusive deep inelastic scattering. The evolution equations encode the perturbative component of transverse momentum generated by collinear parton branchings. The current fragmentation is described via transverse momentum dependent parton densities and fragmentation functions. Target fragmentation instead is described via fracture functions. We present, to leading logarithmic accuracy, the corresponding semi-inclusive deep inelastic scattering cross-section, which applies to the entire phase space of the detected hadron. Some phenomenological implications and further developments are briefly outlined.     

Depth profile measurements of copper in silicon by ion-induced x-ray emission

Abstract

Distributions of axially channeled electrons are calculated at large depths as a function of angular momentum and transverse energy. Due to the influence of multiple scattering the electron distributions become independent of the angular momentum at a depth, where the statistical equilibrium is reached. Furthermore, the flux-peaking effect for negative particles is discussed.     

高能重离子碰撞中的集体流与空间-动量关联

高能重离子碰撞中,末态粒子的侧向流与椭圆流间存在方位角集体关联,该关联对反应中集体流的性质反映敏感.碰撞时,系统在坐标空间的演化与动量空间的演化过程相互影响,表现出明显的空间-动量关联.不同事件中椭圆流形式的差别与此空间-动量关联有关,反映了系统演化过程的涨落.     

受线性阻尼和含时外力作用粒子的量子行为

运用广义线性量子变换理论求解了采用两种不同正则化变换给出的受线性阻尼和含时外力作用粒子的哈密顿量;给出了演化算符的严格解,以及粒子坐标和动量的期望值、 量子涨落.结果表明: 1)两种正则化变换是等价的; 2)线性阻尼对粒子的动量存在压缩效应, 动量的偏差随时间t按负指数规律衰减,阻尼系数越大,衰减越快; 3)粒子坐标和动量的期望值与经典值相同.     

Transverse-momentum fluctuations in pi(+)p and K(+)p Collisions at 250 GeV/c

We report results on event-by-event fluctuations of transverse momentum, Phi(p(t)), in pi(+)p and K(+)p collisions at 250 GeV/c. For the first time, their dependence on rapidity region, transverse momentum acceptance, multiplicity, mean transverse momentum per event, and on the correlation between transverse momentum and multiplicity are systematically presented. The results are compared with those from the PYTHIA Monte Carlo generator. The fluctuations under the same acceptance cuts as used in current heavy-ion experiments are also presented.     

Influence of quantum fluctuations on the stochastic dynamics of the channeling effect of relativistic electrons and positrons

A system of equations describing multiple scattering by crystal nuclei and electrons, and also quantum fluctuations of the coordinate and momentum operators of fast charged particles has been obtained. Quantum corrections to the classical equations of motion have been determined in quasiclassical approximations. A computer simulation of 855-MeV electron and positron motion in the (110) planar channel of a Si crystal has been carried out. The inclusion of quantum fluctuations in the equation of motion affects the dynamics of the electron channeling effect in planar crystal channels considerably; in particular, intense dechanneling (heating) occurs. Intense rechanneling (cooling) occurs in the case of positrons.     

Spatial and angular distribution of the heavy ion charge under channeling in crystals

A kinetic theory of passage of multiply charged heavy ions through crystals is developed that allows for diffusion in the transverse momentum space and ion-crystal charge exchange. The theory provides an adequate explanation for the observed angular distributions of heavy ions passing through oriented crystals, makes it possible to calculate the partial angular distributions of different charge states, and treats the discovered effects of “cooling” and “heating” of channeled ion beams in physical terms. The angular and spatial distribution of channeled ions with different energies is calculated. Whether a channeled beam of multiply charged heavy ions will be cooled or heated is related to the dependence of the electron capture and loss probabilities on the impact parameter when the ions interact with atomic chains. This interaction governs the run of the angular and spatial distribution of the channeled ion charge.     

Fluctuations and transverse momentum distributions in the color clustering approach

We present our results on transverse momentum fluctuations, multiplicity fluctuations and transverse momentum distributions for baryons and mesons in the framework of the clustering of color sources. We determine under what conditions the initial state configurations can lead to color connection, and more specifically, if variations of the initial state can lead to a transition from disconnected to connected color clusters, modifying the number of effective sources. We find that beyond a critical point, one has a condensate, containing interacting and hence color-connected sources. This point thus specifies the onset of color deconfinement. We show that the transverse momentum and multiplicity distributions are related to each other in a defined way. We obtain a non-monotonic dependence of the p _T and multiplicity fluctuations with the number of participants. We present our results for the fluctuations and the transverse momentum distributions at RHIC energies compared to the existing experimental data and our predictions for LHC energies.     

Event-by-event fluctuations of average transverse momentum in central Pb+Pb collisions at 158 GeV per nucleon

We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb+Pb collisions at the CERN SPS. This measurement provides previously unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement.     

Optical filaments and optical bullets in dispersive nonlinear media

We have investigated the evolution of picosecond and femtosecond optical pulses governed by the amplitude vector equation in the optical and UV domains. We have written this equation in different coordinate frames, namely, in the laboratory frame, the Galilean frame, and the moving-in-time frame and have normalized it for the cases of different and equal transverse and longitudinal sizes of optical pulses or modulated optical waves. For optical pulses with a small transverse size and a large longitudinal size (optical filaments), we obtain the well-known paraxial approximation in all the coordinate frames, while for optical pulses with relatively equal transverse and longitudinal sizes (so-called light bullets), we obtain new non-paraxial nonlinear amplitude equations. In the case of optical fields with low intensity, we have reduced the nonlinear amplitude vector equations governing the light-bullet evolution to the linear amplitude equations. We have solved the linear equations using the method of Fourier transform. An unexpected new result is the relative stability of light bullets and the significant decrease in the diffraction enlargement of light bullets with respect to the case of long pulses in the linear propagation regime.     

Dynamics of a Swirling Turbulent Wake past a Sphere

Using a mathematical model, which includes the averaged motion equations, differential transport equations of normal Reynolds stresses and dissipation rate, we carried out numerical modeling of evolution of a swirling turbulent wake with nonzero total excess momentum and angular momentum. The calculations were done to very large distances from the body. For small distances from the body the calculated profiles of averaged motion velocities and intensities of turbulent fluctuations of the longitudinal velocity component are in good agreement with the known experimental data of the Lavrent’ev Institute of Hydrodynamics, SB RAS. A simplified model of the flow is constructed.     

A momentum space analysis of the triple pomeron vertex in pQCD

We study the properties of the momentum space triple pomeron vertex in perturbative QCD. Particular attention is given to the collinear limit where the transverse momenta on one side of the vertex are much larger than on the other side. We also comment on the kernels in the non-linear evolution equations.     

A qualitative description of the transverse motion of axial channeled particles in thin crystals

The qualitative features of the angular distribution of particles emergent from thin ～ 1μ, uniform single crystals of silicon and germanium for incidence at small angles to axial directions are discussed in terms of the continuum picture of particle channeling. Blocking of axially channeled particles in the transverse plane is demonstrated. Implications and possibilities arising from observation of non-equilibrium of the transverse momentum vector are discussed. The use of the radial spreading of the angular distribution to investigate the average inter-atomic potential distribution in the plane transverse to the axial direction is explored and perturbations due to multiple scattering in surface films or inside the crystal and to beam divergence are qualitatively considered.     

Saturation and universality in QCD at small x

We find approximate solutions to the renormalization group equation which governs the quantum evolution of the effective theory for the Color Glass Condensate. This is a functional Fokker–Planck equation which generates in particular the non-linear evolution equations previously derived by Balitsky and Kovchegov within perturbative QCD. In the limit where the transverse momentum of the external probe is large compared to the saturation momentum, our approximations yield the Gaussian ansatz for the effective action of the McLerran–Venugopalan model. In the opposite limit, of a small external momentum, we find that the effective theory is governed by a scale-invariant universal action which has the correct properties to describe gluon saturation.     

Dynamics of rotating two-component Bose-Einstein condensates and its efficient computation

In this paper, we investigate the dynamics of rotating two-component Bose-Einstein condensates (BEC) based on the coupled Gross-Pitaevskii equations (CGPEs) with an angular momentum rotation term and an external driving field, and propose an efficient and accurate method for numerical simulations. We prove the conservation of the angular momentum expectation, derive the dynamic laws for the density of each component and condensate widths, and analyze the dynamics of a stationary state with its center shifted from the trap center. By formulating the CGPEs in either 2D (two-dimensional) polar coordinate or 3D cylindrical coordinate system, the angular momentum rotation term becomes a term with constant coefficients. This allows us to develop an efficient time-splitting method which is time reversible, time transverse invariant, unconditionally stable, efficient and accurate for the problem. Moreover, it conserves the total position density in the discretized level. The numerical method is applied to verify our analytical results and study the dynamics of quantized vortex lattices in rotating two-component BEC with/without an external driving field.     

Characterizing variable for the critical point in momentum space

The possible experimentally observable signal in momentum space for the critical point, which is free from the contamination of statistical fluctuations, is discussed. It is shown that the higher order scaled moment of transverse momentum can serve as an appropriate signal for the critical point, provided the transverse momentum distribution has a sudden change when energy increases passing through this point. A 2-D percolation model with a linear temperature gradient is constructed to check this suggestion. A sudden change of third order scaled moment of transverse momentum is observed.     

Hamiltonian model of a free electron laser including high-density effects

Both the Compton and the Raman regimes of a free electron laser are described by a relativistic Hamiltonian which originates the evolution equations for 2N+2 canonically conjugate electron and field variables, with the space coordinate as the independent variable. Space charge and field contribution to electron transverse velocity are included.