Rescattering Process Research Articles

Inelastic rescattering processes in molecules measured with few-cycle laser pulses

We study electron recollision processes induced in D2 by the nonlinear interaction with 800 nm few-cycle laser pulses. We show that sequential double ionization is suppressed at intensities below 2 × 1014 W cm−2, and the inelastic rescattering processes (electronic excitation and double ionization) become dominant and can be investigated as a function of intensity and ellipticity. At 1 × 1014 W cm−2, the D+ kinetic energy spectrum arises from recollision-induced electronic excitation (D2+→D++D) and is explained by the contributions of two dissociative excited electronic states of D2+ (2Σu+ and 2Πu).

Study ofππphase shifts inψ(2S)→π+π−J/ψ

The $\ensuremath{\pi}\ensuremath{\pi}$ $S$-wave phase shifts below 0.6 GeV are extracted out from the published data of the decay $\ensuremath{\psi}(2S)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$. In fitting to the ${m}_{\ensuremath{\pi}\ensuremath{\pi}}$ distribution, several $\ensuremath{\pi}\ensuremath{\pi}$ production mechanisms are modeled in the amplitude. The fit results show that the amplitude including the $\ensuremath{\pi}\ensuremath{\pi}$ rescattering process with the minimal coupling ${g}_{1}{ϵ}^{\ensuremath{'}}\ifmmode\cdot\else\textperiodcentered\fi{}{ϵ}^{*}$ plus the direct nonresonant three-body decay process yields phase shifts consistent with those measured in scattering experiments and ${K}_{e4}$ decays. This result agrees with the expectation of the Watson theorem.

Many-body effects in multiply charged ion formation in a superstrong laser field

We report the numerical calculations for the multiple ionization of rubidium in a strong laser field. We consider multiply charged ion formation and take into account some of the many-body effects, i.e., the inelastic tunneling effect, the collective tunneling, and $m$ relaxation of an ionic core. In the case of strong fields, with intensities in excess of ${10}^{17}\text{ }\text{W}/{\text{cm}}^{2}$, the free motion of a photoelectron is affected by the magnetic component of the laser field. Because of this, the formation of multiply charged ions as a result of a rescattering process becomes improbable. We present our findings for ${\text{Rb}}^{10+}$ and ${\text{Rb}}^{11+}$ ions, where a significant contribution of collective tunneling was revealed, which was not observed in the weaker fields previously investigated [A. S. Kornev, E. B. Tulenko, and B. A. Zon, Phys. Rev. A 68, 043414 (2003); Phys. Rev. A 69, 065401 (2004)].

Pion-pion scattering lengths from Ke4 and Cusp at NA48/2 experiment

In kaon decays the measurement of ππ scattering lengths ( a 0 and a 2 ) are accessible mainly through the study of kinematical properties in two decay modes. The classic way is based on the form factors analysis in K ± → π + π − e ± ν ( K e 4 ) decay. Thanks to the absence of other hadrons in the final state the ππ interaction can be analyzed in terms of phase shift variation with the ππ invariant mass. The preliminary results on a set of ∼ 1150000 K ± events collected in two years of data taking, will be discussed. The second way to evaluate the ππ scattering lengths is based on the accurate study of K ± → π ± π 0 π 0 Dalitz plot, in which the strong rescattering process π + π − → π 0 π 0 introduces a singularity in the shape of the distribution. The preliminary result based on more than ∼ 60 ⋅ 10 6 K ± → π ± π 0 π 0 decays is in good agreement with the measurement in K e 4 .

Strong-Field Tunneling without Ionization

In the tunneling regime of strong laser field ionization we measure a substantial fraction of neutral atoms surviving the laser pulse in excited states. The measured excited neutral atom yield extends over several orders of magnitude as a function of laser intensity. Our findings are compatible with the strong-field tunneling-plus-rescattering model, confirming the existence of a widely unexplored neutral exit channel (frustrated tunneling ionization). Strong experimental support for this mechanism as origin of excited neutral atoms stems from the dependence of the excited neutral yield on the laser ellipticity, which is as expected for a rescattering process. Theoretical support for the proposed mechanism comes from the agreement of the neutral excited state distribution centered at n = 6-10 obtained from both, a full quantum mechanical and a semiclassical calculation, in agreement with the experimental results.

Relativistic MeV Photoelectrons from the Single Atom Response of Argon to a1019 W/cm2Laser Field

We present photoelectron measurements from argon ionization at 10(19) W/cm(2). Photoelectrons with energies above 400 keV, including a 1.2 MeV cutoff, are in quantitative agreement with a semiclassical, relativistic 3D ionization model that includes a nonparaxial laser field. L-shell photoelectrons have energies and momentum dominated by the field, including the acceleration out of the focus. Yields and angular distributions at 60 keV come from valence shell ionization by strong fields where rescattering and atomic processes determine photoelectron final states.

Ionization of atoms and molecules by a few-cycle laser pulse and interference effects in the rescattering process

We investigate the diffraction pictures arising due to strong-field ionization of a molecule in an ultrashort laser pulse and further field-induced recollision of the ionized electron with the parent molecular ion by direct numerical solution of the non-stationary Schrödinger equation. In molecules the angular distributions of the re-scattered electron are shown to differ dramatically from the simple usually used double-slit diffraction picture. The reason for this consists in the interference between scattered and non-scattered parts of the electron wave packet in the continuum. The found interference effect is demonstrated to play an important role in the formation of angular and momentum distribution both for molecules and atoms.

Two-photon width and gluonic component of [formula omitted

We analyse data on ππ and γγ scattering below 700 MeV within an improved analytic K-matrix model. This model is based on an effective theory with couplings between resonances, hadrons and photons. The two-photon decay of a resonance can proceed through intermediate transition into charged hadrons (here: π + π − ) and their subsequent annihilation or through a “direct” transition into photons. Our analysis confirms the rather large total radiative width of the σ resonance which we find as ( 3.9 ± 0.6 ) keV but suggests its dominance by the ππ rescattering process. This process is not sensitive to the internal structure of the resonance contrary to the direct component which we find small, ( 0.13 ± 0.05 ) keV , and well consistent with the expectations for an unmixed glueball according to the QCD sum rule calculations.

Quantum model for double ionization of atoms in strong laser fields

We discuss double ionization of atoms in strong laser pulses using a reduced dimensionality model. Following the insight obtained from an analysis of the classical mechanics of the process, we confine each electron to move along the lines that point towards the two-particle Stark saddle in the presence of a field. The resulting effective two-dimensional model is similar to the aligned electron model, but it enables correlated escape of electrons with equal momenta, as observed experimentally. The time-dependent solution of the Schr\odinger equation allows us to discuss in detail the time dynamics of the ionization process, the formation of electronic wave packets, and the development of the momentum distribution of the outgoing electrons. In particular, we are able to identify the rescattering process, simultaneous direct double ionization during the same field cycle, as well as other double ionization processes. We also use the model to study the phase dependence of the ionization process.

Photoproduction and rescattering of polarized hyperons in deuterium

Excited states of hadrons are essential for understanding confinement and non-perturbative QCD. Constituent quark models are successful in describing the first excited nucleon (N*) states in each partial wave, but predict more states than have been observed experimentally. Diquark correlations have been suggested as one explanation for these “missing” states. Recent advances in both theory (coupled-channels calculations) and experiment (high-statistics polarization measurements) offer new tools for resolving this question. The g13 experiment at Jefferson Lab, completed in June 2007, forms an important part of this effort. It used linearly and circularly polarized photons and a deuteron target to study N* states produced on the neutron, primarily through their decays into kaons and hyperons. The self-analyzing property of the Λ is ideally suited for this purpose. The general nature and exceptional size of the data set will, however, produce a wide range of results, including opening a new window on the study of hyperon-nucleon interactions through rescattering processes.

Survival probability for diffractive Higgs production in high density QCD

In this paper, the contribution of hard processes described by BFKL pomeron exchange is taken into account by calculating the first enhanced diagram. The survival probability is estimated, using the ratio of the first enhanced diagram and the single pomeron amplitude, taking into account all essential pomeron loop diagrams in the toy model of Mueller. The triple pomeron vertex is calculated explicitly in the momentum representation. This calculation is used for estimating the survival probability, and it turns out that the survival probability is small, at 0.4%. Hard pomeron rescattering processes contribute substantially to the survival probability.

Measurement of ππ scattering lengths in Kaon decay by NA48/2

In kaon decays the measurement of ππ scattering lengths (a0 and a2) are accessible mainly through the study of kinematical properties in two decay modes. The classic one is based on the analysis of the form factors in the K± → π+π−e±v (Ke4). Thanks to the absence of other hadrons in the final state the ππ interaction can be analyzed in terms of variation of phase shift with the ππ invariant mass. The preliminary results on a partial set of ~ 670000 K± will be discussed. The second way to evaluate the ππ scattering lengths is based on the accurate study of K± → πππ0π0 Dalitz plot, in which the strong rescattering process π+π− → π0π0 introduces a singularity in the shape of the distribution. The preliminary result based on ~ 50 · 106 K± → π±π0π0 decays is in good agreement with the measurement in Ke44.

Numerical Observation of the Rescattering Wave Packet in Laser-Atom Interactions

We present a full-quantum nonperturbative method to study the electron rescattering process in the intense laser-atom interactions. We separate the ionized wave function from the background by solving the time-integral equation. Imposing the incoming boundary condition on the wave function, we reproduce the motion of the rescattering wave packet predicted by the rescattering theory. Our calculated rescattering energies differ significantly from the semiclassical ones. The difference would be substantial for the evaluation of the rescattering induced dynamics such as the molecular dissociation.

Electron-diffraction imaging of nuclear dynamics in molecules

We investigate the formation of the diffraction image of a molecule arising in the rescattering process during field-induced molecular ionization. The problem is solved numerically by integration of the non-stationary two-electron Schrödinger equation. The observed diffraction patterns are used to extract the information about molecular orientation and internuclear separation. The validity of a simple double slit diffraction rule is examined, and additional phase corrections are obtained to provide high accuracy. The role of the presence of the bound electron in the parent molecular ion in the scattering process is analysed.

Rescattering of electrons at laser-cluster interactions

The goal of this work is to derive the angular distributions of electrons irradiated at the outer ionization of large atomic clusters from Xe atoms by relativistic laser pulses taking into account rescattering processes. Both the magnetic field of the laser pulse and the Coulomb field of the ionized cluster significantly influence the rescattering of ejected electrons. The multiply inner ionization of atoms occurs at the leading edge of the laser pulse. The atomic ions with charge multiplicities up to Z = 26 are subsequently produced (each atomic ion with the next charge multiplicity appears in 3–5 fs) when the laser intensity increases. The measurements of the angular distributions of electrons allow us to reproduce the imaging dynamics of outer ionization of the cluster at the leading edge of the relativistic femtosecond laser pulse.

The contribution of incoherent photoelectron scattering off neighbouring atoms to the above-threshold ionization and detachment spectra

The role of incoherent scattering in above-threshold ionization (ATI) of atoms and above-threshold detachment of negative ions is investigated. We assume that the ionized (detached) electron may scatter on a target other than its parent ion (atom). We call such a process incoherent in order to distinguish it from the coherent rescattering of an electron on its parent ion (atom). The rescattering process is known to be responsible for high-order ATI (HATI). We show that the contribution to the ionization rate of ATI with a subsequent incoherent scattering can be higher than that of the rescattering-induced HATI if the density of atomic targets is high enough. The spectra of ATI with incoherent scattering have a cutoff-like behaviour, similar to that of ATI and HATI. Our numerical results show that the cutoff energy of the ATI with incoherent scattering is higher than that of the rescattering-induced HATI. These results are supported by classical analysis.

Elliptic flow at RHIC: Where and when was it formed?

Evolution of the elliptic flow of hadrons in heavy-ion collisions at RHIC energies is studied within the microscopic quark–gluon string model. The elliptic flow is shown to have a multi-component structure caused by (i) rescattering and (ii) absorption processes in spatially asymmetric medium. Together with different freeze-out dynamics of mesons and baryons, these processes lead to the following trend in the flow formation: the later the mesons are frozen, the weaker their elliptic flow, whereas baryon fraction develops stronger elliptic flow during the late stages of the fireball evolution. The phase-space distributions of the emitted particles are studied as well. The flow is shown to be formed both in the central and in the fragmentation regions of the reaction. Comparison with the PHOBOS data demonstrates the model ability to reproduce the v2ch(η) signal in different centrality bins.

High harmonic generation by halogen anions and noble gas atoms in a laser field

A comparative study of high harmonic generation (HHG) by atoms and ions with active p-electrons is carried out in the theoretical framework of the rescattering mechanism. The substate with mℓ = 0, i.e. zero orbital momentum projection along the electric vector of a linearly polarized laser wave, is found to give the major contribution to the HHG rate. Our calculations for HHG by an H atom in an excited 2p-state demonstrate that the rate for recombination into a final state with a different value of mℓ (=±1), is higher for lower harmonic orders N, while for higher N (beyond the plateau domain) the difference vanishes. For species with closed electron shells, the mℓ-changing transitions are forbidden by the Pauli exclusion principle. We report absolute HHG rates for halogen ions and noble gas atoms at various intensities. These results demonstrate that the Coulomb binding potential of the atoms considerably enhances both the ionization and recombination steps in the rescattering process. However, the weak binding energy of the anions allows lower orders of HHG to be efficiently produced at relatively low intensities, from which we conclude that observation of HHG by an anion is experimentally feasible.

Exclusive electrodisintegration ofHe3at highQ2. II. Decay function formalism

Based on the theoretical framework of generalized eikonal approximation we study the two-nucleon emission reactions in high $Q^2$ electro-disintegration of $^3He$. Main aim is to investigate those features of the reaction which can be unambiguously identified with the short range properties of the ground state nuclear wave function. To evaluate the differential cross section we work in the formalism of the decay function which characterizes the property of the ground state wave function as well as the decay properties of final two nucleon spectator system. Our main motivation here is to explore the accessibility of two-- and three--nucleon short range correlations in $^3$He as well as to isolate unambiguously single and double rescattering processes in the reaction dynamics. Our analysis allowed us also to identify new approaches for investigating the role of the practically unknown three-nucleon forces in the ground state wave function of $^3He$.

Ndbreakup process in leading order in a three-dimensional approach

A three-dimensional approach based on momentum vectors as variables for solving the three nucleon Faddeev equation in first order is presented. The nucleon-deuteron break-up amplitude is evaluated in leading order in the NN T-matrix, which is also generated directly in three dimensions avoiding a summation of partial wave contributions. A comparison of semi-exclusive observables in the $d(p,n)pp$ reaction calculated in this scheme with those generated by a traditional partial wave expansion shows perfect agreement at lower energies. At about 200 MeV nucleon laboratory energies deviations in the peak of the cross section appear, which may indicate that special care is required in a partial wave approach for energies at and higher than 200 MeV. The role of higher order rescattering processes beyond the leading order in the NN T-matrix is investigated with the result, that at 200 MeV rescattering still provides important contributions to the cross section and certain spin observables. The influence of a relativistic treatment of the kinematics is investigated. It is found that relativistic effects become important at projectile energies higher than 200 MeV.