Recoil Momentum Research Articles

Exact calculation of the angular momentum loss, recoil force, and radiation intensity for an arbitrary source in terms of electric, magnetic, and toroid multipoles.

An exact calculation of the radiation intensity, angular momentum loss, and the recoil force for the most general type of source, characterized by electric, magnetic, and toroid multipole moments and radii of any multipolarity and an arbitrary time dependence, is presented. The results are expressed in terms of time derivatives of the multipole moments and mean radii of the corresponding distributions. Although quite cumbersome, the formulas found by us represent exact results in the correct multipole analysis of configurations of charges and currents that contain toroidal sources. So the longstanding problem in classical electrodynamics of relating the radiation properties of a system to quantities completely describing its internal electromagnetic structure is thereby exactly solved. By particularizations to the first multipole contributions, corrections to the familiar formulas from books are found, mostly on account of the toroid moments and their interference with the usual electric and magnetic ones.

Toroid moments in the momentum and angular momentum loss by a radiating arbitrary source

In the context of experimental evidence concerning a nuclear toroid dipole, we briefly present here an exact but tedious calculation of the angular momentum loss, recoil force, and radiation intensity for an arbitrary source in terms of electric, magnetic, and toroid multipoles, thus emphasizing the importance of the latter in getting the results in closed forms, unbiased by approximations. Corrections to some familiar formulas from books, mostly on account of time varying toroid moments, are found and discussed.

Differential decay rate ofB→πlνsemileptonic decay with lattice nonrelativistic QCD

We present a lattice QCD calculation of $B\to \pi l \nu$ semileptonic decay form factors in the small pion recoil momentum region. The calculation is performed on a quenched $16^3 \times 48$ lattice at $\beta=5.9$ with the NRQCD action including the full 1/M terms. The form factors $f_1(v\cdot k_{\pi})$ and $f_2(v\cdot k_{\pi})$ defined in the heavy quark effective theory for which the heavy quark scaling is manifest are adpoted, and we find that the 1/M correction to the scaling is small for the $B$ meson. The dependence of form factors on the light quark mass and on the recoil energy is found to be mild, and we use a global fit of the form factors at various quark masses and recoil energies to obtain model independent results for the physical differential decay rate. We find that the $B^*$ pole contribution dominates the form factor $f^+(q^2)$ for small pion recoil energy, and obtain the differential decay rate integrated over the kinematic region $q^2 >$ 18 GeV$^2$ to be $|V_{ub}|^2 \times (1.18 \pm 0.37 \pm 0.08 \pm 0.31)$ psec$^{-1}$, where the first error is statistical, the second is that from perturbative calculation, and the third is the systematic error from finite lattice spacing and the chiral extrapolation. We also discuss the systematic errors in the soft pion limit for $f^0(q^2_{max})$ in the present simulation.

High resolution measurement of the16O(γ,pn)14N0,1,2,…reaction

The exclusive ${}^{16}\mathrm{O}(\ensuremath{\gamma}{,pn)}^{14}{\mathrm{N}}_{0,1,2,\dots{}}$ reaction was measured for the photon energy range ${E}_{\ensuremath{\gamma}}=98.5$ to 141.0 MeV with an excitation energy resolution of 2.8 MeV. Protons were detected at $76\ifmmode^\circ\else\textdegree\fi{}$ and $82\ifmmode^\circ\else\textdegree\fi{}$ and coincident neutrons were detected at the opening angle for quasifree deuteron photodisintegration. Only the $T=0,$ ${1}^{+},$ 3.95 MeV state in the residual ${}^{14}\mathrm{N}$ nucleus was significantly populated. This corresponds to a preferred $L=0$ angular momentum transfer to the recoil nucleus as is expected for quasifree kinematics. The absence of significant population to other discrete states is evidence that absorption on correlated proton-neutron pairs with an angular momentum transfer of $L>~2$ is largely suppressed for the low recoil momentum range of the current measurement. As a consequence of this fact, and the absence of unnatural parity states, only absorption on proton-neutron pairs in relative motion $l=0,2$ is expected for all possible shell model couplings. No significant population of the $T=1$ state at 2.31 MeV is consistent with previous measurements, demonstrating that absorption on proton-neutron pairs in an isospin triplet is suppressed. The results of the measurement to discrete states in the residual ${}^{14}\mathrm{N}$ nucleus are compared to microscopic calculations which include contributions above that of the mean field due to the short range and tensor parts of the nuclear potential. Clear separation in the contribution of ${(1p)}^{\ensuremath{-}2}$ and ${(1p)}^{\ensuremath{-}1}{(1s)}^{\ensuremath{-}1}$ proton-neutron pairs is seen to occur at an excitation energy of $20\ifmmode\pm\else\textpm\fi{}2 \mathrm{MeV}.$ Significant population of the ${(1p)}^{\ensuremath{-}1}{(1s)}^{\ensuremath{-}1}$ continuum above 20 MeV indicates that absorption on $L=1$ nucleon pairs is also important near quasifree kinematics.

B c-meson decays and lifetime within QCD sum rules

On the basis of three-point sum rules, the form factors for the semileptonic decays B c + → B s(B s * )l + ν l are calculated with allowance for α s/v Coulomb corrections for the heavy quarkonium. Generalized relations associated with spin symmetry within the approach combining heavy-quark effective theory and nonrelativistic QCD are derived for form factors in the region of recoil momenta close to zero. The nonleptonic decays of the B c meson are studied on the basis of the factorization hypothesis. By summing the main exclusive modes of c-quark decays and by using the results of a previous analysis of b-quark decays, the B c-meson lifetime is estimated within QCD sumrules and within nonrelativistic QCD.

Recoil momentum spectroscopy of highly charged ion collisions on magneto-optically trapped Na.

We have used a cold ( T<<1 mK), laser-cooled target of Na atoms confined in a magneto-optical trap to study electron capture processes during highly charged ion-sodium atom collisions at keV energies. Momentum distributions of target ions were determined by employing time-of-flight and position sensitive detection of the Na ions, produced during the collisions and extracted by a weak electric field. In this way impact parameter sensitive information about multielectron capture processes is obtained.

Rare radiativeBdecays to orbitally excitedKmesons

The exclusive rare radiative B meson decays to orbitally excited axial-vector mesons K_1^*(1270), K_1(1400) and to the tensor meson K_2^*(1430) are investigated in the framework of the relativistic quark model based on the quasipotential approach in quantum field theory. These decays are considered without employing the heavy quark expansion for the s quark. Instead the s quark is treated to be light and the expansion in inverse powers of the large recoil momentum of the final K^{**} meson is used to simplify calculations. It is found that the ratio of the branching fractions of rare radiative B decays to axial vector K^*_1(1270) and K_1(1400) mesons is significantly influenced by relativistic effects. The obtained results for B decays to the tensor meson K_2^*(1430) agree with recent experimental data from CLEO.

Quantum effects in the collective light scattering by coherent atomic recoil in a Bose–Einstein condensate

We extend the semiclassical model of the collective atomic recoil laser (CARL) to include the quantum mechanical description of the center-of-mass motion of the atoms in a Bose–Einstein condensate (BEC). We show that when the average atomic momentum is less than the recoil momentum ℏ q → , the CARL equations reduce to the Maxwell–Bloch equations for two momentum levels. In the conservative regime (no radiation losses), the quantum model depends on a single collective parameter, ρ, that can be interpreted as the average number of photons scattered per atom in the classical limit. When ρ≫1, the semiclassical CARL regime is recovered, with many momentum levels populated at saturation. On the contrary, when ρ⩽1, the average momentum oscillates between zero and ℏ q → , and a periodic train of 2 π hyperbolic secant pulses is emitted. In the dissipative regime (large radiation losses) and in a suitable quantum limit, a sequential superfluorescence scattering occurs, in which after each process atoms emit a π hyperbolic secant pulse and populate a lower momentum state. These results describe the regular arrangement of the momentum pattern observed in recent experiments of superradiant Rayleigh scattering from a BEC.

Dynamics of Atoms in Optical Lattices

Optical lattices are formed when cold atoms get trapped in the periodic array of optical potential wells created by a number of traveling light waves. Exact periodicity is guaranteed when the number of traveling waves exceeds the number of dimensions by no more than one. We present a few simple exactly solvable models for the transport of atoms over a lattice in the tight-binding limit. One model concerns the spreading of an atom by tunneling through the barriers and by momentum recoil induced by optical pumping. Another model gives results for the amplitude of Bloch oscillations, which occur when a uniform is added to the periodic potential. Finally the dissipative spreading of the quasimomentum due to optical pumping is modeled.

Study of the mechanism of steel cutting with the weakly focused radiation from a repetitively pulsed CO2 laser

A study was made of the process of steel plate cutting with a weakly focused radiation from a repetitively pulsed CO2 laser with the output of no more than 500 W without the use of a gas jet. The regimes were determined in which the removal of the melt under the action of the vapour recoil momentum proved to be more efficient than the melt removal under continuous irradiation. The physical mechanism of the process was proposed and its numerical model was elaborated. A comparison with experiments showed that this model provides a qualitatively adequate description of the experimental data and that it can be employed for the evaluation of remote cutting with high-power laser radiation.

Radiative behavior of negatively charged excitons in CdTe-based quantum wells: A spectral and temporal analysis

Using reflectivity and picosecond time-resolved photoluminescence, we have studied the intrinsic optical properties of negatively charged excitons in modulation doped CdTe quantum wells. In emission, we observe simultaneously a low energy exponential tail in the charged exciton spectral line and a linear increase of its radiative lifetime with temperature. In absorption, we find a consistent decrease of the charged exciton oscillator strength with temperature. For low electron concentrations these observations are well reproduced by a model of delocalized and thermalized three-particle complexes. The model takes into account the recoil momentum of the electron during the charged exciton optical transition. It is further found to compare well with lifetime measurements up to high carrier concentrations. Small deviations from the theoretical predictions occur only below 7 K due to localization effects and for the highest carrier concentration of ${n}_{e}\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{}\mathrm{cm}}^{\ensuremath{-}2}.$

Interpretation of momentum distribution of recoil ions from laser-induced nonsequential double ionization by semiclassical rescattering model

Using a semiclassical rescattering model, the momentum distribution of recoil ions from laser-induced nonsequential double ionization is obtained and the result is consistent with the experiment reported recently. We show that the characteristic double-hump structure of the recoil momentum distribution of the ${\mathrm{He}}^{2+}$ ion parallel to the polarization axis is just the consequence of the rescattering dynamic of nonsequential double ionization and the acceleration of the ions in the laser field.

Semileptonic decays of the B c meson

The semileptonic decays of the B c meson into heavy quarkonia J/ψ(ηc) and a pair of leptons are investigated on the basis of three-point sum rules of QCD and nonrelativistic QCD (NRQCD). Calculations of analytic expressions for the spectral densities of QCD and NRQCD correlation functions with allowance for Coulomb-like αs/v terms are presented. At recoil momenta close to zero, generalized relations due to the spin symmetry of NRQCD are derived for the B c → J/ψ(ηc)/νl form factors, with l denoting one of the leptons (e, μ, or τ). This allows one to express all NRQCD form factors in terms of a single universal quantity, an analog of the Isgur-Wise function at the maximal lepton-pair invariant mass. The gluon-condensate corrections to three-point functions are calculated both in full QCD in the Borel transform scheme and in NRQCD in the moment scheme. This enlarges the parametric-stability region of the sum-rule method, thereby rendering the results of the approach more reliable. Numerical estimates of the widths for the transitions B c → J/ψ(ηc)lνl are presented.

Bc decays and lifetime in QCD sum rules

In the framework of three-point QCD sum rules, the form factors for the semileptonic decays of B_c --> B_s(B_s^*) l \nu are calculated with account for the Coulomb-like alpha_s/v-corrections in the heavy quarkonium. The generalized relations due to the spin symmetry of HQET/NRQCD for the form factors are derived at the recoil momentum close to zero. The nonleptonic decays are studied using the assumption on the factorization. The B_c meson lifetime is estimated by summing up the dominating exclusive modes in the c --> s transition combining the current calculations with the previous analysis of b --> c decays in the sum rules of QCD and NRQCD.

Ion-recoil momentum spectroscopy in a laser-cooled atomic sample

We report an experiment on recoil-ion momentum spectroscopy of ${\mathrm{Rb}}^{+}$ ions formed by two-photon ionization of ${\mathrm{Rb}}^{2}{P}_{3/2}$ at 790 nm. Laser-cooled atoms in a magneto-optic trap are used as the target in time-of-flight analysis of the recoil momentum. We demonstrate a resolution of 1 \ensuremath{\mu}eV with a limiting momentum resolution below $\ensuremath{\delta}p=0.05$ a.u. We also show the use of the photoionization technique for the characterization of cold atomic samples.

Multiple ionization in fast ion-atom collisions: simultaneous measurement of recoil momentum and projectile energy loss

We report on the first experiment that measures simultaneously the full momentum vector of recoil ions and projectile energy loss and scattering angle in ion-atom collisions. We studied multiple ionization in the collisions of 0.83-MeV/u O7+ with Ne. Recoil ions ( Ne(q+), q = 1-8) were detected in coincidence with single capture to O6+. The results give the first experimental evidence for the increase of the average electron energy with increasing recoil charge state q. The average ejection angle shows a dramatic decrease with q. Results are compared with n-electron classical trajectory Monte Carlo calculations.

Dynamics of atom-cavity system and elimination of momentum recoil

In the framework of algebraic dynamics, we investigate an atom-cavity system with atomic centre-of-mass motion included. Using nonlinear transformations, the Hamiltonian is linearized in terms of Lie algebraic generators so that the algebraic dynamical structure of the system appears quite clear and its solution is easy to handle by an algebraic dynamical method. In more detail, for the three-level system of Ξ configuration, we show that the momentum recoil of the atom can be eliminated under certain conditions.

Interpretation of Momentum Distribution of Recoil Ions from Laser Induced Nonsequential Double Ionization

We show that the recently reported momentum distribution of recoil ions from laser induced nonsequential double ionization can be interpreted as a combined effect of interelectron correlation and final state field interaction ("Volkov dressing") of the two outgoing electrons. We also find a cutoff formula for the recoil momentum that gives the maximum momenta observed in the experiments.

Semileptonic Bc-meson decays in sum rules of QCD and NRQCD

The semileptonic B c -meson decays into the heavy quarkonia J/ ψ( η c ) and a pair of leptons are investigated in the framework of three-point sum rules of QCD and NRQCD. Calculations of analytical expressions for the spectral densities of QCD and NRQCD correlators with account for the Coulomb-like α s / v terms are presented. The generalized relations due to the spin symmetry of NRQCD for the form factors of B c → J/ ψ( η c ) lν l transitions with l denoting one of the leptons e, μ or τ, are derived at the recoil momentum close to zero. This allows one to express all NRQCD form factors through a single universal quantity, an analogue of Isgur–Wise function at the maximal invariant mass of lepton pair. The gluon condensate corrections to three-point functions are calculated both in full QCD in the Borel transform scheme and in NRQCD in the moment scheme. This enlarges the parameteric stability region of sum rule method that makes the results of the approach to be more reliable. Numerical estimates of widths for the transitions of B c → J/ ψ( η c ) lν l are presented.

Dynamics of explosive boiling of drops at the superheat limit

A physical model for explosive boiling of drops is presented. Loss of stability of the liquid-vapor interface results in occurrence of evaporation fronts. Their propagation in a metastable liquid is determined by the vapor recoil momentum. Detachment of drops from the interface is due to thermocapillary forces. The validity of the model is supported by comparison of calculations with experimental data.