Multiphoton effects in laser-assisted ionization of a helium atom by electron impact

The dynamics of the electron impact multiphoton ionization of a He atom in the presence of an intense laser field (n $\gamma _e$ , 2e) is studied theoretically for laser polarization ( $\vert\vert^l$ ) and perpendicular ( $\bot^r$ ) to the incident momentum. The triple differential (TDCS) as well as the double differential (DDCS) cross sections are studied for the coplanar asymmetric geometry. The results are compared with the only available kinematically complete experiment at high incident energy (1000 eV). Significant laser modification (enhancement) is noted due to multiphoton effects in the present binary and recoil peak intensities of the TDCS for both the geometries, in qualitative agreement with the experiment. In the single photon case, the net effect of the laser field is to suppress the field free (FF) TDCS as well as the DDCS in the zeroth order approximation of the ejected electron wave function (CV), while in the first order (MCV), the cross sections are found to be enhanced. The CV multiphoton cross sections obey the famous Kroll Watson (KW) sum rule while the latter does not hold good in the corresponding MCV approximation.     

Powerful dynamical neutrino source with a hard spectrum

A powerful dynamical neutrino source with a hard spectrum obtained via the (n, γ) activation of ⁷Li and a subsequent β^? decay (T _1/2=0.84 s) of ⁸Li with the emission of high-energy $\tilde \nu _e$ (up to 13 MeV) is discussed. In the dynamical system, lithium is pumped over in a closed cycle through a converter near the reactor core and further to a remote $\tilde \nu _e$ detector. It is shown that, owing to a large growth of the hardness of the total $\tilde \nu _e$ spectrum, the cross section for the interaction with a deuteron can strongly increase both in the neutral ( $\tilde \nu _e + d \uparrow n + p + \tilde \nu _e$ ) and in the charged ( $\tilde \nu _e + d \uparrow n + n + e^ +$ ) channel in relation to the analogous cross sections in the reactor $\tilde \nu _e$ spectrum.     

Coupled-Channels Approach and Simple Models in the Theory of Exotic Atom Formation

Atomic collisions of slow negative particles X ^? (μ^?, $\bar p$ , etc.) are considered using coupled channels semiclassical approximation that takes into account 2- and 3-particle channels. Analytical expression for differential elastic cross section is proposed. Differential cross section reveals essential quantum interference effects. Inelastic $\bar p$ –Ne and $\bar p$ –Ar cross sections are considered using model potentials.     

Charm Production in Antiproton-Proton Annihilation

We study the production of charmed mesons (D) and baryons (?? _c ) in antiproton-proton ${(\bar{p}p)}$ annihilation close to their respective production thresholds. The elementary charm production process is described by either baryon/meson exchange or by quark/gluon dynamics. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on ${\bar{p}p \to \bar{\Lambda} \Lambda}$ and ${\bar{p} p \to \bar{K} K}$ by connecting the processes via SU(4) flavor symmetry. Our predictions for the ${\bar{\Lambda}_c \Lambda_c}$ production cross section are in the order of 1 to 7 mb, i.e. a factor of around 10?C70 smaller than the corresponding cross sections for ${\bar{\Lambda} \Lambda}$ However, they are 100 to 1000 times larger than predictions of other model calculations in the literature. On the other hand, the resulting cross sections for ${\bar{D} D}$ production are found to be in the order of 10^?2 ?C 10^?1 ??b and they turned out to be comparable to those obtained in other studies.     

Cross sections for leptophobic topcolor Z′ decaying to top–antitop

We present numerical calculations of the production cross section of a heavy Z?? resonance in hadron?Chadron collisions with subsequent decay into top?Cantitop pairs. In particular, we consider the leptophobic topcolor Z?? discussed under Model IV of hep-ph/9911288, which has predicted cross sections large enough to be experimentally accessible at the Fermilab Tevatron and the Large Hadron Collider at CERN. This article presents an updated calculation valid for the Tevatron and all proposed LHC collision energies. Cross sections are presented for various Z?? widths, in $p\bar{p}$ collisions at $\sqrt{s}=2\mbox{~TeV}$ , and in pp collisions at $\sqrt{s}=7, 8, 10 \mbox{ and } 14\mbox{~TeV}$ .     

Reichenbachian Common Cause Systems

A partition C_{i i∈ I} of a Boolean algebra $\mathcal{S}$ in a probability measure space $(\mathcal{S},p)$ is called a Reichenbachian common cause system for the correlated pair A,B of events in $\mathcal{S}$ if any two elements in the partition behave like a Reichenbachian common cause and its complement, the cardinality of the index set I is called the size of the common cause system. It is shown that given any correlation in $(\mathcal{S},p)$ , and given any finite size n>2, the probability space $(\mathcal{S},p)$ can be embedded into a larger probability space in such a manner that the larger space contains a Reichenbachian common cause system of size n for the correlation. It also is shown that every totally ordered subset in the partially ordered set of all partitions of $\mathcal{S}$ contains only one Reichenbachian common cause system. Some open problems concerning Reichenbachian common cause systems are formulated.     

{\boldsymbol N}\boldsymbol{\bar N} exotics and antiprotonic atoms

The BES Collaboration measurements of J/ψ radiative decays into $ p{\bar p}$ indicate a strong enhancement at $ p {\bar p}$ threshold. In a related experiment a peak in the invariant π ^?+? π ^???η′ mass is observed. It is shown that both structures may be related to a broad $ N{\bar N}$ quasi-bound state in the $^{11}S_{0} $ wave. The existence of this state finds additional support from the antiprotonic atom level widths. It is also explained by a traditional model of $ N \bar{N} $ interactions based on G-parity transformation. The level widths in H, D and He antiprotonic atoms and the radiochemical studies of $ {\bar p}$ capture in nuclei indicate the existence of another near-threshold quasi-bound state in a P wave.     

Gaussian limit for critical oriented percolation in high dimensions

In this paper, we consider the spread-out oriented bond percolation models inZ ^d ×Z withd>4 and the nearest-neighbor oriented bond percolation model in sufficiently high dimensions. Let η _n ,n=1, 2, ..., be the random measures defined onR ^d by $$\eta _n (A) = \sum\limits_{x \in Z^d } {1_A (x/\sqrt n )1_{\{ (0,0) \to (x,n)\} } } $$ The mean of η _n , denoted by $\bar \eta _n $ , is the measure defined by $$\bar \eta _n (A) = E_p [\eta _n (A)]$$ We use the lace expansion method to show that the sequence of probability measures $[\bar \eta _n (R^d )]^{ - 1} \bar \eta _n $ converges weakly to a Gaussian limit asn→∞ for everyp in the subcritical regime as well as the critical regime of these percolation models. Also we show that for these models the parallel correlation length $\xi (p)~|p_c - p|^{ - 1} $ asp?p_c     

Effects of new neutral currents at linear electron-positron colliders

Effects that are induced by contact four-fermion interactions in the processes e ⁺ e ^? → μ ⁺ μ ^?, $\bar bb$ , and $\bar cc$ at $\sqrt s = 0.5$ TeV linear electron-positron colliders are investigated for the case of longitudinally polarized initial beams. This analysis employs new integrated observables constructed from the polarized cross sections for the scattering of final fermions into the forward (σ _F) and the backward (σ _B) hemisphere in such a way that they single out the helicity cross sections for the processes in question. This property of the observables makes it possible to perform, in the most general form, a model-independent analysis of contact four-fermion interactions and to set constraints on their parameters. It is also shown that the sensitivity of new polarization observables to contact interactions is noticeably higher than the corresponding sensitivity of canonical observables like σ, A _FB, A _LR, and A _LR,FB.     

Forward {{\bar p} d} Elastic Scattering and Total Spin-Dependent pd Cross Sections

Glauber theory is applied to ${{\bar p} d}$ scattering at beam energies 20?C300?MeV using the ${{\bar N} N}$ amplitudes of the Jülich models. The available data for unpolarized differential and total cross section are well described within this approach. The polarized total ${{\bar p} d}$ cross sections are calculated within the single-scattering approximation using the optical theorem.     

Recent Results on Hadron Spectroscopy at Belle

Recent activities of the Belle experiment in Hadron spectroscopy are presented. The discovery of two charged bottomonium-like particles, ${Z_b^{\pm}(10610)}$ and ${Z_b^{\pm}(10650)}$ in the ${\Upsilon (nS)\pi^{\pm}}$ (n = 1, 2, 3) and h _b (m P)π ^± (m = 1, 2) final states is followed by the observation of the corresponding peaks in the ${B^*\bar{B}^{(*)}}$ final states that favors the molecular interpretation of Z _b . In addition, a neutral partner candidate is explored at 10,610 MeV in the ${\Upsilon (2S)\pi^0}$ mass spectrum projection. We have got no evidence of an X(3872) partner in J/ψ π ^± π ⁰, J/ψ η and ${\chi_{c1,2}\gamma}$ final states while an evidence of the narrow peak at 3,823 MeV/c ² in ${\chi_{c1}\gamma}$ is thought to be ³ D ₂ charmonium (ψ ₂) candidate. The feasibilities of the search for X(3872) partner in the B → J/ψ π ⁰ π ⁰ K decays, the measurement of light flavored baryons production cross section, and the study of K–p interaction in ${\phi p}$ final state are also discussed.     

Collision-induced dissociation studies on gas-phase titanium oxide cluster cations

Titanium oxide cluster cations $\mathrm{Ti}_{x}\mathrm{O}_{y}^{+}$ are produced in a molecular beam by combining laser ablation of titanium with the supersonic expansion of oxygen into vacuum. The size distribution of the clusters produced is analyzed by time-of-flight reflectron mass spectrometry. The stable clusters appearing in the mass spectrum can be described by the general formula $(\mathrm{TiO})_{m}(\mathrm{TiO}_{2})_{n}(\mathrm{O}_{2})_{k}^{+}$ (with m,n=0,1,2,?? and k=0,1). Additionally, collision-induced dissociation studies of mass selected clusters colliding with Kr atoms in a gas cell have been performed. The results show that the clusters lose neutral O₂, TiO and/or (TiO₂) _n units, and the remaining charged fragments are those with the lowest ionization potentials. From these results the fragmentation cross section of the selected clusters is obtained.     

Measurement of photo-fission yields and photo-neutron cross-sections in 209Bi with 50 and 65 MeV bremsstrahlung

The photo-fission yields and photo-neutron cross-sections of ( $ \gamma$ , 3n) and ( $ \gamma$ , 4n) on ²⁰⁹Bi induced by 50 and 65MeV bremsstrahlung have been measured by using a recoil catcher and an off-line $ \gamma$ -ray spectrometric technique. The mass-yield distribution of fission products in ²⁰⁹Bi induced by bremsstrahlung photons from the present work and literature data in the energy range 28-85MeV is symmetric around 103 mass units. However, the full width at half maximum of the yields distribution increases from 19 mass units at 28-40MeV to 23 mass units at 85MeV. The ( $ \gamma$ , 3n) reaction cross-section in the 50MeV and the ( $ \gamma$ , 4n) reaction cross-section in the 50 and 65MeV bremsstrahlung-induced reaction of ²⁰⁹Bi were determined for the first time.     

Electron (positron) impact excitation (2p state) of lithium at intermediate energies

In this work, studies have been carried out to investigate theoretically the electron (positron)-impact-induced 2s → 2p lithium (Li) transition at 20 and 60 eV using the coupled-channel optical method (CCOM). The inelastic differential cross sections (DCS) together with the reduced Stokes parameters ( $\bar P_1$ , $\bar P_2$ , $\bar P_3$ ) and other parameters such as the alignment (γ, $\bar P_l$ ), orientation (L _⊥) and coherence parameters (P ⁺) are reported in the present calculations. Comparison is made with other available theoretical and experimental measurements.     

Completeness of Determinantal Hamiltonian Flows on the Matrix Affine Poisson Space

The matrix affine Poisson space (M _m,n , π _m,n ) is the space of complex rectangular matrices equipped with a canonical quadratic Poisson structure which in the square case m = n reduces to the standard Poisson structure on ${{\rm GL}_n(\mathbb{C})}$ . We prove that the Hamiltonian flows of all minors are complete. As a corollary we obtain that all Kogan–Zelevinsky integrable systems on M _n,n are complete and thus induce (analytic) Hamiltonian actions of ${\mathbb{C}^{n(n-1)/2}}$ on (M _n,n , π _n,n ) (as well as on ${{\rm GL}_n(\mathbb{C})}$ and on ${{\rm SL}_n(\mathbb{C})}$ ). We define Gelfand–Zeitlin integrable systems on (M _n,n , π _n,n ) from chains of Poisson projections and prove that their flows are also complete. This is an analog for the quadratic Poisson structure π _n,n of the recent result of Kostant and Wallach (Studies in Lie Theory. Progress in Mathematics, vol 243, pp 319–364. Birkhäuser, Boston, 2006) that the flows of the complexified classical Gelfand–Zeitlin integrable systems are complete.     

Proton-separation vertex constants for sd-shell nuclei from an analysis of peripheral transfer reactions

The differential cross sections for the (³He, d) reactions on ¹⁶O nuclei at $E_{3_{He} } = 42$ MeV and on ¹⁹F and ²⁶Mg nuclei at $E_{3_{He} } = 22.3$ MeV are measured for angles from the forward hemisphere. These data and those from the literature are analyzed by using a procedure that combines the method of distorted waves and the elements of the dispersion approach. It is established that the reactions in question are peripheral. Phenomenological values of nuclear vertex constants for proton separation are obtained both for the ground state and for low-lying excited states of the final nucleus, and the corresponding spectroscopic factors are evaluated. It is indicated that these data can be used for nuclear astrophysics.     

The Polyanalytic Ginibre Ensembles

For integers n,q=1,2,3,…?, let Pol _n,q denote the ${\mathbb{C}}$ -linear space of polynomials in z and $\bar{z}$ , of degree ≤n?1 in z and of degree ≤q?1 in $\bar{z}$ . We supply Pol _n,q with the inner product structure of $$\begin{aligned} L^2 \bigl({\mathbb{C}},\mathrm{e}^{-m|z|^2} {\mathrm{d}}A \bigr),\quad \mbox {where } {\mathrm{d}}A(z)=\pi^{-1}{\mathrm{d}}x {\mathrm{d}}y,\ z= x+ {\mathrm{i}}y; \end{aligned}$$ the resulting Hilbert space is denoted by Pol _m,n,q . Here, it is assumed that m is a positive real. We let K _m,n,q denote the reproducing kernel of Pol _m,n,q , and study the associated determinantal process, in the limit as m,n→+∞ while n=m+O(1); the number q, the degree of polyanalyticity, is kept fixed. We call these processes polyanalytic Ginibre ensembles, because they generalize the Ginibre ensemble—the eigenvalue process of random (normal) matrices with Gaussian weight. There is a physical interpretation in terms of a system of free fermions in a uniform magnetic field so that a fixed number of the first Landau levels have been filled. We consider local blow-ups of the polyanalytic Ginibre ensembles around points in the spectral droplet, which is here the closed unit disk $\bar{\mathbb{D}}:=\{z\in{\mathbb{C}}:|z|\le1\}$ . We obtain asymptotics for the blow-up process, using a blow-up to characteristic distance m ^?1/2; the typical distance is the same both for interior and for boundary points of $\bar{\mathbb{D}}$ . This amounts to obtaining the asymptotical behavior of the generating kernel K _m,n,q . Following (Ameur et al. in Commun. Pure Appl. Math. 63(12):1533–1584, 2010), the asymptotics of the K _m,n,q are rather conveniently expressed in terms of the Berezin measure (and density) For interior points |z|<1, we obtain that ${\mathrm{d}}B^{\langle z\rangle}_{m,n,q}(w)\to{\mathrm{d}}\delta_{z} $ in the weak-star sense, where δ _z denotes the unit point mass at z. Moreover, if we blow up to the scale of m ^?1/2 around z, we get convergence to a measure which is Gaussian for q=1, but exhibits more complicated Fresnel zone behavior for q>1. In contrast, for exterior points |z|>1, we have instead that ${\mathrm{d}}B^{\langle z\rangle}_{m,n,q}(w) \to{\mathrm{d}}\omega(w,z, {\mathbb{D}}^{e}) $ , where ${\mathrm{d}}\omega(w,z,{\mathbb{D}}^{e})$ is the harmonic measure at z with respect to the exterior disk ${\mathbb{D}}^{e}:= \{w\in{\mathbb{C}}:\, |w|>1\}$ . For boundary points, |z|=1, the Berezin measure ${\mathrm{d}}B^{\langle z\rangle}_{m,n,q}$ converges to the unit point mass at z, as with interior points, but the blow-up to the scale m ^?1/2 exhibits quite different behavior at boundary points compared with interior points. We also obtain the asymptotic boundary behavior of the 1-point function at the coarser local scale q ^1/2 m ^?1/2.     

The Percolation Transition in the Zero-Temperature Domany Model

We analyze a deterministic cellular automaton σ ^?=(σ ⁿ :n≥0) corresponding to the zero-temperature case of Domany's stochastic Ising ferromagnet on the hexagonal lattice $\mathbb{N}$ . The state space $\mathcal{S}_\mathbb{H} = \left\{ { - 1, + 1} \right\}^\mathbb{H}$ consists of assignments of ?1 or +1 to each site of $\mathbb{H}$ and the initial state $\sigma ^0 = \left\{ {\sigma _{^x }^0 } \right\}_{x \in \mathbb{H}}$ is chosen randomly with P(σ ⁰ _x=+1)=p∈[0,1]. The sites of $\mathbb{H}$ are partitioned in two sets $\mathcal{A}$ and $\mathcal{B}$ so that all the neighbors of a site x in $\mathcal{A}$ belong to $\mathcal{B}$ and vice versa, and the discrete time dynamics is such that the σ ^? _x 's with ${x \in \mathcal{A}}$ (respectively, $\mathcal{B}$ ) are updated simultaneously at odd (resp., even) times, making σ ^? _x agree with the majority of its three neighbors. In ref. 1 it was proved that there is a percolation transition at p=1/2 in the percolation models defined by σ ⁿ , for all times n∈[1,∞]. In this paper, we study the nature of that transition and prove that the critical exponents β, ν, and η of the dependent percolation models defined by σ ⁿ , n∈[1,∞], have the same values as for standard two-dimensional independent site percolation (on the triangular lattice).     

Spin Effects in the Interaction of Antiprotons with the Deuteron at Low and Intermediate Energies

Antiproton-deuteron scattering is analyzed within the Glauber theory, accounting for the full spin dependence of the underlying \({\bar{N}N}\) amplitudes. The latter are taken from the Jülich \({\bar{N}N}\) models and from a recently published new partial-wave analysis of \({\bar{p}p}\) scattering data. Predictions for differential cross sections and the spin observables \({A_y^d}\) , \({A_y^{\bar{p}}}\) , A _xx , A _yy are presented for antiproton beam energies up to about 300 MeV. The efficiency of the polarization buildup for antiprotons in a storage ring is investigated.