Measurement of the analyzing power in p-->d-->(p p)n with a fast forward 1S0 proton pair

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.     

On the Zakharov–L’vov Stochastic Model for Wave Turbulence

Doklady Mathematics - In this paper we discuss a number of rigorous results in the stochastic model for wave turbulence due to Zakharov–L’vov. Namely, we consider the damped/driven...     

Scalar-isovector K¯ production close to threshold

The reaction pp → dK ⁺ˉ has been investigated at excess energies Q = 47.4 and 104.7MeV above the K ⁺ˉ threshold at COSY Jülich. Coincident dK⁺ pairs were detected with the ANKE spectrometer, and subsequently ∼ 2000 events with a missing ˉ invariant mass were identified, which fully populate the Dalitz plot. The joint analysis of invariant mass and angular distributions reveals s-wave dominance between the two kaons, in conjunction with a p-wave between the deuteron and the kaon pair, i.e. Kˉ production via the a ₀ ⁺(980) channel. Integration of the differential distributions yields total cross-sections of σ(pp → dK ⁺ˉ) = (38±2_stat±14_syst)nb and (190±4_stat±39_syst)nb for the low and high Q value, respectively.     

Near-threshold production of phi mesons in pp collisions

The pp-->ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.     

Near-threshold η-meson production in the dd↦He η reaction

The dd↦⁴Heη reaction has been investigated near threshold using the ANKE facility at COSY-Jülich. Both total and differential cross-sections have been measured at two excess energies, Q = 2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q = - 2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition into partial amplitudes and their consequences for the determination of the s-wave ηα scattering length are discussed.     

Nonequilibrium statistical mechanics of a solid immersed in a continuum

We study actions of the symmetric group S₄ on K3 surfaces X that satisfy the following condition: there exists an equivariant birational contraction \(\bar r:X \to \bar X\) to a K3 surface \(\bar X\) with ADE singularities such that the quotient space \(\bar X\)/S₄ is isomorphic to P². We prove that up to smooth equivariant deformations there exist exactly 15 such actions of the group S₄ on K3 surfaces, and that these actions are realized as actions of the Galois groups on the Galoisations \(\bar X\) of the dualizing coverings of the plane which are associated with plane rational quartics without A₄, A₆, and E₆ singularities as their singular points.     

Nonequilibrium Statistical Mechanics of Weakly Stochastically Perturbed System of Oscillators

We consider a finite region of a d-dimensional lattice, \({d \in \mathbb{N}}\), of weakly coupled harmonic oscillators. The coupling is provided by a nearest-neighbour potential (harmonic or not) of size \({\varepsilon}\). Each oscillator weakly interacts by force of order \({\varepsilon}\) with its own stochastic Langevin thermostat of arbitrary positive temperature. We investigate limiting as \({\varepsilon \rightarrow 0}\) behaviour of solutions of the system and of the local energy of oscillators on long-time intervals of order \({\varepsilon^{-1}}\) and in a stationary regime. We show that it is governed by an effective equation which is a dissipative SDE with nondegenerate diffusion. Next, we assume that the interaction potential is of size \({\varepsilon \lambda}\), where \({\lambda}\) is another small parameter, independent from \({\varepsilon}\). Solutions corresponding to this scaling describe small low temperature oscillations. We prove that in a stationary regime, under the limit \({\varepsilon \rightarrow 0}\), the main order in \({\lambda}\) of the averaged Hamiltonian energy flow is proportional to the gradient of temperature. We show that the coefficient of proportionality, which we call the conductivity, admits a representation through stationary space–time correlations of the energy flow. Most of the results and convergences we obtain are uniform with respect to the number of oscillators in the system.     

Spin Physics at ANKE-COSY

The COSY accelerator (Jülich, Germany) provides beams of polarised protons and deuterons. The ANKE facility at COSY is equipped with polarised hydrogen and deuterium atomic gas targets. The reactions investigated with polarised probes at ANKE include the deuteron break-up at small and large momentum transfer, the pion production processes in pp and pn collisions and the near-threshold η meson production in dip $\vec dp \to ^3 He\eta$ process. Use of the polarised deuteron beam properties allowed a precision measurement of the η meson mass. The future experimental program covers the study of the elementary pp and pn-interaction with polarised beams up to the maximal COSY energy, and a double polarised measurement of the A _{x, z} spin correlation parameter in the pN → {pp} _s π process.