The electron-helium scattering length

A more accurate scattering length of (1.178 ± 0.004)a₀ is derived from the Crompton, Elford and Robertson momentum transfer cross sections by effective range theory.     

Semi-classical limit of scattering length

For scattering by a finite range potential, it is shown that the scattering length is convergent to the capacity of the support of the finite range potential in the semi-classical limit. This result has been already proved by use of probabilistic methods. Here we give an alternative proof without using any probabilistic idea. The proof is purely analytical and very simple.     

Chord length distributions and small-angle scattering

Chord length distributions describe size, shape and spatial arrangement of geometrical objects (particles). The chord length distribution is in principle proportional to the second derivative of the correlation function of small-angle scattering. It is calculable from a relative measurement of the scattering intensity I(h). In structure research, the characterization of numerous particle systems can be achieved by comparing experimental chord distributions with theoretical ones, provided the latter are available with sufficiently high precision for a lot of fundamental, universal shapes. Both sides of this concept are exemplified: – the step from a relative measurement of the scattering intensity of an isotropic two-phase sample to the chord length distribution (errors in and in , limited h-interval, corresponding to the region (1-2) nm < r in real space, must be observed); as well as the geometric matter of calculation of chord distributions as fingerprints for basic geometric figures, including the non-convex case. Received 15 March 1999 and Received in final form 26 April 2000     

Experimental determination of the scattering length for positron scattering from krypton

We report the first experimentally supported determination of the scattering length for positron scattering from krypton. Our result of  ?10.3 ± 1.5 a.u. compares favourably with that from a convergent close coupling calculation performed as a part of this investigation (?9.5 a.u.), and also with an earlier many body theory calculation of  ?10.1 a.u. from Gribakin and Ludlow [Phys. Rev. A 70, 032720 (2004)] and a polarized-orbital result of  ?10.4 a.u. from McEachran et al. [J. Phys. B 13, 1281 (1980)]. The present experimental scattering length supports the existence of a low-lying positron-krypton virtual state (Surko et al. [J. Phys. B 38, R57 (2005)]) at an energy ε = 0.13 eV.     

Neutron polarizability and the two-neutron scattering length

It is shown that the neutron electric polarizability contribution to the two-neutron scattering length is not negligible if the polarizability is as large as available measurements indicate.     

Calculations of the π-deuteron scattering length

Multiple scattering calculations of the π?d scattering length are presented which include higher order scattering with as much care as appears feasible to us.     

Overlapping contributions to the pion-deuteron scattering length

The dependence of the pion-deuteron scattering length on the overlapping region of the two scatterers is studied. It is found that this region contributes almost 30 % to the total result.     

Superfluid Fermi gases with large scattering length

We report quantum Monte Carlo calculations of superfluid Fermi gases with short-range two-body attractive interactions with infinite scattering length. The energy of such gases is estimated to be (0.44+/-0.01) times that of the noninteracting gas, and their pairing gap is approximately twice the energy per particle.     

Determination of the s-wave scattering length of chromium

We have measured the deca-triplet s-wave scattering length of the bosonic chromium isotopes 52Cr and 50Cr. From the time constants for cross-dimensional thermalization in ultracold atomic samples, we have determined the magnitudes |a(52Cr)|=(170+/-39)a(0) and |a(50Cr)|=(40+/-15)a(0), where a(0)=0.053 nm. By measuring the rethermalization rate of 52Cr over a wide temperature range and comparing the temperature dependence with the effective-range theory and numerical single-channel calculations, we have obtained strong evidence that the sign of a(52Cr) is positive. Rescaling our 52Cr model potential to 50Cr strongly suggests that a(50Cr) is positive also.     

New method to extract the neutron-electron scattering length

A novel method to extract the neutron-electron scattering length b _ne from the precise neutron scattering data measured for a noble gas at several different densities n is proposed. The main point of this method is dividing the experimental data into two parts: the first, nearly proportional to n, corresponding to diffraction on neighboring atoms and the second one, a small contribution of n, e scattering independent on n. The proposed technique is demonstrated using the structure factor S(q) for gaseous krypton.Received: 12 October 2004, Revised: 1 December 2004, Published online: 7 March 2005PACS: 28.20.-v, 61.12.-q, 14.20.Dh, 13.40.-f     

Model dependence of the Coulomb-corrected p-p scattering length

It is shown that the requirement of a fixed intermediate-range ¹S₀ proton-proton interaction considerably reduces the model dependence of the Coulomb-corrected p-p scattering length. A possible relation with the off-shell effective range parameter is discussed.     

Quasi-one-dimensional Bose gases with a large scattering length

Bose gases confined in highly elongated harmonic traps are investigated over a wide range of interaction strengths using quantum Monte Carlo techniques. We find that the properties of a Bose gas under tight transverse confinement are well reproduced by a 1D model Hamiltonian with contact interactions. We point out the existence of a unitary regime, where the properties of the quasi-1D Bose gas become independent of the actual value of the 3D scattering length a(3D). In this unitary regime, the energy of the system is well described by a hard-rod equation of state. We investigate the stability of quasi-1D Bose gases with positive and negative a(3D).     

Bunch length measurement at Tsinghua Thomson scattering X-ray source

The length of electron beam from a photocathode RF gun is determined by a spectrometer, according to the relative energy spread induced by the bunch length during the acceleration in a linac. For a photocathode RF gun, different laser injected phase and beam charge are studied. The compression is changed for the different laser phases, as from 10° to 30°, and the bunch length is lengthened due to the strong longitudinal space charge force, caused by the increased charge.     

两相邻有限长圆柱的复合电磁散射研究

基于等效定理和互易性原理研究了两相邻有限长介质圆柱的复合电磁散射问题,推导出该复合散射场的二阶散射场计算公式.将公式所得结果与矩量法结果进行了比较,并分析了两柱距离、圆柱长度和极化状态等参量对复合散射场的影响. 关键词： 等效定理 互易性原理 电磁散射 有限长圆柱     

Three-body recombination in bose gases with large scattering length

An effective field theory for the three-body system with large scattering length is applied to three-body recombination to a weakly bound s-wave state in a Bose gas. Our model independent analysis demonstrates that the three-body recombination constant alpha is not universal, but can take any value between zero and 67.9Planck's over 2pia(4)/m, where a is the scattering length. Other low-energy three-body observables can be predicted in terms of a and alpha. Near a Feshbach resonance, alpha should oscillate between those limits as the magnetic field B approaches the point where a-->infinity. In any interval of B over which a increases by a factor of 22.7, alpha should have a zero.     

Preliminary study of the scattering length from lattice QCD

Noncommutative generalizations of a supersymmetry algebra in two dimensions have been introduced earlier in Abbaspur (Int. J. Mod. Phys. A 18:855?C878, 2003; Mod. Phys. Lett. A 18:587?C599, 2003). In this paper we present a field theoretic realization for these algebras in the context of $\mathcal{N}=1$ supersymmetric U(1) gauge theories in two dimensions. We also describe a possible generalization to 4-dimensional theories.