A new approach to irreversibility in deep inelastic collisions

We use concepts of statistical mechanics to discuss the irreversible character of the experimental data in deep inelastic collisions. A definition of irreversibility proposed by Ruch permits a unified overview on current theories which describe these reactions. An information theoretical analysis of the data leads to a Fokker-Planck equation for the collective variables (excitation energy, charge and mass). The concept of mixing distance can serve as a quantitative measure to characterize the “approach to equilibrium”. We apply it to the brownian motion as an illustration and also to the phenomenological analysis of deep inelastic scattering data with interesting results.     

A classical description of deep inelastic collisions

A classical friction model is applied to describe deep inelastic collisions between heavy ions. With only a very few parameters chosen once and for all, a quantitative fit to the existing fusion data as well as the different features of deep inelastic scattering are obtained.     

Angular-momentum coherence in heavy-ion deep inelastic collisions

It is shown that cross sections describing deep inelastic collisions between complex nuclei can neither be desribed as a coherent nor as an incoherent superposition of partial-wave amplitudes. The number of interfering partial waves increases with the masses of the interacting nuclei and decreases with the interaction time.     

The third particle in deep inelastic collisions

Angular correlations between charged reaction products have been measured for the reaction¹⁴N+²⁷A1 at 70 and 100 MeV. Light particle evaporation from the heavy recoil is shown to be the dominant process. In addition, however fast alphas are observed for all reaction channels. From the three-body kinematics we conclude that these alphas are emitted from the contact zone between the two heavy ions. A comparison of the results forE _Lab=70 and 100 MeV excludes an explanation of this process by the recently suggested “Piston” or “hot-spot” models.     

A theoretical investigation of shell effects in deep inelastic collisions

The relative importance of three different influences of independent-particle shell structure on the nucleon transport process during heavy-ion collisions are discussed. Results of calculations for the 620-MeV⁸⁶Kr +¹⁹⁷Au system are presented.     

Friction coefficients for deep inelastic heavy-ion collisions

The friction coefficients for deep inelastic collisions are re-evaluated microscopically in the framework of the linear response theory, adopting the cutoff procedure of Jensen et al. to take account of lifetime of particle-hole excitations. They have the same order of magnitude as the previous ones with a constant time cutoff parameters.     

Competing scaling laws in deep inelastic hadron collisions

We have investigated the electro-fission of uranium in the energy range from 15 to 40 MeV with electrons and positrons. Bumps in the cross-section ratio σ^?/σ⁺ are explained as E2 admixtures after the onset of higher-chance fission.     

Two-photon collisions in deep inelastic lepton-nucleon and lepton-nucleus scattering

We have calculated the μ-pair production via photon-photon collisions in deep-inelastic charged lepton scattering on proton and nuclei, using the equivalent photon approximation. Specific parametrizations were assumed for the proton and the nuclei form factors and the QED photon structure function. Results are given for lepton energies below 300 GeV and virtual photon massesQ ² less than 50 GeV², as functions of the μ-pair mass, the scaling variablex and the electric chargeZ of the hadron target. Using a photon structure function derived from QPM and VDM we also estimate the contribution of γγ collisions to hadron production in these deep inelastic processes.     

Average polarization in deep inelastic collisions of heavy ions

The polarization averaged over many quantal channels is analyzed. The analytical expressions for probability distribution function and average polarization are derived in cases of pure statistical reactions as well as the planar ones.     

Evidence for shape deformations of fragments in deep inelastic collisions

The number and energy spectra of neutrons evaporated by the heavy and light fragments in deep inelastic collisions have been obtained for the system 240 MeV⁴⁰Ar +¹⁹⁷Au. They indicate that at the scission point the deformation energy is a large part of the total excitation energy espe cially for the light fragment. In the last two years, neutron emission has been studied in deep inelastic reactions^1?6. All the results are similar: the incident energy which is lost during the process is transformed into excitation energy of the final fragments and is shared between the two products proportionnally to their masses. This means that the nuclear temperature was uniform in the composite system. The excitation energy equilibration time is really very short since equilibration is achieved after reaction times as small as 10^?22 s^2,6. Moreover, no preequilibrium emission (direct neutrons-) has been observed.     

Study of deep inelastic collisions within multidimensional dynamical model

Energy, angle, and charge distributions of binary products of the deep inelastic collisions of heavy ions are studied in the framework of a multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations. The model is verified on the example of the ¹³⁶Xe + ²⁰⁹Bi system at several above barrier energies.     

A classical description of deep inelastic collisions with surface friction and deformation

The friction model for heavy ion induced fusion and deep inelastic nuclear reaction is extended to include deformation. Spheroidal deformation and relative motion of the mass centres of the two interacting nuclei are treated as dynamical variables. The radial frictional force has been assumed to be proportional to the rate of change of the separation between the two surfaces instead of the two centres of mass. The friction coefficients remain unaltered. The potential as a function of deformation and separation distance are generated by a single folding procedure. The model is applied to⁴⁰Ar+²³²Th at 379 MeV (Lab) and¹³⁶Xe+²⁰⁹Bi at 1,130 MeV (Lab). In case of the former, the energy loss, which has not been properly accounted for before, is now satisfactorily explained and in the case of the latter the model predicts the absence of fusion in agreement with experiment.     

Helicity representation for deep inelastic collisions of heavy ions

Quantum-mechanical cross-section for the inelastic collisions characterized by large values of the angular momenta is analysed. For the case of a planar mechanism of the reaction the approximation of the small helicity is drawn.     

Charge-drift and dispersion in deep inelastic collisions in an equilibrium model

First and second moments of the charge distribution for the reaction⁸⁶K +¹⁶⁶Er have been calculated assuming a thermal equilibrium model. The moments are calculated microscopically on the basis of a realistic two-center shell model as a function of distance as well as of excitation energy. The experimentally observed constancy of the first moments is reproduced.     

Bombarding energy dependence of angular momentum transfer in deep inelastic collisions

Measurements of first and second moments of γ-ray multiplicity distributions from deep inelastic collisions of ⁸⁶Kr + ¹⁵⁴Sm are reported. A global systematics of the angular momentum distributions from deep inelastic reactions with projectile masses ? 40 is presented. The average angular momentum is found to depend linearly on the incident channel average angular momentum, while no simple systematics for the second moment appears obvious. In order to illuminate the question whether the angular momentum transfer process reaches statistical equilibrium in deep inelastic collisions, numerical calculations have been performed on two models: a two-sphere classical model including the collective modes of twisting, bending, wriggling and tilting, and a statistical equilibrium Fermi-gas model. The two-sphere classical model is not able to account for the observed second moments, and neither does the Fermi-gas model give an explanation of the deep inelastic multiplicity data.     

Delta electrons: An atomic clock for deep inelastic collisions

We calculate the δ-electron distribution resulting from heavy ion collisions with projectile energies above the Coulomb barrier. It is shown that the life time (Δτ?10^?21s) of superheavy composite systems causes pronounced oscillations in the electron spectrum. The width of the oscillations is found to be ΔE=h/Δτ. This effect can be used to measure nuclear sticking times quite accurately.     

136Ba的10+同质异能态

利用450MeV的⁸²Se束流轰击¹³⁹La靶,通过核子转移反应产生了¹³⁶Ba,用在束γ谱学方法测量了其激发态的γ衰变,观测到了它的10⁺态同质异能态并得到该同质异能态的寿命为94ns.     

A study of deep inelastic hadron-hadron collisions with a large acceptance calorimeter trigger

Large transverse energy cross sections of 300 GeV/c pions and protons on hydrogen have been measured with a segmented calorimeter covering the central rapidity region ?0.88 < y < 0.67 and 2π in azimuth. The selected events show large multiplicities and no jet-like event structure. Processes more complicated than the scattering of two constituents appear to dominate these inelastic collisions.     

A new global analysis of deep inelastic scattering data

A new QCD analysis of deep inelastic scattering (DIS) data is presented. All available neutrino and antineutrino cross sections are reanalyzed and included in the fit, along with charged-lepton DIS and Drell–Yan data. A massive factorization scheme is used to describe the charm component of the structure functions. Next-to-leading-order parton distribution functions are provided. In particular, the strange-sea density is determined with a higher accuracy with respect to other global fits. Received: 16 March 1999 / Published online: 8 December 1999     

A new diquark model for deep inelastic structure functions

The bulk of data from deep inelasticep, eD, μp, μN, νp and νN scattering is fitted with a new diquark model of nucleons. The proton is found to be mostly in au(ud) ₀ state, where the (ud)₀ diquark has spin and isospin zero. There is hence no trace ofSU(6) symmetry among diquarks in nucleons.