The use of quasielastic pion-proton backward scattering at 0.7 GeV/c for studying Fermi motion in light nuclei

The plane-wave approximation was used to examine the proton Fermi-momentum distribution in experiments on quasielastic large-momentum-transfer pion-nucleon scattering in light nuclei ⁶Li, ⁷Li, and ¹²C. It was found that, unlike the (e, e′) reaction, the Fermi-gas model is in poor agreement with experiment, whereas the oscillator model adequately describes the spectrum shape. However, the parameters obtained for these distributions are sizably smaller than those derived from the (e, e′)) experiments. This suggests that the plane-wave approach is inadequate and that more complicated theoretical approaches, supposedly allowing for pion-nucleon amplitude modification in nuclear matter, are necessary for the analysis of experimental data.     

Manifestation of quark clusters in the emission of cumulative protons in the experiment on the fragmentation of carbon ions

The proton yields at an angle of 3.5° have been measured in the FRAGM experiment on the fragmentation of carbon ions with the energies T ₀ = 0.6, 0.95, and 2.0 GeV/nucleon on a beryllium target at the heavy-ion accelerator complex TWAC (terawatt accumulator, Institute for Theoretical and Experimental Physics). The data are represented in the form of the dependences of the invariant cross section for proton yield on the cumulative variable x in the range of 0.9 < x < 2.4. This invariant cross section varies within six orders of magnitude. The proton spectra have been analyzed within the theoretical approach of the fragmentation of quark clusters with the fragmentation functions obtained in the quark-gluon string model. The probabilities of the existence of six- and nine-quark clusters in the carbon nuclei are estimated as 8–12 and 0.2–0.6%, respectively. The results are compared to the estimated of quark effects obtained by other methods.     

Nuclear Fragments in 12 C + 9 Be Interactions at an Energy of 2 GeV per Nucleon

Differential cross sections for the production of nuclear fragments at an angle of 3.5° in the fragmentation of 2-GeV/nucleon carbon ions on a beryllium target were measured in the FRAGM experiment performed at the ITEP-TWA heavy-ion accelerator-accumulator complex. The predictions of four Monte Carlo models of ion-ion interactions (BC, INCL, LAQGSM, and QMD) were tested on the basis of a comparison with the momentum spectra of fragments. Successes and drawbacks of these models are discussed. The energy spectra of protons and 3He nuclei in the cumulative region in the projectile rest frame are well described by an exponential dependence, which make it possible to estimate temperature parameters of their emission source.     

Sigma-nucleus potential in A=28

We have studied the (pi(-),K+) reaction on a silicon target to investigate the sigma-nucleus potential. The inclusive spectrum was measured at a beam momentum of 1.2 GeV/c with an energy resolution of 3.3 MeV (FWHM) by employing the superconducting kaon spectrometer system. The spectrum was compared with theoretical calculations within the framework of the distorted-wave impulse approximation, which demonstrates that a strongly repulsive sigma-nucleus potential with a nonzero size of the imaginary part reproduces the observed spectrum.     

Measurement of inclusive pion double charge exchange on 16O at T 0 ≥ 0.5 GeV with the SKS spectrometer at KEK

The inclusive cross section for pion double charge exchange on ¹⁶O at T ₀ = 0.5 and 0.75 GeV was measured with the superconducting kaon spectrometer (SKS) at KEK in a joint ITEP/KEK experiment. The result shows a relatively weak energy dependence of the measured cross section, which is in contradiction with its rapid drop predicted within the conventional model of two sequential single charge exchanges. The data of this experiment agree with the results that were obtained previously from similar measurements at ITEP and which are indicative of a significant contribution from the mechanism of inelastic Glauber rescatterings for T ₀ ? 0.6 GeV.     

Quasielastic deuteron and triton knockout from lithium isotopes by intermediate-energy pions

Quasielastic deuteron and triton knockout from ⁶Li and ⁷Li nuclei that was induced by a π ^?-meson beam of momentum p ₀ = 0.72 and 0.88 GeV/c was studied under conditions of full kinematics. The experiment was performed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) by using a 3-m magnetic spectrometer equipped with spark chambers. The distributions with respect to the momenta of quasideuteron and quasitriton internal motion, the excitation-energy spectra of residual nuclei, and the effective numbers of quasideuterons in ⁶Li and ⁷Li nuclei were obtained.     

Quasielastic knockout of light fragments from 12C and 16O nuclei by intermediate-energy pions

Quasielastic deuteron and triton knockout from ¹²C and ¹⁶O nuclei has been studied infull kinematics using a 0.72-GeV/c pion beam. The momentum distributions of the intranuclear quasideuteron motion, excitation-energy spectra of the residual nuclei, and the effective numbers N _d ^eff of quasideuterons are determined. The parameters of the quasideuteron intranuclear motion are in reasonable agreement with the results obtained in other beams. The N _d ^eff in the nuclei from ⁶Li to ¹⁶O measured in full kinematics are virtually independent of the atomic number in contrast to the analogous values in the inclusive deuteron-knockout reaction induced by protons. The phenomenon of triton knockout from these nuclei is observed, which makes possible estimation of the cross section of backward pion-triton elastic scattering in yet unexplored regions of energy and momentum transfer.     

A dependence of inclusive pion double charge exchange

The A dependence of the forward cross section for inclusive pion double charge exchange on nine target nuclei from ⁶Li to ²⁰⁹Bi at T₀ = 0.59 GeV, as well as the cross section for ⁶Li, ⁷Li, and ¹²C nuclei at T₀ = 0.59, 0.75, and 1.1 GeV, was measured with the 3-m magnetic spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The resulting A dependence is well described within the model involving two sequential single charge exchanges and taking into account the renormalization of the amplitude for pion single charge exchange in a nucleus. A relatively weak energy dependence of the cross section for the ⁶Li, ⁷Li, and ¹²C nuclei agrees with the analogous dependence obtained previously for the ¹⁶O nucleus, but it contradicts the predicted sharp decrease in the cross section within the model involving two sequential single charge exchanges. This result provides an additional piece of evidence that the contribution from the mechanism of inelastic Glauber rescattering is significant at T₀ ? 0.6 GeV.     

Comment on the <Emphasis Type="Italic">A</Emphasis> dependence of quasielastic deuteron knockout from nuclei

The A dependence recently measured in an experiment of our group in full kinematics for quasielastic deuteron knockout by pions revealed that the effective number of quasideuterons in a nucleus is independent of its atomic number. This result differs strongly from the A dependence measured in experiments that studied quasielastic inclusive deuteron knockout by protons, in which case one observes an A ^0.33 power-law dependence. Calculations performed on the basis of a simple deuteron-knockout model show that stronger absorptive effects in measurements under conditions of full kinematics may indeed lead to this change in the A dependence.     

Quasielastic triton knockout from 6Li and 7Li nuclei by intermediate-energy pions

Quasielastic triton knockout from ⁶Li and ⁷Li nuclei by negative pions with momenta p ₀=0.72 and 0.88 GeV/c was studied in the region of backward pion-triton scattering. The experiment was performed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) on a 3-m magnetic spectrometer equipped with spark chambers. The momentum distributions of the intranuclear quasitriton motion and the excitation-energy spectra of residual nuclei were obtained.