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.     

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.     

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.     

Yields of nuclear fragments in the interactions of carbon nuclei with a beryllium target at a projectile energy of 0.6 GeV per nucleon

The yields of long-lived nuclear fragments at an angle of 3.5° that originate fromthe fragmentation of carbon ions with an energy of T₀ = 0.6 GeV per nucleon on a berylliumtarget were measured in the FRAGMexperiment at the ITEP TWA heavy-ion accelerator. The momentum spectra of these fragments cover both the fragmentation-maximum region and the cumulative region. The respective differential cross sections change by about five orders of magnitude. The momentum distributions of fragments in the laboratory frame and their kinetic-energy distributions in the rest frame of the fragmenting nucleus are used to test the predictions of four models of ion–ion interactions: BC, INCL++, LAQGSM03.03, and QMD.     

Search for d' in pion inclusive spectra from pp-interactions

We report on our measurement of the inclusive spectrum of positive pions from the reaction pp→π⁺+X on a CH ₂ internal target of the ITEP proton synchrotron at 1.5 GeV/c with a missing mass resolution of about 1 MeV/c². The goal of our experiment was the search for the hypothetical narrow πNN resonance (0.5\ MeV/c² width and a mass of 2.06\ GeV/c²) with I(J ^P P)=even(0⁻), called d′. We do not see any statistically significant d′-signal. The upper limit for d′ production cross-section in pp-interactions is near 2μb at 84%C.L. Received: 5 November 1997     

Energy dependence of backward π−d elastic scattering in the 1–2 GeV region

Differential cross sections for backward π^?d elastic scattering (?1 ≦ cos θ_c.m ≦ ?0.98) have been measured at fourteen momenta from 0.98 to 1.76 GeV/c and at 2.45 GeV/c. Energy dependence of the cross section exibits a new wide structure at √s ≈ 2.9 GeV. Possible mechanisms of the reaction accounting for this structure are presented. Experimental data are compared with theoretical calculations.     

A search for the effects of nuclear matter in backward pion-deuteron quasielastic scattering by 6Li

Results of a kinematically complete experiment on backward π^? d quasielastic scattering by ⁶Li are presented. The experiment was carried out at the ITEP 3-m magnetic spectrometer with pion beams of momenta 0.72, 0.88, and 1.28 GeV/c. The Fermi-motion parameters of a quasideuteron cluster and the effective number of quasideuterons in ⁶Li are determined for the ⁶Li(π^?, π^? d)⁴He reaction. These values agree well with the proton-and electron-beam measurements. The possibility of observation of the effects of deuteron wave-function modification in nuclear matter is discussed for this reaction.     

Cumulative protons in the 9Be(12C,p)X reaction at 0.2–3.2 GeV/nucleon

The spectra of protons were measured in fragmentation of ¹²C ions in the cumulative region at energies of 0.2–3.2 GeV/nucleon. The energy dependence of the slope parameters in the obtained spectra was traced. The probability of the existence of two- and three-nucleon clusters in the carbon nucleus was estimated within the model of quark-gluon strings.