Projectile stopping in nucleus-nucleus and hadron-nucleus collisions at 4.2 and 10 GeV/c per nucleon

The collisions ofp,²H,⁴He and C with carbon and tantalum nuclei at 4.2 GeV/c per nucleon as well as the collisionsp-C andp-Ta at 10 GeV/c from 2-m propane bubble chamber have been studied. New results on nuclear stopping have been obtained from the examination of proton rapidity distributions and average rapidity of leading protons for collisions of various degree of centrality: our study points out that a proton projectile is fully stopped in the centralp-Ta collisions at 4.2 GeV/c but only partly stopped at 10 Gev/c. The proton multiplicity in the centralp-Ta collisions at 10 GeV/c can be described by the binomial distribution,P(n), which expresses the probability that the projectile meetsn protons among the nucleons being along the diameter of a target nucleus.     

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.     

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.     

Multiparticle azimuthal correlations of negative pions in nucleus-nucleus collisions

Multiparticle azimuthal correlations of ?? ^? mesons have been studied in dC, HeC, CC, CNe, MgMg, (d, He)Ta, CCu, CTa, and OPb collisions at momentum of 4.2, 4.5 GeV/c per nucleon within the standard transverse momentum analysis method of P. Danielewicz and G. Odyniec. The data were obtained by SKM-200-GIBS and Propane Bubble Chamber Collaborations of JINR. The axis has been selected in the phase space and with respect to this axis ?? ^? meson correlations were observed. The values of the coefficient of the correlations linearly depend on the mass numbers of projectile (A _P ) and target (A _T ) nuclei. The Quark-Gluon String Model satisfactorily describes the experimental results.     

Proton spectra from 6.3 GeV/c deuteron break-up on 1H, 2H,C, A1 and Bi nuclei

The proton spectra resulting from 6.3 GeV/c deuteron break-up on ¹H, ²H, C, Al and Bi nuclei were measured at an angle of 103 mr (lab) in the momentum interval from 2.6 to 3.6 GeV/c. The measurements were made at the JINR synchrophasotron with a one-arm magnetic spectrometer on-line with a computer. The results, apart from the effects of pion production, are reasonably reproduced in the framework of the Glauber multiple scattering model, taking into account the relativistic deformation of the deuteron wave function.     

Multiplicity fluctuations of particles produced in interactions of light nuclei with carbon nuclei at a momentum of 4.2 <Emphasis Type="Italic">A</Emphasis> GeV/<Emphasis Type="Italic">c</Emphasis> and their theoretical interpretation

New experimental data on fluctuations in the multiplicities of negatively charged particles in interactions of light nuclei (p, d, ⁴He, ¹²C) with carbon nuclei at a momentum of 4.2 A GeV/c in 4π geometry are reported. The data indicate a behavior similar to that earlier observed by the NA49 Collaboration. The cascade evaporation model, FRITIOF model, and UrQMD 1.3 model are used to analyze the data. The dependence of the fluctuations on nuclear collision centrality is theoretically described without any exotic assumptions. According to the FRITIOF model, the dependence of the multiplicity fluctuations on the collision centrality is to a large extent governed by fluctuations in the number of “wounded” nucleons that are associated with the experimental observation conditions. The NA49 Collaboration data are also described.     

Fragmentation of <Superscript>7</Superscript>Li relativistic nuclei on a proton into the <Superscript>3</Superscript>H + <Superscript>4</Superscript>He channel

In a track nuclear photoemulsion exposed to a beam of ⁷Li nuclei accelerated to a momentum of 3 GeV/c per nucleon at the synchrophasotron of the Joint Institute for Nuclear Research (JINR, Dubna), 13 events in which ⁷Li nuclei interacting with protons break up into ³H and ⁴He fragments were detected among 3730 inelastic-interaction events. For this fragmentation channel, the cross section was found to be 8 ± 2 mb. The average value of the fragment total transverse momentum was 214 ± 5 MeV/c. This value exceeds markedly the average value of the transverse-momentum transfer in the coherent dissociation of ⁷Li nuclei on track-emulsion nuclei (166±5MeV/c). The recoil-proton transverse momentum was on average 98% of the total proton momentum. The longitudinal-momentum distribution of protons was characterized by a variance of 16 MeV/c and a mean value of 37 ± 2MeV/c.     

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.     

Cumulative production of nucleons and extremely light nuclei in 4Hep interactions at an incident momentum of 5 GeV/c

The invariant cross sections for the cumulative production of protons, neutrons, and extremely light nuclei (d, ³H, and ³He) are determined on the basis of experimental data obtained by exposing the 2-m liquid-hydrogen bubble chamber of the Institute of Theoretical and Experimental Physics (ITEP, Moscow) to a 5-GeV/c α-particle beam, the kinetic energy of primary protons in the rest frame of the nucleus involved being T _p = 620 MeV. The results obtained in this way are compared with the predictions of the Frankfurt-Strikman model, which takes into account short-range few-nucleon correlations, and with the predictions of the nuclear coalescence model.     

On evidence for exotic dibaryon <Emphasis Type="Italic">d</Emphasis><Subscript>1</Subscript>* (1956) in selected two-nucleon-two-photon reactions

The narrow NN-decoupled dibaryon resonance with a mass about 1956 MeV was reported in 2000 by DIB2γ Collaboration (JINR, Dubna) on the basis of the measurement of the two-photon energy spectrum in the reaction pp → pp2γ at 216 MeV. The most probable quantum numbers J ^P = 1⁺ prevent the resonance from decaying into two protons due to the exclusion principle, while the pionic decays are impossible energetically. The significance of this resonance (called d ₁* (1956)) for the interpretation of a few other exclusive and inclusive reactions connected with the photon(s) production in nucleon collisions with nucleons and nuclei at different energies is discussed. The importance is stressed of on-going and planned studies of the elastic and inelastic Compton scattering on the lightest nuclei for collecting information on the structure and dynamics of d ₁* (1956) which can shed light on its nature.     

Contributions of excited 6Li and 7Li nuclei to the production of 4He+2H and 4He+3H systems in 16O p collisions at a momentum of 3.25 GeV/c per nucleon

New experimental data on the cross sections for the yield of excited ⁶Li* and ⁷Li* nuclei and on their contributions to the production of ⁴He + ²H and ⁴He+³H light dinuclear systems in ¹⁶O _p collisions at a momentumof 3.25 A GeV/c per nucleon are presented.     

Momentum distributions of <Superscript>4</Superscript>He nuclei from the <Superscript>6</Superscript>He and <Superscript>6</Superscript>Li breakup

Experimental data on the momentum distributions of ⁴He nuclei originating from ⁶He and ⁶Li breakup on various targets are presented over a wide beam energy range. The experiment with ⁶He was performed at the DRIBs accelerator complex for radioactive beams at the Joint Institute for Nuclear Research (JINR, Dubna). The intensity of the ⁶He beam used was 5 × 10⁶ particles per second and its energy was 10 MeV per nucleon. The momentum distributions of breakup products were measured by means of the MSP-144 magnetic spectrometer. The distribution width was shown to be virtually independent of the target mass. A small value of this width, σ ～ 28 MeV/c, confirms the presence of a halo in ⁶He. The measurements performed with ⁶Li beams of energy 18 and 46 MeV per nucleon at the U-400M accelerator yielded a width value of σ ～ 50 MeV/c for the momentum distributions of ⁴He nuclei, which is intermediate between that for ⁶He and those for stable nuclei. A compilation of the widths of the momentum distributions of fragments originating from the breakup of various nuclei is presented versus the binding energy of one or two neutrons in these nuclei, the target mass and the projectile energy.     

Cross sections of the interactions of He nuclei with protons

⁴He-p collisions at two values of⁴He momenta 8.6 GeV/c and 13.6 GeV/c as well as the³He-p collisions at 13.5 GeV/c have been studies using the one-meter JINR hydrogen bubble chamber. Total, elastic, topological and reaction cross sections have been measured. The cross sections have been determined on a sample of minimum biased events.     

Excitation of the Δ resonance in inclusive ed scattering

The parameters of the pion-electroproduction peak in the cross section for inclusive electron scattering on ¹H and d target nuclei are determined for various kinematical conditions of measurements. It is shown that, for low 4-momentum transfers, 0.030≤Q ²≤0.086 (GeV/c)², the Q ² dependence of the shift of the pion-electroproduction peak in the πN invariant mass for a deuteron target with respect to that for a free proton does not exhibit a universal behavior that is characteristic of complex nuclei.     

Experimental study of the subthreshold production of K +-mesons in proton-nucleus collisions

Energy dependence of the differential cross sections for the production of K ⁺-mesons with a momentum of 1.28 GeV/c (c is the speed of light) by protons incident on Be, Al, Cu, and Ta nuclei was measured for energies both above and below the K ⁺-meson production threshold in pp collisions. Evidence is given for the dominance of the mechanism of direct production in the experiment. The characteristics of momentum distribution are determined for nucleons in the Be and Al nuclei up to 650 MeV/c. The data cannot be described in the model of nuclear spectral function.     

Anomalous carbon nuclei

Results are presented from a bubble chamber experiment to search for anomalous mean free path (MFP) phenomena for secondary multicharged fragments (Z _f =5 and 6) of a¹²C beam at 4.2 GeV/c per nucleon. A total of 50,000 primary interactions of carbon with propane (C₃H₈) were treated. Approximately 6,000 beam fragments with charges Z _f =5 and 6 were analyzed in detail to search for an anomalous decrease of MFP. The anomaly is observed only for secondary carbon nuclei. The experiment has been performed at the Laboratory of High Energies, JINR.     

A dependence of the cross sections for the cumulative production of pions and protons in proton-nucleus and nucleus-nucleus interactions

The behavior of the inclusive cross sections for the cumulative production of π ^± mesons and protons in pA, DA, and ⁴HeA interactions is studied versus the atomic mass number of fragmenting nuclei. The primary-beam momenta were 4.5 GeV/c per nucleon. Secondary pions and protons were recorded with a fixed momentum of 0.5 GeV/c at an angle of 120°. Specifically, the experiment explored the fragmentation of D, He, ⁶Li, ⁷Li, C, Si, ⁵⁸Ni, ⁶⁴Ni, ⁶⁴Zn, ¹¹⁴Sn, ¹²⁴Sn, and Pb nuclei. The energy spectra of π ⁺ and π ^? mesons and protons with momenta in the range 0.3–0.7 GeV/c (the emission angle being 120°) were measured in an 8.9-GeV/c proton beam for Ni, Zn, and Sn isotopes. The special features in the behavior of the cross sections are found and discussed, and a comparison is drawn with the results of other studies.     

A search for charmed particles originating from the interactions of 300 GeV/c protons in emulsion nuclei

The associated production of charmed particles by the interactions of 300 GeV/c protons with complex nuclei has been sought using nuclear emulsions. The failure to observe any candidates for this process among some 60,000 interactions investigated implies, provided charmed particles lifetimes are in the range 10^?12 to 10^?14 s, a cross section for their associated production by the interactions of 300 GeV/c protons with nucleons of less than 1.5 microbarns at a 90% confidence level.     

Formation of the mirror nuclei <Superscript>3</Superscript>H and <Superscript>3</Superscript>He in <Superscript>16</Superscript>O<Emphasis Type="Italic">p</Emphasis> collisions at a momentum of 3.25 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

A comparative analysis of the inclusive production of ³H and ³He nuclei in ¹⁶Op interactions at a momentum of 3.25 GeV/c per nucleon is performed, and it is shown that the formation of these mirror nuclei occurs under close physical conditions, the distinction between their binding energies having no significant effect on the formation of the nuclei.     

Cross section of the <Superscript>3</Superscript>H(d, <Superscript>3</Superscript>He)nn reaction at a deuteron beam energy of 37 MeV

Inclusive spectra and differential cross sections of the ³H(d, ³He)nn reaction, measured at E _d = 36.9 MeV are presented. The shape of ³He spectra was reconstructed by modeling amplitudes of the neutron-neutron final state interaction (Watson-Migdal amplitudes), sequential decay via the ⁴He* resonance (E* = 21.2 MeV, Γ = 0.7 MeV), and their interferences. The model allowed the determination of the angular dependence of the differential cross section of the ³H(d, ³He)nn reaction accompanied by singlet nn-pair production. The results are compared to the supermultiplet potential model of the lightest nuclei interaction.