Inclusive hadron photoproduction from longitudinally polarized protons and deuterons

We report measurements of the asymmetry A₆ for inclusive hadron production on longitudinally polarized proton and deuteron targets by circularly polarized photons. The photons were produced via internal and external bremsstrahlung from an electron beam of 48.35 GeV. Asymmetries for both positive and negative signed hadrons, and a subset of identified pions, were measured in the momentum range 10<P<30 GeV at 2.75° and 5.5°. Small non-zero asymmetries are observed for the proton, while the deuteron results are consistent with zero. Recent calculations do not describe the data well.     

Time-dependent hartree-fock study of angular momentum transfer in 6 and 12 MeV/A heavy ion reactions of 86Kr on 166Er

Three-dimensional TDHF calculations are performed for ⁸⁶Kr+¹⁶⁶Er at 6 and 12.2 MeV/A from which we obtain Wilczynski plots and angular momentum loss curves versus incoming angular momentum. These compare well with recent experimental data from GSI and are consistent with the observed fast projectile fission at 12.2 MeV/A. Finite cross sections for capture as nuclear molecules are predicted.     

Thermalization in high energy nuclear collisions

complete events of the symmetric collisions Ca + Ca at E/A = 400 MeV and 1050 MeV and Nb + Nb at E/A = 400 MeV and 650 MeV have been measured with the Plastic Ball/Wall 4π spectrometer. The degree of isotropy expressed by the ratio of the mean transverse to the mean longitudinal momentum in each event is determined as a function of the charged particle multiplicity. Also discussed are proton energy distributions at θ_cm = 90° and their multiplicity dependences.     

Enhancements observed in the two-proton invariant mass distribution in the pionless deuteron breakup at 3.3 GeV/c

A sample of “non-spectator” events in the pionless deuteron breakup at a 3.3 GeV/c momentum has been investigated by means of a 1 m HBC at the JINR, Dubna. The two-proton invariant mass spectrum in the charge exchange channel exhibits two enhancements for masses of 2,010 MeV/c² and 2,160 MeV/c². Theoretical calculations taking into account one-pion exchange diagrams and virtual pion absorption by the deuteron have been carried out. It has been shown that the enhancement atM _pp=2,010 MeV/c² can be explained if some kind of singularity near theN-N threshold is required. The observed maximum atM _pp=2,160 MeV/c² is caused mainly by intermediate Δ production and pion absorption on the deuteron.     

Out-of-plane emission of nuclear matter in Au+Au collisions between 100 and 800 AMeV

We present new experimental results concerning the azimuthal distributions of proton-likes, light and intermediate mass fragments at midrapidity for Au(100–800 A MeV) +Au collisions measured with the FOPI phase-I detector at GSI in Darmstadt. The azimuthal distributions are investigated as a function of the collision centrality, the incident energy, the fragment charge and transverse momentum. The azimuthal anisotropy is maximum for impact parameters around 7 fm. Intermediate mass fragments present a stronger out-of-plane emission signal than light fragments and a saturation is reached for Z ⩾ 4. The azimuthal anisotropy increases with the fragment transverse momentum and decreases as the incident energy increases. The azimuthal anisotropy of Z = 2 particles investigated as a function of the scaled fragment transverse momentum follows an universal curve for bombarding energies between 250–800 A MeV. A signature for a transition from in-plane to out-of-plane emission is evidenced at the lowest beam energies.     

Antiproton production inp+A andd+A reactions at subthreshold energies

The production of antiprotons in proton-nucleus and deuteron-nucleus collisions is analyzed with respect to one-step nucleon-nucleon (NN → NNp¯ p) and secondary Δ-nucleon (ΔN → NNN¯ p) production channels within a phase-space model incorporating the selfenergies of the baryons. It is found that contrary to nucleus-nucleus collisions the Δ induced reaction channels are of minor importance except at very low bombarding energies. The data from KEK are approximately reproduced when accounting for the internal momentum distribution of the deuteron which provides a natural explanation for the large enhancement of the ¯p cross section ind+A as compared top+A.     

d + α Scattering from 12 to 17 MeV

A previous phase-shift analysis of the d + α system had indicated that the solution obtained might not describe the backward-angle tensor analyzing powers very well above about 10 MeV. We have measured differential cross sections and all four analyzing powers A_y, A_xx, A_yy and A_xz at deuteron bombarding energies of 12, 14, 15 and 17 MeV, with some emphasis on the backward-angle region. The discrepancy with the previous phase-shift analysis was confirmed, and we have studied the changes in the phase parameters necessary to improve the fit to our new measurements.     

Polarization effects in inelastic deuteron scattering in the region of baryon-resonance excitation

Within the impulse approximation, polarization effects in inelastic deuteron scattering on nuclei are investigated in the region around the resonance of mass about 2190 MeV/c ². It is shown that the spin-dependent part of the NN → NN*(2190) amplitude plays a significant role at high momentum transfers. Predictions are obtained for some polarization observables and cross sections for various deuteron-spin-flip processes.     

Deuteron production and space-time characteristics of high-energy hadron-nucleus reactions

The contribution of the coalescence mechanism to deuteron production is discussed on the basis of data on inclusive deuteron and proton production in hadron-nucleus interactions. The angular dependence and theA dependence of the coefficient of twonucleon coalescence into a deuteron are analysed for 7.5 GeV/c pA and 5 GeV/cπ ^? A interactions. The results suggest an elongated shape of the interaction region along the trajectory of the incident hadron and a successive knock-out of nucleons during propagation of the incident particle through a nucleus.     

A study of the proton momentum spectrum from deuteron fragmentation at 8.9 GeV/c and an estimate of admixture parameters for the six-quark state in the deuteron

The momentum spectrum of protons emitted at small angles in the stripping reaction d + ¹²C → p + X has been measured at a deuteron momentum of 8.9 GeV/c. The data are described in the framework of the Glauber-Sitenko theory using the hybrid model of the deuteron wave function which includes a six-quark state. The parameters of this state are determined. A shoulder in the spectrum has been observed in the proton momenta region which kinematically corresponds to the production of a dibaryon resonance with a mass from 2.0 to 2.2 GeV.     

The breakup of 16O into He: An event-by-event study of nucleus-nucleus collisions at 75, 175 and 2000 MeV/A

We present an event-by-event study of the breakup of the ¹⁶O in ¹⁶O + emulsion nucleus interactions at 75, 175 and 2000 MeV/A. The events are categorized according to their multiplicity of projectile He nuclei. The multiplicity depends on the degree of target destruction. Although the fragmentation model describes the gross features of inclusive He spectra, an event-by-event study reveals deviations from the model. The momenta of the He nuclei, emitted from the projectile, depend on helium multiplicity and the breakup properties of the target nucleus. The probability that the ¹⁶O projectile breaks up into multiple He fragments is larger at 75 MeV/A than at 2000 MeV/A. At 75 MeV/A the mean velocity of projectile He is on the average 0.06c below the projectile velocity. This recoil velocity depends on the target nucleus destruction also for the most peripheral collisions.     

Measurement of the differential cross section and of the tensor and vector analyzing powers for the fragmentation of 4.5-GeV/c deuterons on beryllium in the reaction involving proton emission at an angle of 80 mrad

The invariant differential cross section, the tensor analyzing power A _yy , and the vector analyzing power A _y for the reaction ⁹Be(d, p)X are measured at an initial deuteron momentum of 4.5 GeV/c and a proton detection angle of about 80 mrad. The data obtained for the differential cross section are consistent with the results of measurements at 3.5 and 5.78 GeV/c and a proton emission angle of 2.5°. The values found for the tensor analyzing power A _yy are compared with similar data obtained previously for the deuteron-fragmentation process occurring on a carbon target at various values of the initial deuteron momentum and leading to proton emission at zero angle. The data on the differential cross section for the reaction ⁹Be(d, p)X can be satisfactorily described within the relativistic impulse approximation by using standard deuteron wave functions; however, the approach based on this conceptual framework proves to be inadequate in dealing with data on the tensor analyzing power. These results indicate that it is necessary either to change the method for describing the relativistic deuteron or to take into account additional mechanisms.     

Investigation of the deuteron spin structure at short nucleon-nucleon distances in the reaction of polarized-deuteron fragmentation to cumulative pions

Experimental results on the vector (A _y ) and tensor (A _yy ) analyzing powers in the fragmentation of 5- and 9-GeV/c polarized deuterons to high-momentum pions in the kinematical region corresponding to pion production on a strongly correlated nucleon pair (cumulative meson production) are presented. The angular and momentum dependences of A _yy are not described by calculations performed in the impulse approximation by using standard deuteron wave functions. An explanation for our data should be sought on the basis of models that treat the deuteron at short distances (deuteron-core region) as a multiquark state—for example, a 6q cluster, whose high orbital angular momentum (D wave) leads to the observed strong dependence of the reaction tensor analyzing power A( $\vec d$ , π)X on the pion transverse momentum.     

Search for proton-proton dibaryon resonances in the dp → (pp)n reaction

The pp mass distribution in the dp → (pp)n reaction has been measured at the deuteron momentum from 1700 to 2280 MeV/c. The results show no prominent peak which suggests the existence of dibaryon resonances in the mass range of 2000 to 2200 MeV/c².     

Measurement of the 2H(p,n) Breakup Reaction at 170 MeV and the Three-Nucleon Force Effects

The effects of three nucleon force (3NF) have been actively studied via the nucleon–deuteron (Nd) scattering states. The differential cross sections and the vector analyzing powers A _y of the ²H(p, n) inclusive breakup reaction at 170 MeV were measured for the study of 3NF effects in the intermediate energy region. The polarized proton beam of 170 MeV was injected to the deuterated polyethylene (CD₂) target and the energy of scattered neutrons were measured by using TOF method. The data were compared with the Faddeev calculations based on modern nucleon–nucleon (NN) forces with and without the 3NF. Concerning the differential cross sections, we can see large discrepancies between the data and the calculations in the region of scattered neutron energies are low, which is similar to the results of the ²H(p, p) inclusive breakup reaction at 250 MeV.     

Neutron-deuteron scattering in high partial waves

The simple formula is derived for calculating the n + d phase shifts for states with high relative orbital angular momentum. The only parameters appearing in the formula are the deuteron binding energy and the triplet effective range. The formula is tested by comparing it with the results of an exactly solvable model, and it is found to be quite accurate at low energies for L ? 3.     

Measurement of the tensor analyzing power for relativistic-deuteron fragmentation as a means for studying the deuteron structure within light-front dynamics

New data on the vector (A_y) and tensor (A_yy) analyzing powers for the reaction ⁹Be (d, p)X at a primary deuteron momentum of 5 GeV/c for a proton emission angle of 178 mrad are obtained by using the synchrophasotron of the Joint Institute for Nuclear Research (JINR, Dubna). The experimental data on A _yy are analyzed within the approach based on light-front dynamics, the relativistic wave function obtained by Karmanov and his colleagues being used for the deuteron. It is shown that, in contrast to what one has from calculations with standard nonrelativistic deuteron wave functions, all relevant data can be explained in this approximation without resort to additional degrees of freedom.     

Study of the mechanism of the reaction 2H(π−, π−p)n at relatively high neutron momenta

The ²H(π^?, π^? p)n reaction is experimentally studied at 1 GeV/c for spectator neutron momenta up to 200 MeV/c. The spectator momentum and polar angle distributions and the Treiman-Yang angle distribution are in good agreement with theoretical calculations allowing for the diagrams in which the initial pion rescatters on the nucleons inside the deuteron not more than twice. We conclude that our understanding of the mechanism of the nucleon knock-out from a deuteron is correct. The simple example of the reaction on a deuteron confirms the possibility of describing direct processes with a small number of Feynman diagrams.