GeV 16O Research Articles

System size dependence of final state hadron sources at Elab = 3.7 A GeV

3.7 A GeV 4He, 16O, and 32S beams from Dubna Synchrophasotron interacting in nuclear emulsion are used. The final state hadrons are approached by the produced shower particles. The dependence on the system size is examined. The data are discriminated according to the emission in the forward and backward zones over the 4π space. Minimum biased samples of events corresponding to average impact parameters are selected randomly. The data are compared to a simulation based on the modified FRITIOF event generator, implementing the Lund model string dynamics. The multiplicity characteristics present an overview of the parameters obtained when the distributions are fitted by the multisource thermal model. The forward emitted shower particles are suggested to be created in hadronization system due to multisource superposition. The backward emitted ones mostly result from target nucleus decay source in the framework of the limiting fragmentation hypothesis. Empirical parameterizations based primarily on fitting procedures are undertaken to fulfill the universality of some uniform relationships. Systematic uncertainties are estimated in terms of standard deviation within errors.

Multisource Evidence for Final State Hadrons in 3.7A GeV 16O–Nucleus Interactions

In 3.7A GeV 16O interactions with emulsion nuclei, the shower particle multiplicity characteristics are investigated. Data are presented in terms of the number of emitted particles in both forward and backward angular zones. The dependence on the target size and emission direction is presented. The target separation of events depends on Glauber's multiple scattering theory approaches. A decay mechanism seems to be a characteristic of the backward production. This production may be during the de–excitation of the excited target nucleus, regarding the nuclear limiting fragmentation hypothesis. The forward emitted particle is due to a creation system. The target size is an effective parameter as well as the projectile size in this system, considering the geometrical concept regarded in the nuclear fireball concept. The data are simulated in the framework of the modified FRITIOF model. The multisource thermal model can predict source numbers responsible for particle production.

Features on Very Peripheral Collisions of 16O-Em at 3.7A GeV

From 1540 inelastic interactions of 3.7 A GeV 16O projectile with emulsion nuclei, we select samples of 87 and 61 events carefully due to interactions of neutron (n) and singly charged particles (Z = 1), respectively. New results concerning the topology of such events are investigated. The average multiplicities of secondary relativistic particles that appear as shower tracks for n and Z = 1 stay more or less constant when compared with analogous data on p-Em at similar energy. The multiplicity distributions and the average values of the various secondary charged particles are studied and compared with the corresponding predictions by the cascade evaporation model. The results assume that the n or Z = 1 from 16O collide peripherally with an emulsion target and are considered as an expansion to the N-N collisions.

Channels of projectile fragmentation of 16O nucleus in nuclear emulsion

Experimental data are presented on the projectile fragments emitted from non-central collisions of 3.7 A GeV 16O projectiles with nuclear emulsion. Charges of all projectile fragments are measured carefully and identified using δ-ray distributions. Each distribution is fitted by Gaussian shape and represented one of the possible charges of projectile fragments. Topology of 16O fragmentation is reported and compared with that obtained at 60 A GeV. The multiplicity distributions for 16O projectile fragments with charge 3 ≤ Z ≤ 7 are studied and it classified according to the size of the target nucleus. In this range of energy, the mechanism responsible for projectile fragmentation is independent on its energy. Experimental observations proved that there is high probability for production α-clusters than all other nuclear fragments. The production rate of α-clusters fragments due to 16O fragmentations is studied at range of energies 2–200 A GeV. The dependence of α-clusters on target components (CNO and AgBr) is formulated. Experimental data indicates that α-cluster represents the main unit of the structure of atomic nucleus.

Two and three particle azimuthal angle correlations among the relativistic particles in nucleus-nucleus collisions at relativistic energies

Two and three particle short-range azimuthal angle correlations among the relativistic produced particles in 12 A GeV 4He-, 3.7 A GeV 16O- and 1.7 A GeV 84Kr-emulsion interactions are investigated. The dependence of the normalized correlation functions upon the impact parameter and target size are discussed.

Two and three particle pseudo-rapidity correlations among the relativistic particles in nucleus-nucleus collisions at relativistic energies

Two and three particle short-range pseudo-rapidity correlations among the relativistic produced particles in 12 A GeV 4He-, 3.7 A GeV 16O- and 1.7 A GeV 84Kr-emulsion interactions are investigated. The dependance of the normalized correlation functions upon the impact parameter, target size and azimuthal angle are discussed. The strong two particle short-range pseudo-rapidity correlation is observed in backward direction in target rest frame, which can be explained by the cumulative pions production. Finally the cumulative pseudo-rapidity gap distribution and hence the cluster characteristics, the pseudo-rapidity width distribution and the maximum pseudo-rapidity gap distribution are presented.

Two and three particle correlations in target fragmentation at relativistic nucleus–nucleus collisions

Two and three particle short-range correlations among the target evaporated fragments as well as the target recoil protons produced in 12 A GeV 4He-, 3.7 A GeV 16O-, 60 A GeV 16O-, 1.7 A GeV 84Kr- and 10.7 A GeV 197Au-AgBr interactions are investigated in emission angle space and azimuthal angle space, respectively. The experimental data exhibit two and three particle correlations among the target fragments in emission angle space, which indicate the occurrence of so-called side splash phenomena and disfavor the evaporation model. In azimuthal angle space the data exhibit strong two particle correlations for both the target evaporated fragments and target recoil protons, and three particle correlations only for target recoil protons.

Sensibility of grey particle production system to energy and centrality in 60A and 200A GeV 16O–Nucleus interactions

The grey particle production following 60 A and 200[Formula: see text]A GeV [Formula: see text]O interactions with emulsion nuclei is investigated at different centralities. The evaporated target fragment multiplicity is voted as a centrality parameter. The target size effect is examined over a wide range, where the C, N and O nuclei present the light target group while the Br and Ag nuclei are the heavy group. In the framework of the nuclear limiting fragmentation hypothesis, the grey particle multiplicity characteristics depend only on the target size and centrality while the projectile size and energy are not effective. The grey particle is suggested to be a multisource production system. The emission direction in the 4[Formula: see text] space depends upon the production source. Either the exponential decay or the Poisson’s peaking curves are the usual characteristic shapes of the grey particle multiplicity distributions. The decay shape is suggested to be a characteristic feature of the source singularity while the peaking shape is a multisource super-position. The sensibility to the centrality varies from a source to other. The distribution shape is identified at each centrality region according to the associated source contribution. In general, the multiplicity characteristics seem to be limited w.r.t. the collision system centrality using light target nuclei. The selection of the black particle multiplicity as a centrality parameter is successful through the collision with the heavy target nuclei. In the collision with the light target nuclei it may be qualitatively better to vote another centrality parameter.

Forward–backward emission of target evaporated fragments in high energy nucleus–nucleus collisions**Supported by National Science Foundation of China (11075100), Natural Science Foundation of Shanxi Province (2011011001-2) and the Shanxi Provincial Foundation for Returned Overseas Chinese Scholars, (2011-058)

The multiplicity distribution, multiplicity moment, scaled variance, entropy and reduced entropy of target evaporated fragments emitted in forward and backward hemispheres in 12 A GeV 4He, 3.7 A GeV 16O, 60 A GeV 16O, 1.7 A GeV 84Kr and 10.7 A GeV 197Au -induced emulsion heavy target (AgBr) interactions are investigated. It is found that the multiplicity distribution of target evaporated fragments emitted in both forward and backward hemispheres can be fitted by a Gaussian distribution. The multiplicity moments of target evaporated particles emitted in the forward and backward hemispheres increase with the order of the moment q, and the second-order multiplicity moment is energy independent over the entire energy range for all the interactions in the forward and backward hemisphere. The scaled variance, a direct measure of multiplicity fluctuations, is close to one for all the interactions, which indicate a correlation among the produced particles. The entropy of target evaporated fragments emitted in both forward and backward hemispheres are the same within experimental errors.

Single source emission of proton projectile fragments in nucleus—emulsion interactions

The projected angular distribution and transverse momentum distribution of proton projectile fragments produced in 3.7A GeV 16O, 500A MeV 56Fe, and 1.7A GeV 84Kr induced by different kinds of emulsion target (H, CNO, and AgBr) interactions are investigated. It is found that the projected angular distribution and transverse momentum distribution can be well represented by a single Gaussian distribution. Comparison of transverse momentum distribution with the Maxwell—Boltzmann distribution reveals that proton projectile fragments are emitted from a single-temperature emission source. The temperature is different for different colliding systems, and linearly depends on the target size.

Interaction mean free paths of He fragments from 3.7A GeV 16O–emulsion collision

The interaction mean free paths of helium projectile fragments produced by the collisions of 16O at 3.7A GeV in nuclear emulsion have been investigated. In the present analysis, 1971 helium projectile fragments giving rise to 321 secondary interactions have been used. Within the present statistics, we do not observe any anomalous behavior in the mean free path of helium projectile fragments. The interaction mean free path is found to be independent of the impact parameter of collisions and the helium projectile fragments multiplicity.

Multifractal analysis of multiplicity fluctuations in 16O–emulsion interactions at 3.7 A GeV

The fractal or intermittent behavior has been investigated for the non-peripheral collisions of 3.7 A GeV 16O with nuclear emulsion using the multifractals in the pseudorapidity and azimuthal angle spaces. The multifractal moments G q as a function of the bin size in pseudorapidity and the azimuthal angle spaces have been calculated. A power-law behavior has been observed in the data. The mass exponents increase, and the generalized dimensions of the fractal and the multifractals decrease with the rank of the moment increase in all the investigated spaces. The anomalous fractal dimension increases linearly with the increase of rank of moments for both spaces, indicates the cascading process of hadronization.

Azimuthal asymmetry and dynamical fluctuation of compound multiplicity in nucleus–nucleus collisions at ultra-relativistic energy

The paper reports a study on azimuthal asymmetry fluctuations in compound (pion combined with proton) multiplicity spectra obtained from interactions of 60A GeV 16O–nucleus and 200A GeV 32S–nucleus with AgBr nuclei. The maximum azimuthal asymmetry is investigated, averaged over different compound multiplicity intervals. The data exhibit the existence of a dynamical component in the emission asymmetry fluctuations. The degree of the asymmetry is found to decrease as the multiplicity increases, and the decrease is found to be faster for a heavier projectile. The latter may provide important information on the production mechanism, when compared to the similar studies of pion fluctuations, where no such dependence has been observed. PACS Nos.: 25.75–q, 24.60 Ky

Intermittency in 3.7 A GeV 16 O-emulsion interactions

The intermittency effect has been studied for an interaction of 3.7 A GeV 16O with emulsion using the distributions of both the pseudorapidity intervals and the azimuthal angle intervals of the shower particles emitted in a central rapidity region. The scaled factorial moments, reduced scaled factorial moments and multifractal moments as functions of the bin size in pseudorapidity and in azimuthal angle have been calculated and have revealed the presence of an intermittent behaviour which may be due to the random cascading property of the reaction. The anomalous fractal dimension has been found to increase with the increase of rank of the moment.

Investigation of the mean free path of projectile fragments produced in 16 O–Em collision at 60 A GeV

Results are presented for an investigation of the mean free path of projectile fragments with charge 3≤Z≤8, produced by 60 A GeV 16O in nuclear emulsion. No dependence of mean free path on the distance from the point of the fragment emission is observed and our result is consistent with the nonexistence of anomalons.

Electromagnetic dissociation of 3.7 A GeV 16 O in nuclear emulsion

The electromagnetic dissociation (ED) of 3.7 A GeV 16O in nuclear emulsion is investigated with high statistics. It is found that the electromagnetically dissociated cross section increases with increasing beam energy, the charge distribution of projectile fragments is the same as the results at 60 and 200 A GeV and the production probability of projectile fragments with charge 3≤Z≤5 is less than that of the other projectile fragments. These results can be well explained by use of Weizsacker and Williams method for calculating the ED contributions. The percentile abundance of various decay modes for ED at 3.7 A GeV is close to the result at 60 and 200 A GeV, but it is different from the result at 14.6 A GeV. The ED of 3.7 A GeV is mainly caused by the giant dipole and quadrupole resonance of E1 and E2, which can be qualitatively explained by the multiplicity distribution of projectile proton in ED. The multiplicity distribution of the α fragments in ED and nuclear events have different functional forms. This difference may be a consequence of the different reaction mechanism involved.

Emission of relativistic heavy fragments at wide angles from the interaction of 58 GeV 16O ions with thick copper target

Relativistic projectile fragmentation has been studied with track detection methods. Heavy fragments produced in the interaction of 58 GeV 16O with thick copper target have been investigated using 10 cm thick stacks of PADC (sometimes called CR-39) nuclear track detectors placed at 25° with respect to the direction of the incoming beam. A computer-controlled automatic scanning system was employed to “trace” the etched damaged trails in respective detectors of the PADC stack. Heavy reaction products producing “through-tracks” in consecutive sheets of 0.82 mm of PADC detectors were observed. The spatial distribution of these tracks with end points at various depths have been recorded. After calibration it has been concluded that these “through-tracks” should be due to relativistic O, N and C. These fragments are emitted from the interaction of 58 GeV 16O ions with thick copper target, their actual number is very tiny. The differential angular cross-section for their formation was found to decrease with increasing angle with respect to the incident beam direction.

Observation of the reaction products formed in the interaction of 3.65 A GeV 16O ions with thick copper target at wide angles

Experiments have been carried out to study the ‘heavy fragments’ emitted at wide angles in the interaction of 3.65 A GeV 16O ions with a thick Cu target, using a stack of CR-39 track detectors. Diametric distribution in a stack registering 16O-beam halo are compared with diameters observed in a stack placed downstream at an angle of 25°. There is a strong indication that the heavy fragments are scattered at large angles.

Emission of light fragments in relativistic nucleus-nucleus collisions

Recoil properties of 24Na and 28Mg fragments emitted in the reactions of 2.35 A GeV and 3.65 A GeV 16O ions with Mn, Cu, Ag, Ta and Au target nuclei have been measured by the thick-target, thick-catcher technique and gamma-ray spectroscopy. The kinematic parameters were deduced from the data. The results are discussed in the framework of the two-step vector velocity model and compared to the systematics of the momentum distributions.

Bose-Einstein correlations in the target fragmentation region of 200 A GEV 16O + nucleus collisions

Correlations of positive pions are investigated in the target fragmentation region of 200 A GeV 16O + nucleus collisions. The pions are measured with the Plastic Ball detector in the WA80 experiment at the CERN SPS. The detailed behaviour of the fitted parameters on rapidity, centrality and the number of spectator nucleons is studied. The data indicate a large source in central O + Au collisions for ylab ⩽ 0. The observations are compatible with a substantial amount of rescattering in the target.