Analysis of charged particle emission sources and coalescence in E/A = 61 MeV 36^{36}Ar + 27^{27}Al, 112^{112}Sn and 124^{124}Sn collisions

Single-particle kinetic energy spectra and two-particle small angle correlations of protons ($p$), deuterons ($d$) and tritons ($t$) have been measured simultaneously in 61A MeV $^{36}$Ar + $^{27}$Al, $^{112}$Sn and $^{124}$Sn collisions. Characteristics of the emission sources have been derived from a ``source identification plot'' ($\beta_{source}$--$E_{CM}$ plot), constructed from the single-particle invariant spectra, and compared to the complementary results from two-particle correlation functions. Furthermore, the source identification plot has been used to determine the conditions when the coalescence mechanism can be applied for composite particles. In our data, this is the case only for the Ar + Al reaction, where $p$, $d$ and $t$ are found to originate from a common source of emission (from the overlap region between target and projectile). In this case, the coalescence model parameter, $\tilde{p}_0$ -- the radius of the complex particle emission source in momentum space, has been analyzed.Comment: 20 pages, 5 figures, submitted to Nuclear Physics

Search for Collective Phenomena in High Multiplicity Events at Nuclotron and U-70

More than ten-year experimental search for collective phenomena in high multiplicity events has been carried out at the Laboratory of high energy physics at JINR. We present main results, which have been received at the U-70 accelerator (IHEP, Protvino) in the proton collisions and at Nuclotron ( JINR, Dubna) in the nuclear interactions. Fo

A measurement of the differential cross section for the two-body photodisintegration of 3He at theta_LAB = 90deg using tagged photons in the energy range 14 -- 31 MeV

The two-body photodisintegration of 3He has been investigated using tagged photons with energies from 14 -- 31 MeV at MAX-lab in Lund, Sweden. The two-body breakup channel was unambiguously identified by the (nonsimultaneous) detection of both protons and deuterons. This approach was made feasible by the over-determined kinematic situation afforded by the tagged-photon technique. Proton- and deuteron-energy spectra were measured using four silicon surface-barrier detector telescopes located at a laboratory angle of 90deg with respect to the incident photon-beam direction. Average statistical and systematic uncertainties of 5.7% and 6.6% in the differential cross section were obtained for 11 photon-energy bins with an average width of 1.2 MeV. The results are compared to previous experimental data measured at comparable photon energies as well as to the results of two recent Faddeev calculations which employ realistic potential models and take into account three-nucleon forces and final-state interactions. Both the accuracy and precision of the present data are improved over the previous measurements. The data are in good agreement with most of the previous results, and favor the inclusion of three-nucleon forces in the calculations.Comment: 12 pages, 13 figures; further Referee comments addresse

Pion emission in 2H, 12C, 27Al, gamma pi+ reactions at threshold

The first data from MAX-lab in Lund, Sweden on pion production in photonuclear reactions at threshold energies, is presented. The decrease of the total yield of pi+ in gamma + 12C, 27Al reactions below 200 MeV as well as differential, dsigma/dOmega, cross sections follow essentially predictions from an intranuclear cascade model with an attractive potential for pion-nucleus interaction in its simplest form. Double differential, d2sigma/dOmegadT, cross sections at 176 MeV show, however, deviations from the model, which call for refinements of nuclear and Coulomb potentials and possibly also for coherent pion production mechanisms.Comment: 19 pages, 7 figure

Beyond the neutron drip line: The unbound oxygen isotopes (25)O and (26)O

This is the publisher's version, and is also available electronically from http://journals.aps.org/prc/abstract/10.1103/PhysRevC.88.034313.The very neutron-rich oxygen isotopes 25O and 26O are investigated experimentally and theoretically. The unbound states are populated in an experiment performed at the R3B-LAND setup at GSI via proton-knockout reactions from 26F and 27F at relativistic energies around 442 and 414 MeV/nucleon, respectively. From the kinematically complete measurement of the decay into 24O plus one or two neutrons, the 25O ground-state energy and width are determined, and upper limits for the 26O ground-state energy and lifetime are extracted. In addition, the results provide indications for an excited state in 26O at around 4 MeV. The experimental findings are compared to theoretical shell-model calculations based on chiral two- and three-nucleon (3N) forces, including for the first time residual 3N forces, which are shown to be amplified as valence neutrons are added

Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets

The multiplicity of inclusive photons has been measured on an event-by-event basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The systematics of the pseudorapidity densities at midrapidity (rho_max) and the width of the pseudorapidity distributions have been studied for varying centralities for these collisions. A power law fit to the photon yield as a function of the number of participating nucleons gives a value of 1.13+-0.03 for the exponent. The mean transverse momentum, , of photons determined from the ratio of the measured electromagnetic transverse energy and photon multiplicity, remains almost constant with increasing rho_max. Results are compared with model predictions.Comment: 16 pages including 4 figure

Pion Freeze-Out Time in Pb+Pb Collisions at 158 A GeV/c Studied via pi-/pi+ and K-/K+ Ratios

The effect of the final state Coulomb interaction on particles produced in Pb+Pb collisions at 158 A GeV/c has been investigated in the WA98 experiment through the study of the pi-/pi+ and K-/K+ ratios measured as a function of transverse mass. While the ratio for kaons shows no significant transverse mass dependence, the pi-/pi+ ratio is enhanced at small transverse mass values with an enhancement that increases with centrality. A silicon pad detector located near the target is used to estimate the contribution of hyperon decays to the pi-/pi+ ratio. The comparison of results with predictions of the RQMD model in which the Coulomb interaction has been incorporated allows to place constraints on the time of the pion freeze-out.Comment: 9 pages, 12 figure

Scaling of Particle and Transverse Energy Production in 208Pb+208Pb collisions at 158 A GeV

Transverse energy, charged particle pseudorapidity distributions and photon transverse momentum spectra have been studied as a function of the number of participants (N_{part}) and the number of binary nucleon-nucleon collisions (N_{coll}) in 158 A GeV Pb+Pb collisions over a wide impact parameter range. A scaling of the transverse energy pseudorapidity density at midrapidity as N_{part}^{1.08 \pm 0.06} and N_{coll}^{0.83 \pm 0.05} is observed. For the charged particle pseudorapidity density at midrapidity we find a scaling as N_{part}^{1.07 \pm 0.04} and N_{coll}^{0.82 \pm 0.03}. This faster than linear scaling with N_{part} indicates a violation of the naive Wounded Nucleon Model.Comment: 13 pages, 16 figures, submitted to European Physical Journal C (revised results for scaling exponents