The hadron multiplicity distributions and factorial moments are studied in the framework of Landau theory of phase transitions. The factorial moments show a scaling law with a scaling exponent ν which characterizes the intermittency properties of the hadron phase for T<${\mathit{T}}_{\mathit{c}}$ (or ${\mathit{T}}_{\mathit{t}}$) where ${\mathit{T}}_{\mathit{c}}$ (or ${\mathit{T}}_{\mathit{t}}$) is the transition temperature for second (or first) order transition. The scaling exponent ν is weakly dependent on the free energy parameters as well as on temperature. It is shown that ν remains practically constant in the hadron phase for which T<${\mathit{T}}_{\mathit{c}}$ or T<${\mathit{T}}_{\mathit{t}}$ whether the transition is second order or first order of second kind where the free energy expansion includes cubic term. This universality in the scaling exponent is also maintained above ${\mathit{T}}_{\mathit{c}}$ over a wide range of temperature even if the transition is strongly first order of first kind where the free energy expansion has only even order coefficients, except around the critical temperature ${\mathit{T}}_{\mathit{t}}$ where ${\mathit{T}}_{\mathit{t}}$≳${\mathit{T}}_{\mathit{c}}$. Therefore, the scaling exponent ν is rather more universal and only indicates the presence of a possible phase transition. It is further shown that the hadron multiplicity distribution is quite sensitive to the free energy parameters. The study of hadron multiplicity distribution at various resolution or bin size reveals more information about the dynamics of the phase transition. The calculated hadron multiplicity distributions are also compared with the negative binomial distribution, often used to explain the experimental multiplicity distributions. © 1996 The American Physical Society.

The effects of anisotropic transverse collective flow on the Hanbury-Brown–Twiss (HBT) correlation function is studied. There exist three different physics contributions related to flow which affect the correlation function: anisotropic source shape, anisotropic space-momentum correlations in pion emission, and the effects related to the HBT measurement of the size of a moving source in different reference frames. Resolution of these contributions experimentally can lead to a detailed understanding of both collective flow in nucleus-nucleus collisions and the HBT technique itself. A method is presented which permits the derivation of model independent relations between the radius of a source measured in a frame in which it is moving and in its rest frame. © 1996 The American Physical Society.

In this paper a simple final-state rescattering model is used in an effort to describe the energy dependence of pion and kaon interferometry measurements obtained in two experiments, one at the CERN SPS (experiment NA44) with 200 GeV/n S+Pb and one at the BNL AGS (experiment E859/E866) with 14.6 GeV/n Si+Au. The method used for the Monte Carlo rescattering calculations is similar to a previous work in which starting from an initially cylindrical geometry pions, kaons, and nucleons are allowed to rescatter until freeze out occurs, particles are symmetrized in pairs from these freeze-out space-time positions, and then two-particle correlation functions are formed to extract boson source parameters. Predictions based on this model are also made for SPS Pb+Pb collisions, data for which have recently been taken and are in the process of being analyzed. It is found that the rescattering model qualitatively agrees with the results of both experiments and is consistent with the picture that freeze out occurs at a constant particle density resulting in a linear dependence of the freeze-out volume on the particle multiplicity. © 1996 The American Physical Society.

We examine the formalism of multiparticle correlations used in Bose-Einstein interferometry with pions produced in ultrarelativistic heavy ion collisions. We include incoherent and quantum optics coherent contributions as well as the effect of contamination from particles included in the correlation that are not pions. We give expressions for the correlation functions and normalized cumulants for orders 2–5 in the presence of these effects. We show that in the presence of coherence the normalized cumulants include an additional contribution besides that usually called the ‘‘true’’ multiparticle correlation. We also consider the Q=0 intercepts of the correlation functions and normalized cumulants in the presence of coherence and of contamination and show that values of the intercept of the normalized cumulant as a function of order can distinguish these two effects. © 1996 The American Physical Society.

The transverse momentum dependence of Hanbury-Brown–Twiss (HBT) interferometry radii for two-body correlation functions provides experimental access to the collective dynamics in heavy-ion collisions. We present an analytical approximation scheme for these HBT radii which combines the recently derived model-independent expressions with an approximate determination of the saddle point of the emission function. The method is illustrated for a longitudinally boost-invariant hydrodynamical model of a heavy-ion collision with freezeout on a sharp hypersurface. The analytical approximation converges rapidly to the width of the numerically computed correlation function and reproduces correctly its exact transverse momentum dependence. However, higher order corrections within our approximation scheme are essential, and the previously published leading order results with simple ${\mathit{m}}_{\mathrm{\perp }}$ scaling behavior are quantitatively and qualitatively unreliable. © 1996 The American Physical Society.

The transverse polarization in a plane perpendicular to the nuclear spin axis has been determined for electrons emitted in the β decay of polarized ${}_{}{}^8{}_{}{}^{}\mathrm{Li}$. Such a spin component signals a violation of time reversal symmetry. Using a sample of ${}_{}{}^8{}_{}{}^{}\mathrm{Li}$ nuclei with vector polarization of ∼0.11 and a polarimeter with average analyzing power S=-0.10, the asymmetry in the Mott scattering of decay electrons was measured with an accuracy of ±4×${10}^{\mathrm{-}5}$. From the asymmetry, the transverse spin polarization of the electrons has been determined with an accuracy of ±4×${10}^{\mathrm{-}4}$, and the amplitude R=(-0.2±4.0) ×${10}^{\mathrm{-}3}$ of the triple correlation between nuclear spin, momentum, and spin of the electron has been obtained. These results represent the most precise measurement of the transverse polarization of leptons emitted in weak decays. Time reversal violating part of the correlation amplitude, ${\mathit{R}}_{\mathrm{TRV}}$=(-0.9±4.0) ×${10}^{\mathrm{-}3}$, is deduced. It provides the first direct determination of the imaginary, charged weak tensor interaction -0.022${\mathit{C}}_{\mathit{T}}$+${\mathit{C}}_{\mathit{T}}^{\prime }$)/${\mathit{C}}_{\mathit{A}}$<0.017 or alternatively -0.004${\mathit{a}}_{\mathit{RL}}^{\mathit{T}}$)<0.005 (90% C.L.). These are the tightest limits for exotic (nonvector or axial vector) time reversal violating couplings in semileptonic weak decays. A report is presented with emphasis on experimental details and data analysis. Relations of this study to other tests of time reversal violation are discussed.

We have calculated exchange corrections for nuclear muon capture by ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ leading to the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ final state using the hard-pion model and realistic nuclear wave functions. These currents modify the vector and axial part of the weak nuclear current. In their absence the rate is 12% smaller than found by experiment. Our final result for the rate is 1502±32 per second. For the analyzing powers we find ${\mathit{A}}_{\mathit{v}}$=0.515±0.005, ${\mathit{A}}_{\mathit{t}}$=-0.375±0.004, and ${\mathit{A}}_{\mathrm{\Delta }}$=-0.110±0.006. These predictions use the PCAC value of ${\mathit{g}}_{\mathit{P}}$. The variation of the observables with ${\mathit{g}}_{\mathit{P}}$ is also reported. © 1996 The American Physical Society.

The neutron capture rate on ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ may be of considerable importance for s-process nucleosynthesis in red giants as well as for the nucleosynthesis in inhomogeneous big bang scenarios. We measured the reaction cross section of ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$(n,γ${)}^{16}$N at the Forschungszentrum Karlsruhe with a fast cyclic neutron activation technique at laboratory neutron energies of 25, 152, and 370 keV. Direct capture and shell model calculations were performed to interpret the results. The presented reaction rate is 30–50 % smaller than the previously used theoretical rates. © 1996 The American Physical Society.

The level scheme of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ is investigated via the ${}_{}{}^1{}_{}{}^{}\mathrm{H}$${(}^{58}$Ni${,}^{57}$Cu-γ)2n reaction by using the recoil mass spectrometer MARS at the Texas A&M Cyclotron Institute. Three low-lying excited states are observed in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ at 1028 ± 4, 1106 ± 4, and 2398 ± 10 keV. The results are compared with well known excited states of the mirror nucleus ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$. The measured excited states of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ allow recalculation of the astrophysical reaction rate for the stellar radiative proton capture reaction ${}_{}{}^{56}{}_{}{}^{}\mathrm{Ni}$(p,γ${)}^{57}$Cu. © 1996 The American Physical Society.

High-spin states in ${}_{}{}^{155}{}_{}{}^{}\mathrm{Tb}$ have been identified via the weak p4n exit channel of the ${}_{}{}^{36}{}_{}{}^{}\mathrm{S}$ + ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$ reaction using the Gammasphere array. The π${\mathit{h}}_{11/2}$ yrast band has been established up to ${\mathit{I}}^{\mathrm{\pi }}$ = 67/$2^{\mathrm{-}}$ filling an important gap in the N = 90 high-spin systematics. The variation of the first ${\mathit{i}}_{13/2}$ neutron backbend as a function of proton number for N = 90 isotones and trends regarding the phenomenon of signature splitting and signature inversion in the odd-Z nuclei are discussed. © 1996 The American Physical Society.

Cross sections for the charge pickup of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ projectiles were measured at E/A=600 and 1000 MeV for seven different targets (Be, C, Al, Cu, In, Au, and U). Events with two fission fragments with a sum charge of 93 in the exit channel were selected. Due to the significant excitation energy, the majority of the produced Np nuclei fission instead of decaying by evaporation to residues. The observed cross sections can be well reproduced by intranuclear-cascade-plus-evaporation calculations and, therefore, confirm recent results that no exotic processes are needed to explain charge-pickup processes. © 1996 The American Physical Society.

The binary decay fragment cross sections and prescission charge multiplicity were measured in the reaction of ${}_{}{}^{84}{}_{}{}^{}\mathrm{Kr}$${+}^{27}$Al (${\mathit{E}}_{\mathrm{lab}}$=10.6 MeV/nucleon) and compared with a statistical model calculation performed with the code GEMINI as a function of fission delay time. The comparison has suggested that a composite system may be formed at the point between the saddle and scission points and make a binary decay. © 1996 The American Physical Society.

The $\gamma$ decay of the giant dipole resonance has been studied with mass-symmetric and mass-asymmetric fusion-evaporation reactions similar to those for which entrance-channel effects were previously reported in the population of superdeformed bands. No entrance-channel effects have been observed in the high-energy $\gamma$-ray spectra associated with the decay of the ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ compound nucleus populated at an excitation energy of 82 MeV via the reactions ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$+${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$+${}_{}{}^{70}{}_{}{}^{}\mathrm{Ge}$. The absence of entrance-channel effects in the present data set is well explained by dissipative collision calculations.

An experimental study of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$+$p$ collisions at $75A$ MeV was performed. The excited state of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ at $E^{*}=1.25\mathrm{}\pm 0.15$ MeV was observed, which is a candidate for a neutron halo excitation. Four other ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ states were manifested (at ∼ 3.0, 4.9, 6.4, and 11.3 MeV). Angular distributions were measured for elastic scattering ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$+$p$ and 8He+$p$. Structure of the ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ halo was investigated using the eikonal approach.

The ${}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}({}_{}{}^{29}{}_{}{}^{}\mathrm{Si}, 5n)$ reaction at 148 MeV with thin targets was used to populate high-angular momentum states in ${}_{}{}^{198}{}_{}{}^{}\mathrm{Po}$. Resulting $\gamma$ rays were observed with Gammasphere. A weakly populated superdeformed band of 10 $\gamma$-ray transitions was found and has been assigned to ${}_{}{}^{198}{}_{}{}^{}\mathrm{Po}$. This is the first observation of an SD band in the $A\approx 190$ region in a nucleus with $Z>\mathrm{}83\mathrm{}$. The ${\mathcal{J}}^{\mathrm{}\left(2\right)\mathrm{}}$ of the new band is very similar to those of the yrast SD bands in ${}_{}{}^{194}{}_{}{}^{}\mathrm{Hg}$ and ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pb}$. The intensity profile suggests that this band is populated through states close to where the SD band crosses the yrast line and the angular momentum at which the fission process dominates.

In the present work we have measured fission fragment angular distributions and fusion excitation functions for the systems ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ at energies around the Coulomb barrier. These results along with the results of our earlier measurements on ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ + ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ system were analyzed following Hinde et al. [Phys. Rev. Lett. 74, 1295 (1995)] where it was pointed out that the anomalous fission fragment angular distributions seen in heavy ion reactions below the Coulomb barrier can be due to possible occurrence of quasifission events caused by the interaction of the projectile with the tip of the deformed target nucleus. The present data do not show the expected saturation behavior of the fission fragment anisotropy at sub-barrier energies for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+ ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ system which exhibits different behavior of the fission fragment anisotropy in the sub-barrier region as compared to the other two systems. The present measurements using different projectiles on the same target nucleus do not seem to conform to the expected behavior of the quasifission mechanism to be caused by the interaction of the projectile with the tip of the deformed target nucleus.

We review the status of the $S_{11}$ N* resonances in light of some recent theoretical and phenomenological results. Whereas the quark model predicts two such resonances around 1.6 GeV, there is considerable evidence for a third $S_{11}$ resonance in this energy range. This suggests that a $K\Sigma$ or $K\Lambda$ quasibound state may indeed exist below the kaon production threshold. We show that kaon production experiments, in particular $K^0$ photoproduction off nucleons, would be very sensitive to the existence of the third $S_{11}$ resonance.

Recently reported measurements of hard photon correlations in the reactions ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ at $95A$ MeV, ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$ on ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ni}$ at $60A$ MeV, and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ on ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ at $39.5A$ MeV are analyzed. A Boltzmann-Ühling-Uhlenbeck transport model is used to describe the photon production by individual nucleon-nucleon collisions. In the lighter systems we find the best agreement with data when taking into account only photons from first-chance collisions of nucleons or photons produced during the passage of the nuclei, while the model predicts also a considerable late-time emission of photons, which leads to a depletion of the calculated correlation function. The accuracy of the present data does not allow firm conclusions on the reliability of this late-time evolution. Our investigations do not support a recently reported interference pattern in the heavy Ta + Au system.

We have measured the spins of $p$-wave resonances in the reaction of low energy neutrons with ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ nuclei and used them to reanalyze the parity violation experiment of the TRIPLE Collaboration carried out with this nucleus. The estimate of the root-mean-square matrix element of the parity violation interaction, $M$, including a bias correction, is found to be $\hat{M}={0.62}_{-0.20\mathrm{}}^{+0.33\mathrm{}}{(68\% \mathrm{C}.\mathrm{L}.\mathrm{})}_{-0.33\mathrm{}}^{+0.88\mathrm{}}(95\% \mathrm{C}.\mathrm{L}.\mathrm{})$ meV. The spin assignments of the resonances improved the analysis.

The reliability of the models describing the final-state interactions in ($e, e^{\prime }p$) scattering at high proton energies is an important issue in view of the experiments planned at CEBAF. One of the most popular approaches adopted, the Glauber method, involves the linearization of the wave equation for the ejected proton traveling through the residual nucleus. We have studied the consequences of such an assumption for the case of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(e, e^{\prime }p){}_{}{}^{11}{}_{}{}^{}\mathrm{B}_{}^{*}{}_{}{}^{}$ reaction at high proton momenta by comparing the results with the predictions obtained when the second-order differential equation for the proton wave is solved exactly for each partial wave. We find that the two methods give well-correlated angular distributions for momenta in the range 1-4 GeV/c, i.e., for kinematics relevant to the transition to the eikonal regime.