High-spin states in ${}^{72}\mathrm{Br}$ were studied with the EUROBALL III spectrometer using the ${}^{40}\mathrm{Ca}{(}^{40}\mathrm{Ca},\alpha 3p1n)$ reaction. The negative-parity band observed in this experiment displays a signature inversion around spin $I=16\mathrm{}$. The interpretation within the cranked Nilsson-Strutinsky approach shows that this signature pattern is a signal of a substantial triaxial shape change with increasing spin where the nucleus evolves from a triaxial shape with rotation about the intermediate axis at low spin through a collective prolate shape to a triaxial shape but with rotation about the shortest principal axis at high spin.

A Comment on the Letter by Yanez, et al., Phys. Rev. Lett. 82, 3585 (1999). The authors of the Letter offer a Reply.

A Reply to the Comment by Moretto, et al.

We develop a scheme to exactly evaluate the correlation energy in the random-phase approximation, based on linear response theory [Y. R. Shimizu, J. D. Garrett, R. A. Broglia, M. Gallardo, and E. Vigezzi, Rev. Mod. Phys. 61, 131 (1989)]. It is demonstrated that our formula is equivalent to a contour integral representation recently proposed [F. Dönau, D. Almehed, and R. G. Nazmitdinov, Phys. Rev. Lett. 83, 280 (1999)] being numerically more efficient for realistic calculations. Examples are presented for pairing correlations in rapidly rotating nuclei.

The size of the average fluctuations of net baryon number and electric charge in a finite volume of hadronic matter differs widely between the confined and deconfined phases. These differences may be exploited as indicators of the formation of a quark-gluon plasma in relativistic heavy-ion collisions, because fluctuations created in the initial state survive until freeze-out due to the rapid expansion of the hot fireball.

In this Letter we argue that the event-by-event fluctuations of the ratio of the positively charged and the negatively charged pions provide a signal for a quark-gluon plasma. The fact that quarks carry fractional charges is ultimately responsible for this distinct signal.

We show that, contrary to recent claims, the $J/\psi$ suppression resulting from its interaction with comovers does not saturate at large transverse energy $E_T$. On the contrary, it shows a characteristic structure—a change of curvature near the knee of the $E_T$ distribution—which is due to the $E_T$ (or multiplicity) fluctuation. This change of curvature is also present in recent experimental results, although the experimetal effect is larger than in our calculation.

Excitation functions $A_N(p_p,{\Theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}})$ of the analyzing power in $p\overrightarrow{p}$ elastic scattering have been measured with a polarized atomic hydrogen target for projectile momenta $p_p$ between 1000 and 3300 MeV/ $c$. The experiment was performed for scattering angles $30°\le {\Theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}\le 90°$ using the recirculating beam of the proton storage ring COSY during acceleration. The resulting excitation functions and angular distributions of high internal consistency have significant impact on the recent phase shift solution SAID SP99, in particular, on the spin triplet phase shifts between 1000 and 1800 MeV, and demonstrate the limited predictive power of single-energy phase shift solutions at these energies.

Taking ${}^{16}\mathrm{O}{+}^{16}\mathrm{O}$ elastic scattering at 124 MeV as an example, we show that a barrier-wave–internal-wave decomposition of the elastic scattering amplitude provides valuable information on the light heavy-ion interaction and complements the more conventional nearside-farside decomposition. In particular, we show that the Airy minima present in the angular distributions are due to a barrier-wave–internal-wave interference mechanism, which sheds additional light on the exceptional transparency displayed by some light heavy-ion scattering systems. Extension of these ideas to other fields, like atomic and molecular collision physics, could prove rewarding.

The electromagnetic cross sections of the double giant dipole resonances (DGDR) in ${}^{136}\mathrm{Xe}$ and ${}^{208}\mathrm{Pb}$ are calculated using the strength functions obtained within the phonon damping model. The parameters of the model have been selected to describe reasonably well the single giant dipole resonance in these nuclei. The results are found in an overall agreement with the recent experimental data for the DGDR cross sections in exclusive measurements at near-relativistic energies.

We have succeeded in observing nuclear excitation by electron transition (NEET) in ${}^{197}\mathrm{Au}$ by a new method. Monochromatic x-rays of synchrotron radiation were used to ionize the $K$ shell of gold atoms in a target foil. The internal-conversion electrons emitted from excited nuclei were detected with a silicon avalanche photodiode. At a photon energy of 80.989 keV, the NEET probability in ${}^{197}\mathrm{Au}$ was determined to be $(5.0\pm 0.6)\times {10}^{-8\mathrm{}}$ from a comparison of the event number per photon between NEET and the nuclear resonance at 77.351 keV.

Cross sections for quasifree Compton scattering from the deuteron were measured for incident energies of $E_{\gamma }=236\mathrm{}–260\mathrm{MeV}$ at the laboratory angle ${\theta }_{{\gamma }^{\prime }}=-135\mathrm{}°$. The recoil nucleons were detected in a liquid-scintillator array situated at ${\theta }_N=20\mathrm{}°$. The measured differential cross sections were used, with the calculations of Levchuk et al., to determine the polarizabilities of the bound nucleons. For the bound proton, the extracted values were consistent with the accepted value for the free proton. Combining our results for the bound neutron with those from Rose et al., we obtain 1-sigma constraints of ${\overline{\alpha }}_n=7.6\mathrm{}–14.0$ and ${\overline{\beta }}_n=1.2\mathrm{}–7.6$.

The first fully on-line use of the angular distribution of beta emission in detection of NMR of nuclei oriented at low temperatures is reported. The magnetic moments of the single valence particle, intermediate mass, isotopes ${}^{67}\mathrm{Ni}\left(\nu p_{1/2}^{-1\mathrm{}}{;1/2\mathrm{}}^{-}\right)$ and ${}^{69}\mathrm{Cu}\left(\pi p_{3/2}^1{;3/2\mathrm{}}^{-}\right)$ are measured to be $+0.601\mathrm{}\left(5\right){\mu }_N$ and $+2.84\mathrm{}\left(1\right){\mu }_N$, respectively, revealing only a small deviation from the neutron $p_{1/2}$ single-particle value in the former and a large deviation from the proton $p_{3/2}$ single-particle value in the latter. Quantitative interpretation is given in terms of core polarization and meson-exchange currents.

The predictions of the interacting boson model two-body random ensemble are compared to empirical results on nuclei from $Z=8\mathrm{}–100$. Heretofore unrecognized but robust empirical trends are identified and related both to the distribution of valence nucleon numbers and to the need for and applicability of specific, nonrandom interactions. Applications to expected trends in exotic nuclei are discussed.

A systematic microscopic study of the anharmonic properties of the double giant dipole resonance (DGDR) has been carried out, for the first time, for nuclei with mass number $A$ spanning the whole mass table. It is concluded that the corrections of the energy centroid of the $J^{\pi }{=0\mathrm{}}^{+}$ and $2^{+}$ components of the DGDR from its harmonic limit are negative, have a value of the order of a few hundred keV, and follow an $A^{-1\mathrm{}}$ dependence.

Photons originating from coherent bremsstrahlung have been measured over a large dynamic range for the reaction of 200 MeV $\alpha$ particles with protons. At low photon energies the bremsstrahlung spectrum exhibits the classical behavior with an approximate $1/E_{\gamma }$ shape. At higher photon energies there is a pronounced contribution from capture into the unbound ground state and first excited state of ${}^5\mathrm{Li}$. These results allow one, for the first time, to test theoretical models for a consistent description of bremsstrahlung and radiative capture in a complex system. Calculations predict both features qualitatively but fail to account for their relative importance.

The $n-n$ final-state interaction (FSI) was investigated via the ${}^2\mathrm{H}(n,np)n$ reaction at 25 MeV, using a geometry which enables the simultaneous observation of $n-p$ quasifree (QFS) scattering. The data were analyzed with Monte Carlo simulations based on rigorous Faddeev calculations with realistic nucleon-nucleon potentials. The value of $a_{\mathrm{nn}}$ deduced from the absolute yield in the FSI peak is $-16.27\mathrm{}\pm 0.40\mathrm{fm}$ while the relative data, normalized in the QFS region, give $-16.06\mathrm{}\pm 0.35\mathrm{fm}$. Thus our results differ from the “recommended” value of $a_{\mathrm{nn}}=-18.5\mathrm{}\pm 0.3\mathrm{fm}$ by more than 5 standard deviations.

It is shown that the Fisher droplet model, percolation, and nuclear multifragmentation share the common features of reducibility (stochasticity in multiplicity distributions) and thermal scaling (one-fragment production probabilities are Boltzmann factors). Barriers obtained, for cluster production on percolation lattices, from the Boltzmann factors show a power-law dependence on cluster size with an exponent of $0.42\pm 0.02$. The EOS Collaboration Au multifragmentation data yield barriers with a power-law exponent of $0.68\pm 0.03$. Values of the surface energy coefficient of a low density nuclear system are also extracted.

We study the superheavy nucleus ${}^{254}\mathrm{No}$ in the framework of the Hartree-Fock-Bogoliubov approximation with the finite-range density-dependent Gogny force, at zero and high angular momentum. The properties of the ground state rotational band and the fission barriers are discussed as a function of angular momentum. We found a two-humped barrier up to spin values of $(30–40)ħ$ and a one-humped barrier for higher spins. We reproduce fairly well with the binding energy, the ground state deformation, the $\gamma -\mathrm{ray}$ energies, and the bound on the fission barrier height measured at high spin.

We have measured the sideward flow of neutral strange ( $K_s^0$) mesons in $6A\mathrm{GeV}\mathrm{Au}+\mathrm{Au}$ collisions. A prominent antiflow signal is observed for an impact parameter range ( $b\lesssim 7\mathrm{fm}$) which spans central and midcentral events. Since the $K_s^0$ scattering cross section is relatively small in nuclear matter, this observation suggests that the in-medium kaon vector potential plays an important role in high density nuclear matter.