High-harmonic generation using ultrashort laser pulses with pulse durations 25 to 200 fs is studied theoretically and experimentally. We observe that the harmonic spectrum of argon taken with 25 fs laser pulses contains harmonics up to 20 orders higher than for 100 fs laser pulses with the same intensity. We show that this increase in harmonics is because the atom survives to higher laser intensities, due in part to the nonadiabatic response of the atomic dipole to the fast rise time of our pulse.

We present shell model Monte Carlo calculations for nuclei in the full major shell 50–82 for both protons and neutrons. For the interaction we use a pairing plus quadrupole derived from a surface-peaked separable force. The methods are illustrated for ${}^{124}$Sn, ${}^{128}$Te, and ${}^{124}$Xe. We calculate shape distributions, moments of inertia, and pairing correlations as functions of temperature and angular velocity. Our calculations are the first microscopic evidence of γ-softness of nuclei in this region.

High-energy $\gamma$ rays associated with the decay of the giant dipole resonance have been measured for two fusion reactions leading to the ${}^{140}\mathrm{Sm}$ compound nucleus at an excitation energy of 71 MeV. The observed yield increases with the asymmetry in the ratios of the number of neutrons to protons in the entrance channel. This is interpreted as resulting from giant dipole phonons excited at the moment of collision in an $N/Z$ asymmetric reaction.

The dilepton spectra from open charm decay in $p+A$ reactions at $\sqrt{s}=200A\mathrm{GeV}$ are proposed to constrain gluon shadowing in nuclei. We show that the required measurements are feasible at the Brookhaven Relativistic Heavy Ion Collider.

Considering a variety of dynamical scenarios within the linear $\sigma$ model, we examine the conditions for pionic modes to be amplified as the chiral field relaxes towards the normal vacuum following the transient restoration of approximate chiral symmetry in a high-energy collision. While Bjorken-type longitudinal expansions appear to be insufficient for amplification for occur, analogous expansions in two or three dimensions may enhance the low-energy power spectrum by up to an order of magnitude.

The annihilation of energetic (1.2 GeV) antiprotons is exploited to deposit maximum thermal excitation (up to 1000 MeV) in massive nuclei (Cu, Ho, Au, and U) while minimizing the contribution from collective excitation such as rotation, shape distortion, and compression. Excitation energy distributions $d\sigma /{\mathrm{dE}}^{*}$ are deduced from eventwise observation of the whole nuclear evaporation chain with two $4\pi$ detectors for neutrons and charged particles. The nuclei produced in this way are found to decay predominantly statistically, i.e., by evaporation.

It is demonstrated that $N\left(\pi {,e}^{+}{e}^{-}\right)N$ measurements will provide new information about the nucleon timelike form factor in the $\phi$ meson region including the value of the $\phi N$ coupling $g_{\phi \mathrm{NN}}$. Using vector meson dominance, $N\left(\pi {,e}^{+}{e}^{-}\right)N$ calculations reveal a 3 order of magnitude enhancement from the $\phi$ resonance coupled to the nucleon compared to the expected background $\phi$ production from the $\rho \pi \phi$ contribution through $\rho$ exchange. The effect from $\phi N$ coupling in the nucleon form factors yields a novel experimental signature for OZI (Okubo-Zweig-Iizuka) violation and the related strangeness content of the nucleon.

Differential cross sections and analyzing powers for the $\overrightarrow{p}p\to d{\pi }^{+}$ reaction have been measured to within $T_{\pi }^{\mathrm{cm}}=85\mathrm{}\mathrm{keV}$ of threshold. The $S$-wave strength is extracted and found to be $\sim 13\%$ larger than that determined from recent measurements of $\mathrm{np}\to d{\pi }^0$. Both the analyzing power and the anisotropy in the angular distribution show the expected energy dependence and these data are used to obtain values for the two contributing $P$-wave amplitudes.

The longitudinal momentum distributions of the core fragment in the dissociation of halo states on light targets provide information pertaining to the external part of the halo. The calculations agree well with the measured momentum widths and cross sections for the reactions ${(}^{11}$Be${,}^{10}$Be) and ${(}^8$B, ${}^7$Be). The measured widths are not expected to be sensitive to the instrumental transverse-momentum acceptance.

The location of several single-neutron states in ${}^{133}\mathrm{Sn}$ has been identified. The $p_{3/2}$, $h_{9/2}$, and $f_{5/2}$ states were found at 853.7, 1560.9, and 2004.6 keV, respectively, by measuring $\gamma$ rays in coincidence with delayed neutrons following the decay of ${}^{134}\mathrm{In}$. Crucial for obtaining the new data were the improved yields at the mass-separator facility ISOLDE-PSB at CERN. A semiempirically adjusted Woods-Saxon calculation, based on parameters from the Pb region and normalized on the mass data at ${}^{132}\mathrm{Sn}$, reproduces the new single particle energies with good precision.

We discuss the notion of partial dynamical symmetry in relation to nuclear spectroscopy. Explicit forms of Hamiltonians with partial $\mathrm{SU}\left(3\right)$ symmetry are presented in the framework of the interacting boson model of nuclei. An analysis of the resulting spectrum and electromagnetic transitions demonstrates the relevance of such partial symmetry to the spectroscopy of axially deformed nuclei.

The azimuthal angular correlations of light charged particles and light intermediate mass fragments emitted from the reaction ${}^{36}\mathrm{Ar}{+}^{197}\mathrm{Au}$ at $E/A=50\mathrm{MeV}$ are found to be reducible to the angular distributions of individual fragments. Thermal scaling is also observed in the coefficients of the angular correlations. Furthermore, the observed scaling with fragment mass seems to imply secondary emission from relatively small ( $A\approx 15–30$) primary fragments.

The ${}^2\mathrm{H}{,}^{12}\mathrm{C}{,}^{40}\mathrm{Ca}{,}^{208}\mathrm{Pb}({\pi }^{+},{\pi }^{+}{\pi }^{\pm })$ reactions have been studied at $T_{{\pi }^{+}}=282.7\mathrm{MeV}$, and the ${\pi }^{+}{\pi }^{\pm }$ invariant mass distributions $M_{{\pi }^{+}{\pi }^{\pm }}^A$ measured down to the ${2m}_{\pi }$ threshold. The $M_{{\pi }^{+}{\pi }^{-}}^A$ yield near threshold is close to zero for $A=2,$ and increases dramatically with increasing A (from 12 to 40 to 208). A phase analysis indicates that the ${\pi }^{+}{\pi }^{-}$ pairs in this range of $M_{{\pi }^{+}{\pi }^{-}}^A$ have $J=I=0\mathrm{}$. In the case of $M_{{\pi }^{+}{\pi }^{+}}^A,$ there is some strength near threshold regardless of A, and the ${\pi }^{+}{\pi }^{+}$ pairs have $J=0,I=2\mathrm{}$. The experimental results indicate that nuclear matter strongly modifies the ππ interaction in the $J=I=0\mathrm{}$ channel.

The giant-dipole resonance (GDR) in ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ is studied as a function of excitation energy, angular momentum, and intrinsic width. Theoretical evaluations of the full width at half maximum (FWHM) for the GDR strength function are compared with recent experimental data and are found to be in overall agreement. Differences observed between ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ are attributed to strong shell corrections in ${}^{208}\mathrm{Pb}$ favoring spherical shapes at low temperatures. At high temperature, the FWHM in ${}^{120}\mathrm{Sn}$ exhibits effects due to the evaporation width of the compound nucleus.

The differential cross section for the ${}^7\mathrm{Be}(d,n{)}^8\mathrm{B}$ reaction at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=5.8\mathrm{}$ MeV has been measured using the ${}^7$Be beam generated by the radioactive nuclear beam facility at China Institute of Atomic Energy. The ${}^8$B ions were detected in full geometry with a two-dimensional position sensitive $\Delta E$- $E$ counter telescope. The reaction cross section was determined to be $58\pm 8$ mb. The angular distribution data were analyzed with the distorted-wave Born approximation calculation. The astrophysical $S_{17}\left(0\right)$ factor for the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction was derived to be $27.4\pm 4.4$ eV b through the asymptotic normalization constant extracted from the experimental data.

The $p+p\to {\pi }^{+}+d$ reaction is studied at excess energies between 0.275 and 3.86 MeV. Differential and total cross section were measured employing a magnetic spectrometer with nearly $4\pi$ acceptance in the center of mass system. The measured anisotropies between 0.008 and 0.29 indicate that the p wave is not negligible even so close to threshold. The data are compared to other data offering no evidence for charge symmetry breaking or time reversal violation. The s-wave and p-wave contributions at threshold are deduced.

Neutron-rich ${}_{39}$Y to ${}_{43}$Tc isotopes have been produced by fission of uranium with a 50 MeV ${\mathrm{H}}_2^{+}$ beam. Beta-decay half-lives, delayed neutron-emission probabilities, and production yields have been measured and compared with theory. Beta decay of 4 new isotopes is reported, and the $\beta$-delayed neutron-emission mode has been discovered for 12 isotopes of the elements niobium and technetium. The results compared to quasiparticle random phase approximation predictions indicate the increasing importance of fast $\beta$ transitions to high-lying states of nuclei with large neutron excess.

Characteristics of ${}^{35}\mathrm{Cl}{+}^{12}\mathrm{C}$ collisions at 43 MeV/nucleon have been studied for events with total charge detected ( $\Sigma Z=23\mathrm{}$). It is shown that, while single-source events are present in the data, the binary nature of the collision is dominant. For binary events, the emitting sources (projectilelike and targetlike) were reconstructed independently allowing a direct measurement of the total dissipated energy. It is found that up to 75% of the available energy is dissipated and the significant momentum transfer of the selected events leads to the “equal temperature limit.”

The use of correlation between two open-charm mesons is suggested to give information about the nature of the medium created in heavy-ion collisions. Insensitivity to the charm production rate is achieved by measuring normalized cumulant. The acollinearity of the $D$ momenta in the transverse plane is a measure of the medium effect. Its dependence on nuclear size or $E_T$ provides a signature for the formation of quark matter.

We point out that events associated with large $E_T$ direct photons in high-energy heavy-ion collisions can be used to study jet energy loss in dense matter. In such events, the $p_T$ spectrum of charged hadrons from jet fragmentation in the direction opposite to the tagged photon is estimated to be well above the background which can be reliably subtracted at moderately large $p_T$. We demonstrate that comparison between the extracted fragmentation function in $\mathrm{AA}$ and $\mathrm{pp}$ collisions can be used to determine the jet energy loss and the interaction mean free path in the dense matter produced in high-energy heavy-ion collisions.