Our knowledge of the possible existence in nature of stable exotic particles depends solely upon experimental observation. Using a sensitive laser spectroscopy technique, we searched for a doubly charged particle accompanied by two electrons as an anomalously heavy isotope of helium in the Earth’s atmosphere. The concentration of noble-gas-like atoms in the atmosphere and the subsequent very large depletion of the light ${}^{3,4}\mathrm{H}\mathrm{e}$ isotopes allow stringent upper limits to be set on the abundance: ${10}^{-12}–{10}^{-17}$ per atom in the solar system over the mass range of 20–10 000 amu.

Pion-kaon correlation functions are constructed from central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ STAR data taken at $\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$ by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The results suggest that pions and kaons are not emitted at the same average space-time point. Space-momentum correlations, i.e., transverse flow, lead to a space-time emission asymmetry of pions and kaons that is consistent with the data. This result provides new independent evidence that the system created at RHIC undergoes a collective transverse expansion.

We discuss spin and pseudospin symmetry in the spectrum of single nucleons and single antinucleons in a nucleus. As an example we use relativistic mean field theory to investigate single antinucleon spectra. We find a very well developed spin symmetry in single antineutron and single antiproton spectra. The dominant components of the wave functions of the spin doublet are almost identical. This spin symmetry in antiparticle spectra and the pseudospin symmetry in particle spectra have the same origin. However, it turns out that the spin symmetry in antinucleon spectra is much better developed than the pseudospin symmetry in normal nuclear single particle spectra.

The Gamow-Teller resonances (GTR) and isobaric analog states (IAS) of a sequence of even-even Sn target nuclei are calculated by using the framework of the relativistic Hartree-Bogoliubov model plus proton-neutron quasiparticle random-phase approximation. The calculation reproduces the experimental data on ground-state properties, as well as the excitation energies of the isovector excitations. It is shown that the isotopic dependence of the energy spacings between the GTR and IAS provides direct information on the evolution of neutron-skin thickness along the Sn isotopic chain. A new method is suggested for determining the difference between the radii of the neutron and proton density distributions along an isotopic chain, based on measurement of the excitation energies of the GTR relative to the IAS.

Data from the first physics run at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory, $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$, have been analyzed by the STAR Collaboration using three-pion correlations with charged pions to study whether pions are emitted independently at freeze-out. We have made a high-statistics measurement of the three-pion correlation function and calculated the normalized three-particle correlator to obtain a quantitative measurement of the degree of chaoticity of the pion source. It is found that the degree of chaoticity seems to increase with increasing particle multiplicity.

We have measured the total energy of the alpha particles following the beta decay of ${}^8\mathrm{B}$ by implanting ${}^8\mathrm{B}$ into a planar silicon surface barrier detector. Calibration was performed using alpha particles following the beta decay of ${}^{20}\mathrm{N}\mathrm{a}$, similarly implanted. The alpha spectrum is used to infer the ${}^8\mathrm{B}$ neutrino spectrum which is an important input in the interpretation of experiments that detect energetic neutrinos from the Sun. The alpha spectrum reported here is in disagreement with the previous best measurement which used two detectors in coincidence.

It is shown that color-superconducting quark matter, where quarks of the same flavor form Cooper pairs with spin one, exhibits an electromagnetic Meissner effect. This is in contrast to spin-zero color superconductors where Cooper pairs consist of quarks with different flavors.

The decay-out process of the yrast superdeformed band in ${}^{59}\mathrm{C}\mathrm{u}$ has been investigated. The firm determination of spin, parity, excitation energy, and configuration of the states involved in this process constitutes a unique situation for a detailed understanding of the decay-out mechanism. A theoretical model is introduced that includes a residual interaction and tunneling matrix element between bands, calculated in the configuration-dependent cranked Nilsson-Strutinsky model. This interaction causes the decay to occur via a small number of observed doorway states.

We show how the charge symmetry of strong interactions can be used to relate the proton and neutron asymptotic normalization coefficients (ANCs) of the one-nucleon overlap integrals for light mirror nuclei. This relation extends to the case of real proton decay where the mirror analog is a virtual neutron decay of a loosely bound state. In this case, a link is obtained between the proton width and the squared ANC of the mirror neutron state. The relation between mirror overlaps can be used to study astrophysically relevant proton capture reactions based on information obtained from transfer reactions with stable beams.

The forward-backward asymmetry in $np\to d{\pi }^0$, which must be zero in the center-of-mass system if charge symmetry is respected, has been measured to be $[17.2\pm 8.0(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 5.5(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})]\times {10}^{-4}$, at an incident neutron energy of 279.5 MeV. This observable is compared to recent chiral effective field theory calculations, with implications regarding the $du$ quark mass difference.

We calculated the contribution of internal nucleon electric dipole moments to the Schiff moment of ${}^{199}\mathrm{H}\mathrm{g}$. The contribution of the proton electric dipole moment was obtained via core polarization effects that were treated in the framework of random phase approximation with effective residual forces. We derived a new upper bound $|d_p|<5.4\times {10}^{-24}e\mathrm{c}\mathrm{m}$ of the proton electric dipole moment.

The chiral quark-soliton model of the nucleon contains a mechanism for an attractive interaction between nucleons. This, along with the exchange of vector mesons between nucleons, is used to compute the saturation properties of infinite nuclear matter. This provides a new way to assess the effects of the nuclear medium on a nucleon that includes valence and sea quarks. We show that the model simultaneously describes the nuclear EMC effect and the related Drell-Yan experiments.

The yield for the multistrange ${\Xi }^{-}$ hyperon has been measured in $6A\mathrm{G}\mathrm{e}\mathrm{V}$ $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions via reconstruction of its decay products ${\pi }^{-}$ and $\Lambda$, the latter also being reconstructed from its daughter tracks of ${\pi }^{-}$ and $p$. The measurement is rather close to the threshold for ${\Xi }^{-}$ production and therefore provides an important test of model predictions. The measured yield for ${\Xi }^{-}$ and $\Lambda$ are compared for several centralities. In central collisions the ${\Xi }^{-}$ yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multistrange hadron production approaches chemical equilibrium in high baryon density nuclear matter.

The liquid-gas phase transition is analyzed from the topologic properties of the event distribution in the observables space. A multicanonical formalism allows one to directly relate the standard phase transition with neutral particles to the case where the nonsaturating Coulomb interaction is present, and to interpret the Coulomb effect as a deformation of the probability distributions and a rotation of the order parameter. This formalism is applied to a statistical multifragmentation model and consequences for the nuclear multifragmentation phase transitions are drawn.

The anisotropy parameter ($v_2$), the second harmonic of the azimuthal particle distribution, has been measured with the PHENIX detector in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$ for identified and inclusive charged particle production at central rapidities ($|\eta |<0.35$) with respect to the reaction plane defined at high rapidities ($|\eta |=3–4$). We observe that the $v_2$ of mesons falls below that of (anti)baryons for $p_T>2\mathrm{G}\mathrm{e}\mathrm{V}/c$, in marked contrast to the predictions of a hydrodynamical model. A quark-coalescence model is also investigated.

Evidence is presented for multiphonon excitations based on a high-spin ($25\hslash$) intrinsic state in the deformed nucleus ${}^{182}\mathrm{O}\mathrm{s}$. Angular momentum generation by this mode competes with collective rotation. The experimental data are compared with tilted-axis cranking calculations, supporting the vibrational interpretation. However, the lower experimental energies provide evidence that more complex interactions of states are playing a role.

The reaction $pp\to d{K}^{+}{\overline{K}}^0$ has been investigated at an excess energy of $Q=46\mathrm{M}\mathrm{e}\mathrm{V}$ above the $K^{+}{\overline{K}}^0$ threshold with ANKE at the cooler synchrotron COSY-Jülich. From the detected coincident $d{K}^{+}$ pairs, about 1000 events with a missing ${\overline{K}}^0$ were identified, corresponding to a total cross section of $\sigma (pp\to d{K}^{+}{\overline{K}}^0)=[38\pm 2(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 14(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})]\mathrm{n}\mathrm{b}$. Invariant-mass and angular distributions have been jointly analyzed and reveal $s$-wave dominance between the two kaons, accompanied by a $p$ wave between the deuteron and the kaon system. This is interpreted in terms of $a_0^{+}(980)$-resonance production.

It is suggested that the falloff in $Q^2$ of the $P\to \Delta$ magnetic form factor $G_M^{*}$ is related to the recently observed falloff of the elastic electric form factor $G_{Ep}/G_{Mp}$. Calculation is carried out in the framework of a generalized parton distribution model whose parameters are determined by fitting the elastic form factors $F_{1p}$ and $F_{2p}$ and isospin symmetry. When applied to the $P\to \Delta$ transition with no additional parameters, the shape of $G_M^{*}$ is found to exhibit the requisite falloff with $Q^2$.

We report high statistics measurements of inclusive charged hadron production in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ and $p+p$ collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. A large, approximately constant hadron suppression is observed in central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions for $5\mathrm{<}{p}_T\mathrm{<}12\mathrm{G}\mathrm{e}\mathrm{V}/c$. The collision energy dependence of the yields and the centrality and $p_T$ dependence of the suppression provide stringent constraints on theoretical models of suppression. Models incorporating initial-state gluon saturation or partonic energy loss in dense matter are largely consistent with observations. We observe no evidence of $p_T$-dependent suppression, which may be expected from models incorporating jet attenuation in cold nuclear matter or scattering of fragmentation hadrons.

We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$ measured at midrapidity by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider. In central collisions at intermediate transverse momenta ($1.5<p_T<4.5\mathrm{G}\mathrm{e}\mathrm{V}/c$) a significant fraction of all produced particles are protons and antiprotons. They show a centrality-scaling behavior different from that of pions. The $\overline{p}/\pi$ and $p/\pi$ ratios are enhanced compared to peripheral $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$, $p+p$, and $e^{+}{e}^{-}$ collisions. This enhancement is limited to $p_T<5\mathrm{G}\mathrm{e}\mathrm{V}/c$ as deduced from the ratio of charged hadrons to ${\pi }^0$ measured in the range $1.5<p_T<9\mathrm{G}\mathrm{e}\mathrm{V}/c$.