The $pp\to pp\varphi$ reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies $ϵ$ near the production threshold. The differential cross section closest to threshold at $ϵ=18.5\mathrm{MeV}$ exhibits a clear $S$ wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for $pp\omega$ production, a significant enhancement of the $\varphi /\omega$ ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

We show that chiral symmetry and gauge invariance enforce relations between the short-distance physics that occurs in a number of electroweak and pionic reactions on light nuclei. Within chiral perturbation theory, this is manifested via the appearance of the same axial isovector two-body contact term in ${\pi }^{-}d\to nn\gamma$, $p$-wave pion production in $NN$ collisions, tritium $\beta$ decay, $pp$ fusion, $\nu d$ scattering, and the hep reaction. Using a Gamow-Teller matrix element obtained from calculations of $pp$ fusion as input, we compute the neutron spectrum obtained in ${\pi }^{-}d\to nn\gamma$. With the short-distance physics in this process controlled from $pp\to d{e}^{+}{\nu }_e$, the theoretical uncertainty in the $nn$ scattering length extracted from ${\pi }^{-}d\to nn\gamma$ is reduced by a factor larger than 3, to $\lesssim 0.05\mathrm{fm}$.

The reduced transition probabilities $B(E2;0^{+}\to 2_1^{+})$ of the neutron-rich ${}^{74}\mathrm{Zn}$ and ${}^{70}\mathrm{Ni}$ nuclei have been measured by Coulomb excitation in a ${}^{208}\mathrm{Pb}$ target at intermediate energy. These nuclei have been produced at Grand Accélérateur National d’Ions Lourds via interactions of a $60A\mathrm{MeV}$ ${}^{76}\mathrm{Ge}$ beam with a Be target. The $B(E2)$ value for ${}^{70}\mathrm{Ni}_{42}$ is unexpectedly large, which indicates that neutrons added above $N=40$ strongly polarize the $Z=28$ proton core. In the Zn isotopic chain, the steep rise of $B(E2)$ values beyond $N=40$ continues up to ${}^{74}\mathrm{Zn}_{44}$. The enhanced proton core polarization in ${}^{70}\mathrm{Ni}$ is attributed to the monopole interaction between the neutron in the $g_{9/2}$ and protons in the $f_{7/2}$ and $f_{5/2}$ spin-orbit partner orbitals. This interaction could result in a weakening of magicity in ${}^{78}\mathrm{Ni}_{50}$.

Deuteron-gold ($d+\mathrm{Au}$) collisions at the Relativistic Heavy Ion Collider provide ideal platforms for testing QCD theories in dense nuclear matter at high energy. In particular, models suggesting strong saturation effects for partons carrying small nucleon momentum fraction ($x$) predict modifications to jet production at forward rapidity (deuteron-going direction) in $d+\mathrm{Au}$ collisions. We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at midrapidity in $d+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. Jet structures observed in the correlations are quantified in terms of the conditional yield and angular width of away-side partners. The kinematic region studied here samples partons in the gold nucleus with $x\sim 0.1$ to $\sim 0.01$. Within this range, we find no $x$ dependence of the jet structure in $d+\mathrm{Au}$ collisions.

We present transverse momentum distributions of charged hadrons produced in $\mathrm{Cu}+\mathrm{Cu}$ collisions at $\sqrt{s_{NN}}=62.4$ and 200 GeV. The spectra are measured for transverse momenta of $0.25<p_T<5.0\mathrm{GeV}/c$ at $\sqrt{s_{NN}}=62.4\mathrm{GeV}$ and $0.25<p_T<7.0\mathrm{GeV}/c$ at $\sqrt{s_{NN}}=200\mathrm{GeV}$, in a pseudorapidity range of $0.2<\eta <1.4$. The nuclear modification factor $R_{AA}$ is calculated relative to $p+p$ data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross section, $R_{AA}$ is observed to be systematically larger in $\mathrm{Cu}+\mathrm{Cu}$ collisions compared to $\mathrm{Au}+\mathrm{Au}$. However, for the same number of participating nucleons, $R_{AA}$ is essentially the same in both systems over the measured range of $p_T$, in spite of the significantly different geometries of the $\mathrm{Cu}+\mathrm{Cu}$ and $\mathrm{Au}+\mathrm{Au}$ systems.

We predict the transverse momentum ($p_T$) dependence of elliptic flow of thermal photons for $\mathrm{Au}+\mathrm{Au}$ collisions at the BNL Relativistic Heavy Ion Collider. We model the system hydrodynamically, with a thermalized quark-gluon plasma at early times followed by hadronization and decoupling. Photons are emitted throughout the expansion history. Contrary to hadron elliptic flow, which increases monotonically with $p_T$, the elliptic flow $v_2(p_T)$ of thermal photons is predicted to first rise and then fall again. Photon elliptic flow at high $p_T$ reflects the quark momentum anisotropy at early times when it is small, while at low $p_T$ it mirrors the large pion momentum anisotropy during the late hadronic emission stage. An interesting structure is predicted at intermediate $p_T\sim 0.4\mathrm{GeV}/c$, where photon elliptic flow reflects the momenta and the (compared to pions) reduced $v_2$ of heavy vector mesons in the late hadronic phase.

Inclusive transverse momentum spectra of $\eta$ mesons have been measured within $p_T=2–10\mathrm{GeV}/c$ at midrapidity by the PHENIX experiment in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. In central $\mathrm{Au}+\mathrm{Au}$ the $\eta$ yields are significantly suppressed compared to peripheral $\mathrm{Au}+\mathrm{Au}$, $d+\mathrm{Au}$, and $p+p$ yields scaled by the corresponding number of nucleon-nucleon collisions. The magnitude, centrality, and $p_T$ dependence of the suppression is common, within errors, for $\eta$ and ${\pi }^0$. The ratio of $\eta$ to ${\pi }^0$ spectra at high $p_T$ amounts to $0.40<R_{\eta /{\pi }^0}<0.48$ for the three systems, in agreement with the world average measured in hadronic and nuclear reactions and, at large scaled momentum, in $e^{+}{e}^{-}$ collisions.

Photoneutron cross sections for ${}^{181}\mathrm{Ta}(\gamma ,n){}^{180}\mathrm{Ta}^m$ were determined from simultaneous measurements of total cross sections (${\sigma }^{\mathrm{tot}}$) and ground-state cross sections (${\sigma }^{\mathrm{gs}}$) for ${}^{180}\mathrm{Ta}$ in photodisintegration of ${}^{181}\mathrm{Ta}$ with laser Compton-backscattered $\gamma$ rays. Techniques of direct neutron counting and photoactivation were used for the measurement of ${\sigma }^{\mathrm{tot}}$ and ${\sigma }^{\mathrm{gs}}$, respectively. The partial cross sections for the isomeric state serves as a novel probe of the nuclear level density of ${}^{180}\mathrm{Ta}$. Implications for the $p$- and $s$-process nucleosynthesis of ${}^{180}\mathrm{Ta}^m$ are given.

An experimental way of testing Bose-Einstein condensation of $\alpha$ clusters in the atomic nucleus is reported. The enhancement of cluster emission and the multiplicity partition of possible emitted clusters could be direct signatures for the condensed states. The barrier for the emission of clusters, such as ${}^8\mathrm{Be}$ and ${}^{12}\mathrm{C}^{*}(0_2^{+})$, is calculated and compared with the barrier for the sequential emission of 2 or $3\alpha$ particles from the compound nucleus. For the calculations, a simple approach using a folded Woods-Saxon potential is used.

This Letter reports on the ${}^1\mathrm{H}({}^{28}\mathrm{Ne},{}^{28}\mathrm{Ne})$ and ${}^1\mathrm{H}({}^{28}\mathrm{Ne},{}^{27}\mathrm{Ne})$ reactions studied at intermediate energy using a liquid hydrogen target. From the cross section populating the first $2^{+}$ excited state of ${}^{28}\mathrm{Ne}$, and using the previously determined $B(E2)$ value, the neutron quadrupole transition matrix element has been calculated to be $M_n=13.8\pm 3.7{\mathrm{fm}}^2$. In the neutron knockout reaction, two low-lying excited states were populated in ${}^{27}\mathrm{Ne}$. Only one of them can be interpreted by the $sd$ shell model while the additional state may intrude from the $fp$ shell. These experimental observations are consistent with the presence of $fp$ shell configurations at low excitation energy in ${}^{27,28}\mathrm{Ne}$ nuclei caused by a vanishing $N=20$ shell gap at $Z=10$.

The possibility of Cherenkov-like gluon bremsstrahlung in dense matter is studied. We point out that the occurrence of Cherenkov radiation in dense matter is sensitive to the presence of partonic bound states. This is illustrated by a calculation of the dispersion relation of a massless particle in a simple model in which it couples to two different massive resonance states. We further argue that detailed spectroscopy of jet correlations can directly probe the index of refraction of this matter, which in turn will provide information about the mass scale of these partonic bound states.

Neutrinos are the principal messengers reaching us from the center of a supernova. Terrestrial neutrino telescopes can provide precious information about the processes in the core of the star. But the information that a neutrino detector can supply is restricted by the fact that little experimental data on the neutrino-nucleus cross sections exist and by the uncertainties in theoretical calculations. In this Letter, we propose a novel procedure that determines the response of a target nucleus in a supernova-neutrino detector, by using low-energy beta beams. We show that fitting “synthetic” spectra, constructed by taking linear combinations of beta-beam spectra, to the original supernova-neutrino spectra reproduces the folded differential cross sections very accurately. Comparing the response in a detector to these synthetic responses provides a direct way to determine the main parameters of the supernova-neutrino energy distribution.

The fusion of ${}^6\mathrm{He}$ with ${}^{206}\mathrm{Pb}$ has been studied at energies close to and below the Coulomb barrier. The experiment was carried out at the Dubna Radioactive Ion Beams complex of FLNR, JINR. The ${}^6\mathrm{He}$ beam intensity was about $5\times {10}^6\mathrm{pps}$, the maximum energy being $60.3\pm 0.4\mathrm{MeV}$. The yield of the ${}^{210}\mathrm{Po}$ isotope, produced in the $2n$-evaporation channel, demonstrates an extremely large enhancement of the sub-barrier fusion cross section as compared with the ${}^4\mathrm{He}+{}^{208}\mathrm{Pb}$ reaction. This enhancement is most likely due to the mechanism of “sequential fusion” with an intermediate neutron transfer from ${}^6\mathrm{He}$ to the Pb nucleus with positive $Q$ values.

We report on a precision measurement of low-mass muon pairs in 158 AGeV indium-indium collisions at the CERN SPS. A significant excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of 360 000 dimuons and the good mass resolution of about 2% allow us to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum is consistent with a dominant contribution from ${\pi }^{+}{\pi }^{-}\to \rho \to {\mu }^{+}{\mu }^{-}$ annihilation. The associated space-time averaged $\rho$ spectral function shows a strong broadening, but essentially no shift in mass. This may rule out theoretical models linking hadron masses directly to the chiral condensate.

The low-energy reaction ${}^{14}\mathrm{C}(n,\gamma ){}^{15}\mathrm{C}$ provides a rare opportunity to test indirect methods for the determination of neutron capture cross sections by radioactive isotopes versus direct measurements. It is also important for various astrophysical scenarios. Currently, puzzling disagreements exist between the ${}^{14}\mathrm{C}(n,\gamma ){}^{15}\mathrm{C}$ cross sections measured directly, determined indirectly, and calculated theoretically. To solve this puzzle, we offer a strong test based on a novel idea that the amplitudes for the virtual ${}^{15}\mathrm{C}\to {}^{14}\mathrm{C}+n$ and the real ${}^{15}\mathrm{F}\to {}^{14}\mathrm{O}+p$ decays are related. Our study of this relation, performed in a microscopic model, shows that existing direct and some indirect measurements strongly contradict charge symmetry in the ${}^{15}\mathrm{C}$ and ${}^{15}\mathrm{F}$ mirror pair. This brings into question the experimental determinations of the astrophysically important ($n,\gamma$) cross sections for short-lived radioactive targets.

The first measurements of double-hadron production in deep-inelastic scattering within the nuclear medium were made with the HERMES spectrometer at DESY HERA using a 27.6 GeV positron beam. By comparing data for deuterium, nitrogen, krypton, and xenon nuclei, the influence of the nuclear medium on the ratio of double-hadron to single-hadron yields was investigated. Nuclear effects on the additional hadron are clearly observed, but with little or no difference among nitrogen, krypton, or xenon, and with smaller magnitude than effects seen on previously measured single-hadron multiplicities. The data are compared with models based on partonic energy loss or prehadronic scattering and with a model based on a purely absorptive treatment of the final-state interactions. Thus, the double-hadron ratio provides an additional tool for studying modifications of hadronization in nuclear matter.

We report on results of a measurement of $\varphi$ meson production in central Pb-Au collisions at $E_{\mathrm{lab}}=158A\mathrm{GeV}$. For the first time in the history of high energy heavy-ion collisions, $\varphi$ mesons were reconstructed both in the $K^{+}{K}^{-}$ and the dilepton decay channels in the same experiment. This measurement yields rapidity densities near midrapidity, from the two decay channels, of $2.05\pm 0.14(\mathrm{stat})\pm 0.25(\mathrm{syst})$ and $2.04\pm 0.49(\mathrm{stat})\pm 0.32(\mathrm{syst})$, respectively. The shape of the measured transverse momentum spectrum is also in close agreement in both decay channels. The data rule out a possible enhancement of the $\varphi$ yield in the leptonic over the hadronic decay channel of a factor 1.6 or larger at the 95% C.L. This rules out the discrepancy reported in the literature between measurements of the hadronic and dimuon decay channels by two different experiments.

The mass of the short-lived radio nuclide ${}^{38}\mathrm{Ca}$ ($T_{1/2}=440\mathrm{ms}$) has been measured with the 9.4-T Penning trap mass spectrometer of the Low-Energy Beam and Ion Trap Facility. A mass uncertainty of $\delta m=280\mathrm{eV}$ has been achieved, corresponding to $\delta m/m=8\times {10}^{-9}$. The result makes ${}^{38}\mathrm{Ca}$, a superallowed beta emitter, a new candidate to test the conserved-vector-current hypothesis. The experiment is also the first demonstration that short-lived radioactive isotopes produced by projectile fragmentation of relativistic heavy-ion beams can be slowed down and prepared such that precision experiments of this kind are possible.

The direct interaction of nuclei with superintense laser fields is studied. We show that present and upcoming high-frequency laser facilities, especially together with a moderate acceleration of the target nuclei to match photon and transition frequency, do allow for resonant laser-nucleus interaction. These direct interactions may be utilized for the model-independent optical measurement of nuclear properties such as the transition frequency and the dipole moment, thus opening the field of nuclear quantum optics. As an ultimate goal, one may hope that direct laser-nucleus interactions could become a versatile tool to enhance preparation, control, and detection in nuclear physics.

We present a new nucleosynthesis process that we denote as the $\nu p$ process, which occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino fluxes create proton-rich ejecta. In this process, antineutrino absorptions in the proton-rich environment produce neutrons that are immediately captured by neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with mass numbers $A>64$, making this process a possible candidate to explain the origin of the solar abundances of ${}^{92,94}\mathrm{Mo}$ and ${}^{96,98}\mathrm{Ru}$. This process also offers a natural explanation for the large abundance of Sr seen in a hyper-metal-poor star.