Octupole-deformed molecular bands in 21Ne

Cluster states up to 12 MeV in the stable light nucleus ²¹Ne, based on the ¹⁶O + n + α molecular configurations, have been populated in the incomplete-fusion reaction ¹⁶ ₈O(⁷₃Li, np)²¹₁₀Ne at 29.4 MeV. The observation of both intra- and inter-band transitions leads to a re-interpretation of some levels in the K^π = ^- and K^π = ^- bands. The implications of this re-ordering on the octupole doublet bands are examined. The data allow a more accurate determination of some previously uncertain level energies. The “missing” I^π = ^- level is also discussed.     

Rapidity equilibration in d + Au and Au + Au systems

In a Relativistic Diffusion Model (RDM), the evolution of net-proton rapidity spectra with in heavy systems is proposed as an indicator for local equilibration and longitudinal expansion. The broad midrapidity valley recently discovered at RHIC in central Au + Au collisions at = 200 GeV suggests rapid local equilibration which is most likely due to deconfinement, and fast longitudinal expansion. Rapidity spectra of produced charged hadrons in d + Au and Au + Au systems at RHIC energies and their centrality dependence are well described in a three-sources RDM. In central collisions, about 19% of the produced particles are in the equilibrated midrapidity region for d + Au.     

The beauty of the electromagnetic probe

Selected results from the first five years of RHIC data taking are reviewed with emphasis on the evidence for thermalization in central Au + Au collisions at = 200GeV.     

Loss of collectivity in 79Rb

High-spin states in ⁷⁹Rb were populated in the reaction at E(beam) = 60 MeV. The lifetimes of the excited states of the positive-parity yrast band and of the negative-parity band in ⁷⁹Rb were measured by the Doppler Shift Attenuation Method. The deduced transition quadrupole moments Q_t are found to have a decreasing trend with rotational frequency for both the bands, consistent with those found experimentally in neighbouring nuclei. An erratum to this article is available at .     

Measurement of the LT-asymmetry in πelectroproduction at the energy of the Δ(1232)-resonance

The reaction p(e, e'p)π⁰ has been studied at Q² = 0.2 (GeV/c)² in the region of W = 1232MeV. From measurements left and right of , cross-section asymmetries ρ_LT have been obtained in forward kinematics ρ_LT( = 20^°) = (- 11.68±2.36_stat±2.36_sys) and backward kinematics ρ_LT( = 160^°) = (12.18±0.27_stat±0.82_sys) π⁰. Multipole ratios {S₁₊ ^* M₁₊}/| M₁₊|² and {S₀₊ ^* M₁₊}/| M₁₊|² were determined in the framework of the MAID2003 model. The results are in agreement with older data. The unusally strong negative {S₀₊ ^* M₁₊}/| M₁₊|² required to bring also the result of Kalleicher et al. in accordance with the rest of the data is almost excluded.     

The modified decay width of the radioactive nucleus

It is reported that the width of the first excited state ( , 37.133keV) of ¹²¹ ₅₁Sb embedded in a ZnSb alloy can be modified by reabsorption of γ -rays scattered backward on the platinum (gold) reflector. Its dependence on the reflector shape is also investigated. The decay rate is reduced about 4.5% at a temperature of 4.2K by a platinum spherical reflector of 5mm radius.     

Lowest- Q2 measurement of the γp → Δ reaction: Probing the pionic contribution

To determine nonspherical angular-momentum amplitudes in hadrons at long ranges (low Q²), data were taken for the p(ˉe, e'p)π⁰ reaction in the Δ region at Q ² = 0.060 (GeV/c)² utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W = 1232 MeV are , Re( )%, and Re( )%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with nonlinear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q² variation, of the pionic contribution at large distances.     

Chiral perturbation theory for nucleon generalized parton distributions

We analyze the moments of the isosinglet generalized parton distributions H, E, , of the nucleon in one-loop order of heavy-baryon chiral perturbation theory. We discuss in detail the construction of the operators in the effective theory that are required to obtain all corrections to a given order in the chiral power counting. The results will serve to improve the extrapolation of lattice results to the chiral limit.     

Isotopic dependence of fusion probabilities for neutron-deficient and -rich colliding nuclei

Isotopic dependence of the fusion dynamics is studied by analyzing the collision of a large number of isotopes of Ca and Ni with 0.6 N/Z 2. This study, which results from the Skyrme energy density formalism, reveals that the addition of neutrons favors fusion of reacting partners, whereas the reverse happens with the removal of neutrons. The fusion barrier heights and positions follow a non-linear second-order dependence on ( -1 ), whereas fusion cross-sections can be parameterized by a straight line.-1     

Improving bounds on flavor changing vertices in the two Higgs doublet model from B^0-\bar{B}^0 mixing

We find some constraints on the flavor changing vertices of the two Higgs doublet model, from the measurement. Although bounds from this observable have already been considered, this paper takes into account the role of a new operator not included previously, as well as the vertices , and . Using the Cheng–Sher parametrization, we find that for a relatively light charged Higgs boson (200–300 GeV), we obtain , while the parameter could have values up to about 50. In addition, we use bounds for and obtained from at next to leading order, and study the case where the only vanishing vertex factors are the ones involving quarks from the first family. We obtain that is not sensitive to the change of the parameter , while .     

Single heavy flavour baryons using Coulomb plus a power law interquark potential

Properties of single heavy flavor baryons in a non-relativistic potential model with colour Coulomb plus a power law confinement potential have been studied using a simple variational method. The ground-state masses of single heavy baryons and the mass difference between the J ^P = ⁺ and J ^P = ⁺ states are computed using a spin-dependent two-body potential. Using the spin-flavour structure of the constituting quarks and by defining an effective confined mass of the constituent quarks within the baryons, the magnetic moments are computed. The masses and magnetic moments of the single heavy baryons are found to be in accordance with the existing experimental values and with other theoretical predictions. It is found that an additional attractive interaction of the order of -200 MeV is required for the antisymmetric states of (Q c, b) . It is also found that the spin-hyperfine interaction parameters play a decisive role in hadron spectroscopy.     

The one-body and two-body density matrices of finite nuclei with an appropriate treatment of the center-of-mass motion⋆

The one-body and two-body density matrices in coordinate space and their Fourier transforms in momentum space are studied for a nucleus (a nonrelativistic, self-bound finite system). Unlike the usual procedure, suitable for infinite or externally bound systems, they are determined as expectation values of appropriate intrinsic operators, dependent on the relative coordinates and momenta (Jacobi variables) and acting on intrinsic wave functions of nuclear states. Thus, translational invariance (TI) is respected. When handling such intrinsic quantities, we use an algebraic technique based upon the Cartesian representation, in which the coordinate and momentum operators are linear combinations of the creation and annihilation operators and for oscillator quanta. Each of the relevant multiplicative operators can then be reduced to the form: one exponential of the set { } times another exponential of the set { }. In the course of such a normal-ordering procedure we offer a fresh look at the appearance of “Tassie-Barker” factors, and point out other model-independent results. The intrinsic wave function of the nucleus in its ground state is constructed from a nontranslationally-invariant (nTI) one via existing projection techniques. As an illustration, the one-body and two-body momentum distributions (MDs) for the ⁴He nucleus are calculated with the Slater determinant of the harmonic-oscillator model as the trial, nTI wave function. We find that the TI introduces quite important effects in the MDs.     

Photo-induced nucleosynthesis: Current problems and experimental approaches

Photon-induced reactions play a key role in the nucleosynthesis of rare neutron-deficient p -nuclei. The paper focuses on , , and reactions which define the corresponding p -process path. The relation between stellar reaction rates and laboratory cross-sections is analyzed for photon-induced reactions and their inverse capture reactions to evaluate various experimental approaches. An improved version S _C(E) of the astrophysical S -factor is suggested which is based on the Coulomb wave functions. S _C(E) avoids the apparent energy dependence which is otherwise obtained for capture reactions on heavy nuclei. It is found that a special type of synchrotron radiation available at SPring-8 that mimics stellar blackbody radiation at billions of kelvins is a promising tool for future experiments. By using the blackbody synchrotron radiation, sufficient event rates for and reactions in the p -process path can be expected. These experiments will provide data to improve the nuclear parameters involved in the statistical model and thus reduce the uncertainties of nucleosynthesis calculations.     

Di-electrons from η -meson Dalitz decay in proton-proton collisions

The reaction is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction . Our focus is on di-electrons from Dalitz decays of η -mesons, , and the role of the corresponding transition form factor . Numerical results are presented for the intermediate-energy kinematics of HADES experiments.     

Hadron production and phase changes in relativistic heavy-ion collisions

We study soft hadron production in relativistic heavy-ion collisions in a wide range of reaction energy, 4.8 GeV < < 200 GeV, and make predictions about yields of particles using the statistical hadronization model. In fits to experimental data, we obtain both the statistical parameters as well as physical properties of the hadron source. We identify the properties of the fireball at the critical energy threshold, 6.26 GeV < < 7.61 GeV, marking for higher energies the hadronization of an entropy-rich phase. In terms of the chemical composition, one sees a phase which at low energy is chemically under-saturated, and which turns into a chemically over-saturated state persisting up to the maximum accessible energy. Assuming that there is no change in physical mechanisms in the energy range 15 > ≥200 GeV, we use continuity of particle yields and statistical parameters to predict the hadron production at = 62.4 GeV, and obtain total yields of hadrons at = 130 GeV. We consider, in depth, the pattern we uncover within the hadronization condition, and discuss possible mechanisms associated with the identified rapid change in system properties at . We propose that the chemically over-saturated 2 + 1 flavor hadron matter system undergoes a 1st-order phase transition.     

Transverse energy and charged-particle multiplicity at various centralities at RHIC: Statistical model estimates⋆

The transverse energy and the charged-particle multiplicity at midrapidity are evaluated in a single-freeze-out model for different centrality bins at RHIC at = 130 and 200GeV. The predictions of the model are done at the freeze-out parameters determined earlier from measured particle yields and p_T spectra. The results agree qualitatively well with the experimental data.     

Production properties of K^\star(892)^\pm vector mesons and their spin alignment as measured in the NOMAD experiment

First measurements of mesons production properties and their spin alignment in charged current (CC) and neutral current (NC) interactions are presented. The analysis of the full data sample of the NOMAD experiment is performed in different kinematic regions. For and mesons produced in CC interactions and decaying into we have found the following yields per event: and respectively, while for the and mesons produced in interactions the corresponding yields per event are: and . The results obtained for the parameter, and for and produced in CC interactions, are compared to theoretical predictions tuned on LEP measurements in annihilation at the pole. For mesons produced in interactions the measured parameter is . PACS 13.15.+g, 13.60.Le, 13.87.Fh, 13.88.+e, 14.40.Ev     

Strange particle production at RHIC in the dual parton model

We compute the mid-rapidity densities of pions, kaons, baryons and antibaryons in Au-Au collisions at GeV in the dual parton model supplemented with final state interaction (comovers interaction). The ratios ( ) increase between peripheral ( ) and central ( collisions by a factor 2.4 (2.0) for the , 4.8 (4.1) for the and 16.5 (13.5) for the . The ratio increases by a factor 1.3 in the same centrality range. A comparison with the available data is presented.Received: 28 April 2003, Published online: 11 July 2003     

Hyperfine structure and isotope shifts in near-infrared transitions of atomic nitrogen

We have obtained Doppler-free spectra of transitions in the → 2p²(³P) and → multiplets of atomic nitrogen using saturated absorption spectroscopy. These multiplets consist of respectively of seven and eight transitions, and have center of gravity wavelengths of 821 nm and 869 nm. Values for the hyperfine structure coupling constants of all the upper and lower states for these multiplets were obtained for both ¹⁴N and ¹⁵N. Isotope shifts of three transitions in each multiplet were also measured, and a significant J-dependence to the shifts was observed.     

Determination of the gluon polarization at RHIC and COMPASS

The most recent determinations of the gluon polarization in the nucleon, , obtained at RHIC and COMPASS experiments, are reviewed. The former accesses the gluon polarization mainly through the production of neutral pions (PHENIX) or jets (STAR) in polarized proton collisions. The latter uses the photon-gluon fusion in polarized lepton-nucleon scattering, tagged either by open charm or high-p_T hadrons production. All the results are in good agreement, and favour values of ΔG roughly between 0 and 0.5 at a few (GeV/c)² , thus in contradiction with what could be derived from the Ellis-Jaffe sum rule and the axial anomaly. Much stronger constraints will be obtained in a near future by both programs, helping us to clarify the role of gluons in the nucleon spin.