[en] The ¹H(e,e'K⁺) Lambda and ¹H(e,e'K⁺) Sigma ⁰ reactions were studied as a function of the squared four-momentum-transfer, Q², and the virtual photon polarization, epsilon , thus enabling the separation of the longitudinal and transverse parts of the cross section. The existence of a sizable longitudinal component for the ¹H(e,e'K⁺) Lambda reaction seems to be indicated by these data

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[en] We present the multiplicity and pseudorapidity distributions of photons produced in Au+Au and Cu+Cu collisions at √s_NN = 62.4 and 200 GeV. The photons are measured in the region -3.7 < η < -2.3 using the photon multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of the collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for Au+Au and Cu+Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 ± 0.1 and 1.2 ± 0.1 for √s_NN = 62.4 GeV and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of η - ybeam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies.

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[en] Correlations and fluctuations of physical quantities are known to play an important role in phase transitions and critical phenomena. In recent years some experimental attempts were made in the scope of the Beam Energy Scan program to locate a possible critical point in the QCD phase diagram. In this work we use the Nambu–Jona-Lasinio model to investigate the off-diagonal quark susceptibility, which is related to the quark–anti-quark scaled correlation at the mean field level. We show that this correlation has a significant peak near the critical point and, therefore, may be a useful quantity to measure in experiment. We further study the effects of a repulsive vector coupling, which reduces the strength of the scaled correlation near the critical point.

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[en] The baryon electromagnetic form factors are expressed in terms of two-dimensional densities describing the distribution of charge and magnetization in transverse space at fixed light-front time. In this paper, we calculate the transverse densities of the spin-1/2 flavor-octet baryons at peripheral distances b=O(M"−"1_π) using methods of relativistic chiral effective field theory (χ EFT) and dispersion analysis. The densities are represented as dispersive integrals over the imaginary parts of the form factors in the timelike region (spectral functions). The isovector spectral functions on the two-pion cut t > 4 M"2_π are calculated using relativistic χEFT including octet and decuplet baryons. The χEFT calculations are extended into the ρ meson mass region using an N/D method that incorporates the pion electromagnetic form factor data. The isoscalar spectral functions are modeled by vector meson poles. We compute the peripheral charge and magnetization densities in the octet baryon states, estimate the uncertainties, and determine the quark flavor decomposition. Finally, the approach can be extended to baryon form factors of other operators and the moments of generalized parton distributions.

[en] The introduction of quark concept in nuclear physics may improve our understanding of the nuclear properties just where such improvements are needed most: at small distances. Strange particles, antiprotons and high energy hadron interaction with nucleus are useful sources of information concerning the short range nuclear force. Deep inelastic scattering of electrons off nuclei will eventually tell us if quarks in nuclei feel that they are not in an isolated hadron but rather in hadrons closely packed in a nucleus. (orig.)

[en] We review the situation of spin-isospin modes ( pionic modes ) in nuclei. It is shown that the excitation energies and transition amplitudes of those states provide an excellent tool to investigate the spin-isospin dependent part of the particle-hole interaction. The force which is deduced from our analysis does not give rise to precritical phenomena which could be attributed to pion condensation. In this connection we discuss especially the (e,e') form factor of the 1⁺(T = 1)-state in ¹²C. (orig.)