Polarization Phenomena by Deuteron Fragmentation into Pions

The fragmentation of deuterons into pions emitted forward in the kinematic region forbidden for free nucleon-nucleon collisions is analyzed. The inclusive relativistic invariant spectrum of pions and the tensor analyzing power T_{20} are investigated within the framework of an impulse approximation using different kinds of the deuteron wave function. The influence of P-wave inclusion in the deuteron wave function is studied, too. The invariant spectrum is shown to be more sensitive to the amplitude of the $NN \to \pi X$ process than the tensor analyzing power T_{20}. It is shown that the inclusion of the non-nucleon degrees of freedom in a deuteron results a satisfactory description of experimental data about the inclusive pion spectrum and improves the description of data about T_{20}. According to the experimental data, T_{20} has the positive sign and very small values, less than 0.2, what contradicts to the theoretical calculations ignoring these degrees of freedom.Comment: 18 pages, 8 eps figures, 1 picture - svjour.cls required; enlarged new version with corrections and additional figure. The Abstract and the section "Summary and outlook" have been also corrected. Final version to appear in Eur.Phys.J. A. A talk given at the International Workshop "Symmetries and Spin" (July 17-22, Prague, Czech Republic

Ultrahigh-energy neutrino-nucleon deep-inelastic scattering and the Froissart bound

We present a simple formula for the total cross section sigma^{nu N} of neutral- and charged-current deep-inelastic scattering of ultrahigh-energy neutrinos on isoscalar nuclear targets, which is proportional to the structure function F_2^{nu N}(M_V^2/s, M_V^2), where M_V is the intermediate-boson mass and s is the square of the center-of-mass energy. The coefficient in the front of F_2^{nu N}(x, Q^2) depends on the asymptotic low-x behavior of F_2^{nu N}. It contains an additional ln(s) term if F_2^{nu N} scales with a power of ln(1/x). Hence, an asymptotic low-x behavior F_2^{nu N} propto ln^2(1/x), which is frequently assumed in the literature, already leads to a violation of the Froissart bound on sigma^{nu N}.Comment: 5 pages, 2 figures, to appear in Physical Review Letter

Deuteron distribution in nuclear matter

We analyze the properties of deuteron-like structures in infinite, correlated nuclear matter, described by a realistic hamiltonian containing the Urbana $v_{14}$ two-nucleon and the Urbana TNI many-body potentials. The distribution of neutron-proton pairs, carrying the deuteron quantum numbers, is obtained as a function of the total momentum by computing the overlap between the nuclear matter in its ground state and the deuteron wave functions in correlated basis functions theory. We study the differences between the S- and D-wave components of the deuteron and those of the deuteron-like pair in the nuclear medium. The total number of deuteron type pairs is computed and compared with the predictions of Levinger's quasideuteron model. The resulting Levinger's factor in nuclear matter at equilibrium densityis 11.63. We use the local density approximation to estimate the Levinger's factor for heavy nuclei, obtaining results which are consistent with the available experimental data from photoreactions.Comment: 22 pages, 7 figures, typeset using REVTe

Probing the deuteron structure at small N-N distances by cumulative pion production

The fragmentation of deuterons into pions emitted forward in the kinematic region forbidden for free nucleon-nucleon collisions is analyzed. It is shown that the inclusion of the non-nucleonic degrees of freedom in a deuteron results in a satisfactory description of the data for the inclusive pion spectrum and improves the description of the data about $T_{20}$. According to the data, $T_{20}$ has very small positive values, less than 0.2, which contradicts the theoretical calculations ignoring these degrees of freedom.Comment: 3 pages, 2 postscript figures; to appear in the proceedings of Conference on Quarks and Nuclear Physics (QNP 2002), Julich, Germany, 9-14 Jun 200