The role of the quark and gluon GPDs in hard vector-meson electroproduction

Electroproduction of light vector mesons is analyzed on the basis of handbag factorization. The required generalized parton distributions are constructed from the CTEQ6 parton distributions with the help of double distributions. The partonic subprocesses are calculated within the modified perturbative approach. The present work extends our previous analysis of the longitudinal cross section to the transverse one and other observables related to both the corresponding amplitudes. Our results are compared to recent experimental findings in detail.     

Cross-section asymmetries in vector-meson electroproduction and in inelastic ep scattering with polarized beam and target

We discuss the cross-section asymmetries for forward diffractive vector meson (ρ⁰) production by inelastic scattering of longitudinally polarized electrons (or muons) on polarized protons. Only for the case when both the beam and the target are polarized can considerable effects be expected. On the basis of the off-diagonal GVDM we give relations between the cross section asymmetries in ep → epρ⁰ (forward direction) and in ep → eX. For a longitudinally polarized target the cross-section asymmetries in ep → epρ⁰ are predicted to be roughly twice as large as in ep → eX.     

Drell-Yan representation for vector-meson spin-density matrix elements in semi-inclusive electroproduction

Polarized vector-meson production in semi-inclusive electron-nucleon scattering with longitudinally polarized electron beam has been investigated. A Drell-Yan-like representation for the spin-density matrix elements of a vector meson that takes into account the leading radiative corrections is derived. The calculations have been performed for two widely used reference systems, the Gottfried-Jackson and the helicity systems.     

The pion pole in hard exclusive vector-meson leptoproduction

Exploiting a set of generalized parton distributions (GPDs) derived from analyses of hard exclusive leptoproduction of ρ ⁰, φ and π ⁺ mesons, we investigate the ω spin density matrix elements (SDMEs) recently measured by the HERMES Collaboration. It turns out, from our study, that the pion pole is an important contribution to ω production. It will be treated as a one-particle exchange since its evaluation from the GPD \(\tilde E\) considerably underestimates its contribution. As an intermediate step of our analysis, we extract the πω transition form factor for photon virtualities less than 4 GeV². From our approach we achieve results for the ω SDMEs in good agreement with the HERMES data. The role of the pion pole in exclusive ρ ⁰ and φ leptoproduction is discussed too.     

Some consequences of the quark parton model in inclusive electroproduction

Consequences of the quark parton model proposed by Feynman for inclusive electroproduction are studies. We show that the SLAC experiment γ_v+p(n) → h^±+anything which distinguishes the outcoming hdrons by their charges only gives the possibility to check sum rules with fractional quark quantum numbers, to determine the charge of the proton quark (neutron quark) and to measure the valence distribution function directly. We predict the multiplicity difference for the charged hadrons as the function of q² which agrees well with the experimental data published recently.     

Distribution of angular momenta in shell-model configurations

Zeitschrift für Physik A Hadrons and nuclei - It is shown how the number ofJ-states in a configuration can be calculated approximately. A particularly simple method for obtaining the moments...     

The double parton distributions in the hard pomeron model

We study the double parton interaction process in collisions between highly virtual pairs in the BFKL regime. Explicit expressions for the double parton distributions are obtained both in the case of direct coupling of the BFKL pomerons to the pair and in the case of triple pomeron interaction. Received: 9 May 2000 / Revised version: 14 August 2000 / Published online: 23 January 2001     

The pairing correlations and nuclear shapes at very high angular momenta

The usual Strutinsky shell corrections include the pairing correlations in the BCS approach. At high-spin states the cranked intrinsic wave functions are not symmetric or antisymmetric under time reversal symmetry for general triaxial shapes. On the basis of the Hartree-Fock-Bogoliubov (HFB) approach two generalizations of the Strutinsky procedure are given to describe pairing correlations also for high-spin states and triaxial shapes. The method is applied to the neutron-deficient rare earth nucleus ¹⁵⁰Gd. It is found that pairing has an important effect on the change of nuclear deformation with increasing angular momentum. The proton pairing persists at least up to I ≈ 40.     

Transversity in hard exclusive electroproduction of pseudoscalar mesons

Estimates for electroproduction of pseudoscalar mesons at small values of skewness are presented. Cross-sections and asymmetries for these processes are calculated within the handbag approach which is based on factorization in hard parton subprocesses and soft generalized parton distributions (GPDs). The latter are constructed from double distributions. Transversity GPDs are taken into account; they are accompanied by twist-3 meson wave functions. For most pseudoscalar-meson channels a combination of ˜_T and [`(E)]_T \bar{{E}}_{T}^{} plays a particularly prominent role. This combination of GPDs, which we constrain by moments obtained from lattice QCD, leads, with the exception of the p⁺ \pi^{+}_{} and h^￠ \eta^{\prime}_{} channels, to large transverse cross-sections.     

Anomalous angular momenta in a quantised theory of monopoles

In this paper a gauge theory with a classical solution corresponding to a magnetic monopole is quantised. By careful handling of the zero frequency modes it is shown that the monopole is capable of absorbing both momentum and charge. The angular momentum operator is considered and it is shown that if the original theory contains an isodoublet scalar field, the quantum excitations may be half odd integer eigenvalue eigenstates of this operator.     

Evidence for a single-spin azimuthal asymmetry in semi-inclusive pion electroproduction

Single-spin asymmetries for semi-inclusive pion production in deep-inelastic scattering have been measured for the first time. A significant target-spin asymmetry of the distribution in the azimuthal angle straight phi of the pion relative to the lepton scattering plane was formed for pi(+) electroproduction on a longitudinally polarized hydrogen target. The corresponding analyzing power in the sinstraight phi moment of the cross section is 0.022+/-0.005+/-0.003. This result can be interpreted as the effect of terms in the cross section involving chiral-odd spin distribution functions in combination with a chiral-odd fragmentation function that is sensitive to the transverse polarization of the fragmenting quark.     

A galactic model II: The gravitationally radiated angular and linear momenta fluxes

Using the linearised theory of general relativity the gravitationally radiated angular and linear momenta from a galactic model ofN gravitational radiators is calculated. The results are presented in terms of the lowest order contributing multipole moments (quadrupole), the orientations of the radiators about a common reference frame, the distances between pairs of radiators and the frequency of each radiator. This work is a continuation of an earlier work in which the galactic model was first proposed and its gravitationally radiated energy flux was computed.     

Quantum generation of angular momenta of crystallites in a nanocrystalline material

It is shown that, under the effect of a point force, ordered deformation states of the Fermi type can arise in a nanocrystal. These states are characterized by an angular momentum whose magnitude (estimated in the units of Planck’s constant) depends on the number of atoms in the deformed nanocrystals and can accept macroscopic values. A qualitative explanation is given to the evolution of the strength, diffusive, and damping properties of compact nanocrystalline materials based on the assumption that the quantum generation of angular momenta of crystallites can result in states of rotational motion.     

Flavour tagging of parton jets and separation of parton subprocesses in hard proton-proton collisions at the ISR

High energy proton-proton interactions yielding a single trigger particle with large transverse momentum give rise to a four-jet event structure with two transverse jets and two jets along the beam direction. The transverse jets are due to the fragmentation of point like scattered partons. It is shown that the quantum numbers of triggering charged pions and positive kaons are correlated with the flavour of the scattered parent parton; thus one can enhance data samples with a particular flavour of a scattered parton. The analysis, which is independent of detailed model calculations, exploits (a) the identification of the leading particles in the trigger jets (trigger particles), (b) the measurement of their relative production rates, (c) short range quantum number correlations within the trigger jets, and (d) long range correlations between leading particles from different jets. The data were obtained at \(\sqrt s \) =62 GeV with the Split Field Magnet detector at the CERN ISR.     

Fragment angular momenta in low and medium energy fission of242Pu

Independent isomeric yield ratios of¹²⁸Sb were determined radiochemically in the thermal neutron induced fission of²⁴¹Pu and 34 MeV alpha particle induced fission of²³⁸U, both involving the same compound nucleus (²⁴²Pu). Fragment angular momenta estimated from the measured isomer ratios using the statistical model analysis showed significantly larger fragment angular momenta in the medium energy fissioning system compared to the low energy fissioning system. This has been attributed to the effect of higher excitation energy and angular momentum in the entrance channel leading to increased fragment temperature, moments of inertia and angular velocity. An attempt was made to calculate the fragment angular momentum in the medium energy fission using the Fermi gas model for the fissioning nucleus, taking into account the multichance fission, saddle shapes of the fissioning nuclei and the angular velocity components of the fissioning nuclei both along and orthogonal to the fission axis. The calculated angular momenta agree well with the experimental results.     

The possible angular momenta of a system of fermions or bosons with spinj

Simple recurrence relations for the multiplicities of angular momenta are presented for a system of fermions or bosons with spinj. Tables are given for fermions withj=13/2 up to 19/2 and for bosons withj=2, 3, 4, 5 and 20 particles at most.     

A coupling scheme relevant to high angular momenta and intermediate nuclear deformations

Based on the particle-plus-rotor model, it is shown that a new coupling scheme should occur in nuclei under certain conditions. In this coupling scheme, j is quantized along the direction of $\text{I}$ rather than along the symmetry axis. Simple approximate wave functions for this scheme have been developed and compared with the exact solutions of the particle-plus-rotor model.