Production of para-- and orthopositronium at relativistic heavy ion colliders

We consider the ortho-- and parapositronium production in the process $AA \to AA+$ Ps where A is a nucleus with the charge number Z. The inclusive cross section and the energy distribution of the relativistic Ps are calculated which are of primary interest from the experimental point of view. The accuracy of the corresponding cross sections is given by omitting terms $\sim (Z\alpha )^2/L^2$ for the para--Ps and $\sim (Z\alpha)^2/L$ for the ortho--Ps production where $L=\ln{\gamma^2} \approx 9$ and 16 for the RHIC and the LHC. Within this accuracy the multiphoton (Coulomb) corrections are taken into account. We show that the RHIC and the LHC will be Ps factories with a productions rate of about $10^5 \div 10^8$ relativistic Ps per day. The fraction of the ortho--Ps is expected to be of the same order as that of the para--Ps for Au--Au and Pb--Pb collisions.Comment: 22 pages, 5 figures, RevTeX, misprint correcte

Perturbative fragmentation

The Berger model of perturbative fragmentation of quarks to pions is improved by providing an absolute normalization and keeping all terms in a (1-z) expansion, which makes the calculation valid at all values of fractional pion momentum z. We also replace the nonrelativistic wave function of a loosely bound pion by the more realistic procedure of projecting to the light-cone pion wave function, which in turn is taken from well known models. The full calculation does not confirm the (1-z)^2 behavior of the fragmentation function (FF) predicted in for $z>0.5$, and only works at very large z>0.95, where it is in reasonable agreement with phenomenological FFs. Otherwise, we observe quite a different z-dependence which grossly underestimates data at smaller z. The disagreement is reduced after the addition of pions from decays of light vector mesons, but still remains considerable. The process dependent higher twist terms are also calculated exactly and found to be important at large z and/or pT.Comment: 10 pages, 8 figure

Bound-state beta-decay of a neutron in a strong magnetic field

The beta-decay of a neutron into a bound $(pe^-)$ state and an antineutrino in the presence of a strong uniform magnetic field ($B \gtrsim 10^{13}$ G) is considered. The beta-decay process is treated within the framework of the standard model of weak interactions. A Bethe-Salpeter formalism is employed for description of the bound $(pe^-)$ system in a strong magnetic field. For the field strengths $10^{13}$ G$\lesssim B \lesssim10^{18}$ G the estimate for the ratio of the bound-state decay rate $w_b$ and the usual (continuum-state) decay rate $w_c$ is derived. It is found that in such strong magnetic fields $w_b/w_c \sim 0.1-0.4$. This is in contrast to the field-free case, where $w_b/w_c \simeq 4.2 \times 10^{-6}$ [J. N. Bahcall, Phys. Rev. {\bf 124}, 495 (1961); L. L. Nemenov, Sov. J. Nucl. Phys. {\bf 15}, 582 (1972); X. Song, J. Phys. G: Nucl. Phys. {\bf 13}, 1023 (1987)]. The dependence of the ratio $w_b/w_c$ on the magnetic field strength $B$ exhibits a logarithmic-like behavior. The obtained results can be important for applications in astrophysics and cosmology.Comment: 22 pages (revtex4), 1 figure; v2: more detailed discussion on astrophysical applications in conclusion section, accepted for publication in Phys. Rev.

Direct calculation of the probability of pionium ionization in the target

We performed the first direct calculation of the probability of pionium (pi+pi- atom) ionization in the target. The dependence of the probability of pionium ionization in the target as a function of the pionium lifetime is established. These calculations are of interest of the DIRAC experiment at CERN, which aims to measure the pionium lifetime with high precision.Comment: 11 pages, 4 figures; submitted to "Physics of Atomic Nuclei" ("Yadernaya Fizika"

Density Matrix Kinetic Equation Describing a Passage of Fast Atomic Systems Through Matter

The quantum-mechanical consideration of a passage of fast dimesoatoms through matter is given. A set of quantum-kinetic equations for the density matrix elements describing their internal state evolution is derived. It is shown that probabilistic description of internal dynamics of hydrogen-like atoms is impossible even at sufficiently low energies because of the ``accidental'' degeneracy of their energy levels.Comment: 12 pages, LATEX, submitted to J. Phys.

Dynamics of the Pionium with the Density Matrix Formalism

The evolution of pionium, the $\pi^+ \pi^-$ hydrogen-like atom, while passing through matter is solved within the density matrix formalism in the first Born approximation. We compare the influence on the pionium break-up probability between the standard probabilistic calculations and the more precise picture of the density matrix formalism accounting for interference effects. We focus our general result in the particular conditions of the DIRAC experiment at CERN.Comment: 14 pages, 2 figures, submitted to J. Phys. B: At. Mol. Phy

THE INTERPLAY OF THE K+K- ATOM AND THE f_0(975) RESONANCE

We predict that production of the K+K- atom in pd-3^HeX and similar reactions exhibits a drastic missing mass spectrum due to the interplay with f_0(975) resonance. We point out that high precision studies of the K+K- atom may shed a new light on the nature of f_0(975).Comment: 13 page

Production of relativistic positronium in collisions of photons and electrons with nuclei and atoms

We consider the production of ultrarelativistic positronium (Ps) in $\gamma A \to Ps + A$ and $e A \to Ps + e A$ processes where $A$ is an atom or a nucleus with charge $Ze$. For the photoproduction of para- and ortho-Ps and the electroproduction of para-Ps we obtain the most complete description compared with previous works. It includes high order $Z \alpha$ corrections and polarization effects. The accuracy of the obtained cross sections is determined by omitted terms of the order of the inverse Ps Lorentz factor squared. The studied high order multi-photon electroproduction of ortho-Ps dominates for the collision of electrons with heavy atoms over the bremsstrahlung production from the electron via a virtual photon proposed by Holvik and Olsen. Our results complete and correct the studies of those authors.Comment: 19 pages, 9 figures, RevTex; v2: minor corrections for the accuracy of the results, a discussion of the literature added in a footnote, one additional reference; v3: diagram of Fig.2 correcte

Production of the Smallest QED Atom: True Muonium (mu^+ mu^-)

The "true muonium" (mu^+ mu-) and "true tauonium" (tau^+ tau^-) bound states are not only the heaviest, but also the most compact pure QED systems. The rapid weak decay of the tau makes the observation of true tauonium difficult. However, as we show, the production and study of true muonium is possible at modern electron-positron colliders.Comment: 4 pages, ReVTeX, 4 eps figures; minor wording changes and reordering of a reference. Version accepted by Phys. Rev. Let