109 research outputs found
Nuclear Breakup of Borromean Nuclei
We study the eikonal model for the nuclear-induced breakup of Borromean
nuclei, using Li11 and He6 as examples. The full eikonal model is difficult to
realize because of six-dimensional integrals, but a number of simplifying
approximations are found to be accurate. The integrated diffractive and
one-nucleon stripping cross sections are rather insensitive to the
neutron-neutron correlation, but the two-nucleon stripping does show some
dependence on the correlation. The distribution of excitation energy in the
neutron-core final state in one-neutron stripping reactions is quite sensitive
to the shell structure of the halo wave function. Experimental data favor
models with comparable amounts of s- and p-wave in the Li11 halo.Comment: 34 pages REVTeX, 14 postscript figures. Small changes in comparison
with experimen
Bremsstrahlung Pair Production In Relativistic Heavy Ion Collision
We calculate production of electron- and muon-pairs by the bremsstrahlung
process in hadron collisions and compare it with the dominant two-photon
process. Results for the total cross section are given for proton-proton and
heavy-ion collisions at energies of the Relativistic Heavy Ion Collider (RHIC)
and the Large Hadron Collider (LHC).Comment: 6 pages, Latex, 9 figures using epsf-style. Accepted for publication
in Z. Phys.
Mechanisms for Direct Breakup Reactions
We review some simple mechanisms of breakup in nuclear reactions. We mention
the spectator breakup, which is described in the post-form DWBA. The relation
to other formulations is also indicated. An especially important mechanism is
Coulomb dissociation. It is a distinct advantage that the perturbation due to
the electric field of the nucleus is exactly known. Therefore firm conclusions
can be drawn from such measurements. Some new applications of Coulomb
dissociation for nuclear astrophysics are discussed.Comment: 17 pages, 5 figures, to appear in the proceedings of the RCNP-TMU
Symposium on Spins in Nuclear and Hadronic Reactions, October 16-18 199
Biomechanical comparison of the track start and the modified one-handed track start in competitive swimming: an intervention study
This study compared the conventional track and a new one-handed track start in elite age group swimmers to determine if the new technique had biomechanical implications on dive performance. Five male and seven female GB national qualifiers participated (mean ± SD:
age 16.7 ± 1.9 years, stretched stature 1.76 ± 0.8 m, body mass 67.4 ± 7.9 kg) and were assigned to a control group (n = 6) or an intervention group (n = 6) that learned the new onehanded dive technique. All swimmers underwent a 4-week intervention comprising 12 ± 3 thirty-minute training sessions. Video cameras synchronized with an audible signal and timing suite captured temporal and kinematic data. A
portable force plate and load cell handrail mounted to a swim starting block collected force data over 3 trials of each technique. A MANCOVA identified Block Time (BT),
Flight Time (FT), Peak Horizontal Force of the lower limbs (PHF) and Horizontal Velocity at Take-off (Vx) as covariates. During the 10-m swim trial, significant differences were found in Time to 10 m (TT10m), Total Time (TT), Peak Vertical Force (PVF), Flight Distance (FD), and Horizontal Velocity at Take-off (Vx) (p < .05). Results indicated that the conventional track start method was faster over 10 m, and therefore may be seen as a superior start after a short intervention. During training, swimmers and coaches should focus on the most statistically significant dive performance variables: peak horizontal force and velocity at take-off, block and flight time
Multiple electromagnetic electron positron pair production in relativistic heavy ion collisions
We calculate the cross sections for the production of one and more
electron-positron pairs due to the strong electromagnetic fields in
relativistic heavy ion collisions. Using the generating functional of fermions
in an external field we derive the N-pair amplitude. Neglecting the
antisymmetrisation in the final state we find that the total probability to
produce N pairs is a Poisson distribution. We calculate total cross sections
for the production of one pair in lowest order and also include higher-order
corrections from the Poisson distribution up to third order. Furthermore we
calculate cross sections for the production of up to five pairs including
corrections from the Poisson distribution.Comment: 13 pages REVTeX, 4 Postscript figures, This and related papers may
also be obtained from http://www.phys.washington.edu/~hencken
Electromagnetic Dissociation as a Tool for Nuclear Structure and Astrophysics
Coulomb dissociation is an especially simple and important reaction
mechanism. Since the perturbation due to the electric field of the nucleus is
exactly known, firm conclusions can be drawn from such measurements.
Electromagnetic matrix elements and astrophysical S-factors for radiative
capture processes can be extracted from experiments. We describe the basic
theory, new results concerning higher order effects in the dissociation of
neutron halo nuclei, and briefly review the experimental results obtained up to
now. Some new applications of Coulomb dissociation for nuclear astrophysics and
nuclear structure physics are discussed.Comment: 10 pages, 1 figure, to appear in Proceedings of the International
School on Nuclear Physics; 22nd Course: ``Radioactive Beams for Nuclear and
Astro Physics'', Erice/Sicily/Italy, September 16 - 24, 200
Coherent photon-photon interactions in very peripheral relativistic heavy ion collisions
Heavy ions at high velocities provide very strong electromagnetic fields for
a very short time. The main characteristics of ultraperipheral relativistic
heavy ion collisions are reviewed, characteristic parameters are identified.
The main interest in ultraperipheral heavy ion collisions at relativistic ion
colliders like the LHC is the interactions of very high energy (equivalent)
photons with the countermoving (equivalent) photons and hadrons (protons/ions).
The physics of these interactions is quite different from and complementary to
the physics of the strong fields achieved with current and future lasers.Comment: 5 pages, 5 figures, invited talk presented at the ELI Workshop and
School on Fundamental Physics with Ultra-high Fields (September 29- October
2, 2008, Frauenwoerth, German
Coherent and incoherent atomic scattering: Formalism and application to pionium interacting with matter
The experimental determination of the lifetime of pionium provides a very
important test on chiral perturbation theory. This quantity is determined in
the DIRAC experiment at CERN. In the analysis of this experiment, the breakup
probabilities of of pionium in matter are needed to high accuracy as a
theoretical input. We study in detail the influence of the target electrons.
They contribute through screening and incoherent effects. We use Dirac-Hartree-
Fock-Slater wavefunctions in order to determine the corresponding form factors.
We find that the inner-shell electrons contribute less than the weakly bound
outer electrons. Furthermore, we establish a more rigorous estimate for the
magnitude of the contributions form the transverse current (magnetic terms thus
far neglected in the calculations).Comment: Journal of Physics B: Atomic, Molecular and Optical Physics;
(accepted; 22 pages, 6 figures, 26 references) Revised version: more detailed
description of DIRAC experiment; failure of simplest models for incoherent
scattering demonstrated by example
Nuclear breakup of Borromean nuclei
We study the eikonal model for the nuclear-induced breakup of Borromean nuclei, using 11 Li and 6 He as examples. The full eikonal model is difficult to realize because of six-dimensional integrals, but a number of simplifying approximations are found to be accurate. The integrated diffractive and one-nucleon stripping cross sections are rather insensitive to the neutron-neutron correlation, but the two-nucleon stripping does show some dependence on the correlation. The distribution of excitation energy in the neutron-core final state in oneneutron stripping reactions is quite sensitive to the shell structure of the halo wave function. Experimental data favor models with comparable amounts of s and p waves in the 11 Li halo. ͓S0556-2813͑98͒03503-1͔ PACS number͑s͒: 25.60. Gc, 25.70.Mn, 21.45.ϩv, 27.20.ϩ
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