12,538 research outputs found
Forward pion production at large transverse momenta in pp collisions and beyond
The inclusive production of high-p_\perp particles (pions) in the beam
fragmentation regions of high-energy hadronic collisions is driven by the
breakup of valence constituents of the beam hadrons into their two-body
Fock-state components,and their subsequent fragmentation. We briefly discuss an
approach, that allows the consistent inclusion of intrinsic and radiatively
generated transverse momenta of initial state partons, and describe an
extension of our approach to nuclear targets.Comment: Talk given at MESON2006, Cracow, June 2006, 4 pages, 1 fi
Binary Black Hole Coalescence in Semi-Analytic Puncture Evolution
Binary black-hole coalescence is treated semi-analytically by a novel
approach. Our prescription employs the conservative Skeleton Hamiltonian that
describes orbiting Brill-Lindquist wormholes (termed punctures in Numerical
Relativity) within a waveless truncation to the Einstein field equations [G.
Faye, P. Jaranowski and G. Sch\"afer, Phys. Rev. D {\bf 69}, 124029 (2004)]. We
incorporate, in a transparent Hamiltonian way and in Burke-Thorne gauge
structure, the effects of gravitational radiation reaction into the above
Skeleton dynamics with the help of 3.5PN accurate angular momentum flux for
compact binaries in quasi-circular orbits to obtain a Semi-Analytic Puncture
Evolution to model merging black-hole binaries. With the help of the TaylorT4
approximant at 3.5PN order, we perform a {\it first-order} comparison between
gravitational wave phase evolutions in Numerical Relativity and our approach
for equal-mass binary black holes. This comparison reveals that a modified
Skeletonian reactive dynamics that employs flexible parameters will be required
to prevent the dephasing between our scheme and Numerical Relativity, similar
to what is pursued in the Effective One Body approach. A rough estimate for the
gravitational waveform associated with the binary black-hole coalescence in our
approach is also provided.Comment: 16 pages, 5 figure
A minimal no-radiation approximation to Einstein's field equations
An approximation to Einstein's field equations in Arnowitt-Deser-Misner (ADM)
canonical formalism is presented which corresponds to the magneto-hydrodynamics
(MHD) approximation in electrodynamics. It results in coupled elliptic
equations which represent the maximum of elliptic-type structure of Einstein's
theory and naturally generalizes previous conformal-flat truncations of the
theory. The Hamiltonian, in this approximation, is identical with the
non-dissipative part of the Einsteinian one through the third post-Newtonian
order. The proposed scheme, where stationary spacetimes are exactly reproduced,
should be useful to construct {\em realistic} initial data for general
relativistic simulations as well as to model astrophysical scenarios, where
gravitational radiation reaction can be neglected.Comment: 9 page
Production of Z^0 bosons with rapidity gaps: exclusive photoproduction in gamma p and p p collisions and inclusive double diffractive Z^0's
We extend the k_\perp-factorization formalism for exclusive photoproduction
of vector mesons to the production of electroweak Z^0 bosons. Predictions for
the gamma p \to Z^0 p and p p \to p p Z^0 reactions are given using an
unintegrated gluon distribution tested against deep inelastic data. We present
distributions in the Z^0 rapidity, transverse momentum of Z^0 as well as in
relative azimuthal angle between outgoing protons. The contributions of
different flavours are discussed. Absorption effects lower the cross section by
a factor of 1.5-2, depending on the Z-boson rapidity. We also discuss the
production of Z^0 bosons in central inclusive production. Here rapidity and
(x_{\Pom,1}, x_{\Pom,2}) distributions of Z^0 are calculated. The corresponding
cross section is about three orders of magnitude larger than that for the
purely exclusive process.Comment: 19 pages, 14 figs, A. Cisek is married name of A. Rybarsk
Nonuniversality Aspects of Nonlinear k_\perp-factorization for Hard Dijets
The origin of the breaking of conventional linear k_\perp-factorization for
hard processes in a nuclear environment is by now well established. The
realization of the nonlinear nuclear k_\perp-factorization which emerges
instead was found to change from one jet observable to another. Here we
demonstrate how the pattern of nonlinear k_\perp-factorization, and especially
the role of diffractive interactions, in the production of dijets off nuclei
depends on the color properties of the underlying pQCD subprocess.Comment: 4 pages, 1 eps-fi
- …