24,631 research outputs found
k_T factorization is violated in production of high-transverse-momentum particles in hadron-hadron collisions
We show that hard-scattering factorization is violated in the production of
high-p_T hadrons in hadron-hadron collisions, in the case that the hadrons are
back-to-back, so that k_T factorization is to be used. The explicit
counterexample that we construct is for the single-spin asymmetry with one beam
transversely polarized. The Sivers function needed here has particular
sensitivity to the Wilson lines in the parton densities. We use a greatly
simplified model theory to make the breakdown of factorization easy to check
explicitly. But the counterexample implies that standard arguments for
factorization fail not just for the single-spin asymmetry but for the
unpolarized cross section for back-to-back hadron production in QCD in
hadron-hadron collisions. This is unlike corresponding cases in e^+e^-
annihilation, Drell-Yan, and deeply inelastic scattering. Moreover, the result
endangers factorization for more general hadroproduction processes.Comment: 10 pages. V. 2: Title change, misprints and minor corrections, as in
journal versio
Nonlinearity of vacuum reggeons and exclusive diffractive production of vector mesons at HERA
The processes of exclusive photo- and electroproduction of vector mesons
(770), (1020) and (3096) at collision energies and transferred momenta squared are considered in
the framework of a phenomenological Regge-eikonal scheme with nonlinear Regge
trajectories in which their QCD asymptotic behavior is taken into account
explicitly. By comparison of available experimental data from ZEUS and H1
Collaborations with the model predictions it is demonstrated that corresponding
angular distributions and integrated cross-sections in the above-mentioned
kinematical range can be quantitatively described with use of two -even
vacuum Regge trajectories. These are the "soft" pomeron dominating the high
energy reactions without a hard scale and the "hard" pomeron giving an
essential contribution to photo- and electroproduction of heavy vector mesons
and deeply virtual electroproduction of light vector mesons.Comment: 25 pages, 12 figure
Gravireggeons and transplanckian scattering in models with one extra dimension
The inelastic scattering of the brane fields induced by -channel
gravireggeons exchanges in the RS model with a small curvature is
considered, and the imaginary part of the eikonal is analytically calculated.
It is demonstrated that the results can be obtained from the corresponding
formulae previously derived in the ADD model with one extra dimension of the
size by formal replacement . The inelastic
cross section for the scattering of ultra-high neutrino off the nucleon is
numerically estimated for the case TeV, where
is a reduced Planck scale in five warped dimensions.Comment: 17 pages, LaTeX2e, 3 eps figure
The Transversity Function and Double Spin Azimuthal Asymmetry in Semi-Inclusive Pion Leptoproduction
We show that the transverse momentum dependent transversity function is
proportional to the longitudinal polarization of a quark in a transversely
polarized proton. This result suggests an alternative, convenient method for
determining transversity, without knowing unusual fragmentation functions. The
method consists of measuring the double spin azimuthal asymmetry in
semi-inclusive pion leptoproduction by a transversely polarized proton target.
The asymmetry, which is twist 3, is estimated to be more than 10% under the
most favorable conditions. The experiment we suggest is feasible at facilities
like DESY and CERN.Comment: extended version; to appear on Int. Jou. Mod. Phys.
Physiologic observations on race car drivers
Physiological and biochemical responses of race car drivers under nonsimulated environmental stres
A stochastic model for early placental development
In the human, placental structure is closely related to placental function and consequent pregnancy outcome. Studies have noted abnormal placental shape in small-for-gestational age infants which extends to increased lifetime risk of cardiovascular disease. The origins and determinants of placental shape are incompletely under-stood and are difficult to study in vivo. In this paper we model the early development of the placenta in the human, based on the hypothesis that this is driven by dynamics dominated by a chemo-attractant effect emanating from proximal spiral arteries in the decidua. We derive and explore a two-dimensional stochastic model for these events, and investigate the effects of loss of spiral arteries in regions near to the cord insertion on the shape of the placenta. This model demonstrates that placental shape is highly variable and disruption of spiral arteries can exert profound effects on placental shape, particularly if this disruption is close to the cord insertion. Thus, placental shape reflects the underlying maternal vascular bed. Abnormal placental shape may reflect an abnormal uterine environment, which predisposes to pregnancy complications
Transverse momentum dependent distribution functions in a covariant parton model approach with quark orbital motion
Transverse parton momentum dependent distribution functions (TMDs) of the
nucleon are studied in a covariant model, which describes the intrinsic motion
of partons in terms of a covariant momentum distribution. The consistency of
the approach is demonstrated, and model relations among TMDs are studied. As a
byproduct it is shown how the approach allows to formulate the non-relativistic
limit.Comment: 16 page
Hard-scattering factorization with heavy quarks: A general treatment
A detailed proof of hard scattering factorization is given with the inclusion
of heavy quark masses. Although the proof is explicitly given for
deep-inelastic scattering, the methods apply more generally The
power-suppressed corrections to the factorization formula are uniformly
suppressed by a power of \Lambda/Q, independently of the size of heavy quark
masses, M, relative to Q.Comment: 52 pages. Version as published plus correction of misprint in Eq.
(45
Sivers effect in Drell Yan at RHIC
On the basis of a fit to the Sivers effect in deep-inelastic scattering, we
make predictions for single-spin asymmetries in the Drell-Yan process at RHIC.Comment: 10 pages, 7 figures, 1 table. v2: References and comments added,
minor correction
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