62 research outputs found
On the rise of proton-proton cross-sections at high energies
The rise of the total, elastic and inelastic hadronic cross sections at high
energies is investigated by means of an analytical parametrization, with the
exponent of the leading logarithm contribution as a free fit parameter. Using
derivative dispersion relations with one subtraction, two different fits to
proton-proton and antiproton-proton total cross section and rho parameter data
are developed, reproducing well the experimental information in the energy
region 5 GeV - 7 TeV. The parametrization for the total cross sections is then
extended to fit the elastic (integrated) cross section data in the same energy
region, with satisfactory results. From these empirical results we extract the
energy dependence of several physical quantities: inelastic cross section,
ratios elastic/total, inelastic/total cross sections, ratio
total-cross-section/elastic-slope, elastic slope and optical point. All data,
fitted and predicted, are quite well described. We find a statistically
consistent solution indicating: (1) an increase of the hadronic cross sections
with the energy faster than the log-squared bound by Froissart and Martin; (2)
asymptotic limits 1/3 and 2/3 for the ratios elastic/total and inelastic/total
cross sections, respectively, a result in agreement with unitarity. These
indications corroborate recent theoretical arguments by Ya. I. Azimov on the
rise of the total cross section.Comment: 35 pages, 12 figures, discussions improved with further
clarifications, references added and updated, one note added, results and
conclusions unchanged. Version to be published in J. Phys. G: Nucl. Part.
Phy
CORE Technology and Exact Hamiltonian Real-Space Renormalization Group Transformations
The COntractor REnormalization group (CORE) method, a new approach to solving
Hamiltonian lattice systems, is presented. The method defines a systematic and
nonperturbative means of implementing Kadanoff-Wilson real-space
renormalization group transformations using cluster expansion and contraction
techniques. We illustrate the approach and demonstrate its effectiveness using
scalar field theory, the Heisenberg antiferromagnetic chain, and the
anisotropic Ising chain. Future applications to the Hubbard and t-J models and
lattice gauge theory are discussed.Comment: 65 pages, 9 Postscript figures, uses epsf.st
Analytic models and forward scattering from accelerator to cosmic-ray energies
Analytic models for hadron-hadron scattering are characterized by analytical
parametrizations for the forward amplitudes and the use of dispersion relation
techniques to study the total cross section and the
parameter. In this paper we investigate four aspects related to the application
of the model to and scattering, from accelerator to cosmic-ray
energies: 1) the effect of different estimations for from
cosmic-ray experiments; 2) the differences between individual and global
(simultaneous) fits to and ; 3) the role of the
subtraction constant in the dispersion relations; 4) the effect of distinct
asymptotic inputs from different analytic models. This is done by using as a
framework the single Pomeron and the maximal Odderon parametrizations for the
total cross section. Our main conclusions are the following: 1) Despite the
small influence from different cosmic-ray estimations, the results allow us to
extract an upper bound for the soft pomeron intercept: ;
2) although global fits present good statistical results, in general, this
procedure constrains the rise of ; 3) the subtraction constant as
a free parameter affects the fit results at both low and high energies; 4)
independently of the cosmic-ray information used and the subtraction constant,
global fits with the odderon parametrization predict that, above GeV, becomes greater than , and
this result is in complete agreement with all the data presently available. In
particular, we infer at GeV and
at 500 GeV (BNL RHIC energies).Comment: 16 pages, 7 figures, aps-revtex, wording changes, corrected typos, to
appear in Physical Review
Effective Regge QCD
A new framework for a high energy limit of quantum gauge field theories is
introduced. Its potency is illustrated on a new derivation of the reggeization
of the gluon.Comment: Latex, 9 pages + 2 figures as PS-file, extended version, to appear in
Phys. Rev. Let
Deep inelastic events containing a forward photon as a probe of small dynamics
We calculate the rate of producing deep inelastic events containing an
energetic isolated forward photon at HERA. We quantify the enhancement arising
from the leading gluon emissions with a view to using such events to
identify the underlying dynamics.Comment: 11 pages, Latex, 7 ps figure
A unified BFKL and GLAP description of data
We argue that the use of the universal unintegrated gluon distribution and
the (or high energy) factorization theorem provides the natural framework
for describing observables at small x. We introduce a coupled pair of evolution
equations for the unintegrated gluon distribution and the sea quark
distribution which incorporate both the resummed leading BFKL
contributions and the resummed leading GLAP contributions. We solve
these unified equations in the perturbative QCD domain using simple parametic
forms of the nonperturbative part of the integrated distributions. With only
two (physically motivated) input parameters we find that this
factorization approach gives an excellent description of the measurements of
at HERA. In this way the unified evolution equations allow us to
determine the gluon and sea quark distributions and, moreover, to see the x
domain where the resummed effects become significant. We use
factorization to predict the longitudinal structure function and
the charm component of .Comment: 25 pages, LaTeX, 9 figure
Accuracy of Malaria Rapid Diagnostic Tests in Community Studies and their Impact on Treatment of Malaria in an Area with Declining Malaria Burden in North-Eastern Tanzania.
Despite some problems related to accuracy and applicability of malaria rapid diagnostic tests (RDTs), they are currently the best option in areas with limited laboratory services for improving case management through parasitological diagnosis and reducing over-treatment. This study was conducted in areas with declining malaria burden to assess; 1) the accuracy of RDTs when used at different community settings, 2) the impact of using RDTs on anti-malarial dispensing by community-owned resource persons (CORPs) and 3) adherence of CORPs to treatment guidelines by providing treatment based on RDT results. Data were obtained from: 1) a longitudinal study of passive case detection of fevers using CORPs in six villages in Korogwe; and 2) cross-sectional surveys (CSS) in six villages of Korogwe and Muheza districts, north-eastern, Tanzania. Performance of RDTs was compared with microscopy as a gold standard, and factors affecting their accuracy were explored using a multivariate logistic regression model. Overall sensitivity and specificity of RDTs in the longitudinal study (of 23,793 febrile cases; 18,154 with microscopy and RDTs results) were 88.6% and 88.2%, respectively. In the CSS, the sensitivity was significantly lower (63.4%; Ï2=367.7, p<0.001), while the specificity was significantly higher (94.3%; Ï2=143.1, p<0.001) when compared to the longitudinal study. As determinants of sensitivity of RDTs in both studies, parasite density of<200 asexual parasites/ÎŒl was significantly associated with high risk of false negative RDTs (ORâ„16.60, p<0.001), while the risk of false negative test was significantly lower among cases with fever (axillary temperature â„37.5 °C) (ORâ€0.63, pâ€0.027). The risk of false positive RDT (as a determinant of specificity) was significantly higher in cases with fever compared to afebrile cases (ORâ„2.40, p<0.001). Using RDTs reduced anti-malarials dispensing from 98.9% to 32.1% in cases aged â„5 years. Although RDTs had low sensitivity and specificity, which varied widely depending on fever and parasite density, using RDTs reduced over-treatment with anti-malarials significantly. Thus, with declining malaria prevalence, RDTs will potentially identify majority of febrile cases with parasites and lead to improved management of malaria and non-malaria fevers
Possible probe of the QCD odderon singularity through the quasidiffractive eta_c production in gamma-gamma collisions
The reactions gamma-gamma to eta_c eta_c and gamma gamma to eta_c + X are
discussed within the three gluon exchange model. We give predictions for the
differential cross-sections and discuss feasibility of measuring these
processes at LEP2 and TESLA. The total cross-sections were estimated to be
approximately equal to 40 fb and 120 fb for gamma-gamma to eta_c eta_c and
gamma-gamma to eta_c + X respectively assuming exchange of elementary gluons
that corresponds to the odderon with intercept equal to unity. These values can
be enhanced by a factor equal to 1.9 and 2.1 for LEP2 and TESLA energies if the
odderon intercept is equal to 1.07. The estimate of cross-sections sigma(e^+
e^- to e^+ e^- eta_c eta_c) and sigma (e^+ e^- to e^+ e^- eta_c + X) for
untagged e^+ and e^- is also given.Comment: 11 pages, Latex, epsf, 5 eps figures include
The Triangle Anomaly in Triple-Regge Limits
Reggeized gluon interactions due to a single quark loop are studied in the
full triple-regge limit and in closely related helicity-flip helicity-pole
limits. Triangle diagram reggeon interactions are generated that include local
axial-vector effective vertices. It is shown that the massless quark triangle
anomaly is present as a chirality-violating infra-red divergence in the
interactions generated by maximally non-planar Feynman diagrams. An asymptotic
dispersion relation formalism is developed which provides a systematic counting
of anomaly contributions. The asymptotic amplitude is written as a sum over
dispersion integrals of triple discontinuities, one set of which is unphysical
and can produce chirality transitions. The physical-region anomaly appears in
the generalized real parts, determined by multi-regge theory, of the unphysical
discontinuities. The amplitudes satisfy a signature conservation rule that
implies color parity is not conserved by vertices containing the anomaly. In
the scattering of elementary quarks or gluons the signature and color parity of
the exchanged reggeon states are such that the anomaly cancels. At
lowest-order, it cancels in individual diagrams after the transverse momentum
integrations are performed.Comment: 116 pages, with 66 ps figures in the tex
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