2,739 research outputs found
Unexpected features of e+e-->ppbar and e+e-->lambda-lambdabar cross sections near threshold
Unexpected features of the BaBar data on e+e- in baryon-antibaryon cross
sections are discussed. These data have been collected, with unprecedented
accuracy, by means of the initial state radiation technique, which is
particularly suitable in giving good acceptance and energy resolution at
threshold. A striking feature observed in the BaBar data is the non-vanishing
cross section at threshold for all these processes. This is the expectation due
to the Coulomb enhancement factor acting on a charged fermion pair. In the case
of e+e- in proton-antiproton it is found that Coulomb final state interactions
largely dominate the cross section and the form factor is |G^p(4M^2_p)|~1,
which could be a general feature for baryons. In the case of neutral baryons an
interpretation of the non-vanishing cross section at threshold is suggested,
based on quark electromagnetic interaction and taking into account the
asymmetry between attractive and repulsive Coulomb factors. Besides strange
baryon cross sections are compared to U-spin invariance predictions.Comment: 12 pages, 11 figure
A practical guide to unravel time-like transition form factors
A method to determine masses, widths and coupling constants of vector mesons,
like phi(1020), omega(782) and rho0(770) recurrences is defined. Starting from
data on decay rates and cross sections for the processes: phi -> M_I gamma, phi
-> M_I e+e- and e+e- -> M_I phi, where M_I is a pseudoscalar or scalar meson
with isospin I=0,1, the time-like transition form factors, which describe the
vertex phi-gamma-M_I, are parametrized using a vector meson-propagators
description in the low energy region <3-4 GeV, the quark-counting rule
prescription for the high energy behavior, and the analyticity imposed by means
of the dispersion relations.Comment: 20 pages, 15 eps figure
Hunting for asymptotia at LHC
We discuss whether the behaviour of some hadronic quantities, such as the
total cross-section, the ratio of the elastic to the total cross-section, are
presently exhibiting the asymptotic behaviour expected at very large energies.
We find phenomenological evidence that at LHC7 there is still space for further
evolution.Comment: 5 pages, 2 figures, talk given by G. Pancheri at International
Workshop on Diffraction in High-Energy Physics, DIFFRACTION 2012, Puerto del
Carmen, Canary Islands, Spain. To appear in AIP Conf. Pro
Baryon Form Factors at Threshold
An extensive study of the e + e − → p p ¯ BaBar cross section data is presented. Two unexpected outcomes have been found: the modulus of the proton form factor is normalized to one at threshold, i.e.: | G p ( 4 M p 2 ) | = 1 , as a pointlike fermion, and the resummation factor in the Sommerfeld formula is not needed. Other e+e− → baryon-antibaryon cross sections show a similar behavior near threshold
Comments on ISR method in modern experiment and influence of final state radiation
We study the effect of final state radiation in the process , in the kinematical conditions of BaBar and BESIII experiment. We show
that this effect could be large, in particular in the low region ( is
the photon energy fraction) and should be taken into account.Comment: 8 pages, 5 figure
Asymptotia for total and elastic pp and ¯pp cross-sections
We discuss recent LHC data for total and elastic pp scattering collected at √s = 7TeV through the asymptotic properties of the scattering amplitude, such as saturation of the Froissart bound and the black-disk limit. A simple model with two exponentials and a phase is used to describe the elastic differential crosssection for both pp and ¯pp and test two asymptotic rules derived from the hypothesis of total absorption
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