48 research outputs found
Hadron Diffractive Processes: the Structure of Soft Pomeron and Colour Screening
On the basis of the experimental data on diffractive processes in ,
and collisions at intermediate, moderately high and high
energies, we restore the scattering amplitude related to the -channel
exchange by vacuum quantum numbers by taking account of the diffractive
-channel rescatterings. At intermediate and moderately high energies, the
-channel exchange amplitude turns, with a good accuracy, into an effective
pomeron which renders the results of the additive quark model. At superhigh
energies the scattering amplitude provides a Froissart-type behaviour, with an
asymptotic universality of cross sections such as at . The quark structure of hadrons
being taken into account at the level of constituent quarks, the cross sections
of pion and proton (antiproton) in the impact parameter space of quarks,
and , are found as functions of
. These cross sections implicate the phenomenon of colour screening: they
tend to zero at . The effective colour
screening radius for pion (proton) is found for different . The predictions
for the diffractive cross sections at superhigh energies are presented.Comment: LaTeX, epsfig.st
Phenomenological analysis of the double pion production in nucleon-nucleon collisions up to 2.2 GeV
With an effective Lagrangian approach, we analyze several NN \to NN\pi\pi
channels by including various resonances with mass up to 1.72 GeV. For the
channels with the pion pair of isospin zero, we confirm the dominance of
N*(1440)\to N\sigma in the near threshold region. At higher energies and for
channels with the final pion pair of isospin one, we find large contributions
from N*(1440)\to \Delta\pi, double-Delta, \Delta(1600) \to N*(1440)\pi,
\Delta(1600) \to \Delta\pi and \Delta(1620) \to \Delta\pi. There are also
sizeable contributions from \Delta \to \Delta\pi, \Delta \to N\pi, N \to
\Delta\pi and nucleon pole at energies close to the threshold. We well
reproduce the total cross sections up to beam energies of 2.2 GeV except for
the pp\to pp\pi^0\pi^0 channel at energies around 1.1 GeV and our results agree
with the existing data of differential cross sections of pp \to pp\pi^+\pi^-,
pp \to nn\pi^+\pi^+ and pp \to pp\pi^0\pi^0 which are measured at CELSIUS and
COSY.Comment: 36 pages, 18 figure
D^+_s -> pi^+ pi^+ pi^- decay: the 1^3P_0 s anti-s component in scalar-isoscalar mesons
On the basis of data on the decay D^+_s -> pi^+ pi^+ pi^-, which goes
dominantly via the transition D_s -> pi^+ s anti-s, we evaluate the 1^3P_0 s
anti-s components in the scalar-isoscalar resonances f0(980), f0(1300),
f0(1500) and broad state f0(1200-1600)$. The data point to a large s anti-s
component in the f0(980): 40% < s anti-s < 70%. Nearly 30% of the 1^3P_0 s
anti-s component flows to the mass region 1300-1500 MeV being shared by
f0(1300), f0(1500) and broad state f0(1200-1600): the interference of these
states results in a peak near 1400 MeV with the width around 200 MeV.Comment: 17 pages, 4 figures, epsfi
Pomeron in diffractive processes and at large Q^2: the onset of pQCD
We study the reactions and
at large Q^2 and and small
momentum transfer, , to the nucleon where the pomeron exchange
dominates. At large Q^2 the virtual photon selects a hard pair, thus
selecting the hard pomeron component (the BFKL pomeron). The amplitudes for
both transverse and longitudinal polarizations of the initial photon and
outgoing -meson (photon) are calculated in the framework of the BFKL
pomeron exchange. Our calculations show that one cannot expect the early onset
of the pure perturbative regime in the discussed diffractive processes: the
small interquark distances, fm, start to dominate not
earlier than at in
and in
.Comment: 20 pages, LaTeX, epsfig.st
Luminosity determination for the pd reaction at 2.14 GeV with WASA-at-COSY
The luminosity for a WASA-at-COSY experiment involving the pd reaction at
2.14 GeV proton-beam energy is determined by the forward pd elastic scattering,
which yields an average beam-on-target value of
[5.2\pm0.3(stat)\pm0.3(syst)]*10^{30} s^{-1}cm^{-2}. In addition, the forward
pd elastic-scattering angular distribution is obtained with four-momentum
transfer squared -t between 0.16 (GeV/c)^{2} and 0.78 (GeV/c)^{2} at this beam
energy, which is compared with other experimental data and the pd double
scattering model.Comment: 5 pages, 6 figure
The study of the negative pion production in neutron-proton collisions at beam momenta below 1.8 GeV/c
A detailed investigation of the reaction np -> pp\pi^{-} has been carried out
using the data obtained with the continuous neutron beam produced by charge
exchange scattering of protons off a deuterium target. A partial wave
event-by-event based maximum likelihood analysis was applied to determine
contributions of different partial waves to the pion production process. The
combined analysis of the np -> pp\pi^{-} and pp -> pp\pi^{0} data measured in
the same energy region allows us to determine the contribution of isoscalar
partial waves (I=0) in the momentum range from 1.1 up to 1.8 GeV/c. The decay
of isoscalar partial waves into (^1S_0)_{pp}\pi$ channel provides a good tool
for a determination of the pp S-wave scalar scattering length in the final
state which was found to be a_{pp}=-7.5\pm 0.3 fm.Comment: 6 pages, 6 figure
Charmed quark component of the photon wave function
We determine the c-anti-c component of the photon wave function on the basis
of (i) the data on the transitions e+ e- -> J/psi(3096), psi(3686), psi(4040),
psi(4415), (ii) partial widths of the two-photon decays eta_{c0}(2979),
chi_{c0}(3415), chi_{c2}(3556) -> gamma-gamma, and (iii) wave functions of the
charmonium states obtained by solving the Bethe-Salpeter equation for the
c-anti-c system. Using the obtained c-anti-c component of the photon wave
function we calculate the gamma-gamma decay partial widths for radial
excitation 2S state, eta_{c0}(3594) -> gamma-gamma, and 2P states
chi_{c0}(3849), chi_{c2}(3950) -> gamma-gamma.Comment: 20 pages, 8 figure
Quark--antiquark states and their radiative transitions in terms of the spectral integral equation. {\Huge III.} Light mesons
We continue the investigation of mesons in terms of the spectral integral
equation initiated before [hep-ph/0510410, hep-ph/0511005] for the
and systems: in this paper we consider the light-quark ()
mesons with masses GeV. The calculations have been performed for the
mesons lying on linear trajectories in the -planes, where is the
radial quantum number. Our consideration relates to the states with
one component in the flavor space, with the quark and antiquark masses equal to
each other, such as , , ,
, , , , ,
, , , ,
, at . We obtained the wave functions
and mass values of mesons lying on these trajectories. The corresponding
trajectories are linear, in agreement with data. We have calculated the
two-photon decays , ,
, , and radiative transitions ,
, that agree qualitatively with the experiment. On this
basis, we extract the singular part of the interaction amplitude, which
corresponds to the so-called "confinement interaction". The description of the
data requires the presence of the strong -channel singularities for both
scalar and vector exchanges.Comment: 48 pages, 24 figure