281 research outputs found
Final state interaction contribution to the response of confined relativistic particles
We report studies of the response of a massless particle confined by a
potential. At large momentum transfer q it exhibits \tilde{y} or equivalently
Nachtmann \xi scaling, and acquires a constant width independent of q. This
width has a contribution from the final state interactions of the struck
particle, which persists in the q->\infty limit. The width of the response
predicted using plane wave impulse approximation is smaller because of the
neglect of final state interactions in that approximation. However, the exact
response may be obtained by folding the approximate response with a function
representing final state interaction effects. We also study the response
obtained from the momentum distribution assuming that the particle is on the
energy shell both before and after being struck. Quantitative results are
presented for the special case of a linear confining potential. In this case
the response predicted with the on-shell approximation has correct values for
the total strength, mean energy and width, however its shape is wrong.Comment: 11 pages, 3 figures, submitted to Phys. Rev.
Anomalous Soft Photons in Hadron Production
Anomalous soft photons in excess of what is expected from electromagnetic
bremsstrahlung have been observed in association with the production of
hadrons, mostly mesons, in high-energy (K+)p, (pi+)p, (pi-)p, pp, and (e+)(e-)
collisions. We propose a model for the simultaneous production of anomalous
soft photons and mesons in quantum field theory, in which the meson production
arises from the oscillation of color charge densities of the quarks of the
underlying vacuum in the flux tube. As a quark carries both a color charge and
an electric charge, the oscillation of the color charge densities will be
accompanied by the oscillation of electric charge densities, which will in turn
lead to the simultaneous production of soft photons during the meson production
process. How the production of these soft photons may explain the anomalous
soft photon data will be discussed. Further experimental measurements to test
the model will be proposed.Comment: 19 pages, 2 figures, to be published in Physical Review
CP Violation and the Width
We discuss the effect of CP-violating , and
couplings on the width . The
presence of such couplings leads in a natural way to an increase of this width
relative to the prediction of the standard model. Various strategies of a
direct search for such CP-violating couplings by using CP-odd observables are
outlined. The number of bosons required to obtain significant information
on the couplings in this way is well within the reach of present LEP
experiments.Comment: 18 pages, LaTeX, no figure
Testing Anomalous Color-Electric Dipole Moment of the c-Quark from psi'->J/psi+pi(+)+pi(-) at Beijing Spectrometer
If the c-quark has an anomalous color-electric dipole moment (CEDM), it may
serve as a new source of CP violation. The strength of such a CP violation
depends on the size of the CEDM, d'_c. We propose two effective ways of testing
it from the large sample of psi'->J/psi+pi(+)+pi(-) at the Beijing
Spectrometer, and the obtained result, |d'_c|<3X10^{-14} e cm (95% C.L.), gives
the first experimentally determined upper bound on the CEDM of the c quark.Comment: 26 pages RevTex4 file with 4 eps files for the figures. Some
discussions and new references adde
Modified Wandzura-Wilczek Relation with the Nachtmann Variable
If one retains M^2/Q^2 terms in the kinematics, the Nachtmann variable \xi
seems to be more appropriate to describe deep inelastic lepton-nucleon
scattering. Up to the first power of M^2/Q^2, a modified Wandzura-Wilczek
relation with respect to \xi was derived. Kinematical correction factors are
given as functions of \xi and Q^2. A comparison of the modified g_2^WW(\xi) and
original g_2^WW(x) with the most recent g_2 data is shown.Comment: 10 pages, 3 figures, revised version with minor correction
Soft Photons in Hadron-Hadron Collisions: Synchrotron Radiation from the QCD Vacuum?
We discuss the production of soft photons in high energy hadron-hadron
collisions. We present a model where quarks and antiquarks in the hadrons emit
``synchrotron light'' when being deflected by the chromomagnetic fields of the
QCD vacuum, which we assume to have a nonperturbative structure. This gives a
source of prompt soft photons with frequencies in the c.m.
system of the collision in addition to hadronic bremsstrahlung. In comparing
the frequency spectrum and rate of ``synchrotron'' photons to experimental
results we find some supporting evidence for their existence. We make an
exclusive--inclusive connection argument to deduce from the ``synchrotron''
effect a behaviour of the neutron electric formfactor proportional
to for . We find this to be consistent with
available data. In our view, soft photon production in high energy
hadron-hadron and lepton-hadron collisions as well as the behaviour of
electromagnetic hadron formfactors for low are thus sensitive probes of
the nonperturbative structure of the QCD vacuum.Comment: Heidelberg preprint HD-THEP-94-36, 31 pages, LaTeX + ZJCITE.sty
(included), 12 figures appended as uuencoded compressed ps-fil
Determining the global minimum of Higgs potentials via Groebner bases - applied to the NMSSM
Determining the global minimum of Higgs potentials with several Higgs fields
like the next-to-minimal supersymmetric extension of the Standard Model (NMSSM)
is a non-trivial task already at the tree level. The global minimum of a Higgs
potential can be found from the set of all its stationary points defined by a
multivariate polynomial system of equations. We introduce here the algebraic
Groebner basis approach to solve this system of equations. We apply the method
to the NMSSM with CP conserving as well as CP violating parameters. The results
reveal an interesting stationary-point structure of the potential. Requiring
the global minimum to give the electroweak symmetry breaking observed in Nature
excludes large parts of the parameter space.Comment: 10 pages, 2 figure
Jet lag effect and leading hadron production
We propose a solution for the long standing puzzle of a too steeply falling
fragmentation function for a quark fragmenting into a pion, calculated by
Berger [1] in the Born approximation. Contrary to the simple anticipation that
gluon resummation worsens the problem, we find good agreement with data. Higher
quark Fock states slow down the quark, an effect which we call jet lag. It can
be also expressed in terms of vacuum energy loss. As a result, the space-time
development of the jet shrinks and the -dependence becomes flatter than in
the Born approximation. The space-time pattern is also of great importance for
in-medium hadronization.Comment: 11 pages, 5 figure
Odd C-P contributions to diffractive processes
We investigate contributions to diffractive scattering, which are odd under
C- and P-parity. Comparison of p- and p-p scattering indicates that
these odderon contributions are very small and we show how a diquark clustering
in the proton can explain this effect. A good probe for the odderon exchange is
the photo- and electroproduction of pseudo-scalar mesons. We concentrate on the
pi^0 and show that the quasi elastic pi^0-production is again strongly
suppressed for a diquark structure of the proton whereas the cross sections for
diffractive proton dissociation are larger by orders of magnitude and rather
independent of the proton structure.Comment: 18 pages, LaTex2e, graphicx package, 14 eps figures include
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