54 research outputs found
Hard exclusive production of a vector meson
The processes of a light neutral vector meson, V=\rho^0, \omega, \phi,
electroproduction and a heavy quarkonium, V=J/\Psi, \Upsilon, photoproduction
are studied in the framework of QCD factorization. We derive a complete set of
hard-scattering amplitudes which describe these processes at next-to-leading
order (NLO).Comment: 3 pages, prepared for Diffraction 2004, International Workshop on
Diffraction in High-Energy Physics, Cala Gonone, Sardinia, Italy, September
18 - 23, 200
Light vector meson photoproduction at large t
We have studied in perturbative QCD all independent helicity amplitudes
describing the photoproduction of light vector mesons at large . We found a
new hard production mechanism which is related to the possibility for a real
photon to fluctuate into a massless pair in a chiral-odd spin
configuration. Each helicity amplitude is given as a sum of a usual chiral-even
contribution (when the helicities of quark and antiquark are antiparallel) and
this additional chiral-odd part (where the helicities of quark and antiquark
are parallel). The chiral-odd contribution is large, it leads to a dominance of
the non spin-flip amplitude in a very broad region of intermediately high
. All amplitudes are expressed in terms of short distance asymptotics of
the light-cone wave functions of vector meson (photon). We demonstrate that for
each helicity amplitude there exists a soft non-factorizable contribution. We
give arguments that for dominant non spin-flip helicity amplitude the relative
contribution of the soft nonfactorizable interactions is numerically not large.Comment: 21 pages LATEX, 2 .eps figures, the colour factor of chiral-odd
contributions is corrected, qualitative results remain unchange
Production of pairs to all orders in for collisions of high-energy muons with heavy nuclei
The pair production in collisions of muon with atoms is considered
to all orders in the parameter . We obtain energy distribution of
and as well as energy loss of muon passing through matter with
heavy atoms. The found corrections to the Born contribution do not depend on
the details of the target properties except of a simple factor. For the
considered example of Pb target the muon energy loss corrections vary from -65
% to -10 % depending on the pair energy.Comment: 9 pages, 3 figures, LaTex; Introduction slightly enlarged, 2
references adde
Coulomb corrections and multiple e+e- pair production in ultra-relativistic nuclear collisions
We consider the problem of Coulomb corrections to the inclusive cross
section. We show that these corrections in the limiting case of small charge
number of one of the nuclei coincide with those to the exclusive cross section.
Within our approach we also obtain the Coulomb corrections for the case of
large charge numbers of both nuclei.Comment: 7 pages, REVTeX
QCD factorization for the pion diffractive dissociation to two jets
We calculate the cross section of a pion diffraction dissociation in two jets
with large transverse momenta originating from a hard gluon exchange between
the pion constituents. To the leading logarithmic accuracy (in energy), the
contribution coming from small transverse separations between the quark and the
antiquark in the pion acquires the expected factorized form, the longitudinal
momentum distribution of the jets being proportional to the pion distribution
amplitude. The hard gluon exchange can in this case be considered as a part of
the unintegrated gluon distribution. Beyond the leading logarithms (in energy)
this proportionality does not hold. Moreover, the collinear factorization
appears to be broken by the end-point singularities. Remarkably enough, the
longitudinal momentum distribution of the jets for the non-factorizable
contribution is calculable, and turns out to be the same as for the
factorizable contribution with the asymptotic pion distribution amplitude.Comment: Original version from 9 April restore
Proton dissociation into three jets
We explore the possibility to observe hard exclusive three-jet production in
early LHC runs, corresponding to diffractive dissociation of the incident
proton into three jets with large but compensating transverse momenta. This
process is sensitive to the proton unintegrated gluon distribution at small x
and to the distribution of the three valence quarks in the proton at small
transverse distances. The corresponding cross section is calculated using an
approach based on k_t factorization. According to our estimates, observation of
hard diffractive three-jet production at LHC is feasible for jet transverse
momenta q_perp \sim 5 GeV.Comment: 10 pages, 3 figure
Electroproduction of two light vector mesons in next-to-leading BFKL: study of systematic effects
The forward electroproduction of two light vector mesons is the first example
of a collision process between strongly interacting colorless particles for
which the amplitude can be written completely within perturbative QCD in the
Regge limit with next-to-leading accuracy. In a previous paper we have given a
numerical determination of the amplitude in the case of equal photon
virtualities by using a definite representation for the amplitude and a
definite optimization method for the perturbative series. Here we estimate the
systematic uncertainty of our previous determination, by considering a
different representation of the amplitude and different optimization methods of
the perturbative series. Moreover, we compare our result for the differential
cross section at the minimum momentum transfer with a different approach, based
on collinear kernel improvement.Comment: 17 pages, 11 figures; journal version, new figures and discussion
adde
Contribution of -terms to the total interaction cross sections of relativistic elementary atoms with atoms of matter
It is shown that the corrections of order to the total cross
sections for interaction of elementary hydrogen-like atoms with target atoms,
reported in the previously published paper [S.Mrowczynski, Phys.Rev. D36, 1520
(1987)], do not include some terms of the same order of magnitude. That results
in a significant contribution of these corrections in particular cases. The
full -corrections have been derived and it is shown that they are
really small and could be omitted for most practical applications.Comment: 5 page
The next-to-leading order forward jet vertex in the small-cone approximation
We consider within QCD collinear factorization the process p+p to jet + jet
+X, where two forward high- jets are produced with a large separation in
rapidity (Mueller-Navelet jets). In this case the (calculable) hard
part of the reaction receives large higher-order corrections , which can be accounted for in the BFKL approach. In particular,
we calculate in the next-to-leading order the impact factor (vertex) for the
production of a forward high- jet, in the approximation of small aperture
of the jet cone in the pseudorapidity-azimuthal angle plane. The final
expression for the vertex turns out to be simple and easy to implement in
numerical calculations.Comment: 32 pages, 4 figures; a few comments and one reference added; a few
inessential misprints removed; version to appear on JHE
On the pion electroproduction amplitude
We analyze amplitudes for the pion electroproduction on proton derived from
Lagrangians based on the local chiral SU(2) x SU(2) symmetries. We show that
such amplitudes do contain information on the nucleon axial form factor F_A in
both soft and hard pion regimes. This result invalidates recent Haberzettl's
claim that the pion electroproduction at threshold cannot be used to extract
any information regarding F_A.Comment: 14 pages, 6 figures, revised version, accepted for publication in
Phys. Rev.
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