11 research outputs found
Azimuthal decorrelation of forward and backward jets at the Tevatron
We analyse the azimuthal decorrelation of Mueller-Navelet dijets produced in
the collisions at Tevatron energies using a BFKL framework which incorporates
dominant subleading effects. We show that these effects significantly reduce
the decorrelation yet they are still insufficient to give satisfactory
description of experimental data. However a good description of the data is
obtained after incorporating within formalism the effective rapidity defined by
Del Duca and Schmidt.Comment: 1+9 pages, 6 eps figures; the final version to appear in Phys. Lett.
B; one reference added, the use of effective rapidity and the need for BFKL
resummmation for small azimuthal angles better motivate
The non-forward BFKL amplitude and rapidity gap physics
We discuss the BFKL approach to processes with large momentum transferred
through a rapidity gap. The Mueller and Tang scheme to the BFKL non-forward
parton-parton elastic scattering amplitude at large , is extended to include
higher conformal spins. The new contributions are found to decrease with
increasing energy, as follows from the gluon reggeisation phenomenon, and to
vanish for asymptotically high energies. However, at moderate energies and high
, the higher conformal spins dominate the amplitude. We illustrate the
effects by studying the production of two high jets separated by a
rapidity gap at HERA energies. In a simplified framework, we find excellent
agreement with the HERA photoproduction data once we incorporate the rapidity
gap survival probability against soft rescattering effects. We emphasize that
measurements of the analogous process in electroproduction may probe different
summations over conformal spins.Comment: Latex, 14 pages, 3 figures; the final version to appear in Phys.
Lett. B; a short discussion of the Tevatron data added; a previously missing
factor of i^n introduced in eq. (13
NLO corrections to ultra-high energy neutrino-nucleon scattering, shadowing and small x
We reconsider the Standard Model interactions of ultra-high energy neutrinos
with matter. The next to leading order QCD corrections are presented for
charged-current and neutral-current processes. Contrary to popular
expectations, these corrections are found to be quite substantial, especially
for very large (anti-) neutrino energies. Hence, they need to be taken into
account in any search for new physics effects in high-energy neutrino
interactions. In our extrapolation of the parton densities to kinematical
regions as yet unexplored directly in terrestrial accelerators, we are guided
by double asymptotic scaling in the large Q^2 and small Bjorken x region and to
models of saturation in the low Q^2 and low x regime. The sizes of the
consequent uncertainties are commented upon. We also briefly discuss some
variables which are insensitive to higher order QCD corrections and are hence
suitable in any search for new physics.Comment: 21 pages, LaTeX2e, uses JHEP3.cls (included), 8 ps files for figures
published versio
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
Theoretical issues of small physics
The perturbative QCD predictions concerning deep inelastic scattering at low
are summarized. The theoretical framework based on the leading log
resummation and factorization theorem is described and some recent
developments concerning the BFKL equation and its generalization are discussed.
The QCD expectations concerning the small behaviour of the spin dependent
structure function are briefly summarized and the importance of
the double logarithmic terms which sum contributions containing the leading
powers of is emphasised. The role of studying final states
in deep inelastic scattering for revealing the details of the underlying
dynamics at low is pointed out and some dedicated measurements, like deep
inelastic scattering accompanied by an energetic jet, the measurement of the
transverse energy flow etc., are briefly discussed.Comment: 17 pages, LATEX, 7 uuencoded eps figures include
Hard pomeron enhancement of ultrahigh-energy neutrino-nucleon cross-sections
An unknown small-x behavior of nucleon structure functions gives appreciable
uncertainties to high-energy neutrino-nucleon cross-sections. We construct
structure functions using at small x Regge inspired description by A. Donnachie
and P. V. Landshoff with soft and hard pomerons, and employing at larger x the
perturbative QCD expressions. The smooth interpolation between two regimes for
each Q^2 is provided with the help of simple polynomial functions. To obtain
low-x neutrino-nucleon structure functions and
singlet part of from Donnachie-Landshoff
function , we use the Q^2-dependent ratios R_2(Q^2) and
R_3(Q^2) derived from perturbative QCD calculations. Non-singlet part of F_3 at
low x, which is very small, is taken as power-law extrapolation of perturbative
function at larger x. This procedure gives a full set of smooth
neutrino-nucleon structure functions in the whole range of x and Q^2 at
interest.
Using these structure functions, we have calculated the neutrino-nucleon
cross-sections and compared them with some other cross-sections known in
literature. Our cross-sections turn out to be the highest among them at the
highest energies, which is explained by contribution of the hard pomeron.Comment: Final revised version, accepted by Phys. Rev. D; 18 pages, 7 figure
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