289 research outputs found
Gaps between Jets: Matching two Approaches
We calculate the parton level cross section for the production of two jets
that are far apart in rapidity, subject to a limitation on the total transverse
momentum Q_0 in the interjet region. We specifically address the question of
how to combine the approach which sums all leading logarithms in Q/Q_0 (where Q
is the jet transverse momentum) with the BFKL approach, in which leading
logarithms of the scattering energy are summed. Using an "all orders" matching,
we obtain results for the cross section which correctly reproduce the two
approaches in the appropriate limits.Comment: Talk given at 13th International Workshop on Deep Inelastic
Scattering (DIS 2005), Madison/Wisconsin, USA, April 27 - May 1, 200
The colour evolution of the process q q -> q q g
We calculate the soft anomalous dimension matrix for a five-parton process,
qq -> qqg. Considering different bases we unveil some interesting properties of
this matrix.Comment: 11 pages; calculation extended to general 5-parton kinematic
Massive c\bar c g - Calculation in Diffractive DIS and Diffractive D^* - Production at HERA
We calculate the cross section for -production in diffractive DIS
with finite quark masses at zero momentum transfer . The calculation is done
in the leading log(1/) approximation and is valid in the region of high
diffractive masses (small ). We apply our cross section formula
including both - and in a Monte Carlo simulation to
diffractive meson production at HERA. We compare our predictions to
results of H1 using three parameterizations for the unintegrated gluon density.Comment: 11 pages, 5 figure
Breakdown of QCD coherence ?
We reconsider the calculation of a non-global QCD observable and find the
possible breakdown of QCD coherence. This breakdown arises as a result of wide
angle soft gluon emission developing a sensitivity to emission at small angles
and it leads to the appearance of super-leading logarithms. We use the `gaps
between jets' cross-section as a concrete example and illustrate that the new
logarithms are intimately connected with the presence of Coulomb gluon
contributions. Numerical estimates of their potential phenomenological
significance are presented.Comment: 7 pages, 3 figures; proceedings of Workshop on Diffraction in
High-Energy Physics - DIFFRACTION 2006, Sep. 5-10 2006, Adamantas, Milos
island, Greec
Precise Predictions for Higgs Production in Neutralino Decays in the Complex MSSM
Complete one-loop results are obtained for the class of processes
chi^0_i->chi^0_j h_a in the MSSM where all parameters entering this process
beyond lowest order are allowed to have arbitrary CP-violating phases. An
on-shell renormalisation scheme is worked out for the chargino-neutralino
sector that properly takes account of imaginary parts arising from complex
parameters and from absorptive parts of loop integrals. The genuine vertex
contributions to the neutralino decay amplitudes are combined with two-loop
propagator-type corrections for the outgoing Higgs boson. In this way the
currently most precise prediction for this class of processes is obtained. The
numerical impact of the genuine vertex corrections is studied for several
examples of CP-conserving and CP-violating scenarios. We find that significant
effects on the decay widths and branching ratios are possible even in the
CP-conserving MSSM. In the CP-violating CPX benchmark scenario the corrections
to the decay width are found to be particularly large, namely, of order 45% for
a Higgs mass of 40 GeV. This parameter region of the CPX scenario where a very
light Higgs boson is unexcluded by present data is analysed in detail. We find
that in this parameter region, which will be difficult to cover by standard
Higgs search channels at the LHC, the branching ratio for the decay
chi^0_2->chi^0_1 h_1 is large. This may offer good prospects to detect such a
light Higgs boson in cascade decays of supersymmetric particles.Comment: 24 pages, 6 figure
The Real Corrections to the Gamma* Impact Factor: First Numerical Results
We have performed analytically the transverse momentum integrations in the
real corrections to the longitudinal \gamma^*_L impact factor and carried out
numerically the remaining integrations. I outline the analytical integration
and present the numerical results: we have performed a numerical test and
computed those parts of the impact factor that depend upon the energy scale
s_0.Comment: 4 pages, 3 figures, to appear in proceedings of "DIS 2004", XII
International Workshop on Deep Inelastic Scattering (April 2004, Strbske
Pleso, Slovakia
Color evolution of 2 -> 3 processes
The color structure needed for resummation of all colored 2 -> 3 processes is
calculated using multiplet inspired s-channel bases. In this way the resulting
matrices, describing the color structure, are guaranteed to obey simplifying
symmetries.Comment: 25 page
The Process \gamma^{*}_L+ q \to q\bar{q}g + q: Real Corrections to the Virtual Photon Impact Factor
We calculate, for the longitudinally polarized virtual photon, the cross
section of the process \gamma^{*}+q\to (q\bar{q}g)+q at high energies with a
large rapidity gap between the fragmentation system q\bar{q}g and the other
quark. This process provides the real corrections of the virtual photon impact
factor in the next-to leading order. Evidence is given for the appearance of a
new q\bar{q}g Fock-component of the photon state.Comment: 17 pages, 4 figures, revte
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