33 research outputs found
The T-Wilson Line
We argue that soft-collinear effective theory, as is currently formulated,
lacks an ingredient which is essential for obtaining a gauge invariant
definitions of certain non-perturbative matrix elements relevant for
semi-inclusive high-energy processes. Those processes and the companion
cross-sections are to be analyzed and measured at the Large Hadron Collider.
The missing feature is a gauge link constructed only from the transverse
component of the gluon field denoted by the "-Wilson line"'. It is neither
soft nor collinear. As such it is a new feature of the theory.Comment: 4 pages. To appear in the proceedings of "Quark Confinement and
Hadron Nuclei", Madrid 201
Pair Production of Color-Octet Scalars at the LHC
Heavy colored scalar particles, which exist in many models of new physics,
can be pair produced at the Large Hadron Collider (LHC) via gluon-gluon fusion
and possibly form quarkonium-like bound states. If the scalars are also charged
under the electroweak gauge group, these bound states can then decay into
electroweak bosons. This yields a resonant cross section for final states such
as gamma gamma that can exceed Standard Model backgrounds. This paper studies
this process in the Manohar-Wise model of color-octet scalars (COS). Important
threshold logarithms and final state Coulomb-like QCD interactions are resummed
using effective field theory. We compute the resummed cross section for
gluon-gluon fusion to COS pairs at the LHC as well as the resonant cross
section for octetonium decaying to gamma gamma. The latter cross section
exceeds the Standard Model di-photon cross section when the COS mass is less
than 500 (350) GeV for sqrt{s} = 14 (7) TeV. Nonobservation of resonances below
these energies can significantly improve existing bounds on COS masses.Comment: 19 pages, 5 figures, published versio
Extending Soft-Collinear-Effective-Theory to describe hard jets in dense QCD media
An extension to the Soft-Collinear-Effective Theory (SCET) description of
hard jets is motivated to include the leading contributions between the
propagating partons within the jet with partons radiated from a dense extended
medium. The resulting effective Lagrangian, containing both a leading and a
power suppressed (in the hard scale ) contribution, arises primarily from
interactions between the hard collinear modes in the jet with Glauber modes
from the medium. In this first attempt, the interactions between the hard jet
and soft and collinear partonic modes have been ignored, in an effort to focus
solely on the interactions with the Glauber modes. While the effect of such
modes on vacuum cross sections are suppressed by powers of the hard scale
compared to the terms from the SCET Lagrangian, such sub-leading contributions
are enhanced by the extent of the medium and result in measurable corrections.
The veracity of the derived Lagrangian is checked by direct comparison with
known results from full QCD calculations of two physical observables: the
transverse momentum broadening of hard jets in dense media and a reanalysis of
the transverse momentum dependent parton distribution function (TMDPDF).Comment: 19 pages, 6 figures, revtex4, discussion on power counting updated,
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