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INT Program INT-11-3|
Frontiers in QCD
September 19 - November 18, 2011
Week 6 Schedule - All talks in seminar room C421
Monday, October 24
11 am: Leonardo Vernazza, "Infrared singularities of gauge-theory scattering amplitudes
from the anomalous-dimension matrix of n-jet operators in SCET"
Abstract: Recently, an all-order conjecture for the anomalous-dimension matrix
of n-jet operators in SCET was proposed, which allows one to predict
the structure of the infrared divergences of dimensionally
regularized, massless gauge-theory scattering amplitudes with an
arbitrary number of legs and loops. The conjecture is severely
constrained by soft-collinear factorization, non-abelian
exponentiation, and the behaviour of amplitudes in collinear limits.
Using these constraints, a diagrammatic analysis has shown that the
anomalous dimension involves only two-parton correlators up to three
loop order. The only exception is given by a single color structure
multiplying a function of conformal cross ratios depending on the
momenta of four external partons, which would have to vanish in all
two-particle collinear limits. We extend this analysis by completing
the diagrammatic analysis at four loop, and we find that additional
functions which vanish in all two-particle collinear limits may
Tuesday, October 25
11 am: Alex Kovner, "On angular correlations in gluon emission at high energy"
Abstract: I discuss a simple picture which illustrates how forward
correlations in gluon emission naturally arise at high energy. I suggest
that this mechanism can be relevant to "ridge" type correlations observed
by CMS. I also argue that to understand quantitative such correlations
within the framework of high energy evolution, one has to include the so
called "Pomeron loop" effects.
Wednesday October 26
11 am: Bowen Xiao, "From Dipoles to Quadrupoles"
Abstract:The dipole amplitudes (S-matrices) have been the focus of the
saturation physics for decades. However, little progress was known for
higher-point functions, such as quadrupoles. Recently, we find that
there are two fundamental unintegrated gluon distributions in high
density QCD, and these two gluon distributions are related to dipoles
and quadrupoles, respectively. The first unintegrated gluon
distribution, defined as the Fourier transform of the color-dipole
amplitude, can be probed in the direct photon-jet correlation in pA
collisions; whereas the second unintegrated gluon distribution, which
measures the number density of gluons inside the target nucleus, can
be related to quadrupoles and directly measured in DIS dijet
production. Furthermore, through the recent study of the evolution
equation of quadrupoles, we find that quadrupoles should also exhibit
geometrical scaling behavior as dipoles. Last but not least, I would
like to demonstrate that two additional new gluon distributions (which
are also related to dipoles and quadrupoles, respectively), i.e. the
linearly polarized gluon distributions, naturally appears in the
small-x formalism in DIS and DY dijet processes.
Thursday, October 27
11 am: Alberto Guffanti, "(NN)PDFs for the LHC"
Abstract: Parton Distribution Functions are one of the fundamental ingredient for
predictions for observables
at the LHC experiments and a precise knowledge of PDFs and their
uncertainties is crucial for exploiting
the phyics potential of the experiments.
I will give an overview of the present status of PDF fits, concentrating
mostly on the work of the NNPDF
Collaboration which uses Monte Carlo methods and Neural Networks to
extract an unbiased set on PDFs.
In the context of the NNPDF analysis I will also discuss a recent study
possible deviations from DGLAP
evolution at small-x
Friday, October 28
No talks scheduled today.