Thomas Mehen
Duke University
mehen@phy.duke.edu

Anna Stasto
Pennsylvania State University
astasto@phys.psu.edu

Program Coordinator:
Inge Dolan
inge@u.washington.edu
(206) 685-4286

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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 arise.

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.