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: We study the pion structure in terms of the pion Distribution Amplitude (DA), the electromagnetic Form Factor (FF), and the transition pion-photon form factor in framework of QCD sum rules with nonlocal condensate and light-cone sum rules. The significance of the condensate's nonlocality is demonstrated. A global fit of pion DA to the data from different collaborations (CELLO, CLEO, BaBar) on the pion-photon transition form factor is carried out using light-cone sum rules. The analysis includes the next-to-leading QCD radiative corrections and the twist-four contributions, while the main next-to-next-to-leading term and the twist-six contribution are taken into account in the form of theoretical uncertainties.

Tuesday, 10/4

11 am: Iain Stewart, "Jet Physics from Static Charges in AdS"

Abstract: The Wilson lines describing soft interactions with jets can be transformed into static charges on an AdS space with a special set of coordinates. Many of the interesting properties of multi-Wilson line soft functions are easily understood from this point of view. Motivated by this I will introduce a new class of gauges, dubbed conformal gauges, which avoid mixing in AdS, and show how they simplify computations at two loops and beyond.

Wednesday, 10/5

11 am: Randall Kelley, "Towards precision jet observables"

Abstract: Calculating the distribution of jet masses in high-energy collisions is challenging because fixed- order perturbation theory breaks down near the peak region, and because multiple scales complicate the resummation. To avoid using a jet veto, one can consider inclusive observables, in which every particle is in a jet. We give an example of such an observable, asymmetric thrust, which can be resummed to next-to-next-to-leading logarithmic accuracy. Exclusive observabes with out-of-jet regions are more complicated. Even for e+e- dijet events at energy Q, to calculate the mass m of jets of size R, one must impose a veto on the energy ω of extra jets to force dijet kinematics; then there are both log m/Q and log m/ω singularities. These extra scales prevent the simplest resummation from being valid beyond the leading-logarithmic level. To proceed, we derive a refactorization of the soft function in the small R and small ω limit which allows us to resum additional logs of the jet mass. The expansion of the resummed distribution is shown to have excellent agreement with fixed order even at moderate R. Prospects for jet mass calculations at hadron colliders are also discussed.

Thursday, 10/6

10 am: Michael Fickinger, "Precision determination of alpha_S(m_Z) from thrust data"

Abstract: I will present an extraction of the strong coupling constant, alpha_S(m_Z), from thrust data using Effective Field Theory techniques. Our calculation yields one of the most precise measurements of alpha_S(m_Z) to date. We perform a simultaneous two parameter fit to all available data at energies Q = 35 GeV to 207 GeV. We find alpha_S(m_Z) = 0.1135 +- (0.0002)expt +- (0.0005)hadr +- (0.0009)pert, with chi²/dof = 0.91, where the displayed 1-sigma errors are the total experimental uncertainty, the hadronization uncertainty, and the perturbative theory uncertainty, respectively.

11 am: Ambar Jain, "Rapidity Renormalization Group Formalism"

Abstract: I will talk about some formal aspects of the rapidity renormalization group that is useful for factorization theorems in SCET_II. Several examples of factorization theorems exists in SCET_II, such as Sudakov form factor, Higgs transverse momentum distribution, jet broadening and some exclusive B-decays. I will include discussion of Sudakov form factor and exclusive decays in the new formalism and other details about calculation and setting up the new RGE.

Friday, 10/7

No seminars