Breakdown of Conventional Factorization for Isolated Photon Cross Sections

Using $e^+e^-\rightarrow\gamma + X$ as an example, we show that the conventional factorization theorem in perturbative quantum chromodynamics breaks down for isolated photon cross sections in a well defined part of phase space. Implications and physical consequences are discussed.Comment: 11 pages, RevTex, 1 figure in postscrip

Direct photon production in a nuclear environment

The photon is a very good probe of short distance physics in strong interactions. It can be produced directly at short-distance or through fragmentation processes. Through one-loop order in perturbation theory of quantum chromodynamics (QCD), this thesis provides complete analytic expressions for both the inclusive and the isolated prompt photon production cross sections in hadronic final states of e+e- annihilations. It is the first time that the full angular dependence of the cross sections is derived. Extraction of photon fragmentation functions from e+e- annihilations is addressed. Using e+e-→[gamma]+X as an example, this work demonstrates for the first time that conventional perturbative QCD factorization breaks down for isolated photon production in e+e- annihilations in a specific region of phase space. The impact of this breakdown for computations of prompt photon production in hadron-hadron reactions is also discussed. In hadron-nucleus collisions, high energy photons can be produced through a single hard scattering as well as through multiple scattering. The contribution from the multiple scattering can be presented in terms of multi-parton correlation functions. Using information on the multi-parton correlation functions extracted from photon-nucleus experiments, for the first time, the nuclear dependence of direct photon production in hadron-nucleus collisions was predicted without any free parameter, and was tested at Fermi Lab experiment E706

xFx_F Dependence of Drell-Yan Transverse Moemtum Broadening

We analyze $x_F$ dependence of Drell-Yan transverse momentum broadening in hadron-nucleus collisions. In terms of generalized factorization theorem, we show that the $x_F$ dependence of transverse momentum broadening, $\Delta < q_T^2 > (x_F)$, can be calculated in perturbative QCD. We demonstrate that $\Delta (x_F)$ is a good observable for studying the effects of initial-state multiple scattering and extracting quark-gluon correlation functions.Comment: 10 pages, 3 figure

Planar k-cycle resonant graphs with k=1,2

AbstractA connected graph is said to be k-cycle resonant if, for 1⩽t⩽k, any t disjoint cycles in G are mutually resonant, that is, there is a perfect matching M of G such that each of the t cycles is an M-alternating cycle. The concept of k-cycle resonant graphs was introduced by the present authors in 1994. Some necessary and sufficient conditions for a graph to be k-cycle resonant were also given. In this paper, we improve the proof of the necessary and sufficient conditions for a graph to be k-cycle resonant, and further investigate planar k-cycle resonant graphs with k=1,2. Some new necessary and sufficient conditions for a planar graph to be 1-cycle resonant and 2-cycle resonant are established