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Title: Spin and QCD Instanton & Stringy Pomeron
Authors: Zahed, Ismail
Qian, Yachao
Department of Physics
Zahed, Ismail
Shuryak, Edward
Du, Xu
Pisarski, Robert
Issue Date: 1-May-2017
Publisher: The Graduate School, Stony Brook University: Stony Brook, NY.
Abstract: We summarize some of the works on understanding the nonperturbative effects in QCD. In the first part of the thesis, we review some aspects of spin physics where QCD instantons play an important role. In particular, their large contributions in semi-inclusive deep-inelastic scattering and polarized proton on proton scattering. We also review their possible contribution in the P-odd pion azimuthal charge correlations in peripheral AA scattering at collider energies. The QCD vacuum is dominated by large instanton and anti-instanton fluctuations in the infrared, which are largely responsible for the spontaneous breaking of chiral symmetry and the anomalously large η′ mass. The QCD instanton intrinsic spin-color polarization makes them ideal for generating non-perturbative and large spin asymmetries in deep inelastic scattering using polarized proton targets and polarized proton on proton scattering. The large spin asymmetries observed experimentally are triggered by T-odd contributions in the scattering amplitude. Since perturbative QCD does not accommodate these effects, it was initially suggested that these T-odd contributions are either induced in the initial state (Sivers effect) or in the fragmentation function (Collins effect) thereby preserving the integrity of QCD perturbation theory and factorization. QCD instantons offer a natural mechanism for generating T-odd amplitudes that is fully rooted in QCD and beyond perturbation theory. In the second part, we show that a single closed string exchange contribution to the eikonalized dipole-dipole scattering amplitude yields a Regge behavior of the elastic amplitude. The overall dipole-dipole scattering amplitude in the soft pomeron kinematics is shown to be sensitive to the extrinsic curvature of the string for finite momentum transfer. The characteristics of the diffractive peak in the differential elastic pp scattering are affected by a small extrinsic curvature of the string. After discretizing the string in N string bits, we analyze its length, mass and spatial distribution for large N and away from its Hagedorn point. The string bit distribution shows sizable asymmetries in the transverse plane that may translate to azimuthal asymmetries in primordial particle production in the Pomeron kinematics, and the flow moments in minimum bias pp and pA events. We also analyze the length, mass and spatial distribution of a discretized transverse string near its Hagedorn temperature. We suggest that such a string may dominate the (holographic) Pomeron kinematics for dipole-dipole scattering at intermediate and small impact parameters. Attractive self-string interactions cause the transverse string size to contract away from its diffusive size, a mechanism reminiscent of the string-black-hole transmutation. The string shows sizable asymmetries in the transverse plane that translate to primordial azimuthal asymmetries in the stringy particle production in the Pomeron kinematics for current pp and pA collisions at collider energies.
Description: 182 pgs
Appears in Collections:Stony Brook Theses and Dissertations Collection

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