Pakistan Research Repository


Muhammad, Nzar (1995) HARD PROCESSES IN PARTICLES AND NUCLEI. PhD thesis, Quaid-i-Azam University, Islamabad.



This thesis concerns hard processes i.e., reactions in which the large transfer of momentum to quarks and gluons allows for the application of perturbative QCD. Three problems, described below, were tackled. The first research problem relates to deep inelastic scattering of leptons from a J≥ 1 target. There exists a leading twist structure function ∆(x, Q2) which can be measured in deep inelastic scattering from polarized targets with spin ≥ 1, and which is a measure of the polarized gluon distribution in the target. I have estimated ∆(x, Q2) for the deuteron, assuming a model for the deuteron which contains a ∆ - ∆ isobar component, and in which the virtual photon interacts with each isobar independently. Although the predicted transverse asymmetry cross section is small, the results could be tested in view of a proposed experiment to measure ∆(x, Q2). The second research problem considered in this thesis relates to nuclear gluon shadowing. I have investigated the possibility of studying the nuclear gluon distribution by looking at large transverse momentum jets in deep inelastic lepton-nucleus scattering. Provided that a colliding beam of leptons and nuclei, rather than a fixed nuclear target, can be arranged, a clean measurement of gluon shadowing appears possible. The third, and final, research problem concerns quark fragmentation into specific baryons. Fragmentation of partons produced in a high-energy process into definite hadronic states is a problem in QCD of considerable current interest. I have used a simple quark-diquark model for nucleon and Λ structure to calculate leading twist light-cone fragmentation functions for a quark to inclusively decay into P or Λ. The parameters of the model are determined by fitting to the known deep inelastic structure functions of the nucleon. The calculated fragmentation functions are in remarkable agreement with those extracted from partially inclusive e - P and e+ e- experiments at high energies. Predictions are made, using no additional parameters, for a longitudinally and transversely polarized quark to fragment into P or Λ.

Item Type:Thesis (PhD)
Uncontrolled Keywords:hard processes, perturbative qcd, nuclear gluon, lepton, hadronic states, quark-diquark model, double helicity-flip, quark fragmentation
Subjects:Physical Sciences (f) > Physics(f1)
ID Code:2655
Deposited By:Mr. Javed Memon
Deposited On:18 Jul 2009 10:53
Last Modified:18 Jul 2009 10:53

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