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Title of Thesis

Institute/University/Department Details
Department of Physics/ Quaid-i-Azam University, Islamabad
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
hard processes, perturbative qcd, nuclear gluon, lepton, hadronic states, quark-diquark model, double helicity-flip, quark fragmentation

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 ˆ†(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 ˆ†(x, Q2) for the deuteron, assuming a model for the deuteron which contains a ˆ† - ˆ† 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 ˆ†(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 › structure to calculate leading twist light-cone fragmentation functions for a quark to inclusively decay into P or ›. 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 ›.

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855.79 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
66.56 KB
2 1 Introduction 1
167.58 KB
  1.1 General survey 1
  1.2 Brief description of Ph.D. research work 9
3 2 Estimation of the double helicity -flip deuteron structure function 15
324.37 KB
  2.1 Introduction 15
  2.2 Kinematics 18
  2.3 Operator product expansion and parton model 21
  2.4 Estimation of ˆ† ( x , Q 2 ) for the ˆ†+ + 29
  2.5 Estimation of ˆ†(x, Q 2 ) for the deuteron 33
  2.6 Discussion and conclusions 44
4 3 Measuring nuclear gluon shadowing through 3-jet production in electron-nucleus collisions 48
176.88 KB
  3.1 Introduction 48
  3.2 The kinematics of 3-jet production 53
  3.3 Three-jet contribution to F I (x) 58
  3.4 Results and discussion 60
5 4 Quark fragmentation functions in a diquark model for proton and › hyperon production 67
238.26 KB
  4.1 Introduction 67
  4.2 Unpolarized quark distribution f I (X) in a quark- diquark model for the nucleon 69
  4.3 Quark fragmentation functions for production of spin- 1/2 hadrons. 73
  4.4 Quark fragmentation functions in a diquark model 75
  4.5 Results and discussion 79
  4.6 Conclusion 91