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Title of Thesis

Muhammad Jamil Aslam
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)
b mesons, radiative leptonic decays, hamiltonian, decay distribution, decay kinematics, heavy qurak effective theory

This PhD thesis presents the exclusive radiative decays of B meson within the Standard Model (SM). In particular, we consider the decays B†’γ„“v„“ and B†’ (K1, bl , h1) γ where K1, b1 and h1 are orbitally excited axial vector mesons of K*, p and w respectively. At quark level, all these decays are governed by the flavor changing neutral currents b†’ (s, d) γ transitions, which are not allowed at tree level in the SM. These processes will provide quantitative information on the Standard Model parameters especially the CKM matrix elements and are also sensitive to the presence of physics beyond the SM. The exclusive decays are experimentally better accessible but pose more problem for the theoretical analysis. It is therefore imperative to firm up theoretical predictions in exclusive decays for precision tests of SM and to interpret data for possible new physics effects in these decays.

The main results of our work are the following:

Form factors parameterizing radiative leptonic decays of heavy mesons (B+†’γl+vl) for photon energy are computed in the language of dispersion relations. The contributing states to the absorptive part in the dispersion relation are the multi particle continuum, estimated by quark triangle graph and resonances with quantum numbers 1- and 1+ which includes B* and B*A. and their radial excitations, which model the higher state contributions. Constraints provided by the asymptotic behavior of the structure dependent amplitude, Ward Identities and gauge invariance are used to provide useful information for parameters needed. The couplings gBB*γ and fBB*Aγ are predicted if we restrict to first radial excitation; otherwise using these as an input the radiative decay coupling constants for radial excitations are predicted. The value of the branching ratio for the process B+†’γµ+vµ is found to be in the range 0.5 x 10-6. A detailed comparison is given with other approaches.

For B†’ (K1, bl , h1) γ decays we calculate the hard spectator corrections in 0 (as) in the leading-twist approximation using Large Energy Effective Theory (LEET) techniques. Combining with the hard vertex, already calculated in the literature, and annihilation contributions, they are used to compute the branching ratios for these decays in the next-to-leading order (NLO) in the strong coupling as and in leading power in AQCD/MB. It is found that the theoretical branching ratios for the decays B†’ K1 γ in the LEET approach can be compared with the data only for significantly large values of the form factors than their estimates in the Light Cone Sum Rules (LCSR). Using the SU (3) symmetry for the form factors, the branching ratio for B†’ (bl , h1) γ is expressed in terms of the branching ratio of the B†’ K1 γ and they are found to be B (B†’b1γ) = 0.53 x 10-6 and B (B†’h1γ) = 0.51 x 10-6.

We also calculate the direct GP asymmetry for the decays B†’ (K1, bl , h1) γ and find, in conformity with the observations made in the literature, that the hard spectator contributions significantly reduce the asymmetry arising from the vertex corrections. The sensitivity of the GP asymmetry on the underlying parameters is found to be significantly large.

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2846.88 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
155.83 KB
2 1 Introduction 1
166.51 KB
3 2 Basis Concepts 7
483.55 KB
  2.1 Standard Model 7
  2.2 Renormalization And Renormalization Group 11
  2.3 Operator Product Expansion 17
  2.4 Effective Hamiltonian 18
4 3 Approaches To Non-Leptonic Decays 25
425.44 KB
  3.1 The Effective B†’ S “ Hamiltonian 25
  3.2 Heavy Qurak Effective Theory 28
  3.3 QCD Factorization 30
5 3.4 Large Energy Effective Theory ( Leet ) 34
425.44 KB
6 4 Study Of The Leptonic Decay Modes Of B Meson 45
502.47 KB
  4.1 The Standard Model Pure Leptonic Decay B( P ) †’ L ( P l ) V l ( P v ) 45
  4.2 Decay Kinematics And Current Matrix Elements For B + †’ L + V l “ Decay 48
  4.3 Asymptotic Behavior 54
  4.4 Ward Identity Constraints 60
  4.5 Decay Distribution 67
7 5 Basic Formulas And Phenomenology Of B†’ K 1 “ 72
625.19 KB
  5.1 Introduction And Developments 73
  5.2 Leading Order Contribution 75
  5.3 Matrix Elements At Next-To-Leading Order Of O ( ‘ s ) 76
  5.4 O ( ‘ s )-Corrected Matrix Elements Of B†’ K 1 “ Decay 85
  5.5 Annihilation Contributions And Cp-Asymmetry 93
8 6 Branching Ration For B†’1 1 p 1 “ Decays 100
296.61 KB
  6.1 Introduction 100
  6.2 Effective Hamiltonian 101
  6.3 Theoretical Framework For B†’1 1 p 1 “ Decays 103
9 7 Conclusions 110
352.88 KB