Contents
1. Introduction 9
2. Deep inelastic scattering 12
2.1. DIS kinematics . . . . 12
2.2. DIS cross section and structure functions . . . . 14
2.3. Structure functions and gluons . . . . 16
2.4. Direct∆g/gmeasurements . . . . 19
3. Previous∆G measurements 21 3.1. Scaling violation ofg1 . . . . 21
3.2. Direct measurements of∆g/g. . . . 22
3.3. Measurements ofALLas a function of jet or hadronpT. . . . 26
4. Experimental set-up 30 4.1. The muon beam . . . . 30
4.2. The polarised target . . . . 31
4.3. COMPASS spectrometer . . . . 31
4.4. Trigger system . . . . 32
4.5. Data analysis chain . . . . 33
5. Methods of∆g/gextraction 35 5.1. Previous∆g/gextraction method . . . . 35
5.2. The all-pTmethod . . . . 39
6. Data selection and experimental inputs 43 6.1. Data selection . . . . 43
6.2. Analysis inputs from the experimental data . . . . 44
7. Monte Carlo and neural network 48 7.1. Monte Carlo . . . . 48
7.2. Neural networks . . . . 52
8. Systematic studies 57 8.1. MC tests of the new method . . . . 57
8.2. Global vs consecutive configuration . . . . 57
8 Direct Measurement of the Gluon Polarisation in the Nucleon Using the All-pT Method
8.3. False asymmetries . . . . 58
8.4. Neural network stability . . . . 60
8.5.f, Pb, Ptuncertainties . . . . 61
8.6. MC studies . . . . 61
8.7. Radiative corrections . . . . 65
8.8. Summary of systematic uncertainties . . . . 66
9. Results 67 9.1. Possible reduction of the statistical uncertainty of∆g/g. . . . 71
9.2. Analysis of the proton data . . . . 71
10.Summary and outlook 73
Bibliography 75
Acknowledgement 78
