10 - H1 - Desy

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6 Theoretical framework Neutral and Charged Current dσ/dQ 2 / pb GeV -2 10 1 10 -1 10 -2 H1 e - p NC 98-99 CC 98-99 H1 e + p NC 94-00 CC 94-00 10 -3 10 -4 10 -5 10 -6 10 -7 √s = 319 GeV y
1.2 Basics of electron - proton scattering 7 1.2.2 The strong interaction and renormalisation The QPM fails to explain why quarks are never observed in the final state, although they appear to be quasi free in deep-inelastic scattering experiments. The model also fails to describe the scaling violation observed at lower and higher x values. The quantum chromodynamics (QCD) theory instead was very successful in describing the measurements. The QCD provides the quarks with additional quantum number, the colour charge red, green or blue. The mediating gauge bosons of QCD are eight massless, spin one particles with no electrical charge. Instead, each gluon carries a combination of colour-anticolour charge allowing for gluon self-interaction (i.e. splitting g → gg is possible). Gluon selfcoupling is a reason for an anti-screening effect, which causes the strong coupling constant α s to behave differently than the electromagnetic coupling α. At small momentum scales (large distances) α s becomes very large and partons interact strongly. This forces the partons to be bound into colour neutral states, called hadrons. The mentioned effect is called confinement. With increasing momentum scale, α s becomes very small, until the parton is effectively observed as a free particle. This effect is usually called asymptotic freedom. In perturbative QCD (pQCD) particle scattering cross sections are given as a power series in α s . Quark and gluon loop diagrams, such as shown in figure 1.4 start contributing beyond leading order (LO). The calculation of such loop contributions incorporates an integration over all particle momenta p in the loop. In the limit p → ∞ ultraviolet (UV) divergences occur which can be absorbed by introducing an arbitrary dimensionless renormalisation scale µ R . Above µ R scale all loops are absorbed into the coupling constant. The strong coupling constant α s at scale µ R > Λ QCD can be written as α s (µ 2 R ) = 12π (1.11) (33 − 2N f ) · ln(µ 2 R /Λ2 QCD ), where N f is the number of quark flavours with m q < µ R . The parameter Λ QCD determines the scale at which α s becomes large, so that power series in α s do not longer converge and perturbation theory is not applicable anymore. Experimentally Λ QCD was found to be of order ∼ 200 MeV. The scale dependence of the strong coupling constant α s can be observed in figure 1.5, the effect often referred to as the running α s . 2 A4?A4 " G; 2G h !6K 2 A4?A4 " G; 2G h !6K a) b) Figure 1.4: Higher order loop corrections to the scattering process. Gluon loop (a) and fermion loop (b). RV- 6 G2 -2 G !262G 04- O Y 6 6-!6K RV6K RV- 6 G2 -2 G !262G 04- 3FHG.IKJKIBL$MNL$Ï O Y 6 6-!6K RV6K ¢¡¤£¦¥¨§©¤¦ !#"$%%!"'&%(*)+ -,.*%,/10¨2¢(&34*5(67*)0!8:9;$:567*)+5?@8BA¢C&!>;
Page 1: PROMPT PHOTON PRODUCTION IN PHOTOPR
Page 5: Abstract This thesis presents measu
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Page 10 and 11: x Contents 4 Event reconstruction a
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Page 14 and 15: xiv Contents the two photon decay c
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Page 18 and 19: 2 Theoretical framework Gene- Quark
Page 20 and 21: 4 Theoretical framework charged W
Page 24 and 25: 8 Theoretical framework α s 0.20 H
Page 26 and 27: 10 Theoretical framework 1.2.4.1 DG
Page 28 and 29: 12 Theoretical framework for the em
Page 30 and 31: 14 Theoretical framework F 2 ⋅ 2
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Page 34 and 35: 18 Theoretical framework e e e a) b
Page 36 and 37: 20 Theoretical framework than in th
Page 38 and 39: 22 Theoretical framework ZEUS dσ/E
Page 40 and 41: 24 Theoretical framework claim thou
Page 42 and 43: 26 Theoretical framework Figure 1.2
Page 44 and 45: 28 Theoretical framework Inclusive
Page 46 and 47: 30 Theoretical predictions partons
Page 48 and 49: 32 Theoretical predictions 2.1.2 MC
Page 50 and 51: 34 Theoretical predictions rejectio
Page 52 and 53: MC set Generator Comments Simulatio
Page 54 and 55: 38 Theoretical predictions contribu
Page 56 and 57: 40 The H1 experiment at HERA Hall N
Page 58 and 59: 42 The H1 experiment at HERA y θ z
Page 60 and 61: 44 The H1 experiment at HERA resolu
Page 62 and 63: 46 The H1 experiment at HERA the el
Page 64 and 65: 48 The H1 experiment at HERA under
Page 66 and 67: 50 The H1 experiment at HERA not be
Page 68 and 69: 52 Event reconstruction and presele
Page 70 and 71: 54 Event reconstruction and presele
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56 Event reconstruction and presele
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64 Prompt photon selection the rema
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66 Prompt photon selection ∆η <
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68 Prompt photon selection reconstr
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70 Prompt photon selection Events 5
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72 Prompt photon selection Selectio
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74 Photon signal extraction γ π0
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76 Photon signal extraction Events
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78 Photon signal extraction CB1 CB2
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80 Photon signal extraction Figure
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82 Photon signal extraction n∏ va
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84 Photon signal extraction 〈S〉
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86 Calibration and tuning • Backg
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88 Calibration and tuning χ 2 /NDF
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90 Calibration and tuning energy on
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92 Calibration and tuning D Ej 1.1
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94 Calibration and tuning
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96 Cross section building The corre
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98 Cross section building • L-cur
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100 Cross section building (Reconst
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102 Cross section building 8.2.1.1
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104 Cross section building Figure 8
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106 Cross section building section
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108 Cross section building the Pull
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110 Cross section building contribu
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112 Cross section building 8.3.2 Sy
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114 Cross section building 8.4 Cros
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116 Cross section building 8.4.3 Cr
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118 Cross section building The doub
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120 Cross section building 8.6.2 To
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122 Cross section building one outp
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124 Cross section building MPI f th
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f f f f f f f f f f f f 126 Cross s
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128 Cross section building PDF unce
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130 Results description of the shap
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132 Results 9.2 Prompt photon + jet
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134 Results [pb] LO dσ / dx γ 100
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136 Results 9.3 NLO corrections The
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138 Results [pb/GeV] dσ / dp 15 10
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140 Results transverse momentum imb
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142 Results [pb/GeV] γ dσ / E T 2
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144 Conclusions and outlook is cons
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A Analysis Binning 147 A Analysis B
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A Analysis Binning 149 Bin E γ T,O
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B Alternative classifier definition
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C Cross Section Tables 153 C Cross
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C Cross Section Tables 155 η γ E
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C Cross Section Tables 157 η γ d
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C Cross Section Tables 159 η jet d
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C Cross Section Tables 161 x LO γ
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C Cross Section Tables 163 x LO γ
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List of Figures 1.1 Lowest order Fe
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List of Figures 167 6.2 Shower shap
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List of Tables 169 List of Tables 1
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List of Tables 171 C-8b Corrections
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References [1] C. Amsler et al.,
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References 175 [32] R. Nisius, “T
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References 177 [63] P. A. Aarnio et
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References 179 [97] W. Braunschweig
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References 181 [129] J. M. Butterwo
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10 - H1 - Desy

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