292
9. Deep Inelastic Electron–Nucleon Scattering and the Parton Model
FIGURE 9.19
Angular distribution of jets in two-jet events, measured in the two-jet rest
+
frame, relative to the incident beam direction, in the process e e
−
→ two jets
(Althoff et al. 1984). The full curve is the (1 + cos
2 θ) distribution. Since it
is not possible to say which jet corresponded to the quark and which to the
antiquark, only half the angular distribution can be plotted. The asymmetry
visible in figure 8.20(b) is therefore not apparent.
observes events in which hadrons emerge from the interaction region in two
relatively well-collimated cones or ‘jets’ – see figure 9.18. The distribution
of events as a function of the (inferred) angle of the jet axis is shown in
figure 9.19 and is in good agreement with (9.102). The interpretation is that
the primary process is e
+ e
−
→ q¯ q, the quark and the antiquark then turning
into hadrons as they separate and experience the very strong colour forces,
but without losing the memory of the original quark angular distribution. We
shall discuss jets more fully in chapter 14 of volume 2, in the context of QCD.
Problems
9.1 The various normalization factors in equations (9.3) and (9.11) may be
checked in the following way. The cross section for inclusive electron–proton
scattering may be written (equation (9.11)):
(
) 2
4πα
1
d
3
k
′
dσ =
4πM L μν W
μν
(9.103)
q 2
4[(k · p) 2 − m 2 M 2 ] 1/2
2ω ′ (2π) 3
in the usual one-photon exchange approximation, and the tensor W
μν is related to hadronic matrix elements of the electromagnetic current operator by
9. Deep Inelastic Electron–Nucleon Scattering and the Parton Model
FIGURE 9.19
Angular distribution of jets in two-jet events, measured in the two-jet rest
+
frame, relative to the incident beam direction, in the process e e
−
→ two jets
(Althoff et al. 1984). The full curve is the (1 + cos
2 θ) distribution. Since it
is not possible to say which jet corresponded to the quark and which to the
antiquark, only half the angular distribution can be plotted. The asymmetry
visible in figure 8.20(b) is therefore not apparent.
observes events in which hadrons emerge from the interaction region in two
relatively well-collimated cones or ‘jets’ – see figure 9.18. The distribution
of events as a function of the (inferred) angle of the jet axis is shown in
figure 9.19 and is in good agreement with (9.102). The interpretation is that
the primary process is e
+ e
−
→ q¯ q, the quark and the antiquark then turning
into hadrons as they separate and experience the very strong colour forces,
but without losing the memory of the original quark angular distribution. We
shall discuss jets more fully in chapter 14 of volume 2, in the context of QCD.
Problems
9.1 The various normalization factors in equations (9.3) and (9.11) may be
checked in the following way. The cross section for inclusive electron–proton
scattering may be written (equation (9.11)):
(
) 2
4πα
1
d
3
k
′
dσ =
4πM L μν W
μν
(9.103)
q 2
4[(k · p) 2 − m 2 M 2 ] 1/2
2ω ′ (2π) 3
in the usual one-photon exchange approximation, and the tensor W
μν is related to hadronic matrix elements of the electromagnetic current operator by