Kinematics

The processes in deep inelastic scattering (DIS) are described by the following kinematic variables.

k and denote the four-momenta of the incoming and the final state lepton, P is the four-momentum of the incoming proton and y is the fractional energy transfer in the proton rest frame.

As the ZEUS detector is a nearly hermetic detector (99.7 %), there exist various methods to reconstruct the kinematic variables. For our analysis we have used two different methods:

1. electron method; (in this method only the scattered electron is observed and its scattering angle and energy are measured.)
2. double angle (DA) method; (this relies on the measurement of two scattering angles, that of the scattered electron and that for the final hadronic state. In the naive Quark Parton Model the latter is the angle of the scattered quark.)

Method 1 gives a better resolution in x at low Q² while method 2 is less sensitive to the absolute calorimeter energy scale and gives better resolution over the whole x - Q² plane. Comparing the results obtained by both methods gives a good systematic check of our analysis.

The range of x and Q² that is accessible with these two methods is shown in figure 1.

  
Figure 1: Distribution of events in the x and Q² plane. Also shown are the bins used and the range covered by previous experiments.