10 - H1 - Desy

Chapter 7
Calibration and tuning
In this analysis MC is used to correct the detector level measurement to hadron level cross
sections. For the correction being valid, MC events need to resemble data to high precision
level and to ensure it, additional checks and calibrations explained in this chapter were
performed. All the selection described in chapters 4 and 5, together with multivariate
analysis introduced in chapter 6 were repeated with the corrected properties.
The most influential tuning, being the check of the cluster shape description in MC is
discussed in section 7.1. Sections 7.2 and 7.3 describe electromagnetic and hadronic
energy calibrations. The method of direct and resolved relative scale tuning is explained
in section 7.4.
7.1 Cluster shapes tuning
The multivariable analysis introduced in chapter 6 heavily relies on the proper description
of the cluster shape variables in MC. A special effort was taken to tune the MC cluster
shape simulation and to correctly evaluate systematic uncertainty associated with its
description.
Three data samples were used for the study of the cluster shape description:
• BH electrons.
The first sample is a selection of Bethe-Heitler (BH) electons produced in a process
visualised with the diagrams presented in figure 7.1a and 7.1b. Events are selected
with a scattered electron in the LAr calorimeter, identified as an electromagnetic
cluster with a track pointing to it, a photon in the SPACAL and nothing else in the
detector.
• DVCS photons.
The complementary sample to BH electrons is the selection of deeply virtual Compton
scattering (DVCS) events with electron reconstructed in the SPACAL and a
photon in LAr. The Feyman diagram of the DVCS event is pictured in figure 7.1c.