Unfolding algorithms and their application in the first diphoton measurement at 13 TeV

One of the main goals of the Large Hadron Collider (LHC) was the measurements of the Higgs boson. Several experiments like ATLAS and CMS were set up and they found the Higgs boson 2012 [1] when the LHC was running at the center of mass energy $\sqrt{s}$ = 8 TeV. One of the decay channel, where the mass of the Higgs boson is measured, is the Higgs to two photons. In this decay channel all the other Diphoton production processes are the background. Therefore the measurement of the Higgs boson was only possible because the background of the Diphoton process was measured and well known. For the data taken in a part of Run 2 (2015-2016) the analysis is repeated to improve the knowledge of the process for further particle searches and measurements. Analysis of ATLAS data are done in several steps. For example, all the processes that are not of interest in the analysis have to be eliminated in the background subtraction. The last step of the analysis is usually the so called unfolding. Here the effects of the detector, like for example the finite resolution, have to be corrected to compare data of different experiments and to make a theory comparison easy. In this work, several unfolding methods are discussed and the unfolding of the first 13 TeV Diphoton ATLAS analysis is presented.