Measurement of the Jet Energy Scale in the CMS experiment ... - IIHE

CHAPTER 5: Estimating of the Jet Energy Scale Calibration Factor 123#Events1008060tt+jets semi-ele (146.8 entries)tt+jets other (23.4 entries)SingleTop+jets (7.5 entries)Z+jets (3.5 entries)W+jets (15.1 entries)QCD (4.6 entries)Data (36.1 pb-1) (176.0 entries)#Events2101040120-1100 0.2 0.4 0.6 0.8 1max Probability of the KinFit0 0.2 0.4 0.6 0.8 1max Probability of the KinFitFigure 5.34: The distribution of the maximum probability returned by the kinematicfit shown in normal scale (left) and logarithmic scale (right). The collision data eventsare overimposed to the simulation for comparison purpose.one may expect to obtain a number of e+jets t¯t events which survive the PKinFit max tobe about 36.1 × 75 ∼ 27, given that the same event selection cuts are applied. As it100can be seen from Table 5.16, there are about 42 e+jets t¯t events remained at the samelevel of the selection procedure, hence more events than what is expected. This canbe explained since a looser set of cuts has been applied on the reconstructed jets whenrunning on the data.With the 34 events in the collision data passing the full event selection, one can startestimating the residual light and b jet energy correction factors. For each of the surviveddata events, the twoi-dimensional grid of points which is filled with the kinematicfit probabilities, P KinFit (∆E l , ∆E b ), is transformed to a χ 2 denoted as χ 2 (∆E l , ∆E b ).The χ 2 values in each point of the grid are summed for all of the final selected dataevents. The results can be found in Figure 5.35.The final estimated light and b jet energy corrections are determined at the minimumpoint of the χ 2 (∆E l , ∆E b ) distribution which is shown in Figure 5.35. Theprojected χ 2 distribution in the direction of the ∆E l and ∆E b , shown in Figure 5.36,are fitted with a second-degree polynomial and the points with the minimum valuesare quoted as the light and b jet energy calibration factors, respectively. The finalestimated residual jet energy corrections, which are obtained using the 36.1pb −1 of theaccumulated collision data, are listed in Table 5.17.In order to compare the results derived from the collision data events with the resultsobtained from the simulation, the same procedure to determine the residual jetenergy corrections can be applied using only the final survived simulated events whichare listed in Table 5.16. The results of the residual jet energy corrections estimatedbased on the simulation are also shown in Table 5.17.It should be noted that the statistical uncertainties on the estimated jet energy correctionslisted in Table 5.17, are corrected for the non-unity width of the pull distributions.The systematical uncertainties on the estimated residual light and b jet energy correctionsderived from the simulation are also quoted. Clearly the uncertainties on theestimated results are dominated by the statistics. The statistical uncertainties can be