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

CHAPTER 5: Estimating of the Jet Energy Scale Calibration Factor 97using a jet-parton matching algorithm, as described in Section 5.1.1. Therefore for apair of matched jet-parton, the expected residual correction can be obtained byE jet (1 + ∆ε expjet ) = E parton.Hence, in the topology of the hadronic top quark decay t → Wb → q¯qb, one cancalculate the expected corrections for the light and b jets, asand∆ε expl∆ε expb= E light quark − E light jetE light jet,= E b quark − E b jetE b jet.The distributions of the expected light as well as the b jet energy corrections, which arefitted with a Gaussian function in a range of ±1.5 times the Root Mean Square (RMS)of the distribution around the mean, are shown in Figure 5.19. They are obtainedusing those selected events for which a true jet-parton matching exists.#events500 Entries 6527χ 2/ ndf5.95 / 12400Constant 482.3Mean -0.08673Sigma 0.1239300#events250200150Entries 3263χ 2/ ndf20.25 / 12Constant 230.2Mean -0.02078Sigma 0.1314200100100500-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1exp∆ε l0-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1exp∆ε bFigure 5.19: The distributions of the expected residual jet energy corrections for (left)light and (right) b jets. They are fitted with a Gaussian in the range of ±1.5 times theRMS around the mean.For each of the plots shown in Figure 5.19, the expectation value of the fittedGaussian and its uncertainty are taken as the expected residual jet energy correctionswhich are found to be∆ε l exp = −8.67 ± 0.23%,and∆ε b exp = −2.08 ± 0.36%.The fit results strongly depend on the range which is used to perform the Gaussian fit.For example, the expected residual corrections, obtained for various ranges of the fit,are listed in Table 5.4.As seen from Table 5.4, the expectation values of the fitted Gaussian functions forthe light quark jets varies from -8.83% to -7.43% when increasing the fit range from