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

104 CHAPTER 5: Estimating of the Jet Energy Scale Calibration Factorand shown in Table 5.10.∆ε expl(%) ∆ε estl(%) ∆ε estl− ∆ε expl(%)nominal -9.38±0.25 -8.75±0.14 0.63±0.29Q 2 up -9.30±0.32 -8.76±0.18 0.54±0.37Q 2 down -10.14±0.32 -9.20±0.17 0.94±0.36∆ε expb(%) ∆ε estb(%)∆ε estb− ∆ε expb(%)nominal -2.66±0.36 -2.81±0.20 -0.15±0.41Q 2 up -2.52±0.49 -2.57±0.26 -0.05±0.55Q 2 down -3.41±0.47 -3.00±0.25 0.41±0.53Table 5.10: The expected and estimated residual jet energy corrections and the biason the estimations for the samples with higher and lower values of the Q 2 parameter.As seen from the results shown in Table 5.10, the effects of changing the inputQ 2 parameter on the final estimated results are minor and the estimation follows theexpected value since the bias on the estimated results is compatible with zero. Also theeffect of Q 2 on the bias is compatible with zero. The systematical uncertainties thatcan be assigned due to the changes in the Q 2 scale can be evaluated as follows. Theestimated light jet energy correction changes from -8.76%, corresponding to the samplewith larger Q 2 scale, to -9.20%, which is obtained when considering the simulatedsample with smaller value of the Q 2 scale. Compared to the nominal value which is-8.75%, the maximum deviation of the estimated light jet energy correction is taken asthe systematic uncertainty due to the changes in the Q 2 scale, being 0.45%. In case ofb jets, the maximum deviation would reach 0.24% which is quoted as the systematicuncertainty on the estimated b jet energy correction due to the variation of the Q 2 scale.It should be noted that, when a more precise estimation of the jet energy correctionsis aimed for, these systematic uncertainties should be estimated with larger simulatedsamples.Matching Matrix Element to Parton ShowerIn the procedure of simulating physics collisions, the events are fed to a parton showerprogram to apply the showering process on the partons which are generated in thecollision, as already explained in Section 4.1.2. Subsequently a matching scheme isapplied in order to avoid double counting of the radiation. Therefore, the jets producedby the parton shower method are compared with the partons produced with the matrixelement method, given that the jets exceeding a pre-defined threshold on the transverseenergy. The choice of this threshod might have some effects on the final results of thephysics analysis. Hence alternative samples are simulated with a higher and lowerthreshold on the transverse energy of the jets used in the matching scheme. The effects