TOP-14-017
Measurement of the W boson helicity using ttbar events in the dilepton final state at √s = 8 TeV

Abstract

A measurement of the W boson helicity fractions in top quark decays is presented. The measurement is performed using a sample of top quark pair events with two opposite-sign leptons (electron or muon) in the final state. The sample was recorded in proton-proton collisions at a center-of-mass energy of 8 TeV, and corresponds to an integrated luminosity of 19.7 fb-1. The longitudinal, left-handed and right handed helicity fractions are measured to be F0 = 0.653 0.016(stat) 0.024(syst), FL = 0.329 0.009(stat) 0.025(syst) and FR = 0.018 0.008(stat) 0.026(syst), respectively. The results are found to be in agreement with predictions of the standard model.

Public Document

The CMS Physics Analysis Summary is available here.

Results

Figure Caption
W_PT.png

Figure 1a: Distributions of the transverse momentum of the reconstructed W bosons for the e+e-, μ+μ-, and eμ channel summed. The ratio of the number of events in data to the total number of events from simulation is shown in the lower panel. The distributions are presented after top quark pT re-weighting. Only the shape systematic uncertainties are shown.

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W_Rapidity.png

Figure 1b: Distributions of the rapidity of the reconstructed W bosons for the e+e-, μ+μ- and eμ channel summed. The ratio of the number of events in data to the total number of events from simulation is shown in the lower panel. The distributions are presented after top quark pT re-weighting. Only the shape systematic uncertainties are shown.

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Top_PT.png

Figure 1c: Distributions of the transverse momentum of the top quark for the e+e-, μ+μ-, and eμ channel summed. The ratio of the number of events in data to the total number of events from simulation is shown in the lower panel. The distributions are presented after top quark pT re-weighting. Only the shape systematic uncertainties are shown.

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Top_Rapidity.png

Figure 1d: Distributions of the rapidity of the top quark for the e+e-, μ+μ-, and eμ channel summed. The ratio of the number of events in data to the total number of events from simulation is shown in the lower panel. The distributions are presented after top quark pT re-weighting. Only the shape systematic uncertainties are shown.

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Costheta.png

Figure 2: Distribution of the cos θfor the e+e-+μ- , and eμ channel summed. The ratio of the number of events in data to the total number of events from simulation is shown in the lower panel. The distribution is presented after top quark pT re-weighting. Only the shape systematic uncertainties are shown.

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Sys_Table.png

Table1: Summary of systematic uncertainties.

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Results.png

Table2: The measured W helicity fractions in μ+μ-, e+e- , eμ, and all channels.

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contour_2Sigma.png

Figure 3: The 95% region in the (F0,FL) plane obtained from the fit to data. The measured and theoretical values of the W boson helicity fractions are shown as well.

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comparisonv4.png

Figure 4: Measured W boson helicity fractions in the ttbar dilepton compared with results in different final states from the CMS experiment and from other collaborations.

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-- AndreasMeyer - 2015-07-16

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf Costheta.pdf r1 manage 18.8 K 2015-07-13 - 12:39 MohsenNaseri  
PNGpng Costheta.png r1 manage 28.2 K 2015-07-13 - 12:39 MohsenNaseri  
PDFpdf Results.pdf r1 manage 109.3 K 2015-07-08 - 13:38 MohsenNaseri  
PNGpng Results.png r1 manage 120.5 K 2015-07-08 - 13:38 MohsenNaseri  
PDFpdf Sys_Table.pdf r1 manage 103.5 K 2015-07-13 - 12:47 MohsenNaseri  
PNGpng Sys_Table.png r1 manage 117.5 K 2015-07-13 - 12:47 MohsenNaseri  
PDFpdf Top_PT.pdf r1 manage 24.3 K 2015-07-13 - 12:35 MohsenNaseri  
PNGpng Top_PT.png r1 manage 33.1 K 2015-07-13 - 12:34 MohsenNaseri  
PDFpdf Top_Rapidity.pdf r1 manage 22.3 K 2015-07-13 - 12:35 MohsenNaseri  
PNGpng Top_Rapidity.png r1 manage 29.2 K 2015-07-13 - 12:34 MohsenNaseri  
PDFpdf W_PT.pdf r1 manage 24.3 K 2015-07-11 - 13:09 MohsenNaseri  
PNGpng W_PT.png r1 manage 32.6 K 2015-07-11 - 13:11 MohsenNaseri  
PDFpdf W_Rapidity.pdf r1 manage 22.2 K 2015-07-13 - 12:32 MohsenNaseri  
PNGpng W_Rapidity.png r1 manage 28.9 K 2015-07-13 - 12:32 MohsenNaseri  
PDFpdf comparisonv4.pdf r1 manage 15.5 K 2015-07-15 - 15:43 MohsenNaseri  
PNGpng comparisonv4.png r1 manage 25.7 K 2015-07-15 - 15:43 MohsenNaseri  
PDFpdf contour_2Sigma.pdf r1 manage 28.2 K 2015-07-07 - 21:39 MohsenNaseri  
PNGpng contour_2Sigma.png r1 manage 21.6 K 2015-07-07 - 21:39 MohsenNaseri  
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Topic revision: r13 - 2015-07-17 - AndreasMeyer
 
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