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TOP-13-001:
Measurement of top-quark polarization in t-channel single-top production

Abstract

This note documents the measurement of top-quark polarization in t-channel single-top production, analyzing approximately $20~fb^{-1}$ of pp collisions at a center-of-mass energy of 8 TeV. A high-purity sample of t-channel single-top events is defined, signal and background components are estimated by a fit to data, and an unfolding technique is applied to infer the parton-level distribution of an angular observable sensitive to the top-quark polarization. The unfolded distribution, which is compatible with the standard model expectation, is used to extract the top-quark spin asymmetry, $A_l = 0.41 \pm 0.06 (stat.) \pm 0.16 (syst.)$. That corresponds to a top-quark polarization $P_t = 0.82 \pm 0.12 (stat.) \pm 0.32 (syst.)$ under the assumption that the spin analyzing power of a charged lepton is 100%.

Result

$A_l = 0.41 \pm 0.06 (stat.) \pm 0.16 (syst.)$

$P_t = 0.82 \pm 0.12 (stat.) \pm 0.32 (syst.)$ under the assumption that the spin analyzing power of a charged lepton is 100%.

Figures in PAS

Click on image for pdf version of figure.

All processes are normalized to the outcome of the fit. The uncertainty on the MC, illustrated by the dashed lines, takes into account the systematic uncertainties.

Figure Caption
Figure 1 (top) BDT response in the muon (left) and electron (right) channel.
Figure 1 (middle) Zoom to signal enriched region.
Figure 1 (bottom) cosθ* distribution for events passing the analysis threshold on the BDT discriminant.
Figure 2 (top) Control plots of the BDT discriminant in "2jets 0tags" control region in muon channel (left) and electron channel (right), using the MADGRAPH generator for W+jets after reweighting. The uncertainty on the MC, illustrated by the dashed lines, takes into account the systematic uncertainties.
Figure 2 (bottom) Control plots of cosθ* in "2jets 0tags" control region in muon channel (left) and electron channel (right), using the MADGRAPH generator for W+jets after reweighting. The uncertainty on the MC, illustrated by the dashed lines, takes into account the systematic uncertainties.
Figure 3 (top) Control plots of the BDT discriminant in "3jets 1tag" control region in muon channel (left) and electron channel (right). The uncertainty on the MC, illustrated by the dashed lines, takes into account the systematic uncertainties.
Figure 3 (bottom) Control plots of cosθ* in "3jets 1tag" control region in muon channel (left) and electron channel (right). The uncertainty on the MC, illustrated by the dashed lines, takes into account the systematic uncertainties.
Figure 4 (top) Control plots of the BDT discriminant in "3jets 2tags" control region in muon channel (left) and electron channel (right). The uncertainty on the MC, illustrated by the dashed lines, takes into account the systematic uncertainties.
Figure 4 (bottom) Control plots of cosθ* in "3jets 2tags" control region in muon channel (left) and electron channel (right). The uncertainty on the MC, illustrated by the dashed lines, takes into account the systematic uncertainties.
Figure 5 Unfolded data distribution cosθ*unfolded compared to the generated distribution from POWHEG and COMPHEP, in the muon (left) and electron (right) channel. Error bars represent statistical uncertainties.

Tables in PAS

Table Caption
table1.png Table 1 Scale factors and uncertainties for the BDT fit.
table2.png Table 2 Event yields for the main processes in the signal region after the BDT selection. The yields are normalized to the results of the fit to the BDT response.
table3.png Table 3 List of systematic uncertainties and their impact to the measurement of $A_l$ for the muon ($\delta A_l^{\mu}$) and electron channel ($\delta A_l^{e}$).

Attachments Attachments
Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf 2j0t_BDT_el.pdf r1 manage 20.1 K 2013-09-13 - 12:18 AndreaGiammanco  
PNGpng 2j0t_BDT_el.png r2 r1 manage 50.9 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf 2j0t_BDT_mu.pdf r1 manage 20.1 K 2013-09-13 - 12:18 AndreaGiammanco  
PNGpng 2j0t_BDT_mu.png r2 r1 manage 50.9 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf 2j0t_cosTheta_el.pdf r1 manage 19.0 K 2013-09-13 - 12:18 AndreaGiammanco  
PNGpng 2j0t_cosTheta_el.png r2 r1 manage 44.5 K 2013-09-13 - 15:01 JoosepPata  
PDFpdf 2j0t_cosTheta_mu.pdf r1 manage 19.2 K 2013-09-13 - 12:18 AndreaGiammanco  
PNGpng 2j0t_cosTheta_mu.png r2 r1 manage 46.1 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf 3j1t_BDT_el.pdf r1 manage 20.3 K 2013-09-13 - 12:18 AndreaGiammanco  
PNGpng 3j1t_BDT_el.png r2 r1 manage 53.4 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf 3j1t_BDT_mu.pdf r1 manage 20.3 K 2013-09-13 - 12:18 AndreaGiammanco  
PNGpng 3j1t_BDT_mu.png r2 r1 manage 52.6 K 2013-09-13 - 15:07 JoosepPata  
PDFpdf 3j1t_cosTheta_el.pdf r1 manage 19.6 K 2013-09-13 - 12:18 AndreaGiammanco  
PNGpng 3j1t_cosTheta_el.png r2 r1 manage 46.0 K 2013-09-13 - 15:09 JoosepPata  
PDFpdf 3j1t_cosTheta_mu.pdf r1 manage 19.6 K 2013-09-13 - 12:18 AndreaGiammanco  
PNGpng 3j1t_cosTheta_mu.png r2 r1 manage 46.6 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf 3j2t_BDT_el.pdf r1 manage 20.3 K 2013-09-13 - 12:19 AndreaGiammanco  
PNGpng 3j2t_BDT_el.png r2 r1 manage 56.2 K 2013-09-13 - 15:07 JoosepPata  
PDFpdf 3j2t_BDT_mu.pdf r1 manage 20.4 K 2013-09-13 - 12:19 AndreaGiammanco  
PNGpng 3j2t_BDT_mu.png r2 r1 manage 53.9 K 2013-09-13 - 15:07 JoosepPata  
PDFpdf 3j2t_cosTheta_el.pdf r1 manage 20.0 K 2013-09-13 - 12:19 AndreaGiammanco  
PNGpng 3j2t_cosTheta_el.png r2 r1 manage 48.2 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf 3j2t_cosTheta_mu.pdf r1 manage 20.1 K 2013-09-13 - 12:19 AndreaGiammanco  
PNGpng 3j2t_cosTheta_mu.png r2 r1 manage 47.2 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf costheta_unfolded_el.pdf r1 manage 18.7 K 2013-09-13 - 12:39 AndreaGiammanco fig.5
PNGpng costheta_unfolded_el.png r1 manage 156.2 K 2013-09-13 - 12:39 AndreaGiammanco fig.5
PDFpdf costheta_unfolded_mu.pdf r1 manage 18.5 K 2013-09-13 - 12:39 AndreaGiammanco fig.5
PNGpng costheta_unfolded_mu.png r1 manage 147.1 K 2013-09-13 - 12:39 AndreaGiammanco fig.5
PDFpdf final_cosTheta_mva_loose_fit_el.pdf r1 manage 20.2 K 2013-09-13 - 12:08 AndreaGiammanco fig.1
PNGpng final_cosTheta_mva_loose_fit_el.png r2 r1 manage 55.4 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf final_cosTheta_mva_loose_fit_mu.pdf r1 manage 20.2 K 2013-09-13 - 12:08 AndreaGiammanco fig.1
PNGpng final_cosTheta_mva_loose_fit_mu.png r2 r1 manage 52.3 K 2013-09-13 - 15:06 JoosepPata  
PDFpdf mva_bdt_el.pdf r1 manage 20.0 K 2013-09-13 - 12:08 AndreaGiammanco fig.1
PNGpng mva_bdt_el.png r2 r1 manage 52.1 K 2013-09-13 - 15:07 JoosepPata  
PDFpdf mva_bdt_mu.pdf r1 manage 20.0 K 2013-09-13 - 12:08 AndreaGiammanco fig.1
PNGpng mva_bdt_mu.png r2 r1 manage 51.0 K 2013-09-13 - 15:07 JoosepPata  
PDFpdf mva_bdt_zoom_el.pdf r1 manage 19.9 K 2013-09-13 - 12:08 AndreaGiammanco fig.1
PNGpng mva_bdt_zoom_el.png r2 r1 manage 54.9 K 2013-09-13 - 15:07 JoosepPata  
PDFpdf mva_bdt_zoom_mu.pdf r1 manage 20.1 K 2013-09-13 - 12:08 AndreaGiammanco fig.1
PNGpng mva_bdt_zoom_mu.png r2 r1 manage 55.1 K 2013-09-13 - 15:07 JoosepPata  
PNGpng table1.png r2 r1 manage 29.6 K 2013-09-13 - 11:44 AndreaGiammanco Tables from the PAS
PNGpng table2.png r2 r1 manage 73.2 K 2013-09-13 - 11:45 AndreaGiammanco Tables from the PAS
PNGpng table3.png r2 r1 manage 106.2 K 2013-09-13 - 11:45 AndreaGiammanco Tables from the PAS
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Topic revision: r6 - 2014-03-26 - AndreasMeyer
 
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