TOP-14-006 (ATLAS-CONF-2014-012)

Combination of ATLAS and CMS ttbar charge asymmetry measurements using LHC proton-proton collisions at 7 TeV


A combination of measurements of the charge asymmetry in ttbar events performed by the ATLAS and CMS collaborations is presented. The analyzed datasets of LHC proton collisions at a centre-of-mass energy of 7 TeV correspond to an integrated luminosity of 4.7/fb for ATLAS and 5.0/fb for CMS. In both analyses events with a lepton+jets signature, i.e. one electron or muon and at least four jets, are analyzed. The resulting combined LHC measurement of the charge asymmetry in ttbar events at a 7 TeV is: Ac = 0.005 +- 0.007 (stat.) +-0.006 (syst.) which is consistent with the prediction from the Standard Model.

Input Measurements

ATLAS l+jets (4.7/fb at 7 TeV) : arXiv:1311.6724 (accepted by JHEP)

CMS l+jets (5.0/fb at 7 TeV): Phys. Lett. B717 (2012) 129

Public Document

CMS PAS TOP-14-006: CDS entry


The combined value for the ttbar charge asymmetry at 7 TeV is: Ac = 0.005 +- 0.007 (stat.) +-0.006 (syst.).


Figure Caption
AcSummary.png Figure 1: Summary of the single measurements and the LHC combination compared to the theory prediction (calculated at NLO including electroweak corrections). The inner red error bars indicate the statistical uncertainty, the blue outer error bars indicate the total uncertainty. The grey band illustrates the total uncertainty of the combined result. [Get pdf version] [Get eps version]


Table Caption
Table 1: Results and uncertainties of the single measurements and the combination along with the assumed correlations. The negligible systematic uncertainties (<0.001) are set to zero in the actual combination. Uncertainties that are evaluated only in one analysis are marked (*) in the table and are set to zero in the combination for the experiment that did not evaluate them.
Table 2: Weights and pulls of the two correlated estimates. Listed are the central value weight (CVW), the intrinsic information weight (IIW), and the marginal information weight (MIW).

-- ThorstenChwalek - 24 Mar 2014

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf Ac_combination2_Obs_0.pdf r1 manage 13.5 K 2014-03-24 - 14:58 ThorstenChwalek  
PNGpng Ac_combination2_Obs_0.png r1 manage 19.2 K 2014-03-24 - 15:03 ThorstenChwalek  
PNGpng CombinationPicture.png r1 manage 27.6 K 2014-03-24 - 14:46 ThorstenChwalek  
PNGpng Table1.png r1 manage 66.3 K 2014-03-25 - 09:29 ThorstenChwalek  
PNGpng Table2.png r1 manage 15.0 K 2014-03-25 - 09:30 ThorstenChwalek  
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Topic revision: r4 - 2014-03-26 - AndreasMeyer
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