Combination of ATLAS and CMS results on the mass of the top quark using up to 4.9/fb of data


A combination of top-quark mass measurements performed by the ATLAS and CMS experiments at the LHC is presented. The dataset used corresponds to an integrated luminosity per experiment of up to 4.9/fb of proton-proton collisions at a centre-of-mass energy of 7 TeV. The combination includes measurements in the lepton+jets, di-lepton and all-jets channels. The resulting preliminary combined LHC measurement of the top-quark mass is mtop = 173.3  0.5 (stat)  1.3 (syst) GeV, with a total uncertainty of 1.4 GeV.

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This document is available both as CMS Physics Analysis Summary: CMS-PAS-TOP-12-001 and as ATLAS Conference note: ATLAS-CONF-2012-095.




Figure Caption
Summary.png Fig1(a). Input measurements and result of the LHC combination (see also Table 4). [Get pdf version]
BlueCoefficients.png Fig1(b). Linear combination coefficients calculated with the BLUE method for the input measurements in the combination. [Get pdf version]
BlueImportance.png Fig1(c). The relative importance of a measurement is defined as ImportanceFormula.png, where Wi.png is the absolute value of the BLUE combination coefficient for the i^th input measurement. [Get pdf version]
DeltaMvsCorrelation.png Fig2(a). Variation of the combined mtop result as a function of the correlation assumption. The correlation between "fully correlated" systematics sources is varied from the default value of 100% to 0% simultaneously in steps of 10%.[Get pdf version]
DeltaSigmavsCorrelation.png Fig2(b). Variation of the total uncertainty on the combined mtop result as a function of the correlation assumption. The correlation between "fully correlated" systematics sources is varied from the default value of 100% to 0% simultaneously in steps of 10%. [Get pdf version]


Table Caption
Table1.png Tab1: Summary of ATLAS 2010 and 2011 top mass results (in GeV). The 2010 measurements in each lepton channel are combined assuming the correlation factor specified by rho. The BLUE combination coefficients for the individual e+jets and mu+jets channels in the 2010 l+jets combination are also reported. Symbols n/a and n/e stand for not-applicable and not-evaluated respectively. (*) for the all jets analysis, the MC generator systematics includes also hadronisation systematics.
Table2.png Tab2: Summary of CMS 2010 and 2011 top mass results (in GeV). Symbols n/a and n/e stand for not-applicable and not-evaluated respectively. (*) Preliminary estimates for the colour reconnection uncertainty have only recently been estimated for the 2011 measurements. While not quoted in [6] and [8] they are included in the LHC top-quark mass combination presented here.
Table3.png Tab3: Uncertainty categories mapping. In the right most columns, rho_exp is the assumed correlation between measurements from the same experiment, while rho_LHC indicates the correlation assumed between measurements across experiments. A revised CMS uncertainty categorisation has been adopted: the b-JES uncertainty has been taken from [15]; in addition the background components for the CMS 2010 lepton+jets analysis have been divided into MC and data driven components. Colour reconnection effects are presently evaluated only for the ATLAS 2011 lepton+jets measurement, and the CMS 2011 measurements. Assuming that the effects do not vary across tt decay channels nor within different analyses, the uncertainty is assigned to all input measurements in the same experiment and in the same channel if available (value in italics), and is assumed to be fully correlated across all measurements. Similarly, the ATLAS 2011 Underlying Event uncertainty is assigned to all input measurements for which this uncertainty has not been evaluated (value in italics). (*) for the ATLAS all jets analysis, the MC generator uncertainty also includes hadronisation systematics.
Table4.png Tab4: Inputs to the LHC combination and the results obtained using the categories grouping and correlation from Table 3. Symbols n/a and n/e stand for not-applicable and not evaluated respectively. For comparison, the results from the Tevatron 2011 combination, as taken from [1], are reported in the last column. (*) for the Tevatron combination this includes all signal modelling systematics sources (MC, Rad, CR and PDF); (**) refers to the original UN/MI category, only used for D0 Run I measurements
CorrelationMatrix.png Correlation Matrix calculated by BLUE

-- MartijnMulders - 03-Jul-2012

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf Absweights_sep.pdf r1 manage 12.9 K 2012-07-03 - 16:57 MartijnMulders  
PNGpng BlueCoefficients.png r1 manage 62.4 K 2012-07-03 - 15:20 MartijnMulders Linear coefficients for input measurements used in combination
PNGpng BlueImportance.png r1 manage 60.6 K 2012-07-03 - 15:20 MartijnMulders Relative importance of the imput measurements
PNGpng CorrelationMatrix.png r1 manage 107.2 K 2012-07-03 - 16:41 MartijnMulders Matrix of correlations between the input measurements
PNGpng DeltaMvsCorrelation.png r1 manage 43.1 K 2012-07-03 - 15:42 MartijnMulders Change in combined mass vs correlation
PNGpng DeltaSigmavsCorrelation.png r1 manage 44.6 K 2012-07-03 - 15:43 MartijnMulders Change in combined uncertainty vs correlation
PNGpng ImportanceFormula.png r1 manage 9.2 K 2012-07-03 - 16:02 MartijnMulders Definition of Importance
PDFpdf Plot_corr_mtop.pdf r1 manage 13.5 K 2012-07-03 - 16:57 MartijnMulders  
PDFpdf Plot_corr_unc.pdf r1 manage 13.6 K 2012-07-03 - 16:57 MartijnMulders  
PNGpng Summary.png r1 manage 98.5 K 2012-07-03 - 15:19 MartijnMulders Overview of input measurement, combination and comparison to Tevatron
PNGpng Table1.png r1 manage 217.4 K 2012-07-03 - 16:23 MartijnMulders Table 1
PNGpng Table2.png r1 manage 187.4 K 2012-07-03 - 16:25 MartijnMulders Table 2
PNGpng Table3.png r1 manage 218.8 K 2012-07-03 - 16:24 MartijnMulders Table 3
PNGpng Table4.png r1 manage 190.9 K 2012-07-03 - 16:24 MartijnMulders Table 4
PNGpng TheResultText.png r1 manage 18.1 K 2012-07-03 - 15:02 MartijnMulders Text of the result
PDFpdf TopMassSummary.pdf r1 manage 14.1 K 2012-07-03 - 16:56 MartijnMulders  
PDFpdf Weights_sep.pdf r1 manage 12.8 K 2012-07-03 - 16:58 MartijnMulders  
PNGpng Wi.png r1 manage 7.4 K 2012-07-03 - 16:03 MartijnMulders Formula version of w_i
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Topic revision: r5 - 2013-09-13 - StephenWimpenny
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