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CMS-PAS-TOP-13-006
Determination of the normalised invariant mass distribution of $\mathrm{t\bar{t}}$+jet and extraction of the top quark mass
Abstract: A measurement of the top quark mass from top quark pair ($\mathrm{t\bar{t}}$) events produced in association with additional hard jets is performed in pp collisions at $\sqrt{s}= $ 8 TeV with the CMS detector using data recorded in 2012, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The mass is extracted from the normalised invariant mass distribution of the $\mathrm{t\bar{t}}$+jet system at reconstruction level as well as from the related normalised differential cross section. Both measurements are performed in the dileptonic decay channels ($\mathrm{e^+e^-}$, $\mu^+\mu^-$ and $\mathrm{e^{\pm}}\mu^{\pm}$) of the $\mathrm{t\bar{t}}$ quark pairs.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1-a:
Invariant mass of the ${\mathrm{ t \bar{t} } }$ system (a), transverse momentum of the leading additional jet (b) and $\rho _s$ (c) at reconstruction level for the combined dilepton channel. The ${\mathrm{ t \bar{t} } }$ sample is simulated using MadGraph and is assuming a top mass of $ {m_{\mathrm {t}}} = $ 172.5 GeV. The label `` ${\mathrm{ t \bar{t} } }$ signal'' refers to the events decaying dileptonically, while `` ${\mathrm{ t \bar{t} } }$ other'' refers to the other decay modes including ${\mathrm{ t \bar{t} } }$ decays into prompt $\tau $-leptons. The hatched regions correspond to all shape uncertainties of the simulation (cf. Section 5).

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Figure 1-b:
Invariant mass of the ${\mathrm{ t \bar{t} } }$ system (a), transverse momentum of the leading additional jet (b) and $\rho _s$ (c) at reconstruction level for the combined dilepton channel. The ${\mathrm{ t \bar{t} } }$ sample is simulated using MadGraph and is assuming a top mass of $ {m_{\mathrm {t}}} = $ 172.5 GeV. The label `` ${\mathrm{ t \bar{t} } }$ signal'' refers to the events decaying dileptonically, while `` ${\mathrm{ t \bar{t} } }$ other'' refers to the other decay modes including ${\mathrm{ t \bar{t} } }$ decays into prompt $\tau $-leptons. The hatched regions correspond to all shape uncertainties of the simulation (cf. Section 5).

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Figure 1-c:
Invariant mass of the ${\mathrm{ t \bar{t} } }$ system (a), transverse momentum of the leading additional jet (b) and $\rho _s$ (c) at reconstruction level for the combined dilepton channel. The ${\mathrm{ t \bar{t} } }$ sample is simulated using MadGraph and is assuming a top mass of $ {m_{\mathrm {t}}} = $ 172.5 GeV. The label `` ${\mathrm{ t \bar{t} } }$ signal'' refers to the events decaying dileptonically, while `` ${\mathrm{ t \bar{t} } }$ other'' refers to the other decay modes including ${\mathrm{ t \bar{t} } }$ decays into prompt $\tau $-leptons. The hatched regions correspond to all shape uncertainties of the simulation (cf. Section 5).

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Figure 2:
Global $\chi ^2$ distribution obtained as the sum of the $\chi ^2_i$ distributions of the individual bins for the dilepton combined channel. The most probable top quark mass is extracted from the minimum, the statistical uncertainty from a $\chi ^{2}+1$ variation around the minimum.

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Figure 3:
Top quark mass obtained from pseudo data generated from each of the MadGraph samples with varied mass values. Neither a favoured mass value nor a bias towards higher or lower masses can be observed.

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Figure 4:
Normalized differential ${\mathrm{ t \bar{t} } }$ cross section in the visible phase space after unfolding as a function of the observable $\rho _s$ in the dilepton channels, compared to the predictions from POWHEG $\mathrm{ t \bar{t} }$+jet simulated with a top quark mass of 172.5 GeV as well as $\pm$3 and 6 GeV variations with respect to the central value. The grey band represents the statistical uncertainty, the yellow band corresponds to the total systematic uncertainty.

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Figure 5-a:
Distributions of the differential cross section for simulation and data for all mass samples in the different bins of the $\rho _s$ distribution, shown for the three dilepton final states combined. The error bands correspond to the statistical error on data and the confidence interval of the second order polynomial for the simulation.

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Figure 5-b:
Distributions of the differential cross section for simulation and data for all mass samples in the different bins of the $\rho _s$ distribution, shown for the three dilepton final states combined. The error bands correspond to the statistical error on data and the confidence interval of the second order polynomial for the simulation.

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Figure 5-c:
Distributions of the differential cross section for simulation and data for all mass samples in the different bins of the $\rho _s$ distribution, shown for the three dilepton final states combined. The error bands correspond to the statistical error on data and the confidence interval of the second order polynomial for the simulation.

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Figure 5-d:
Distributions of the differential cross section for simulation and data for all mass samples in the different bins of the $\rho _s$ distribution, shown for the three dilepton final states combined. The error bands correspond to the statistical error on data and the confidence interval of the second order polynomial for the simulation.

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Figure 6:
Global $\chi ^2$ distribution for the normalized differential cross section as a function of $\rho _s$ in the dilepton combined channel.

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Figure 7:
Top quark mass obtained by using each of the MadGraph samples with varied mass values as pseudo data, for the dilepton combined channel.
Tables

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Table 1:
Breakdown of the systematic uncertainties for the top quark mass extracted from the normalized event yield for the dilepton combined channels. All systematic uncertainties are found to be statistically significant. For the asymmetric uncertainties due to scale variations, the first reported value corresponds to an increase of the corresponding scale and the second one to a decrease.

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Table 2:
Breakdown of the systematic uncertainties for the top quark mass measured from the dileptonic channel. All systematic uncertainties are found to be statistically significant. For the asymmetric uncertainties due to scale variations, the first reported value corresponds to an increase of the corresponding scale and the second one to a decrease.
Summary
The top quark mass is measured from the inverse of the invariant mass of the $\mathrm{t\bar{t}}$+jet system, an observable proposed in [3]. The mass extraction has been performed with a global template fit using the shape of the distribution at reconstruction level as well as using the normalised differential cross section in the visible phase space. The first approach avoids statistical correlations and uncertainties arising from the unfolding procedure, however it cannot be compared to predictions given at generator level, while the second eases the comparisons with theory models.

The top quark mass obtained from the normalized differential $\mathrm{t\bar{t}}$+jet cross section using an NLO calculation interfaced with parton shower yields 169.9 $\pm$ 1.1 (stat) $^{+2.5}_{-3.1}$ (syst) $^{+3.6}_{-1.6}$ (theo) GeV. The precision is mostly limited by the systematic uncertainties arising from modelling sources and the theory uncertainties in the POWHEG $\mathrm{t\bar{t}}$+jet simulation. The result is in agreement within the uncertainties with other measurements performed following the same approach [4] as well as complementary measurements of the mass from the inclusive $\mathrm{ t \bar{t} }$ production cross section [39-41].
References
1 ATLAS, CDF, CMS, and D0 Collaborations First combination of Tevatron and LHC measurements of the top-quark mass 1403.4427
2 CMS Collaboration Measurement of the top quark mass using proton-proton data at $ \sqrt{s} $ = 7 and 8 TeV CMS-TOP-14-022
1509.04044
3 S. Alioli et al. A new observable to measure the top-quark mass at hadron colliders Eur.Phys.J. C73 (2013) 2438 1303.6415
4 ATLAS Collaboration Determination of the top-quark pole mass using $ t\overline{t} $ + 1-jet events collected with the ATLAS experiment in 7 TeV pp collisions JHEP 10 (2015) 121 1507.01769
5 CMS Collaboration The CMS experiment at the CERN LHC JINST 03 (2008) S08004 CMS-00-001
6 CMS Collaboration Measurement of Top Quark Pair Differential Cross Sections at sqrt(s) = 8 TeV CMS-PAS-TOP-12-028 CMS-PAS-TOP-12-028
7 CMS Collaboration Measurement of the Jet Multiplicity in dileptonic Top Quark Pair Events at 8 TeV CDS
8 P. Artoisenet et al. Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations JHEP 03 (2013) 015 1212.3460
9 J. Pumplin et al. New generation of parton distributions with uncertainties from global QCD analysis JHEP 07 (2002) 012 hep-ph/0201195
10 T. Sj\"ostrand, S. Mrenna, and P. Skands PYTHIA 6.4 physics and manual JHEP 05 (2006) 026 hep-ph/0603175
11 M. L. Mangano, M. Moretti, F. Piccinini, and M. Treccani Matching matrix elements and shower evolution for top-quark production in hadronic collisions JHEP 0701 (2007) 013 hep-ph/0611129
12 CMS Collaboration Measurement of the underlying event activity at the LHC with $ \sqrt{s} $ =7 TeV and comparison with $ \sqrt{s} $ =0.9 TeV JHEP 09 (2011) 109 CMS-QCD-10-010
1107.0330
13 S. Agostinelli et al. $ \GEANTfour $ -- a simulation toolkit NIMA 506 (2003) 250
14 N. Kidonakis Two-loop soft anomalous dimensions for single top quark associated production with W- or H- PRD82 (2010) 054018 hep-ph/1005.4451
15 J. M. Campbell, R. K. Ellis, and C. Williams Vector boson pair production at the LHC JHEP 1107 (2011) 018 1105.0020
16 J. Campbell and R. Ellis $ t\bar t W^{+-} $ production and decay at NLO JHEP 07 (2012) 052 1204.5678
17 W. Kilian, T. Ohl, and J. Reuter WHIZARD: Simulating multi-particle processes at LHC and ILC EPJC 71 (2011) 1742 hep-ph/9905386
18 K. Melnikov, M. Schulze, and A. Scharf QCD corrections to top quark pair production in association with a photon at hadron colliders PRD 83 (2011) 074013 hep-ph/1102.1967
19 R. Corke and T. Sjostrand Interleaved Parton Showers and Tuning Prospects JHEP 03 (2011) 032 1011.1759
20 CMS Collaboration Commissioning of the Particle-Flow Reconstruction in Minimum-Bias and Jet Events from pp Collisions at 7 TeV CDS
21 M. Cacciari, G. P. Salam, and G. Soyez The Catchment Area of Jets JHEP 04 (2008) 005 0802.1188
22 CMS Collaboration Determination of the jet energy scale in CMS with pp Collisions at $ \sqrt{s} $ = 7$ TeV $ CDS
23 M. Cacciari, G. P. Salam, and G. Soyez The anti-$ k_t $ jet clustering algorithm JHEP 04 (2008) 063 hep-ph/0802.1189
24 CMS Collaboration Identification of b-quark jets with the CMS experiment JINST 08 (2013) P04013 hep-ex/1211.4462
25 CMS Collaboration Missing transverse energy performance of the CMS detector JINST 06 (2011) P09001 CMS-JME-10-009
1106.5048
26 D0 Collaboration Measurement of the top quark mass using dilepton events PRL 80 (1998) 2063 hep-ex/9706014
27 CMS Collaboration Measurement of differential top-quark pair production cross sections in pp collisions at $ \texorpdfstring $$ \sqrt{s} = $ 7 TeVsqrt(s) = 7 TeV EPJC 73 (2013) 2339 hep-ph/1211.2220
28 CMS Collaboration Measurement of jet multiplicity distributions in $ t\bar{t} $ production in pp collisions at $ \sqrt{s} $ = 7 TeV EPJC 74 (Apr, 2014) 3014 CMS-TOP-12-018
1404.3171
29 CMS Collaboration Measurement of the $ t\bar t $ production cross section and the top quark mass in the dilepton channel in pp collisions at $ \sqrt{s} $ = 7 TeV JHEP 07 (2011) 049 hep-ex/1105.5661
30 CMS Collaboration Determination of jet energy calibration and transverse momentum resolution in CMS JINST 06 (2011) P11002 CMS-JME-10-011
1107.4277
31 CMS Collaboration Jet energy resolution in CMS at $ \sqrt{s} $ = 7 TeV CDS
32 CMS Collaboration Measurement of the $ t\bar{t} $ production cross section in the dilepton channel in $ pp $ collisions at $ \sqrt{s}=7 $ TeV JHEP 1211 (2012) 067 CMS-TOP-11-005
1208.2671
33 TOTEM Collaboration First measurement of the total proton-proton cross section at the LHC energy of $ \sqrt{s} $ =7 TeV Europhys. Lett. 96 (2011) 21002 hep-ex/1110.1395
34 P. Z. Skands and D. Wicke Non-perturbative QCD effects and the top mass at the Tevatron EPJC 52 (2007) 133 hep-ph/0703081
35 P. Z. Skands Tuning Monte Carlo generators: The Perugia tunes PRD 82 (2010) 074018 1005.3457
36 A. Hoecker and V. Kartvelishvili SVD approach to data unfolding NIMA 372 (1996) 469 hep-ph/9509307
37 V. Blobel An unfolding method for high energy physics experiments hep-ex/0208022
38 F. James Statistical methods in experimental physics World Scientific, $2^nd$ edition
39 CMS Collaboration Collaboration Measurement of the ttbar production cross section in the emu channel in pp collisions at 7 and 8 TeV Technical Report CMS-PAS-TOP-13-004, CERN, Geneva
40 R. Astalos et al. Proceedings of the sixth international workshop on multiple partonic interactions at the Large Hadron Collider 1506.05829
41 CMS Collaboration Determination of the top-quark pole mass and strong coupling constant from the $ {\rm t bar{t}} $ production cross section in pp collisions at $ \sqrt{s} $ = 7 TeV PLB 728 (2014) 496--517, , [Erratum: Phys. Lett.B728,526(2014)] CMS-TOP-12-022
1307.1907
Compact Muon Solenoid
LHC, CERN