CMS-TOP-12-006

CMS-TOP-12-006 ; CERN-EP-2016-016
Measurements of the $\mathrm{ t \bar{t} }$ production cross section in lepton+jets final states in pp collisions at 8 TeV and ratio of 8 to 7 TeV cross sections
CMS Collaboration
29 February 2016
EPJC 77 (2017) 15
Abstract: A measurement of the top quark pair production ($\mathrm{ t \bar{t} }$) cross section in proton-proton collisions at the centre-of-mass energy of 8 TeV is presented using data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.6 fb$^{-1}$. This analysis is performed in the $\mathrm{ t \bar{t} }$ decay channels with one isolated, high transverse momentum electron or muon and at least four jets, at least one of which is required to be identified as originating from hadronization of a b quark. The calibration of the jet energy scale and the efficiency of b~jet identification are determined from data. The measured $\mathrm{ t \bar{t} }$ cross section is 228.5 $\pm$ 3.8 (stat) $\pm$ 13.7 (syst) $\pm$ 6.0 (lumi) pb. This measurement is compared with an analysis of 7 TeV data, corresponding to an integrated luminosity of 5.0 fb$^{-1}$, to determine the ratio of 8 TeV to 7 TeV cross sections, which is found to be 1.43 $\pm$ 0.04 (stat) $\pm$ 0.07 (syst) $\pm$ 0.05 (lumi). The measurements are in agreement with QCD predictions up to next-to-next-to-leading order.
Links: e-print arXiv:1602.09024 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Transverse momentum distributions of the first- and second-leading jet (a,b), the muon and $ {E_{\mathrm {T}}^{\text {miss}}} $ distribution (c,d) for all relevant processes in the muon+jets channel with the requirement of at least one b-tagged jet. The simulation is normalized to the standard model cross section values and $ {p_{\mathrm {T}}} $-reweighting is applied to the $\mathrm{ t \bar{t} }$ contribution. The multijet background is negligible and not shown. The distributions are already corrected for the b tagging efficiency scale factor. The hashed area shows the uncertainty in the luminosity measurement and the b tagging systematic uncertainty. The ratio between data and simulation is shown in the lower panels for bins with non-zero entries.
png pdf	Figure 1-a: Transverse momentum distributions of the first- and second-leading jet (a,b), the muon and $ {E_{\mathrm {T}}^{\text {miss}}} $ distribution (c,d) for all relevant processes in the muon+jets channel with the requirement of at least one b-tagged jet. The simulation is normalized to the standard model cross section values and $ {p_{\mathrm {T}}} $-reweighting is applied to the $\mathrm{ t \bar{t} }$ contribution. The multijet background is negligible and not shown. The distributions are already corrected for the b tagging efficiency scale factor. The hashed area shows the uncertainty in the luminosity measurement and the b tagging systematic uncertainty. The ratio between data and simulation is shown in the lower panels for bins with non-zero entries.
png pdf	Figure 1-b: Transverse momentum distributions of the first- and second-leading jet (a,b), the muon and $ {E_{\mathrm {T}}^{\text {miss}}} $ distribution (c,d) for all relevant processes in the muon+jets channel with the requirement of at least one b-tagged jet. The simulation is normalized to the standard model cross section values and $ {p_{\mathrm {T}}} $-reweighting is applied to the $\mathrm{ t \bar{t} }$ contribution. The multijet background is negligible and not shown. The distributions are already corrected for the b tagging efficiency scale factor. The hashed area shows the uncertainty in the luminosity measurement and the b tagging systematic uncertainty. The ratio between data and simulation is shown in the lower panels for bins with non-zero entries.
png pdf	Figure 1-c: Transverse momentum distributions of the first- and second-leading jet (a,b), the muon and $ {E_{\mathrm {T}}^{\text {miss}}} $ distribution (c,d) for all relevant processes in the muon+jets channel with the requirement of at least one b-tagged jet. The simulation is normalized to the standard model cross section values and $ {p_{\mathrm {T}}} $-reweighting is applied to the $\mathrm{ t \bar{t} }$ contribution. The multijet background is negligible and not shown. The distributions are already corrected for the b tagging efficiency scale factor. The hashed area shows the uncertainty in the luminosity measurement and the b tagging systematic uncertainty. The ratio between data and simulation is shown in the lower panels for bins with non-zero entries.
png pdf	Figure 1-d: Transverse momentum distributions of the first- and second-leading jet (a,b), the muon and $ {E_{\mathrm {T}}^{\text {miss}}} $ distribution (c,d) for all relevant processes in the muon+jets channel with the requirement of at least one b-tagged jet. The simulation is normalized to the standard model cross section values and $ {p_{\mathrm {T}}} $-reweighting is applied to the $\mathrm{ t \bar{t} }$ contribution. The multijet background is negligible and not shown. The distributions are already corrected for the b tagging efficiency scale factor. The hashed area shows the uncertainty in the luminosity measurement and the b tagging systematic uncertainty. The ratio between data and simulation is shown in the lower panels for bins with non-zero entries.
png pdf	Figure 2: Distributions of the lepton-jet mass in the muon+jets (a) and electron+jets (b) channels, rescaled to the fit results.
png pdf	Figure 2-a: Distributions of the lepton-jet mass in the muon+jets (a) and electron+jets (b) channels, rescaled to the fit results.
png pdf	Figure 2-b: Distributions of the lepton-jet mass in the muon+jets (a) and electron+jets (b) channels, rescaled to the fit results.
png pdf	Figure 3: Distributions of the $M_3$ mass in the 8 TeV data, for the muon+jets (a) and electron+jets (b) channels, rescaled to the template likelihood fit results.
png pdf	Figure 3-a: Distributions of the $M_3$ mass in the 8 TeV data, for the muon+jets (a) and electron+jets (b) channels, rescaled to the template likelihood fit results.
png pdf	Figure 3-b: Distributions of the $M_3$ mass in the 8 TeV data, for the muon+jets (a) and electron+jets (b) channels, rescaled to the template likelihood fit results.

Tables
png pdf	Table 1: Average acceptance values for the muon and electron channels obtained with MADGRAPH and POWHEG at $\sqrt s = $ 7 and 8 TeV, without and with top quark $ {p_{\mathrm {T}}} $-reweighting applied. The statistical uncertainty is 0.0004, i.e. below 3%. The theoretical uncertainties are at the level of 2%, as discussed in the text.
png pdf	Table 2: Signal selection efficiencies, at $\sqrt s =$ 8 TeV, determined from simulation using MADGRAPH. The non-reweighted acceptance from Table 1 is used. The relative statistical uncertainty on these numbers is below 3%.
png pdf	Table 3: Components (in %) of the JES uncertainty at 8 TeV in the muon and electron channels. The correlation coefficients used in their combination are also shown.
png pdf	Table 4: Overview of the systematic uncertainties in the measurement of the $\mathrm{ t \bar{t} } $ cross sections at 8 TeV, both for the total and the visible cross sections. For the ``signal modeling'' uncertainty the larger between the matrix element (ME) and parton shower (PS) uncertainties is taken, as explained in Section 6. The correlations assumed for the combination of the muon and electron channels are also given.
png pdf	Table 5: Overview of the systematic uncertainties in the measurement of the $\mathrm{ t \bar{t} } $ cross sections at 7 TeV, both for the total and the visible cross sections. For the ``signal modeling'' uncertainty the larger between the matrix element (ME) and parton shower (PS) uncertainties is taken, as explained in Section 6. The correlations assumed for the combination of the muon and electron channels are also shown.
png pdf	Table 6: Visible cross section measurements at $\sqrt s =$ 7 and 8 TeV with the reference analysis $M_{\ell \mathrm{b} }$ and the alternative analysis $M_3$ (described in Section 6). Results obtained for $m_{\mathrm{t} }=$ 172.5 GeV with MADGRAPH and with POWHEG are shown. The uncertainties are in the order: statistical, systematic, and due to the luminosity determination.
png pdf	Table 7: Total cross section measurements at $\sqrt s =$ 7 and 8 TeV with the reference analysis $M_{\ell \mathrm{b} }$ and the alternative analysis $M_3$ (described in Section 6). Results obtained for $m_{\mathrm{t} }=$ 172.5 GeV with MADGRAPH and with POWHEG are shown. The uncertainties are in the order: statistical, systematic, and due to the luminosity determination.
png pdf	Table 8: Slope values for the muon and electron channels obtained with linear fits to the cross section values at $\sqrt s = $ 8 TeV as a function of the top quark mass. The MADGRAPH generator is used. The change in sign is due to the acceptance $A$.

Summary

A measurement of the $\mathrm{ t \bar{t} }$ production cross section at $\sqrt{s} =$ 8 TeV is presented, using the data collected with the CMS detector and corresponding to an integrated luminosity of 19.6 fb$^{-1}$. The analysis is performed in the $\mathrm{ t \bar{t} }$ semileptonic decay channel with one muon or electron and at least four jets in the final state with at least one b-tagged jet. The $\mathrm{ t \bar{t} }$ cross section is extracted using a binned maximum-likelihood fit of templates from simulated events to the data sample. The results from the two semileptonic channels are combined using the BLUE method. Techniques based on control samples in data are used to determine the b tagging efficiency and to calibrate the jet energy scale. These techniques allow for a better determination of the corresponding systematic uncertainties, particularly for the JES, which is a dominant source of experimental uncertainty.

In the kinematic range defined in the simulation with exactly one muon or electron with $p_{\mathrm{T}} >$ 32 GeV and $| \eta | <$ 2.1, one neutrino with $p_{\mathrm{T}} > $40 GeV, and at least four jets with $p_{\mathrm{T}} >$ 40 GeV and $| \eta | < $ 2.5, the measured visible $\mathrm{ t \bar{t} }$ cross section at $\sqrt{s} = $ 8 TeV is 3.80 $\pm$ 0.06 (stat) $\pm$ 0.18 (syst) $\pm$ 0.10 (lumi) pb.

Using the MADGRAPH generator for the extrapolation to the full phase space, the total $\mathrm{ t \bar{t} }$ cross section at 8 TeV is 228.5 $\pm$ 3.8 (stat) $\pm$13.7 (syst) $\pm$ 6.0 (lumi) pb. The result of an alternative analysis, which makes use of the observable M3, is in good agreement with this value. Furthermore, the analysis performed using data at $\sqrt{s} = $ 7 TeV, yields a total cross section measurement of 161.7 $\pm$ 6.0 (stat) $\pm$ 12.0 (syst) $\pm$ 3.6 (lumi) pb. The measured cross section ratio, where a number of experimental uncertainties cancel out, is 1.43 $\pm$ 0.04 (stat) $\pm$ 0.07 (syst) $\pm$ 0.05 (lumi).

All measurements are in agreement with the NNLO theoretical predictions.

References
1	CMS Collaboration	Determination of the top-quark pole mass and strong coupling constant from the $ \mathrm{ t \bar{t} } $ production cross section in pp collisions at $ \sqrt{s} = $ 7 TeV	PLB 728 (2014) 496	CMS-TOP-12-022 1307.1907
2	M. Czakon, M. L. Mangano, A. Mitov, and J. Rojo	Constraints on the gluon PDF from top quark pair production at hadron colliders	JHEP 07 (2013) 167	1303.7215
3	CMS Collaboration	First measurement of the cross section for top-quark pair production in proton-proton collisions at $ \sqrt{s} = $ 7 TeV	PLB 695 (2011) 424
4	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section and the top quark mass in the dilepton channel in pp collisions at 7 TeV	JHEP 07 (2011) 049	CMS-TOP-11-002 1105.5661
5	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in pp collisions at $ \sqrt{s} = $ 7 tev using the kinematic properties of events with leptons and jets	EPJC 71 (2011) 1721
6	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in pp collisions at 7 TeV in lepton+jets events using b-quark jet identification	PRD 84 (2011) 092004	CMS-TOP-10-003 1108.3773
7	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in the dilepton channel in pp collisions at 7 TeV	JHEP 11 (2012) 067	CMS-TOP-11-005 1208.2671
8	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in pp collisions at $ \sqrt{s} = $ 7 TeV with lepton+jets final states	PLB 720 (2013) 83	CMS-TOP-11-003 1212.6682
9	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in the all-jet final state in pp collisions at $ \sqrt{s} = $ 7 TeV	JHEP 05 (2013) 065	CMS-TOP-11-007 1302.0508
10	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in the $ \tau $+jets channel in pp collisions at $ \sqrt{s} = $ 7 TeV	EPJC 73 (2013) 2386	CMS-TOP-11-004 1301.5755
11	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in pp collisions at $ \sqrt{s} = $ 7 TeV in dilepton final states containing a $ \tau $	PRD 85 (2012) 112007	CMS-TOP-11-006 1203.6810
12	ATLAS Collaboration	Measurement of the top quark-pair production cross section with ATLAS in pp collisions at $ \sqrt{s} = $ 7 TeV	EPJC 71 (2011) 1577	1012.1792
13	ATLAS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in the tau+jets channel using the ATLAS detector	EPJC 73 (2013) 2328	1211.7205
14	ATLAS Collaboration	Measurement of the top quark pair production cross-section with ATLAS in the single lepton channel	PLB 711 (2012) 244	1201.1889
15	ATLAS Collaboration	Measurement of the top quark pair cross-section with ATLAS in pp collisions at $ \sqrt{s} = $ 7 TeV using final states with an electron or a muon and a hadronically decaying $ \tau $ lepton	PLB 717 (2012) 89	1205.2067
16	ATLAS Collaboration	Measurement of the cross section for top-quark pair production in pp collisions at $ \sqrt{s} = $ 7 TeV with the ATLAS detector using final states with two high-$ p_{\mathrm{T}} $ leptons	JHEP 05 (2012) 059	1202.4892
17	ATLAS Collaboration	Measurement of the top quark pair production cross section in pp collisions at $ \sqrt{s} = $ 7 TeV in dilepton final states with ATLAS	PLB 707 (2012) 459	1108.3699
18	ATLAS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section using $ \mathrm{ e }\mu $ events with b-tagged jets in pp collisions at $ \sqrt{s} = $ 7 and 8 TeV with the ATLAS detector	EPJC 74 (2014) 3109	1406.5375
19	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in the dilepton channel in pp collisions at $ \sqrt{s} = $ 8 TeV	JHEP 02 (2014) 024	CMS-TOP-12-007 1312.7582
20	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in pp collisions at $ \sqrt{s} = $ 8 TeV in dilepton final states containing one $ \tau $ lepton	PLB 739 (2014) 23	CMS-TOP-12-026 1407.6643
21	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in the all-jet final state in pp collisions at $ \sqrt{s} = $ 8 TeV	EPJC 76 (2016) 128
22	ATLAS Collaboration	Simultaneous measurements of the $ \mathrm{ t \bar{t} }, W^+W^- $, and $ Z/\gamma^* \rightarrow \tau\tau $ production cross section in pp collisions at $ \sqrt{s} = $ 7 TeV with the ATLAS detector	PRD 91 (2015) 052005
23	ATLAS Collaboration	Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in the lepton+jets final states with ATLAS	PRD 91 (2015) 112013	1504.04251
24	ATLAS Collaboration	Measurement of the top quark branching ratios into channels with leptons and quarks with the ATLAS detector	PRD 92 (2015) 072005
25	CMS Collaboration	Measurement of the $ \mathrm{ t \bar{t} } $ production cross section in the $ \mathrm{ e }\mu $ channel in proton-proton collisions at $ \sqrt{s} = $ 7 and 8 TeV with the CMS experiment	Submitted to J. High Energy Phys	CMS-TOP-13-004 1603.02303
26	CMS Collaboration	Identification of b-quark jets with the cms experiment	JINST 08 (2013) P04013	CMS-BTV-12-001 1211.4462
27	CMS Collaboration	Performance of b tagging at $ \sqrt{s}=8\tev $ in multijet, $ \mathrm{ t \bar{t} } $ and boosted topology events	CMS-PAS-BTV-13-001	CMS-PAS-BTV-13-001
28	M. Maes		PhD thesis, Vrije Universiteit Brussels
29	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
30	CMS Collaboration	Cms luminosity based on pixel cluster counting --- summer 2013 update	CMS-PAS-LUM-13-001	CMS-PAS-LUM-13-001
31	CMS Collaboration	Absolute calibration of the luminosity measurement at CMS: Winter 2012 update	CDS
32	J. Alwall et al.	MadGraph 5: going beyond	JHEP 06 (2011) 128	1106.0522
33	J. Alwall et al.	The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations	JHEP 07 (2014) 079	1405.0301
34	S. Alioli, P. Nason, C. Oleari, and E. Re	NLO vector-boson production matched with shower in POWHEG	JHEP 07 (2008) 060	0805.4802
35	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with parton shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
36	J. Gao et al.	The CT10 NNLO global analysis of QCD	PRD 89 (2014) 033009	1302.6246
37	S. Alekhin et al.	The PDF4LHC Working Group interim report		1101.0536
38	M. Botje et al.	The PDF4LHC Working Group interim recommendations		1101.0538
39	R. D. Ball et al.	Parton distributions with LHC data	NPB 867 (2013) 244	1207.1303
40	T. Sjostrand, S. Mrenna, and P. Z. Skands	PYTHIA 6.4 physics and manual	JHEP 05 (2006) 026	hep-ph/0603175
41	G. Corcella et al.	HERWIG 6.5: an event generator for hadron emission reactions with interfering gluons (including supersymmetric processes)	JHEP 01 (2001) 010	hep-ph/0011363
42	M. L. Mangano, M. Moretti, F. Piccinini, and M. Treccani	Matching matrix elements and shower evolution for top- quark production in hadronic collisions	JHEP 01 (2007) 013	hep-ph/0611129
43	J. Alwall, S. de Visscher, and F. Maltoni	QCD radiation in the production of heavy colored particles at the LHC	JHEP 02 (2009) 017	0810.5350
44	M. Czakon, P. Fiedler, and A. Mitov	Top++: a program for the calculation of the top-pair cross-section at hadron colliders	Comp. Phys. Commun. 185 (2014) 2930	1112.5675
45	CMS Collaboration	Measurement of differential top-quark pair production cross sections in pp collisions at $ \sqrt{s} = $ 7 TeV	EPJC 73 (2013) 2339	CMS-TOP-11-013 1211.2220
46	CMS Collaboration	Measurement of the differential cross section for top quark pair production in pp collisions at $ \sqrt{s} = $ 8 TeV	EPJC 75 (2015) 542	CMS-TOP-12-028 1505.04480
47	R. Gavin, Y. Li, F. Petriello, and S. Quackenbush	FEWZ 2.0: A code for hadronic Z production at next-to-next-to-leading order	Comp. Phys. Commun. 182 (2011) 2388	:1011.3540
48	R. Gavin, Y. Li, F. Petriello, and S. Quackenbush	W physics at the LHC with FEWZ 2.1	CPC 184 (2013) 208	1201.5896
49	J. M. Campbell and R. K. Ellis	MCFM for the Tevatron and the LHC	NPPS 205-206 (2010) 10	1007.3492
50	J. M. Campbell and F. Tramontano	Next-to-leading order corrections to $ \mathrm{ W }\mathrm{ t } $ production and decay	NPB 726 (2005) 109	hep-ph/0506289
51	J. M. Campbell, R. K. Ellis, and F. Tramontano	Single top production and decay at next-to-leading order	PRD 70 (2004) 094012	hep-ph/0408158
52	GEANT4 Collaboration	GEANT4: a simulation toolkit	Nucl. Inst. Meth. A 506 (2003) 250
53	CMS Collaboration	Particle--flow event reconstruction in CMS and performance for jets, taus, and $ E_{\mathrm{T}}^{\text{miss}} $	CDS
54	CMS Collaboration	Commissioning of the particle-flow reconstruction in minimum-bias and jet events from pp collisions at 7 TeV	CDS
55	CMS Collaboration	Performance of CMS muon reconstruction in pp collision events at $ \sqrt{s} = $ 7 TeV	JINST 7 (2012) P10002	CMS-MUO-10-004 1206.4071
56	CMS Collaboration	Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $ \sqrt{s} = $ 8 TeV	JINST 10 (2015) P06005	CMS-EGM-13-001 1502.02701
57	CMS Collaboration	Measurement of the inclusive W and Z production cross section in pp collisions at $ \sqrt{s} = $ 7 TeV with the CMS experiment	JHEP 10 (2011) 070	CMS-EWK-10-007 1108.0566
58	CMS Collaboration	Description and performance of track and primary-vertex reconstruction with the CMS tracker	JINST 9 (2014) P10009	CMS-TRK-11-001 1405.6569
59	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ k_t $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
60	CMS Collaboration	Determination of jet energy calibration and transverse momentum resolution in CMS	JINST 06 (2011) P11002	CMS-JME-10-011 1107.4277
61	CMS and ATLAS Collaboration	Jet energy scale uncertainty correlations between ATLAS and CMS
62	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	1110.1395
63	CMS Collaboration	Measurement of the W$ ^+ $W$ ^- $ and ZZ production cross section in pp collisions at $ \sqrt{s} = $ 8 TeV	PLB 721 (2013) 190,.%%CITATION = ARXIV:%%
64	CMS Collaboration	Measurement of the W$ ^+ $W$ ^- $ cross section at $ \sqrt{s} = $ 7 TeV and limits on anomalous WW$ \gamma $ and WWZ couplings	EPJC 73 (2013) 2610
65	CMS Collaboration	Measurement of the zz production cross section and search for anomalous couplings in 2$ \ell\ell^\prime $ final states in pp collisions at $ \sqrt{s} = $ 7 TeV	JHEP 01 (2013) 063
66	J. Pumplin et al.	Uncertainties of predictions from parton distribution functions II: the Hessian method	PRD 65 (2001) 014013	hep-ph/0101032
67	P. M. Nadolsky et al.	Implications of CTEQ global analysis for collider observables	PRD 78 (2008) 013004	0802.0007
68	L. Lyons, D. Gibaut, and P. Clifford	How to combine correlated estimates of a single physical quantity	Nucl. Inst. Meth. A 270 (1988) 110
69	A. Valassi	Combining correlated measurements of several different physical quantities	Nucl. Inst. Meth. A 500 (2003) 391
70	A. Valassi and R. Chierici	Information and treatment of unknown correlations in the combination of measurements using the BLUE method	EPJC 74 (2014) 2717	1307.4003
71	ATLAS, CDF, CMS, and D0 Collaborations	First combination of Tevatron and LHC measurements of the top-quark mass		1403.4427