The Compact Muon Solenoid Experiment. Conference Report. Mailing address: CMS CERN, CH-1211 GENEVA 23, Switzerland

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1 Available on CMS information server CMS CR -2017/094 The Compact Muon Solenoid Experiment Conference Report Mailing address: CMS CERN, CH211 GENEVA 23, Switzerland 18 March 2017 (v3, 20 March 2017) Recent inclusive cross section measurements (for the ATLAS and CMS collaborations) Abstract The results of the recent measurements for the inclusive production cross section in the proton-proton collisions at LHC are presented. The analyses use proton-proton collision data recorded by the ATLAS and CMS experiments at LHC at center-of-mass energies of 7, 8, and 13. The results are also reported on the measurement of the production cross sections of t tb b, t tw, t tz, and t tγ processes. Presented at CKM2016 9th International Workshop on the CKM Unitarity Triangle

2 Recent inclusive tt cross section measurements Institute of Physics, Bhubaneswar, India The results of the recent measurements for the inclusive tt production cross section in the protonproton collisions at LHC are presented. The analyses use proton-proton collision data recorded by the ATLAS and CMS experiments at LHC at center-of-mass energies of 7, 8, and 13 TeV. The results are also reported on the measurement of the production cross sections of ttbb, ttw, ttz, and ttγ processes. 9th International Workshop on the CKM Unitarity Triangle 28 November - 3 December 2016 Tata Institute for Fundamental Research (TIFR), Mumbai, India Speaker. On behalf of the ATLAS and CMS collaborations c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).

3 1. Introduction Measurements of the production cross section of the top-quark pair at proton-proton(antiproton) collisions are important tests of the Standard Model (SM). As the production cross sections can be predicted by the quantum chromodynamics (QCD) calculations its measurements are useful in constraining the essential ingredients of the calculation, such as the parton distribution functions, strong coupling constant, and top quark mass. The production of tt constitutes a large background contribution to many new physics searches at LHC, for example Higgs boson production in association with tt. Thus, the measurement of the production cross section of the tt will provide better estimate of the background rates. Furthermore, the deviation of the measured cross section from the theoretical prediction may provide indirect evidence for the presence of new physics beyond Standard Model. This article presents the results from the recent measurements of inclusive cross sections of tt productions (σ tt ), including processes with additional particles. Results are presented for the recent measurements carried out using ATLAS and CMS detectors at LHC [1, 2] with the proton-proton collision data recorded at s = 7, 8, and 13 TeV. 2. Measurement of inclusive tt cross section In the SM the top quark decays to a b quark and a W boson with a branching fraction B(t W + b) 1. Thus, the final states of the tt production process are categorized according to the decay of the W bosons. The σ tt is measured in the following final states: (1) where both W bosons decay to leptons, (2) where only one W boson decays to lepton while the other decays to quarks, and (3) where both the W bosons decay to quarks. 2.1 Measurement in e ± µ +jets final state The events are selected in this final state when one of the W boson decays to an electron and ν e while the other decays to a muon and ν µ. This channel corresponds to the smallest branching fraction, however, has the minimal background contribution leading to better precision in the measurement of the cross section. The events are selected with exactly one isolated electron and one isolated muon having opposite charge. The CMS analysis using data at 7 and 8 TeV requires no additional selection on the number of jets and b-tagged jets [4]. However, the events are categorized according to the number of b- tagged jets and additional non-b-tagged jets. The event selection in ATLAS requires one or two b-tagged jets, thus, dividing events in to two sub-categories. The ATLAS performed a simultaneous measurement of σ tt and b-tagging efficiency by solving the two simultaneous equations defined by the number of events with one or two b-tagged jets [3]. The inclusive cross section measured by ATLAS at 7 and 8 TeV are σ tt = ± 3.1 (stat) ± 4.2 (syst) ± 3.6 (lumi) ± 3.3 (beam) pb and σ tt = ± 1.7 (stat) ± 5.5 (syst) ± 7.5 (lumi) ± 4.2 (beam) pb, respectively [3]. The b-tagging efficiency is measured to be ε b = ± and ε b = 0.55 ± at 7 and 8 TeV, respectively, which agree well with the estimation from the Monte Carlo simulation. The cross section is also measured in the fiducial region, defined with events containing an eµ pair. The CMS measurement used a binned likelihood fit to the softest non-tagged jet p T distribution 1

4 in each category simultaneously to both 7 and 8 TeV data. Results were obtained for inclusive tt production cross sections (σ tt ) as well as the cross section in the fiducial region defined with events containing an eµ pair with p T > 20 GeV and η < 2.4. The inclusive cross section measured by CMS at 7 and 8 TeV are σ tt = ± 2.1 (stat) (syst) ± 3.8 (lumi) pb and σ tt = ± 1.4 (stat) (syst) ± 6.4 (lumi) pb, respectively [4]. Both ATLAS and CMS experiments have also performed the measurements in this channel using 13 TeV data recorded during the year 2015 [5, 6]. ATLAS used a total integrated luminosity of 3.2 fb 1 while the CMS used 2.2 fb 1 of data. The analysis strategy in ATLAS is similar to that of the 7 and 8 TeV analyses. However, the CMS performed the cross section measurement by simply counting the number of events with exactly one isolated, opposite charged eµ pair having at least two jets where at least one of them is a b-tagged jet. The measured value of the cross section in CMS is σ tt = 792 ± 8 (stat) ± 37 (syst) ± 21 (lumi) pb. The inclusive cross section measured by ATLAS is σ tt = 818 ± 8 (stat) ± 27 (syst) ± 19 (lumi) ± 12 (beam) pb and the fiducial cross section is σ f id = ± 0.1 (stat) ± 0.29 (syst) ± 0.26 (lumi) ± 0.17 (beam) pb. The tt estimated b-tagging efficiency is ε b = ± (stat) ± (syst) which is consistent with the simulation. The CMS experiment also measured the cross section at s = 5.02 TeV using data provided by LHC during a very short run in 2015 [6]. The analysis is performed using the similar strategy as for 13 TeV excluding the requirement of b-tagged jets. Only 24 events are observed from data while 17 ± 0.2 events are expected for the signal (tt e ± µ ) and 3.9 ± 0.8 events are expected for background. Thus, the measurement is dominated by the statistical uncertainty. The value of the measured cross section is σ tt = 82 ± 20 (stat) ± 5 (syst) ± 10 (lumi) pb, which agree with the theoretical prediction within the measured uncertainties. 2.2 Measurement in e + e and µ + µ final states The most recent measurement of σ tt in the final states tt e + e + jets and tt µ + µ + jets is performed by ATLAS experiment using 85 pb 1 of data recorded s = 13 TeV during early days of 2015 data recording [8]. The events are selected with a pair of isolated, opposite charged, and same flavour leptons (e or µ). To suppress contribution from Z+jets process the events with dilepton mass within M Z ± 10 GeV are rejected. The σ tt is measured using similar strategy as in eµ analysis by counting the number of events with exactly one and two b-tagged jets. A simultaneous estimation of σ tt and b-tagging efficiency is obtained. The measured value of cross sections are σ tt (e + e ) = 824 ± 88 (stat) ± 91 (syst) ± 82 (lumi) pb, σ tt (µ + µ ) = 683 ± 74 (stat) ± 76 (syst) ± 68 (lumi) pb, and σ tt (e + e + µ + µ ) = 749 ± 57 (stat) ± 79 (syst) ± 74 (lumi) pb. 2.3 Measurement in e/µ+jets final states The events are selected in this final state when one of the W boson decays to an electron or a muon and a neutrino, while the other decays to jets. The events are selected with exactly one isolated, high p T e/µ, and a number of additional jets. The ATLAS analysis using the data recorded at s = 8 TeV requires the presence of at least 3 jets of which at least one is a b-tagged jet. The number of events in the signal region are determined using a template fit to a likelihood discriminant that is constructed from the distribution of kinematic variables. The measured values 2

5 of the inclusive cross sections at 8 TeV are σ tt (e + jets) = 256 ± 2 (stat) ± 25 (syst) ± 7 (lumi) ± 4 (beam), σ tt (µ + jets) = 260 ± 1 (stat) (syst) ± 8 (lumi) ± 4 (beam), and the combination is σ tt (l + jets) = 258 ± 1 (stat) (syst) ± 8 (lumi) ± 4 (beam) [9]. The CMS analysis using the data recorded at s = 7 and 8 TeV requires the presence of at least 4 jets of which at least one is a b-tagged jet. The number of events in the signal region are extracted using a fit to the distribution of M lb (mass of lepton plus b-tagged jet system). A cross check analysis is performed with a fit to the M 3 (mass of combination of 3 highest p T jets) distribution. The shape of the QCD background is obtained from data. Two different event generators, MADGRAPH and POWHEG, are used to model signal template. The measured values of the cross sections at 8 TeV are σ tt (l + jets) = ± 3.8 ± 13.7 ± 6.0 pb (using MADGRAPH) and σ tt (l + jets) = ± 3.9 ± 14.2 ± 6.2 pb (using POWHEG), obtained using fit to M lb [10]. The results obtained with the cross check analysis are σ tt (l + jets) = ± 2.5 ± 19.1 ± 6.0 pb (using MADGRAPH) and σ tt (l + jets) = ± 2.8 ± 20.0 ± 6.2 pb (using POWHEG). The uncertainties are due to statistical, systematic, and luminosity, respectively. The cross section measured at 7 TeV (using MADGRAPH) is σ tt (l+jets) = ± 6.0 ± 12.0 ± 3.6 pb. The measured ratio of the cross sections for 7 to 8 TeV is 1.43 ± 0.04(stat) ± 0.07 (syst) ± 0.05 (lumi) [10]. ATLAS also performed measurements in this channel using data recorded in 2015 during early 13 TeV runs corresponding to an integrated luminosity of 85 pb 1 [11]. The cross section is measured using a simple counting of number of selected events. The measured value of the cross section is σ tt (l + jets) = 817 ± 13 (stat) ± 103 (syst) ± 88 (lumi) pb. The CMS performed analysis with full 2015 data at 13 TeV corresponding to the luminosity of 2.3 pb 1 [12]. The events are categorized on the basis of number of jets and number of b-tagged jets. The cross section is measured by employing a simultaneous binned likelihood fit to M lb or min(m lb ) distributions in all categories. The measured value of the cross section is σ tt (l + jets) = ± 2.5 (stat) ± 22.8 (syst) ± 22.5 (lumi) pb. 2.4 Measurement in fully hadronic final states The CMS experiment has also performed measurement of σ tt in fully hadronic final state where both W bosons decay to hadrons. Though, this final state corresponds to largest branching ratio ( 46%) it suffers from very large QCD multijet backgrounds. The events are triggered using a multijet trigger and selected in offline requiring at least six jets from which two or more are b- tagged jets. To discriminate signal from multijet background full tt system have been reconstructed using kinematic fit. The kinematic fit restores the reconstructed mass of top quark (m t ) to its nominal value and improves the resolution significantly which helps in separating it from the QCD background. An unbinned maximum likelihood fit to the m t distribution is performed to extract the signal and background normalizations. The analysis has been carried out using data recorded in 2012 at s = 8 TeV as well as data recorded in 2015 at s = 13 TeV [13, 14]. The measured cross section using 8 TeV data corresponding to a luminosity of 18.4 fb 1 is σ tt (all jets) = ± 6.1 (stat) ± 37.8 (syst) ± 7.2 (lumi) pb. The measured value with 2.53 fb 1 of 13 TeV data is σ tt (all jets) = 834 ± 25 (stat) (syst) ± 23 (lumi) pb. The measurement is also performed in the scenario where the top quark is boosted and is reconstructed as a single jet with a large distance parameter R = 0.8 using the Anti-K T algorithm. The measured cross section in the boosted scenario using 2.53 fb 1 of 13 TeV data is σ tt (all jets) = 727 ± 46 (stat) (syst) ± 20 (lumi) pb. 3

6 3. Measurement of tt + bb production cross section Measurements are performed by the ATLAS and CMS experiments at LHC on the production cross section of the tt in association with two b quarks (σ tt+bb ) [15, 16, 17]. This process is an irreducible background to the production of Higgs boson in association with a top-quark pair, tth, where the Higgs boson decays to a bb pair. The ATLAS experiment performed analysis, using 20.3 fb 1 of 8 TeV data, in both dilepton and lepton-plus-jets final states. The number of signal events are extracted by fitting the distribution of the b-tagging MVA discriminant. Measurements are performed for fiducial cross section of tt with one or two b-tagged jets. A cut-based analysis is also performed with very tight event selection criteria to cross check the fit-based results. Both results are found to be compatible within their measured uncertainties. The ratio R tt+bb = σ tt+bb /σ tt is measured to be 1.30 ± 0.33 (stat) ± 0.28 (syst)%. The CMS experiment also performed similar analysis, using 8 TeV data corresponding to an integrated luminosity of 19.6 fb 1, in dilepton final states with four or more jets, including two b-tagged jets. The ratio R tt+bb is determined for a minimum jet p T of both 20 and 40 GeV. The measured ratio is ± (stat) ± (syst) for p T > 20 GeV. The CMS has also performed this measurement, employing a similar analysis strategy, using 2.3 fb 1 of 13 TeV data recorded during The measured ratio is ± (stat) ± (syst), which is compatible with the previous CMS result. 4. Measurement of ttw, ttz, and ttγ production cross sections Both ATLAS and CMS experiments have performed measurements for the production cross section of ttw and ttz processes using data recorded at s = 8 and 13 TeV [18, 19, 20, 21]. Events with two same charge leptons or three leptons are used to measure σ ttw, while events with three or four leptons are used to measure σ ttz. The measurements are still dominated by uncertainties due to small statistics of selected events. Both experiments also performed measurements of the ttγ production cross section using data recorded at s = 7 and 8 TeV [22, 23]. Events are selected with an isolated lepton, an isolated photon, and additional jets. The measured cross section agrees with the theoretical prediction within the uncertainties. 5. Summary The ATLAS and CMS experiments have measured the inclusive cross section of the tt production at s = 7, 8, and 13 TeV using proton-proton collision data provided by the LHC. Only the results from the recent measurements have been presented in this article. The measured cross sections are in excellent agreement with the prediction from theoretical calculations as shown in Fig. 1. The measurements are also performed for the production cross section of tt + bb, ttw, ttz, and ttγ processes. The measured cross sections agree with the theoretical calculation within their measured uncertainties. References [1] ATLAS Collaboration, JINST 3:S08003 (2008) 4

7 cross section [pb] Inclusive tt Tevatron combined 1.96 TeV (L 8.8 fb ) CMS eµ* 5.02 TeV (L = 26 pb ) ATLAS eµ 7 TeV (L = 4.6 fb ) CMS eµ 7 TeV (L = 5 fb ) ATLAS eµ 8 TeV (L = 20.3 fb ) CMS eµ 8 TeV (L = 19.7 fb ) LHC combined eµ 8 TeV (L = fb ) ATLAS eµ 13 TeV (L = 3.2 fb ) CMS eµ* 13 TeV (L = 2.2 fb ) ATLAS ee/µµ* 13 TeV (L = 85 pb ) ATLAS l+jets* 13 TeV (L = 85 pb ) CMS l+jets* 13 TeV (L = 2.3 fb ) CMS all-jets* 13 TeV (L = 2.53 fb ) * Preliminary ATLAS+CMS Preliminary Aug 2016 LHCtop WG NNLO+NNLL (pp) NNLO+NNLL (pp) Czakon, Fiedler, Mitov, PRL 110 (2013) NNPDF3.0, m = GeV, α s (M ) = ± top Z s [TeV] s [TeV] 13 Figure 1: The measured values of the inclusive tt production cross section as function of the centre-of-mass energy in proton-(anti)proton collisions at Tevatron and LHC. The measurements are in good agreement with the theoretical predictions using NNLO+NNLL calculations. [2] CMS Collaboration, JINST 3:S08004 (2008) [3] ATLAS Collaboration, Eur.Phys.J. C74 (2014) 3109 [4] CMS Collaboration, JHEP 08 (2016) 029 [5] ATLAS Collaboration, Phys. Lett. B761 (2016) 136 [6] CMS Collaboration, arxiv: [hep-ex] [7] CMS Collaboration, CMS-PAS-TOP6-015 [8] ATLAS Collaboration, ATLAS-CONF [9] ATLAS Collaboration, Phys. Rev. D 91, (2015) [10] CMS Collaboration, arxiv: [hep-ex] [11] ATLAS Collaboration, ATLAS-CONF [12] CMS Collaboration, CMS-PAS-TOP6-006 [13] CMS Collaboration, Eur. Phys. J. C 76 (2016) 128 [14] CMS Collaboration, CMS-PAS-TOP6-013 [15] ATLAS Collaboration, Eur.Phys.J. C76(2016) 11 [16] CMS Collaboration, Phys. Lett. B746 (2015) 132 [17] CMS Collaboration, CMS-PAS-TOP6-010 [18] ATLAS Collaboration, JHEP 11 (2015) 172 [19] CMS Collaboration, Eur.Phys.J. C74 (2014) 3060 [20] ATLAS Collaboration, arxiv: [hep-ex] [21] CMS Collaboration, CMS-PAS-TOP6-017 [22] ATLAS Collaboration, Phys. Rev. D 91, (2015) [23] CMS Collaboration, PAS-TOP