Measurements of top-quark pair differential cross-sections in the lepton+jets channel in pp collisions at [Formula: see text] using the ATLAS detector

Abstract

Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, [Formula: see text] system and event-level kinematic observables in proton-proton collisions at a centre-of-mass energy of [Formula: see text]. The observables have been chosen to emphasize the [Formula: see text] production process and to be sensitive to effects of initial- and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3 fb[Formula: see text], recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in fair agreement with the predictions over a wide kinematic range. Nevertheless, most generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. Predictions beyond NLO accuracy improve the agreement with data at high top-quark transverse momenta. Using the current settings and parton distribution functions, the rapidity distributions are not well modelled by any generator under consideration. However, the level of agreement is improved when more recent sets of parton distribution functions are used.

Fig. 1

Kinematic distributions of the combined electron and muon selections at the detector level: a lepton transverse momentum and b missing transverse momentum $E_{\mathrm{T}}^{\mathrm{miss}}$, c jet multiplicity, d jet transverse momentum, e b-tagged jet multiplicity and f leading b-tagged jet $p_{\mathrm{T}}$. Data distributions are compared to predictions using Powheg +Pythia as the $t\overline{t}$ signal model. The hashed area indicates the combined statistical and systematic uncertainties on the total prediction, excluding systematic uncertainties related to the modelling of the $t\overline{t}$ system

Fig. 2

Distributions of observables of the combined electron and muon selections at detector level: a hadronic top-quark transverse momentum $p_{\mathrm{T}}^{t,\mathrm{had}}$ and b absolute value of the rapidity $|y^{t,\mathrm{had}}|$ , c $t\overline{t}$  invariant mass $m^{t\overline{t}}$, d transverse momentum $p_{\mathrm{T}}^{t\overline{t}}$ and e absolute value of the rapidity $|y^{t\overline{t}}|$ . Data distributions are compared to predictions, using Powheg +Pythia as the $t\overline{t}$ signal model. The hashed area indicates the combined statistical and systematic uncertainties (described in Sect. 9) on the total prediction, excluding systematic uncertainties related to the modelling of the $t\overline{t}$ system

Fig. 3

Distributions of observables of the combined electron and muon selections at the detector level: a absolute value of the out-of-plane momentum $p_{\mathrm{out}}^{t\overline{t}}$, b azimuthal angle between the two top quarks $\mathrm{\Delta }{\mathit{\varphi }}^{t\overline{t}}$, c production angle ${\mathit{\chi }}^{t\overline{t}}$, d longitudinal boost $y_{\mathrm{boost}}^{t\overline{t}}$, e scalar sum of hadronic and leptonic top-quarks transverse momenta and f ratio of the hadronic W boson and the hadronic top-quark transverse momenta. Data distributions are compared to predictions, using Powheg +Pythia as the $t\overline{t}$ signal model. The hashed area indicates the combined statistical and systematic uncertainties (described in Sect. 9) on the total prediction, excluding systematic uncertainties related to the modelling of the $t\overline{t}$ system

Fig. 4

The a acceptance, b matching and c efficiency corrections, and the d detector-to-particle level migration matrix for the hadronic top-quark transverse momentum evaluated with the Powheg +Pythia simulation sample with $h_{\mathrm{damp}}=m_t$ and using CT10nlo PDF. In Fig. a–c the dashed linesillustrate the corrections evaluated on alternative ISR/FSR-varied samples. In Fig. d, the empty bins contain either no events or the number of events is less than 0.5 %

Fig. 5

Fiducial phase-space normalized differential cross-sections as a function of the a transverse momentum ($p_{\mathrm{T}}^{t,\mathrm{had}}$) and b absolute value of the rapidity ($|y^{t,\mathrm{had}}|$) of the hadronic top quark. The yellow bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 6

Fiducial phase-space normalized differential cross-sections as a function of the a invariant mass ($m^{t\overline{t}}$), b transverse momentum ($p_{\mathrm{T}}^{t\overline{t}}$) and c absolute value of the rapidity ($|y^{t\overline{t}}|$ ) of the $t\overline{t}$  system. The yellow bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 7

Fiducial phase-space normalized differential cross-sections as a function of the $t\overline{t}$  a production angle (${\mathit{\chi }}^{t\overline{t}}$) and b longitudinal boost ($y_{\mathrm{boost}}^{t\overline{t}}$). The yellow bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 8

Fiducial phase-space normalized differential cross-sections as a function of the $t\overline{t}$  a out-of-plane momentum ($|p_{\mathrm{out}}^{t\overline{t}}|$) and b azimuthal angle ($\mathrm{\Delta }{\mathit{\varphi }}^{t\overline{t}}$). The yellow bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 9

Fiducial phase-space normalized differential cross-sections as a function of the a  scalar sum of the transverse momenta of the hadronic and leptonic top quarks ($H_{\mathrm{T}}^{t\overline{t}}$) and b  the ratio of the hadronic W and the hadronic top transverse momenta ($R_{Wt}$). The yellow bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 10

Fiducial phase-space normalized differential cross-sections as a function of the a absolute value of the rapidity of the hadronic top quark ($|y^{t,\mathrm{had}}|$), b absolute value of the rapidity ($|y^{t\overline{t}}|$ ) of the $t\overline{t}$  system and c longitudinal boost ($y_{\mathrm{boost}}^{t\overline{t}}$). The yellow bands indicate the total uncertainty on the data in each bin. The MC@NLO +Herwig generator is reweighted using the new PDF sets to produce the different predictions. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 11

Full phase-space normalized differential cross-sections as a function of the a transverse momentum ($p_{\mathrm{T}}^t$) and b the absolute value of the rapidity ($|y^t|$ ) of the top quark. The grey bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 12

Full phase-space normalized differential cross-sections as a function of the  a invariant mass ($m^{t\overline{t}}$), b transverse momentum ($p_{\mathrm{T}}^{t\overline{t}}$) and c absolute value of the rapidity ($|y^{t\overline{t}}|$ ) of the $t\overline{t}$ system. The grey bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 13

Full phase-space normalized differential cross-sections as a function of the  a production angle (${\mathit{\chi }}^{t\overline{t}}$) and b longitudinal boost ($y_{\mathrm{boost}}^{t\overline{t}}$) of the $t\overline{t}$ system. The grey bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 14

Full phase-space normalized differential cross-sections as a function of the  a out-of-plane momentum ($|p_{\mathrm{out}}^{t\overline{t}}|$), b azimuthal angle ($\mathrm{\Delta }{\mathit{\varphi }}^{t\overline{t}}$), and c  scalar sum of the transverse momenta of the hadronic and leptonic top quarks ($H_{\mathrm{T}}^{t\overline{t}}$)) of the $t\overline{t}$ system. The grey bands indicate the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 15

Full phase-space normalized differential cross-section as a function of the a transverse momentum ($p_{\mathrm{T}}^t$) and b absolute value of the rapidity of the top quark ($|y^t|$) compared to higher-order theoretical calculations. The grey band indicates the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 16

Full phase-space normalized differential cross-section as a function of the a transverse momentum ($p_{\mathrm{T}}^t$) and b absolute value of the rapidity of the top quark ($|y^t|$) compared to NNLO theoretical calculations [85] using the MSTW2008nnlo PDF set. The grey band indicates the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 17

Full phase-space normalized differential cross-section as a function of the a invariant mass ($m^{t\overline{t}}$ ) and b transverse momentum ($p_{\mathrm{T}}^{t\overline{t}}$) of the $t\overline{t}$ system compared to higher-order theoretical calculations. The grey band indicates the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects

Fig. 18

Full phase-space normalized differential cross-section as a function of the a invariant mass ($m^{t\overline{t}}$ ) and b absolute value of the rapidity ($|y^{t\overline{t}}|$) of the $t\overline{t}$ system compared to NNLO theoretical calculations [85] using the MSTW2008nnlo PDF set. The grey band indicates the total uncertainty on the data in each bin. The Powheg +Pythia generator with $h_{\mathrm{damp}}=m_t$ and the CT10nlo PDF is used as the nominal prediction to correct for detector effects