Abstract
We present a comparative study of various approaches for modelling of the \( {e}^{+}{v}_e{\mu}^{-}{\overline{v}}_{\mu }b\overline{b}\gamma \) final state in \( t\overline{t}\gamma \) production at the LHC. Working at the NLO in QCD we compare the fully realistic description of the top quark decay chain with the one provided by the narrow-width-approximation. The former approach comprises all double, single and non-resonant diagrams, interferences, and off-shell effects of the top quarks. The latter incorporates only double resonant contributions and restricts the unstable top quarks to on-shell states. We confirm that for the integrated cross sections the finite top quark width effects are small and of the order of \( \mathcal{O}\left({\Gamma}_t/{m}_t\right) \). We show, however, that they are strongly enhanced for more exclusive observables. In addition, we investigate fractions of events where the photon is radiated either in the production or in the decay stage. We find that large fraction of isolated photons comes from radiative decays of top quarks. Based on our findings, selection criteria might be developed to reduce such contributions, that constitute a background for the measurement of the anomalous couplings in the \( t\overline{t}\upgamma \) vertex.
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CDF collaboration, Evidence for \( t\overline{t}\gamma \) production and measurement of σt \( \overline{t}\gamma \)/σt \( \overline{t} \), Phys. Rev. D 84 (2011) 031104 [arXiv:1106.3970] [INSPIRE].
ATLAS collaboration, Observation of top-quark pair production in association with a photon and measurement of the \( t\overline{t}\gamma \) production cross section in pp collisions at \( \sqrt{s} \) = 7 TeV using the ATLAS detector, Phys. Rev. D 91 (2015) 072007 [arXiv:1502.00586] [INSPIRE].
ATLAS collaboration, Measurement of the \( t\overline{t}\gamma \) production cross section in proton-proton collisions at \( \sqrt{s} \) = 8 TeV with the ATLAS detector, JHEP 11 (2017) 086 [arXiv:1706.03046] [INSPIRE].
CMS collaboration, Measurement of the semileptonic \( t\overline{t} \)+ γ production cross section in pp collisions at \( \sqrt{s} \) = 8 TeV, JHEP 10 (2017) 006 [arXiv:1706.08128] [INSPIRE].
ATLAS collaboration, Measurements of inclusive and differential fiducial cross-sections of \( t\overline{t}\gamma \) production in leptonic final states at \( \sqrt{s} \) = 13 TeV in ATLAS, Eur. Phys. J. C 79 (2019) 382 [arXiv:1812.01697] [INSPIRE].
ATLAS collaboration, Measurements of inclusive and differential cross-sections of \( t\overline{t}\gamma \) production in the eμ channel at 13 TeV with the ATLAS detector, ATLAS-CONF-2019-042 (2019).
U. Baur, M. Buice and L.H. Orr, Direct measurement of the top quark charge at hadron colliders, Phys. Rev. D 64 (2001) 094019 [hep-ph/0106341] [INSPIRE].
CDF collaboration, Exclusion of exotic top-like quarks with −4/3 electric charge using jet-charge tagging in single-lepton \( t\overline{t} \) events at CDF, Phys. Rev. D 88 (2013) 032003 [arXiv:1304.4141] [INSPIRE].
ATLAS collaboration, Measurement of the top quark charge in pp collisions at \( \sqrt{s} \) = 7 TeV with the ATLAS detector, JHEP 11 (2013) 031 [arXiv:1307.4568] [INSPIRE].
J.A. Aguilar-Saavedra, A minimal set of top anomalous couplings, Nucl. Phys. B 812 (2009) 181 [arXiv:0811.3842] [INSPIRE].
U. Baur, A. Juste, L.H. Orr and D. Rainwater, Probing electroweak top quark couplings at hadron colliders, Phys. Rev. D 71 (2005) 054013 [hep-ph/0412021] [INSPIRE].
A.O. Bouzas and F. Larios, Electromagnetic dipole moments of the Top quark, Phys. Rev. D 87 (2013) 074015 [arXiv:1212.6575] [INSPIRE].
M. Schulze and Y. Soreq, Pinning down electroweak dipole operators of the top quark, Eur. Phys. J. C 76 (2016) 466 [arXiv:1603.08911] [INSPIRE].
O. Bessidskaia Bylund et al., Probing top quark neutral couplings in the standard model effective field theory at NLO in QCD, JHEP 05 (2016) 052 [arXiv:1601.08193] [INSPIRE].
G. Bevilacqua et al., Precise predictions for \( t\overline{t}\gamma \)/\( t\overline{t} \) cross section ratios at the LHC, JHEP 01 (2019) 188 [arXiv:1809.08562] [INSPIRE].
J.A. Aguilar-Saavedra, E. Á lvarez, A. Juste and F. Rubbo, Shedding light on the \( t\overline{t} \) asymmetry: the photon handle, JHEP 04 (2014) 188 [arXiv:1402.3598] [INSPIRE].
J.A. Aguilar-Saavedra, Single lepton charge asymmetries in \( t\overline{t} \) and \( t\overline{t}\gamma \) production at the LHC, Eur. Phys. J. C 78 (2018) 434 [arXiv:1802.05721] [INSPIRE].
J. Bergner and M. Schulze, The top quark charge asymmetry in \( t\overline{t}\gamma \) production at the LHC, Eur. Phys. J. C 79 (2019) 189 [arXiv:1812.10535] [INSPIRE].
P.-F. Duan et al., QCD corrections to associated production of \( t\overline{t}\gamma \) at hadron colliders, Phys. Rev. D 80 (2009) 014022 [arXiv:0907.1324] [INSPIRE].
P.-F. Duan et al., Next-to-leading order QCD corrections to \( t\overline{t}\gamma \) production at the 7 TeV LHC, Chin. Phys. Lett. 28 (2011) 111401 [arXiv:1110.2315] [INSPIRE].
F. Maltoni, D. Pagani and I. Tsinikos, Associated production of a top-quark pair with vector bosons at NLO in QCD: impact on \( t\overline{t}\mathrm{H} \) searches at the LHC, JHEP 02 (2016) 113 [arXiv:1507.05640] [INSPIRE].
P.-F. Duan et al., Electroweak corrections to top quark pair production in association with a hard photon at hadron colliders, Phys. Lett. B 766 (2017) 102 [arXiv:1612.00248] [INSPIRE].
A. Kardos and Z. Trócsányi, Hadroproduction of \( t\overline{t} \) pair in association with an isolated photon at NLO accuracy matched with parton shower, JHEP 05 (2015) 090 [arXiv:1406.2324] [INSPIRE].
S. Frixione, P. Nason and C. Oleari, Matching NLO QCD computations with Parton Shower simulations: the POWHEG method, JHEP 11 (2007) 070 [arXiv:0709.2092] [INSPIRE].
S. Alioli, P. Nason, C. Oleari and E. Re, A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX, JHEP 06 (2010) 043 [arXiv:1002.2581] [INSPIRE].
G. Bevilacqua et al., HELAC-NLO, Comput. Phys. Commun. 184 (2013) 986 [arXiv:1110.1499] [INSPIRE].
T. Sjöstrand et al., An introduction to PYTHIA 8.2, Comput. Phys. Commun. 191 (2015) 159 [arXiv:1410.3012] [INSPIRE].
M. Bahr et al., HERWIG++ physics and manual, Eur. Phys. J. C 58 (2008) 639 [arXiv:0803.0883] [INSPIRE].
K. Melnikov, M. Schulze and A. Scharf, QCD corrections to top quark pair production in association with a photon at hadron colliders, Phys. Rev. D 83 (2011) 074013 [arXiv:1102.1967] [INSPIRE].
G. Bevilacqua et al., Hard photons in hadroproduction of top quarks with realistic final states, JHEP 10 (2018) 158 [arXiv:1803.09916] [INSPIRE].
A. van Hameren, C.G. Papadopoulos and R. Pittau, Automated one-loop calculations: a proof of concept, JHEP 09 (2009) 106 [arXiv:0903.4665] [INSPIRE].
M. Czakon, C.G. Papadopoulos and M. Worek, Polarizing the dipoles, JHEP 08 (2009) 085 [arXiv:0905.0883] [INSPIRE].
N. Kauer and D. Zeppenfeld, Finite width effects in top quark production at hadron colliders, Phys. Rev. D 65 (2002) 014021 [hep-ph/0107181] [INSPIRE].
C.F. Uhlemann and N. Kauer, Narrow-width approximation accuracy, Nucl. Phys. B 814 (2009) 195 [arXiv:0807.4112] [INSPIRE].
W. Bernreuther, A. Brandenburg, Z.G. Si and P. Uwer, Top quark pair production and decay at hadron colliders, Nucl. Phys. B 690 (2004) 81 [hep-ph/0403035] [INSPIRE].
K. Melnikov and M. Schulze, NLO QCD corrections to top quark pair production and decay at hadron colliders, JHEP 08 (2009) 049 [arXiv:0907.3090] [INSPIRE].
K. Melnikov, A. Scharf and M. Schulze, Top quark pair production in association with a jet: QCD corrections and jet radiation in top quark decays, Phys. Rev. D 85 (2012) 054002 [arXiv:1111.4991] [INSPIRE].
J.M. Campbell and R.K. Ellis, Top-quark processes at NLO in production and decay, J. Phys. G 42 (2015) 015005 [arXiv:1204.1513] [INSPIRE].
A. Behring et al., Higher order corrections to spin correlations in top quark pair production at the LHC, Phys. Rev. Lett. 123 (2019) 082001 [arXiv:1901.05407] [INSPIRE].
V.S. Fadin, V.A. Khoze and A.D. Martin, How suppressed are the radiative interference effects in heavy instable particle production?, Phys. Lett. B 320 (1994) 141 [hep-ph/9309234] [INSPIRE].
SM and NLO MULTILEG Working Group, SM MC Working Group collaboration, The SM and NLO multileg and SM MC working groups: summary report, arXiv:1203.6803 [INSPIRE].
A. Denner, S. Dittmaier, S. Kallweit and S. Pozzorini, NLO QCD corrections to off-shell ttbar production at hadron colliders, PoS LL2012 (2012) 015 [arXiv:1208.4053] [INSPIRE].
R. Röntsch and M. Schulze, Constraining couplings of top quarks to the Z boson in \( t\overline{t} \) + Z production at the LHC, JHEP 07 (2014) 091 [Erratum ibid. 09 (2015) 132] [arXiv:1404.1005] [INSPIRE].
K. Melnikov and M. Schulze, NLO QCD corrections to top quark pair production in association with one hard jet at hadron colliders, Nucl. Phys. B 840 (2010) 129 [arXiv:1004.3284] [INSPIRE].
J.M. Campbell and R.K. Ellis, \( t\overline{t} \)W ± production and decay at NLO, JHEP 07 (2012) 052 [arXiv:1204.5678] [INSPIRE].
A. Bredenstein, A. Denner, S. Dittmaier and S. Pozzorini, NLO QCD corrections to pp → \( t\overline{t}b\overline{b} \) + X at the LHC, Phys. Rev. Lett. 103 (2009) 012002 [arXiv:0905.0110] [INSPIRE].
G. Bevilacqua et al., Assault on the NLO Wishlist: pp → \( t\overline{t}b\overline{b} \), JHEP 09 (2009) 109 [arXiv:0907.4723] [INSPIRE].
A. Bredenstein, A. Denner, S. Dittmaier and S. Pozzorini, NLO QCD corrections to top anti-top bottom anti-bottom production at the LHC: 2. Full hadronic results, JHEP 03 (2010) 021 [arXiv:1001.4006] [INSPIRE].
G. Bevilacqua, M. Czakon, C.G. Papadopoulos and M. Worek, Dominant QCD backgrounds in Higgs boson analyses at the LHC: a study of pp → \( t\overline{t} \)+ 2 jets next-to-leading order, Phys. Rev. Lett. 104 (2010) 162002 [arXiv:1002.4009] [INSPIRE].
G. Bevilacqua, M. Czakon, C.G. Papadopoulos and M. Worek, Hadronic top-quark pair production in association with two jets at next-to-leading order QCD, Phys. Rev. D 84 (2011) 114017 [arXiv:1108.2851] [INSPIRE].
G. Bevilacqua and M. Worek, Constraining BSM physics at the LHC: four top final states with NLO accuracy in perturbative QCD, JHEP 07 (2012) 111 [arXiv:1206.3064] [INSPIRE].
R. Frederix, D. Pagani and M. Zaro, Large NLO corrections in \( t\overline{t} \)W ± and \( t\overline{t}t\overline{t} \) hadroproduction from supposedly subleading EW contributions, JHEP 02 (2018) 031 [arXiv:1711.02116] [INSPIRE].
M.V. Garzelli, A. Kardos and Z. Trócsányi, Hadroproduction of \( t\overline{t}b\overline{b} \) final states at LHC: predictions at NLO accuracy matched with Parton Shower, JHEP 03 (2015) 083 [arXiv:1408.0266] [INSPIRE].
G. Bevilacqua, M.V. Garzelli and A. Kardos, \( t\overline{t}b\overline{b} \) hadroproduction with massive bottom quarks with PowHel, arXiv:1709.06915 [INSPIRE].
T. Ježo, J.M. Lindert, N. Moretti and S. Pozzorini, New NLOPS predictions for \( t\overline{t} \)+ b-jet production at the LHC, Eur. Phys. J. C 78 (2018) 502 [arXiv:1802.00426] [INSPIRE].
A. Kanaki and C.G. Papadopoulos, HELAC: a package to compute electroweak helicity amplitudes, Comput. Phys. Commun. 132 (2000) 306 [hep-ph/0002082] [INSPIRE].
A. Cafarella, C.G. Papadopoulos and M. Worek, Helac-phegas: a generator for all parton level processes, Comput. Phys. Commun. 180 (2009) 1941 [arXiv:0710.2427] [INSPIRE].
G. Bevilacqua et al., Complete off-shell effects in top quark pair hadroproduction with leptonic decay at next-to-leading order, JHEP 02 (2011) 083 [arXiv:1012.4230] [INSPIRE].
G. Bevilacqua, H.B. Hartanto, M. Kraus and M. Worek, Top quark pair production in association with a jet with next-to-leading-order QCD off-shell effects at the Large Hadron Collider, Phys. Rev. Lett. 116 (2016) 052003 [arXiv:1509.09242] [INSPIRE].
G. Bevilacqua, H.B. Hartanto, M. Kraus and M. Worek, Off-shell top quarks with one jet at the LHC: a comprehensive analysis at NLO QCD, JHEP 11 (2016) 098 [arXiv:1609.01659] [INSPIRE].
G. Bevilacqua et al., Top quark mass studies with ttj at the LHC, JHEP 03 (2018) 169 [arXiv:1710.07515] [INSPIRE].
G. Bevilacqua et al., Towards constraining dark matter at the LHC: higher order QCD predictions for \( t\overline{t} \) + Z (Z → \( {v}_{\mathrm{\ell}}{\overline{v}}_{\mathrm{\ell}} \) ), JHEP 11 (2019) 001 [arXiv:1907.09359] [INSPIRE].
S. Catani and M.H. Seymour, A general algorithm for calculating jet cross-sections in NLO QCD, Nucl. Phys. B 485 (1997) 291 [Erratum ibid. B 510 (1998) 503] [hep-ph/9605323] [INSPIRE].
S. Catani, S. Dittmaier, M.H. Seymour and Z. Trócsányi, The dipole formalism for next-to-leading order QCD calculations with massive partons, Nucl. Phys. B 627 (2002) 189 [hep-ph/0201036] [INSPIRE].
J.M. Campbell, R.K. Ellis and F. Tramontano, Single top production and decay at next-to-leading order, Phys. Rev. D 70 (2004) 094012 [hep-ph/0408158] [INSPIRE].
Z. Nagy and Z. Trócsányi, Next-to-leading order calculation of four jet observables in electron positron annihilation, Phys. Rev. D 59 (1999) 014020 [Erratum ibid. D 62 (2000) 099902] [hep-ph/9806317] [INSPIRE].
Z. Nagy, Next-to-leading order calculation of three jet observables in hadron hadron collision, Phys. Rev. D 68 (2003) 094002 [hep-ph/0307268] [INSPIRE].
S. Dulat et al., New parton distribution functions from a global analysis of quantum chromodynamics, Phys. Rev. D 93 (2016) 033006 [arXiv:1506.07443] [INSPIRE].
NNPDF collaboration, Parton distributions for the LHC Run II, JHEP 04 (2015) 040 [arXiv:1410.8849] [INSPIRE].
L.A. Harland-Lang, A.D. Martin, P. Motylinski and R.S. Thorne, Parton distributions in the LHC era: MMHT 2014 PDFs, Eur. Phys. J. C 75 (2015) 204 [arXiv:1412.3989] [INSPIRE].
M. Cacciari, G.P. Salam and G. Soyez, The anti-kt jet clustering algorithm, JHEP 04 (2008) 063 [arXiv:0802.1189] [INSPIRE].
S. Frixione, Isolated photons in perturbative QCD, Phys. Lett. B 429 (1998) 369 [hep-ph/9801442] [INSPIRE].
M. Jezabek and J.H. Kuhn, QCD corrections to semileptonic decays of heavy quarks, Nucl. Phys. B 314 (1989) 1 [INSPIRE].
K.G. Chetyrkin, R. Harlander, T. Seidensticker and M. Steinhauser, Second order QCD corrections to Γ(t → W b), Phys. Rev. D 60 (1999) 114015 [hep-ph/9906273] [INSPIRE].
A. Denner, S. Dittmaier, S. Kallweit and S. Pozzorini, NLO QCD corrections to off-shell top-antitop production with leptonic decays at hadron colliders, JHEP 10 (2012) 110 [arXiv:1207.5018] [INSPIRE].
J. Butterworth et al., PDF4LHC recommendations for LHC Run II, J. Phys. G 43 (2016) 023001 [arXiv:1510.03865] [INSPIRE].
G. Heinrich, A. Maier, R. Nisius, J. Schlenk and J. Winter, NLO QCD corrections to W + W − \( b\overline{b} \) production with leptonic decays in the light of top quark mass and asymmetry measurements, JHEP 06 (2014) 158 [arXiv:1312.6659] [INSPIRE].
G. Heinrich et al., NLO and off-shell effects in top quark mass determinations, JHEP 07 (2018) 129 [arXiv:1709.08615] [INSPIRE].
S. Ferrario Ravasio, T. Ježo, P. Nason and C. Oleari, A theoretical study of top-mass measurements at the LHC using NLO+PS generators of increasing accuracy, Eur. Phys. J. C 78 (2018) 458 [arXiv:1801.03944] [INSPIRE].
M. Beneke et al., Top quark physics, in the proceedings of the 1999 CERN Workshop on standard model physics (and more) at the LHC, May 25–26, CERN, Geneva, Switzerland (2000), hep-ph/0003033 [INSPIRE].
S. Liebler, G. Moortgat-Pick and A.S. Papanastasiou, Probing the top-quark width through ratios of resonance contributions of e+ e− → W + W − \( b\overline{b} \), JHEP 03 (2016) 099 [arXiv:1511.02350] [INSPIRE].
A. Baskakov, E. Boos and L. Dudko, Model independent top quark width measurement using a combination of resonant and nonresonant cross sections, Phys. Rev. D 98 (2018) 116011 [arXiv:1807.11193] [INSPIRE].
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Bevilacqua, G., Hartanto, H., Kraus, M. et al. Off-shell vs on-shell modelling of top quarks in photon associated production. J. High Energ. Phys. 2020, 154 (2020). https://doi.org/10.1007/JHEP03(2020)154
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DOI: https://doi.org/10.1007/JHEP03(2020)154