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1. SMEFT chromomagnetic dipole operator contributions to $$t{{\bar{t}}}$$ production at approximate NNLO in QCD

   https://doi.org/10.1140/epjc/s10052-024-12938-9  

   Kidonakis, Nikolaos; Tonero, Alberto (June 2024, The European Physical Journal C)

   Abstract We study higher-order QCD corrections for the production of a top–antitop quark pair ($$t{{\bar{t}}}$$ $t\overline{t}$production) at the Large Hadron Collider in the Standard Model Effective Field Theory. We consider effects of new physics parametrized by the top-quark chromomagnetic dipole operator. We calculate new physics contributions to the total cross section at approximate NNLO, with second-order soft-gluon corrections added to the complete NLO result, including uncertainties from scale dependence and from parton distributions. We also calculate new physics contributions at approximate NNLO for differential distributions in top-quark transverse momentum. 

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2. Measurement of the production cross section of prompt $$\Xi ^0_{\textrm{c}}$$ baryons in p–Pb collisions at $$\sqrt{s_{{\textrm{NN}}}}=5.02$$ TeV

   https://doi.org/10.1140/epjc/s10052-024-13531-w  

   Acharya, S; Adamová, D; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; et al (January 2025, The European Physical Journal C)

   Abstract The transverse momentum ($$p_{\textrm{T}}$$ $p_{\text{T}}$) differential production cross section of the promptly produced charm-strange baryon$$\mathrm {\Xi _{c}^{0}}$$ ${\Xi }_c^0$(and its charge conjugate$$\overline{\mathrm {\Xi _{c}^{0}}}$$ $\overline{{\Xi }_c^0}$) is measured at midrapidity via its hadronic decay into$$\mathrm{\pi ^{+}}\Xi ^{-}$$ ${\pi }^{+}{\Xi }^{-}$in p–Pb collisions at a centre-of-mass energy per nucleon–nucleon collision$$\sqrt{s_{\textrm{NN}}}~=~5.02$$ $\sqrt{s_{\text{NN}}}=5.02$ TeV with the ALICE detector at the LHC. The$$\mathrm {\Xi _{c}^{0}}$$ ${\Xi }_c^0$nuclear modification factor ($$R_{\textrm{pPb}}$$ $R_{\text{pPb}}$), calculated from the cross sections in pp and p–Pb collisions, is presented and compared with the$$R_{\textrm{pPb}}$$ $R_{\text{pPb}}$of$$\mathrm {\Lambda _{c}^{+}}$$ ${\Lambda }_c^{+}$baryons. The ratios between the$$p_{\textrm{T}}$$ $p_{\text{T}}$-differential production cross section of$$\mathrm {\Xi _{c}^{0}}$$ ${\Xi }_c^0$baryons and those of$$\mathrm {D^0}$$ $D^0$mesons and$$\mathrm {\Lambda _{c}^{+}}$$ ${\Lambda }_c^{+}$baryons are also reported and compared with results at forward and backward rapidity from the LHCb Collaboration. The measurements of the production cross section of prompt$$\Xi ^0_\textrm{c}$$ ${\Xi }_{\text{c}}^0$baryons are compared with a model based on perturbative QCD calculations of charm-quark production cross sections, which includes only cold nuclear matter effects in p–Pb collisions, and underestimates the measurement by a factor of about 50. This discrepancy is reduced when the data is compared with a model that includes string formation beyond leading-colour approximation or in which hadronisation is implemented via quark coalescence. The$$p_{\textrm{T}}$$ $p_{\text{T}}$-integrated cross section of prompt$$\Xi ^0_\textrm{c}$$ ${\Xi }_{\text{c}}^0$-baryon production at midrapidity extrapolated down to$$p_{\textrm{T}}$$ $p_{\text{T}}$= 0 is also reported. These measurements offer insights and constraints for theoretical calculations of the hadronisation process. Additionally, they provide inputs for the calculation of the charm production cross section in p–Pb collisions at midrapidity. 

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3. Observation of four-top-quark production in the multilepton final state with the ATLAS detector

   https://doi.org/10.1140/epjc/s10052-023-11573-0  

   Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Hoffman, A. C.; et al (June 2023, The European Physical Journal C)

   Abstract This paper presents the observation of four-top-quark ($$t\bar{t}t\bar{t}$$ $t\overline{t}t\overline{t}$) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 $$\hbox {fb}^{-1}$$ ${\text{fb}}^{-1}$at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured$$t\bar{t}t\bar{t}$$ $t\overline{t}t\overline{t}$signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The$$t\bar{t}t\bar{t}$$ $t\overline{t}t\overline{t}$production cross section is measured to be$$22.5^{+6.6}_{-5.5}$$ $22.5_{-5.5}^{+6.6}$ fb, consistent with the SM prediction of$$12.0 \pm 2.4$$ $12.0\pm 2.4$fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect$$t\bar{t}t\bar{t}$$ $t\overline{t}t\overline{t}$production. 

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4. Measurement of inclusive and differential cross sections for single top quark production in association with a W boson in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

   https://doi.org/10.1007/JHEP07(2023)046  

   Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Damanakis, K.; Dragicevic, M.; Escalante Del Valle, A.; Hussain, P. S.; Jeitler, M.; et al (July 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> Measurements of the inclusive and normalised differential cross sections are presented for the production of single top quarks in association with a W boson in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data used were recorded with the CMS detector at the LHC during 2016–2018, and correspond to an integrated luminosity of 138 fb⁻¹. Events containing one electron and one muon in the final state are analysed. For the inclusive measurement, a multivariate discriminant, exploiting the kinematic properties of the events is used to separate the signal from the dominant$$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$background. A cross section of$$ 79.2\pm 0.9{\left(\textrm{stat}\right)}_{-8.0}^{+7.7}\left(\textrm{syst}\right)\pm 1.2\left(\textrm{lumi}\right) $$ $79.2\pm 0.9{\left(\text{stat}\right)}_{-8.0}^{+7.7}\left(\text{syst}\right)\pm 1.2\left(\text{lumi}\right)$pb is obtained, consistent with the predictions of the standard model. For the differential measurements, a fiducial region is defined according to the detector acceptance, and the requirement of exactly one jet coming from the fragmentation of a bottom quark. The resulting distributions are unfolded to particle level and agree with the predictions at next-to-leading order in perturbative quantum chromodynamics. 

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5. Inclusive and differential cross section measurements of $$ \textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$ production in the lepton+jets channel at $$ \sqrt{s} $$ = 13 TeV

   https://doi.org/10.1007/JHEP05(2024)042  

   Hayrapetyan, A; Tumasyan, A; Adam, W; Andrejkovic, J W; Bergauer, T; Chatterjee, S; Damanakis, K; Dragicevic, M; Escalante_Del_Valle, A; Hussain, P S; et al (May 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> Measurements of inclusive and normalized differential cross sections of the associated production of top quark-antiquark and bottom quark-antiquark pairs,$$ \textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$ $t\overline{t}b\overline{b}$, are presented. The results are based on data from proton-proton collisions collected by the CMS detector at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb⁻¹. The cross sections are measured in the lepton+jets decay channel of the top quark pair, using events containing exactly one isolated electron or muon and at least five jets. Measurements are made in four fiducial phase space regions, targeting different aspects of the$$ \textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$ $t\overline{t}b\overline{b}$process. Distributions are unfolded to the particle level through maximum likelihood fits, and compared with predictions from several event generators. The inclusive cross section measurements of this process in the fiducial phase space regions are the most precise to date. In most cases, the measured inclusive cross sections exceed the predictions with the chosen generator settings. The only exception is when using a particular choice of dynamic renormalization scale,$$ {\mu}_{\textrm{R}}=\frac{1}{2}{\prod}_{i=\textrm{t},\overline{\textrm{t}},\textrm{b},\overline{\textrm{b}}}{m}_{\textrm{T},i}^{1/4} $$ ${\mu }_R=\frac{1}{2}{\prod }_{i=t,\overline{t},b,\overline{b}}{m}_{T,i}^{1/4}$, where$$ {m}_{\textrm{T},i}^2={m}_i^2+{p}_{\textrm{T},i}^2 $$ $m_{T,i}^2=m_i^2+p_{T,i}^2$are the transverse masses of top and bottom quarks. The differential cross sections show varying degrees of compatibility with the theoretical predictions, and none of the tested generators with the chosen settings simultaneously describe all the measured distributions. 

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