Articoli di riviste: "Four-top-quark"

1

Blekman, Freya, Fréderic Déliot, Valentina Dutta e Emanuele Usai. "Four-top quark physics at the LHC". Universe 8, n. 12 (30 novembre 2022): 638. http://dx.doi.org/10.3390/universe8120638.

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The production of four top quarks presents a rare process in the Standard Model that provides unique opportunities and sensitivity to Standard Model observables including potential enhancement of many popular new physics extensions. This article summarises the latest experimental measurements of the four-top quark production cross section at the LHC. An overview is provided detailing interpretations of the experimental results regarding the top quark Yukawa coupling in addition to the limits on physics beyond the Standard Model. Further, prospects for future measurements and opportunities offered by this challenging final state are given herein.

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2

Darmé, Luc, Benjamin Fuks e Mark Goodsell. "Cornering sgluons with four-top-quark events". Physics Letters B 784 (settembre 2018): 223–28. http://dx.doi.org/10.1016/j.physletb.2018.08.001.

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3

Cao, Qing-Hong, Jun-Ning Fu, Yandong Liu, Xiao-Hu Wang e Rui Zhang. "Probing top-philic new physics via four-top-quark production *". Chinese Physics C 45, n. 9 (1 settembre 2021): 093107. http://dx.doi.org/10.1088/1674-1137/ac0c6f.

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4

Fariborz, Amir H., Renata Jora, Salah Nasri e Joseph Schechter. "A hierarchy of the quark masses in a top condensate model with multiple Higgses". Modern Physics Letters A 29, n. 06 (28 febbraio 2014): 1450030. http://dx.doi.org/10.1142/s0217732314500308.

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We discuss the quark masses in a top condensate model where not only two quark but also four quark composite states may exist. We show that the presence of the top color group SU (3)1× SU (3)2 with the correct quark representations can justify even in the absence of the additional technicolor interactions a hierarchy of the quark masses where the light quarks masses have the same size, the charm and bottom masses are higher and similar and the top is the heaviest.

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5

Morozumi, Takuya, Apriadi Salim Adam, Yuta Kawamura, Albertus Hariwangsa Panuluh, Yusuke Shimizu e Kei Yamamoto. "Effective theory for universal seesaw model and FCNC". Journal of Physics: Conference Series 2446, n. 1 (1 febbraio 2023): 012046. http://dx.doi.org/10.1088/1742-6596/2446/1/012046.

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Abstract We study the quark sector of the universal seesaw model with SU(2) L × SU(2) R × U(1). The model incorporates the seesaw mechanism with the vector-like quarks (VLQs). The purpose of this work is to study the model with the effective theory. After integrating the heavy five VLQs, we derive the effective theory with four up-type quark and three down type quark. In this work, the FCNC of Z boson for top quark and top′ quark is derived.

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6

Castro, Andrea. "Top-quark mass at hadron colliders". International Journal of Modern Physics A 29, n. 22 (29 agosto 2014): 1430029. http://dx.doi.org/10.1142/s0217751x14300294.

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Top-quarks can be produced abundantly at hadron colliders like the Tevatron at Fermilab and the Large Hadron Collider at CERN, and a variety of measurements of top-quark properties have been gathered in the recent years from four experiments: CDF and D0 at the Tevatron and ATLAS and CMS at the Large Hadron Collider. In this review the most recent results on the measurement of the top-quark mass by the four different collaborations, with various techniques and considering different topologies, are reported.

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7

Malekhosseini, Maliheh, e Mehrdad Ghominejad. "Top quark flavor changing neutral currents and dipole moments through three and four top-quark productions at the LHC". Journal of Physics: Conference Series 1137 (gennaio 2019): 012014. http://dx.doi.org/10.1088/1742-6596/1137/1/012014.

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8

Carena, M., H. E. Haber e C. E. M. Wagner. "Four-generation low energy supersymmetry with a light top quark". Nuclear Physics B 472, n. 1-2 (luglio 1996): 55–78. http://dx.doi.org/10.1016/0550-3213(96)00257-x.

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9

Alici, E., e M. Köksal. "Probing the anomalous tqγ couplings through single top production at the future lepton–hadron colliders". Modern Physics Letters A 34, n. 36 (27 novembre 2019): 1950298. http://dx.doi.org/10.1142/s0217732319502985.

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The measurements of the top quark flavor changing neutral current interactions are one of the most important goals of the top quark physics program in the present and the future collider experiments. These measurements provide direct information on nonstandard interactions of the top quark. Within the framework of new physics beyond the Standard Model, these interactions can be defined by an effective Lagrangian. In this study, we have investigated the potential of the future [Formula: see text] colliders on the top quark flavor changing neutral current interactions through the subprocesses [Formula: see text], where [Formula: see text]. These subprocesses have been produced through the main reaction [Formula: see text] at the LHC-[Formula: see text], the FCC-[Formula: see text] and the SPPC-[Formula: see text]. For the main reaction, the total cross-sections have been calculated as a function of the anomalous [Formula: see text] couplings. In addition, sensitivities on [Formula: see text] at 95% Confidence Level have been calculated. We obtain that the best constraints on [Formula: see text] are at the order of [Formula: see text] which is four orders of magnitude better than the LHC’s experimental results.

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10

Ferreira da Silva, P. "Physics of the Top Quark at the LHC: An Appraisal and Outlook of the Road Ahead". Annual Review of Nuclear and Particle Science 73, n. 1 (25 settembre 2023): 255–84. http://dx.doi.org/10.1146/annurev-nucl-102419-052854.

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Since its start, the Large Hadron Collider (LHC) has helped advance both theory and experiment on the production and properties of the heaviest fundamental particle, the top quark. This review focuses on a selected set of measurements and associated searches for new physics, which have opened the door for unprecedented precision in this area of high-energy physics. Fundamental parameters of the theory such as m t, αS, V tb, and y t are measured from top quark events with relative uncertainties that are smaller than 0.5%, 1.8%, 2%, and 10%, respectively, and that are expected to improve with more data, better experimental methods, and more accurate theory predictions. Several results, even if statistically limited, already significantly constrain the phase space of new physics: measurements of associated production with bosons, processes with four top quarks, and searches for rare decays, among others. It is expected that until the completion of the LHC program, top quark physics will keep providing unique insights regarding the consistency of the Standard Model and the energy scale of new physics.

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11

B, Bayarsaikhan, Enkhbat Ts e Erdenebulgan L. "Top quark phenomena in association with new vector bosons". Физик сэтгүүл 25, n. 478 (25 febbraio 2022): 212–14. http://dx.doi.org/10.22353/physics.v25i478.236.

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In this work, we study collider phenomenology of pair produced new heavy vector bosons further decaying into top quark pair and quartic top, top pair plus bottom pair production in proton-proton collisions at CERN LHC with 13 TeV center of mass energy in the presence of new color octet vector boson. The complete simulation chain analysis from parton to the detector level is done for the pair production, As for the four quark production through pair of the new heavy vector particles is doneat the matrix level. In doing so we have preparatory work . The extension of SM is implemented by Mathematica—FeynRule package. Calculations are done by MadGraph5 /+ Phythia6, Delphes / simulation program and results are analysed in ROOT CERN. In conclusion, we compared Standard model extension results with the SM.

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12

Pois, Heath, Thomas J. Weiler e Tzu Chiang Yuan. "Higgs-boson decay to four fermions including a single top quark belowtt¯threshold". Physical Review D 47, n. 9 (1 maggio 1993): 3886–97. http://dx.doi.org/10.1103/physrevd.47.3886.

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13

NOWAKOWSKI, MAREK, e APOSTOLOS PILAFTSIS. "CP-ODD PHENOMENA DUE TO FINITE WIDTH EFFECTS OF THE TOP QUARK". Modern Physics Letters A 06, n. 21 (10 luglio 1991): 1933–42. http://dx.doi.org/10.1142/s0217732391002086.

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Strong experimental indications exist that the top quark mass in the Standard Model (SM) exceeds the mass of the W gauge boson. Since this opens the decay mode t → Wb a suitable regularization of the top quark propagator in the s-channel is required in many tree reactions. As in the Z0 case this regularization essentially results in an. additional imaginary contribution (iΓtmt) to the propagator. This absorptive phase can combine with complex coupling constants of the charged current sector to give rise to new CP violating effects. Theoretical upper bounds for the size of these CP-odd signals are estimated in various extensions of the SM such as: the four generation SM, left-right symmetric models and models with two or three Higgs doublets.

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14

HUNG, P. Q. "A PHENOMENOLOGICAL THEORY OF FERMION MASSES AND MIXINGS". Modern Physics Letters A 09, n. 19 (21 giugno 1994): 1745–53. http://dx.doi.org/10.1142/s0217732394001593.

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A phenomenological theory of fermion masses and mixings is constructed within the framework of a four-family symmetry. It is found that the most favored set of relevant CKM elements are |Vus| ≈ 0.222, |Vcb| ≈ 0.044, |Vub/Vcb| ≈ 0.082, |Vud| ≈ 0.974, |Vcs| ≈0.9736, |Vcd| ≈ 0.224 with [Formula: see text]. The top quark mass is predicted to be 258 GeV at 1 GeV with its physical mass approximately in the range of 153 GeV to 165 GeV. Some remarks on the relationship between the lepton sector and the quark sector will be made.

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15

Wachirapusitanand, V., N. Srimanobhas e F. Blekman. "Application of pivoting adversarial networks in search for four top quark production in CMS". Journal of Physics: Conference Series 1380 (novembre 2019): 012069. http://dx.doi.org/10.1088/1742-6596/1380/1/012069.

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16

FUJIWARA, T., e S. KITAKADO. "TOPLESS ELECTROWEAK MODEL AS ANOMALOUS GAUGE THEORY". Modern Physics Letters A 08, n. 18 (14 giugno 1993): 1639–47. http://dx.doi.org/10.1142/s0217732393001380.

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General framework for quantizing anomalous gauge theories in four dimensions is applied to the description of electroweak theory that lacks the top quark. Auxiliary fields introduced to recover the gauge invariance substitute for the Higgs bosons of the standard model. The gauge invariant action contains the anomaly canceling Wess-Zumino-Witten term.

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17

Lu, Wei. "A Clifford algebra approach to chiral symmetry breaking and fermion mass hierarchies". International Journal of Modern Physics A 32, n. 26 (20 settembre 2017): 1750159. http://dx.doi.org/10.1142/s0217751x17501597.

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We propose a Clifford algebra approach to chiral symmetry breaking and fermion mass hierarchies in the context of composite Higgs bosons. Standard model fermions are represented by algebraic spinors of six-dimensional binary Clifford algebra, while ternary Clifford algebra-related flavor projection operators control allowable flavor-mixing interactions. There are three composite electroweak Higgs bosons resulted from top quark, tau neutrino, and tau lepton condensations. Each of the three condensations gives rise to masses of four different fermions. The fermion mass hierarchies within these three groups are determined by four-fermion condensations, which break two global chiral symmetries. The four-fermion condensations induce axion-like pseudo-Nambu–Goldstone bosons and can be dark matter candidates. In addition to the 125 GeV Higgs boson observed at the Large Hadron Collider, we anticipate detection of tau neutrino composite Higgs boson via the charm quark decay channel.

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18

Gronau, M., R. Johnson e J. Schechter. "Can a four-generation “Fritzsch” model with a light top quark explain BdB̄d mixing?" Physics Letters B 201, n. 1 (gennaio 1988): 151–54. http://dx.doi.org/10.1016/0370-2693(88)90098-6.

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19

Kang, Sin Kyu, e Gye T. Park. "Higgs Boson Mass Bounds in the Standard and Minimal Supersymmetric Standard Model with Four Generations". Modern Physics Letters A 12, n. 08 (14 marzo 1997): 553–59. http://dx.doi.org/10.1142/s0217732397000571.

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We study the question of distinguishability of the Higgs sector between the standard model with four generations (SM4) and the minimal supersymmetric standard model with four generations (MSSM4). We find that a gap exists between the SM4 and MSSM4 Higgs boson masses for a range of fourth generation fermion mass considered in the analysis at a fixed top quark mass. We also compare the Higgs boson mass bounds in these models with those in the standard and the minimal supersymmetric standard models.

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20

Zerwekh, Alfonso R. "The axigluon, a four-site model and the top quark forward–backward asymmetry at the Tevatron". Physics Letters B 704, n. 1-2 (ottobre 2011): 62–65. http://dx.doi.org/10.1016/j.physletb.2011.08.064.

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21

XUE, SHE-SHENG. "FINE-TUNING THE LOW-ENERGY PHYSICS". Modern Physics Letters A 15, n. 17 (7 giugno 2000): 1089–98. http://dx.doi.org/10.1142/s021773230000133x.

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In this letter we discuss the problem of the extreme fine-tuning necessary to achieve the quark mass scale mt within the dynamical symmetry breaking of the phenomenological [Formula: see text] condensate model. Inspired by the vector-like phenomenon of chiral gauge theories at short distances, we postulate that the W±-gauge bosons possess a vector-like gauge coupling and contribute to the gap-equations of quark self-energy functions in the high-energy region. We find that the gap-equations of different charge sectors are coupled, and as a result the unnatural fine-tuning is overcome and the ratio of the top and bottom masses is related to the electric charge: [Formula: see text], provided the quadratic divergence is removed by setting the four-fermion coupling [Formula: see text].

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22

MOFFAT, J. W. "FINITE ELECTROWEAK THEORY WITHOUT A HIGGS PARTICLE". Modern Physics Letters A 06, n. 11 (10 aprile 1991): 1011–21. http://dx.doi.org/10.1142/s0217732391001068.

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A unified electroweak theory is formulated using non-local field theory without including a Higgs particle. The W and Z gauge boson masses are induced from one-loop vacuum polarization graphs and the non-local weak scale is determined by the W boson mass and the Fermi constant to be Λw=424 GeV . The tree graphs for the gauge bosons are identical to those of the standard local electroweak theory, so any violation of locality occurs only at the quantum level for the finite loop graphs. The fermion masses are obtained from a four-Fermi interaction with a spontaneously broken vacuum based on the fermion condensate [Formula: see text]. The problem of severe fine tuning for the quark condensates in the standard local point field theory is avoided in our non-local field theory. The theory contains only the known particle spectrum of leptons, quarks, the anticipated top quark, the W and Z gauge bosons and the photon. The quark condensates could generate a spectrum of heavy vector bound states at an energy scale ~1−2 TeV .

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23

Osipov, Alexander A., Brigitte Hiller, Alex H. Blin e Marcos Sampaio. "Top–Bottom Condensation Model: Symmetries and Spectrum of the Induced 2HDM". Symmetry 13, n. 7 (24 giugno 2021): 1130. http://dx.doi.org/10.3390/sym13071130.

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Here, we use the Schwinger–DeWitt approach to address the four-fermion composite Higgs effective model proposed by Miransky, Tanabashi and Yamawaki (MTY). The surprising benefit of such an approach is that it is possible to ascribe to a SM-type Higgs a quark–antiquark structure of predominantly a b¯b nature with a small t¯t admixture, which in turn yields a Higgs mass compatible with the observed value of 125 GeV. We discuss this result in a detailed and pedagogical way, as it goes against the common belief that this model and akin composite descriptions should predict a Higgs mass-of-order of twice the top quark mass, contrary to empirical evidence. A further aspect of this approach is that it highlights the link of the SU(2)L×U(1)R symmetric four-fermion MTY model interactions of the heavy quark family to a specific two-Higgs-doublet model (2HDM), and the necessity to go beyond the one Higgs doublet to obtain the empirical Higgs mass within composite models. By appropriately fixing the symmetry-defining interaction parameters, we show that the resulting CP-preserving spectrum harbors the following collective states at the electroweak scale ΛEW=246 GeV: a light scalar to which the standard Higgs is associated; a heavier neutral state preconized as the Nambu partner of the standard Higgs within the Nambu sum rule; the expected triplet of Goldstone bosons associated with the longitudinal polarizations of the electroweak massive bosons; and a neutral pseudoscalar state that in the limit of a global U(1)A symmetry would be a Goldstone mode. The anomalous breaking of this axial symmetry is a subleading effect in a large Nc counting scheme, and we discuss how it modifies the leading-order Nambu sum rule result and its relevance for the qualitative description of the spectrum.

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24

Hioki, Zenrō, Kazumasa Ohkuma e Akira Uejima. "Studying flavor-changing neutral tqZ couplings: Current constraints and future prospects". Modern Physics Letters A 34, n. 34 (5 novembre 2019): 1950278. http://dx.doi.org/10.1142/s021773231950278x.

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Possible nonstandard tuZ and tcZ interactions, which induce flavor-changing neutral-current decays of the top quark, are studied in the effective-Lagrangian framework. The corresponding Lagrangian consists of four kinds of nonstandard couplings coming from [Formula: see text] invariant dimension-6 effective operators. The four coupling constants in each interaction are treated as complex numbers independent of each other and constraints on them are derived by using the present experimental limits of the branching fractions for [Formula: see text] and [Formula: see text] processes. Future improvements of those constraints are also discussed as well as possibilities of measurements of these couplings at the High-Luminosity Large Hadron Collider.

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25

Dordevic, Milos. "Higgs physics at CMS". EPJ Web of Conferences 222 (2019): 01001. http://dx.doi.org/10.1051/epjconf/201922201001.

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The most recent results of a Higgs boson production and properties from the CMS Collaboration using the LHC Run 1 and Run 2 data are reported. These include analyses of a Higgs boson decaying to a pair of photons, four leptons via Z boson pair decays and the associated production of a Higgs boson with top quark pair, predicted by the Standard Model (SM). The studies of a Higgs boson decays to a pair of bottom quarks, a pair of tau leptons and a charm quark pair are also presented. The Higgs boson production via vector boson fusion (VBF) and decaying to invisible particles is reported here as well. The analysis of a Higgs boson decay to a pair of muons is also presented. The study of a Higgs boson pair production at 13 TeV is performed as well and projections of a Higgs boson self couplings together with the couplings to other particles at the HL-LHC are made.

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HE, XIAO-GANG, SHU-YU HO, JUSAK TANDEAN e HO-CHIN TSAI. "SCALAR DARK MATTER AND STANDARD MODEL WITH FOUR GENERATIONS". International Journal of Modern Physics D 20, n. 08 (15 agosto 2011): 1423–31. http://dx.doi.org/10.1142/s0218271811019608.

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This talk is based on the previous paper [X. G. He et al., Phys. Rev. D82 (2010) 035016]. We consider a scalar dark-matter model, the SM4+D, consisting of the standard model with four generations (SM4) and a real gauge-singlet scalar called darkon, D, as the weakly interacting massive particle (WIMP) dark-matter (DM) candidate. We explore constraints on the darkon sector of the SM4+D from WIMP DM direct-search experiments, and from the decay of a B meson into a kaon plus missing energy. Since the darkon-Higgs interaction may give rise to considerable enhancement of the Higgs invisible decay mode, the existence of the darkon could lead to the weakening or evasion of some of the restrictions on the Higgs mass in the presence of fourth-generation quarks. In addition, it can affect the flavor-changing decays of these new heavy quarks into a lighter quark and the Higgs boson, as the Higgs may subsequently decay invisibly. Therefore, we also study these flavor-changing neutral transitions involving the darkon, as well as the corresponding top-quark decay t → cDD, some of which may be observable at the Tevatron or LHC and thus provide additional tests for the SM4+D.

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STICHELBAUT, F. "STUDY OF e+e− INTERACTIONS AT CENTER-OF-MASS ENERGIES OF 130 AND 136 GeV". Modern Physics Letters A 11, n. 36 (30 novembre 1996): 2809–23. http://dx.doi.org/10.1142/s0217732396002800.

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At the end of 1995, the LEP collider at CERN was operated at center-of-mass energies of 130 and 136 GeV and data corresponding to about 6 pb−1 were collected by each of the four LEP experiments. The cross-sections for fermion-pair production processes and the forward-backward asymmetries for charged lepton pairs were measured and compared to the standard model predictions. Events containing only energetic photons in the final state were used to look for effects arising from new physics. Direct searches for new particles predicted by various models beyond the standard model were performed. Searches for pair or singly produced excited leptons, for unstable charged and neutral heavy leptons, and for supersymmetric particles (chargino, neutralino, scalar leptons and scalar top quark) resulted in new exclusion limits. The ALEPH collaboration reported an excess of four-jet events in its data, which was not confirmed by the other LEP experiments.

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Wang, Ziming, Yong Gao, Dicong Liang, Junjie Zhao e Lijing Shao. "Vetting quark-star models with gravitational waves in the hierarchical Bayesian framework". Journal of Cosmology and Astroparticle Physics 2024, n. 11 (1 novembre 2024): 038. http://dx.doi.org/10.1088/1475-7516/2024/11/038.

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Abstract The recent discovery of gravitational waves (GWs) has opened a new avenue for investigating the equation of state (EOS) of dense matter in compact stars, which is an outstanding problem in astronomy and nuclear physics. In the future, next-generation (XG) GW detectors will be constructed, deemed to provide a large number of high-precision observations. We investigate the potential of constraining the EOS of quark stars (QSs) with high-precision measurements of mass m and tidal deformability Λ from the XG GW observatories. We adopt the widely-used bag model for QSs, consisting of four microscopic parameters: the effective bag constant B eff, the perturbative quantum chromodynamics correction parameter a 4, the strange quark mass m s , and the pairing energy gap Δ. With the help of hierarchical Bayesian inference, for the first time we are able to infer the EOS of QSs combining multiple GW observations. Using the top 25 loudest GW events in our simulation, we find that, the constraints on B eff and Δ are tightened by several times, while a 4 and m s are still poorly constrained. We also study a simplified 2-dimensional (2-d) EOS model which was recently proposed in literature. The 2-d model is found to exhibit significant parameter-estimation biases as more GW events are analyzed, while the predicted m–Λ relation remains consistent with the full model.

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Degrande, C., R. Rosenfeld e A. Vasquez. "Collider sensitivity to SMEFT heavy-quark operators at one-loop in top-quark processes". Journal of High Energy Physics 2024, n. 7 (11 luglio 2024). http://dx.doi.org/10.1007/jhep07(2024)114.

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Abstract We study the effects of four-heavy-quark operators in the production of top quarks in the framework of the Standard Model Effective Field Theory (SMEFT) at the LHC. In particular, we compute for the first time the total contribution of the four-top-quark operator which enters only at the one-loop level in the top-quark pair production process. Analytical results at one-loop are presented for the gluon- and quark-initiated sub-processes, which allowed a first complete validation of the SMEFT@NLO in MadGraph5_aMC@NLO. The 95% CL bounds on four-heavy-quark operators from the available top-quark pair and four-top-quark production data are provided, which are complementary to other bounds found in the literature. We focus on the comparison of the sensitivities of the top-quark pair and the four-top-quark production processes, where in the latter case the four-top-quark operator contributes at tree-level. We conclude that the sensitivities of the two processes to four-heavy-quark operators are comparable. The projected sensitivities of both processes at HL-LHC are also presented.

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Zhou, Ning, Daniel Whiteson e Tim M. P. Tait. "Limits on four-top-quark production from the ATLAS same-sign top-quark search". Physical Review D 85, n. 9 (7 maggio 2012). http://dx.doi.org/10.1103/physrevd.85.091501.

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Darmé, Luc, Benjamin Fuks e Fabio Maltoni. "Top-philic heavy resonances in four-top final states and their EFT interpretation". Journal of High Energy Physics 2021, n. 9 (settembre 2021). http://dx.doi.org/10.1007/jhep09(2021)143.

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Abstract With an expected rate of about one event per 100,000 top-quark pairs, four top-quark final states very rarely arise at the LHC. Though scarce, they offer a unique window onto top-quark compositeness, self-interactions and more generically, onto any top-philic new physics. By employing simplified models featuring heavy resonances, we study the range of validity of effective theory interpretations of current four top-quark analyses at the LHC and establish their future reach at the HL-LHC. We find that for the class of models under consideration, the effective field theory interpretations are not applicable. We therefore present the most up-to-date limits obtained from public CMS analyses using simplified models. Finally, we put forward a novel recasting strategy for the experimental results based on the production of top quarks with large transverse momentum.

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Tumasyan, A., W. Adam, J. W. Andrejkovic, T. Bergauer, S. Chatterjee, K. Damanakis, M. Dragicevic et al. "Measurement of the top quark mass using a profile likelihood approach with the lepton + jets final states in proton–proton collisions at $$\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V} $$". European Physical Journal C 83, n. 10 (25 ottobre 2023). http://dx.doi.org/10.1140/epjc/s10052-023-12050-4.

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AbstractThe mass of the top quark is measured in 36.3$$\,\text {fb}^{-1}$$ fb - 1 of LHC proton–proton collision data collected with the CMS detector at $$\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V} $$ s = 13 Te V . The measurement uses a sample of top quark pair candidate events containing one isolated electron or muon and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a top quark pair hypothesis. A profile likelihood method is applied using up to four observables per event to extract the top quark mass. The top quark mass is measured to be $$171.77\pm 0.37\,\text {Ge}\hspace{-.08em}\text {V} $$ 171.77 ± 0.37 Ge V . This approach significantly improves the precision over previous measurements.

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Dimitrakopoulos, Nikolaos, e Malgorzata Worek. "Four top final states with NLO accuracy in perturbative QCD: 4 lepton channel". Journal of High Energy Physics 2024, n. 6 (19 giugno 2024). http://dx.doi.org/10.1007/jhep06(2024)129.

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Abstract Triggered by the observation of four top-quark production at the LHC by the ATLAS and CMS collaboration we report on the calculation of the next-to-leading order QCD corrections to the Standard Model process pp → $$ t\overline{t}t\overline{t} $$ t t ¯ t t ¯ in the 4ℓ top-quark decay channel. We take into account higher-order QCD effects in both the production and decays of the four top quarks. The latter effects are treated in the narrow width approximation, which preserves top-quark spin correlations throughout the calculation. We present results for two selected renormalisation and factorisation scale settings and three different PDF sets. Furthermore, we study the main theoretical uncertainties that are associated with the neglected higher-order terms in the perturbative expansion and with the parameterisation of the PDF sets. The results at the integrated and differential fiducial cross-section level are shown for the LHC Run III center-of-mass energy of $$ \sqrt{s} $$ s = 13.6 TeV. Our findings are particularly relevant for precise measurements of the four top-quark fiducial cross sections and for the modelling of top-quark decays at the LHC.

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34

Ake, Daniel, Antonio O. Bouzas e F. Larios. "Top Quark Flavor Changing Couplings at a Muon Collider". Advances in High Energy Physics 2024, n. 1 (gennaio 2024). http://dx.doi.org/10.1155/2024/2038180.

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Abstract (sommario):

There is growing interest in the development of a muon collider that would make it possible to produce lepton collisions at energies of several TeV. Among others, there can be significant contributions to electroweak gauge boson, Higgs boson, and top quark physics. In this work, we pay attention to the latter, in particular, effective flavor‐changing (FC) top‐quark interactions. We discuss the flavor‐changing production processes that can be a good probe of the dimension‐six top quark four‐fermion and fermion‐boson operators in the SMEFT. We consider all sixteen operators that can generate flavor‐changing top quark couplings. After comparing with the current LHC bounds, we find potential limits three or four orders of magnitude stronger for four‐fermion operators. Concerning fermion‐boson couplings, for the tensor operators QuW and QuB, we obtain the highest sensitivity. We also observe that the effective W approximation (EWA) does not apply with QuB.

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35

Banelli, Giovanni, Ennio Salvioni, Javi Serra, Tobias Theil e Andreas Weiler. "The present and future of four top operators". Journal of High Energy Physics 2021, n. 2 (febbraio 2021). http://dx.doi.org/10.1007/jhep02(2021)043.

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Abstract (sommario):

Abstract We study the phenomenology of a strongly-interacting top quark at future hadron and lepton colliders, showing that the characteristic four-top contact operators give rise to the most significant effects. We demonstrate the extraordinary potential of a 100 TeV proton-proton collider to directly test such non-standard interactions in four-top production, a process that we thoroughly analyze in the same-sign dilepton and trilepton channels, and explore in the fully hadronic channel. Furthermore, high-energy electron-positron colliders, such as CLIC or the ILC, are shown to exhibit an indirect yet remarkable sensitivity to four-top operators, since these constitute, via renormalization group evolution, the leading new-physics deformations in top-quark pair production. We investigate the impact of our results on the parameter space of composite Higgs models with a strongly-coupled (right-handed) top quark, finding that four-top probes provide the best sensitivity on the compositeness scale at the future energy frontier. In addition, we investigate mild yet persisting LHC excesses in multilepton plus jets final states, showing that they can be consistently described in the effective field theory of such a new-physics scenario.

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36

Malekhosseini, Malihe, Mehrdad Ghominejad, Hamzeh Khanpour e Mojtaba Mohammadi Najafabadi. "Constraining top quark flavor violation and dipole moments through three and four top quark productions at the LHC". Physical Review D 98, n. 9 (1 novembre 2018). http://dx.doi.org/10.1103/physrevd.98.095001.

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37

Alasfar, Lina, Jorge de Blas e Ramona Gröber. "Higgs probes of top quark contact interactions and their interplay with the Higgs self-coupling". Journal of High Energy Physics 2022, n. 5 (maggio 2022). http://dx.doi.org/10.1007/jhep05(2022)111.

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Abstract (sommario):

Abstract We calculate the dominant contributions of third generation four-quark operators to single-Higgs production and decay. They enter via loop corrections to Higgs decays into gluons, photons and $$ b\overline{b} $$ b b ¯ , and in Higgs production via gluon fusion and in association with top quark pairs. We show that these loop effects can, in some cases, lead to better constraints than those from fits to top quark data. Finally, we investigate whether these four-fermion operators can spoil the determination of the trilinear Higgs self-coupling from fits to single-Higgs data.

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38

Aad, G., B. Abbott, D. C. Abbott, A. Abed Abud, K. Abeling, D. K. Abhayasinghe, S. H. Abidi et al. "Search for a light charged Higgs boson in t → H±b decays, with H± → cb, in the lepton+jets final state in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector". Journal of High Energy Physics 2023, n. 9 (1 settembre 2023). http://dx.doi.org/10.1007/jhep09(2023)004.

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Abstract (sommario):

Abstract A search for a charged Higgs boson, H±, produced in top-quark decays, t → H±b, is presented. The search targets H± decays into a bottom and a charm quark, H± → cb. The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying W boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing b-hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy $$ \sqrt{s} $$ s = 13 TeV between 2015 and 2018 with the ATLAS detector at CERN’s Large Hadron Collider, amounting to an integrated luminosity of 139 fb−1. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions $$ \mathcal{B} $$ B (t → H±b) × B(H± → cb) for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs.

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39

Grza̧dkowski, Bohdan, Zenrō Hioki e Michał Szafrański. "Four-Fermi effective operators in top-quark production and decay". Physical Review D 58, n. 3 (15 giugno 1998). http://dx.doi.org/10.1103/physrevd.58.035002.

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40

Dimitrakopoulos, Nikolaos, e Malgorzata Worek. "Four top final states with NLO accuracy in perturbative QCD: 3 lepton channel". Journal of High Energy Physics 2025, n. 3 (5 marzo 2025). https://doi.org/10.1007/jhep03(2025)025.

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Abstract (sommario):

Abstract We examine the effect of higher-order QCD corrections on the four top-quark production cross section in the 3 lepton decay channel. Top-quark and W gauge-boson decays are included at next-to-leading order in perturbative QCD. The narrow-width approximation, that preserves spin correlations, is used to perform the calculation for this complex 2 → 12 (13) process. We present differential cross-section distributions of top-quark decay products for the LHC Run III energy of $$ \sqrt{s} $$ s = 13.6 TeV, using realistic selection cuts. Our results show that QCD corrections and jet radiation in top-quark and W decays can lead to significant changes in shapes of basic kinematic distributions and, therefore, need to be included for the accurate description of pp → $$ t\overline{t}t\overline{t} $$ t t ¯ t t ¯ + X process in the 3ℓ decay channel. The NLO QCD results obtained in this work are important in the context of the recent observation of the pp → $$ t\overline{t}t\overline{t} $$ t t ¯ t t ¯ + X process by the ATLAS and CMS collaborations and are of great significance for the High-Luminosity phase of the LHC.

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41

Chung, Yi. "Naturalness-motivated composite Higgs model for generating the top Yukawa coupling". Physical Review D 109, n. 9 (14 maggio 2024). http://dx.doi.org/10.1103/physrevd.109.095021.

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Abstract (sommario):

The large top Yukawa coupling results in the top quark contributing significantly to the quantum correction of the Higgs mass term. Traditionally, this effect is canceled by the presence of top partners in symmetry-based models. However, the absence of light top partners poses a challenge to the naturalness of these models. In this paper, we study a model based on composite Higgs with the top Yukawa coupling originating from dimension-six four-fermion operators. The low cutoff scale of the top quark loop required by the naturalness principle can be realized with a light gauge boson Eμ that connects the hyperfermions and top quarks. A scalarless dynamical model with weakly coupled extended SU(4)EC gauge group is presented. The model features an Eμ boson and a ZE′ boson both at the sub-TeV scale, which lead to a rich phenomenology, especially in the top quark physics. Published by the American Physical Society 2024

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42

Aad, G., B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz et al. "Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t → qX (q = u, c), with X → $$ b\overline{b} $$, in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector". Journal of High Energy Physics 2023, n. 7 (26 luglio 2023). http://dx.doi.org/10.1007/jhep07(2023)199.

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Abstract (sommario):

Abstract A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle X decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to qX, with X → $$ b\overline{b} $$ b b ¯ , and the other top quark decays according to the Standard Model, with the W boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from b-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction $$ \mathcal{B} $$ B (t → uX) and between 0.018% and 0.078% for the branching fraction $$ \mathcal{B} $$ B (t → cX), for masses of the scalar particle X between 20 and 160 GeV.

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43

Aoude, Rafael, Hesham El Faham, Fabio Maltoni e Eleni Vryonidou. "Complete SMEFT predictions for four top quark production at hadron colliders". Journal of High Energy Physics 2022, n. 10 (25 ottobre 2022). http://dx.doi.org/10.1007/jhep10(2022)163.

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Abstract (sommario):

Abstract We study four top quark production at hadron colliders in the Standard Model Effective Field Theory (SMEFT). We perform an analysis at the tree-level, including all possible QCD- and EW-coupling orders and relevant dimension-six operators. We find several cases where formally subleading terms give rise to significant contributions, potentially providing sensitivity to a broad class of operators. Inclusive and differential predictions are presented for the LHC and a future pp circular collider operating at 100 TeV. We estimate the sensitivity of different operators and perform a simplified chi-square fit to set limits on SMEFT Wilson coefficients. In so doing, we assess the importance of including subleading terms and differential information in constraining new physics contributions. Finally, we compute the SMEFT predictions for the double insertion of dimension-six operators and scrutinise the possible enhancements to the sensitivity induced by a specific class of higher order terms in the EFT series.

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44

Fabbrichesi, Marco, Roberto Floreanini e Emidio Gabrielli. "Constraining new physics in entangled two-qubit systems: top-quark, tau-lepton and photon pairs". European Physical Journal C 83, n. 2 (19 febbraio 2023). http://dx.doi.org/10.1140/epjc/s10052-023-11307-2.

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AbstractThe measurement of quantum entanglement can provide a new and most sensitive probe to physics beyond the Standard Model. We use the concurrence of the top-quark pair spin states produced at colliders to constrain the magnetic dipole term in the coupling between top quark and gluons, that of $$\tau $$ τ -lepton pair spin states to bound contact interactions and that of $$\tau $$ τ -lepton pairs or two-photons spin states from the decay of the Higgs boson in trying to distinguish between CP-even and odd couplings. These four examples show the power of the new approach as well as its limitations. We show that differences in the entanglement in the top-quark and $$\tau $$ τ -lepton pair production cross sections can provide constraints better than those previously estimated from total cross sections or classical correlations. Instead, the final states in the decays of the Higgs boson remain maximally entangled even in the presence of CP-odd couplings and cannot be used to set bounds on new physics. We discuss the violation of Bell inequalities featured in all four processes.

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45

d'Enterria, David, e Dung Van Le. "Rare and exclusive few-body decays of the Higgs, Z, W bosons, and the top quark". Journal of Physics G: Nuclear and Particle Physics, 9 aprile 2024. http://dx.doi.org/10.1088/1361-6471/ad3c59.

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Abstract (sommario):

Abstract We perform an extensive survey of rare and exclusive few-body decays ---defined as those with branching fractions $\mathcal{B} \lesssim 10^{-5}$ and two or three final particles--- of the Higgs, Z, W bosons, and the top quark. Such rare decays can probe physics beyond the Standard Model (BSM), constitute a background for exotic decays into new BSM particles, and provide precise information on quantum chromodynamics factorization with small nonperturbative corrections. We tabulate the theoretical $\mathcal{B}$ values for almost 200 rare decay channels of the four heaviest elementary particles, indicating the current experimental limits in their observation. Among those, we have computed for the first time ultrarare Higgs boson decays into photons and/or neutrinos, H and Z radiative decays into leptonium states, radiative H and Z quark-flavour-changing decays, and semiexclusive top-quark decays into a quark plus a meson, while updating predictions for a few other rare H, Z, and top quark partial widths. The feasibility of measuring each of these unobserved decays is estimated for p-p collisions at the high-luminosity Large Hadron Collider (HL-LHC), and for $e^+e^-$ and p-p collisions at the future circular collider (FCC).

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46

Flesher, Forrest, Katherine Fraser, Charles Hutchison, Bryan Ostdiek e Matthew D. Schwartz. "Parameter inference from event ensembles and the top-quark mass". Journal of High Energy Physics 2021, n. 9 (settembre 2021). http://dx.doi.org/10.1007/jhep09(2021)058.

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Abstract (sommario):

Abstract One of the key tasks of any particle collider is measurement. In practice, this is often done by fitting data to a simulation, which depends on many parameters. Sometimes, when the effects of varying different parameters are highly correlated, a large ensemble of data may be needed to resolve parameter-space degeneracies. An important example is measuring the top-quark mass, where other physical and unphysical parameters in the simulation must be profiled when fitting the top-quark mass parameter. We compare four different methodologies for top-quark mass measurement: a classical histogram fit similar to one commonly used in experiment augmented by soft-drop jet grooming; a 2D profile likelihood fit with a nuisance parameter; a machine-learning method called DCTR; and a linear regression approach, either using a least-squares fit or with a dense linearly-activated neural network. Despite the fact that individual events are totally uncorrelated, we find that the linear regression methods work most effectively when we input an ensemble of events sorted by mass, rather than training them on individual events. Although all methods provide robust extraction of the top-quark mass parameter, the linear network does marginally best and is remarkably simple. For the top study, we conclude that the Monte-Carlo-based uncertainty on current extractions of the top-quark mass from LHC data can be reduced significantly (by perhaps a factor of 2) using networks trained on sorted event ensembles. More generally, machine learning from ensembles for parameter estimation has broad potential for collider physics measurements.

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47

Aad, G., B. Abbott, D. C. Abbott, A. Abed Abud, K. Abeling, D. K. Abhayasinghe, S. H. Abidi et al. "Measurement of the t$$ \overline{t} $$t$$ \overline{t} $$ production cross section in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector". Journal of High Energy Physics 2021, n. 11 (novembre 2021). http://dx.doi.org/10.1007/jhep11(2021)118.

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Abstract (sommario):

Abstract A measurement of four-top-quark production using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 139 fb−1 is presented. Events are selected if they contain a single lepton (electron or muon) or an opposite-sign lepton pair, in association with multiple jets. The events are categorised according to the number of jets and how likely these are to contain b-hadrons. A multivariate technique is then used to discriminate between signal and background events. The measured four-top-quark production cross section is found to be $$ {26}_{-15}^{+17} $$ 26 − 15 + 17 fb, with a corresponding observed (expected) significance of 1.9 (1.0) standard deviations over the background-only hypothesis. The result is combined with the previous measurement performed by the ATLAS Collaboration in the multilepton final state. The combined four-top-quark production cross section is measured to be $$ {24}_{-6}^{+7} $$ 24 − 6 + 7 fb, with a corresponding observed (expected) signal significance of 4.7 (2.6) standard deviations over the background-only predictions. It is consistent within 2.0 standard deviations with the Standard Model expectation of 12.0 ± 2.4 fb.

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48

Tumasyan, A., W. Adam, T. Bergauer, M. Dragicevic, A. Escalante Del Valle, R. Frühwirth, M. Jeitler et al. "Search for CP violating top quark couplings in pp collisions at $$ \sqrt{s} $$ = 13 TeV". Journal of High Energy Physics 2023, n. 7 (4 luglio 2023). http://dx.doi.org/10.1007/jhep07(2023)023.

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Abstract (sommario):

Abstract Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13 TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fb−1. The search uses two observables, $$ \mathcal{O} $$ O 1 and $$ \mathcal{O} $$ O 3, which are Lorentz scalars. The observable $$ \mathcal{O} $$ O 1 is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while $$ \mathcal{O} $$ O 3 consists of the four-momenta of the charged leptons and the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model.

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49

Jung, Sunghoon, P. Ko, Yeo Woong Yoon e Chaehyun Yu. "Renormalization group-induced phenomena of top pairs from four-quark effective operators". Journal of High Energy Physics 2014, n. 8 (agosto 2014). http://dx.doi.org/10.1007/jhep08(2014)120.

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50

Bruggisser, Sebastian, Danny van Dyk e Susanne Westhoff. "Resolving the flavor structure in the MFV-SMEFT". Journal of High Energy Physics 2023, n. 2 (22 febbraio 2023). http://dx.doi.org/10.1007/jhep02(2023)225.

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Abstract (sommario):

Abstract We constrain the flavor structure of Wilson coefficients in the Standard Model Effective Field Theory (SMEFT) from data. In the SMEFT, new physics effects in couplings of up-type and down-type quarks are related through the Cabibbo-Kobayashi-Maskawa mixing matrix. We exploit this relation to pin down potential new sources of flavor symmetry breaking in a global analysis of high- and low-energy data from the LHC, LEP, and b factory experiments. We demonstrate the power of such an analysis by performing a combined fit of effective four-quark and two-quark couplings contributing to a large set of flavor, top-quark, electroweak, and dijet observables. All four sectors are needed to fully resolve the flavor structure of left-chiral four-quark couplings without leaving blind directions in the parameter space. Although we work in the framework of minimal flavor violation, our strategy applies as well to other flavor patterns, like U(2) flavor symmetry or leptoquark scenarios.

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