First measurement of the top quark pair production cross section at s=13.6 TeV\sqrt{s} = 13.6 \, \mathrm{TeV} at the CMS experiment

We present the first measurement of the top quark pair production cross section at the new LHC center-of-mass energy of $\sqrt{s} = 13.6 \, \mathrm{TeV}$, using $1.20 \, \mathrm{fb}^{-1}$ of data recorded at the CMS detector. We use a new method combining dilepton and lepton+jets decay channels, constraining several experimental uncertainties in situ. A cross section of $887^{+43}_{-41}(\mathrm{stat+syst}) \pm 53 (\mathrm{lumi}) \, \mathrm{pb}$ is measured, in agreement with the standard model. This result constitutes a first validation of the new data taken by CMS in LHC Run 3.Comment: Poster at the 15th International Workshop on Top Quark Physics, Durham, UK, 4-9 September 202

ALP-ine quests at the LHC: hunting axion-like particles via peaks and dips in ttˉt \bar{t} production

We present an analysis of the sensitivity of current and future LHC searches for new spin-0 particles in top-anti-top-quark ($t\bar{t}$) final states, focusing on generic axion-like particles (ALPs) that are coupled to top quarks and gluons. As a first step, we derive new limits on the effective ALP Lagrangian in terms of the Wilson coefficients $c_t$ and $c_{\tilde{G}}$ based on the results of the CMS search using $35.9$ fb$^{-1}$ of data, collected at $\sqrt{s} = 13$ TeV. We then investigate how the production of an ALP with generic couplings to gluons and top quarks can be distinguished from the production of a pseudoscalar which couples to gluons exclusively via a top-quark loop. To this end, we make use of the invariant $t\bar{t}$ mass distribution and angular correlations that are sensitive to the $t\bar{t}$ spin correlation. Using a mass of 400 GeV as an example, we find that already the data collected during Run 2 and Run 3 of the LHC provides an interesting sensitivity to the underlying nature of a possible new particle. We also analyze the prospects for data anticipated to be collected during the high-luminosity phase of the LHC. Finally, we compare the limits obtained from the $t \bar t$ searches to existing experimental bounds from LHC searches for narrow di-photon resonances, from measurements of the production of four top quarks, and from global analyses of ALP-SMEFT interference effects.Comment: 28 pages, 9 figure

Observation of γγ → ττ in proton-proton collisions and limits on the anomalous electromagnetic moments of the τ lepton

The production of a pair of τ leptons via photon–photon fusion, γγ → ττ, is observed for the f irst time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb−1. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of γγ → ττ is σfid obs = 12.4+3.8 −3.1 fb. Constraints are set on the contributions to the anomalous magnetic moment (aτ) and electric dipole moments (dτ) of the τ lepton originating from potential effects of new physics on the γττ vertex: aτ = 0.0009+0.0032 −0.0031 and |dτ| < 2.9×10−17ecm (95% confidence level), consistent with the standard model

News on top quark physics from the CMS experiment

An overview of several new top quark physics results from the CMS experiment at the LHC is presented. They consist of measurements of four top production, including the first observation at CMS; a precision differential measurement of ttbb production; new physics searches using an Effective Field Theory approach both in a generic multilepton tt + X final state as well as specialized for flavor-changing neutral currents and lepton flavor violation; and the first measurement of tt production at sqrt(s) = 13.6 TeV. In all cases, a brief summary of the analysis as well as the resulting numbers or limits are shown

Search for heavy scalar or pseudoscalar states in ttˉ\mathrm{t \bar{t}} events at CMS

A search for scalar or pseudoscalar states decaying to a top quark-antiquark pair ($\mathrm{t \bar{t}}$), using $138\,\mathrm{fb}^{-1}$ of pp collision data taken at $\sqrt{s} = 13\,\mathrm{TeV}$ using the CMS detector, is presented. Events with one or two leptons are analyzed using the invariant $\mathrm{t \bar{t}}$ mass ($m_{\mathrm{t \bar{t}}}$) as well as angular and spin correlation observables. An excess in the data is observed for low values of $m_{\mathrm{t \bar{t}}}$, preferring a pseudoscalar over a scalar hypothesis. It is interpreted in terms of a generic model of (pseudo)scalar boson production, as well as a simplified model of a $\mathrm{t \bar{t}}$ bound state ($\eta_{\mathrm{t}}$), yielding good agreement with the data. Moreover, limits on the couplings of additional (pseudo)scalar bosons to top quarks are set

Messung des inklusiven tt-Wirkungsquerschnitts und Suche nach zusätzlichen Skalaren in tt-Endzuständen mit dem CMS-Experiment

Two key measurements and two phenomenological studies of top quark pair (tt) production with the CMS experiment at the CERN Large Hadron Collider are presented. They include the first measurement of the tt cross section at the new energy frontier, a detailed analysis of the tt threshold culminating in the first observation of tt bound state effects, and searches for new physics in tt final states, such as heavy scalars, pseudoscalars or Axion-Like Particles. The inclusive tt production cross section σ(tt) is measured for the first time at the world-record energy of √s = 13.6 TeV, using 1.21 fb^(-1) of early LHC Run 3 data. By combining the dilepton and lepton+jets (l+jets) decay channels and constraining the lepton and b tagging efficiencies in situ, a precision of 3.4%, comparable to previous σ(tt) measurements, is achieved. This constitutes the first measurement of proton-proton scattering at √s = 13.6 TeV worldwide. Furthermore, a search for heavy spin-0 states decaying to tt using 138 fb^(-1) of LHC Run 2 data at √s = 13 TeV in the dilepton channels is presented. The invariant tt mass m(tt) is combined with spin correlation observables to gain sensitivity to the spin and CP structure of possible new intermediate states. The analysis is supported by a detailed modeling study of off-shell tt production and of the interference between tt and tW production. An excess of events over the tt continuum background is observed at low values of m(tt), with spin correlations consistent with a pseudoscalar state. It is interpreted in terms of a pseudoscalar tt bound state ηt, and its cross section is measured to be σ(ηt) = 8.7 ± 1.1 pb using a simplified model inspired by non-relativistic quantum chromodynamics. The excess is statistically significant at more than five standard deviations, constituting the first observation of tt bound state effects. Other interpretations of the observed excess are similarly possible. In particular, scenarios with generic pseudoscalar or scalar bosons are explored, and exclusion regions on their coupling to the top quark are derived both for the dilepton channels alone as well as in a combination with a separate analysis of the l+jets channels. In addition, Axion-Like Particles (ALPs) decaying to tt are considered in the case of vanishing tree-level ALP-gluon couplings, while the more generic case is investigated phenomenologically in simulation.Es werden zwei essentielle Messungen und zwei phänomenologische Studien zur Produktion von Top-Quark-Paaren (tt) mit dem CMS-Experiment am CERN Large Hadron Collider vorgestellt. Sie umfassen die erste Messung des tt-Wirkungsquerschnitts bei der weltweit höchsten Schwerpunktsenergie, eine detaillierte Analyse der tt-Produktionsschwelle, die in die erste Beobachtung von einem gebundenen Zustand des tt-Systems mündet, sowie Suchen nach neuer Physik in tt-Endzuständen, wie etwa schwere Skalar- oder Pseudoskalarbosonen oder Axion-Like Particles. Der inklusive tt-Produktionsquerschnitt σ(tt) wird zum ersten Mal bei √s = 13.6 TeV gemessen, unter Verwendung von frühen LHC Run 3-Daten mit integrierter Luminosität von 1.21 fb^(-1). Durch Kombination der Dilepton- und Lepton+Jets (l+jets)-Zerfallskanäle von tt und simultane Bestimmung der Lepton- und b-tagging-Effizienzen in situ wird eine Präzision von 3.4% erreicht, die mit früheren σ(tt)-Messungen vergleichbar ist. Dies stellt die weltweit erste Messung von Proton-Proton-Streuprozessen bei √s = 13.6 TeV dar. Darüber hinaus wird eine Suche nach schweren Spin-0-Zuständen, die zu tt zerfallen, in den Dilepton-Kanälen mit 138 fb^(-1) Daten von LHC Run 2 bei √s = 13 TeV vorgestellt. Die invariante Masse von tt (m(tt)) wird mit Spinkorrelations-Observablen kombiniert, um die Sensitivität gegenüber dem Spin und der CP-Struktur möglicher neuer intermediärer Zustände zu erhöhen. Die Analyse wird durch detaillierte Studien zur Modellierung der Off-Shell-tt-Produktion sowie zur Interferenz zwischen tt- und tW-Produktion untermauert. Ein Überschuss von Ereignissen gegenüber dem tt-Kontinuums-Hintergrund wird bei niedrigen Werten von m(tt) und mit Spinkorrelationen konsistent mit einem pseudoskalaren Zustand beobachtet. Er wird als pseudoskalarer gebundener tt-Zustand ηt interpretiert, und dessen Produktionsquerschnitt wird mithilfe eines vereinfachten, von nichtrelativistischer Quantenchromodynamik inspirierten Modells zu σ(ηt) = 8.7 ± 1.1 pb gemessen. Der Überschuss ist mit einer Signifikanz von mehr als fünf Standardabweichungen statistisch belegt und stellt somit die erste Beobachtung von gebundenen Zuständen im tt-System dar. Weitere Interpretationen des beobachteten Überschusses sind ebenfalls möglich. Insbesondere werden Szenarios mit generischen pseudoskalaren oder skalaren Bosonen untersucht, und Ausschlussregionen hinsichtlich ihrer Kopplungen an das Top-Quark werden sowohl für die Dilepton-Kanäle allein als in Kombination mit einer separaten Analyse der l+jets-Kanäle berechnet. Zusätzlich werden zu tt zerfallende Axion-Like Particles (ALPs) betrachtet: einerseits im Fall verschwindender ALP-Gluon-Kopplungen, andererseits im allgemeinen Fall, der phänomenologisch in Simulationen untersucht wird