Quarks In Final States Research Articles

Search for W′ bosons decaying to a top and a bottom quark in leptonic final states in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV

A search for W′ bosons decaying to a top and a bottom quark in final states including an electron or a muon is performed with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 138 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV. Good agreement with the standard model expectation is observed and no evidence for the existence of the W′ boson is found over the mass range examined. The largest observed deviation from the standard model expectation is found for a W′ boson mass (mW′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_{{\ extrm{W}}^{\\prime }} $$\\end{document}) hypothesis of 3.8 TeV with a relative decay width of 1%, with a local (global) significance of 2.6 (2.0) standard deviations. Upper limits on the production cross sections of W′ bosons decaying to a top and a bottom quark are set. Left- and right-handed W′ bosons with mW′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_{{\ extrm{W}}^{\\prime }} $$\\end{document} below 3.9 and 4.3 TeV, respectively, are excluded at the 95% confidence level, under the assumption that the new particle has a narrow decay width. Limits are also set for relative decay widths up to 30%.

Effective 2HDM Yukawa interactions and a strong first-order electroweak phase transition

The top quark as the heaviest particle in the Standard Model (SM) defines an important mass scale for Higgs physics and the electroweak scale itself. It is therefore a well-motivated degree of freedom which could reveal the presence of new interactions beyond the SM. Correlating modifications of the top-Higgs interactions in the 2-Higgs-Doublet Model (2HDM), we analyse effective field theory deformations of these interactions from the point of view of a strong first-order electroweak phase transition (SFOEWPT). We show that such modifications are compatible with current Higgs data and that an SFOEWPT can be tantamount to a current overestimate of exotic Higgs searches’ sensitivity at the LHC in tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document} and four top quark final states. We argue that these searches remain robust from the point of accidental signal-background interference so that the current experimental strategy might well lead to 2HDM-like discoveries in the near future.

Unweighting multijet event generation using factorisation-aware neural networks

In this article we combine a recently proposed method for factorisation-aware matrix element surrogates with an unbiased unweighting algorithm. We show that employing a sophisticated neural network emulation of QCD multijet matrix elements based on dipole factorisation can lead to a drastic acceleration of unweighted event generation. We train neural networks for a selection of partonic channels contributing at the tree-level to Z+4,5Z+4,5 jets and t\bar{t}+3,4tt‾+3,4 jets production at the LHC which necessitates a generalisation of the dipole emulation model to include initial state partons as well as massive final state quarks. We also present first steps towards the emulation of colour-sampled amplitudes. We incorporate these emulations as fast and accurate surrogates in a two-stage rejection sampling algorithm within the SHERPA Monte Carlo that yields unbiased unweighted events suitable for phenomenological analyses and post-processing in experimental workflows, e.g. as input to a time-consuming detector simulation. For the computational cost of unweighted events we achieve a reduction by factors between 16 and 350 for the considered channels.

Revisiting semileptonic B meson decays at next-to-next-to-leading order

We compute next-to-next-to-leading order corrections to the semileptonic decay rate of B mesons for arbitrary values of the final-state quark mass. For the contribution with one massive quark in the final state, we extend the literature result and obtain analytic expressions in terms of iterated integrals. For the complete contribution, which also includes contributions with three massive quarks in the final state, we present a semi-analytic method, which leads to a precise approximation formula for the decay rate. Our results agree with the expansions available for b → cℓν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\overline{\ u} $$\\end{document}ℓ and b → uℓν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\overline{\ u} $$\\end{document}ℓ in the literature. The main emphasize of this paper is on the technical aspects of the calculation which are useful for a wider range of applications.

Measurement of the effective weak mixing angle at the CEPC* *Supported by the "USTC Research Funds of the Double First-Class Initiative", the International Partnership Program of Chinese Academy of Sciences (113111KYSB20190030) and the Innovative Scientific Program of Institute of High Energy Physics

We present a study of the measurement of the effective weak mixing angle parameter () at the Circular Electron Positron Collider (CEPC). As a fundamental physics parameter, plays a key role not only in the global test of the standard model electroweak sector, but also in constraining the potential beyond standard model new physics at the high energy frontier. CEPC proposes a two year running period around the Z boson mass pole at high instataneous luminosity, providing a large data sample with candidates generated in total. It allows a high precision measurement of both in the lepton and quark final states, where the uncertainty can be one order of magnitude lower than any previous measurement at the LEP, SLC, Tevatron, and LHC. It will improve the overall precision of the experimental determination to be comparable to the preicision of the theoretical calculation with two-loop radiative corrections, and it will also provide direct comparisons between different final states. In this paper, we also study the measurement of in the high mass region. Taking data for one month, the precision of measured at 130 GeV from b quark final state is 0.00010, which will be an important experimental observation on the energy-running effect of .

Collinear factorization at subasymptotic kinematics and validation in a diquark spectator model

We revisit the derivation of collinear factorization for Deep Inelastic Scattering at subasymptotic values of the four-momentum transfer squared, where the masses of the particles participating in the interaction cannot be neglected. By using an inclusive jet function to describe the scattered quark final state, we can restrict the needed parton kinematic approximations just to the four-momentum conservation of the hard scattering process, and explicitly expand the rest of the diagram in powers of the unobserved parton transverse momenta rather than neglecting those. This procedure provides one with more flexibility in fixing the virtuality of the scattered and recoiling partons than in the standard derivation, and naturally leads to scaling variables that more faithfully represent the partonic kinematic at subasymptotic energy than the Bjorken's ${x}_{B}$ variable. We then verify the validity of the obtained factorization formula by considering a diquark spectator model designed to reproduce the main features of electron-proton scattering at large ${x}_{B}$ in Quantum Chromodynamics. In the model, the Deep Inelastic Scattering contribution to the cross section can be explicitly isolated and analytically calculated, then compared to the factorized approximation. Limiting ourselves to the leading twist contribution, we then show that use of the new scaling variables maximizes the kinematic range of validity of collinear factorization, and highlight the intrinsic limitations of this approach due to the unavoidably approximate treatment of four-momentum conservation in factorized diagrams. Finally, we briefly discuss how these limitations may be overcome by including higher-twist corrections to the factorized calculation.

NLO QCD corrections to inclusive semitauonic weak decays of heavy hadrons up to 1/mb3

This paper presents ${\ensuremath{\alpha}}_{s}$ corrections to the inclusive semitauonic $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\tau}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ decay width and leptonic invariant mass spectrum up to order $1/{m}_{b}^{3}$ in the heavy quark expansion. Analytical results with full dependence on the final-state quark and tau lepton masses are obtained. The results up to $1/{m}_{b}^{2}$ can be extrapolated to the $B\ensuremath{\rightarrow}{X}_{u}\ensuremath{\tau}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ decay by taking the limit of vanishing final-state quark mass.

Search for Higgs Boson Pair Production in the Four b Quark Final State in Proton-Proton Collisions at s=13 TeV

A search for pairs of Higgs bosons produced via gluon and vector boson fusion is presented, focusing on the four b quark final state. The data sample consists of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC, and corresponds to an integrated luminosity of 138 fb−1. No deviation from the background-only hypothesis is observed. A 95% confidence level upper limit on the Higgs boson pair production cross section is observed at 3.9 times the standard model prediction for an expected value of 7.8. Constraints are also set on the modifiers of the Higgs field self-coupling, κλ, and of the coupling of two Higgs bosons to two vector bosons, κ2 V. The observed (expected) allowed intervals at the 95% confidence level are −2.3<κλ<9.4 (−5.0<κλ<12.0) and −0.1<κ2 V<2.2 (−0.4<κ2 V<2.5). These are the most stringent observed constraints to date on the HH production cross section and on the κ2 V coupling.Received 19 February 2022Accepted 7 July 2022DOI:https://doi.org/10.1103/PhysRevLett.129.081802Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2022 CERN, for the CMS CollaborationPhysics Subject Headings (PhySH)Physical SystemsBottom quarkHiggs bosonsTechniquesHadron collidersParticles & Fields

Searches for new phenomena in final states with third-generation quarks using the ATLAS detector

Many theories beyond the Standard Model (SM) predict new phenomena, such as [Formula: see text] and vector-like quarks, in final states containing bottom- or top-quarks. It is challenging to reconstruct and identify the decay products and model the major background processes. Nevertheless, such final states offer great potential to reduce the SM backgrounds due to their characteristic decay signature. The latest searches in the third-generation quark final states using the full Run-2 proton–proton collision data collected by the ATLAS experiment are presented. Particularly, the recent results of di-bjet and top-antitop resonance searches and dark matter produced in association with a top-quark are discussed in these proceedings. The associated improvements in [Formula: see text]-quark and top-quark identification techniques are also highlighted.

NLO QCD corrections to inclusive b→cℓν¯ decay spectra up to 1/mQ3

We present analytical results for higher order corrections to the decay spectra of inclusive semileptonic heavy hadron weak decays, using the heavy quark expansion (HQE). We compute analytically the spectrum of the leptonic invariant mass for $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}\overline{\ensuremath{\nu}}$ up to and including terms of order $1/{m}_{Q}^{3}$ within the HQE at next-to-leading order in ${\ensuremath{\alpha}}_{s}$. The full dependence of the differential rate on the mass of the final-state quark is taken into account. We discuss the implications of our results for the precision determination of the Cabbibo-Kobayashi-Maskawa matrix element $|{V}_{cb}|$.

Searching for heavy leptoquarks at a muon collider

The LHCb Collaboration recently gave an update on testing lepton flavour universality with B+→ K+ℓ+ℓ−, in which a 3.1 standard deviations from the standard model prediction was observed. The g-2 experiment also reports a 3.3 standard deviations from the standard model on muon anomalous magnetic moment measurement. These deviations could be explained by introducing new particles including leptoquarks. In this paper, we show the possibility to search for heavy spin-1 leptoquarks at a future TeV scale muon collider by performing studies from three channels: 1) same flavour final states with either two bottom or two light quarks, 2) different flavour quark final states, and 3) a so-called “VXS” process representing the scattering between a vector boson and a leptoquark to probe the coupling between leptoquark and tau lepton. We conclude that a 3 TeV muon collider with 3 ab−1 of integrated luminosity is already sufficient to cover the leptoquark parameter space in order to explain the LHCb lepton flavour universality anomaly.

On interference effects in top-philic decay chains

Sizeable exotic Higgs boson production through gluon fusion via top quark loops is correlated with large Higgs decay probabilities into top quark final states, if these are kinematically accessible. It is known that gg→S→tt¯ is particularly susceptible to signal-background interference effects that can significantly impact discovery sensitivities. In such an instance, identifying more robust signatures to enhance the discovery sensitivity becomes necessary, shifting phenomenological focus to final states that show a reduced destructive signal-background interference. In this work, we discuss the phenomenological relevance of signal-signal and signal-background interference effects for decay chains. In particular, we identify asymmetric cascade decays in models of scalar extensions of the SM Higgs sector as new promising candidates. In parallel, characteristic interference patterns can provide a formidable tool for indirect CP spectroscopy of BSM sectors if a discovery is made in the future. This motivates associated searches at present and future colliders as robust discovery modes of new physics, in addition to serving as a sensitive tool for the reconstruction of the underlying UV electroweak potential.

Multi-TeV signals of baryogenesis in a Higgs troika model

A modest extension of the Standard Model by two additional Higgs doublets - the Higgs Troika Model - can provide a well-motivated scenario for successful baryogenesis if neutrinos are Dirac fermions. Adapting the "Spontaneous Flavor Violation" framework, we consider a version of the Troika model where light quarks have significant couplings to the new multi-TeV Higgs states. Resonant production of new scalars leading to di-jet or top-pair signals are typical predictions of this setup. The initial and final state quarks relevant to the collider phenomenology also play a key role in baryogenesis, potentially providing direct access to the relevant early Universe physics in high energy experiments. Viable baryogenesis generally prefers some hierarchy of masses between the observed and the postulated Higgs states. We show that there is a complementarity between direct searches at a future 100 TeV $pp$ collider and indirect searches at flavor experiments, with both sensitive to different regions of parameter space relevant for baryogenesis. In particular, measurements of $D-\bar{D}$ mixing at LHCb probe much of the interesting parameter space. Direct and indirect searches can uncover the new Higgs states up to masses of $\mathcal{O}(10)$ TeV, thereby providing an impressive reach to investigate this model.

Measurement of the Higgs boson production rate in association with top quarks in final states with electrons, muons, and hadronically decaying tau leptons at sqrt{s} = 13,text {TeV}

The rate for Higgs ({mathrm{H}} ) bosons production in association with either one ({mathrm{t}} {mathrm{H}} ) or two ({mathrm{t}} {{overline{{{mathrm{t}}}}}} {mathrm{H}} ) top quarks is measured in final states containing multiple electrons, muons, or tau leptons decaying to hadrons and a neutrino, using proton–proton collisions recorded at a center-of-mass energy of 13,text {TeV} by the CMS experiment. The analyzed data correspond to an integrated luminosity of 137,text {fb}^{-1}. The analysis is aimed at events that contain {mathrm{H}} rightarrow {mathrm{W}} {mathrm{W}} , {mathrm{H}} rightarrow {uptau } {uptau } , or {mathrm{H}} rightarrow {mathrm{Z}} {mathrm{Z}} decays and each of the top quark(s) decays either to lepton+jets or all-jet channels. Sensitivity to signal is maximized by including ten signatures in the analysis, depending on the lepton multiplicity. The separation among {mathrm{t}} {mathrm{H}} , {mathrm{t}} {{overline{{{mathrm{t}}}}}} {mathrm{H}} , and the backgrounds is enhanced through machine-learning techniques and matrix-element methods. The measured production rates for the {mathrm{t}} {{overline{{{mathrm{t}}}}}} {mathrm{H}} and {mathrm{t}} {mathrm{H}} signals correspond to 0.92 pm 0.19,text {(stat)} ^{+0.17}_{-0.13},text {(syst)} and 5.7 pm 2.7,text {(stat)} pm 3.0,text {(syst)} of their respective standard model (SM) expectations. The corresponding observed (expected) significance amounts to 4.7 (5.2) standard deviations for {mathrm{t}} {{overline{{{mathrm{t}}}}}} {mathrm{H}} , and to 1.4 (0.3) for {mathrm{t}} {mathrm{H}} production. Assuming that the Higgs boson coupling to the tau lepton is equal in strength to its expectation in the SM, the coupling y_{{mathrm{t}}} of the Higgs boson to the top quark divided by its SM expectation, kappa _{{mathrm{t}}}=y_{{mathrm{t}}}/y_{{mathrm{t}}}^{mathrm {SM}}, is constrained to be within -0.9< kappa _{{mathrm{t}}}< -0.7 or 0.7< kappa _{{mathrm{t}}}< 1.1, at 95% confidence level. This result is the most sensitive measurement of the {mathrm{t}} {{overline{{{mathrm{t}}}}}} {mathrm{H}} production rate to date.

Top-induced contributions to H \u2192 boverline{b} and H \u2192 coverline{c} at mathcal{O}left({alpha}_s^3right)

In this paper we present a fully-differential calculation for the contributions to the partial widths H → boverline{b} and H → coverline{c} that are sensitive to the top quark Yukawa coupling yt to order {alpha}_s^3 . These contributions first enter at order {alpha}_s^2 through terms proportional to ytyq (q = b, c). At order {alpha}_s^3 corrections to the mixed terms are present as well as a new contribution proportional to {y}_t^2 . Our results retain the mass of the final-state quarks throughout, while the top quark is integrated out resulting in an effective field theory (EFT). Our results are implemented into a Monte Carlo code allowing for the application of arbitrary final-state selection cuts. As an example we present differential distributions for observables in the Higgs boson rest frame using the Durham jet clustering algorithm. We find that the total impact of the top-induced (i.e. EFT) pieces is sensitive to the nature of the final-state cuts, particularly b-tagging and c-tagging requirements. For bottom quarks, the EFT pieces contribute to the total width (and differential distributions) at around the percent level. The impact is much bigger for the H → coverline{c} channel, with effects as large as 15%. We show however that their impact can be significantly reduced by the application of jet-tagging selection cuts.

Search for production of four top quarks in final states with same-sign or multiple leptons in proton\u2013proton collisions at sqrt{s}=13,text {TeV}

The standard model (SM) production of four top quarks (text {t} {}{overline{text {t}}} text {t} {}{overline{text {t}}} ) in proton–proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016–2018 data taking of the LHC, corresponds to an integrated luminosity of 137,text {fb}^{-1} at a center-of-mass energy of 13,text {TeV}. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the text {t} {}{overline{text {t}}} text {t} {}{overline{text {t}}} signal are respectively 2.6 and 2.7 standard deviations, and the text {t} {}{overline{text {t}}} text {t} {}{overline{text {t}}} cross section is measured to be 12.6^{+5.8}_{-5.2},text {fb} . The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, y_{text {t}}, yielding a limit of |y_{text {t}}/y_{text {t}}^{mathrm {SM}} | < 1.7 at 95% confidence level, where y_{text {t}}^{mathrm {SM}} is the SM value of y_{text {t}}. They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework, hat{H}<0.12. Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350–470,text {GeV} and 350–550,text {GeV} for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.

Di-Higgs boson peaks and top valleys: Interference effects in Higgs sector extensions

In models with extended scalars and CP violation, resonance searches in double Higgs final states stand in competition with related searches in top quark final states as optimal channels for the discovery of beyond the Standard Model (BSM) physics. This complementarity is particularly relevant for benchmark scenarios that aim to highlight multi-Higgs production as a standard candle for the study of BSM phenomena. In this note, we compare interference effects in $t\bar t$ final states with correlated phenomena in double Higgs production in the complex singlet and the complex 2-Higgs-Doublet Models. Our results indicate that the BSM discovery potential in di-Higgs searches can be underestimated in comparison to $t\bar t $ resonance searches. Top pair final states are typically suppressed due to destructive signal-background interference, while $hh$ final states can be enhanced due to signal-signal interference. For parameter choices where the two heavy Higgs resonances are well separated in mass, top final states are suppressed relative to the naive signal expectation, while estimates of the production cross section times branching ratio remain accurate at the ${\cal{O}}(10\%)$ level for double Higgs final states.

A fragmentation-based study of heavy quark production

Processes involving heavy quarks are a crucial component of the LHC physics program, both by themselves and as backgrounds for Higgs physics and new physics searches. In this work, we critically reconsider the validity of the widely-adopted approximation in which heavy quarks are generated at the matrix-element level, with special emphasis on the impact of the collinear logarithms associated with final-state heavy quark and gluon splittings. Our study, based on a perturbative fragmentation-function approach, explicitly shows that neglecting the resummation of collinear logarithms may yield inaccurate predictions, in particular when observables exclusive in the heavy quark degrees of freedom are considered. Our findings motivate the use of schemes which encompass the resummation of final-state collinear logarithms.

Search for resonances decaying to a pair of Higgs bosons in the b overline{mathrm{b}} q overline{mathrm{q}} \u2019\u2113\u03bd final state in proton-proton collisions at sqrt{s} = 13 TeV

A search for new massive particles decaying into a pair of Higgs bosons in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. Data were collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb−1. The search is performed for resonances with a mass between 0.8 and 3.5 TeV using events in which one Higgs boson decays into a bottom quark pair and the other decays into two W bosons that subsequently decay into a lepton, a neutrino, and a quark pair. The Higgs boson decays are reconstructed with techniques that identify final state quarks as substructure within boosted jets. The data are consistent with standard model expectations. Exclusion limits are placed on the product of the cross section and branching fraction for generic spin-0 and spin-2 massive resonances. The results are interpreted in the context of radion and bulk graviton production in models with a warped extra spatial dimension. These are the best results to date from searches for an HH resonance decaying to this final state, and they are comparable to the results from searches in other channels for resonances with masses below 1.5 TeV.

Search for pair-produced three-jet resonances in proton-proton collisions at s=13 TeV

A search has been performed for pair-produced resonances decaying into three jets. The proton-proton collision data used for this analysis were collected with the CMS detector in 2016 at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The mass range from 200 to 2000 GeV is explored in four separate mass regions. The observations show agreement with standard model expectations. The results are interpreted within the framework of $R$-parity violating SUSY, where pair-produced gluinos decay to a six quark final state. Gluino masses below 1500 GeV are excluded at 95% confidence level. An analysis based on data with multijet events reconstructed at the trigger level extends the reach to masses as low as 200 GeV. Improved analysis techniques have led to enhanced sensitivity, allowing the most stringent limits to date to be set on gluino pair production.