Jets Final State Research Articles

Expanding the Gluino Exclusion Limits Using Events with One Highly Energetic Final State Jet and Missing Transverse Momentum

Multiple searches of theoretically hypothesized particles in Supersym-metry scenarios have been conducted through the years, many of which take place at the Large Hadron Collider (LHC) facility. A recent search of the ATLAS Collaboration [ 7] focuses on √s = 13 TeV pp collisions characterized by highly energetic jets and missing transverse momentum, resulting in model-independent limits for selected Signal Regions and providing exclusion limits for squarks. In this paper, we reinterpret the observations in terms of exclusion limits on gluino pair production. Monte Carlo simulations of gluino pair production events are made, varying both the masses of gluino and neutralino. In the end, we present the results in the mass plane of m˜g vs. m˜g − m ˜χ0 1 , including the effect of various sources of uncertainty.

Probing new physics with charge asymmetries in 2 same-sign leptons plus jets final states at the LHC

We study the impact of new physics models in the charge asymmetry defined for LHC final states consisting of two same-sign leptons (2SSl, with l = e, μ) plus jets (Njets ≥ 2), with a center-of-mass energy of 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, where the main SM contribution is tt¯W\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t}W $$\\end{document} production. Concretely, we consider three different new physics sources for the charge asymmetries: a heavy neutral scalar/pseudoscalar arising from the general two Higgs doublet model, an effective theory with dimension-6 four-quark operators, and a simplified R-parity-violating supersymmetric model with electroweakino production (higgsino-like or wino-like). We propose measuring the charge asymmetries differentially with respect to several kinematic observables, and inclusively/exclusively with the number of b-tagged jets in the final state (Nb ≥ {1, 2, 3}). Results are compared with the SM prediction using the χ2 criteria, expressing sensitivity in terms of the normal Gaussian significance. We show that some of the proposed new physics scenarios can be probed at the LHC even for the already recorded integrated luminosity of 139 fb−1. Finally, we also estimate the prospects for the potential LHC sensitivity to the considered new physics models in its high-luminosity phase.

Search for resonances in events with photon and jet 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 resonances in events with the γ+jet final state has been performed using proton-proton collision data collected 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 by the CMS experiment at the LHC. The total data analyzed correspond to an integrated luminosity of 138 fb−1. Models of excited quarks and quantum black holes are considered. Using a wide-jet reconstruction for the candidate jet, the γ+jet invariant mass spectrum measured in data is examined for the presence of resonances over the standard model continuum background. The background is estimated by fitting this mass distribution with a functional form. The data exhibit no statistically significant deviations from the expected standard model background. Exclusion limits at 95% confidence level on the resonance mass and other parameters are set. Excited light-flavor quarks (excited bottom quarks) are excluded up to a mass of 6.0 (3.8) TeV. Quantum black hole production is excluded for masses up to 7.5 (5.2) TeV in the Arkani-Hamed-Dimopoulos-Dvali (Randall-Sundrum) model. These lower mass bounds are the most stringent to date among those obtained in the γ+jet final state.

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 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 with the ATLAS detector

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 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 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 B\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{B} $$\\end{document}(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.

Resolving the Scales of the Quark-Gluon Plasma with Energy Correlators.

Jets provide us with ideal probes of the quark-gluon plasma (QGP) produced in heavy-ion collisions, since its dynamics at its different scales is imprinted into the multiscale substructure of the final state jets. We present a new approach to jet substructure in heavy-ion collisions based on the study of correlation functions of energy flow operators. By analyzing the two-point correlator of an in-medium quark jet, we demonstrate that the spectra of correlation functions robustly identify the scales defined by the properties of the QGP, particularly those associated with the onset of color coherence.

Search for nonresonant Higgs boson pair production in the four leptons plus twob jets final state in proton-proton collisions at sqrt{s} = 13 TeV

The first search for nonresonant production of Higgs boson pairs (HH) with one H decaying into four leptons and the other into a pair of b quarks is presented, using proton-proton collisions recorded at a center-of-mass energy of sqrt{s} = 13 TeV by the CMS experiment. The analyzed data correspond to an integrated luminosity of 138 fb−1. A 95% confidence level upper limit of 32.4 is set on the signal strength modifier μ, defined as the ratio of the observed HH production rate in the textrm{HH}to {textrm{ZZ}}^{ast}textrm{b}overline{textrm{b}}to 4ell textrm{b}overline{textrm{b}} decay channel to the standard model (SM) expectation. Possible modifications of the H trilinear coupling λHHH with respect to the SM value are investigated. The coupling modifier κλ, defined as λHHH divided by its SM prediction, is constrained to be within the observed (expected) range −8.8 (−9.8) < κλ< 13.4 (15.0) at 95% confidence level.

Investigating Higgs self-interaction through di-Higgs plus jet production at a 100 TeV hadron collider

The Higgs self coupling measurement is quite essential for determining the shape of the Higgs potential and nature of the Higgs boson. We propose the di-Higgs plus jet final states at hadron colliders to increase the discovery sensitivity of the Higgs self coupling at the low invariant mass region. Our simulation indicates that the allowed region of the Higgs self coupling would be further narrowed from $[-1.5,6.7]$ from the most recent ATLAS report down to $[0.5, 1.7]$. Furthermore, we find negative Higgs self couplings would be disfavored beyond $2\sigma$ confidence level at a future 100TeV collider with the help of this signal.

Towards NNLO+PS matching with sector showers

We outline a new technique for the fully-differential matching of final-state parton showers to NNLO calculations, focussing here on the simplest case of leptonic collisions with two final-state jets. The strategy is facilitated by working in the antenna formalism, making use of NNLO antenna subtraction on the fixed-order side and the sector-antenna framework on the shower side. As long as the combined real-virtual and double-real corrections do not overcompensate the real-emission term in the three-jet region, negative weights can be eliminated from the matching scheme. We describe the implementation of all necessary components in the Vincia antenna shower in Pythia 8.3.

Probing axion-like particles coupling to gluons at the LHC

Assuming ALPs couple to gluons only, they can be produced via the pp → aj process and decay into two jets at the LHC. When the coupling parameter, {C}_{overset{sim }{G}} /fa, is small, the lifetime of ALPs can be long enough leading to displaced final state jets. In this paper, we consider the signal including both the prompt and long-lived cases of ALPs by employing a specialized Delphes module to handle displaced jets. Relevant background processes are generated and simulated at the detector level, and multivariate analyses based on machine-learning are performed to discriminate signal and background events and achieve the best sensitivities. Based on the data accumulated for this study, we forecast the expected upper limits on {C}_{overset{sim }{G}} /fa for ALP mass ma in the range 5–2300 GeV at 2-, 3- and 5-σ significances at the High Luminosity-LHC with 14 TeV center-of-mass energy and 3 ab−1 integrated luminosity. Vast previously unprobed regions in the parameter space spanned by {C}_{overset{sim }{G}} /fa and ma are probed and the best upper limits on {C}_{overset{sim }{G}} /fa at 2-σ significance are found to be around 1.0 × 10−2 TeV−1 for ma∼ 500 GeV. The ALP mass is reconstructed from the kinematics of final state jets and we find that it is measurable with this method when ma is below about 1 TeV at the HL-LHC. The effects of systematic uncertainties and validation of the EFT framework are also checked and discussed.

Jet rapidity distributions and jet-jet correlation functions

Multi-particle production studies have always been an important tool in the effort to study the properties of the strong force already from the fifties of the previous century. As the center-of-mass energy of present day hadron colliders and in particular the Large Hadron Collider (LHC) has increased enormously over the years and the focus currently is on the study of multi-jet final states, it would be instructive to see whether the early days phenomenological models applied some 50–60 years ago to describe multi-particle production have anything to offer in the study of multi-jet final states as well as whether they offer predictions different from the QCD based ones. In this paper, we will consider events with two jets well separated in rapidity with similar transverse momenta whereas a number of mini-jets or jets is to be found in between these two bounding jets. Such configurations are relevant for the high energy scattering limit of QCD. We fix the final jet multiplicity to take particular values and we report on a first comparison between the predictions of the old multiperipheral Chew-Pignotti model applied for final state jets and those of BFKL. We compare single jet rapidity distributions as well as jet-jet rapidity correlations.

Measurement of the inclusive and differential t overline{t} γ cross sections in the dilepton channel and effective field theory interpretation in proton-proton collisions at sqrt{s} = 13 TeV

The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions in the decay channel with two oppositely charged leptons (e±μ∓, e+e−, or μ+μ−). The measurement is performed using 138 fb−1 of proton-proton collision data recorded by the CMS experiment at sqrt{s} = 13 TeV during the 2016–2018 data-taking period of the CERN LHC. A fiducial phase space is defined such that photons radiated by initial-state particles, top quarks, or any of their decay products are included. An inclusive cross section of 175.2 ± 2.5(stat) ± 6.3(syst) fb is measured in a signal region with at least one jet coming from the hadronization of a bottom quark and exactly one photon with transverse momentum above 20 GeV. Differential cross sections are measured as functions of several kinematic observables of the photon, leptons, and jets, and compared to standard model predictions. The measurements are also interpreted in the standard model effective field theory framework, and limits are found on the relevant Wilson coefficients from these results alone and in combination with a previous CMS measurement of the t overline{t} γ production process using the lepton+jets final state.

Search for a heavy resonance decaying into a top quark and a W boson in the lepton+jets final state at sqrt{s} = 13 TeV

A search for a heavy resonance decaying into a top quark and a W boson in proton-proton collisions at sqrt{s} = 13 TeV is presented. The data analyzed were recorded with the CMS detector at the LHC and correspond to an integrated luminosity of 138 fb−1. The top quark is reconstructed as a single jet and the W boson, from its decay into an electron or muon and the corresponding neutrino. A top quark tagging technique based on jet clustering with a variable distance parameter and simultaneous jet grooming is used to identify jets from the collimated top quark decay. The results are interpreted in the context of two benchmark models, where the heavy resonance is either an excited bottom quark b∗ or a vector-like quark B. A statistical combination with an earlier search by the CMS Collaboration in the all-hadronic final state is performed to place upper cross section limits on these two models. The new analysis extends the lower range of resonance mass probed from 1.4 down to 0.7 TeV. For left-handed, right-handed, and vector-like couplings, b∗ masses up to 3.0, 3.0, and 3.2 TeV are excluded at 95% confidence level, respectively. The observed upper limits represent the most stringent constraints on the b∗ model to date.

Heavy quark jet production near threshold

In this paper, we study the fragmentation of a heavy quark into a jet near threshold, meaning that final state jet carries most of the energy of the fragmenting heavy quark. Using the heavy quark fragmentation function, we simultaneously resum large logarithms of the jet radius R and 1 − z, where z is the ratio of the jet energy to the initiating heavy quark energy. There are numerically significant corrections to the leading order rate due to this resummation. We also investigate the heavy quark fragmentation to a groomed jet, using the soft drop grooming algorithm as an example. In order to do so, we introduce a collinear-ultrasoft mode sensitive to the grooming region determined by the algorithm’s zcut parameter. This allows us to resum large logarithms of zcut/(1 − z), again leading to large numerical corrections near the endpoint. A nice feature of the analysis of the heavy quark fragmenting to a groomed jet is the heavy quark mass m renders the algorithm infrared finite, allowing a perturbative calculation. We analyze this for EJR ∼ m and EJR » m, where EJ is the jet energy. To do the latter case, we introduce an ultracollinear-soft mode, allowing us to resum large logarithms of EJR/m. Finally, as an application we calculate the rate for e+e− collisions to produce a heavy quark jet in the endpoint region, where we show that grooming effects have a sizable contribution near the endpoint.

Spin correlations in final-state parton showers and jet observables

As part of a programme to develop parton showers with controlled logarithmic accuracy, we consider the question of collinear spin correlations within the PanScales family of parton showers. We adapt the well-known Collins–Knowles spin-correlation algorithm to PanScales antenna and dipole showers, using an approach with similarities to that taken by Richardson and Webster. To study the impact of spin correlations, we develop Lund-declustering based observables that are sensitive to spin-correlation effects both within and between jets and extend the MicroJets collinear single-logarithmic resummation code to include spin correlations. Together with a 3-point energy correlation observable proposed recently by Chen, Moult and Zhu, this provides a powerful set of constraints for validating the logarithmic accuracy of our shower results. The new observables and their resummation further open the pathway to phenomenological studies of these important quantum mechanical effects.

Search for a heavy neutral Higgs boson in a left-right model with an inverse seesaw mechanism at the LHC

We develop a low scale left-right symmetric model based on $SU(3)_C\times SU(2)_L\times SU(2)_R\times U(1)_{B-L}\times Z_2$ with a simplified Higgs sector consisting of only one bidoublet and one $SU(2)_R$ doublet. In this model, the tiny values of light neutrino masses are generated through an inverse-seesaw mechanism. We emphasize that in this setup, the tree-level flavor changing neutral current can be strongly suppressed, consistent with the current experimental constraints. We show that the lightest $CP$-even Higgs boson, which is like the standard model Higgs boson, and the next lightest Higgs boson, $h'$, are generated from the neutral components of the bidoublet. We show that the mass of the next lightest Higgs boson can be of an order a few hundred~\text{GeVs}. We analyze the detection of $h'$ at the Large Hadron Collider (LHC) for a center-of-mass energy $\sqrt{s}=14~\text{TeV}$ and integrated luminosity $L_{\text{int}}=300~{\text{fb}}^{-1}$ via di-Higgs channel: $h'\to hh\to b\bar{b}\gamma\gamma$ and also in the $ZZ$ channel: $h'\to ZZ\to 4\ell~(\ell=e,~\mu)$ at an integrated luminosity $L_{\text{int}}=3000~{\text{fb}}^{-1}$. We consider three benchmark points for this analysis with $m_{h'}=250~\text{GeV},~400~\text{GeV}$, and $600~\text{GeV}$. We show that promising signals with good statistical significances can be obtained in di-Higgs channel, with $2\gamma+2b$-jets final states.

The present and future of four top operators

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.

Inclusive prompt photon-jet correlations as a probe of gluon saturation in electron-nucleus scattering at small x

We compute the differential cross-section for inclusive prompt photon+quark production in deeply inelastic scattering of electrons off nuclei at small x (e + A DIS) in the framework of the Color Glass Condensate effective field theory. The result is expressed as a convolution of the leading order (in the strong coupling αs) impact factor for the process and universal dipole matrix elements, in the limit of hard photon transverse momentum relative to the nuclear saturation scale Qs,A(x). We perform a numerical study of this process for the kinematics of the Electron-Ion Collider (EIC), exploring in particular the azimuthal angle correlations between the final state photon and quark. We observe a systematic suppression and broadening pattern of the back-to-back peak in the relative azimuthal angle distribution, as the saturation scale is increased by replacing proton targets with gold nuclei. Our results suggest that photon+jet final states in inclusive e + A DIS at high energies are in general a promising channel for exploring gluon saturation that is complementary to inclusive and diffractive dijet production. They also provide a sensitive empirical test of the universality of dipole matrix elements when compared to identical measurements in proton-nucleus collisions. However because photon+jet correlations at small x in EIC kinematics require jet reconstruction at small k⊥, it will be important to study their feasibility relative to photon-hadron correlations.

Implementation of the CMS-HIG-18-011 analysis in the MadAnalysis 5 framework (exotic Higgs decays via two pseudoscalars with two muons and two b-jets; 35.9 fb−1)

We present the implementation in the MadAnalysis 5 framework of the CMS-HIG-18-011 search for exotic decays of the Standard Model Higgs boson, in which the Higgs boson is assumed to decay into a pair of light pseudoscalar [Formula: see text], that then further decay into a di-muon and di-[Formula: see text]-jet final state. This analysis considers proton-proton collisions at a center-of-mass energy of 13 TeV and data collected by the CMS experiment in 2016, with an integrated luminosity of 35.9 fb[Formula: see text]. We present a selection of recast predictions, obtained with MadAnalysis 5 and Delphes 3, that include a few differential distributions, yields, and efficiencies. We show that they agree at a level of a few percent with public CMS results.

Loop-induced ZZ production at the LHC: An improved description by matrix-element matching

Loop-induced $ZZ$ production can be enhanced by the large gluon flux at the LHC, and thus should be taken into account in relevant experimental analyses. We present for the first time the results of a fully exclusive simulation based on the matrix elements for loop-induced $ZZ + 0,1,2$-parton processes at leading order, matched to parton showers. The new description is studied and validated by comparing it with well-established simulation with jets from parton showers. We find that the matched simulation provides a state-of-the-art description of the final state jets. We also briefly discuss the physics impact on vector boson scattering (VBS) measurements at the LHC, where event yields are found to be smaller by about 40% in a VBS $ZZjj$ baseline search region, compared to previous simulations. We hence advocate relevant analyses to employ a more accurate jet description for the modeling of the loop-induced process.

One-loop jet functions by geometric subtraction

In factorization formulae for cross sections of scattering processes, final-state jets are described by jet functions, which are a crucial ingredient in the resummation of large logarithms. We present an approach to calculate generic one-loop jet functions, by using the geometric subtraction scheme. This method leads to local counterterms generated from a slicing procedure; and whose analytic integration is particularly simple. The poles are obtained analytically, up to an integration over the azimuthal angle for the observable- dependent soft counterterm. The poles depend only on the soft limit of the observable, characterized by a power law, and the finite term is written as a numerical integral. We illustrate our method by reproducing the known expressions for the jet function for angularities, the jet shape, and jets defined through a cone or kT algorithm. As a new result, we obtain the one-loop jet function for an angularity measurement in e+e− collisions, that accounts for the formally power-suppressed but potentially large effect of recoil. An implementation of our approach is made available as the GOJet Mathematica package accompanying this paper.