B-tagged Jets Research Articles

Jet charge: A new tool to probe the anomalous [formula omitted] couplings at the EIC

We propose to probe the Zbb¯ interactions at the Electron-Ion Collider (EIC) by utilizing the average jet charge weighted single-spin asymmetry AebQ, which is induced by different cross sections of a left-handed and right-handed electron beam scattering off an unpolarized proton beam in the neutral current deeply-inelastic scattering processes with one observed b-tagged jet. This novel observable at the EIC is sensitive to the axial-vector component of the Zbb¯ coupling, providing similar information as the gg→Zh cross section measurement at the high-luminosity Large Hadron Collider, and is complementary to the single-spin asymmetry measurement at the EIC which is sensitive to the vector component of the Zbb¯ coupling. We show that the apparent degeneracy of the allowed Zbb¯ coupling in its vector and axial-vector components, implied by the Large Electron-Positron Collider (LEP) and the Stanford Linear Collider (SLC) precision electroweak data, can be broken by the AebQ measurement at the EIC. With a large enough integrated luminosity collected at the EIC, the measurement of AebQ could also resolve the long-standing discrepancy between bottom quark forward-backward asymmetry AFBb at the LEP and the Standard Model prediction, with a strong dependence on the b-tagging efficiency.

NNLO event generation for ppto Zhto {mathrm{ell}}^{+}{mathrm{ell}}^{-}boverline{b} production in the SM effective field theory

We consider associated Zh production with Z → ℓ+ℓ− and hto boverline{b} decays in hadronic collisions. In the framework of the Standard Model effective field theory (SMEFT) we calculate the QCD corrections to this process and achieve next-to-next-to-leading order plus parton shower (NNLO+PS) accuracy using the MiNNLOPS method. This precision is obtained for a subset of six SMEFT operators, including the corrections from effective Yukawa- and chromomagnetic dipole-type interactions. Missing higher-order QCD effects associated with the considered dimension-six operators are estimated to have a relative numerical impact of less than a percent on the total rate once existing experimental limits on the relevant Wilson coefficients are taken into account. We provide a dedicated Monte Carlo (MC) code that evaluates the NNLO SMEFT corrections on-the-fly in the event generation. This MC generator is used to study the numerical impact of NNLO+PS corrections on the kinematic distributions in ppto Zhto {mathrm{ell}}^{+}{mathrm{ell}}^{-}boverline{b} production employing simple SMEFT benchmark scenarios. We identify the invariant mass {m}_{boverline{b}} of the two b-tagged jets as well as the three-invariant jet mass {m}_{boverline{b}j} as particularly interesting observables to study SMEFT effects. These distributions receive contributions that change both their normalisation and shape with the latter modifications depending on the exact jet definition. To our knowledge SMEFT effects of this type have so far not been discussed in the literature. The presented MC generator can also serve as a starting point to obtain NNLO+PS accuracy for a suitable enlarged set of effective operators in the future.

Inclusive nonresonant multilepton probes of new phenomena at s=13 TeV

An inclusive search for nonresonant signatures of beyond the standard model (SM) phenomena in events with three or more charged leptons, including hadronically decaying $\tau$ leptons, is presented. The analysis is based on a data sample corresponding to an integrated luminosity of 138 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} =$ 13 TeV, collected by the CMS experiment at the LHC in 2016-2018. Events are categorized based on the lepton and b-tagged jet multiplicities and various kinematic variables. Three scenarios of physics beyond the SM are probed, and signal-specific boosted decision trees are used for enhancing sensitivity. No significant deviations from the background expectations are observed. Lower limits are set at 95% confidence level on the mass of type-III seesaw heavy fermions in the range 845-1065 GeV for various decay branching fraction combinations to SM leptons. Doublet and singlet vector-like $\tau$ lepton extensions of the SM are excluded for masses below 1045 GeV and in the mass range 125-150 GeV, respectively. Scalar leptoquarks decaying exclusively to a top quark and a lepton are excluded below 1.12-1.42 TeV, depending on the lepton flavor. For the type-III seesaw as well as the vector-like doublet model, these constraints are the most stringent to date. For the vector-like singlet model, these are the first constraints from the LHC experiments. Detailed results are also presented to facilitate alternative theoretical interpretations.

Towards ruling out the charged Higgs interpretation of the {R}_{D^{left(ast right)}} anomaly

Motivated by the notorious anomaly in the lepton flavor universality ratios {R}_{D^{left(ast right)}} , we study the sensitivity of the Large Hadron Collider (LHC) to a low-mass charged Higgs boson H− lighter than 400 GeV in a generic two Higgs doublet model. A combination of current constraints from the Bc→ τν decay, Bs meson mixing data, tau sleptons and di-jet searches at the LHC allows to explain the {R}_{D^{left(ast right)}} anomaly at the 1σ level by a low-mass charged Higgs. In this context, we estimate the reach of an LHC search for resonant H− production, where the final state contains an energetic τ lepton decaying hadronically, a neutrino with large transverse momentum, and an additional b-jet (pp → b + τh + ν). Requiring the additional b-tagged jet in the τν resonance search profits from the suppression of the Standard Model background, and therefore it allows us to judge the low-mass H− interpretation of the {R}_{D^{left(ast right)}} anomaly. To demonstrate this, we perform a fast collider simulation for the τν resonance search with an additional b-tagged jet, and find that most of the interesting parameter region of the whole mass range can already be probed with the current integrated luminosity of 139 fb−1.

Search for flavour-changing neutral-current interactions of a top quark and a gluon in pp collisions at sqrt{s}=13 TeV with the ATLAS detector

A search is presented for the production of a single top quark via left-handed flavour-changing neutral-current (FCNC) interactions of a top quark, a gluon and an up or charm quark. Two production processes are considered: u+grightarrow t and c+grightarrow t. The analysis is based on proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. The data set corresponds to an integrated luminosity of 139 fb^{-1}. Events with exactly one electron or muon, exactly one b-tagged jet and missing transverse momentum are selected, resembling the decay products of a singly produced top quark. Neural networks based on kinematic variables differentiate between events from the two signal processes and events from background processes. The measured data are consistent with the background-only hypothesis, and limits are set on the production cross-sections of the signal processes: sigma (u+grightarrow t)times mathcal {B}(trightarrow Wb)times mathcal {B}(Wrightarrow ell nu )<3.0,pb and sigma (c+grightarrow t)times mathcal {B}(trightarrow Wb)times mathcal {B}(Wrightarrow ell nu )<4.7,pb at the 95% confidence level, with mathcal {B}(Wrightarrow ell nu )=0.325 being the sum of branching ratios of all three leptonic decay modes of the W boson. Based on the framework of an effective field theory, the cross-section limits are translated into limits on the strengths of the tug and tcg couplings occurring in the theory: |C^{,ut}_{uG}|/Lambda ^2 < 0.057,TeV^{-2} and |C^{,ct}_{uG}|/Lambda ^2 < 0.14,TeV^{-2}. These bounds correspond to limits on the branching ratios of FCNC-induced top-quark decays: mathcal {B}(trightarrow u+g)< 0.61times 10^{-4} and mathcal {B}(trightarrow c+g)< 3.7times 10^{-4}.

Search for R-parity-violating supersymmetry in a final state containing leptons and many jets with the ATLAS experiment using sqrt{s} = 13hbox { TeV} proton\u2013proton collision data

A search for R-parity-violating supersymmetry in final states characterized by high jet multiplicity, at least one isolated light lepton and either zero or at least three b-tagged jets is presented. The search uses {139},{text {fb}^{-1}} of sqrt{s} = {13}hbox { TeV} proton–proton collision data collected by the ATLAS experiment during Run 2 of the Large Hadron Collider. The results are interpreted in the context of R-parity-violating supersymmetry models that feature gluino production, top-squark production, or electroweakino production. The dominant sources of background are estimated using a data-driven model, based on observables at medium jet multiplicity, to predict the b-tagged jet multiplicity distribution at the higher jet multiplicities used in the search. Machine-learning techniques are used to reach sensitivity to electroweakino production, extending the data-driven background estimation to the shape of the machine-learning discriminant. No significant excess over the Standard Model expectation is observed and exclusion limits at the 95% confidence level are extracted, reaching as high as 2.4 TeV in gluino mass, 1.35 TeV in top-squark mass, and 320 (365) GeV in higgsino (wino) mass.

Search for dark matter produced in association with a Standard Model Higgs boson decaying into b-quarks using the full Run 2 dataset from the ATLAS detector

The production of dark matter in association with Higgs bosons is predicted in several extensions of the Standard Model. An exploration of such scenarios is presented, considering final states with missing transverse momentum and b-tagged jets consistent with a Higgs boson. The analysis uses proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the LHC during Run 2, amounting to an integrated luminosity of 139 fb−1. The analysis, when compared with previous searches, benefits from a larger dataset, but also has further improvements providing sensitivity to a wider spectrum of signal scenarios. These improvements include both an optimised event selection and advances in the object identification, such as the use of the likelihood-based significance of the missing transverse momentum and variable-radius track-jets. No significant deviation from Standard Model expectations is observed. Limits are set, at 95% confidence level, in two benchmark models with two Higgs doublets extended by either a heavy vector boson Z′ or a pseudoscalar singlet a and which both provide a dark matter candidate χ. In the case of the two-Higgs-doublet model with an additional vector boson Z′, the observed limits extend up to a Z′ mass of 3 TeV for a mass of 100 GeV for the dark matter candidate. The two-Higgs-doublet model with a dark matter particle mass of 10 GeV and an additional pseudoscalar a is excluded for masses of the a up to 520 GeV and 240 GeV for tan β = 1 and tan β = 10 respectively. Limits on the visible cross-sections are set and range from to 0.05 fb to 3.26 fb, depending on the missing transverse momentum and b-quark jet multiplicity requirements.

Search for New Phenomena in Final States with Two Leptons and One or No b-Tagged Jets at sqrt[s]=13 TeV Using the ATLAS Detector.

A search for new phenomena is presented in final states with two leptons and one or no b-tagged jets. The event selection requires the two leptons to have opposite charge, the same flavor (electrons or muons), and a large invariant mass. The analysis is based on the full run-2 proton-proton collision dataset recorded at a center-of-mass energy of sqrt[s]=13 TeV by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 139 fb^{-1}. No significant deviation from the expected background is observed in the data. Inspired by the B-meson decay anomalies, a four-fermion contact interaction between two quarks (b, s) and two leptons (ee or μμ) is used as a benchmark signal model, which is characterized by the energy scale and coupling, Λ and g_{*}, respectively. Contact interactions with Λ/g_{*} lower than 2.0 (2.4)TeV are excluded for electrons (muons) at the 95%confidence level, still far below the value that is favored by the B-meson decay anomalies. Model-independent limits are set as a function of the minimum dilepton invariant mass, which allow the results to be reinterpreted in various signal scenarios.

The anomalous [formula omitted] couplings at the HERA and EIC

To resolve the long-standing discrepancy between the precision measurement of bottom quark forward-backward asymmetry at LEP/SLC and the Standard Model prediction, we propose a novel method to probe the Zbb¯ coupling by measuring the single-spin asymmetry Aeb of the polarized lepton cross section in neutral current DIS processes with a b-tagged jet at HERA and EIC. Depending on the tagging efficiency of the final state b-jet, the measurement of Aeb at HERA can already partially break the degeneracy found in the anomalous Zbb¯ coupling, as implied by the LEP and SLC precision electroweak data. In the first year run of the EIC, the measurement of Aeb can already break the degeneracy, due to its much larger luminosity and higher electron beam polarization. With enough integrated luminosity collected at the EIC, it is possible to either verify or exclude the LEP data and resolve the AFBb puzzle. We also discuss the complementary roles between the proposed Aeb measurement at EIC and the measurement of gg→Zh cross section at the HL-LHC in constraining the anomalous Zbb¯ coupling.

Search for charged Higgs bosons decaying into a top quark and a bottom quark at sqrt{mathrm{s}} = 13 TeV with the ATLAS detector

A search for charged Higgs bosons decaying into a top quark and a bottom quark is presented. The data analysed correspond to 139 fb−1 of proton-proton collisions at sqrt{s} = 13 TeV, recorded with the ATLAS detector at the LHC. The production of a heavy charged Higgs boson in association with a top quark and a bottom quark, pp → tbH+ → tbtb, is explored in the H+ mass range from 200 to 2000 GeV using final states with jets and one electron or muon. Events are categorised according to the multiplicity of jets and b-tagged jets, and multivariate analysis techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass; they range from 3.6 pb at 200 GeV to 0.036 pb at 2000 GeV at 95% confidence level. The results are interpreted in the hMSSM and {M}_h^{125} scenarios.

Studying squark mass spectrum through gluino decay at 100 TeV future hadron colliders

We study the prospect of determining the decay properties of the gluino in the supersymmetric (SUSY) standard model at a 100 TeV future hadron collider. We consider the case where the neutral Wino is the lightest superparticle. In this case, the long-lived charged Wino can be used to eliminate standard model backgrounds, which enables us to study the details of superparticles. We show that, based on the analysis of the numbers of high pT leptons, boosted W-jets, and b-tagged jets, we may determine the gaugino species and the quark flavors in the gluino decay. With such determinations, we can obtain information about the mass spectrum of squarks even if squarks are out of the kinematical reach.

Topping-up multilepton plus b-jets anomalies at the LHC with a Z\u2032 boson

During the last years ATLAS and CMS have reported a number of slight to mild discrepancies in signatures of multileptons plus b-jets in analyses such as toverline{t}H , toverline{t}{W}^{pm } , toverline{t}Z and toverline{t}toverline{t} . Among them, a recent ATLAS result on toverline{t}H production has also reported an excess in the charge asymmetry in the same-sign dilepton channel with two or more b-tagged jets. Motivated by these tantalizing discrepancies, we study a phenomenological New Physics model consisting of a Z′ boson that couples to up-type quarks via right-handed currents: {t}_R{gamma}^{mu }{overline{t}}_R , {t}_R{gamma}^{mu }{overline{c}}_R , and {t}_R{gamma}^{mu }{overline{u}}_R . The latter vertex allows to translate the charge asymmetry at the LHC initial state protons to a final state with top quarks which, decaying to a positive lepton and a b-jet, provides a crucial contribution to some of the observed discrepancies. Through an analysis at a detector level, we select the region in parameter space of our model that best reproduces the data in the aforementioned toverline{t}H study, and in a recent ATLAS toverline{t}toverline{t} search. We find that our model provides a better fit to the experimental data than the Standard Model for a New Physics scale of approximately ∼500 GeV, and with a hierarchical coupling of the Z′ boson that favours the top quark and the presence of FCNC currents. In order to estimate the LHC sensitivity to this signal, we design a broadband search featuring many kinematic regions with different signal-to-background ratio, and perform a global analysis. We also define signal-enhanced regions and study observables that could further distinguish signal from background. We find that the region in parameter space of our model that best fits the analysed data could be probed with a significance exceeding 3 standard deviations with just the full Run-2 dataset.

Single-top final states as a probe of top-flavoured dark matter models at the LHC

Models incorporating flavoured dark matter provide an elegant solution to the dark matter problem, evading the tight LHC and direct direction constraints on simple WIMP models. In Dark Minimal Flavour Violation, a simple framework of flavoured dark matter with new sources of flavour violation, the constraints from thermal freeze-out, direct detection experiments, and flavour physics create well-defined benchmark scenarios for these models. We study the LHC phenomenology of four such scenarios, focusing on final states where a single top quark is produced accompanied by no jets, one jet from the fragmentation of light quarks or a b-tagged jet. For each of these signatures we develop a realistic LHC analysis, and we show that the proposed analyses would increase the parameter space coverage for the four benchmarks, compared to existing flavour-conserving LHC analyses. Finally we show the projected discovery potential of the considered signatures for the full LHC statistics at 14 TeV, and for the High Luminosity LHC.

Prospects of measuring $$R_b$$ in hadronic $$\mathrm{Z}$$ decays at the CEPC

With an integrated luminosity of 45 $$\mathrm{ab}^{-1}$$ at $$\sqrt{s} = 91.2$$ GeV, more than $$10^{12}$$ $$\mathrm{Z}$$ bosons will be produced at the Circular Electron Positron Collider (CEPC). As a real $$\mathrm{Z}$$ boson factory, the precise study of $$\mathrm{Z}$$ boson physics can be achieved. In this paper, the relative partial width, $$R_{b}$$ , of $$\mathrm{Z}$$ boson into b quarks, is measured on the CEPC Monte Carlo level. Based on the latest CEPC detector concept, the $$\mathrm{Z}$$ hadronic decay channel is simulated and reconstructed by the CEPC software framework. By using the double-tagging method, $$R_b$$ can be solved from several equations referring to the ratios of b-tagged jet hemispheres in $$\mathrm{Z}$$ hadronic events. With the high performance of the b-tagging algorithm for CEPC, the b-tagging correlation between the two jet hemispheres can be reduced. By carrying out a closure test, the double-tagging method is verified to work well as we expected. We further estimated the dependence of systematic errors on the b-tagging efficiencies of the charm and light jet, as well as the b-tagging correlation between two jet hemispheres. The sources of systematic errors, such as physics modeling and hemisphere correlation, are investigated and studied preliminarily. Several kinds of error sources related to the hemisphere correlation are studied with the characterized variables.

Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using sqrt{s} = 13 TeV proton-proton collisions recorded by ATLAS in Run 2 of the LHC

Results of a search for new particles decaying into eight or more jets and moderate missing transverse momentum are presented. The analysis uses 139 fb−1 of proton-proton collision data at sqrt{s} = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. The selection rejects events containing isolated electrons or muons, and makes requirements according to the number of b-tagged jets and the scalar sum of masses of large-radius jets. The search extends previous analyses both in using a larger dataset and by employing improved jet and missing transverse momentum reconstruction methods which more cleanly separate signal from background processes. No evidence for physics beyond the Standard Model is found. The results are interpreted in the context of supersymmetry-inspired simplified models, significantly extending the limits on the gluino mass in those models. In particular, limits on the gluino mass are set at 2 TeV when the lightest neutralino is nearly massless in a model assuming a two-step cascade decay via the lightest chargino and second-lightest neutralino.

Search for direct production of electroweakinos in final states with one lepton, missing transverse momentum and a Higgs boson decaying into two b-jets in pp collisions at sqrt{s}=13\xa0TeV with the ATLAS detector

The results of a search for electroweakino pair production pp rightarrow tilde{chi }^pm _1 tilde{chi }^0_2 in which the chargino (tilde{chi }^pm _1) decays into a W boson and the lightest neutralino (tilde{chi }^0_1), while the heavier neutralino (tilde{chi }^0_2) decays into the Standard Model 125 GeV Higgs boson and a second tilde{chi }^0_1 are presented. The signal selection requires a pair of b-tagged jets consistent with those from a Higgs boson decay, and either an electron or a muon from the W boson decay, together with missing transverse momentum from the corresponding neutrino and the stable neutralinos. The analysis is based on data corresponding to 139 mathrm {fb}^{-1} of sqrt{s}=13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. No statistically significant evidence of an excess of events above the Standard Model expectation is found. Limits are set on the direct production of the electroweakinos in simplified models, assuming pure wino cross-sections. Masses of tilde{chi }^{pm }_{1}/tilde{chi }^{0}_{2} up to 740 GeV are excluded at 95% confidence level for a massless tilde{chi }^{0}_{1}.

Heavy-flavour correlations and jets with ALICE at the LHC

This contribution summarises the results on heavy-flavour correlations and jets measured with ALICE detector. Studies of D0-tagged jets are presented in various collision systems and energies. The measurement of the fraction of jet momentum carried by the D0 meson in the direction of the jet axis in pp collisions at and 13 TeV as well as the nuclear modification factor in p–Pb and Pb–Pb collisions are presented. The measurements of the production of jets tagged by electrons from heavy-flavour decays in pp and p–Pb are compared to expectations from POWHEG+PYTHIA8 simulations. The p T-differential cross section of b-tagged jets in p–Pb collisions is also reported and compared to expectations from POWHEG event generator. The azimuthal correlation of D mesons with charged particles in pp and p–Pb collisions are also presented.

Searching for New Physics with [formula omitted] contact interactions

We study the impact of contact interactions involving two leptons (electrons or muons) and two b-quarks (bb¯ℓ+ℓ−) on the high-mass di-lepton region at the LHC. We consider different selections of b-tagged jet multiplicities in the di-lepton final states: inclusive (no selection), 0, 1 and 2 b-tagged jets, and show that the single b-jet selection significantly improves the sensitivity to New Physics (NP) in the form of the bb¯ℓ+ℓ− contact term. We obtain a better sensitivity compared to the currently existing searches of NP in the di-lepton inclusive channel. In particular, the expected limits go beyond competitive bounds set by LEP (for electrons) on the scale of NP, Λ, by a factor of 1.2−3.1, depending on the chirality structure of the operator. In addition, the expected limits on Λ, set by using a non-resonant LHC di-lepton inclusive search, are expected to be improved by a factor of 1.3−1.4 for both electrons and muons.

Signs of new physics in top quark pair production associated with a neutrino pair at the LHC

In this paper, we examine the interactions of the top quarks with the $Z$ boson using the top quark pair production associated with neutrino pair ($t\bar{t}\nu_{l}\bar{\nu_{l}}$) at the LHC. In particular, potential constraints on the anomalous electroweak top-quark interactions are determined by considering two opposite-sign charged leptons, missing energy, and two b-tagged jets in the final state. The analysis is performed for a High Luminosity scenario of the LHC with an integrated luminosity of 3 ab$^{-1}$ of proton-proton collisions at a center-of-mass energy of 14 TeV. The $95\%$ confidence intervals are computed on the anomalous couplings considering a realistic detector simulation of an upgraded CMS detector including an average of 200 proton-proton interactions per bunch crossing. We find that the $t\bar{t}\nu_{l}\bar{\nu_{l}}$ channel can provide stringent bounds on the relevant Wilson coefficients and has the potential to serve as an additional handle beside the $t\bar{t}Z(Z\rightarrow l^{+}l^{-})$ and other channels to search for new physics.

Search for non-resonant Higgs boson pair production in the bbℓνℓν final state with the ATLAS detector in pp collisions at [formula omitted] TeV

A search for non-resonant Higgs boson pair production, as predicted by the Standard Model, is presented, where one of the Higgs bosons decays via the H→bb channel and the other via one of the H→WW⁎/ZZ⁎/ττ channels. The analysis selection requires events to have at least two b-tagged jets and exactly two leptons (electrons or muons) with opposite electric charge in the final state. Candidate events consistent with Higgs boson pair production are selected using a multi-class neural network discriminant. The analysis uses 139 fb−1 of pp collision data recorded at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. An observed (expected) upper limit of 1.2 (0.9−0.3+0.4) pb is set on the non-resonant Higgs boson pair production cross-section at 95% confidence level, which is equivalent to 40 (29−9+14) times the value predicted in the Standard Model.