Third-generation Scalar Leptoquarks Research Articles

LHC study of third-generation scalar leptoquarks with machine-learned likelihoods

LHC study of third-generation scalar leptoquarks with machine-learned likelihoods

Precise probing and discrimination of third-generation scalar leptoquarks

Precise probing and discrimination of third-generation scalar leptoquarks

Search for pair production of third-generation scalar leptoquarks decaying into a top quark and a \u03c4-lepton in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ-lepton is presented. The search is based on a dataset of pp collisions at sqrt{s} = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. Events are selected if they have one light lepton (electron or muon) and at least one hadronically decaying τ -lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as containing b-hadrons, are required. Six final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The signal-rich event categories require at least one hadronically decaying τ-lepton candidate and exploit the presence of energetic final-state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, for different assumptions about the branching fractions into tτ and bν. Scalar leptoquarks decaying exclusively into tτ are excluded up to masses of 1.43 TeV while, for a branching fraction of 50% into tτ, the lower mass limit is 1.22 TeV.

Dark Matter EFT, the Third -- Neutrino WIMPs

Sterile neutrinos coupling only to third-generation fermions are attractive dark matter candidates. In an EFT approach we demonstrate that they can generate the observed relic density without violating constraints from direct and indirect detection. Such an EFT represents a gauged third-generation B-L model, as well as third-generation scalar or vector leptoquarks. LHC measurements naturally distinguish the different underlying models.

Search for heavy neutrinos and third-generation leptoquarks in hadronic states of two \u03c4 leptons and two jets in proton-proton collisions at sqrt{s}=13 TeV

A search for new particles has been conducted using events with two high transverse momentum τ leptons that decay hadronically and at least two energetic jets. The analysis is performed using data from proton-proton collisions at sqrt{s}=13 TeV, collected by the CMS experiment at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb−1. The observed data are consistent with standard model expectations. The results are interpreted in the context of two physics models. The first model involves right-handed charged bosons, WR, that decay to heavy right-handed Majorana neutrinos, Nℓ (ℓ = e, μ, τ), arising in a left-right symmetric extension of the standard model. The model considers that Ne and Nμ are too heavy to be detected at the LHC. Assuming that the Nτ mass is half of the WR mass, masses of the WR boson below 3.50 TeV are excluded at 95% confidence level. Exclusion limits are also presented considering different scenarios for the mass ratio between Nτ and WR, as a function of WR mass. In the second model, pair production of third-generation scalar leptoquarks that decay into ττbb is considered, resulting in an observed exclusion region with leptoquark masses below 1.02 TeV, assuming a 100% branching fraction for the leptoquark decay to a τ lepton and a bottom quark. These results represent the most stringent limits to date on these models.

Search for a singly produced third-generation scalar leptoquark decaying to a \u03c4 lepton and a bottom quark in proton-proton collisions at sqrt{s}=13 TeV

A search is presented for a singly produced third-generation scalar leptoquark decaying to a τ lepton and a bottom quark. Associated production of a leptoquark and a τ lepton is considered, leading to a final state with a bottom quark and two τ leptons. The search uses proton-proton collision data at a center-of-mass energy of 13 TeV recorded with the CMS detector, corresponding to an integrated luminosity of 35.9 fb−1. Upper limits are set at 95% confidence level on the production cross section of the third-generation scalar leptoquarks as a function of their mass. From a comparison of the results with the theoretical predictions, a third-generation scalar leptoquark decaying to a τ lepton and a bottom quark, assuming unit Yukawa coupling (λ), is excluded for masses below 740 GeV. Limits are also set on λ of the hypothesized leptoquark as a function of its mass. Above λ = 1.4, this result provides the best upper limit on the mass of a third-generation scalar leptoquark decaying to a τ lepton and a bottom quark.

Search for third-generation scalar leptoquarks and heavy right-handed neutrinos in final states with two tau leptons and two jets in proton-proton collisions at sqrt{s}=13 TeV

A search is performed for third-generation scalar leptoquarks and heavy right-handed neutrinos in events containing one electron or muon, one hadronically decaying τ lepton, and at least two jets, using a sqrt{s}=13 TeV pp collision data sample corresponding to an integrated luminosity of 12.9 fb-1 collected with the CMS detector at the LHC in 2016. The number of observed events is found to be in agreement with the standard model prediction. A limit is set at 95% confidence level on the product of the leptoquark pair production cross section and β2, where β is the branching fraction of leptoquark decay to a τ lepton and a bottom quark. Assuming β = 1, third-generation leptoquarks with masses below 850 GeV are excluded at 95% confidence level. An additional search based on the same event topology involves heavy right-handed neutrinos, NR, and right-handed W bosons, WR, arising in a left-right symmetric extension of the standard model. In this search, WR bosons are assumed to decay to a tau lepton and NR followed by the decay of the NR to a tau lepton and an off-shell WR boson. Assuming the mass of the right-handed neutrino to be half of the mass of the right-handed W boson, WR boson masses below 2.9 TeV are excluded at 95% confidence level. These results improve on the limits from previous searches for third-generation leptoquarks and heavy right-handed neutrinos with τ leptons in the final state.

Search for heavy neutrinos or third-generation leptoquarks in final states with two hadronically decaying \u03c4 leptons and two jets in proton-proton collisions at sqrt{s}=13 TeV

A search for new particles has been conducted using events with two high transverse momentum (pT) τ leptons that decay hadronically, at least two high-pT jets, and missing transverse energy from the τ lepton decays. The analysis is performed using data from proton-proton collisions, collected by the CMS experiment in 2015 at sqrt{s}=13 TeV, corresponding to an integrated luminosity of 2.1 fb−1. The results are interpreted in two physics models. The first model involves heavy right-handed neutrinos, Nℓ (ℓ = e, μ, τ), and right-handed charged bosons, WR, arising in a left-right symmetric extension of the standard model. Masses of the WR boson below 2.35 (1.63) TeV are excluded at 95% confidence level, assuming the Nτ mass is 0.8 (0.2) times the mass of the WR boson and that only the Nτ flavor contributes to the WR decay width. In the second model, pair production of third-generation scalar leptoquarks that decay into ττbb is considered. Third-generation scalar leptoquarks with masses below 740 GeV are excluded, assuming a 100% branching fraction for the leptoquark decay to a τ lepton and a bottom quark. This is the first search at hadron colliders for the third-generation Majorana neutrino, as well as the first search for third-generation leptoquarks in the final state with a pair of hadronically decaying τ leptons and jets.

Erratum to: Search for third-generation scalar leptoquarks in the tτ channel in proton-proton collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

Erratum to: Search for third-generation scalar leptoquarks in the tτ channel in proton-proton collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

Search for leptoquark-like signatures with the ATLAS and CMS detectors

The most recent results from searches of leptoquark-like signatures are presented using 1.03 and 4.7 fb−1 of pp collision data collected by the ATLAS detector with s=7 TeV and 19.6 fb−1 of pp collision data collected by the CMS detector with s=8 TeV at the LHC. First- and second-generation scalar leptoquarks are looked for in the final states with either two leptons and two jets (ℓℓ+jj, ℓ=e, μ) or one lepton, missing transverse energy, and two jets (ℓν+jj, ℓ=e, μ). Apart from leptoquark investigations, the ℓℓ+jj final states are further studied in a search for W bosons with right-handed couplings that arise in left-right models. Third-generation scalar leptoquarks are looked for in the final state with two tau leptons and two b quarks or two top quarks (ττ+bb and ττ+tt). The ττ+bb final state is also sensitive to stop pairs decaying through R-parity violating and conserving processes that are foreseen in some models of supersymmetry. In addition, results are shown for third-generation scalar leptoquarks in the final states bb+νν and tt+νν, reinterpreting searches for bottom and top squark pair production. 95% confidence level upper limits are set on the scalar leptoquark pair production cross section times branching fraction in each decay channel as a function of the leptoquark mass and the branching ratio of decay.

Search for third-generation scalar leptoquarks in the tτ channel in proton-proton collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

A search for pair production of third-generation scalar leptoquarks decaying to top quark and tau lepton pairs is presented using proton-proton collision data at a center-of-mass energy of sqrt(s) = 8 TeV collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 19.7 inverse femtobarns. The search is performed using events that contain an electron or a muon, a hadronically decaying tau lepton, and two or more jets. The observations are found to be consistent with the standard model predictions. Assuming that all leptoquarks decay to a top quark and a tau lepton, the existence of pair produced, charge -1/3, third-generation leptoquarks up to a mass of 685 GeV is excluded at 95% confidence level. This result constitutes the first direct limit for leptoquarks decaying into a top quark and a tau lepton, and may also be applied directly to the pair production of bottom squarks decaying predominantly via the R-parity violating coupling lambda'[333].

Search for pair production of third-generation scalar leptoquarks and top squarks in proton–proton collisions at [formula omitted

A search for pair production of third-generation scalar leptoquarks and supersymmetric top quark partners, top squarks, in final states involving tau leptons and bottom quarks is presented. The search uses events from a data sample of proton–proton collisions corresponding to an integrated luminosity of 19.7 fb−1, collected with the CMS detector at the LHC with s=8 TeV. The number of observed events is found to be in agreement with the expected standard model background. Third-generation scalar leptoquarks with masses below 740 GeV are excluded at 95% confidence level, assuming a 100% branching fraction for the leptoquark decay to a tau lepton and a bottom quark. In addition, this mass limit applies directly to top squarks decaying via an R-parity violating coupling λ333′. The search also considers a similar signature from top squarks undergoing a chargino-mediated decay involving the R-parity violating coupling λ3jk′. Each top squark decays to a tau lepton, a bottom quark, and two light quarks. Top squarks in this model with masses below 580 GeV are excluded at 95% confidence level. The constraint on the leptoquark mass is the most stringent to date, and this is the first search for top squarks decaying via λ3jk′.

Search for Pair Production of Third-Generation Leptoquarks and Top Squarks inppCollisions ats=7 TeV

Results are presented from a search for the pair production of third-generation scalar and vector leptoquarks, as well as for top squarks in R-parity-violating supersymmetric models. In either scenario, the new, heavy particle decays into a τ lepton and a b quark. The search is based on a data sample of pp collisions at sqrt[s] = 7 TeV, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 4.8 fb(-1). The number of observed events is found to be in agreement with the standard model prediction, and exclusion limits on mass parameters are obtained at the 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to a τ lepton and a b quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, and limits on the coupling between the top squark, τ lepton, and b quark, λ(333)(') are obtained. These results are the most stringent for these scenarios to date.

Search for scalar bottom quarks and third-generation leptoquarks in [formula omitted] collisions at [formula omitted

We report the results of a search for pair production of scalar bottom quarks (b˜1) and scalar third-generation leptoquarks (LQ3) in 5.2 fb−1 of pp¯ collisions at the D0 experiment of the Fermilab Tevatron Collider. Scalar bottom quarks are assumed to decay to a neutralino (χ˜10) and a b quark, and we set 95% C.L. lower limits on their production in the (mb˜1, mχ˜10) mass plane such as mb˜1>247 GeV for mχ˜10=0 and mχ˜10>110 GeV for 160<mb˜1<200 GeV. The leptoquarks are assumed to decay to a tau neutrino and a b quark, and we set a 95% C.L. lower limit of 247 GeV on the mass of a charge-1/3 third-generation scalar leptoquark.

Search for Pair Production of Scalar Top Quarks Decaying to aτLepton and abQuark inpp¯Collisions ats=1.96 TeV

We search for pair production of supersymmetric top quarks (t˜1), followed by R-parity violating decay t˜1→τb with a branching ratio β, using 322 pb−1 of pp¯ collisions at s=1.96 TeV collected by the upgraded Collider Detector at Fermilab. Two candidate events pass our final selection criteria, consistent with the standard model expectation. We set upper limits on the cross section σ(t˜1t˜¯1)×β2 as a function of the top-squark mass m(t˜1). Assuming β=1, we set a 95% confidence level limit m(t˜1)>153 GeV/c2. The limits are also applicable to the case of a third-generation scalar leptoquark (LQ3) decaying LQ3→τb.Received 27 February 2008Publisher error corrected 14 August 2008DOI:https://doi.org/10.1103/PhysRevLett.101.071802©2008 American Physical Society

Search for Third-Generation Scalar Leptoquarks inpp¯Collisions ats=1.96 TeV

We report on a search for charge-1/3 third-generation leptoquarks (LQ) produced in pp collisions at square root s =1.96 TeV using the D0 detector at Fermilab. Third-generation leptoquarks are assumed to be produced in pairs and to decay to a tau neutrino and a b quark with branching fraction B. We place upper limits on sigma(pp --> LQLQ)B2 as a function of the leptoquark mass M(LQ). Assuming B=1, we exclude at the 95% confidence level third-generation scalar leptoquarks with M(LQ)<229 GeV.

Search forCharge−1/3Third-Generation Leptoquarks inpp¯Collisions ats=1.8TeV

We report on a search for $\mathrm{charge}\ensuremath{-}1/3$ third-generation leptoquarks (LQ) produced in $p\overline{p}$ collisions at $\ensuremath{\surd}s\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ using the $\mathrm{D}0$ detector at Fermilab. Third-generation leptoquarks are assumed to be produced in pairs and to decay to a tau neutrino and a $b$ quark with branching fraction $B$. We place upper limits on $\ensuremath{\sigma}(p\overline{p}\ensuremath{\rightarrow}\mathrm{LQ}\overline{\mathrm{LQ}}){B}^{2}$ as a function of the leptoquark mass ${M}_{\mathrm{LQ}}$. Assuming $B\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$, we exclude at the 95% confidence level third-generation scalar leptoquarks with ${M}_{\mathrm{LQ}}l94\mathrm{GeV}{/c}^{2}$, and third-generation vector leptoquarks with ${M}_{\mathrm{LQ}}l216\mathrm{GeV}{/c}^{2}({M}_{\mathrm{LQ}}l148\mathrm{GeV}{/c}^{2}$) assuming Yang-Mills (anomalous) coupling.

Third-generation leptoquark decays and collider searches

Collider searches for first-, second-, and third-generation scalar (S) or vector (V) leptoquarks (LQs) focus on the quark-lepton decay modes S,V -> q l. For SU(2)-doublet and -triplet leptoquarks with a sufficiently large splitting between the components, decays involving real W-boson emission (such as S_2^{(+5/3)} -> S_2^{(+2/3)} W^{+} and others) become possible and can change the patterns of leptoquark decays. For third-generation leptoquarks, where these mass splittings might be large, such modes could dominate certain leptoquark decays as they are (if kinematically allowed) guaranteed to be of order g^2 where g is the electroweak coupling. We calculate the decay rates for all such processes involving SU(2)-doublet and triplet, scalar and vector leptoquarks. Standard limits on mass splittings from precision electroweak measurements imply that only such decays involving SU(2)-doublet scalar LQs are likely kinematically possible.