Generation Scalar Leptoquarks Research Articles

Signals of the first generation scalar leptoquarks at LHeC

We consider single production of the first generation scalar leptoquarks (SLQs) at large hadron electron collider (LHeC) in the context of two simplified SLQ models. Our numerical results show that the production cross-sections are much larger than those at LHC. The possible signals of SLQs might be discovered at LHeC in the near future.

Constraints on the First Generation Scalar Leptoquarks**Supported by the National Natural Science Foundation of China under Grants Nos 11275088 and 11545012, and the Natural Science Foundation of Liaoning Scientific Committee under Grant No 2014020151.

Inspired by the CMS excess in eejj and evjj channels and possible interpretation using the first generation scalar leptoquarks (SLQs), we consider their contributions to non-standard neutrino interaction and the pion meson leptonic decay π → lv. Compared with the relevant experimental data, the constraints on the first generation SLQs are obtained. Their corrections to the anomalous magnetic moment αμ are further calculated and the numerical results show that it is possible to explain the deviation from its standard model prediction.

Single productions of colored particles at the LHC: an example with scalar leptoquarks

Current LHC searches for new colored particles generally focus on their pair production channels and assume any single production to be negligible. We argue that such an assumption may be unnecessary in some cases. Inclusion of model dependent single productions in pair production searches (or vice versa) can give us new information about model parameters or better exclusion limits. Considering the example of the recent CMS search for first generation scalar leptoquarks in the pair production channel, we illustrate how single productions can be systematically included in the signal estimations and demonstrate how it can affect the mass exclusion limits and give new bounds on leptoquark-lepton-quark couplings. We also estimate the effect of the pair production in the more recent CMS search for scalar leptoquarks in single production channels.

Searches for the pair production of scalar leptoquarks at CMS

Results are presented for searches for leptoquark (LQ) pair production using 1.8 –5.0 fb−1 of proton–proton collision data at = 7 TeV collected by the CMS detector at the LHC. First– and second–generation scalar leptoquarks are searched for in final states with either two leptons and two jets (ℓℓjj) or one lepton, missing transverse energy (), and two jets (ℓvjj). Third–generation leptoquarks are searched for in the final state with two b–tagged jets and large (vvbb). No significant excess beyond the standard model predictions is found and 95% confidence level (CL) upper limits are set on the scalar leptoquark pair production cross section in each channel. Limits are calculated for a range of leptoquark mass and for a variable branching fraction (β) of the leptoquark to a charge lepton and a quark. These limits are the most stringent to date.

Search for third generation scalar leptoquarks in pp collisions at $ \sqrt{s}=7 $ TeV with the ATLAS detector

AbstractA search for pair-produced third generation scalar leptoquarks is presented, using proton-proton collisions at$ \sqrt{s}=7 $TeV at the LHC. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 4.7 fb−1. Each leptoquark is assumed to decay to a tau lepton and ab-quark with a branching fraction equal to 100%. No statistically significant excess above the Standard Model expectation is observed. Third generation leptoquarks are therefore excluded at 95% confidence level for masses less than 534GeV.

Searches for new physics with tau leptons at the ATLAS detector

Searches for heavy particles decaying to a pair of tau leptons, and searches for pair produced third- generation scalar leptoquarks decaying to a b-jet and a tau lepton are reported. The studies use the full data sample recorded in 2011 at √ s = 7TeV centre-of-mass energy by the ATLAS experiment at the LHC.

Search for second generation scalar leptoquarks in pp collisions at $\sqrt{s}=7~\mbox{TeV}$ with the ATLAS detector

AbstractThe results of a search for the production of second generation scalar leptoquarks are presented for final states consisting of either two muons and at least two jets or a muon plus missing transverse momentum and at least two jets. A total of 1.03 fb−1 integrated luminosity of proton-proton collision data produced by the Large Hadron Collider at $\sqrt{s}=7~\mbox{TeV}$ and recorded by the ATLAS detector is used for the search. The event yields in the signal regions are found to be consistent with the Standard Model background expectations. The production of second generation leptoquarks is excluded for a leptoquark mass mLQ<594 (685) GeV at 95 % confidence level, for a branching ratio of 0.5 (1.0) for leptoquark decay to a muon and a quark.

Search for first generation scalar leptoquarks in pp collisions at [formula omitted] with the ATLAS detector

We report a search for first generation scalar leptoquarks using 1.03 fb−1 of proton–proton collisions data produced by the Large Hadron Collider at s=7 TeV and recorded by the ATLAS experiment. Leptoquarks are sought via their decay into an electron or neutrino and a quark, producing events with two oppositely charged electrons and at least two jets, or events with an electron, missing transverse momentum and at least two jets. Control data samples are used to validate background predictions from Monte Carlo simulation. In the signal region, the observed event yields are consistent with the background expectations. We exclude at 95% confidence level the production of first generation scalar leptoquark with masses mLQ<660(607) GeV when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).

Search for first generation leptoquark pair production in the electron + missing energy + jets final state

We present a search for the pair production of first generation scalar leptoquarks (LQ) in data corresponding to an integrated luminosity of 5.4 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron Collider in ppbar collisions at $\sqrt{s}=1.96$ TeV. In the channel $LQ \bar{LQ} \rightarrow e\nu_e qq'$, where q, q' are u or d quarks, no significant excess of data over background is observed, and we set a 95% C.L. lower limit of 326 GeV on the leptoquark mass, assuming equal probabilities of leptoquark decays to eq and $\nu_e q'$.

Search for first generation leptoquarks in ep collisions at HERA

A search for first generation scalar and vector leptoquarks produced in ep collisions is performed by the H1 experiment at HERA. The full H1 data sample is used in the analysis, corresponding to an integrated luminosity of 446 pb−1. No evidence for the production of leptoquarks is observed in final states with a large transverse momentum electron or with large missing transverse momentum, and constraints on leptoquark models are derived. For leptoquark couplings of electromagnetic strength λ=0.3, first generation leptoquarks with masses up to 800 GeV are excluded at 95% confidence level.

Search for first generation scalar leptoquarks in the [formula omitted] channel in pp collisions at [formula omitted

A search for pair-production of first generation scalar leptoquarks is performed in the final state containing an electron, a neutrino, and at least two jets using proton–proton collision data at s=7 TeV. The data were collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 36 pb−1. The number of observed events is in good agreement with the predictions for standard model processes. Prior CMS results in the dielectron channel are combined with this electron+neutrino search. A 95% confidence level combined lower limit is set on the mass of a first generation scalar leptoquark at 339 GeV for β=0.5, where β is the branching fraction of the leptoquark to an electron and a quark. These results represent the most stringent direct limits to date for values of β greater than 0.05.

Search for pair production of first or second generation leptoquarks in proton-proton collisions ats=7 TeVusing the ATLAS detector at the LHC

This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35/pb of proton-proton collision data recorded by the ATLAS detector at sqrt(s)=7 TeV. Leptoquarks are seached in events with two oppositely charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses mLQ<376 (319) GeV and mLQ<422 (362) GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).

Search for lepton flavour violation at HERA

A search for second and third generation scalar and vector leptoquarks produced in ep collisions via the lepton flavour violating processes ep→μX and ep→τX is performed by the H1 experiment at HERA. The full data sample taken at a centre-of-mass energy s=319 GeV is used for the analysis, corresponding to an integrated luminosity of 245 pb−1 of e+p and 166 pb−1 of e−p collision data. No evidence for the production of such leptoquarks is observed in the H1 data. Leptoquarks produced in e±p collisions with a coupling strength of λ=0.3 and decaying with the same coupling strength to a muon–quark pair or a tau–quark pair are excluded at 95% confidence level up to leptoquark masses of 712 GeV and 479 GeV, respectively.

Search for pair production of second generation scalar leptoquarks

We report on a search for the pair production of second generation scalar leptoquarks (LQ) in pp¯ collisions at the center of mass energy s=1.96 TeV using a data set corresponding to an integrated luminosity of 1.0 fb−1 collected with the DØ experiment at the Fermilab Tevatron Collider. Topologies arising from the LQLQ¯→μqνq and LQLQ¯→μqμq decay modes are investigated. No excess of data over the standard model prediction is observed and upper limits on the leptoquark pair production cross section are derived at the 95% C.L. as a function of the leptoquark mass and the branching fraction β for the decay LQ→μq. These are interpreted as lower limits on the leptoquark mass as a function of β. For β=1(0.5), scalar second generation leptoquarks with masses up to 316 GeV (270 GeV) are excluded.

Executive function measures in healthy relatives of bipolar and schizophrenia probands

We report on a search for second generation leptoquarks (LQ2) which decay into a muon plus quark in pp¯ collisions at a center-of-mass energy of s=1.96TeV in the D0 detector using an integrated luminosity of about 300 pb−1. No evidence for a leptoquark signal is observed and an upper bound on the product of the cross section for single leptoquark production times branching fraction β into a quark and a muon was determined for second generation scalar leptoquarks as a function of the leptoquark mass. This result has been combined with a previously published D0 search for leptoquark pair production to obtain leptoquark mass limits as a function of the leptoquark–muon–quark coupling, λ. Assuming λ=1, lower limits on the mass of a second generation scalar leptoquark coupling to a u quark and a muon are mLQ2>274GeV and mLQ2>226GeV for β=1 and β=1/2, respectively.

Search for single production of scalar leptoquarks in pp¯ collisions decaying into muons and quarks with the D0 detector

We report on a search for second generation leptoquarks LQ_2 which decay into a muon plus quark in p\bar{p} collisions at a center-of-mass energy of sqrt{s} = 1.96 TeV in the D0 detector using an integrated luminosity of about 300 pb-1. No evidence for a leptoquark signal is observed and an upper bound on the product of the cross section for single leptoquark production times branching fraction beta into a quark and a muon was determined for second generation scalar leptoquarks as a function of the leptoquark mass. This result has been combined with a previously published D0 search for leptoquark pair production to obtain leptoquark mass limits as a function of the leptoquark-muon-quark coupling, lambda. Assuming lambda=1, lower limits on the mass of a second generation scalar leptoquark are m{LQ_2}>274 GeV and m{LQ_2}>226 GeV for beta=1 and beta=1/2, respectively.

Search for pair production of second generation scalar leptoquarks in [formula omitted] collisions at [formula omitted

We report on a search for the pair production of second generation scalar leptoquarks (LQ2) in pp¯ collisions at the center-of-mass energy s=1.96 TeV, using data corresponding to an integrated luminosity of 294±19 pb−1 recorded with the DØ detector. No evidence for a leptoquark signal in the LQ2LQ¯2→μqμq channel has been observed, and upper bounds on the product of cross section times branching fraction were set. This yields lower mass limits of mLQ2>247 GeV/c2 for β=B(LQ2→μq)=1 and mLQ2>182 GeV/c2 for β=1/2. Combining these limits with previous DØ results, the lower limits on the mass of a second generation scalar leptoquark are mLQ2>251 GeV/c2 and mLQ2>204 GeV/c2 for β=1 and β=1/2, respectively.

Search for second-generation scalar leptoquarks inpp¯collisions ats=1.96 TeV

Results on a search for pair production of second generation scalar leptoquark in $p \bar{p}$ collisions at $\sqrt{s}$=1.96 TeV are reported. The data analyzed were collected by the CDF detector during the 2002-2003 Tevatron Run II and correspond to an integrated luminosity of 198 pb$^{-1}$. Leptoquarks (LQ) are sought through their decay into (charged) leptons and quarks, with final state signatures represented by two muons and jets and one muon, large transverse missing energy and jets. We observe no evidence for $LQ$ production and derive 95% C.L. upper limits on the $LQ$ production cross sections as well as lower limits on their mass as a function of $\beta$, where $\beta$ is the branching fraction for $LQ \to \mu q$.

Search for single leptoquark and squark production in electron-photon scattering at $\sqrt{s_{\rm ee}}=189$ GeV at LEP

A search for first generation scalar and vector leptoquarks (LQ) as well as for squarks in R-parity violating SUSY models has been performed using e+e- collisions collected with the OPAL detector at LEP at an e+e- centre-of-mass energy sqrt(s_ee) of 189 GeV. The data correspond to an integrated luminosity of about 160 pb-1. The dominant process for this search is e q -> LQ/squark -> e q, nu q, where a photon, which has been radiated by one of the beam electrons, serves as a source of quarks. The numbers of selected events found in the two decay channels are in agreement with the expectations from Standard Model processes. This result allows to set lower limits at the 95% confidence level on the mass of first generation scalar and vector leptoquarks, and of squarks in R-parity violating SUSY models. For Yukawa couplings lambda to fermions larger than sqrt{4 pi alpha_em}, the mass limits range from 121 GeV/c^2 to 175 GeV/c^2 (149 GeV/c^2 to 188 GeV/c^2) depending on the branching ratio beta of the scalar (vector) leptoquark state. Furthermore, limits are set on the Yukawa couplings lambda for leptoquarks and lambda'_1jk for squarks, and on beta as a function of the scalar leptoquark/squark mass.

Search for leptoquarks in electron–photon scattering at up to 209 GeV at LEP

Searches for first generation scalar and vector leptoquarks, and for squarks in R-parity violating SUSY models with the direct decay of the squark into Standard Model particles, have been performed using e+e− collisions collected with the OPAL detector at LEP at e+e− centre-of-mass energies between 189 and 209 GeV. No excess of events is found over the expectation from Standard Model background processes. Limits are computed on the leptoquark couplings for different values of the branching ratio to electron–quark final states.