Recent results of searches for leptoquarks, lepton flavour violating leptoquarks and excited fermions (electrons, neutrinos and quarks) with the H1 experiment at HERA are presented, which use up to the full ep H1 data set. No evidence for the direct or indirect production of such particles is found. The results are interpreted in terms of limits on the Yukawa coupling of leptoquarks and lepton flavour violating processes and for excited fermions on the ratio of the coupling parameter to the compositeness scale f/Lambda, mainly in the framework of gauge mediated interactions. The derived limits extend the excluded regions to higher masses than those reported in previous results.
Recent searches for leptoquark production in proton-antiproton collisions at sqrt(s)=1.96TeV are presented using data samples with integrated luminosities up to 1fb^(-1) recorded with the D0 detector.
We report on a search for vector-like quarks and leptoquarks at D0. In the absence of any significant excess over the expectations, we present the most stringent limits to date.
Leptoquarks (LQ) are predicted by many new physics theories to describe the similarities between the lepton and quark sectors of the Standard Model and offer an attractive potential explanation for the lepton flavour anomalies observed at LHCb and flavour factories. The ATLAS experiment has a broad program of direct searches for Leptoquarks, coupling to the first-, second- or third-generation particles. The most recent 13 TeV results on the searches for Leptoquarks and contact interactions with the ATLAS detector are reviewed, covering flavour-diagonal and cross-generational final states.
Recent searches for leptoquark production and compositeness in p-anti-p collisions at sqrt{s}=1.96 TeV are presented using data samples with integrated luminosities up to 4 fb^{-1} recorded with the D0 and CDF detectors at the Tevatron collider.
The existence of leptoquarks (LQ), color-triplets of bosons with lepton and quark quantum numbers, is predicted by various theories beyond the Standard Model. This article summarizes the D-Zero Run I searches for the three different LQ generations in ppbar collisions at a center-of-mass energy of 1.8 TeV and presents ongoing studies at Run II.
Various searches for leptoquarks, scalar quarks in $R_p$-violating supersymmetric models, and excited fermions performed by the HERA experiments H1 and ZEUS are reviewed. No evidence for new particle production was observed from data collected by both experiments since 1994 in either electron-proton and positron-proton collisions. Stringent limits derived on the masses and couplings of these new particles are compared whenever appropriate with those from LEP, the Tevatron and low energy experiments.
Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 100pb-1 of e^+p data and 16pb-1 of e^-p data per experiment, taken in the years 1994-2000, the H1 and ZEUS collaborations have derived new exclusion limits for the direct production of excited fermion states and leptoquarks. The latter are searched for in different decay channels, including lepton-flavor violating decays. The production of R_P-violating squarks followed by leptoquark-like decays to lepton and quark is studied, as are cascade decays yielding multi-jet plus lepton sig…
Leptoquarks (LQs) are hypothetical bosons, each coupling to a lepton and a quark of a given generation. They recently got particular attention, as the "TeV-scale LQ" might explain observed anomalies reported by dedicated B physics experiments. In these proceedings, the recent progress of the direct searches on LQs at CMS experiment is presented. The results are based on a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, recorded with the CMS detector corresponding to an integrated luminosity of 35.9 fb-1.
This talk summarizes the status of Leptoquark searches performed at Tevatron, LEP and HERA. Prospects for Leptoquark searches at future colliders at LHC and TESLA are given.
Searches for pair-produced scalar leptoquarks are performed using 20 fb$^{-1}$ of proton-proton collision data provided by the LHC and recorded by the ATLAS detector at $\sqrt{s}=8$ TeV. Events with two electrons (muons) and two or more jets in the final state are used to search for first (second)-generation leptoquarks. The results from two previously published ATLAS analyses are interpreted in terms of third-generation leptoquarks decaying to $bν_τ\bar{b}\bar{ν_τ}$ and $tν_τ\bar{t}\bar{ν_τ}$ final states. No statistically significant excess above the Standard Model expectation is observed in…
We present in this paper the current status of searches for leptoquarks at D0. These results include the use of next leading order theoretical predictions for the cross section for pair production of leptoquarks at hadron colliders. We also present a new optimized analysis for first generation leptoquarks with significant increase in sensitivity relative to earlier searches using D0 data. The mass limits derived from this first generation leptoquark search are relevant to the recently reported high mass events at HERA.
Limits are set on the pair production of scalar leptoquarks, where all possible decays of the leptoquark into a quark ($t$, $b$) and a lepton ($τ$, $ν$) of the third generation are considered. The limits are presented as a function of the leptoquark mass and the branching ratio into charged leptons for up-type ($\mathrm{LQ}_{3}^{u}$ $\rightarrow t ν/ b τ$) and down-type ($\mathrm{LQ}_{3}^{d}$ $\rightarrow b ν/ t τ$) leptoquarks. Many results are reinterpretations of previously published ATLAS searches. In all cases, LHC proton-proton collision data at a centre-of-mass energy of $\sqrt{s}$ = 13…
Leptoquarks with masses at the TeV scale have been proposed as possible solutions to flavor anomalies reported in the b-flavor sector. Based on data taken in proton-proton collisions at $\sqrt{s} = 13\,\mathrm{TeV}$ at the LHC, different leptoquark flavors can be probed in various final states. In this article, the results of direct searches for single and pair production of leptoquarks conducted by the ATLAS and CMS Collaborations are summarized.
We have searched for the pair production of first generation scalar leptoquarks using the full data set (123 pb**-1) collected with the D0 detector at the Fermilab Tevatron during 1992-1996. We observe no candidates, consistent with the expected background. We combine these new results from the ee + jets and enu + jets channels with the published nunu + jets result to obtain a 95% CL upper limits on the LQ pair production cross section as a function of mass and beta, the branching ratio to a charged lepton and a quark. Comparing to the NLO theory predictions, we set 95% CL lower limits on the …
Searches for scalar leptoquarks pair-produced in proton-proton collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider are performed by the ATLAS experiment. A data set corresponding to an integrated luminosity of 36.1 fb$^{-1}$ is used. Final states containing two electrons or two muons and two or more jets are studied, as are states with one electron or muon, missing transverse momentum and two or more jets. No statistically significant excess above the Standard Model expectation is observed. The observed and expected lower limits on the leptoquark mass at 95% confidence level extend up…
We present results from several searches for various exotic physics phenomena like large extra dimensions, leptoquarks, and dark matter, in proton-proton collisions at $\sqrt{s}$ = 7 and 8 TeV delivered by the LHC and collected with the CMS detector. Many different final states are analyzed using data collected in 2011 and 2012 corresponding to an integrated luminosity up to 5.0 fb$^{-1}$ and 19.7 fb$^{-1}$. No sign of physics beyond the standard model has been observed so far and the results are used to set new limits on various new physics model parameters.
Searches have been made for first generation scalar and vector leptoquarks by the D0 collaboration and for second generation scalar leptoquarks by the CDF collaboration. Lower leptoquark mass limits were set. A search for squarks and gluinos, predicted by Supersymmetric models, was made by D0 in the three or more jets plus missing Et channel. The number of events observed was consistent with background. Squark and gluino mass limits were set.
This article summarizes the status of the Tevatron Run II searches for leptoquarks in $p\bar{p}$ collisions at $\sqrt{s}=1.96 $ TeV. The analyses discussed use datasets with integrated luminosities ranging from 72 pb$^{-1}$ to 200 pb$^{-1}$.}
The HERA ep collider and the experiments H1 and ZEUS operated from 1994-2007. A total integrated luminosity of almost 1 fb^-1 was collected at centre-of-mass energies up to 320 GeV. Results from searches for leptoquarks and squarks, final states with an isolated lepton and missing transverse momentum and final states with multi-leptons are presented. The leptoquark limits are interpreted in terms of limits on squark production in SUSY models with R-parity violating couplings.
Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 40pb-1 of e^+p data taken in the years 1994-1997, the H1 and ZEUS collaborations have derived new exclusion limits for the direct production of excited fermion states and of leptoquarks in different decay channels, including lepton-flavor violating decays. The results of searches for contact interactions further constrain the parameter space for such particles and their couplings in the high-mass regime, where direct production is kinematically prohibited. Also preliminary analyses …
We report on D0 searches for leptoquarks (LQ) predicted in extended gauge theories and composite models to explain the symmetry between quarks and leptons. Data samples obtained with the D0 detector from proton-antiproton collisions at a center-of-mass energy of 1.96 TeV corresponding to intergrated luminosities of 1--4 inverse-fb were analyzed. No evidence for the production of such particles were observed and lower limits on leptoquark masses are set.
A search for pair-produced leptoquarks is performed using e+e- collision events collected by the OPAL detector at LEP at centre-of-mass energies between 189 and 209 GeV. The data sample corresponds to a total integrated luminosity of 596 pb^-1. The leptoquarks are assumed to be produced via couplings to the photon and the Z0. For a given search channel only leptoquark decays involving a single lepton generation are considered. No evidence for leptoquark pair production is observed. Lower limits on masses for scalar and vector leptoquarks are calculated. The results improve most of the LEP limi…
We perform a model-independent search for leptoquarks (LQs) at the Large Hadron Collider through their pair-production and subsequent decay into $t\bar t ττ$ intermediate states. We show that, assuming full luminosity of the Run 2, a fully hadronic signal emerging from this intermediate state can surpass in sensitivity the established searches relying on leptons in the final state. Our conclusion is supported by a thorough Monte-Carlo analysis, and we advocate the deployment of our proposed search channel in the proper experimental setting of the Run 3. Furthermore, in order to highlight the f…
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.
Leptoquarks (LQ) with couplings to the third generation of Standard Model (SM) quarks have been proposed as possible explanations of the flavour anomalies indicating the violation of lepton flavour universality (LFV). The CMS collaboration has initiated an extensive search programme for these new states in the LHC run-2 data recorded at $\sqrt{s}=13$ TeV. In this article, the CMS search results in the LQ pair-production final states $τb\,τb$, $νt\,νt$, $νb\,νb$, $τt\,τt$, and $μt\,μt$, as well as in the LQ single-production final state $τ\,τb$ are discussed. No significant deviation from the S…
A search for scalar and vector leptoquarks coupling to first generation fermions is performed in the H1 experiment at the ep collider HERA. The analysis uses e^- p data collected in 1998 and 1999 at a centre-of-mass energy of 320 GeV, corresponding to an integrated luminosity of 15 pb^-1. No evidence for the direct production of such particles is found in a data sample with a large transverse momentum final state electron or with large missing transverse momentum, and constraints on leptoquark models are established. For a Yukawa coupling of electromagnetic strength leptoquarks are excluded fo…
We present recent results on Technicolor and Leptoquark searches obtained analyzing up to 0.4 fb-1 of data taken at Fermilab by the D0 experiment during the firs part of the Tevatron Run II.
We have searched for the pair production of first generation scalar leptoquarks in the eejj channel using the full data set (123 pb-1) collected with the D0 detector at the Fermilab Tevatron during 1992--1996. We observe no candidates with an expected background of approximately 0.4 events. Comparing the experimental 95% confidence level upper limit to theoretical calculations of the cross section with the assumption of a 100% branching fraction to eq, we set a lower limit on the mass of a first generation scalar leptoquark of 225 GeV/c^2. The results of this analysis rule out the interpretati…
In this article we perform a combined analysis of low energy precision constraints and LHC searches for leptoquarks which couple to first generation fermions. Considering all ten leptoquark representations, five scalar and five vector ones, we study at the precision frontier the constraints from $K\toπνν$, $K\toπe^+e^-$, $K^0-\bar K^0$ and $D^0-\bar D^0$ mixing, as well as from experiments searching for parity violation (APV and QWEAK). We include LHC searches for $s$-channel single resonant production, pair production and Drell-Yan-like signatures of leptoquarks. Interestingly, we find that t…
A search for events with one jet and at most one isolated lepton used data taken at LEP-2 by the DELPHI detector.These data were accumulated at a center-of-mass energy of 183 GeV and correspond to an integrated luminosity of 47.7 1/pb. Production of single scalar and vector leptoquarks was searched for. Limits at 95% confidence level were derived on the masses (ranging from $134 GeV/c^2$ to $171 GeV/c^2$ for electromagnetic type couplings) and couplings of the leptoquark states.A search for top-charm flavour changing neutral currents($e^+ e^- \to \bar t c$ or charge conjugate) used the semilep…
A search for leptoquarks at HERA was performed in H1 using 1994 $e^+ p$ data corresponding to an integrated luminosity of about $3 \pb^{-1}$. Single leptoquarks were searched for in direct positron-quark fusion processes taking into account possible decays into lepton-quark pairs of either the first, the second, or the third generation. No significant deviation from the Standard Model predictions is found in the various final states studied and mass dependent exclusion limits are derived on the Yukawa couplings of the leptoquarks. Compared with earlier results from an analysis of $e^-p$ data, …
Searches for physics beyond the Standard Model are reported from electron-proton collisions at a center of mass energy of 318 GeV. Results on a completely model independent search for deviations from Standard Model predictions at large transverse momenta are reported as well as generic searches for contact interactions, leptoquarks and excited fermions from the H1 and ZEUS experiments.
Search strategies for the third-generation leptoquarks (LQs) are distinct from other LQ searches, especially when they decay to a top quark and a $τ$ lepton. We investigate the cases of all TeV-scale scalar and vector LQs that decay to either a top-tau pair (charge-$1/3$ and $5/3$ LQs) or a top-neutrino pair (charge-$2/3$ LQs). One can then use the boosted top (which can be tagged efficiently using jet-substructure techniques) and high-$p_{\rm T}$ $τ$ leptons to search for these LQs. We consider two search channels with either one or two taus along with at least one hadronically decaying boost…
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…
Searches for contact interactions, leptoquark bosons and excited fermions carried out at the HERA ep collider are presented here. The searches are based on ~ 40 pb^-1 of e+ p data per experiment collected at a centre of mass energy ~ 300 GeV. First results on e- p data collected in 1998-1999 are also presented.
We have searched for second generation leptoquark (LQ) pairs in the μμ+jets channel using 94+-5 pb^{-1} of pbar-p collider data collected by the D0 experiment at the Fermilab Tevatron during 1993-1996. No evidence for a signal is observed. These results are combined with those from the μν+jets and νν+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and $beta, the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c^2 for β=1(1/2) are set at the 95% C.L. on the mass of sca…
We present results from several new searches for physics beyond the Standard Model. We describe a search based on the scalar sum of the transverse energy of the event, a global quantity nearly independent of the event topology. We summarize our searches for first generation leptoquarks into all three decay channels, eq eq, eq nu q, and nu q nu q, and note that this is the first time that the triumvirate of decay channels has been searched. We do not find any evidence for production of first generation leptoquarks and set a lower limit on the mass of the leptoquark of 175 GeV/c^2, assuming the …
An inclusive search for a new-physics signature of lepton-jet resonances has been performed by the ATLAS experiment. Scalar leptoquarks, pair-produced in $pp$ collisions at $\sqrt{s}$ = 13 TeV at the Large Hadron Collider, have been considered. An integrated luminosity of 3.2 fb$^{-1}$, corresponding to the full 2015 dataset was used. First (second) generation leptoquarks were sought in events with two electrons (muons) and two or more jets. The observed event yield in each channel is consistent with Standard Model background expectations. The observed (expected) lower limits on the leptoquark…
The searches for extra-dimensions, top resonances, 4th generation quarks and leptoquark signatures are presented. The results are based on proton-proton collision data for a center-of mass energy of7 or 8 TeV, corresponding to various integrated luminosities. No signal of physics beyond the Standard Model has been observed so far.
We propose a mechanism that allows for sizeable flavour violation in quark-lepton currents, while suppressing flavour changing neutral currents in quark-quark and lepton-lepton sectors. The mechanism is applied to the recently proposed 4321 renormalizable model, which can accommodate the current experimental anomalies in $B$-meson decays, both in charged and neutral currents, while remaining consistent with all other indirect flavour and electroweak precision measurements and direct searches at high-$p_T$. To support this claim, we present an exhaustive phenomenological survey of this fully ca…
At the LHC, a TeV-scale leptoquark (LQ) that decays dominantly to a top quark ($t$) and a light charged lepton ($\ell=e,μ$) would form a resonance system of \emph{boosted-$t$ $+$ high-$p_{\rm T}$-$\ell$}. We consider all possible vector LQ models within the Buchmüller-Rückl-Wyler classifications with the desired decay. We propose simple phenomenological Lagrangians that are suitable for bottom-up/experimental studies and, at the same time, can cover the relevant parameter spaces of these models. In this simplified framework, we study the pair and single production channels of vector LQs at the…
Results of searches at the Tevatron for physics (non-SUSY and non-Higgs) beyond the Standard Model using 200/pb to 480/pb of data are discussed. Searches at DO and CDF for Z', Lepton-Quark compositeness, Randall-Sundrum Gravitons, Large Extra Dimensions, W', Leptoquarks and Excited Electrons are presented here.
We have searched for first generation scalar leptoquark (LQ) pairs in the enu+jets channel using ppbar collider data (integrated luminosity= 115 pb^-1) collected by the DZero experiment at the Fermilab Tevatron during 1992-96. The analysis yields no candidate events. We combine the results with those from the ee+jets and nunu+jets channels to obtain 95% confidence level (CL) upper limits on the LQ pair production cross section as a function of mass and of beta, the branching fraction to a charged lepton. Comparing with the next-to-leading order theory, we set 95% CL lower limits on the LQ mass…
Purely leptonic $B$ meson decays provide unique probes for physics Beyond the Standard Model. We study the impact of a scalar leptoquark, $S_1$, on $B \to μ\barν$ decay. We find that, for $m_{S_1}\sim 1$ TeV, the $S_1$ leptoquark can modify the $B \to μ\barν$ rate significantly. Such a leptoquark can in prinicple also alter the $B \to τ\barν$ rate. However, current searches from LHC and low energy physics provide some constraints on the parameter space.
We present the result of direct leptoquark searches based on 110 pb-1 of integrated luminosity collected by the Collider Detector at Fermilab during the 1992-93 and 1994-95 Tevatron runs at \sqrt{s}=1.8 TeV. We present upper limits on the production cross sections as a function of the leptoquark mass. Using the NLO calculation of the leptoquark-pair production cross sections we extract lower-mass limits for first, second and third generation leptoquarks. We also present the result of an indirect search for Pati-Salam leptoquarks via exclusive e-mu decay modes of B^{0}_{s} and B^{0}_{d}.
We study implications of large lepton-quark-leptoquark couplings for direct leptoquark searches at Large Hadron Collider. We present all existing flavor constraints on the strength of these couplings assuming that leptoquarks under consideration interact exclusively with charged leptons and quarks of the same generation. We find that these leptoquarks can have sizeable couplings to the Standard Model fermions. This insures a self consistency of our study. We discuss the leptoquark production mechanisms at LHC and demonstrate the importance of inclusion of a t-channel pair production and, in pa…
Recent searches for physics beyond the standard model at high-energy colliders are reviewed, with emphasis on supersymmetry, additional space dimensions, extra gauge bosons, leptoquarks, and model-independent searches. The results reported are based on data samples of up to 0.5 and 2.5 fb-1 collected at HERA and at the Tevatron, respectively.
A search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced in $pp$ collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider are considered using an integrated luminosity of 139 fb$^{-1}$, corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation of $c$- or $b$-quarks. The observed yield in each channel is consistent with the Standard Model background expectation. Leptoquark…
During the year 2000, LEP has been operated at centre-of-mass energies up to sqrt(s) = 209 GeV. New particle searches have been performed using these data samples. Model independent limits on the production cross-sections and mass limits in the context of the Minimal Supersymmetric Standard Model (MSSM) assuming R-parity violation and in the context of gauge-mediated supersymmetry breaking theories (GMSB) are presented. Searches for technicolor, excited leptons and leptoquarks are also reviewed.
CMS has recently reported a moderate excess in the $μνjj$ final state in a second generation Leptoquark search, but they have disregarded it because the excess is not present in the $μμjj$ final state and because they do not observe the expected resonant peak in the distributions. As a proof of concept we show that a simple Leptoquark model including second and third generation couplings with non-negligible single- and non-resonant production in addition to usual pair production could explain the data: excess ($μνjj$), lack of excess ($μμjj$) and missing peak in the distributions; while being …
We present the results of searches for non-standard model phenomena in photon and jet final states. These searches use data from integrated luminosities of 0.7--2.7/fb of p-pbar collisions at sqrt(s)=1.96 TeV, collected with the CDF and D0 detectors at the Fermilab Tevatron. No significant excess in data has been observed. We report limits on the parameters of several models, including: large extra dimension, compositeness, leptoquarks, and supersymmetry.
This paper summarizes searches at the Fermilab Tevatron for a wide variety of signatures for physics beyond the Standard Model. These include searches for supersymmetric particles, in the two collider detectors and in one fixed target experiment. Also covered are searches for leptoquarks, dijet resonances, heavy gauge bosons, and particles from a fourth generation, as well as searches for deviations from the Standard Model predictions in dijet angular distributions, dilepton mass distributions, and trilinear gauge boson couplings.
We present some new results on searches for new physics at the Tevatron Run 1 (1992 -- 1996). The topics covered are searches for R-Parity violating and conserving mSUGRA, large extra dimensions in di-photon and monojet channels, leptoquark in jets + missing Et channel, and two model independent searches. All results were finalized during the past year.
Leptoquarks have recently received much attention especially because they may provide an explanation to the $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies in rare $B$ meson decays. In a previous paper we proposed a systematic search strategy for all possible leptoquark flavors by focusing on leptoquark pair production. In this paper, we extend this strategy to large (order unity) leptoquark couplings which offer new search opportunities: single leptoquark production and $t$-channel leptoquark exchange with dilepton final states. We discuss the unique features of the different search channels and sh…
