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Search for pair production of first and second generation leptoquarks in proton-proton collisions at sqrt(s) = 8 TeV

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CMS Collaboration

High Energy Physics - Experiment · Submitted 12 Sep 2015 · 80 references

Pith's verdict: A solid, standard CMS leptoquark search whose exclusion curves hold up; the abstract's headline numbers are the weak part, not the analysis.

T0 · AI review

How this review was made: An AI referee (selfhosted/deepseek-v4.1-flash) read the paper on November 10, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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arXiv ID1509.03744 (version 2)
Pith IDK7T2XMVK, Pith's permanent record of this paper and its review
CitationCMS Collaboration. "Search for pair production of first and second generation leptoquarks in proton-proton collisions at sqrt(s) = 8 TeV." arXiv:1509.03744 (2015). https://pith.science/paper/K7T2XMVK
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The paper

The paper claims

A search for leptoquarks in two-lepton and one-lepton-plus-missing-energy events finds no signal, and pushes the mass exclusion for first- and second-generation leptoquarks to about 1 TeV.

The reading

A leptoquark is a hypothetical particle that carries both colour charge and lepton number, so it can turn a quark into a lepton or vice versa; many extensions of the standard model predict them, and their mass is the free parameter that decides whether the LHC can see them. This paper looks for leptoquarks produced in pairs, each decaying into a quark and a charged lepton, which gives two experimental shapes: two leptons plus two jets (when both decay to charged leptons) or one lepton, missing transverse momentum and two jets (when one decays to a neutrino). Using 19.7 inverse femtobarns of 8 TeV proton-proton collisions recorded by CMS, the analysis counts events in these four channels after cuts tuned separately for each hypothesised leptoquark mass, and compares the counts with standard-model predictions whose normalisations are fixed in data control regions. No leptoquark signal is established, so the result is a set of 95% confidence-level upper limits on the production rate, translated into lower bounds on the mass. The bounds matter because they close off a mass range for any coloured particle that decays to a quark and a lepton, and the same event shapes let the authors constrain vector leptoquarks and an R-parity-violating supersymmetric top squark as well.

What carries the argument

The machinery is a per-mass-hypothesis cut optimisation combined with a data-driven background normalisation. For each hypothesised leptoquark mass, the thresholds on the summed transverse momentum $S_T$, the dilepton mass, and the minimum lepton-jet mass are chosen to maximise $S/sqrt{S+B}$ separately in each of the four channels, so the analysis is a family of nested searches rather than a single counting experiment. The dominant backgrounds are then fixed from data: $Z/gamma^*+$jets is normalised in the $Z$ mass window with correction factors $R_Z = 0.97$ ($eejj$) and $0.92$ ($mu mu jj$), $t bar{t}$ in the dilepton channels from an electron-muon sample, and $W+$jets and $t bar{t}$ in the single-lepton channels from a transverse-mass sideband $70 < M_T < 110$ GeV using two jet-multiplicity selections solved simultaneously. Upper limits on $sigma times beta^2$ and $sigma times 2beta(1-beta)$ come from the modified-frequentist $CL_s$ method with log-normal treatment of systematic uncertainties and gamma-distributed statistical terms. The pair-production cross sections that the limits are compared against are next-to-leading-order QCD calculations, so the quoted mass reach is a ratio of an observed count to a theoretical rate.

Extended reading notes

Core claim

The paper's claim is an exclusion: at 95% confidence level, pair-produced first-generation scalar leptoquarks are excluded below 1010 GeV for a branching fraction $LQ to l q$ of $beta = 1.0$, and below 850 GeV for $beta = 0.5$; second-generation scalar leptoquarks are excluded below 1080 GeV for $beta = 1.0$ and 760 GeV for $beta = 0.5$ in the muon channels, rising to about 800 GeV for $beta = 0.5$ once the dilepton and single-lepton channels are combined. The expected (median) limits under the background-only hypothesis are 1030 and 890 GeV for the first generation and 1050 and 820 GeV for the second, so the observed limits sit close to expectation. The same data are reinterpreted for vector leptoquarks with four choices of anomalous coupling, excluding masses in the ranges 1150-1660 GeV (electron channels) and 1200-1720 GeV (muon channels) for $beta = 1.0$, and 1050-1560 GeV and 980-1480 GeV respectively for $beta = 0.5$. A Higgsino-mediated R-parity-violating top-squark model with the same final state is excluded below 710 GeV for the $lambda'_{132}$ coupling and below 860 GeV for $lambda'_{232}$. The authors also report a broad excess in the electron channels, 2.3 standard deviations in $eejj$ and 2.6 in $e nu jj$ at the selection tuned for a 650 GeV leptoquark, and argue it is background-like because it does not peak in the lepton-jet mass distributions the way a leptoquark signal would.

Load-bearing premise

The limits assume that the background normalisation factors measured in the $Z$ mass window and the low-transverse-mass sidebands, where events are plentiful, continue to hold unchanged in the high-$S_T$, high-lepton-jet-mass regions where the signal is counted and where only a handful of events remain.

Editorial extensions

If this is right

  • Any model predicting a coloured scalar or vector that decays promptly to a quark plus an electron or muon is now constrained to lie above roughly 1 TeV for the scalar case, which removes a substantial part of the natural parameter space for leptoquark explanations of lepton-flavour anomalies.
  • The vector-leptoquark limits span 1150 to 1720 GeV depending on the anomalous coupling scenario, so the same data discriminate between coupling choices through the different production cross sections rather than through different event kinematics.
  • The R-parity-violating top-squark limits of 710 GeV ($lambda'_{132}$) and 860 GeV ($lambda'_{232}$) are the first bounds on that Higgsino-mediated decay topology, giving a target for dedicated supersymmetry searches.
  • The 650 GeV selection excess in the electron channels sets a floor on how far the electron-channel limit can be pushed at low $beta$, because the same events that weaken the limit also have to be explained.
  • The techniques transfer directly to higher-energy data: the same four final states and the same optimisation can be rerun at 13 TeV, where the cross section for a given leptoquark mass is larger and the mass reach grows accordingly.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The observed limits land slightly below the expected ones in the electron channels and slightly above in the muon channels, which is the pattern one expects if the electron-channel excess is a downward fluctuation of a background whose high-$S_T$ tail is not perfectly modelled; a dedicated high-$S_T$ measurement of $Z+$jets and $t bar{t}$ would sharpen every limit quoted here.
  • Because the analysis is $lambda_{lq}$-independent as long as the leptoquark decays within a few millimetres, the limits apply to long-lived-but-not-stable leptoquarks too, and a displaced-vertex search in the same final states would cover the gap below the couplings assumed here.
  • The absence of a peak in the lepton-jet mass in the excess region is the strongest single argument in the paper against a leptoquark interpretation, and it is a test that a future analysis with more statistics can repeat bin by bin rather than at a single optimised working point.
  • The overlap between the leptoquark and R-parity-violating top-squark final states means the two interpretations are limited by the same data; a joint fit that floated both signal strengths would make the complementarity explicit instead of quoting two separate exclusions from one event sample.
Original abstract

A search for pair production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at sqrt(s) = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 inverse femtobarns were recorded with the CMS detector at the LHC. First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for beta = 1.0 (0.5), where beta is the branching fraction of a leptoquark decaying to a charged lepton and a quark. Similarly, second-generation scalar leptoquarks with masses less than 1080 (760) GeV are excluded for beta = 1.0 (0.5). Mass limits are also set for vector leptoquark production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark pair production resulting in similar final-state signatures. These are the most stringent limits placed on the masses of leptoquarks and RPV top squarks to date.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 5,178 input tokens.

What the abstract itself states, as probabilities: claims first 0.08 · states limitation 0.18 · human participants 0.01 · controlled comparison 0.04 · randomized assignment 0.01 · states quantitative result 0.99 · compares with prior results 0.74 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

A search for pair production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at sqrt(s) = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 inverse femtobarns were recorded with the CMS detector at the LHC. First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for beta = 1.0 (0.5), where beta is the branching fraction of a leptoquark decaying to a charged lepton and a quark. Similarly, second-generation scalar leptoquarks with masses less than 1080 (760) GeV are excluded for beta = 1.0 (0.5). Mass limits are also set for vector leptoquark production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark pair production resulting in similar final-state signatures. These are the most stringent limits placed on the masses of leptoquarks and RPV top squarks to date.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 A search for pair production of first and second generation leptoquarks is performed in final states containing either two charged leptons and two jets, or one charged lepton, one neutrino and two jets, using proton-proton collision data at sqrt(s) = 8 TeV. contribution 0.95 0.96 0.03 asserted 0.97
s1 The data, corresponding to an integrated luminosity of 19.7 inverse femtobarns were recorded with the CMS detector at the LHC. method 1.00 0.65 0.01 asserted 1.00
s2 First-generation scalar leptoquarks with masses less than 1010 (850) GeV are excluded for beta = 1.0 (0.5), where beta is the branching fraction of a leptoquark decaying to a charged lepton and a quark. result 1.00 0.95 0.33 asserted 1.00
s3 Similarly, second-generation scalar leptoquarks with masses less than 1080 (760) GeV are excluded for beta = 1.0 (0.5). result 1.00 0.94 0.21 asserted 1.00
s4 Mass limits are also set for vector leptoquark production scenarios with anomalous vector couplings, and for R-parity violating supersymmetric scenarios of top squark pair production resulting in similar final-state signatures. result 0.70 0.91 0.07 asserted 1.00
s5 These are the most stringent limits placed on the masses of leptoquarks and RPV top squarks to date. interpretation 0.91 0.53 0.51 asserted 1.00

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 0.76.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Dominant leading order diagrams for the pair production of scalar leptoquarks.
Figure 2. Diagram of the Higgsino-mediated top squark decay via the RPV
Figure 3. Distributions of ST (left) and Mmin `j (right) at the initial selection level in the eejj (top) and µµjj (bottom) channels. “Other background” includes: diboson, W+jets, γ+jets, and single top quark contributions. The horizontal lines on the data points show the variable bin width. The primary backgrounds that can mimic the LQ signal in the `νjj channels fall into three cat￾egories: events with genuine W bosons such as those from W+jets, tt, single top quark pro￾duction, and WW and WZ processes; events with misidentified leptons and misreconstructed E miss T in the final state caused
Figure 4. Distributions of ST (left), and M`j (right) at the initial selection level in the eνjj (top) and µνjj (bottom) channels. “Other background” includes: diboson, Z/γ ∗+jets, and single top quark contributions. The horizontal lines on the data points show the variable bin width
Figure 5. Distributions of ST (left) and Mmin µj (right) for the final selection for a LQ mass of 450 GeV (top) and 650 GeV (bottom) in the µµjj channel. The dark shaded region indicates the statistical and systematic uncertainty in the total background prediction. “Other background” includes diboson, W+jets, and single top quark contributions. The horizontal lines on the data points show the variable bin width
Figure 6. Distributions of ST (left) and Mµj (right) for the final selection for a LQ mass of 450 GeV (top) and 650 GeV (bottom) in the µνjj channel. The dark shaded region indicates the statistical and systematic uncertainty in the total background prediction. “Other background” includes diboson, Z/γ ∗+jets, and single top quark contributions. The horizontal lines on the data points show the variable bin width
Figure 7. The ST (left) and Mmin ej (right) distributions for events passing the eejj selection op￾timized for MLQ = 450 GeV (top) and MLQ = 650 GeV (bottom). The dark shaded region indicates the statistical and systematic uncertainty in the background total prediction. “Other background” includes diboson, W+jets, and single top quark contributions. The horizontal lines on the data points show the variable bin width
Figure 8. The ST (left) and Mej (right) distributions for events passing the full eνjj selection optimized for MLQ = 450 GeV (top) and MLQ = 650 GeV (bottom). The dark shaded region indicates the statistical and systematic uncertainty in the total background prediction. “Other background” includes diboson, Z/γ ∗+jets, and single top quark contributions. The horizontal lines on the data points show the variable bin width
Figure 9. The Mmin ej distribution for the eejj channel (left) and the Mej distribution for the eνjj channel (right) after the selection criteria optimized for a LQ mass of 650 GeV have been applied. The dark shaded region indicates the statistical and systematic uncertainty in the total background prediction. The signal corresponds to a LQ mass of 650 GeV and β = 0.075. The signal is multiplied by a factor of ten in the left plot. In the case of the eejj analysis, less than one signal event is expected to pass the selection. The horizontal lines on the data points show the variable bin…
Figure 10. Frame on left (right): the expected and observed upper limits at 95% CL on the LQ
Figure 11. Frame on left (right): the expected and observed upper limits at 95% CL on the LQ
Figure 12. The expected and observed exclusion limits at 95% CL on the first (left) and second
Figure 13. Frame on left (right): the expected and observed upper limits at 95% CL on the
Figure 14. Frame on left (right): the expected and observed upper limits at 95% CL on the vec
Figure 15. Frame on left (right): the expected and observed upper limits at 95% CL on the top

Figures reproduced from arXiv:1509.03744 by the authors.

References
How later papers used it

45 later papers cite it

Evidence: substantial. 39 of the citing papers share no author with it, and 19 of those carry a confident label from Pith's citation classifier.

Pith read 20 of the 66 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Uses its data or values 3 of 18 papers with this label

  • Used the CMS searches in this paper to constrain the combined X to e j and X to mu j channels, since the pair-production cross section of X is fixed by QCD.

    Massive vectors and loop observables: the $g-2$ case (2016) · 0.85 · paraphrased: the licence does not allow quoting

  • Showed its exclusion limit of leptoquark X in the M_X-BR_X plane given by the CMS result of this paper, with solid and dashed lines for first and second generation leptoquarks respectively.

    Neutrino Catalyzed Diphoton Excess (2015) · 0.95 · paraphrased: the licence does not allow quoting

  • Cited this paper's recent CMS analysis as a compilation of results relevant to its model 1, noting the cross-section varies from about 1 pb for M_U around 0.5 TeV to 3x10^-3 pb for M_U around 1.0 TeV.

    Anomalies in $B$-decays and $U(2)$ flavour symmetry (2015) · 0.84 · paraphrased: the licence does not allow quoting

How the literature uses it

43 arXiv papers cite this in 63 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 34 sentences without a confident label

Uses its data or values 16 papers
Compares with it 1 paper
  • Refs. [ref] also noted the potential for their models to explain the $B$ decay anomalies.[Leptoquarks are also viable explanations of the CMS $ℓℓj j$ anomaly [ref] , see e.g. [ref] .] In contrast with those works, we study a model involving a scalar singlet and vector leptoquarks.

    Vector Leptoquarks and the 750 GeV Diphoton Resonance at the LHC · Introduction · 0.81

Cites it as background 7 papers

What it cites · 25 sentences without a confident label

Uses the method or tool of 23 papers
Uses data or values from 5 papers
Compares with 4 papers
Cites as background 5 papers

Discussion

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