CMS-EXO-22-013

CMS-EXO-22-013 ; CERN-EP-2024-275
Search for $t$ -channel scalar and vector leptoquark exchange in the high-mass dimuon and dielectron spectra in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
25 March 2025
Submitted to J. High Energy Phys.
Abstract: A search for $t$ -channel exchange of leptoquarks (LQs) is performed in dimuon and dielectron spectra using proton-proton collision data collected at $\sqrt{s}=$ 13 TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 138 fb $^{-1}$ . Eight scenarios are considered, in which scalar or vector LQs couple up or down quarks to muons or electrons, for dilepton invariant masses above 500 GeV. The LQ masses are probed up to 5 TeV, beyond a regime probed by previous pair-production and single-production searches. The differential distributions of dilepton events are fit to templates that model the nonresonant LQ exchange and various standard model background processes. Limits are set on LQ-fermion coupling strengths for scalar and vector LQ masses in the 1-5 TeV range at 95% confidence level, establishing stringent limits on first- and second-generation LQs.
Links: e-print arXiv:2503.20023 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Leading order Feynman diagrams for SM DY production (left) and $t$ -channel LQ exchange (right). The LQ amplitude interferes with the $\mathrm{Z}/\gamma^{*}$ amplitude.
png pdf	Figure 2: A comparison of data and expected background distributions in the dilepton invariant mass (upper row), $c_\mathrm{R}$ (middle row), and dilepton rapidity (lower row). The left (right) plots show the $\mu\mu$ ( $\mathrm{e}\mathrm{e}$ ) channel. The blue histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{S_{\mu u}}$ ( $\mathrm{S_{e u}}$ ) with $y_{\mathrm{\mu u}}\,(y_{\mathrm{e u}})=$ 2.0, while the yellow histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{V_{\mu u}}\, (\mathrm{V_{e u}})$ with $g_{\mathrm{\mu u}}\,(g_{\mathrm{e u}})=$ 1.0. The black points with error bars represent the data and their statistical uncertainties. The background expectation is shown as stacked histograms. The hatched band shows the total systematic uncertainty in the expected background yield. The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 2-a: A comparison of data and expected background distributions in the dilepton invariant mass (upper row), $c_\mathrm{R}$ (middle row), and dilepton rapidity (lower row). The left (right) plots show the $\mu\mu$ ( $\mathrm{e}\mathrm{e}$ ) channel. The blue histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{S_{\mu u}}$ ( $\mathrm{S_{e u}}$ ) with $y_{\mathrm{\mu u}}\,(y_{\mathrm{e u}})=$ 2.0, while the yellow histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{V_{\mu u}}\, (\mathrm{V_{e u}})$ with $g_{\mathrm{\mu u}}\,(g_{\mathrm{e u}})=$ 1.0. The black points with error bars represent the data and their statistical uncertainties. The background expectation is shown as stacked histograms. The hatched band shows the total systematic uncertainty in the expected background yield. The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 2-b: A comparison of data and expected background distributions in the dilepton invariant mass (upper row), $c_\mathrm{R}$ (middle row), and dilepton rapidity (lower row). The left (right) plots show the $\mu\mu$ ( $\mathrm{e}\mathrm{e}$ ) channel. The blue histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{S_{\mu u}}$ ( $\mathrm{S_{e u}}$ ) with $y_{\mathrm{\mu u}}\,(y_{\mathrm{e u}})=$ 2.0, while the yellow histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{V_{\mu u}}\, (\mathrm{V_{e u}})$ with $g_{\mathrm{\mu u}}\,(g_{\mathrm{e u}})=$ 1.0. The black points with error bars represent the data and their statistical uncertainties. The background expectation is shown as stacked histograms. The hatched band shows the total systematic uncertainty in the expected background yield. The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 2-c: A comparison of data and expected background distributions in the dilepton invariant mass (upper row), $c_\mathrm{R}$ (middle row), and dilepton rapidity (lower row). The left (right) plots show the $\mu\mu$ ( $\mathrm{e}\mathrm{e}$ ) channel. The blue histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{S_{\mu u}}$ ( $\mathrm{S_{e u}}$ ) with $y_{\mathrm{\mu u}}\,(y_{\mathrm{e u}})=$ 2.0, while the yellow histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{V_{\mu u}}\, (\mathrm{V_{e u}})$ with $g_{\mathrm{\mu u}}\,(g_{\mathrm{e u}})=$ 1.0. The black points with error bars represent the data and their statistical uncertainties. The background expectation is shown as stacked histograms. The hatched band shows the total systematic uncertainty in the expected background yield. The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 2-d: A comparison of data and expected background distributions in the dilepton invariant mass (upper row), $c_\mathrm{R}$ (middle row), and dilepton rapidity (lower row). The left (right) plots show the $\mu\mu$ ( $\mathrm{e}\mathrm{e}$ ) channel. The blue histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{S_{\mu u}}$ ( $\mathrm{S_{e u}}$ ) with $y_{\mathrm{\mu u}}\,(y_{\mathrm{e u}})=$ 2.0, while the yellow histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{V_{\mu u}}\, (\mathrm{V_{e u}})$ with $g_{\mathrm{\mu u}}\,(g_{\mathrm{e u}})=$ 1.0. The black points with error bars represent the data and their statistical uncertainties. The background expectation is shown as stacked histograms. The hatched band shows the total systematic uncertainty in the expected background yield. The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 2-e: A comparison of data and expected background distributions in the dilepton invariant mass (upper row), $c_\mathrm{R}$ (middle row), and dilepton rapidity (lower row). The left (right) plots show the $\mu\mu$ ( $\mathrm{e}\mathrm{e}$ ) channel. The blue histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{S_{\mu u}}$ ( $\mathrm{S_{e u}}$ ) with $y_{\mathrm{\mu u}}\,(y_{\mathrm{e u}})=$ 2.0, while the yellow histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{V_{\mu u}}\, (\mathrm{V_{e u}})$ with $g_{\mathrm{\mu u}}\,(g_{\mathrm{e u}})=$ 1.0. The black points with error bars represent the data and their statistical uncertainties. The background expectation is shown as stacked histograms. The hatched band shows the total systematic uncertainty in the expected background yield. The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 2-f: A comparison of data and expected background distributions in the dilepton invariant mass (upper row), $c_\mathrm{R}$ (middle row), and dilepton rapidity (lower row). The left (right) plots show the $\mu\mu$ ( $\mathrm{e}\mathrm{e}$ ) channel. The blue histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{S_{\mu u}}$ ( $\mathrm{S_{e u}}$ ) with $y_{\mathrm{\mu u}}\,(y_{\mathrm{e u}})=$ 2.0, while the yellow histogram represents the signal yield of a hypothetical 2.5 TeV $\mathrm{V_{\mu u}}\, (\mathrm{V_{e u}})$ with $g_{\mathrm{\mu u}}\,(g_{\mathrm{e u}})=$ 1.0. The black points with error bars represent the data and their statistical uncertainties. The background expectation is shown as stacked histograms. The hatched band shows the total systematic uncertainty in the expected background yield. The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 3: The observed data in the dimuon channel and the fitted signal-plus-background templates, shown for the $\mathrm{S_{\mu u}}$ (left) and $\mathrm{S_{\mu d}}$ (right) scenarios with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by $-$ 10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 3-a: The observed data in the dimuon channel and the fitted signal-plus-background templates, shown for the $\mathrm{S_{\mu u}}$ (left) and $\mathrm{S_{\mu d}}$ (right) scenarios with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by $-$ 10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 3-b: The observed data in the dimuon channel and the fitted signal-plus-background templates, shown for the $\mathrm{S_{\mu u}}$ (left) and $\mathrm{S_{\mu d}}$ (right) scenarios with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by $-$ 10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 4: The observed data in the dielectron channel and the fitted signal-plus-background templates, shown for the $\mathrm{S_{e u}}$ (left) and $\mathrm{S_{e d}}$ (right) scenarios with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 4-a: The observed data in the dielectron channel and the fitted signal-plus-background templates, shown for the $\mathrm{S_{e u}}$ (left) and $\mathrm{S_{e d}}$ (right) scenarios with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 4-b: The observed data in the dielectron channel and the fitted signal-plus-background templates, shown for the $\mathrm{S_{e u}}$ (left) and $\mathrm{S_{e d}}$ (right) scenarios with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 5: The observed data in the dimuon channel and the fitted signal-plus-background templates, shown for the $\mathrm{V_{\mu u}}$ (left) and $\mathrm{V_{\mu d}}$ (right) scenario with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 5-a: The observed data in the dimuon channel and the fitted signal-plus-background templates, shown for the $\mathrm{V_{\mu u}}$ (left) and $\mathrm{V_{\mu d}}$ (right) scenario with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 5-b: The observed data in the dimuon channel and the fitted signal-plus-background templates, shown for the $\mathrm{V_{\mu u}}$ (left) and $\mathrm{V_{\mu d}}$ (right) scenario with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 6: The observed data in the dielectron channel and the fitted signal-plus-background templates, shown for the $\mathrm{V_{e u}}$ (left) and $\mathrm{V_{e d}}$ (right) scenario with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 6-a: The observed data in the dielectron channel and the fitted signal-plus-background templates, shown for the $\mathrm{V_{e u}}$ (left) and $\mathrm{V_{e d}}$ (right) scenario with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 6-b: The observed data in the dielectron channel and the fitted signal-plus-background templates, shown for the $\mathrm{V_{e u}}$ (left) and $\mathrm{V_{e d}}$ (right) scenario with a candidate $m_{\text{LQ}}$ of 2.5 TeV. The black points are the observed data, the stacked histograms represent the backgrounds, and the yellow histogram shows the fitted LQ signal scaled by-10. Distributions of events are binned in the reconstructed $m_{\ell\ell}$ (vertical red dashed lines), $\|y\|$ (vertical black dashed lines), and $c_\mathrm{R}$ (Section 7). The lower panels show the ratios of the data to the expectation. The gray bands represent the normalized uncertainty in the predicted yield. The error bars in the ratio plot represent the normalized statistical uncertainty in the data.
png pdf	Figure 7: Upper limits at 95% CL on the LQ-fermion couplings, $\|y_{\mathrm{\mu u}}\|$ (left) and $\|y_{\mathrm{\mu d}}\|$ (right), as a function of $m_{\text{LQ}}$ for scalar LQs coupled to muons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 7-a: Upper limits at 95% CL on the LQ-fermion couplings, $\|y_{\mathrm{\mu u}}\|$ (left) and $\|y_{\mathrm{\mu d}}\|$ (right), as a function of $m_{\text{LQ}}$ for scalar LQs coupled to muons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 7-b: Upper limits at 95% CL on the LQ-fermion couplings, $\|y_{\mathrm{\mu u}}\|$ (left) and $\|y_{\mathrm{\mu d}}\|$ (right), as a function of $m_{\text{LQ}}$ for scalar LQs coupled to muons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 8: Upper limits at 95% CL on the LQ-fermion couplings, $\|y_{\mathrm{e u}}\|$ (left) and $\|y_{\mathrm{e d}}\|$ (right), as a function of $m_{\text{LQ}}$ for scalar LQs coupled to electrons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 8-a: Upper limits at 95% CL on the LQ-fermion couplings, $\|y_{\mathrm{e u}}\|$ (left) and $\|y_{\mathrm{e d}}\|$ (right), as a function of $m_{\text{LQ}}$ for scalar LQs coupled to electrons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 8-b: Upper limits at 95% CL on the LQ-fermion couplings, $\|y_{\mathrm{e u}}\|$ (left) and $\|y_{\mathrm{e d}}\|$ (right), as a function of $m_{\text{LQ}}$ for scalar LQs coupled to electrons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 9: Upper limits at 95% CL on the LQ-fermion couplings, $\|g_{\mathrm{\mu u}}\|$ (left) and $\|g_{\mathrm{\mu d}}\|$ (right), as a function of $m_{\text{LQ}}$ for vector LQs coupled to muons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 9-a: Upper limits at 95% CL on the LQ-fermion couplings, $\|g_{\mathrm{\mu u}}\|$ (left) and $\|g_{\mathrm{\mu d}}\|$ (right), as a function of $m_{\text{LQ}}$ for vector LQs coupled to muons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 9-b: Upper limits at 95% CL on the LQ-fermion couplings, $\|g_{\mathrm{\mu u}}\|$ (left) and $\|g_{\mathrm{\mu d}}\|$ (right), as a function of $m_{\text{LQ}}$ for vector LQs coupled to muons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 10: Upper limits at 95% CL on the LQ-fermion couplings, $\|g_{\mathrm{e u}}\|$ (left) and $\|g_{\mathrm{e d}}\|$ (right), as a function of $m_{\text{LQ}}$ for vector LQs coupled to electrons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 10-a: Upper limits at 95% CL on the LQ-fermion couplings, $\|g_{\mathrm{e u}}\|$ (left) and $\|g_{\mathrm{e d}}\|$ (right), as a function of $m_{\text{LQ}}$ for vector LQs coupled to electrons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.
png pdf	Figure 10-b: Upper limits at 95% CL on the LQ-fermion couplings, $\|g_{\mathrm{e u}}\|$ (left) and $\|g_{\mathrm{e d}}\|$ (right), as a function of $m_{\text{LQ}}$ for vector LQs coupled to electrons. The black points show the observed limits, the red line shows the expected limits, and the yellow and blue bands show the variations on the expected limit at 68% and 95% CL, respectively.

Tables
png pdf	Table 1: Properties of the $R_2$ , $\widetilde{R}_2$ , and $U_3$ LQs from Ref. [18]. This paper describes a search for $R_2$ LQs with RL couplings and charge 5/3, $\widetilde{R}_2$ LQs with RL couplings and charge 2/3, and $U_3$ LQs with charges 2/3 and 5/3.
png pdf	Table 2: The contributions of the statistical uncertainty and of individual sources of systematic uncertainty to the total variance in the fitted value of $y_{\text{LQ}}^2$ ( $g_{\text{LQ}}^2$ ) for a scalar (vector) $m_{\text{LQ}}$ of 2.5 TeV. For a given source of uncertainty, the impact is determined by fixing its associated nuisance parameter to the postfit value and evaluating the change in the total uncertainty.
png pdf	Table 3: Best fit values of $A_0$ , $A_4$ , and $y_{\text{LQ}}^2$ for scalar LQ models. The Feldman-Cousins confidence interval for $y_{\text{LQ}}^2$ is shown at 68% CL. Results are shown for a candidate $m_{\text{LQ}}$ of 2.5 TeV.
png pdf	Table 4: Best fit values of $A_0$ , $A_4$ , and $g_{\text{LQ}}^2$ for vector LQ models. The Feldman-Cousins confidence interval for $g_{\text{LQ}}^2$ is shown at 68% CL. Results are shown for a candidate $m_{\text{LQ}}$ of 2.5 TeV.

Summary

A search for the

$t$ -channel exchange of leptoquarks (LQs) coupled to first- and second-gen\-eration fermions has been presented. The search uses proton-proton collision data at

$\sqrt{s}=$ 13 TeV, corresponding to an integrated luminosity of 138 fb

$^{-1}$ . Both scalar and vector LQs are considered, with masses between 1 and 5 TeV, for exclusive LQ couplings to an up or a down quark and a muon or an electron. The

$t$ -channel exchange of an LQ modifies the dilepton angular distributions at masses well below the resonance mass of the LQ. A template fit to the angular and invariant mass distributions of high-mass dilepton events is used to distinguish the signal process from the dominant Drell-Yan background, incorporating the interference effects. No evidence for such LQs is observed. Limits are set at 95% confidence level on the LQ-fermion couplings. For scalar LQs with masses in the 1-5 TeV range, coupling values greater than 0.4-1.3 (0.3-1.0) are excluded for LQs coupled to a muon or an electron, and an up (down) quark, and couplings greater than 0.3-1.4 (0.1-0.5) are excluded for the respective vector LQs. This search is sensitive to LQs with significantly higher masses than prior single- and pair-production searches, establishing stringent limits on LQs with masses up to 5 TeV.

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