CMS-EXO-16-023

CMS-EXO-16-023 ; CERN-EP-2017-025
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
CMS Collaboration
11 March 2017
JHEP 07 (2017) 121
Abstract: A search is performed for third-generation scalar leptoquarks and heavy right-handed neutrinos in events containing one electron or muon, one hadronically decaying $\tau$ 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 $\beta^2$, where $\beta$ is the branching fraction of leptoquark decay to a $\tau$ lepton and a bottom quark. Assuming $\beta=$ 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, $\mathrm{N_R} $, and right-handed W bosons, $\mathrm{W_R} $, arising in a left-right symmetric extension of the standard model. In this search, $\mathrm{W_R} $ bosons are assumed to decay to a tau lepton and $\mathrm{N_R} $ followed by the decay of the $\mathrm{N_R} $ to a tau lepton and an off-shell $\mathrm{W_R} $ boson. Assuming the mass of the right-handed neutrino to be half of the mass of the right-handed W boson, $\mathrm{W_R} $ 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 $\tau$ leptons in the final state.
Links: e-print arXiv:1703.03995 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: Measured $ {S_{\mathrm {T}}} $ distribution in the $ {\mu {\tau _\mathrm {h}} } $ (left) and $ {\mathrm{ e } {\tau _\mathrm {h}} } $ (right) channels of the LQ (upper) and heavy RH neutrino (lower) analyses, compared to the expected SM background contribution. A hypothetical LQ signal of mass $ M_\mathrm {LQ}= $ 900 GeV and a hypothetical heavy $\mathrm{W_R} $ signal of mass ${M}_{\mathrm{W_R} }= $ 3 TeV are overlaid to illustrate the sensitivity. The electroweak background represents the sum of W boson, Z boson, and diboson production. The last bin of each plot contains overflow events. A binned maximum likelihood fit is performed on the $ {S_{\mathrm {T}}} $ distribution. The uncertainty bands represent the sum in quadrature of statistical and systematic uncertainties, obtained from the fit. The lower panels in all plots compare the observed and expected events in each bin of distribution.
png pdf	Figure 1-a: Measured $ {S_{\mathrm {T}}} $ distribution in the $ {\mu {\tau _\mathrm {h}} } $ channel of the LQ analysis, compared to the expected SM background contribution. A hypothetical LQ signal of mass $ M_\mathrm {LQ}= $ 900 GeV and a hypothetical heavy $\mathrm{W_R} $ signal of mass ${M}_{\mathrm{W_R} }= $ 3 TeV are overlaid to illustrate the sensitivity. The electroweak background represents the sum of W boson, Z boson, and diboson production. The last bin of the plot contains overflow events. A binned maximum likelihood fit is performed on the $ {S_{\mathrm {T}}} $ distribution. The uncertainty bands represent the sum in quadrature of statistical and systematic uncertainties, obtained from the fit. The lower panel compares the observed and expected events in each bin of distribution.
png pdf	Figure 1-b: Measured $ {S_{\mathrm {T}}} $ distribution in the $ {\mathrm{ e } {\tau _\mathrm {h}} } $ channel of the LQ analysis, compared to the expected SM background contribution. A hypothetical LQ signal of mass $ M_\mathrm {LQ}= $ 900 GeV and a hypothetical heavy $\mathrm{W_R} $ signal of mass ${M}_{\mathrm{W_R} }= $ 3 TeV are overlaid to illustrate the sensitivity. The electroweak background represents the sum of W boson, Z boson, and diboson production. The last bin of the plot contains overflow events. A binned maximum likelihood fit is performed on the $ {S_{\mathrm {T}}} $ distribution. The uncertainty bands represent the sum in quadrature of statistical and systematic uncertainties, obtained from the fit. The lower panel compares the observed and expected events in each bin of distribution.
png pdf	Figure 1-c: Measured $ {S_{\mathrm {T}}} $ distribution in the $ {\mu {\tau _\mathrm {h}} } $ channel of the heavy RH neutrino analysis, compared to the expected SM background contribution. A hypothetical LQ signal of mass $ M_\mathrm {LQ}= $ 900 GeV and a hypothetical heavy $\mathrm{W_R} $ signal of mass ${M}_{\mathrm{W_R} }= $ 3 TeV are overlaid to illustrate the sensitivity. The electroweak background represents the sum of W boson, Z boson, and diboson production. The last bin of the plot contains overflow events. A binned maximum likelihood fit is performed on the $ {S_{\mathrm {T}}} $ distribution. The uncertainty bands represent the sum in quadrature of statistical and systematic uncertainties, obtained from the fit. The lower panel compares the observed and expected events in each bin of distribution.
png pdf	Figure 1-d: Measured $ {S_{\mathrm {T}}} $ distribution in the $ {\mathrm{ e } {\tau _\mathrm {h}} } $ channel of the heavy RH neutrino analysis, compared to the expected SM background contribution. A hypothetical LQ signal of mass $ M_\mathrm {LQ}= $ 900 GeV and a hypothetical heavy $\mathrm{W_R} $ signal of mass ${M}_{\mathrm{W_R} }= $ 3 TeV are overlaid to illustrate the sensitivity. The electroweak background represents the sum of W boson, Z boson, and diboson production. The last bin of the plot contains overflow events. A binned maximum likelihood fit is performed on the $ {S_{\mathrm {T}}} $ distribution. The uncertainty bands represent the sum in quadrature of statistical and systematic uncertainties, obtained from the fit. The lower panel compares the observed and expected events in each bin of distribution.
png pdf	Figure 2: Observed and expected limits at 95% CL on the product of cross section and branching fraction squared, obtained from the combination of the $ {\mathrm{ e } {\tau _\mathrm {h}} } $ and $ {\mu {\tau _\mathrm {h}} } $ channels, in the LQ analysis (left) and 95% CL observed and expected exclusion limits on the LQ mass, as a function of $\beta $ (right). In the left plot, the green and yellow bands represent the one and two standard deviation uncertainties in the expected limits. The dashed dark blue curve represents the theoretical LQ pair production cross section, assuming $\beta = $ 100% [20,21]. In the right plot, the grey band represents the one standard deviation uncertainty in the expected limit.
png pdf	Figure 2-a: Observed and expected limits at 95% CL on the product of cross section and branching fraction squared, obtained from the combination of the $ {\mathrm{ e } {\tau _\mathrm {h}} } $ and $ {\mu {\tau _\mathrm {h}} } $ channels, in the LQ analysis.The green and yellow bands represent the one and two standard deviation uncertainties in the expected limits. The dashed dark blue curve represents the theoretical LQ pair production cross section, assuming $\beta = $ 100% [20,21].
png pdf	Figure 2-b: 95% CL observed and expected exclusion limits on the LQ mass, as a function of $\beta $. The grey band represents the one standard deviation uncertainty in the expected limit.
png pdf	Figure 3: Observed and expected limits at 95% CL on the product of cross section and branching fraction, obtained from the combination of the $ {\mathrm{ e } {\tau _\mathrm {h}} } $ and $ {\mu {\tau _\mathrm {h}} } $ channels in the heavy right-handed neutrino analysis (left) and the observed and expected limits at 95% CL on the production cross section as a function of $M_{\mathrm{W_R} }$ and $M_{ {\mathrm {N}_\mathrm {R}} }$ (right). The green and yellow bands represent the one and two standard deviation uncertainties in the expected limits. The dashed dark blue curve represents the theoretical prediction for the product of the $\mathrm{W_R} $ boson production cross section and the branching fraction for decay to a $\tau $ lepton and RH neutrino, assuming the mass of the RH neutrino to be half the mass of the $\mathrm{W_R} $ boson [22].
png pdf	Figure 3-a: Observed and expected limits at 95% CL on the product of cross section and branching fraction, obtained from the combination of the $ {\mathrm{ e } {\tau _\mathrm {h}} } $ and $ {\mu {\tau _\mathrm {h}} } $ channels in the heavy right-handed neutrino analysis. The green and yellow bands represent the one and two standard deviation uncertainties in the expected limits. The dashed dark blue curve represents the theoretical prediction for the product of the $\mathrm{W_R} $ boson production cross section and the branching fraction for decay to a $\tau $ lepton and RH neutrino, assuming the mass of the RH neutrino to be half the mass of the $\mathrm{W_R} $ boson [22].
png pdf	Figure 3-b: The observed and expected limits at 95% CL on the production cross section as a function of $M_{\mathrm{W_R} }$ and $M_{ {\mathrm {N}_\mathrm {R}} }$. The green and yellow bands represent the one and two standard deviation uncertainties in the expected limits. The dashed dark blue curve represents the theoretical prediction for the product of the $\mathrm{W_R} $ boson production cross section and the branching fraction for decay to a $\tau $ lepton and RH neutrino, assuming the mass of the RH neutrino to be half the mass of the $\mathrm{W_R} $ boson [22].

Summary

Searches have been performed for third-generation scalar leptoquarks and for heavy right-handed neutrinos in events containing one electron or muon, one hadronically decaying $\tau$ lepton, and two or more jets, using pp collision data at $\sqrt{s} = $ 13 TeV, recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 12.9 fb$^{-1}$. The data are found to be in good agreement with the standard model prediction in both analyses. A limit at 95% confidence level is set on the product of the leptoquark pair production cross section and $\beta^2$, where $\beta$ denotes the branching fraction for the decay of the leptoquark into a $\tau$ lepton and a bottom quark. Assuming $\beta=$ 1, third-generation leptoquarks with masses below 850 GeV are excluded at 95% confidence level. In the heavy RH neutrino analysis, considering the decay $\mathrm{W_R} \to\tau\mathrm{N_R} $ and assuming the mass of the heavy neutrino to be half the mass of the $\mathrm{W_R} $ boson, we exclude $\mathrm{W_R} $ boson masses below 2.9 TeV at 95% confidence level. These are the best mass limits to date for third-generation leptoquarks and heavy right-handed neutrinos with $\tau$ leptons in the final state.

Additional Figures
png pdf	Additional Figure 1: Measured $S_{\mathrm{T}} $ distribution in the ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ control region in e$\mu $ channel for the LQ selection (left) and heavy RH neutrino selection (right), compared to the expected SM background contribution. The electroweak background represents the sum of W boson, Z boson, and diboson production. The last bin of each plot contains overflow events. The lower panels in all plots compare the observed and expected events in each bin.
png pdf	Additional Figure 1-a: Measured $S_{\mathrm{T}} $ distribution in the ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ control region in e$\mu $ channel for the LQ selection, compared to the expected SM background contribution. The electroweak background represents the sum of W boson, Z boson, and diboson production. The last bin contains overflow events. The lower panel compares the observed and expected events in each bin.
png pdf	Additional Figure 1-b: Measured $S_{\mathrm{T}} $ distribution in the ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ control region in e$\mu $ channel for the heavy RH neutrino selection, compared to the expected SM background contribution. The electroweak background represents the sum of W boson, Z boson, and diboson production. The last bin contains overflow events. The lower panel compares the observed and expected events in each bin.
png pdf	Additional Figure 2: Measured $\mathrm {M_{T}}(l, {\vec{p}_{\mathrm {T}}^{\text {miss}}} )$ distribution in the $ {\mu \tau _\mathrm {h} } $ (left) and $ {\mathrm{ e } {\tau _\mathrm {h}} }$ (right) channels in the W control region compared to the expected SM background contribution. A binned maximum likelihood fit is performed on the $\mathrm {M_{T}}(l, {\vec{p}_{\mathrm {T}}^{\text {miss}}} )$ distribution. The uncertainty bands represent the sum in quadrature of statistical and systematic uncertainties, obtained from the fit. The lower panels in all plots compare the observed and expected events in each bin.
png pdf	Additional Figure 2-a: Measured $\mathrm {M_{T}}(l, {\vec{p}_{\mathrm {T}}^{\text {miss}}} )$ distribution in the $ {\mu {\tau _\mathrm {h}} } $ channel in the W control region compared to the expected SM background contribution. A binned maximum likelihood fit is performed on the $\mathrm {M_{T}}(l, {\vec{p}_{\mathrm {T}}^{\text {miss}}} )$ distribution. The uncertainty band represents the sum in quadrature of statistical and systematic uncertainties, obtained from the fit. The lower panel compares the observed and expected events in each bin.
png pdf	Additional Figure 2-b: Measured $\mathrm {M_{T}}(l, {\vec{p}_{\mathrm {T}}^{\text {miss}}} )$ distribution in the $ {\mathrm{ e } {\tau _\mathrm {h}} } $ channel in the W control region compared to the expected SM background contribution. A binned maximum likelihood fit is performed on the $\mathrm {M_{T}}(l, {\vec{p}_{\mathrm {T}}^{\text {miss}}} )$ distribution. The uncertainty band represents the sum in quadrature of statistical and systematic uncertainties, obtained from the fit. The lower panel compares the observed and expected events in each bin.

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