CMS-PAS-EXO-16-023

CMS-PAS-EXO-16-023
Search for the third-generation scalar leptoquarks and heavy right-handed neutrinos in $\tau_{\ell} \tau_{h}$jj final states in pp collisions at 13 TeV
CMS Collaboration
August 2016

Abstract: A search is performed for the 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 12.9 fb$^{-1}$ collected by the CMS detector at the LHC in 2016. The number of observed events is found to be in agreement with the standard model prediction in both search analyses. A 95% CL limit is set on the product of the leptoquark pair production cross section and $\beta^2$, where $\beta$ is the branching fraction of the leptoquark decay to a $\tau$ lepton and a b quark. Assuming $\beta=1$, the third-generation leptoquarks with masses below 900 GeV are excluded at 95% CL. The right-handed neutrinos are searched in decays of right-handed $\mathrm{ W }_{\mathrm{R}}$ bosons. The heavy right-handed neutrinos are excluded at 95% CL for a range of neutrino masses below the $\mathrm{ W }_{\mathrm{R}}$ mass, dependent on the value of $M_{ \mathrm{ W }_{\mathrm{R}} }$. Assuming the mass of neutrino to be half of the mass of W boson, W boson masses below 3.2 TeV are excluded at 95% CL.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 07 (2017) 121. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1-a: Distribution in ${S_{\rm {T}}}$ observed in the ${\mu {\tau _{\text {h}}} }$ (a,c) and $ {e {\tau _{\text {h}}} }$ (b,d) channel of the LQ (a,b) and heavy RH neutrino (c,d) analysis, compared to the expected SM background contribution and to a hypothetic LQ signal of mass $m_{LQ}=$ 900 GeV and a hypothetic heavy RH neutrino signal of mass $m_{ { {\mathrm {W}}_{\mathrm {R}}}}=$ 3 TeV. A binned maximum likelihood fit is performed to the ${S_{\rm {T}}}$ distribution. ``Electroweak" background is the sum of W boson, Z boson, and dibosons. The uncertainty bands represent the sum of statistical and systematic uncertainties, added in quadrature.
png pdf	Figure 1-b: Distribution in ${S_{\rm {T}}}$ observed in the ${\mu {\tau _{\text {h}}} }$ (a,c) and $ {e {\tau _{\text {h}}} }$ (b,d) channel of the LQ (a,b) and heavy RH neutrino (c,d) analysis, compared to the expected SM background contribution and to a hypothetic LQ signal of mass $m_{LQ}=$ 900 GeV and a hypothetic heavy RH neutrino signal of mass $m_{ { {\mathrm {W}}_{\mathrm {R}}}}=$ 3 TeV. A binned maximum likelihood fit is performed to the ${S_{\rm {T}}}$ distribution. ``Electroweak" background is the sum of W boson, Z boson, and dibosons. The uncertainty bands represent the sum of statistical and systematic uncertainties, added in quadrature.
png pdf	Figure 1-c: Distribution in ${S_{\rm {T}}}$ observed in the ${\mu {\tau _{\text {h}}} }$ (a,c) and $ {e {\tau _{\text {h}}} }$ (b,d) channel of the LQ (a,b) and heavy RH neutrino (c,d) analysis, compared to the expected SM background contribution and to a hypothetic LQ signal of mass $m_{LQ}=$ 900 GeV and a hypothetic heavy RH neutrino signal of mass $m_{ { {\mathrm {W}}_{\mathrm {R}}}}=$ 3 TeV. A binned maximum likelihood fit is performed to the ${S_{\rm {T}}}$ distribution. ``Electroweak" background is the sum of W boson, Z boson, and dibosons. The uncertainty bands represent the sum of statistical and systematic uncertainties, added in quadrature.
png pdf	Figure 1-d: Distribution in ${S_{\rm {T}}}$ observed in the ${\mu {\tau _{\text {h}}} }$ (a,c) and $ {e {\tau _{\text {h}}} }$ (b,d) channel of the LQ (a,b) and heavy RH neutrino (c,d) analysis, compared to the expected SM background contribution and to a hypothetic LQ signal of mass $m_{LQ}=$ 900 GeV and a hypothetic heavy RH neutrino signal of mass $m_{ { {\mathrm {W}}_{\mathrm {R}}}}=$ 3 TeV. A binned maximum likelihood fit is performed to the ${S_{\rm {T}}}$ distribution. ``Electroweak" background is the sum of W boson, Z boson, and dibosons. The uncertainty bands represent the sum of statistical and systematic uncertainties, added in quadrature.
png pdf	Figure 2: Observed and expected 95% CL upper limit on the product of signal cross section times branching fraction, obtained from the combination of ${e {\tau _{\text {h}}} }$ and ${\mu {\tau _{\text {h}}} }$ channels, in the LQ analysis. The 1$\sigma $ and 2$\sigma $ bands represent the 1 and 2 standard deviation uncertainties on the expected limits.
png pdf	Figure 3: Observed and expected upper limits at 95% CL on the product of cross section and branching fraction for combined $e\tau $ and $\mu \tau $ in heavy right handed neutrino analysis. The 1$\sigma $ and 2$\sigma $ bands represent the 1 and 2 standard deviation uncertainties on the expected limits.

Tables
png pdf	Table 1: Systematic uncertainties. Those uncertainties marked with * are treated correlated between ${\mu {\tau _{\text {h}}} }$ and ${e {\tau _{\text {h}}} }$ channels.

Summary

A search is 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 a pp collision data at $\sqrt{s} =$ 13 TeV centre-of-mass energy recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 12.9 fb$^{-1}$. The events observed in data is found to be in good agreement with the SM prediction in both search analyses. A 95% CL limit is set on the product of the leptoquark pair production cross section and $\beta^2$, where $\beta$ denotes the branching fraction of decay of the leptoquark to a $\tau$ lepton and a b quark. Assuming $\beta=1$, third generation leptoquarks with masses below 900 GeV are excluded at 95% CL. In the heavy RH neutrino analysis, considering $\mathrm{ W }_{\mathrm{R}}\rightarrow\tau \mathrm{N}_{\ell}$ decay and assuming the mass of heavy neutrino to be half of the mass of $\mathrm{ W }_{\mathrm{R}}$ boson W boson masses below 3.2 TeV are excluded at 95% confidence level. These results improve the limits from the previous searches for third generation leptoquarks and heavy right handed neutrino with $\tau$ lepton in final state.

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