CMS-PAS-EXO-16-016

CMS-PAS-EXO-16-016
Search for heavy neutrinos and third-generation leptoquarks in final states with two hadronically decaying $\tau$ leptons and two jets in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
June 2016

Abstract: A search for heavy, right-handed neutrinos, $N_{l}$, and right-handed $W_{R}$ bosons, which arise in the left-right symmetric extensions of the standard model, has been performed. The search focuses on the scenario where the $W_{R}$ and $N_{l}$ decay chains result in a pair of high-$p_{\mathrm{T}}$ $\tau$ leptons which decay hadronically, in addition to two high-$p_{\mathrm{T}}$ jets and missing transverse energy from the $\tau$ lepton decays. The analysis is performed using 2.1 fb$^{-1}$ of data collected by the CMS experiment in 2015 at $\sqrt{s} = $ 13 TeV. For models with strict left-right symmetry, and assuming only $N_{\tau}$ flavor contributes significantly to the $W_{R}$ decay width, $W_{R}$ masses below 2.35 (1.63) TeV are excluded at a 95% confidence level, assuming the $N_{\tau}$ mass is 0.8 (0.2) times the mass of $W_{R}$ boson. To illustrate the sensitivity of this analysis to other new physics models, focus is also placed on pair production of third-generation scalar leptoquarks with decay into $\tau\tau \mathrm{bb}$. Third-generation scalar leptoquarks with masses below 740 GeV are excluded, assuming a 100% branching fraction for the leptoquark decay to a $\tau$ lepton and a bottom quark.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 03 (2017) 077. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png	Figure 1-a: QCD shape closure test in $N_{j}< $ 2 data, which shows that the mass shape in non-isolated $\tau _{h}\tau _{h}$ control sample correctly models the ``true" shape in the isolated region (``Data").
png	Figure 1-b: QCD closure test of the ABCD method applied in $N_{j} < $ 2 data, which shows there is a good agreement between the nominal yield/shape and the predicted yield/shape.
png	Figure 1-c: QCD closure test in $N_{j} \geq$ 2 data, which shows the mass shape in non-isolated $\tau _{h}\tau _{h}$ control samples (``QCD" in the legend) correctly models the ``true" shape in the isolated region (``Data" in the legend).
png	Figure 1-d: QCD closure test in $N_{j} \geq$ 2 data, which shows the $S_{T}$ shape in non-isolated $\tau _{h}\tau _{h}$ control samples (``QCD" in the legend) correctly models the ``true" shape in the isolated region (``Data" in the legend).
png	Figure 2-a: $m(\tau _{h},\tau _{h},j,j, {E_{\mathrm {T}}^{\text {miss}}} )$ distribution in the SR.
png	Figure 2-b: $S_{T}$ distribution in the SR.
png	Figure 3-a: a: Expected and observed limits, at 95% confidence level, as functions of $m(W_{R})$ mass. b: Expected and observed limits, at 95% confidence level, as functions of LQ mass. The bands on the expected limits represent the one and two standard deviations obtained using a large sample of pseudo-experiments based on the background-only hypothesis for each bin of the mass and $S_{T}$ distributions.
png	Figure 3-b: a: Expected and observed limits, at 95% confidence level, as functions of $m(W_{R})$ mass. b: Expected and observed limits, at 95% confidence level, as functions of LQ mass. The bands on the expected limits represent the one and two standard deviations obtained using a large sample of pseudo-experiments based on the background-only hypothesis for each bin of the mass and $S_{T}$ distributions.
png	Figure 4: Observed and expected 95% CL upper limits on the production cross section for the ratio between $m(N_{\tau })$ and $m(W_{R})$ as a function of $m(W_{R})$.

Tables
png pdf	Table 1: Number of observed events in data and estimated background and signal rates in the SR.

Summary

A search is performed for physics beyond the SM in events with two energetic $\tau$ leptons, two energetic jets, and large momentum imbalance, using data corresponding to an integrated luminosity of 2.1 fb$^{-1}$ collected by the CMS detector in proton-proton collisions at $\sqrt{s}=$ 13 TeV. The search focuses on two benchmark new physics scenarios: (1) production of heavy right-handed neutrinos, $N_{l}$, and right-handed $W_{R}$ bosons which arise in the left-right symmetric extensions of the SM and where the $W_{R}$ and $N_{l}$ decay chains result in a pair of high-$p_{\mathrm{T}}$ $\tau$ leptons; (2) pair production of third-generation scalar leptoquarks which decay to $\tau\tau$bb. The observed $m(\tau_{h},\tau_{h},j,j,E_{\mathrm{T}}^{\text{miss}})$ and $S_{T}$ distributions do not reveal any evidence for new physics. Assuming only $N_{\tau}$ flavor contributes significantly to the $W_{R}$ decay width, $W_{R}$ masses below 2.35 (1.63) TeV are excluded at a 95% confidence level, assuming the $N_{\tau}$ mass is 0.8 (0.2) times the mass of $W_{R}$ boson. This is the first LHC result for $N_{l}$ searches with $\tau$ leptons. This analysis is the first to focus on searches for pair production of third-generation scalar leptoquarks using the $\tau_{h}\tau_{h} jj$ final state, resulting in an expected 95% CL exclusion of $m($LQ$)<$ 790 GeV and an observed exclusion of approximately 740 GeV.

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