CMS-PAS-EXO-16-026

CMS-PAS-EXO-16-026
Search for heavy composite Majorana neutrinos produced in association with a lepton and decaying into a same-flavour lepton plus two quarks at $ \sqrt{s} = $ 13 TeV with the CMS detector
CMS Collaboration
August 2016

Abstract: We present a search for physics beyond the standard model in the final state with two same-flavour leptons (electrons or muons) and two quarks. The results of the measurement are interpreted in the framework of a recently proposed model, in which a heavy Majorana neutrino stems from a composite scenario. The analysis is performed using proton-proton collisions at $ \sqrt{s} = $ 13 TeV recorded by the CMS experiment at the CERN LHC. The data correspond to an integrated luminosity of 2.3 fb$^{-1}$ collected in 2015. The observed data are in good agreement with the standard model prediction. An upper limit at 95% CL on the product of the cross section of the heavy composite Majorana neutrino, $N$, produced in association with a lepton times branching fraction of $N$ into a same-flavour lepton and a quark pair is calculated as a function of its mass. In this model, the presence of the heavy composite Majorana neutrinos is excluded for masses up to 4.35 TeV and 4.50 TeV for a value of $\Lambda$ of 5 TeV, having analysed the $\mathrm{ee qq}$ channel and the $\mu\mu\mathrm{qq}$ channel, respectively.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 775 (2017) 315. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The fermion interaction as sum of the gauge and contact contributions.
png pdf	Figure 2-a: (a) Production cross section of the heavy composite Majorana neutrino for gauge and contact interaction at $\Lambda = $ 5 TeV. (b) Decay amplitude of the heavy composite Majorana neutrino for $\Lambda =$ 5 TeV as a function of its mass. The figures illustrate results of calculations based on [11].
png pdf	Figure 2-b: (a) Production cross section of the heavy composite Majorana neutrino for gauge and contact interaction at $\Lambda = $ 5 TeV. (b) Decay amplitude of the heavy composite Majorana neutrino for $\Lambda =$ 5 TeV as a function of its mass. The figures illustrate results of calculations based on [11].
png pdf	Figure 3-a: Data events in the $e\mu qq$ control regions defined to estimate the $t\bar{t}$ plus $tW$ contribution in the $ee qq$ (a) and $\mu \mu qq$ (b) channels, compared to the MC expectations for the background.
png pdf	Figure 3-b: Data events in the $e\mu qq$ control regions defined to estimate the $t\bar{t}$ plus $tW$ contribution in the $ee qq$ (a) and $\mu \mu qq$ (b) channels, compared to the MC expectations for the background.
png pdf	Figure 4-a: Distribution of the variable $M(\ell \ell J)$ for the data (black points), the estimated SM backgrounds (stackplots), and the signal (lines) having considered the parameters $\Lambda =$ 5 TeV and two masses of N equal to 2500 and 3500 GeV , for the $eeqq$ (a) and the $\mu \mu qq$ (b) channels. The error bars stand for the statistical and systematic uncertainty. The last bin includes the overflow entries.
png pdf	Figure 4-b: Distribution of the variable $M(\ell \ell J)$ for the data (black points), the estimated SM backgrounds (stackplots), and the signal (lines) having considered the parameters $\Lambda =$ 5 TeV and two masses of N equal to 2500 and 3500 GeV , for the $eeqq$ (a) and the $\mu \mu qq$ (b) channels. The error bars stand for the statistical and systematic uncertainty. The last bin includes the overflow entries.
png pdf	Figure 5-a: The observed 95% CL upper limits (solid black lines) on $\sigma (pp \rightarrow \ell N) \times {\cal B}(N \rightarrow \ell qq)$, obtained in the analysis of the $ee qq$ (a) and the $\mu \mu qq$ (b) final states, as a function of the mass of the heavy composite Majorana neutrino, $N$. The corresponding expected limits are shown by the dotted lines, and the coloured bands represent expected variation of the limit to one (green) and two (yellow) standard deviations. The blue curves indicates the theoretical prediction of $\sigma (pp \rightarrow \ell N) \times {\cal B}(N \rightarrow \ell qq)$ and its uncertainty for $\Lambda =$ 5 TeV and different values of the mass of $N$.
png pdf	Figure 5-b: The observed 95% CL upper limits (solid black lines) on $\sigma (pp \rightarrow \ell N) \times {\cal B}(N \rightarrow \ell qq)$, obtained in the analysis of the $ee qq$ (a) and the $\mu \mu qq$ (b) final states, as a function of the mass of the heavy composite Majorana neutrino, $N$. The corresponding expected limits are shown by the dotted lines, and the coloured bands represent expected variation of the limit to one (green) and two (yellow) standard deviations. The blue curves indicates the theoretical prediction of $\sigma (pp \rightarrow \ell N) \times {\cal B}(N \rightarrow \ell qq)$ and its uncertainty for $\Lambda =$ 5 TeV and different values of the mass of $N$.

Tables

png pdf

Table 1:
Number of events observed in data compared to expected background yields and hypothetical heavy composite Majorana neutrino signals of mass 2.5 and 3.5 TeV . The expected signal yields are computed at LO accuracy. The first uncertainty quoted on the background and MC signal yields represents the statistical one, while the second uncertainty is the systematic one. The top table gives inclusive yields, while the bottom one gives yields in the region where $M(\ell \ell J) >$ 1.4 TeV .

Summary

A search for new physics beyond the standard model has been performed considering a new model [11] based on a heavy Majorana neutrino, $N$, that originates from a composite scenario. We have used the 2015 dataset corresponding to an integrated luminosity of 2.3 fb$^{-1}$ collected by the CMS detector in pp collisions at $\sqrt{s} = $13 TeV. The data is in good agreement with the standard model prediction and we set an upper limit at 95% CL on $\sigma(pp \rightarrow \ell N) \times {\cal B}(N \rightarrow \ell qq)$. We have analysed the the $ee qq$ ($\mu\mu qq$) channel, for which we can exclude a heavy composite Majorana neutrino of mass up to 4.35 (4.50) TeV, for a value of $\Lambda$ of 5 TeV. The observed limits are comparable to the expectations of 4.30 (4.50) TeV in the $ee qq$ ($\mu\mu qq$) channel. This measurement represents the first search that considers as benchmark scenario the model described in [11].

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