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| CMS-PAS-FTR-18-006 | ||
| Search for heavy composite Majorana neutrinos at the High-Luminosity and the High-Energy LHC | ||
| CMS Collaboration | ||
| December 2018 | ||
| Abstract: The sensitivity of a search for heavy Majorana neutrinos with the CMS Phase-2 detector in a final state with two leptons and at least one large-radius jet is investigated. Such new particles arise in theories beyond the standard model with compositeness. The study is based on searches previously performed with Run 2 CMS data, where no evidence for a signal was found. The High-Luminosity LHC (HL-LHC) with a centre-of-mass energy of 14 TeV and an integrated luminosity of 3 ab$^{-1}$ will allow an extension of the sensitivity to cross sections of order of a few ab for heavy neutrino masses $M(N_\ell)$ ranging from 3 to 9 TeV for the $\ell \ell q\bar{q}^\prime$ channel, where $\ell$ is an electron or a muon and $q$ is a quark. For the compositeness scale $\Lambda=M(N_\ell)$, the existence of a heavy Majorana neutrino could be excluded for masses up to 8 TeV at the 95% confidence level. The projection of the study to the High-Energy LHC (HE-LHC) scenario, with a centre-of-mass energy of 27 TeV, is also presented here. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The production of a heavy composite Majorana neutrino via the fermion interaction discussed in the text as a sum of the gauge and contact contributions. |
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Figure 2:
Production cross sections of the heavy composite Majorana neutrino for gauge and contact interactions at $\Lambda = $ 12 TeV for pp collisions at $\sqrt {s}=$ 14 TeV, obtained with CalcHEP (v3.6) [29]. |
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Figure 3:
Decay amplitude of the heavy composite Majorana neutrino to a lepton and two quarks, for $\Lambda =$ 5 TeV (left), $\Lambda =$ 15 TeV (centre), and $\Lambda = $ 25 TeV (right), as a function of its mass, obtained with CalcHEP (v3.6) [29]. The x-axis range has been restricted to emphasize the interplay. |
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Figure 3-a:
Decay amplitude of the heavy composite Majorana neutrino to a lepton and two quarks, for $\Lambda =$ 5 TeV, as a function of its mass, obtained with CalcHEP (v3.6) [29]. The x-axis range has been restricted to emphasize the interplay. |
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Figure 3-b:
Decay amplitude of the heavy composite Majorana neutrino to a lepton and two quarks, for $\Lambda =$ 15 TeV, as a function of its mass, obtained with CalcHEP (v3.6) [29]. The x-axis range has been restricted to emphasize the interplay. |
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Figure 3-c:
Decay amplitude of the heavy composite Majorana neutrino to a lepton and two quarks, for $\Lambda =$ 25 TeV, as a function of its mass, obtained with CalcHEP (v3.6) [29]. The x-axis range has been restricted to emphasize the interplay. |
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Figure 4:
The Feynman diagram of the process for the production and decay of a heavy composite Majorana neutrino, according to the decay chain $pp\rightarrow \ell N_\ell \rightarrow \ell \ell q\bar{q}^\prime $. |
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Figure 5:
Distribution of the variable $M(\ell \ell J)$ of backgrounds (stacked plots) and expected signal (lines) in the signal region, considering the model parameters $\Lambda =M(N_\ell)= $ 6 TeV, for the $ee q\bar{q}^\prime $ channel (left) and for the $\mu \mu q\bar{q}^\prime $ channel (right). The background statistical and systematic uncertainties have been combined. |
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Figure 5-a:
Distribution of the variable $M(\ell \ell J)$ of backgrounds (stacked plots) and expected signal (lines) in the signal region, considering the model parameters $\Lambda =M(N_\ell)= $ 6 TeV, for the $ee q\bar{q}^\prime $ channel. The background statistical and systematic uncertainties have been combined. |
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Figure 5-b:
Distribution of the variable $M(\ell \ell J)$ of backgrounds (stacked plots) and expected signal (lines) in the signal region, considering the model parameters $\Lambda =M(N_\ell)= $ 6 TeV, for the $\mu \mu q\bar{q}^\prime $ channel. The background statistical and systematic uncertainties have been combined. |
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Figure 6:
The expected statistical significance for both the $eeq\bar{q}^\prime $ (red line) and $\mu \mu q\bar{q}^\prime $ (blue line) channel for the case $\Lambda =M(N_\ell)$. The gray solid (dotted) line represents 5 (3) standard deviations, respectively. |
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Figure 7:
The expected 95% CL upper limits (black dotted lines) on $\sigma (pp \rightarrow \ell N_\ell) \times {\cal B}(N_\ell \rightarrow \ell q\bar{q}^\prime)$, obtained in the analysis of the $ee q\bar{q}^\prime $ (top) and the $\mu \mu q\bar{q}^\prime $ (bottom) final states, as a function of the mass of the heavy composite Majorana neutrino. The corresponding green and yellow bands represent the expected variation of the limit to one and two standard deviation(s). The solid blue curve indicates the theoretical prediction of $\Lambda =M(N_\ell)$. The textured curves give the theoretical predictions for $\Lambda $ values ranging from 12 to 35 TeV. |
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Figure 7-a:
The expected 95% CL upper limits (black dotted lines) on $\sigma (pp \rightarrow \ell N_\ell) \times {\cal B}(N_\ell \rightarrow \ell q\bar{q}^\prime)$, obtained in the analysis of the $ee q\bar{q}^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino. The corresponding green and yellow bands represent the expected variation of the limit to one and two standard deviation(s). The solid blue curve indicates the theoretical prediction of $\Lambda =M(N_\ell)$. The textured curves give the theoretical predictions for $\Lambda $ values ranging from 12 to 35 TeV. |
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Figure 7-b:
The expected 95% CL upper limits (black dotted lines) on $\sigma (pp \rightarrow \ell N_\ell) \times {\cal B}(N_\ell \rightarrow \ell q\bar{q}^\prime)$, obtained in the analysis of the $\mu \mu q\bar{q}^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino. The corresponding green and yellow bands represent the expected variation of the limit to one and two standard deviation(s). The solid blue curve indicates the theoretical prediction of $\Lambda =M(N_\ell)$. The textured curves give the theoretical predictions for $\Lambda $ values ranging from 12 to 35 TeV. |
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Figure 8:
The expected 95% CL lower limits (black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $eeq\bar{q}^\prime $ (top) and the $\mu \mu q\bar{q}^\prime $ (bottom) final states, as a function of the mass of the heavy composite Majorana neutrino. The gray zone corresponds to the phase space $\Lambda < M(N_\ell)$ not allowed by the model. |
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Figure 8-a:
The expected 95% CL lower limits (black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $eeq\bar{q}^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino. The gray zone corresponds to the phase space $\Lambda < M(N_\ell)$ not allowed by the model. |
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Figure 8-b:
The expected 95% CL lower limits (black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $\mu \mu q\bar{q}^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino. The gray zone corresponds to the phase space $\Lambda < M(N_\ell)$ not allowed by the model. |
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Figure 9:
Distribution of the invariant mass of two leptons and leading large-radius jet of backgrounds and three signal samples for the $ee q\bar{q}^\prime $ channel (left) and $\mu \mu q\bar{q}^\prime $ channel (right) for the HE-LHC. The error bands are given by the combination of systematic and statistical uncertainties. |
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Figure 9-a:
Distribution of the invariant mass of two leptons and leading large-radius jet of backgrounds and three signal samples for the $ee q\bar{q}^\prime $ channel for the HE-LHC. The error bands are given by the combination of systematic and statistical uncertainties. |
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Figure 9-b:
Distribution of the invariant mass of two leptons and leading large-radius jet of backgrounds and three signal samples for the $\mu \mu q\bar{q}^\prime $ channel for the HE-LHC. The error bands are given by the combination of systematic and statistical uncertainties. |
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Figure 10:
The expected statistical significance for the HE-LHC projection of the $eeq\bar{q}^\prime $ (red line) and the $\mu \mu q\bar{q}^\prime $ (blue line) channel for the case $\Lambda =M(N_\ell)$. The gray solid (dotted) line represents 5 (3) standard deviations, respectively. |
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Figure 11:
The expected 95% CL upper limits for the HE-LHC projection of the $ee q\bar{q}^\prime $ channel (top) and the $\mu \mu q\bar{q}^\prime $ channel (bottom). The cross section limits are higher in the HE case because of the much larger background expectation at 27 TeV. |
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Figure 11-a:
The expected 95% CL upper limits for the HE-LHC projection of the $ee q\bar{q}^\prime $ channel. The cross section limits are higher in the HE case because of the much larger background expectation at 27 TeV. |
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Figure 11-b:
The expected 95% CL upper limits for the HE-LHC projection of the $\mu \mu q\bar{q}^\prime $ channel. The cross section limits are higher in the HE case because of the much larger background expectation at 27 TeV. |
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Figure 12:
The expected 95% CL lower limits (black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $eeq\bar{q}^\prime $ (top) and the $\mu \mu q\bar{q}^\prime $ (bottom) final states, as a function of the mass of the heavy composite Majorana neutrino for the HE-LHC projection. The red shaded zone highlights the excluded parameter space. The gray zones are not allowed by the model. |
png pdf |
Figure 12-a:
The expected 95% CL lower limits (black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $eeq\bar{q}^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino for the HE-LHC projection. The red shaded zone highlights the excluded parameter space. The gray zones are not allowed by the model. |
png pdf |
Figure 12-b:
The expected 95% CL lower limits (black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $\mu \mu q\bar{q}^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino for the HE-LHC projection. The red shaded zone highlights the excluded parameter space. The gray zones are not allowed by the model. |
| Tables | |
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Table 1:
Parameters used in the HL-LHC analysis, $\ell =e, \mu $. |
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Table 2:
List of systematic uncertainties used in the present analysis. |
| Summary |
| Studies have been conducted of the expected performance at the HL-LHC and at the HE-LHC of a search for a composite Majorana neutrino. The study has been carried out considering a heavy composite Majorana neutrino produced in association with a lepton and decaying into a same-flavor lepton plus two quarks, with the requirement of two leptons and at least one large-radius jet in the signal region. The HL-LHC running conditions and Phase-2 detector allow a significant extension of the parameter space that can be probed. |
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