CMS-EXO-16-026 ; CERN-EP-2017-125 | ||
Search for a heavy composite Majorana neutrino in the final state with two leptons and two quarks at $ \sqrt{s} = $ 13 TeV | ||
CMS Collaboration | ||
26 June 2017 | ||
Phys. Lett. B 775 (2017) 315 | ||
Abstract: A search for physics beyond the standard model in the final state with two same-flavour leptons (electrons or muons) and two quarks produced in proton-proton collisions at $ \sqrt{s} = $ 13 TeV is presented. The data were recorded by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 2.3 fb$^{-1}$. The observed data are in good agreement with the standard model background prediction. The results of the measurement are interpreted in the framework of a recently proposed model in which a heavy Majorana neutrino, $\textrm{N}_{\ell}$, stems from a composite-fermion scenario. Exclusion limits are set for the first time on the mass of the heavy composite Majorana neutrino, $m_{\textrm{N}_{\ell}}$, and the compositeness scale $\Lambda$. For the case $m_{\textrm{N}_{\ell}} = \Lambda$, the existence of $\textrm{N}_{\textrm{e}}$ ($\textrm{N}_{\mu}$) is excluded for masses up to 4.60 (4.70) TeV at 95% confidence level. | ||
Links: e-print arXiv:1706.08578 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
Leading order diagrams representing heavy composite Majorana neutrino production. The total interaction is the coherent sum of the gauge and contact interactions. Charge-conjugate reactions are implied. See Ref. [11]. |
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Figure 2:
Production cross section in pp collisions at $ \sqrt{s} = $ 13 TeV of the heavy composite Majorana neutrino via gauge and contact interactions as a function of Majorana mass at $\Lambda = $ 9 TeV (left) and decay width of the heavy composite Majorana neutrino for $\Lambda = $ 9 TeV as a function of its mass (right). The figures illustrate LO results of calculations based on Ref. [11]. |
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Figure 2-a:
Production cross section in pp collisions at $ \sqrt{s} = $ 13 TeV of the heavy composite Majorana neutrino via gauge and contact interactions as a function of Majorana mass at $\Lambda = $ 9 TeV. The figure illustrates LO results of calculations based on Ref. [11]. |
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Figure 2-b:
Decay width of the heavy composite Majorana neutrino for $\Lambda = $ 9 TeV as a function of its mass. The figure illustrates LO results of calculations based on Ref. [11]. |
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Figure 3:
Data events in the $\textrm {e}\mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ control regions used to estimate the $\mathrm{ t \bar{t} } + \textrm {tW}$ contribution in the $\textrm {ee} \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ (left) and $\mu \mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ (right) channels, compared to the expectations of the background simulations. |
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Figure 3-a:
Data events in the $\textrm {e}\mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ control regions used to estimate the $\mathrm{ t \bar{t} } + \textrm {tW}$ contribution in the $\textrm {ee} \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ channel, compared to the expectations of the background simulations. |
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Figure 3-b:
Data events in the $\textrm {e}\mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ control regions used to estimate the $\mathrm{ t \bar{t} } + \textrm {tW}$ contribution in the $\mu \mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ channel, compared to the expectations of the background simulations. |
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Figure 4:
Distribution of the variable $m_{\ell \ell \mathrm {J}}$ for the data (black points), the estimated SM backgrounds (stacked filled histograms), and the signal (lines) with $\Lambda = $ 9 TeV and masses of $\textrm {N}_{\ell }$ equal to 1.5 and 2.5 TeV , for the $\textrm {ee} \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ (left) and the $\mu \mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ (right) channels. The background uncertainties are the combined statistical and systematic uncertainties. |
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Figure 4-a:
Distribution of the variable $m_{\ell \ell \mathrm {J}}$ for the data (black points), the estimated SM backgrounds (stacked filled histograms), and the signal (lines) with $\Lambda = $ 9 TeV and masses of $\textrm {N}_{\ell }$ equal to 1.5 and 2.5 TeV , for the $\textrm {ee} \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ channel. The background uncertainties are the combined statistical and systematic uncertainties. |
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Figure 4-b:
Distribution of the variable $m_{\ell \ell \mathrm {J}}$ for the data (black points), the estimated SM backgrounds (stacked filled histograms), and the signal (lines) with $\Lambda = $ 9 TeV and masses of $\textrm {N}_{\ell }$ equal to 1.5 and 2.5 TeV , for the $\mu \mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ channel. The background uncertainties are the combined statistical and systematic uncertainties. |
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Figure 5:
The observed 95% CL upper limits (solid black lines) on $\sigma (\textrm {pp} \rightarrow \ell \textrm {N}_{\ell }) {\cal B}(\textrm {N}_{\ell } \rightarrow \ell \mathrm{ q } \mathrm{ \bar{q} } ^\prime )$, obtained in the analysis of the $\textrm {ee} \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ (left) and the $\mu \mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ (right) final states, as a function of the mass of the heavy composite Majorana neutrino, $\textrm {N}_{\ell }$. The corresponding expected limits are shown by the dotted lines, and the bands represent the expected variation of the limit to one and two standard deviation(s). The solid blue curve indicates the theoretical prediction of $\sigma (\textrm {pp} \rightarrow \ell \textrm {N}_{\ell }) {\cal B}(\textrm {N}_{\ell } \rightarrow \ell \mathrm{ q } \mathrm{ \bar{q} } ^\prime )$ for $\Lambda = m_{\textrm {N}_{\ell }}$. The uncertainty in the theoretical prediction is derived by taking into account the factorization and normalization scales. The light red textured curves give the theoretical predictions for three $\Lambda $ values ranging from 6 to 12 TeV in steps of 3 TeV . |
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Figure 5-a:
The observed 95% CL upper limits (solid black lines) on $\sigma (\textrm {pp} \rightarrow \ell \textrm {N}_{\ell }) {\cal B}(\textrm {N}_{\ell } \rightarrow \ell \mathrm{ q } \mathrm{ \bar{q} } ^\prime )$, obtained in the analysis of the $\textrm {ee} \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino, $\textrm {N}_{\ell }$. The corresponding expected limits are shown by the dotted lines, and the bands represent the expected variation of the limit to one and two standard deviation(s). The solid blue curve indicates the theoretical prediction of $\sigma (\textrm {pp} \rightarrow \ell \textrm {N}_{\ell }) {\cal B}(\textrm {N}_{\ell } \rightarrow \ell \mathrm{ q } \mathrm{ \bar{q} } ^\prime )$ for $\Lambda = m_{\textrm {N}_{\ell }}$. The uncertainty in the theoretical prediction is derived by taking into account the factorization and normalization scales. The light red textured curves give the theoretical predictions for three $\Lambda $ values ranging from 6 to 12 TeV in steps of 3 TeV . |
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Figure 5-b:
The observed 95% CL upper limits (solid black lines) on $\sigma (\textrm {pp} \rightarrow \ell \textrm {N}_{\ell }) {\cal B}(\textrm {N}_{\ell } \rightarrow \ell \mathrm{ q } \mathrm{ \bar{q} } ^\prime )$, obtained in the analysis of the $\mu \mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino, $\textrm {N}_{\ell }$. The corresponding expected limits are shown by the dotted lines, and the bands represent the expected variation of the limit to one and two standard deviation(s). The solid blue curve indicates the theoretical prediction of $\sigma (\textrm {pp} \rightarrow \ell \textrm {N}_{\ell }) {\cal B}(\textrm {N}_{\ell } \rightarrow \ell \mathrm{ q } \mathrm{ \bar{q} } ^\prime )$ for $\Lambda = m_{\textrm {N}_{\ell }}$. The uncertainty in the theoretical prediction is derived by taking into account the factorization and normalization scales. The light red textured curves give the theoretical predictions for three $\Lambda $ values ranging from 6 to 12 TeV in steps of 3 TeV . |
png pdf |
Figure 6:
The observed 95% CL lower limits (solid black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $\textrm {ee} \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ (left) and the $\mu \mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ (right) final states, as a function of the mass of the heavy composite Majorana neutrino, $\textrm {N}_{\ell }$. The dotted lines represent the corresponding expected limits and the bands, the expected variation to one and two standard deviation(s). The grey zone represents the phase space $\Lambda < M_{\textrm {N}_{\ell }}$, which is not allowed by the model. |
png pdf |
Figure 6-a:
The observed 95% CL lower limits (solid black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $\textrm {ee} \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino, $\textrm {N}_{\ell }$. The dotted lines represent the corresponding expected limits and the bands, the expected variation to one and two standard deviation(s). The grey zone represents the phase space $\Lambda < M_{\textrm {N}_{\ell }}$, which is not allowed by the model. |
png pdf |
Figure 6-b:
The observed 95% CL lower limits (solid black lines) on the compositeness scale $\Lambda $, obtained in the analysis of the $\mu \mu \mathrm{ q } \mathrm{ \bar{q} } ^\prime $ final state, as a function of the mass of the heavy composite Majorana neutrino, $\textrm {N}_{\ell }$. The dotted lines represent the corresponding expected limits and the bands, the expected variation to one and two standard deviation(s). The grey zone represents the phase space $\Lambda < M_{\textrm {N}_{\ell }}$, which is not allowed by the model. |
Tables | |
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Table 1:
Number of events observed in data are compared to the expected background yields and those of a hypothetical heavy composite Majorana neutrino of mass 1.5 and 2.5 TeV , and $\Lambda = $ 9 TeV , given for all values of $m_{\ell \ell \mathrm {J}}$ (upper table) and for $m_{\ell \ell \mathrm {J}}> $ 1.4 TeV (lower table). The expected signal yields are computed at LO accuracy. The background and signal simulation yields are given with both statistical and systematic uncertainties. Statistical uncertainties given as 0.0 correspond to values much smaller than the systematical uncertainty. |
Summary |
A search for physics beyond the standard model has been performed in the framework of a new model [11] predicting a heavy Majorana neutrino, $\textrm{N}_{\ell}$, that originates from a composite-fermion scenario and is produced in association with a matched-flavour charged lepton. The measurement is performed analysing the final state with two leptons and at least one large-radius jet, a signature not previously utilized in searches for heavy neutrinos. The data set used corresponds to an integrated luminosity of 2.3 fb$^{-1}$ collected with the CMS detector at the LHC in pp collisions at $\sqrt{s}= $ 13 TeV. Good agreement between the data and the standard model prediction is observed. Upper limits are set at 95% confidence level both on the product of the cross section $\sigma(\textrm{pp} \rightarrow \ell \textrm{N}_{\ell})$ and the branching fraction ${\cal B}(\textrm{N}_{\ell} \rightarrow \ell \mathrm{ q \bar{q} }^\prime)$, and on the compositeness scale $\Lambda$, as a function of $m_{\textrm{N}_{\ell}}$, $\ell$ being an electron or a muon. For the representative case $\Lambda = m_{\textrm{N}_{\ell}}$, $\textrm{N}_{\textrm{e}}$ masses up to 4.60 TeV and $\textrm{N}_{\mu}$ masses up to 4.70 TeV are excluded. This measurement represents the first search that places constraints on the model described in Ref. [11]. |
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Compact Muon Solenoid LHC, CERN |