Probing right handed neutrinos at the LHeC and lepton colliders using fat jet signatures

The inclusion of heavy neutral leptons (right-handed neutrinos) to the Standard Model (SM) particle content is one of the best motivated ways to account for the observed neutrino masses and flavor mixing. The modification of the charged and neutral currents from active-sterile mixing of the neutral leptons can provide novel signatures which can be tested at the future collider experiments. In this article, we explore the discovery prospect of a very heavy right handed neutrino to probe such extensions at the future collider experiments like Large Hadron electron Collider (LHeC) and linear collider. We consider the production of the heavy neutrino via the $t$ and $s$-channel processes and its subsequent decays into the semileptonic final states. We specifically focus on the scenario where the gauge boson produced from heavy neutrino decay is highly boosted, leading to a fat jet. We study the bounds on the sterile neutrino properties from several past experiments and compare with our results.

Figure 1

Heavy neutrino branching ratios (${\mathrm{BR}}_i$) for different decay modes are shown with respect to the heavy neutrino mass ($M_N$).

Figure 2

Production process, $ep\to N_1{j}_1$, of the RHN at the LHeC through a $t$ channel $W$ boson exchange.

Figure 3

RHN production cross section at the LHeC considering $ep\to N_{1}j$ process for the $ep$ collider at $\sqrt{s}=318\mathrm{GeV}$ (HERA, top left panel), $\sqrt{s}=1.3\mathrm{TeV}$ (LHeC, top right panel) and $\sqrt{s}=1.8\mathrm{TeV}$ (HE-LHeC, bottom panel).

Figure 4

RHN production processes at the linear collider. The left panel is the dominant $t$ channel process and the right panel is $s$ channel process to produce the $e^{+}{e}^{-}\to N_1{\nu }_1$. To produce $N_2{\nu }_2$ and $N_3{\nu }_3$, the $Z$ mediated $s$ channel process will act.

Figure 5

RHN production cross section at the linear collider considering $e^{+}{e}^{-}\to N_1{\nu }_1$ process at the different center of mass energies.

Figure 6

RHN production cross section at the linear collider considering $e^{+}{e}^{-}\to N_2{\nu }_2(N_3{\nu }_3)$ process at the different center of mass energies from the $s$ channel $Z$ boson exchange.

Figure 7

$e+J+j_1$ final state at the LHeC and HE-LHeC.

Figure 8

$e+J+p_T^{\mathrm{miss}}$ and $J_b+p_T^{\mathrm{miss}}$ final states at the linear colliders.

Figure 9

Transverse momentum distribution of the associated jet ($p_T^{j_1}$) from the signal and background events for $M_N=600\mathrm{GeV}$ and 700 GeV at the $\sqrt{s}=1.3\mathrm{TeV}$ LHeC (left panel) and $M_N=900\mathrm{GeV}$ and 1 TeV at the $\sqrt{s}=1.8\mathrm{TeV}$ LHeC (right panel).

Figure 10

Transverse momentum distribution of the electron ($p_T^e$) from the signal and background events for $M_N=600\mathrm{GeV}$ and 700 GeV at the $\sqrt{s}=1.3\mathrm{TeV}$ LHeC (left panel) and $M_N=900\mathrm{GeV}$ and 1 TeV at the $\sqrt{s}=1.8\mathrm{TeV}$ HE-LHeC (right panel).

Figure 11

Transverse momentum distribution of the fat jet ($p_T^J$) from the signal and background events for $M_N=600\mathrm{GeV}$ and 700 GeV at the $\sqrt{s}=1.3\mathrm{TeV}$ LHeC (left panel) and $M_N=900\mathrm{GeV}$ and 1 TeV at the $\sqrt{s}=1.8\mathrm{TeV}$ HE-LHeC (right panel).

Figure 12

Jet mass ($M_J$) distribution of the fat jet from the signal and background events for $M_N=600\mathrm{GeV}$ and 700 GeV at the $\sqrt{s}=1.3\mathrm{TeV}$ LHeC (left panel) and $M_N=900\mathrm{GeV}$ and 1 TeV at the $\sqrt{s}=1.8\mathrm{TeV}$ HE-LHeC (right panel).

Figure 13

Invariant mass distribution of the fat jet and electron system ($M_{eJ}$) from the signal and background events for $M_N=600\mathrm{GeV}$ and 700 GeV at the $\sqrt{s}=1.3\mathrm{TeV}$ LHeC (left panel) and $M_N=900\mathrm{GeV}$ and 1 TeV at the $\sqrt{s}=1.8\mathrm{TeV}$ HE-LHeC (right panel).

Figure 14

Missing momentum distribution of the signal and background events for $M_N=500\mathrm{GeV}$ and 800 GeV at the $\sqrt{s}=1\mathrm{TeV}$ (left panel) and $M_N=800\mathrm{GeV}$ and 2 TeV at the $\sqrt{s}=3\mathrm{TeV}$ (right panel) linear colliders.

Figure 15

Transverse momentum distribution of the electron ($p_T^e$) from the signal and background events for $M_N=500\mathrm{GeV}$ and 800 GeV at the $\sqrt{s}=1\mathrm{TeV}$ (left panel) and $M_N=800\mathrm{GeV}$ and 2 TeV at the $\sqrt{s}=3\mathrm{TeV}$ (right panel) linear colliders.

Figure 16

Transverse momentum distribution of the fat jet ($p_T^J$) from the signal and background events for $M_N=500\mathrm{GeV}$ and 800 GeV at the $\sqrt{s}=1\mathrm{TeV}$ (left panel) and $M_N=800\mathrm{GeV}$ and 2 TeV at the $\sqrt{s}=3\mathrm{TeV}$ linear colliders.

Figure 17

Jet mass ($M_J$) distribution of the fat jet from the signal and background events for $M_N=500\mathrm{GeV}$ and 800 GeV at the $\sqrt{s}=1\mathrm{TeV}$ (left panel) and $M_N=800\mathrm{GeV}$ and 2 TeV at the $\sqrt{s}=3\mathrm{TeV}$ (right panel) linear colliders.

Figure 18

$\cos {\theta }_{J(e)}$ distributions for the $J(e)$ in the first row (second row) for the 1 TeV (left column) and 3 TeV (right column) linear colliders.

Figure 19

$p_T^{\mathrm{miss}}$ distribution of the signal and background events for $M_N=700\mathrm{GeV}$ and 800 GeV at the $\sqrt{s}=1\mathrm{TeV}$ (left panel) and $M_N=1.5\mathrm{TeV}$ and 2 TeV at the $\sqrt{s}=3\mathrm{TeV}$ (right panel) linear colliders.

Figure 20

Transverse momentum distribution of $J_b$ $(p_T^{J_b})$ from the signal and background events for $M_N=700\mathrm{GeV}$ and 800 GeV at the $\sqrt{s}=1\mathrm{TeV}$ (left panel) and $M_N=1.5\mathrm{TeV}$ and 2 TeV at the $\sqrt{s}=3\mathrm{TeV}$ (right panel) linear colliders.

Figure 21

Fat b-Jet mass $(M_{J_b})$ distribution from the signal and background events for $M_N=700\mathrm{GeV}$ and 800 GeV at the $\sqrt{s}=1\mathrm{TeV}$ (left panel) and $M_N=1.5\mathrm{TeV}$ and 2 TeV at the $\sqrt{s}=3\mathrm{TeV}$ (right panel) linear colliders.

Figure 22

The prospective upper limits on $|V_{eN}{|}^2$ at the 1.3 TeV LHeC (blue band) and 1.8 TeV HE-LHeC (red band) at the $1{\mathrm{ab}}^{-1}$ luminosity compared to EWPD [105, 106, 107], LEP2 [108], GERDA [109] $0\nu 2\beta$ study from [13], ATLAS (ATLAS8-$ee$) [111], CMS (CMS8-$ee$) [112] at the 8 TeV LHC, 13 TeV CMS search for $e^{\pm }{e}^{\pm }+2j$ (CMS13-$ee$) [113] and 13 TeV CMS search for $3\ell$ (CMS13-$ee$) [113], respectively.

Figure 23

Same as Fig. 22 with $3{\mathrm{ab}}^{-1}$ luminosity at the 1.3 TeV LHeC and 1.8 TeV HE-LHeC.

Figure 24

The prospective upper limits on $|V_{eN}{|}^2$ at the 1 TeV (red band) and 3 TeV (blue band) linear colliders at the $1{\mathrm{ab}}^{-1}$ luminosity for $e+J+p_T^{\mathrm{miss}}$ signal compared to EWPD [105, 106, 107], LEP2 [108], GERDA [109] $0\nu 2\beta$ study from [13], ATLAS (ATLAS8-$ee$) [111], CMS (CMS8-$ee$) [112] at the 8 TeV LHC, 13 TeV CMS search for $e^{\pm }{e}^{\pm }+2j$ (CMS13-$ee$) [113] and 13 TeV CMS search for $3\ell$ (CMS13-$ee$) [113], respectively.

Figure 25

Same as Fig. 24 with $3(5){\mathrm{ab}}^{-1}$ luminosity at the 1(3) TeV linear collider.

Figure 26

The prospective upper limits on $|V_{eN}{|}^2$ at the 1 TeV (red band) and 3 TeV (blue band) linear colliders at the $1{\mathrm{ab}}^{-1}$ luminosity for $J_b+p_T^{\mathrm{miss}}$ signal compared to EWPD [105, 106, 107], LEP2 [108], GERDA [109] $0\nu 2\beta$ study from [13], ATLAS (ATLAS8-$ee$) [111], CMS (CMS8-$ee$) [112] at the 8 TeV LHC, 13 TeV CMS search for $e^{\pm }{e}^{\pm }+2j$ (CMS13-$ee$) [113] and 13 TeV CMS search for $3\ell$ (CMS13-$ee$) [113], respectively.

Figure 27

Same as Fig. 26 with $3(5){\mathrm{ab}}^{-1}$ luminosity at the 1(3) TeV linear collider.