Within the framework of the phenomenological type-I seesaw mechanism, heavy singlet Majorana neutrinos are introduced to explain the origin of neutrino masses. We propose a novel search strategy for these heavy Majorana neutrinos through the lepton-number-violating process $$e^{-}p \rightarrow jN\rightarrow j(\mu ^{+}W^{-})$$ at the Future Circular electron-hadron Collider (FCC-eh), which would utilize a 60 GeV electron beam colliding with a 50 TeV proton beam. Focusing on the decay mode $$N\rightarrow \mu ^{+}W^{-}\rightarrow \mu ^{+}J$$ , where $\textit{J}$ denotes a fat-jet from the hadronic decays of a highly boosted $\textit{W}$ boson, we investigate the discovery potential of this signature. By performing a detailed signal-to-background analysis and detector simulations, we present $$2\sigma $$ exclusion limits and $$5\sigma $$ discovery reaches in terms of parameter space regions.

China

Jie-Fen Shen

Yan-Ju Zhang

Lin Han

Searching for heavy majorana neutrinos at the FCC-eh via lepton-number-violating and fat-jet final states

In a simplified model including an exotic vector-like X-quark (VLQ-X) with electric charge 5/3, we investigate the process  $$e^{+}p \rightarrow \bar{\nu }_{e}X+\bar{\nu }_{e}X\bar{t}$$  <math> <mrow> <msup> <mi>e</mi> <mo>+</mo> </msup> <mi>p</mi> <mo>→</mo> <msub> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> <mi>e</mi> </msub> <mi>X</mi> <mo>+</mo> <msub> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> <mi>e</mi> </msub> <mi>X</mi> <mover> <mrow> <mi>t</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   induced by the couplings between the VLQ-X and the first- and third-generation quarks at the future ep colliders. We further explore the prospects of discovering the VLQ-X via the  $$X\rightarrow tW$$  <math> <mrow> <mi>X</mi> <mo>→</mo> <mi>t</mi> <mi>W</mi> </mrow> </math>   decay model at the electron–hadron Future Circular Collider (FCC-eh) with its proposed 60 GeV electron beam and 50 TeV proton beam. We focus our analysis on the final states, including two same-sign lepton (electrons or muons) or  $$\mu \mu $$  <math> <mrow> <mi>μ</mi> <mi>μ</mi> </mrow> </math>   pairs, at least one b-tagged jet, and large missing transverse momentum. By performing a detailed signal-to-background analysis and detector simulations, the 95% confidence level exclusion limits and  $$5\sigma $$  <math> <mrow> <mn>5</mn> <mi>σ</mi> </mrow> </math>   discovery reaches are presented in terms of parameter space regions.

Yong-Tao Zhu

Yan-Ping Bi

Tai-Gang Liu

Searching for the vector-like X-quark at the future electron–proton colliders

Based on a simplified model including a singlet vector-like top quark T with charge |Q|=  $ 2/3 $  , we analyze the prospects of observing T via the single T production in the   $ 2/3 $   channel with Z decaying to neutrinos at the hadron-hadron colliders. This simplified model only includes two free parameters, the coupling constant   $ 2/3 $   and the T quark mass   $ 2/3 $  . To investigate the observability of the single T production, we perform a detailed background analysis and detector simulation for the collision energies 14 TeV, 27 TeV, and 100 TeV. We scan the   $ 2/3 $   parameter space and show the exclusion and discovery capabilities on the T quark with the highest integrated luminosity designed at these colliders. Moreover, the limits from the narrow-width approximation and electroweak precision observables are considered.

Shiyu Wang

Liangliang Shang

Bingfang Yang

Search for the singlet vector-like top quark in the Channel With At Hadron Colliders  

Vector-like quarks are predicted by several theoretical scenarios of new physics which could solve the hierarchy problem in particular and might be produced through electroweak interactions. In this work, we investigate the prospects for discovering the SU(2) singlet vector-like bottom quark (VLQ-B) in  $$e^{+}e^{-}$$  <math> <mrow> <msup> <mi>e</mi> <mo>+</mo> </msup> <msup> <mi>e</mi> <mo>-</mo> </msup> </mrow> </math>   collisions at the future proposed 3 TeV Compact Linear Collider (CLIC). The analysis is performed within the framework of a simplified model featuring only two free parameters: the VLQ-B mass  $$m_B$$  <math> <msub> <mi>m</mi> <mi>B</mi> </msub> </math>   and the coupling constant  $$g^{*}$$  <math> <msup> <mi>g</mi> <mrow> <mrow></mrow> <mo>∗</mo> </mrow> </msup> </math>  . We study its single production process  $$e^{+}e^{-}\rightarrow B{\bar{b}}$$  <math> <mrow> <msup> <mi>e</mi> <mo>+</mo> </msup> <msup> <mi>e</mi> <mo>-</mo> </msup> <mo>→</mo> <mi>B</mi> <mover> <mrow> <mi>b</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   and perform a detailed analysis in the decay channel  $$B\rightarrow tW^{-}$$  <math> <mrow> <mi>B</mi> <mo>→</mo> <mi>t</mi> <msup> <mi>W</mi> <mo>-</mo> </msup> </mrow> </math>   at the 3 TeV CLIC. The  $$2\sigma $$  <math> <mrow> <mn>2</mn> <mi>σ</mi> </mrow> </math>   exclusion limit and  $$5\sigma $$  <math> <mrow> <mn>5</mn> <mi>σ</mi> </mrow> </math>   discovery prospects are obtained for the model parameters, respectively. Our results show that the future CLIC will be an ideal hunting ground for such vector-like quarks which have electroweak interactions.

Yao-Bei Liu

Searching for a vector-like B quark through a tW decay channel at future electron–positron colliders

Based on a model-independent framework including the vectorlike top partner (VLQ-<math><mi>T</mi></math>), we investigate the prospect of discovering the singlet or doublet VLQ-<math><mi>T</mi></math> via the single production process <math><msup><mi>e</mi><mo>−</mo></msup><msup><mi>e</mi><mo>+</mo></msup><mo>→</mo><mi>T</mi><mover><mi>t</mi><mo>¯</mo></mover><mo>+</mo><mi>t</mi><mover><mi>T</mi><mo>¯</mo></mover></math> with the <math><mi>T</mi><mo>→</mo><mi>Z</mi><mi>t</mi></math> decay channel at a future high-energy linear <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collider with <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>3</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>. We focus on the hadronic decay of the top quark and two types of decay channels for the <math><mi>Z</mi></math> boson: <math><mi>Z</mi><mo>→</mo><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> and <math><mi>Z</mi><mo>→</mo><mi>ν</mi><mover><mi>ν</mi><mo>¯</mo></mover></math>. By carrying out a full simulation for the signals and the relevant Standard Model backgrounds, the <math><mn>2</mn><mi>σ</mi></math> exclusion limit and <math><mn>5</mn><mi>σ</mi></math> discovery prospects are, respectively, obtained on the VLQ-<math><mi>T</mi></math> mass and the coupling strength <math><msup><mi>g</mi><mo>*</mo></msup></math> with the integrated luminosity of <math><mrow><mn>5</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>ab</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>. In addition, we considered the initial state radiation and beamstrahlung effects as well as the systematic uncertainty effects of backgrounds, which are found to reduce the excluding or discovery capability.

Liu-Feng Du

Single production of vectorlike <math><mrow><mi>T</mi></mrow></math> quark at future high-energy linear <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collider

New vector-like quarks are predicted in many new physics scenarios beyond the Standard Model (SM). Based on a model-independent framework, we investigate the prospect of discovering the SU(2) singlet vector-like bottom quark (VLQ-B) in  $$e^{+}e^{-}$$  <math> <mrow> <msup> <mi>e</mi> <mo>+</mo> </msup> <msup> <mi>e</mi> <mo>-</mo> </msup> </mrow> </math>   collisions at 3 TeV Compact Linear Collider. We study the single VLQ-B production process  $$e^{-}e^{+}\rightarrow B{\bar{b}}\rightarrow Zb{\bar{b}}$$  <math> <mrow> <msup> <mi>e</mi> <mo>-</mo> </msup> <msup> <mi>e</mi> <mo>+</mo> </msup> <mo>→</mo> <mi>B</mi> <mover> <mrow> <mi>b</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> <mo>→</mo> <mi>Z</mi> <mi>b</mi> <mover> <mrow> <mi>b</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   with two types of decay channel:  $$Z\rightarrow \ell ^{+}\ell ^{-}$$  <math> <mrow> <mi>Z</mi> <mo>→</mo> <msup> <mi>ℓ</mi> <mo>+</mo> </msup> <msup> <mi>ℓ</mi> <mo>-</mo> </msup> </mrow> </math>  , and  $$Z\rightarrow \nu {\bar{\nu }}$$  <math> <mrow> <mi>Z</mi> <mo>→</mo> <mi>ν</mi> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>  . By carrying out a full simulation for the signals and the relevant SM backgrounds, the  $$2\sigma $$  <math> <mrow> <mn>2</mn> <mi>σ</mi> </mrow> </math>   exclusion limit and  $$5\sigma $$  <math> <mrow> <mn>5</mn> <mi>σ</mi> </mrow> </math>   discovery prospects are, respectively, obtained on the B quark mass and the coupling strength  $$g^{*}$$  <math> <msup> <mi>g</mi> <mrow> <mrow></mrow> <mo>∗</mo> </mrow> </msup> </math>   with the integrated luminosity of 5  $$\hbox {ab}^{-1}$$  <math> <msup> <mtext>ab</mtext> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> </math>  . Our numerical results show that the possible signals of the singlet VLQ-B might be detected at the future high-energy  $$e^{+}e^{-}$$  <math> <mrow> <msup> <mi>e</mi> <mo>+</mo> </msup> <msup> <mi>e</mi> <mo>-</mo> </msup> </mrow> </math>   linear colliders.

Search for single production of vector-like B quark decaying to bZ at future linear colliders

In this letter, we analyze the prospects of observing the new vector-like T-quark in the leptonic <math><mi>T</mi><mo>→</mo><mi>b</mi><mi>W</mi></math> decay channel at the Large Hadron Electron Collider (LHeC). The results show that the mixing between the T-quark with the first generation quarks can largely enhance the production cross section. We further study the observability of the single T through the process <math><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><mi>p</mi><mo>→</mo><mi>T</mi><mo>(</mo><mo>→</mo><mi>b</mi><msup><mrow><mi>W</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>)</mo><msub><mrow><mover><mrow><mi>ν</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mrow><mi>e</mi></mrow></msub><mo>→</mo><mi>b</mi><msup><mrow><mi>ℓ</mi></mrow><mrow><mo>+</mo></mrow></msup><mo>+</mo><msubsup><mrow><mi>E̸</mi></mrow><mrow><mi>T</mi></mrow><mrow><mi>m</mi><mi>i</mi><mi>s</mi><mi>s</mi></mrow></msubsup></math> at the LHeC with the proposed 140 GeV electron beam (with <math><mn>80</mn><mtext>%</mtext></math> polarization) and 7 TeV proton beam. To be as model-independent as possible, a simplified model method with only two free parameters (<math><msup><mrow><mi>g</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math> and <math><msub><mrow><mi>R</mi></mrow><mrow><mi>L</mi></mrow></msub></math>) has been applied. For three typical T-quark masses, the 3σ exclusion limits as well as the 5σ discovery region are respectively presented in terms of parameter space regions.

Single vector-like -quark Search via the → decay channel at the LHeC

In this paper, we study the possibility of detecting the heavy vector-like top partner T in a simplified model with the decay channel T→tZ at the Large Hadron Electron Collider (LHeC). We first investigate the single top partner production process including the intergenerational mixing and the results show that the mixing between the top partner with the first generation can largely enhance the production cross section. We further study the observability of the single top partner through the process e+p→T(→tZ)ν¯e→t(→bjj′)Z(→ℓ+ℓ−)ν¯e at the LHeC with the proposed 140 GeV electron beam and 7 TeV proton beam. For some typical heavy T quark masses, the 3 σ exclusion limits as well as the 5 σ discovery region are respectively presented in terms of parameter space regions.

Single production of the top partner in the T → tZ channel at the LHeC

Considering the constraints from collider experiments and dark matter detection, we investigate the SUSY effects in the Higgs production channels e+ e− → Zh at an e+ e− collider with a center-of-mass energy above 240 GeV and γγ → h → bb̄ at a photon collider with a center-of-mass energy above 125 GeV. In the parameter space allowed by current experiments, we find that the SUSY corrections to e+ e− → Zh can reach a few percent and the production rate of γγ → h → bb̄ can be enhanced by a factor of 1.2 over the SM prediction. We also calculate the exotic Higgs production e+ e−→ Zh1 in the next-to-minimal supersymmetric model (NMSSM) (h is the SM-like Higgs, h1 is the CP-even Higgs bosons which can be much lighter than h). We find that at a 250 GeV e+ e− collider the production rates of e+ e−→ Zh1 can reach 60 fb.

Junjie Cao

South Korea

Japan

Chengcheng Han

Jie Ren

Australia

Lei Wu

Jin-Min Yang

Yang Zhang

SUSY effects in Higgs production at high energy e+ e− collidersSupported by National Natural Science Foundation of China (NNSFC)(10821504, 11222548, 11305049, 11135003), Program for New Century Excellent Talents in University, and ARC Center of Excellence for Particle Physics at Tera-scale. C. Han is supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan