arXiv subjects

Saiyad Ashanujjaman

Publications and source records attributed to Saiyad Ashanujjaman.

22 records · Page 2Linked to original sources

arXiv2021

Type-III see-saw: Search for triplet fermions in final states with multiple leptons and fat-jets at 13 TeV LHC

The type-III see-saw model holding out a riveting rationale for the minuscule neutrino masses caters for a well-to-do phenomenology at the Large Hadron Collider (LHC). Several searches targetting the triplet fermions have been performed at the LHC. Not only are the signals for the leptonic final states considered in these searches suppressed by the branching fractions of the Standard Model (SM) bosons, but they are also beset with considerably large SM backgrounds. Thus, these searches are deemed not to be sensitive enough in probing the triplet fermions much heavier than 1 TeV. To this end, we perform a search for the triplet fermions in final states with multiple leptons and fat-jets that are cleaner than the usual LHC searches and allow kinematic reconstruction of the triplets. After performing a systematic and comprehensive analysis with seven distinct final states, we project the required luminosities for both $3σ$ and $5σ$ discoveries of the triplet fermions as a function of their mass. The triplet fermions with mass as large as 1265 (1380) and 1480 (1600) GeV could be discovered with $5σ$ ($3σ$) significance at 500 and 3000 fb$^{-1}$ luminosities, respectively.

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arXiv2021

Revisiting Type-II see-saw: Present Limits and Future Prospects at LHC

The type-II see-saw mechanism based on the annexation of the Standard Model by weak gauge triplet scalar field proffers a natural explanation for the very minuteness of neutrino masses. Noting that the phenomenology for the non-degenerate triplet Higgs spectrum is substantially contrasting than that for the degenerate one, we perform a comprehensive study for an extensive model parameter space parametrised by the triplet scalar vacuum expectation value (VEV), the mass-splitting between the triplet-like doubly and singly charged scalars and the mass of the doubly charged scalar. Considering all Drell-Yan production mechanisms for the triplet-like scalars and taking into account the all-encompassing complexity of their decays, we derive the most stringent 95% CL lower limits on the mass of the doubly charged scalar for a vast model parameter space by implementing already existing direct collider searches by CMS and ATLAS. These estimated limits are beyond those from the existing LHC searches by approximately 50-230 GeV. However, we also find that a specific region of the parameter space is not constrained by the LHC searches. Then, we forecast future limits by extending an ATLAS search at high-luminosity, and we propose a search strategy that yields improved limits for a part of the parameter space.

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arXiv2021

Type-III Seesaw: Phenomenological Implications of the Information Lost in Decoupling from High-Energy to Low-Energy

The type-III seesaw seems to explain the very minuteness of neutrino masses readily and naturally. The high-energy see-saw theories usually involve a larger number of effective parametres than the physical and measurable parametres appearing in the low-energy neutrino phenomenology. Casas-Ibarra parametrisation facilitates to encode the information lost in integrating the heavy fermions out in an arbitrary complex orthogonal matrix. The CMS collaboration has already searched for triplet fermions in the type-III seesaw model with only one generation of triplet fermion flavour democratically decaying into SM leptons. We reinterpret this CMS search in the context of a realistic type-III seesaw model with two or three generations of triplet fermions, and endeavour to comprehend the implications of the foregoing matrix on the $95\%$ CL lower limit on the mass of the triplet fermions. We also discuss the phenomenological implication of the aforesaid matrix in view of charged lepton flavour violating observables and displaced decays of the triplet fermions at colliders.

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arXiv2020

The Genuine Type-V Seesaw Model: Phenomenological Introduction

We study a model which generates Majorana neutrino masses at tree-level via low-energy effective operator with mass-dimension-9. Introduction of such a higher dimensional operator brings down the lepton number violating mass scale to TeV making such model potentially testable at present or near future colliders. This model possesses several new $SU(2)_L$ fermionic multiplets, in particular, three generations of triplets, quadruplets and quintuplets, and thus a rich phenomenology at the LHC. As the lepton flavour violation arises very naturally in such setup, we put constraints on the Yukawa couplings and heavy fermion masses from the current experimental bounds on lepton flavour violating processes. We also obtain 95% CL lower bounds on the masses of the triplets, quadruplets and quintuplets using a recent CMS search for multilepton final states with 137 inverse femtobarn integrated luminosity data at 13 TeV center of mass energy. The possibility that the heavy fermions could be long-lived leaving disappearing charge track signatures or displaced vertex at the future colliders like LHeC, FCC-he, MATHUSLA, etc. is also discussed.

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