Search for the Exicted Leptons in pp Collisions at Center of Mass Energy s 13 TeV

Abstract

newline Search for Excited Leptons in pp Collisions at Center of Mass Energy, and#8730;s = 13 TeV. newlineABSTRACT newlineThe main aim of the particle physics is to understand and investigate the most fundamental constituents/building blocks of the matter and the forces governing them. Within the Standard Model (SM) framework quarks and leptons are considered to be the fundamental particles. The existences of these particles and their various properties have been verified by the different experiments over the period of time. In spite its great success, SM is not regarded as the complete theory of universe, which gives rise to the possibility of new physics beyond SM. The existence of three nearly identical generations of quarks and leptons strongly suggest the possibility of underlying sub-structure of these particles. A search for the leptonic sub-structure or study of lepton compositeness is one of the important physics motivations of the Large Hadron Collider (LHC). A group of models have been developed assuming the compositeness of leptons and quarks which are considered to be made up of more fundamental particles known as preons . Various past and present experiments have put different lower bound on compositeness scale (and#923;) and mass of excited leptons (and#119872;and#119902;and#8727;). These excited leptons are considered to interact with their SM counterparts via gauge interactions as well as the contact interactions for the compositeness scale, and#923; and#8804; and#8730;s. For the present research work we are considering the decay of excited leptons via gauge interactions and the possible decay mode is neutral-current decays and#8467;*and#8594;and#8467;Z. newlineA search for dileptons (muon or electron), originating from the production of pair of a SM lepton and excited lepton is presented. Excited lepton subsequently decays into a SM lepton and boosted Z boson thus forming a dilepton and Z boson final state. The analyzed data corresponds to an integrated luminosity of 35.9 fb-1 recorded with the CMS detector at the LHC in 2016 in proton-proton collisions at center-of-mass energy and#8730;s = 13 TeV. The search is conducted in the decays of the lepton-excited lepton pairs and#8467;and#8467;*and#8594;and#8467;and#8467;Z with the Z boson decaying hadronically to a pair of quarks and normal standard model lepton. As and#8467;* is very massive so its decay results in very highly boosted Z boson which further decays into two highly collimated daughter quarks. The daughter quarks are reconstructed as a fat jet . The final state of the decay comprises of two SM leptons (muon or electron) and a fat jet. The exclusion limits are set xi newlineon the sigma times branching ratio (and#963;×BR) as a function of excited lepton mass and the compositeness scale and#923;. newlineKeywords: SM, Compositeness, LHC, CMS, Excited Lepton, Preons, Luminosity, Highly Boosted, Cross-Section, Branching Ratio. newlinexii