The ILC as a natural SUSY discovery machine and precision microscope: from light higgsinos to tests of unification

The requirement of electroweak naturalness in simple supersymmetric models implies the existence of a cluster of four light higgsinos with mass $\sim 100-300$\,GeV, the lighter the better. While such light compressed spectra may be challenging to observe at LHC, the International Linear $e^+e^-$ Collider (ILC) with $\sqrt{s}>2m_{\rm higgsino}$ would serve as both a SUSY discovery machine and a precision microscope. We study higgsino pair production signatures at the ILC based on full, \texttt{Geant4-}based simulation of the ILD detector concept. We examine several benchmark scenarios that may be challenging for discovery at HL-LHC due to mass differences between the higgsino states between $20$ and $4$\,GeV. Assuming $\sqrt{s}= 500$\,GeV and 1000\,fb$^{-1}$ of integrated luminosity, the individual higgsino masses can be measured to $1-2\%$ precision in case of the larger mass differences, and at the level of $5\%$ for the smallest mass difference case. The higgsino mass splittings are sensitive to the electroweak gaugino masses and allow extraction of gaugino masses to $\sim 3-20\%$ (depending on the model). Extrapolation of gaugino masses via renormalization group running can test the hypothesis of gaugino mass unification. We also examine a case with natural generalized mirage mediation where the unification of gaugino masses at an intermediate scale apparently gives rise to a natural SUSY spectrum somewhat beyond the reach of HL-LHC.Comment: 43 pages, 33 figure

Photon-Photon processes at the International Linear Collider and BSM signatures with small mass differences

The International Linear Collider is a proposed $e^{+}e^{-}$ collider with tunable centre-of-mass energies and polarised beams. By performing high-precision measurements of Standard Model observables and searches for new particles the ILC can serve as a complementary machine to the LHC.In supersymmetric extensions of the Standard Model, higgsino-like charginos and neutralinos are preferred to have masses of the order of the electroweak scale by naturalness arguments. Such light $\tilde{\chi}_{1}^{\pm}$, $\tilde{\chi}^{0}_{1}$ and $\tilde{\chi}^{0}_{2}$ states can be almost mass degenerate. Due to their mass degeneracy it is very difficult to observe the decay of such higgsinos at hadron colliders. ILC being an $e^+e^-$ collider has the prospect of providing a very clean physics environment to observe or exclude such scenarios. However, in addition to the desired $e^{+}e^{-}\rightarrow\tilde{\chi}^{+}\tilde{\chi}^{-}$ processes, parasitic collisions of real and virtual photons radiated off the $e^+e^-$ beams occurat the rates depending on the centre-of-mass energy (250 GeV - 1 TeV) and other beam parameters. In this thesis the effects of such $\gamma\gamma\rightarrow$ low $p_{T}$ hadron overlay on the low $\Delta M$ higgsino analysis is studied.The study considers two benchmark points that exhibits mass differences of $\mathcal{O}$ [1 GeV] in the higgsino sector. In the given higgsino scenarios, the visible decay products have low transverse momenta due to the small mass differences between the higgsinos. The $\gamma\gamma\rightarrow$ low $p_{T}$ hadron overlay has a very similartopology to the signal event which makes the removal of the overlay very challenging.The standard methods to remove $\gamma\gamma$ background, e.g methods based on jet clustering remain inadequate. The study presents a newly developed track grouping algorithm which is based on the concept of displaced signal and $\gamma\gamma\rightarrow$ low $p_{T}$ hadron overlay vertices. By applying the track grouping algorithm to separate $\gamma\gamma\rightarrow$ low $p_{T}$ hadron tracks from the higgsino decay tracks, ananalysis has been performed using the full detector simulation for the International Large Detector (ILD). It is shown that the group tracking algorithm can very efficiently separate $\gamma\gamma\rightarrow$ low $p_{T}$ hadron tracks from the higgsinodecay tracks. The results from the analysis show that even with the presence of $\gamma\gamma\rightarrow$ low $p_{T}$ hadron overlay, the key observables of the higgsinos can be reconstructed with an uncertainty of a few percent. A comparison with the previous study which was performedwithout the inclusion of $\gamma\gamma\rightarrow$ low $p_{T}$ hadron events is made to enhance the understanding about the effects of the overlay on the higgsino analysis

Hadron Production in Photon-Photon Processes at the International Linear Collider

The International linear Collider(ILC) is a proposed e+− collider,designed to operate at energies from 91 GeV upto about 500 GeV range(with the possibility to upgrade to 1TeV). The highly clean conditionsprovided by ILC enables us to make high precision measurements e.gof the Higgs bosons and to search for new particles. In addition to thedesired e+− collisions, parasitic collisions of real and virtual photonsradiated off the e± beams occur at the rates of a few collisionsper bunch crossings. The centre of mass energies reach from few100 MeV up to the full e+− centre of mass energy. For all theseenergies, in particular the production of hadrons needs to be modelledcorrectly in order to estimate the impact of these backgrounds whichpile-up on each e+− event.Contributing in this context,we discuss thecurrent simulations of → hadron processes, evaluate their impacton the detector and introduce new methods to remove them from theinteresting physics events

Hadron Production in Photon-Photon Processes at the International Linear Collider

the ILC physics program enables us to make high precision measurements of themost celebrated “Higgs Boson” and to know more about the BSM particles. The γγbackgrounds are one of the major challenges we are facing today. As far as now wehave tried to suppress these backgrounds using the KT algorithm methods and havebeen successful in a certain ways. But the precision measurements of a few cases likeHiggsinos with very small mass differences and important cases like Higgs selfcouplingare very difficult due to γγ overlay. As the decay products of Higgsinoshave low momentum they move along the z-axis and thus cannot be distinguishedamong the γγ backgrounds using the KT algorithm methods. Higgs self-couplingevents are so very rare that while eradicating γγ backgrounds using KT algorithmthere are fair chances of loosing the important signals. In this presentation, we discussthe need of reliable simulation of the detailed properties of γγ events. We study the γγevents used in DBD simulations and compare it to the alternative descriptions andthus try to determine their properties