Yeong Gyun Kim

Measuring superparticle masses at hadron collider using the transverse mass kink

We present a detailed study of the collider observable mT2 applied for pair-produced superparticles decaying to visible particles and a pair of invisible lightest supersymmetric particles (LSPs). Analytic expressions of the maximum of mT2 over all events (mT2max) are derived. It is noticed that if the decay product of each superparticle involves more than one visible particle, mT2max being a function of the trial LSP mass mχ has a kink structure at mχ = true LSP mass, which can be used to determine the mother superparticle mass and the LSP mass simultaneously. To see how well mT2max can be constructed from collider data, a Monte-Carlo analysis of the gluino mT2 is performed for some superparticle spectra.

Singlet fermionic dark matter

We propose a renormalizable model of a fermionic dark matter by introducing a gauge singlet Dirac fermion and a real singlet scalar. The bridges between the singlet sector and the standard model sector are only the singlet scalar interaction terms with the standard model Higgs field. The singlet fermion couples to the standard model particles through the mixing between the standard model Higgs and singlet scalar and is naturally a weakly interacting massive particle (WIMP). The measured relic abundance can be explained by the singlet fermionic dark matter as the WIMP within this model. Collider implication of the singlet fermionic dark matter is also discussed. Predicted is the elastic scattering cross section of the singlet fermion into target nuclei for a direct detection of the dark matter. Search of the direct detection of the dark matter provides severe constraints on the parameters of our model.

M(T2)-assisted on-shell reconstruction of missing momenta and its application to spin measurement at the LHC

We propose a scheme to assign a 4-momentum to each WIMP in new physics event producing a pair of mother particles each of which decays to an invisible weakly interacting massive particle (WIMP) plus some visible particle(s). The transverse components are given by the value that determines the event variable M{sub T2}, while the longitudinal component is determined by the on-shell condition on the mother particle. Although it does not give the true WIMP momentum in general, this M{sub T2}-assisted on-shell reconstruction of missing momenta provides kinematic variables well correlated to the true WIMP momentum and thus can be useful for an experimental determination of new particle properties. We apply this scheme to some processes to measure the mother particle spin and find that spin determination is possible even without good knowledge of the new particle masses.

Neutralino dark matter in mirage mediation

We study the phenomenology of neutralino dark matter (DM) in a mirage mediation scenario of supersymmetry breaking which results from the moduli stabilization in some string/brane models. Depending upon the model parameters, especially the anomaly to modulus mediation ratio determined by the moduli stabilization mechanism, the nature of the lightest supersymmetric particle (LSP) changes from bino-like neutralino to Higgsino-like neutralino via a bino–Higgsino mixing region. For the bino-like LSP, the standard thermal production mechanism can give the right amount of relic DM density through the stop/stau–neutralino coannihilation or the pseudoscalar Higgs resonance process. We also examine the prospect of direct and indirect DM detection in various parameter regions of mirage mediation. Neutralino DM in the galactic halo might be detected by near future direct detection experiments in the case of the bino–Higgsino mixed LSP. The gamma ray flux from the galactic centre might be detectable also if the DM density profile takes a cuspy shape.

Singlet Fermionic Dark Matter explains DAMA signal

It has been suggested that, considering channeling effect, the order of a few GeV dark matters which are elastically scattered from detector nuclei might be plausible candidates reconciling the DAMA annual modulation signal with the results of other null experiments. We show that Singlet Fermionic Dark Matter can be such a dark matter candidate, simultaneously providing the correct thermal relic density which is consistent with the WMAP data.

LHC signature of mirage mediation

We study LHC phenomenology of mirage mediation scenario in which anomaly and modulus contributions to soft SUSY breaking terms are comparable to each other. A Monte Carlo study of mirage mediation, with model parameters α = 1, M0 = 500 GeV, nM = 1/2, nH = 1 and tan β = 10, is presented. It is shown that masses of supersymmetric particles can be measured in a model independent way, providing information on SUSY breaking sector. In particular, the mass ratio of gluino to the lightest neutralino for the benchmark scenario is determined to be 1.9 m/m10 3.1, well reproducing theoretical input value of m/m10 2.5 which is quite distinctive from the predictions m/m10 6 of other SUSY scenarios in which gaugino masses are unified at the GUT scale. The model parameters of mirage mediation can be also determined from various kinematic distributions.

Measuring the top quark mass with m_T2 at the LHC

We investigate the possibility to measure the top quark mass using the collider variable

Measuring the top quark mass with m(T2) at the LHC

m_{T2}

TeV scale partial mirage unification and neutralino dark matter

at the LHC experiment. Monte Carlo studies of

Comment on `A collider signature of the supersymmetric golden region'

m_{T2}