Prospects of Discovery for Supersymmetry at the Tevatron

We summarize a discovery potential for supersymmetric particles at the \ppbar collider of Tevatron with center-of-mass energy \sqrt{s} = 2 TeV and integrated luminosity \intlum = 15-30 \invfb. Any direct search is kinematically limited to below 450 \mgev. We, however, have a unique opportunity to test various supersymmetric scenarios by a measurement of the branching ratio for the rare decay mode \bsmumu. Using the background estimate in the CDF analysis of \bsmumu in Run I, we investigate the prospects for studying this mode in Run II. CDF would be sensitive to this decay for a branching ratio > 1.2 \times 10^{-8} with 15 \invfb (or, if a similar analysis holds for \Dzero, >6.5\times 10^{-9} for the combined data). For \tanb > 30, the \bsmumu search can probe the SUSY parameter space that cannot be probed by direct production of SUSY particles at Run II. An observation of \bsmumu with a large branching ratio > 7(14) \times 10^{-8} (feasible with only 2 \invfb) would be sufficient to exclude the mSUGRA model for \tan\beta \leq 50 (55) including other experimental constraints. For some models, the branching ratio can be large enough to be detected even for small $\tan\beta$ and large \mhalf.Comment: 16 pages, latex, 4 figures, talk at 10th International Conference on Supersymmetry and Unification of Fundamental Interactions (SUSY02),June 17-23, 2002, DESY, Hamburg, German

Probing Light Nonthermal Dark Matter at the LHC

This paper investigates the collider phenomenolgy of a minimal nonthermal dark matter model with a 1-GeV dark matter candidate, which naturally explain baryongensis. Since the light dark matter is not parity-protected, it can be singly produced at the LHC. This leads to large missing energy associated with an energetic jet whose transverse momentum distribution is featured by a Jacobian-like shape. The monojet, dijet, paired dijet and 2 jets + missing energy channels are studied. Currently existing data at Tevatron and LHC offer significant bounds on our model.Comment: 10 pages, 7 figure

Heavy Neutrino Search via the Higgs boson at the LHC

In the inverse see-saw model the effective neutrino Yukawa couplings can be sizable due to a large mixing angle between the light $(\nu)$and heavy neutrinos $(N)$. When the right handed neutrino $(N)$ can be lighter than the Standard Model (SM) Higgs boson $(h)$. It can be produced via the on-shell decay of the Higgs, $h\to N\nu$ at a significant branching fraction at the LHC. In such a process $N$ mass can be reconstructed in its dominant $N\rightarrow W \ell$ decays. We perform an analysis on this channel and its relevant backgrounds, among which the $W+$jets background is the largest. Considering the existing mixing constraints from the Higgs and electroweak precision data, the best sensitivity of the heavy neutrino search is achieved for benchmark $N$ mass at 100 and 110 GeV for upcoming high luminosity LHC runs.Comment: 22 pages, 7 Figures, updated analysis, model part extended, matched journal version in EPJ

Prospects for discovery and spin discrimination of dark matter in Higgs portal DM models and their extensions at 100 TeV pppp collider

We study the discovery and discriminating prospects of the Higgs portal dark matter (DM) models for scalar, fermion and vector DM and their extensions in proton-proton ($pp$) collisions. The $t\bar{t}+$DM associated production in dileptonic final states is considered, in which the stransverse mass of two leptons is found to be effective in suppressing the Standard Model backgrounds along with the missing transverse energy and the angle between two leptons. The distributions of missing transverse energy and polar angle between two leptons are used for a discrimination of the spin nature of DM. For the proposed benchmark points, the discovery/exclusion can be made with an integrated luminosity less than 1 ab$^{-1}$ given a 1\% systematic uncertainty, while the spin discrimination require integrated luminosity of a few O(10) ab$^{-1}$ given a 0.5\% systematic uncertainty. The DM phenomenology is also discussed. A consistent DM candidate can be obtained either by extending our model where the Higgs portal couples to excited dark states that decay into DM, or modifying the coupling form into pseudoscalar.Comment: 25 pages, 13 figures; discussions of systematic uncertainty added; matches the published versio

Searching for Top Squarks at the LHC in Fully Hadronic Final State

We pursue a scenario where the lighter top squark (stop) mass is accessible for the Large Hadron Collider (LHC) in the near future, while gluinos and first two generation squarks are heavier. At $\sqrt{s} = 8$ TeV, we investigate the identification of stops which decay predominantly into a top quark and the stable lightest supersymmetric particle. We use a simple kinematical variable, $M3$, to reconstruct two top quarks which are pair-produced from the stops, in the fully hadronic channel. The dominant Standard Model (SM) background for this signal stems from $t\bar t$ plus jets, with one top quark decaying into $bl\nu$, where the lepton is undetected and the $\nu$ produces missing transverse momentum. The lepton identification efficiency is thus crucial in order to estimate the background correctly. We identify kinematical variables to reduce the SM background. We find that it is possible to achieve signal and background cross-section at similar levels for stop masses around $350 - 500$ GeV for a neutralino mass of 100 GeV.Comment: 7 pages, 6 figure

p38 Mitogen-activated Protein Kinase Regulates Oscillation of Chick Pineal Circadian Clock

Extracellular signal-regulated kinase (ERK) and p38 are members of the mitogen-activated protein kinase (MAPK) family, and in some cases these kinases serve for closely related cellular functions within a cell. In a wide range of animal clock structures, ERK plays an important role in the circadian time-keeping mechanism. Here we found that immunoreactivity to p38 protein was uniformly distributed among cells in the chick pineal gland. On the other hand, a constant level of activated p38 was detected over the day, predominantly in the follicular and parafollicular pinealocytes that are potential circadian clock-containing cells. Chronic application of SB203580, a selective and reversible inhibitor of p38, to the cultured chick pineal cells markedly lengthened the period of the circadian rhythm of the melatonin release (up to 28.7 h). Noticeably, despite no significant temporal change of activated p38 level, a 4-h pulse treatment with SB203580 delayed the phase of the rhythm only when delivered during the subjective day. These results indicate a time-of-day-specific role of continuously activated p38 in the period length regulation of the chick pineal clock and suggest temporally separated regulation of the clock by two MAPKs, nighttime-activated ERK and daytime-working p38