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

Characterizing Higgs portal dark matter models at the ILC

We study the Dark Matter (DM) discovery prospect and its spin discrimination in the theoretical framework of gauge invariant and renormalizable Higgs portal DM models at the ILC with $\sqrt{s} = 500$ GeV. In such models, the DM pair is produced in association with a $Z$ boson. In case the singlet scalar DM, the mediator is just the SM Higgs boson, whereas for the fermion or vector DM there is an additional singlet scalar mediator that mixes with the SM Higgs boson, which produces significant observable differences. After careful investigation of the signal and backgrounds both at parton level and at detector level, we find the signal with hadronically decaying $Z$ boson provides a better search sensitivity than the signal with leptonically decaying $Z$ boson. Taking the fermion DM model as a benchmark scenario, when the DM-mediator coupling $g_\chi$ is relatively small, the DM signals are discoverable only for benchmark points with relatively light scalar mediator $H_2$. And the spin discriminating from scalar DM is always promising while it is difficult to discriminate from vector DM. As for $g_\chi$ approaching the perturbative limit, benchmark points with the mediator $H_2$ in the full mass region of interest are discoverable. And the spin discriminating from both the scalar and fermion DM are quite promising.Comment: 26 pages, 9 figures, version accepted for publication in EPJ

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

Minimal SUGRA Model and Collider Signals

The SUSY signals in the dominant stau-neutralino coannihilation region at a 500(800) GeV linear collider are investigated. The region is consistent with the WMAP measurement of the cold dark matter relic density as well as all other current experimental bounds within the mSUGRA framework. The signals are characterized by an existence of very low-energy tau leptons in the final state due to small mass difference between stau_1 and chi_1 (5-15 GeV). We study the accuracy of the mass difference measurement with a 1^deg active mask to reduce a huge SM two-photon background.Comment: 4 pages, 3 figures, Talk presented at ICHEP04, Aug.16-22, Beijing, China, Numerical typos in Table 5 and 6 are corrected, no changes in figures and in other numerical result