Neutralino Decays at the CERN LHC

We study the distribution of lepton pairs from the second lightest neutralino decay \tchi^0_2\to\tchi^0_1 l^+l^-. This decay mode is important to measure the mass difference between \tchi^0_2 and the lightest neutralino \tchi^0_1, which helps to determine the parameters of the minimal supersymmetric standard model at the CERN LHC. We found that the decay distribution strongly depends on the values of underlying MSSM parameters. For some extreme cases, the amplitude near the end point of the lepton invariant mass distribution can be suppressed so strongly that one needs the information of the whole m_{ll} distribution to extract m_{\tchi^0_2}-m_{\tchi^0_1}. On the other hand, if systematic errors on the acceptance can be controlled, this distribution can be used to constrain slepton masses and the Z\tchi^0_2\tchi^0_1 coupling. Measurements of the velocity distribution of \tchi^0_2 from samples near the end point of the m_{ll} distribution, and of the asymmetry of the p_T of leptons, would be useful to reduce the systematic errors.Comment: 23 pages, latex2e, 9 figures, minor change, accepted to PR

Using Tau Polarization for Charged Higgs Boson and SUSY Searches at LHC

The $\tau$ polarization can be easily measured at LHC in the 1-prong hadronic $\tau$ decay channel by measuring what fraction of the $\tau$-jet momentum is carried by the charged track. A simple cut requiring this fraction to be >0.8 retains most of the polarization of $\tau=$+1 $\tau$-jet signal while suppressing the polarization of $\tau=$-1 $\tau$-jet background and practically eliminating the fake $\tau$ background. This can be utilized to extract the charged Higgs signal. It can be also utilized to extract the SUSY signal in the stau NLSP region, and in particular the stau co-annihilaton region.Comment: 8 pages, 9 figures; Fig.8 and Fig.9 are replaced, published in "Physics at the Large Hadron Collider", A Platinum Jubilee Special Issue of the Indian National Science Academy, Springer (2009) p 20

Constraints on the Charged Higgs Sector from the Tevatron Collider Data on Top Quark Decay

The top quark data in the lepton plus $\tau$ channel offers a viable probe for the charged Higgs boson signal. We analyse the recent Tevatron collider data in this channel to obtain a significant limit on the $H^\pm$ mass in the large $\tan\beta$ region.Comment: 8 pages, LaTeX file; 2 figures included (PS files

Physics Prospects at the Hadron Colliders

I start with a brief introduction to the elementary particles and their interactions, Higgs mechanism and supersymmetry. The major physics objectives of the Tevatron and LHC colliders are identified. The status and prospects of the top quark, charged Higgs boson and superparticle searches are discussed in detail, while those of the neutral Higgs boson(s) are covered in a parallel talk by R.J.N. Phillips at this workshop.Comment: 16 pages Latex + 15 figures (available on request

CP Phases in Correlated Production and Decay of Neutralinos in the Minimal Supersymmetric Standard Model

We investigate the associated production of neutralinos $e^+e^-\to\tilde{\chi}^0_1\tilde{\chi}^0_2$ accompanied by the neutralino leptonic decay $\tilde{\chi}^0_2\to\tilde{\chi}^0_1 \ell^+\ell^-$, taking into account initial beam polarization and production-decay spin correlations in the minimal supersymmetric standard model with general CP phases but without generational mixing in the slepton sector. The stringent constraints from the electron EDM on the CP phases are also included in the discussion. Initial beam polarizations lead to three CP--even distributions and one CP--odd distribution, which can be studied independently of the details of the neutralino decays. We find that the production cross section and the branching fractions of the leptonic neutralino decays are very sensitive to the CP phases. In addition, the production--decay spin correlations lead to several CP--even observables such as lepton invariant mass distribution, and lepton angular distribution, and one interesting T--odd (CP--odd) triple product of the initial electron momentum and two final lepton momenta, the size of which might be large enough to be measured at the high--luminosity future electron--positron collider or can play a complementary role in constraining the CP phases with the EDM constraints.Comment: Revtex, 37 pages, 12 eps figure

Charged Higgs Boson Search at the Tevatron Upgrade Using Tau Polarization

We explore the prospect of charged Higgs boson search in top quark decay at the Tevatron collider upgrade, taking advantage of the opposite states of $\tau$ polarization resulting from the $H^\pm$ and $W^\pm$ decays. Methods of distinguishing the two contributions in the inclusive 1-prong hadronic decay channel of $\tau$ are suggested. The resulting signature and discovery limit of $H^\pm$ are presented for the Tevatron upgrade as well as the Tevatron$^\star$ and the Ditevatron options.Comment: 19 pages LaTeX + 6 figures (available on request

Probing Minimal Supergravity at the CERN LHC for Large tan⁡β\tan\beta

For large values of the minimal supergravity model parameter $\tan\beta$, the tau lepton and the bottom quark Yukawa couplings become large, leading to reduced masses of $\tau$-sleptons and $b$-squarks relative to their first and second generation counterparts, and to enhanced decays of charginos and neutralinos to $\tau$-leptons and $b$-quarks. We evaluate the reach of the CERN LHC $pp$ collider for supersymmetry in the mSUGRA model parameter space. We find that values of $m_{\tg}\sim 1500-2000$ GeV can be probed with just 10 fb$^{-1}$ of integrated luminosity for $\tan\beta$ values as high as 45, so that mSUGRA cannot escape the scrutiny of LHC experiments by virtue of having a large value of $\tan\beta$. We also perform a case study of an mSUGRA model at $\tan\beta =45$ where \tz_2\to \tau\ttau_1 and \tw_1\to \ttau_1\nu_\tau with $\sim 100$ branching fraction. In this case, at least within our simplistic study, we show that a di-tau mass edge, which determines the value of m_{\tz_2}-m_{\tz_1}, can still be reconstructed. This information can be used as a starting point for reconstructing SUSY cascade decays on an event-by-event basis, and can provide a strong constraint in determining the underlying model parameters. Finally, we show that for large $\tan\beta$ there can be an observable excess of $\tau$ leptons, and argue that $\tau$ signals might serve to provide new information about the underlying model framework.Comment: 22 page REVTEX file including 8 figure

Tau Polarization Asymmetry in B→Xsτ+τ−B\to X_s\tau^+\tau^-

Rare $B$ decays provide an opportunity to probe for new physics beyond the Standard Model. In this paper, we propose to measure the tau polarization in the inclusive decay $B\to X_s\tau^+\tau^-$ and discuss how it can be used, in conjunction with other observables, to completely determine the parameters of the flavor-changing low-energy effective Hamiltonian. Both the Standard Model and several new physics scenarios are examined. This process has a large enough branching fraction, $\sim {\rm few}\times 10^{-7}$, such that sufficient statistics will be provided by the B-Factories currently under construction.Comment: 11 pages, LaTex file with psfig. Figures included via uufiles. Lengthened version. Includes new calculation of Monte Carlo fit to Wilson coefficient

CP Violation in τ→3πντ\tau\rightarrow 3\pi\nu_\tau

We consider CP violating effects in the decays $\tau\rightarrow (3\pi)\nu_\tau$ where both the ${\rm J}^{\rm P}=1^+$ resonance, $a_1$, and ${\rm J}^{\rm P}=0^-$ resonance, $\pi^\prime$, can contribute. The interference between the $a_1$ and $\pi^\prime$ resonances can lead to enhanced CP-violating asymmetries whose magnitudes depend crucially on the $\pi^\prime$ decay constant, $f_{\pi^\prime}$. We make an estimate of $f_{\pi^\prime}$ with a simplified chiral Lagrangian coupled to a massive pseudoscalar field, and we compare the estimates from the non-relativistic quark model and from the QCD sum rule with the estimate from the `mock' meson model. We then estimate quantitatively the size of CP-violating effects in a multi-Higgs-doublet model and scalar-leptoquark models. We find that, while CP-violating effects in the scalar-leptoquark models may require more than $10^{10}$ $\tau$ leptons, CP-violating effects from the multi-Higgs-doublet model can be seen at the $2\sigma$ level with about $10^7$ $\tau$ leptons using the chiral Lagrangian estimate of $f_{\pi^\prime}=(1\sim 5)\times 10^{-3}$ GeV.Comment: Latex, 30 pages, 2 figures (not included). Three compressed postscript files of the paper available at ftp://ftp.kek.jp/kek/preprints/TH/TH-419/kekth419.ps.gz, Tau1.ps.gz, Tau2.ps.g