Supersymmetric lepton flavour violation in a linear collider: the role of charginos

The occurrence of a significant amount of supersymmetric lepton flavour violation at laboratory energies, through $\tilde\nu_\mu - \tilde\nu_\tau$ mixing, has become a realistic possibility in the wake of the super-Kamiokande atmospheric neutrino result. This effect can be observed in an e+e- linear collider with the distinct final state tau+mu+ jets+E_T. We show that the pair production of charginos can make an important contribution to this process and has to be taken into account in addition to that of sneutrinos or charged sleptons. Some case studies are presented with CM energies of 500 and 800 GeV and integrated luminosities of 50, 500 and 1000 fb-1.Comment: 15 pages, latex, including 2 figure

CP Phases in Supersymmetric Tri-lepton Signals at the Tevatron

We have analyzed the supersymmetric tri-lepton signals for sparticle searches at the Tevatron in the minimal supersymmetric standard model with general CP phases without generational mixing. The CP phases may affect very strongly the chargino and neutralino mass spectrums and $\sigma(p\bar{p}\to\tilde{\chi}^-_1\tilde{\chi}^0_2)$ as well as ${\cal B}(\tilde{\chi}^-_1\to\tilde{\chi}^0_1\ell^-\nu)$ and ${\cal B}(\tilde{\chi}^0_2\to\tilde{\chi}^0_1\ell^+\ell^-)$. Even under the stringent constraints from the electron electric dipole moment the CP phases can lead to a minimum of the tri-lepton event rate for their non-trivial values.Comment: 10 pages, 3 eps figures, largely revised by including the electron EDM constraint

Chargino Pair Production at e+e−e^+e^- Colliders with Polarized Beams

The chargino $\tilde{\chi}^\pm_{1,2}$ system can be reconstructed completely in $e^+e^-$ collisions. By measuring the total cross sections and the asymmetries with polarized beams in $e^+e^-\to\tilde{\chi}_i^+ \tilde{\chi}_j^- [i,j=1,2]$, the chargino masses and the gaugino-higgsino mixing angles of these states can be determined very accurately. If only the lightest charginos $\tilde{\chi}_1^\pm$ are kinematically accessible, transverse beam polarization is needed to determine the mixing angles unambiguously. From these observables the fundamental SUSY parameters can be derived: the SU(2) gaugino mass $M_2$, the modulus and the cosine of the CP-violating phase of the higgsino mass parameter $\mu$, and $\tan\beta = v_2/v_1$, the ratio of the vacuum expectation values of the two neutral Higgs doublet fields. [The remaining two-fold ambiguity of the phase can be resolved by measuring the normal polarization of the charginos.]Comment: 19 pages including 4 figure

The interplay between the charged Higgs and squark-gluino events at the LHC

In some extensions of the standard model with extended Higgs sectors, events from new particle production may pass the selection criteria for Higgs search in different channels at the LHC - 14 TeV and mimic Higgs signals. This intriguing possibility is illustrated by PYTHIA based simulations using several representative points in the parameter space of the minimal supersymmetric standard model (MSSM) including a point in the minimal supergravity model consistent with the Dark matter (DM) relic density data. Our simulations explore the interplay between the charged Higgs signal and typical squark-gluino events. We argue that the standard selections like the one based on the polarization properties of the $\tau$'s from charged Higgs decay, though adequate for handling the SM background, may not be very efficient in the presence of SUSY backgrounds. We then propose an alternative search strategy based on pure kinematics which sufficiently controls both the SM and the MSSM backgrounds. For charged Higgs masses ($H^{\pm}$) in the deep decoupling regime (600 GeV \lsim m_{H^{\pm}} \lsim 800 GeV) this method works well and extends the LHC reach close to 800 GeV for an integrated luminosity of 30 $fb^{-1}$ with or without the SUSY background. For a lighter charged Higgs a judicious combination of the old selections and some of the cuts proposed by us may disentangle the Higgs signal from the squark-gluino backgrounds quite effectively

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

Higgs and SUSY Searches at LHC

I start with a brief introduction to Higgs mechanism and supersymmetry. Then I discuss the theoretical expectations, current limits and search strategies for Higgs boson(s) at LHC --- first in the SM and then in the MSSM. Finally I discuss the signatures and search strategies for the superparticles.Comment: Typos and figure styles corrected; LaTeX (28 pages) including 13 ps files containing 11 figures; Invited talk at the 5th Workshop on High Energy Physics Phenomenology (WHEPP-5), Pune, India, 12 - 25 January 199