Signature of Charged to Neutral Higgs Boson Decay at the LHC in SUSY Models

We study the signature of $H^\pm$ decay into $h^0W$ at the LHC in SUSY models. It has only marginal viability in the MSSM. But in the singlet extensions like the NMSSM one can have a spectacular signature for $H^\pm$ decay into $(h^0,A^0)W$ over a significant domain of parameter space.Comment: LaTeX file, 11 pages plus two PostScript figure

The Hadronic Tau Decay Signature of a Heavy Charged Higgs Boson at LHC

The hadronic tau decay channel offers by far the best signature for heavy charged Higgs boson search at the LHC in the large $\tan\beta$ region. By exploiting the distinct polarization of the tau and its large transverse mass, along with the accompanying missing--$p_T$, one can probe for a charged Higgs boson up to a mass of about 600 GeV in an essentially background-free environment. The transverse mass distribution of the tau jet also provides a fairly unambiguous estimate of the charged Higgs boson mass.Comment: 11 pages, latex, including 3 figure

Detecting heavy charged Higgs bosons at the LHC with triple b-tagging

We investigate the charged Higgs boson signal at the LHC using its dominant production and decay modes with triple b-tagging, i.e. $tH^- \to t\bar tb \to b\bar bb W^+ W^-$, followed by leptonic decay of one W and hadronic decay of the other. We consider the continuum background from the associated production of $t\bar t$ with a b- or a light quark or gluon jet, which can be mis-tagged as b-jet. We reconstruct the top quark masses to identify the 3rd b-jet accompanying the $t\bar t$ pair, and use its p_T distribution to distinguish the signal from the background. Combining this with the reconstruction of the $H^\pm$ mass gives a viable signature over two interesting regions of the parameter space - i.e. $\tan\beta \sim 1$ and $\sim m_t/m_b$.Comment: 10 pages, latex, 4 figure

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

A Minimal See-Saw Model for Hierarchical Neutrino Masses with Large Mixing

The atmospheric and solar neutrino oscillation data suggest hierarchical neutrino masses with at least one large mixing. The simplest see-saw models for reconciling the two features are U(1) extensions of the SM with flavour dependent gauge charges. I discuss a minimal model of this type containing two heavy right-handed neutrinos, which have normal Dirac couplings to $\nu_\mu$ and $\nu_\tau$ but suppressed ones to $\nu_e$. It can naturally account for the large (small) mixing solutions to the atmospheric (solar) neutrino oscillation data.Comment: 6 pages, Latex, Invited Talk at the 6th San Miniato Topical Seminar on `Neutrino and Astroparticle Physics', to appear in Nuclear Physics B (Proc. Suppl.

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

SUSY Contributions to RbR_b and Top Decay

I report on a systematic analysis of the MSSM parameter space to obtain the best SUSY solution to the $R_b$ anomaly within the constraint of top quark decay. Phenomenological implications for top decay and direct stop production at the Tevatron collider are discussed.Comment: Latex file (3 pages)+ 2 ps files containing figures. Invited talk at SUSY96, Maryland, May 199

Using Tau Polarization to Sharpen up the SUGRA Signal at Tevatron

The most promising source of SUGRA signal at the Tevatron collider is the pair-production of electroweak gauginos, followed by their leptonic decay. In the parameter range corresponding to dominant leptonic decay of these gauginos one or more of the leptons are expected to be $\tau$ with $P_\tau \simeq +1$. This polarization can be effectively used to distinguish the signal from the background in the 1-prong hadronic decay channel of $\tau$ by looking at the fractional $\tau$-jet momentum carried by the charged prong.Comment: 11 pages, LateX, 2 figures, discussion on polarization effect added, final version to be published in PL

Using Tau Polarization as a Distinctive SUGRA Signature at LHC

In the minimal SUGRA model the lighter tau slepton is expected to be the second lightest superparticle over a large parameter range at large $\tan\beta$. Consequently one expects a viable SUGRA signal at LHC in the tau lepton channel coming from the decay of these tau sleptons. The model predicts the polarization of this tau lepton to be +1 to a very good accuracy. We show how this prediction can be tested by looking at the momentum fraction of the tau-jet, carried by the charged prong, in its 1-prong hadronic decay channel.Comment: 13 pages, 3 figures. Minor changes and one reference added. Version to be published in PLB. Reprot: TIFR/TH/02-1

Muon Spectra of Quasi-Elastic and 1-Pion Production Events in LBL Neutrino Oscillation Experiments

The muon energy spectra of the quasi-elastic and 1-pion production events in a LBL experiment, like K2K, are predicted to follow closely the neutrino energy spectrum, with downward shifts of the energy scale by $/2 M$ and $( + M_\Delta^2 - M^2)/2 M$ respectively. These predictions seem to agree with the observed muon spectra in the K2K nearby detector. The corresponding muon spectra in the far-away (SK) detector are predicted to show characteristic spectral distortions induced by $\nu_\mu$ oscillation. Comparison of the predicted spectral distortions with the observed muon spectra of the 1-Ring and 2-Ring muon events in the SK detector will help to determine the oscillation parameters. The results will be applicable to other LBL experiments as well.Comment: 13 pages. One figure and a few comments added, final version to appear in P