219 research outputs found

    Are light sneutrinos buried in LEP data?

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    Supersymmetry may resolve the disagreement between the precision electroweak data and the direct limit on the higgs mass, if there are light sneutrinos in the mass range 55 GeV < m_{\snu} < 80 GeV. Such sneutrinos should decay invisibly with 100% branching ratio and contribute to the γ\gamma + missing energy signal, investigated by all the LEP groups. It is shown that while the data accumulated by a single group may not be adequate to reveal such sneutrinos, a combined analysis of the data collected by all four groups will be sensitive to m_{\snu} in the above range. If no signal is found a lower bound on m_{\snu} stronger than that obtained from the ZZ-pole data may emerge.Comment: 12 pages, LaTeX, 1 postscript figure included, uses epsfig.sty Minor revisions in the discussion of future prospects, 1 ref adde

    Next to Minimal Higgs : Mass Bounds and Search Prospects

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    The Standard Model of electroweak interactions has one scalar doublet. The minimal extension of this sector is effected by adding a neutral, singlet scalar field. Depending on whether the singlet field has a non-zero vacuum expectation value, x, or not, the scenario has quite distinctive predictions. In particular, x unequal to 0 produces a mixing between the usual SU(2) doublet and the singlet, giving rise to two physical states and a goldstone boson with non-vanishing coupling to these. Presence of this coupling modifies the 2 jets + missing energy signal of the Bjorken process at LEP. We update the bounds on the Higgs mass using the LEP-1 data. We then explore, using parton-level Monte Carlo event generators, the production of these scalars at the LHC via gluon-gluon fusion and subsequent detection. We compare the signals with the expected backgrounds.Comment: 16 pages and 7 Postscript figures, Late

    Associated Higgs Production in CP-violating supersymmetry: probing the `open hole' at the Large Hadron Collider

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    A benchmark CP-violating supersymmetric scenario (known in the literature as `CPX-scenario') is studied in the context of the Large Hadron Collider (LHC). It is shown that the LHC, with low to moderate accumulated luminosity, will be able to probe the existing `hole' in the mh1m_{h_1}-tanβ\tan\beta plane, which cannot be ruled out by the Large Electron Positron Collider data. This can be done through associated production of Higgs bosons with top quark and top squark pairs leading to the signal \emph{dilepton + 5\leq{5} jets (including 3 b-jets) + missing pT{p_T}}. Efficient discrimination of such a CP-violating supersymmetric scenario from other contending ones is also possible at the LHC with a moderate volume of data.Comment: LaTeX, 19 pages, 5 figures, added references for section 2, typos correcte

    Lepton Flavours at the Early LHC Experiments as the Footprints of the Dark Matter Producing Mechanisms

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    The mSUGRA parameter space corresponding to light sleptons well within the reach of LHC and relatively light squarks and gluinos (mass \le 1 TeV) has three regions consistent with the WMAP data on dark matter relic density and direct mass bounds from LEP 2. Each region can lead to distinct leptonic signatures from squark-gluino events during the early LHC experiments (integrated luminosity 10 fb1\sim 10 ~fb^{-1} or even smaller). In the much studied stau-LSP coannihilation region with a vanishing common trilinear coupling (A0A_0) at the GUT scale a large fraction of the final states contain electrons and / or muons and ee - μ\mu - τ\tau universality holds to a good approximation. In the not so well studied scenarios with non-vanishing A0A_0 both LSP pair annihilation and stau-LSP coannihilation could contribute significantly to the dark matter relic density for even smaller squark-gluino masses. Our simulations indicate that the corresponding signatures are final states rich in τ\tau-leptons while final states with electrons and muons are suppressed leading to a violation of lepton universality. These features may be observed to a lesser extent even in the modified parameter space (with non-zero A0A_0) where the coannihilation process dominates. We also show that the generic mm-leptons + nn-jets+ ET\not! E_T signatures without flavour tagging can also discriminate among the three scenarios. However, the signals become more informative if the τ\tau and bb-jet tagging facilities at the LHC experiments are utilized.Comment: 28 page

    LHC Signature of the Minimal SUGRA Model with a Large Soft Scalar Mass

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    Thanks to the focus point phenomenon, it is quite {\it natural} for the minimal SUGRA model to have a large soft scalar mass m_0 > 1 TeV. A distinctive feature of this model is an inverted hierarchy, where the lighter stop has a significantly smaller mass than the other squarks and sleptons. Consequently, the gluino is predicted to decay dominantly via stop exchange into a channel containing 2b and 2W along with the LSP. We exploit this feature to construct a robust signature for this model at the LHC in leptonic channels with 3-4 b-tags and a large missing-E_T.Comment: Small clarifications added. Final version to appear in Phys. Lett.

    New Limits on Heavier Electroweakinos and their LHC Signatures

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    We investigate the heavier electroweakino sectors in several versions of the MSSM, which has not been explored so far in the light of the LHC data, and obtain new bounds using the ATLAS Run I constraints in the 3l+E ⁣ ⁣ ⁣ ⁣/T3l + {E\!\!\!\!/_T} channel. We also venture beyond the trilepton events and predict several novel multilepton + E ⁣ ⁣ ⁣ ⁣/T{E\!\!\!\!/_T} signatures of these electroweakinos which may show up before the next shutdown of the LHC.Comment: 12 pages;3 tables and some texts are added;numerical results remain unchange