1,321 research outputs found

    Proposing "b-Parity" - a New Approximate Quantum Number in Inclusive b-jet Production - as an Efficient Probe of New Flavor Physics

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    We consider the inclusive reaction \ell^+ \ell^- -> nb +X (n = number of b-jets) in lepton colliders for which we propose a useful approximately conserved quantum number b_P=(-1)^n that we call b-Parity (b_P). We make the observation that the Standard Model (SM) is essentially b_P-even since SM b_P-violating signals are necessarily CKM suppressed. In contrast new flavor physics can produce b_P=-1 signals whose only significant SM background is due to b-jet misidentification. Thus, we show that b-jet counting, which relies primarily on b-tagging, becomes a very simple and sensitive probe of new flavor physics (i.e., of b_P-violation).Comment: 5 pages using revtex, 2 figures embadded in the text using epsfig. As will appear in Phys.Rev.Lett.. Considerable improvement was made in the background calculation as compared to version 1, by including purity parameters, QCD effects and 4-jets processe

    A Configurationally-Resolved-Super-Transition-Arrays method for calculation of the spectral absorption coefficient in hot plasmas

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    A new method, 'Configurationally-Resolved-Super-Transition-Arrays', for calculation of the spectral absorption coefficient in hot plasmas is presented. In the new method, the spectrum of each Super-Transition-Array is evaluated as the Fourier transform of a single Complex Pseudo Partition Function, which represents the exact analytical sum of the contributions of all constituting unresolved transition arrays sharing the same set of one-electron solutions. Thus, in the new method, the spectrum of each Super-Transition-Array is resolved down to the level of the (unresolved) transition arrays. It is shown that the corresponding spectrum, evaluated by the traditional Super-Transition-Arrays (STA) method [A. Bar Shalom, J. Oreg, W.H. Goldstein, D. Shvarts and A. Zigler, Phys. Rev. A 40, 3183 (1989)], is just the coarse grained Gaussian approximation of the Configurationally-Resolved-Super-Transition-Array. A new computer program is presented, capable of evaluating the absorption coefficient by both the new configurationally resolved and the traditional Gaussian Super-Transition-Arrays methods. A numerical example of gold at temperature 1keV and density 0.5 gr/cm^{3}, is presented, demonstrating the simplicity, efficiency and accuracy of the new method

    New scalar resonances from sneutrino-Higgs mixing in supersymmetry with small lepton number (R-parity) violation

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    We consider new s-channel scalar exchanges in top quark and massive gauge-bosons pair production in e+e- collisions, in supersymmetry with a small lepton number violation. We show that a soft bilinear lepton number violating term in the scalar potential which mixes the Higgs and the slepton fields can give rise to a significant scalar resonance enhancement in e+e- -> ZZ, W+W- and in e+e- -> t t(bar). The sneutrino-Higgs mixed state couples to the incoming light leptons through its sneutrino component and to either the top quark or the massive gauge bosons through its Higgs component. Such a scalar resonance in these specific production channels cannot result from trilinear Yukawa-like R-parity violation alone, and may, therefore, stand as strong evidence for the existence of R-parity violating bilinears in the supersymmetric scalar potential. We use the LEP2 measurements of the WW and ZZ cross-sections to place useful constrains on this scenario, and investigate the expectations for the sensitivity of a future linear collider to these signals. We find that signals of these scalar resonances, in particular in top-pair production, are well within the reach of linear colliders in the small lepton number violation scenario.Comment: 22 pages in revtex, 10 figures embadded in the text using epsfi

    Production and decay of the neutral top-pion in high energy e+e−e^{+}e^{-} colliders

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    We study the production and decay of the neutral top-pion πt0\pi_{t}^{0} predicted by topcolor-assisted technicolor(TC2) theory. Our results show that, except the dominant decay modes bbˉb\bar{b}, tˉc\bar{t}c and gggg, the πt0\pi_{t}^{0} can also decay into γγ\gamma\gamma and ZγZ \gamma modes. It can be significantly produced at high energy e+e−e^{+}e^{-} collider(LC) experiments via the processes e+e−→πt0γe^{+}e^{-}\to \pi_{t}^{0}\gamma and e+e−→Zπt0e^{+}e^{-}\to Z\pi_{t}^{0}. We further calculate the production cross sections of the processes e+e−→γπt0→γtˉce^{+}e^{-}\to\gamma\pi_{t}^{0}\to\gamma\bar{t}c and e+e−→Zπt0→Ztˉce^{+}e^{-}\to Z\pi_{t}^{0}\to Z\bar{t}c. We find that the signatures of the neutral top-pion πt0\pi_{t}^{0} can be detected via these processes.Comment: Latex file, 13 Pages, 6 eps figures. to be published in Phys.Rev.

    CP Nonconservation in ppˉ→tbˉXp\bar p\to t\bar b X at the Tevatron

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    The reaction ppˉ→tbˉXp\bar p\to t\bar bX is found to be rather rich in exhibiting several different types of CP asymmetries. The spin of the top quark plays an important role. Asymmetries are related to form factors arising from radiative corrections of the tbWtbW production vertex due to non-standard physics. As illustrations, effects are studied in two Higgs Doublet Models and in Supersymmetric Models; asymmetries up to a few percent may be possible.Comment: 14 pages, 3 figures. Note: replaced due to minor problems that appeared on some postscript previewers. No change in conten

    The flavor changing top decay t-->c+sneutrino or sneutrino-->t+c(bar) in the MSSM without R-parity

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    Widths for the new flavor changing top quark decay t-->c+sneutrino or for the reversed sneutrino decay sneutrino-->t+c(bar) are calculated in the MSSM without R-parity conservation. For large \tan\beta, e.g., \tan\beta ~ m_t/m_b ~ 40, Br(t-->c+sneutrino) > 10^{-5} or Br(sneutrino-->t+c(bar)) > 10^{-6} in a relatively wide range of the supersymmetric parameter space as long as there is more than one non-zero R-parity violating coupling. In the best cases, with a typical squark mass around 100 GeV, we find that Br(t-->c+sneutrino) ~ 10^{-4} - 10^{-3} or Br(sneutrino-->t+c(bar)) ~ 10^{-5} - 10^{-4}. For \tan\beta ~ O(1) the corresponding branching ratios for both top or sneutrino decays are too small to be measured at the LHC. Therefore, the decays t-->c+sneutrino or sneutrino-->t+c(bar) appear to be sensitive to \tan\beta and may be detected at the LHC. The branching ratios of the corresponding decays to an up quark instead of a charm quark, e.g., t-->u+sneutrino or sneutrino-->t+u(bar), may also be similar.Comment: 23 pages, plain latex, 8 figures embadded in the text using epsfi

    Low-temperature dependence of the thermo-magnetic transport properties of the SrTiO3/LaAlO3 interface

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    We report transport measurements, including: Hall, Seebeck and Nernst Effect. All these transport properties exhibit anomalous field and temperature dependences, with a change of behavior observed at about H 1.5T and T 15K. We were able to reconcile the low-temperature-low-field behavior of all transport properties using a simple two band analysis. A more detailed model is required in order to explain the high magnetic field regime.Comment: 6 pages, 7 figure
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