• S P Singh

      Articles written in Pramana – Journal of Physics

    • Composition dependence of density of states in a-Se$_{100−x}$Sn$_{x}$ thin films

      N Sharma S P Singh S Kumar

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      The present paper reports the DC conductivity measurements at high electric fields in vacuum evaporated amorphous thin films of a-Se$_{100−x}$Sn$_{x}$ ($x = 0, 2, 4, 6$) glassy alloys. Current–voltage ($I–V$) characteristics have been measured at various fixed temperatures. In these samples, at low electric fields, ohmic behaviour is observed. However, at high electric fields ($E \sim 10^{4}$ V/cm), non-ohmic behaviour is observed. An analysis of the experimental data confirms the presence of space charge limited conduction (SCLC) in the glassy materials studied in the present case. From the fitting of the data to the theory of SCLC, the density of defect states (DOS) near Fermi level is calculated. Increase in DOS with increase in Sn concentration has been found which could be correlated with the electronegativity difference between the two elements used here in making the glassy alloys. The peculiar role of the element Sn as an impurity in the pure Se glassy alloy is also discussed.

    • Search for $B_{s} \rightarrow \mu \mu \gamma$ at Large Hadron Collider

      S P Singh K Mazumdar J B Singh

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      The branching ratio for $B_{s} \rightarrow \ell^{+} \ell^{−}$ γ mode is of the same order as $B_{s} \rightarrow \ell^{+} \ell^{−}$, since there is no helicity suppression in the 3-body decay mode. New Physics beyond Standard Model may affect these rates favourably for experimental observation at LHC and simultaneous measurements of the modes $B_{s} \rightarrow \mu^{+} \mu^{−}$ and $B_{s} \rightarrow \mu^{+} \mu^{−} \gamma$ at LHC experiment will indicate the basic nature of the interaction at play. A simulation study has been performed to evaluate the potential of CMS detector to observe the more difficult mode of $B_{s} \rightarrow \mu^{+} \mu^{−} \gamma$. An upper limit of $2.08 \times 10^{−7}$ on the branching ratio is expected to be achieved corresponding to an integrated luminosity of 10 fb-1.

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