2,275 research outputs found

    Study of the Ξ›bβ†’Nβˆ—β„“+β„“βˆ’\Lambda_{b} \to N^\ast \ell^+ \ell^- decay in light cone sum rules

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    The form factors of the Ξ›bβ†’Nβˆ—β„“+β„“βˆ’\Lambda_{b} \to N^\ast \ell^+ \ell^- decay are calculated in the framework of the light cone QCD sum rules. In the calculations the contribution of the negative parity Ξ›bβˆ—\Lambda_b^\ast baryon is eliminated by constructing the sum rules for different Lorentz structures. Furthermore the branching ratio of the semileptonic Ξ›bβ†’Nβˆ—β„“+β„“βˆ’\Lambda_b \to N^\ast \ell^+ \ell^- decay is calculated. The numerical study for the branching ratio of the Ξ›bβ†’Nβˆ—β„“+β„“βˆ’\Lambda_{b} \to N^\ast \ell^+ \ell^- decay indicates that it is quite large and could be measurable at future planned experiments to be conducted at LHCb.Comment: 21 pages, 2 figures, LaTeX formatte

    Analysis of the radiative decays Ξ£Qβ†’Ξ›QΞ³\Sigma_Q \to \Lambda_Q \gamma and ΞQβ€²β†’ΞžQΞ³\Xi^\prime_Q \to \Xi_Q \gamma in light cone sum rules

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    The light cone sum rules method is used in studying the radiative decays Ξ£Qβ†’Ξ›QΞ³\Sigma_Q \to \Lambda_Q \gamma and ΞQβ€²β†’ΞžQΞ³\Xi^\prime_Q \to \Xi_Q \gamma. Firstly, the sum rules for the form factor F2(Q2=0)F_2(Q^2=0) responsible for these transitions is constructed. Using this result the decay widths of the above--mentioned decays are calculated and analyzed. A comparison of our predictions on the decay widths of considered transitions with the predictions of the other approaches is presented.Comment: 13 pages, no figures, LaTeX formatte

    Adaptive fair channel allocation for QoS enhancement in IEEE 802.11 wireless LANs

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    The emerging widespread use of real-time multimedia applications over wireless networks makes the support of quality of service (QoS) a key problem. In this paper, we focus on QoS support mechanisms for IEEE 802.11 wireless ad-hoc networks. First, we review limitations of the upcoming IEEE 802.11e enhanced DCF (EDCF) and other enhanced MAC schemes that have been proposed to support QoS for 802.11 ad-hoc networks. Then, we describe a new scheme called adaptive fair EDCF that extends EDCF, by increasing the contention window during deferring periods when the channel is busy, and by using an adaptive fast backoff mechanism when the channel is idle. Our scheme computes an adaptive backoff threshold for each priority level by taking into account the channel load. The new scheme significantly improves the quality of multimedia applications. Moreover, it increases the overall throughput obtained both in medium and high load cases. Simulution results show that our new scheme outperforms EDCF and other enhanced schemes. Finally, we show that the adaptive fair EDCF scheme achieves a high degree of fairness among applications of the same priority level
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