• Mohammad Ebrahim Zomorrodian

      Articles written in Pramana – Journal of Physics

    • Next-to-next-leading order correction to 3-jet rate and event-shape distribution

      Mohammad Ebrahim Zomorrodian Alireza Sepehri Tooraj Ghaffary Parvin Eslami

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      The hadronic events from the $e^+ e^−$ annihilation data at the centre-of-mass energies ranging from 60 to 197 GeV were studied. The AMY and OPAL Collaborations offered a unique opportunity to test QCD by measuring the energy dependence of different observables. The coupling constant, $\alpha_s$, was measured by two different methods: first by employing the three-jet observables. Combining all the data, the value of as at next-to-next leading order (NNLO) was determined to be $0.117 \pm 0.004$(hard) ± 0.006(theo). Secondly, from the event-shape distributions, the strong coupling constant, $\alpha_s$, was extracted at NNLO and it’s evaluation was tested with the energy scale. The results were consistent with the running of $\alpha_s$, expected from QCD predictions. Averaging over different observables, $\alpha_s$ was determined to be $0.115 \pm 0.007$(hard) $\pm 0.003$(theo).

    • Next-to-next-to-leading order calculation of the strong coupling constant $\alpha_{s}$ by using moments of event-shape variables

      Samira Shoeibi Mohsenabadi Mohammad Ebrahim Zomorrodian

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      The next-to-next-to-leading order (NNLO) quantum chromodynamics (QCD) correction to the first three moments of the four event-shape variables in electron–positron annihilation, the thrust, heavy jet mass, wide, and total jet broadening, is computed. It is observed that the NNLO correction gives a better agreement between the theory and the experimental data. Also, by using the above observables, the strong coupling constant ($\alpha_{s}$) is determined and how much its value is affected by the NNLO correction is demonstrated. By combining the results for all variables at different centre-of-mass energies $\alpha_{s} (M_{Z^{\circ}}) = 0.1248 \pm 0.0009 ({\text{exp.}})_{-0.0144}^{+0.0283} ({\text{theo.}})$ is obtained.

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