Dutta, Deepanwita2015-09-232023-10-262015-09-232023-10-262014ROLL NO. 09612105http://172.17.1.107:4000/handle/123456789/537Supervisor: Bipul BhuyanWe measure the branching fraction for the decay B0 s and search for the decay B0 s using 121.4 fb of data collected at the resonance with the Belle detector at the KEKB asymmetric energy B-factory located at the High Energy Accelerator Research Organization (KEK), Japan. B0 s branching fraction is computed to be (3.7+0.6 0.7) स 10 with a signal significance of 10.6 including the systematic uncertainties. This result is in good agreement with the theoretical predictions and a recent indirect estimate from LHCb. We do not observe any significant signal for the B0 s and have thus set the 90% confidence level upper limit on its branching fraction to be 3.1 This result improves on the previously published 90% confidence level upper limit by a factor of about 3 and provides the most stringent limit till date.enPHYSICSThesis