BEYOND THE BORN APPROXIMATION: A PRECISE COMPARISON OF e + p AND e − p ELASTIC SCATTERING IN THE CEBAF LARGE ACCEPTANCE

How well we know the structure of the proton depends on our knowledge of the form factors of the proton. The ratio of the electromagnetic form factors of the proton measured by the Rosenbluth and the polarization transfer methods differ by a factor of 3 at four momentum transfer squared (Q 2)=5.6 GeV 2. The two photon exchange (TPE) effect is the leading candidate to explain this discrepancy. The theoretical estimates of the TPE effect are model dependent so precise measurement is required to resolve this problem. The TPE effect can be measured in a model independent way by measuring the ratio of positron-proton to electron-proton elastic scattering cross-sections. We produced a simultaneously mixed electron-positron beam in the engineering test run conducted in October 2006 and measured the e + p/e − p ratio using the CEBAF large acceptance spectrometer (CLAS). Due to the luminosity constraint our kinematic coverage is limited to low Q2 and high ε (longitudinal polarization of the virtual photon). We continued our background study through GEANT4 simulation developed for the test run design in order to find more background sources and to design required shielding. The simulation is validated by using the test run data and is used further to optimize the luminosity for the final experiment. We are able to increase the luninosity by an order of magnitude for the upcoming final run. The final experiment will extend the data in high Q2 and low ε region where TPE effec

Original Article Study on the refractive errors of school going children of Pokhara city in Nepal

Objectives: Refractive errors are the one of the most common visual disorders found worldwide in school going children and it is also one of the causes of blindness. It can easily be prevented, if timely proper measures are taken. In Kathmandu valley and Mechi Zone of Nepal, the distribution of refractive errors was found to be very high. No records are available from the Western part of Nepal. Considering the importance of the refractive errors the present study had been undertaken in Pokhara city. Materials and methods: Nine hundred and sixty four subjects (474 boys, 490 girls) were selected between age groups 10 to 19 years from six schools representing different region of Pokhara. After Preliminary examination: on acuity of vision with Snellen’s and Jaeger’s charts, the subjects were referred to the Manipal Teaching Hospital, Pokhara for con�rmation of the refractive errors. Results: Sixty two schools children (6.43%), out of 964 had refractive errors. Myopia was found to be most common (4.05%). The refractive errors were found more in Private school children (9.29%) than Government school children (4.23%), which is statistically signi�cant (P < 0.05). More boys (7.59%) were found to have suffered from refractive errors than girls (5.31%). Further, children with vegetarian diet (10.52%) had greater number of refractive errors than non-vegetarian diet children (6.17%). Conclusion: In the present study, percentage distribution of myopia was found to be higher (4.05%) than the hyperopia (1.24%) and astigmatism (1.14%). Interestingly, in the present study the refractive errors were found signi�cantly higher in Private schools children than Government schools because the children who read in Private schools have higher socioeconomic status; spend more time in home work, watching Television and Computer as compared to government schools children. These near activities of the eyes causes stress on eyes of the children and might be one of the causes of developing myopia