Plasma processing apparatus and data analysis apparatus

In time-series data indicating light emission of plasma when plasma processing is carried out on a sample by generating the plasma, an analysis apparatus creates combinations of a plurality of light emission wavelengths of elements and a plurality of time intervals within a plasma processing interval and calculates, for each of the combinations of the wavelengths and the time intervals, a correlation between an average value of light emission intensity and the number of times the plasma processing is carried out on the samples for each of the combinations of the wavelengths and the time intervals that have been created. Thereafter, the data analysis apparatus selects, as a combination of the wavelength and the time interval used to observe or control the plasma processing, a combination of a wavelength of light emitting from a specific element and a specific time interval having a maximum correlation.