Plasma processing apparatus, data processing apparatus and data processing method

According to an embodiment of the present invention, a plasma processing apparatus includes: a processing chamber in which plasma processing is performed to a sample; a radio frequency power source that supplies radio frequency power for generating plasma in the processing chamber; and a data processing apparatus that performs processing to light emission data of the plasma. The data processing apparatus performs the processing to the light emission by using an adaptive double exponential smoothing method for varying a smoothing parameter based on an error between input data and a predicted value of smoothed data. A response coefficient of the smoothing parameter is derived by a probability density function including the error as a parameter.