Nuclear temperature measurement and secondary decay

In heavy ion collisions, the products produced in the reaction are dominated by their phase space. It is quite common to interpret data by statistical physics. Temperature, which is a basic quantity of any statistical physics, needs to be addressed experimentally. Assuming thermal and chemical equilibrium are reached at freeze out time, two method can be used to measure nuclear temperature. One method is to measure the yields of particle unstable states in correlation experiments, from the ratios of the yields of excited states in the same isotope, temperatures are deduced by applying Bolztman factor1. Another method to measure temperature is based on the double ratios of two isotope pairs2, (y 1/y 2) and (y 3/y 4) differing by the number of neutrons and/ or protons. These two methods are only valid when measured yields are the same as the primary yields. The problem of nuclei temperature has been studied extensively in the last decad. Most work focus on the temperature measurement by excited states method3,4,5,6. These experimental results show that the temperatures deduced from excited states are around 5 MeV. More recently, nuclear temperature was studied by looking double isotope ratios for Au + Au collisions at E/A=600 MeV. The temperatures deduced from double ratio of (Y(6 Li)/Y(7 Li))/((Y(3 He)/Y(4 He)) remain relatively constant as a function of deduced excitation energy for 2.5 ≤ [ E/A ≤ 10 MeV but increase rapidly at E/A ≥ 10 MeV7, indicates a first order liquid gas phase transition. Since the fragments produced in the reaction normally are highly excited. The final isotope distribution could be quite different from primary distribution due to secondary decays, therefore it is very important to calibrate the thermometers used in the experiment due to secondary decay effect. In this report, we will show experimental results for temperature measurements both form excited states population and double isotope ratios. We will also compare experimental data to a model which take care of secondary decays carefully.