coulomb excitation data analysis codes; gosia 2007 - Physics and ...

8 SIMULTANEOUS COULOMB EXCITATION: PROGRAM GOSIA2GOSIA2 is a special version of GOSIA that is intended to handle both target and projectile excitation simultaneously.This avoids introducing free parameters (normalization constants) which is important when onlya very limited number of experimental data results from the experiment, like in case using radioactive beamsand when the Rutherford scattering cross section is not measured simultaneously to provide a normalization.As an extreme case one can imagine the situation in which only the lowest transition is observed, then thereare at least two parameters;the matrix element and the normalization constant. Simultaneous inclusionof the lines originating from the second partner and possibly known spectroscopic data makes it possibleto achieve a unique solution. The problem of arbitrary normalization constants does not exist in case ofmultiple COULEX, where both the number of fitted matrix elements and the number of experimental datais large enough to neglect the impact of introducing few more parameters fitted by regular GOSIA.GOSIA2 requires two parallel inputs describing both collision partners. It was chosen to keep separateinputs rather than merging them to form a single one to preserve maximum compatibility with the regularGOSIA input. One can switch to GOSIA by deleting only three input records. Using GOSIA relieves somerestriction imposed by GOSIA2 when the use of GOSIA is justified. At the stage of fitting matrix elementsGOSIA2 will switch between the two inputs. This results in the necessity of observing some conventionsimposed by the GOSIA2 logic. The most important one is that experiments in both inputs and experimentaldata sets should be ordered parallel, i.e. experiment #n in the first input should be the same as experiment#n in the second. Then the common normalization constant will be found by the code. All geometricfactors are included in the calculations without arbitrary renormalization. In the best case the experimentsshould be coupled together, like in GOSIA (although this is not required). In this situation there is only oneconstant remaining, reflecting “flux” or the total number of particles irradiating the target. An example ofsuch organization of inputs is given below.GOSIA2, as with GOSIA, has two main modes. The first is the Coulomb Excitation calculation whichis designated by the OP,COUL section. The other is the experimental fit which is designated by OP,GOSI.Both of these options are input to GOSIA2 in the same manner as one would with GOSIA. The process forrunning the two functions is different.To run the OP,COUL calculation the input files must be created using the guidelines described inthe manual, I shall refer to the projectile and target input files as input1.inp and input2.inp respectively. Itis important to note that each file requires a separate execution when calculating the gamma-ray yields. Toexecute each file type the following:gosia2 < input1.inpThe output will then be written according to the designated output fileinOP,FILE.Thesamelineisused to execute the target file for target excitation, making sure to replace input1.inp with input2.inp.To run the OP,GOSI portion of GOSIA2 the process is slightly more complicated. As with GOSIAeach file must be run three separate times for the fit to be executed, once with OP,CORR, once with OP,MAPand once with OP,MINI. Once the inputs are prepared the execution is done as follows. First run each file,projectile and target, with OP,CORR using,gosia2 < input1.inpgosia2 < input2.inpA file should be written with the corrected yields for both the projectile and target. Where the files arelocated will depend on whether or not there was a specific designation for the output in OP,FILE. Next eachfile should be run with OP,MAP. The execution is the same as before. Finally the projectile file should berun with OP,MINI. Again, the execution is the same as before.An example of inputs is intended to reflect a typical MINIBALL experiment. Note that actual numbersare not real (e.g. level schemes are not, so krypton is not really krypton, carbon is not really carbon etc.The aim of the inputs is to demonstrate their structure. The inputs illustrate the situation of “Kr” beamscattered on “C” target. Particle detectors form the ring in such a way that only “C” particles can bedetected, “Kr” going through a central hole. The GOSIA2 commands are in bold, the non-bold commentsshould not be entered into the input file..139