Above shows the corrections with an old pair background model (CLAS/Fersch), old target dilution calculation (see below), and an E' cut at 800 MeV.
Recently, I have updated the background simulation with Oscar's pion cross section fits. This improved the background dilution to the point where a sensitivity to radiative corrections shows, manifesting itself as a relative balance between the two corrections. This will be discussed below. Also, I improved the low x reach of the DIS model being used (F1F209+NMC95).
Q: Why bother with low x? There is a lot of good low x data for A1 already.
A: Using existing A1 data as the benchmark for the target and background dilutions provides a nice systematic check of the procedures.
Since lower x is further in the DIS, agreement builds confidence in the treatment of the target/background/radiative corrections.
Above shows the corrections with an old pair background model (CLAS/Fersch), old target dilution calculation (see below), and an E' cut at 800 MeV.
Above shows the corrections with the improved pair background model, old target dilution calculation, and an E' cut at 800 MeV.
Radiative corrections show up twice in the analysis thus far; here, for calculating the pion/electron cross section ratio (especially at low E'), and previously in calculating the target dilution factor. At this point I revisit the target dilution factor. It is good to consistently use the same cross sections throughout the whole analysis.
Previously my target dilution factor was calculated with the just Born cross sections, without the inclusion of the proton elastic radiative tail or the inelastic tails. This was within the error bars of Narbe's analysis (so I pressed forward).
Now, I am able to return to the dilution with radiative corrections. First, only the inelastic radiative tail is included. Clearly, falling off at low energies, the proton/nuclear ratio seemed too low, that is, the inelastic radiative tail pushed it in the wrong direction. But of course, the elastic radiative gets large there too! After adding only the proton's elastic radiative tail, the dilution gets larger at low x (as desired to bring down the asymmetry at low x).
It is worth noting at this point, that I have not included the Helium elastic tail (or larger nuclei). It is assumed negligible.
Above shows the corrections with the improved pair background model, with new target dilution calculation, and an E' cut at 800 MeV.
Again, moving forward to the background dilution, an important piece was left out of the simulated cross sections: the elastic radiative tail. Even though we will subsequently subtract this tail, it is important to include it in both the target and background dilutions, if the lower x data is to be fully understood.
Above shows the corrections with the improved pair background model reduced by 1/2.
At the low x it seems the ratio is perhaps converging to the right value,
but the region between negligible background (high x) and a saturated background, where the slope is steepest, is not correct.
The reduction by 1/2 above is justified for the lowest x where the elastic tail gets to the same order of magnitude as the DIS cross section (and has not been included in the background dilution).
Once my simulation jobs are through the farm, these curves will be redone.
I predict the shape of the elastic tail will yield a better result for the
electron/pion ratio where its slope is changing the most.
That is, it will increase the electron rate towards lower E', thus pushing the onset of the increasing ratio to lower E' (and x).
At this point it is also worth noting the feature (although perhaps model dependent) that the inelastic radiative tail correction is much larger at low x for the perpendicular asymmetry! It is very small for the parallel asymmetry.
This could have a rather large impact on the extraction of the higher twist from the perpendicular data.
There is a difference between the RCS and Protvino asymmetries. I do not understand the source of this. The Protvino (lower part of BigCal) asymmetries appear to be the problem. The RCS asymmetries are well behaved.
Above shows A1 and A2 for 5.9 GeV, after elastic tail subtraction.
The triangles indicate RCS (pointing up) and protvino (pointing down).
Above shows A1 and A2 for 5.9 GeV, before background and radiative corrections.
The triangles indicate RCS (pointing up) and Protvino (pointing down).
This difference is most visible in the parallel asymmetries.
Above shows A180 for 4.7 GeV data.
The triangles indicate RCS and Protvino (circles).
Suggestions on investigating are welcome!
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