Dear @gtsileda
If I look at your plots I see you have a gain of ~4500 in both gas mixtures. Having 5x more electrons on the readout pad would mean that also your gain with AvalancheMC (for electrons) is 5 times higher. What is the gain you expect for this detector for these gasmixtures and this electric field (64kV/cm)? 5000 or 25000?
A loss of 30% due to 1% oxygen is probably too high. The problem with Oxygen is that the attachment mostly happens in the three-body process. This 3-body attachment is implemented in Magboltz as if it was for a gasmixture of 100% O2. Therefore you have to change manually the value for the variable T3B in the magboltz.f file, setting it to the fraction of Oxygen, in your case it would be 0.01. Thereafter you have to recompile your garfieldpp code and source it with setupGarfield.sh. Of course also correct gasfiles for 1% oxygen should be generated with this modified compiled garfieldpp version.
C THREE BODY ATTACHMENT
C ***************************************************************
C ENTER HERE SCALING FACTOR FOR THREE BODY ATTACHMENT IN MIXTURES:
C FOR NORMAL SCALING T3B=1.0
T3B=1.0
C SCALING FACTOR NORMALLY PROPORTIONAL TO OXYGEN FRACTION
C IN RARE GAS MIXTURES
C
C***********************************************************
More details are in this post.
greets
Piet