pAu An Day126

With only one day's data, the FMS is showing an indication of large TSSA (AN) for  pi0 production  in pAu collisions at large pT. This could be really exciting.

As we know, the big mystery in forward AN goes to the question :

"How it can be that the forward pi0 TSSA asymmetry, a PQCD higher twist observable, can grow with pT rather than fall as a power of pT ( as expected for higher twist effects?)"  

This growing AN  with pT is seen at XF<.4, both for rootS=500 GeV and rootS=200 GeV FMS data.

The assumption is that there must be a mechanism to produce large pT pi0 events that is not subject to the details of the ordinary production and fragmentation. The question for pAu is:

"Given that the mechanism for pi0 production, leading to AN, is apparently anomoulous,  what will be the effect on this asymmetry if the participating particles pass through a nuclear filter.  "

The anomolous component of pion production could be filtered more or less than the ordinalry component. This leads to  smaller AN or larger AN respectively as the mix between ordinary and anomoulous processes are filtered differently.
It looks like our anonomoulus process contributes with less than average absorption by the gold nucleus when pT is large. 

The nucleus appears more transparent for the subprocess that contributes to large AN at large pT. I think that this is the most exciting of possible outcomes.

In the figure below we see AN results for 0.3<XF<0.4. Events are selected to satisfy any of the FMS triggers and photons are collected into a very large cone (cone angle - 0.20 Rad).  For the pi0 signal, events are collected within a nominal  pi0 mass cut and required to have 2 photons only in the cone. For single photons we demant only 1 photon be in the cone. 

1) In Red: The pi0 asymmetry AN for part of the Run15 pp data set (about 15 pb^(-1)).  
2) In Blue: The pi0 asymmetry AN but for pAu data taken on Day126 of Run 15.
3) In Black: The asymmetry AN for isolated photons in the FMS for data daten on Day126 of Run 15.