Star-tpc-l mailing list

["Van Buren, Gene" <gene AT bnl.gov>]

Hi, all

A couple items following today's discussion on ETOF track projections and the 
possibility of impacts from fringe magnetic fields beyond |z|>200 cm (where 
the fields begin to have a radial component).

1) It occurs to me that we have data which perhaps could help clarify whether 
the fringe field is the issue: the two magnetic fields of the OO200 data. The 
unaccounted radial component of the field should point in opposite directions 
for the FF and RFF data, so the effect on extrapolations should be too large 
in one field and too mall in the other if I've thought about this properly 
(though I can believe I haven't). I do see that the ETOF was in the data 
stream for that data, if Yannick can perhaps have a look?

2) There was uncertainty about whether Victor's Xtrak code did anything 
regarding the fringe magnetic fields. Victor's code is viewable here on AFS:
/afs/rhic.bnl.gov/star/packages/SL23e/StRoot/StXTrakMaker
or here on the web:
https://github.com/star-bnl/star-sw/tree/SL23e/StRoot/StXTrakMaker

Victor has this comment in his code:
"Tracking accounts energy loss and magnetic field.... The current version is 
working only with mag field along Z. "

And unless I've missed something, here's the code where I think Victor gets 
his magnetic field, which is straightforward:
>>>>>>>>>>
void MyMag::operator()(const double x[3],double b[3])
{

static const double EC = 2.99792458e-4;
static StarMagField *magf = StarMagField::Instance();
     magf->BField(x,b);
     b[0]*=EC;
     b[1]*=EC;
     b[2]*=EC;
}
>>>>>>>>>>

Thanks,
-Gene