[d2n-analysis-talk] (fwd) Fwd: ExTgtCor_L.p variable

[Brad Sawatzky]

----- Forwarded message from David Flay <flay at jlab.org> -----

From: David Flay <flay at jlab.org>
Subject: Fwd: ExTgtCor_L.p variable
To: Diana Parno <dseymour at andrew.cmu.edu>, Brad Sawatzky <brads at jlab.org>,
	Matthew R Posik <matthew.posik at temple.edu>

---------- Forwarded message ----------
From: Vincent Sulkosky <vasulk at jlab.org>
Date: Tue, Dec 8, 2009 at 5:22 PM
Subject: Re: ExTgtCor_L.p variable
To: David Flay <flay at jlab.org>
Cc: Chiranjib Dutta <chiran at jlab.org>



Hi David,

It seems that in the recent past that ~src/THaExtTarCor.C was modified.

If you look at line # 120 under the "DefineVariables" method, you will see
this line:

DefineVarsFromList( THaTrackingModule::GetRVarDef(), mode );

Variables can either be defined from a list, such as follows

const RVarDef var2[] = {
   { "delta_p",  "Size of momentum correction",    "fDeltaP" },
   { "delta_dp", "Size of delta correction",       "fDeltaDp" },
   { "delta_th", "Size of theta correction (rad)", "fDeltaTh" },
   { 0 }
 };
 DefineVarsFromList( var2, mode );

or from another module.  In this case, THaTrackingModule.  If you look in
this module under the method "GetRVarDef", you will find this:

//_____________________________________________________________________________
const RVarDef* THaTrackingModule::GetRVarDef()
{
 // Return definition block of global variables for the fTrkIfo object

 static const RVarDef vars[] = {
   { "x",        "Target x coordinate",            "fTrkIfo.fX"},
   { "y",        "Target y coordinate",            "fTrkIfo.fY"},
   { "th",       "Tangent of target theta angle",  "fTrkIfo.fTheta"},
   { "ph",       "Tangent of target phi angle",    "fTrkIfo.fPhi"},
   { "dp",       "Target delta",                   "fTrkIfo.fDp"},
   { "p",        "Lab momentum (GeV)",             "fTrkIfo.fP"},
   { "px",       "Lab momentum x (GeV)",           "fTrkIfo.GetPx()"},
   { "py",       "Lab momentum y (GeV)",           "fTrkIfo.GetPy()"},
   { "pz",       "Lab momentum z (GeV)",           "fTrkIfo.GetPz()"},
   { "ok",       "Data valid status flag (1=ok)",  "fTrkIfo.fOK"},
   { 0 }
 };

 return vars;
}

Hence, THaExtTarCor.C does define ExTgtCor_L.p as a variable.  However, it
is hidden under inside another class now.

The momentum is calculated in the "Process" method as shown below on line #
161:

Double_t p  = spectro->GetPcentral() * ( 1.0+dp );

The difference between L.tr.p[0] and this variable is that the extended
target correction has been applied.  This deals with the fact that the
vertical position in the target coordinate system (x_tg) is not 0 and has a
significant dependence on the vertex position.

For either of these variables, the central momentum of the run needs to be
set correctly in the db_run.dat file.  I doubt that the momentum is the
cause of the problem, unless the central spetrometer momentum is not set
correctly.

Cheers,
Vince

--

Vincent A. Sulkosky, MIT Postdoctoral Associate

CEBAF Center F358
Jefferson Lab               Phone: (757) 269-5487
12000 Jefferson Avenue      Pager: (757) 584-5487
Suite #4, MS 12             email: vasulk at jlab.org
Newport News, VA 23606      Fax:   (757) 269-5703


On Tue, 8 Dec 2009, David Flay wrote:

 Hey Chiranjib,
>
> I'm investigating that (strange) drift in E/p as a function of p, and I was
> trying to find in the source code where the ExTgtCor_L.p variable is
> constructed (since the *.odef file uses it in the formula for prl_E_P), but
> I can't seem to find it -- it's not in ~src/THaExtTarCor.C, which is where
> I
> thought it would've been... and a 'grep' command on the src directory
> yields
> nothing.
>
> Have you investigated this variable before?
>
> Subsequently, as a check on the prl_E_P variable, I'm comparing it to a
> calculation of E/p as:
>
> (L.prl1.e+L.prl2.e)/(1000*L.tr.p[0]*(1. + L.tr.tg_dp[0]))
>
> where L.tr.p[0] is the track momentum (in GeV) and L.tr.tg_dp[0] is delta-p
> (as usual).
>
> Thanks,
>
> Dave
>
> -----------------------------------------------------------
> David Flay
> Physics Department
> Temple University
> Philadelphia, PA 19122
>
> office: Barton Hall, BA319
> phone: (215) 204-1331
>
> e-mail: flay at jlab.org
>         david.flay at temple.edu
>
> website: http://www.jlab.org/~flay
> -----------------------------------------------------------
>
>


-- 
-----------------------------------------------------------
David Flay
Physics Department
Temple University
Philadelphia, PA 19122

office: Barton Hall, BA319
phone: (215) 204-1331

e-mail: flay at jlab.org
          david.flay at temple.edu

website: http://www.jlab.org/~flay
-----------------------------------------------------------

----- End forwarded message -----

-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
  Ph: 757-269-5947 -<>- Pager: 757-584-5947 -<>- Fax: 757-269-7848
The most exciting phrase to hear in science, the one that heralds new
  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov