Instrument Response Functions for DC1

 12/02/2003 05:29 -0800

The plan:

Use the irfAnalysis package to encapsulate and allow reproducible generation of the constants, in the defined set of bins. There is some documentation and browsing capability for this package here, with plots for current fits here.

Input is the result of an all_gamma run, currently run with GR v3r3p7 and the Rome classification trees. Available via ftp here. This will be replaced by a new version with better trees.

The class Irf:

• Defines binning in 0.2 intervals in cos theta, and 3 bins per decade in energy, providing functions to implement this. 
• Defines cuts for good energy, psf, and background rejection (latter coded by Luis)

The class Fitter (written by Jim Chiang) is a useful utility that makes a ROOT table of its fit parameters, and is designed to be subclassed to define specific fit functions, etc.

The Response Functions:

• PSF (Claudia+Monica+Francesca) Function is a sum of a gaussian and a exponential to a variable power. There are 5 parameters. The following is the expression that is sent to the ROOT fitter:
   
  "x * ([0] * exp (- 0.5 * x * x /( [1] * [1])) + [2] * exp (- (x * [3])^[4]) )"

  We use an empirical power law to scale the psf error as a function of energy and whether it is in the front or back sections. The scaling function needs to be made available to the latResponse implementation as well. Currently it is:
  
  

  double PSF::psf_scale(double energy, double zdir, bool isthin){
    // the scaling function: parameters determined by fits at Perugia
    static double power=-0.8, // exponent of energy
         thin100=0.08, thick100=0.14, // value (radians) at 100 MeV, for thin or thick
         cutoff=1e4; // flat above this energy
    double t = pow(std::min(energy, cutoff)/100., power);
    return isthin ? thin100*t : thick100*t;
  }

   

• Energy response (Luis) Simple gaussian fit to  EvtEnergySumOpt/McEnergy  for both thin and thick is adequate for now. The ROOT expression is
   
  "x*[0]*exp(-0.5*pow((x-[1])/[2], 2))"

• Aeff (Nico, Johann) Depends critically on background cuts. (See below.)  Needed separately for front and back sections. Empirical function in logE and costheta looks good.

Implementation of the functions for likelihood, etc. (Jim)

Jim will implement each of the functions by defining concrete classes to implement the abstract intefaces IEdisp, IPsf, and IAeff, found in the latResponse package. The tables with the constants will be put into its CALDB directory.

Implementation of the Atwood CT cuts (Toby)

The psf cuts depend on proper calculation of four variables designed by Bill Atwood. These are properly implemented in the merit package. However, the background cuts are not reproduced.

A new application in the merit package (run_classification) allows creation or replacement of the CT variables from an existing merit root tuple. This has been applied to the all_gamma, data set,  with the result for all events,

The updated file is available here: The filename is  ag-v3r3p7-merituple-prune20031102-fulltup.root

This has better high energy response, but still falls off.