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CLAS Cerenkov efficiency

CLAS Cerenkov detector efficiency analysis based on e1b run period (1999).

The goal of this analysis is to obtain the Cerenkov detector efficiency. It is based on e1b (e1c) run period , for initial energy 1.5 GeV and low TORUS currents : 750 and 1500 A.

Selection procedure and applied cuts

e1b cooked ntuples were used. The idea is to define the mean number of photoelectrons as a function of projective angles THETA,PHY of the cross-point of the electron track with the special plane. This plane was defined so that data at different TORUS current values will be compartible to each other. Then Cerenkov detector efficiency is defined, using these numbers of photoelectrons. The fuctional dependence of efficiency versus number of photoelectrons was derived from data with no CC in the trigger.

CUTS:


Results :

As an example, there is the plot of the mean number of detected photoelectrons as a function of Theta and Phy for Sector 1 .

The electron inefficiency plot shows the revised dependence of electron detection efficiency vs number of photoelectrons. It based on eg1 data and only fiducial region data are involved. The dependence was approximated as follows: 

 

      function fit2(x)
c
      if(x .lt. 2.2) then
        fit2 = exp(-0.739159727*x)
      else if(x .ge. 2.2 .and. x .lt. 6.7) then
        fit2 = 0.52947 - 0.20349*x + 0.026204*x*x -0.0011208*x*x*x
      else if(x .ge. 6.7) then
        fit2 = 0.0052893896*exp(0.8*(6.7 - x ))
      end if
      return
      end

New efficiency function was produced, based on these data.
Function call from c : 

 
int cceffn(int run_number, int sector_number, float *point, float *dir,
              float *Nphe, float *Nphe_err, float *cc_eff)
  {
  /*
C-   Purpose and Methods : calculates the  Cerenkov efficiency
C-                         for given track.
C-                         Needed initialization is done at first call.
C-
C-   Inputs  :   run_number - number of a run - to trace possible
C-                            changes in efficiency
C-               sector_number - number of the sector
C-               point(3) - coordinates of the point on the track
C-                          somewhere after CC (where B=0): 
C-                          it could be EC or SC  matching point.
C-               dir(3)   - direction vector at that point.
C-     *** IMPORTANT ! *** Point and direction must be in Sector RS
C-
C-   Outputs :   Nphe - estimated number of photoelectrons
C-                       for the track.
C-               Nphe_err - estimated error in Nphe
C-               cc_eff - estimated Cerenkov detector efficiency
C-
C-   Controls:   Function returnes :
C-            
C-                0 : no errors
C-               -1 : can't read initialization file
C-               -2 : Wrong sector number ( must be from 1 to 6 )
C-               -3 : No crossing with the plane - check coordinates 
C-                    and direction - possible wrong coordinate system
C-               -4 : Not enough data to define efficiency
C-
C-   Created    23-NOV-1998   Alexander V. Vlassov
C-   Modified   15-MAY-2000   Alexander V. Vlassov
C-
C----------------------------------------------------------------------

It also can be called from FORTRAN:
ires = cceffn(irun,isect,point,dir,anphe,anphe_err,effic)
with the same parameters.

New features: 

 
  /*
C-  Changes made by A. Vlassov - May, 2000
C-
C-   1.  :     Special function, described the Cerenkov efficiency
C-             as a function of the Photoelectron number, is included.
C-             function name : cc_eff_nphe
C-
C-   2.  :     Number of point in the table is changed :
C-             #define MAXT 225 ( angle theta )
C-             #define MAXP 120 ( angle phy )
C-   
C-   3.  :     Name of the data file was changed to "cc_eff_new.dat"
C-
C-   4.  :     Add error flag (-4) when it is not enough data
C-             to define the efficiency
  */

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