Acceptance of ET_8 tagger in 1998-1999.

V.Andreev, 26-April-2000

     The new electron tagger ET8 was installed in the HERA tunnel
 in 1998 at the distance 8 m from the interaction point. This
 detector effectively accepts the scattered electrons with energy
 several GeV that gives opportunity to tag the photoproduction
 processes with the higher possible photon energy Wgp=300 GeV.

     More details about the calorimeter design, performance, 
 procedure of acceptance determination and obtained results during
 1998-1999 HERA Luminosity Runs are described in the H1 note.

     The acceptance of the ET8 is determinated with the same
 procedure which is used at the analyses of ET33 and ET44 taggers.

     The information about the acceptance behaviour and the trigger 
 efficiency for the different sub-samples is stored in the new (run-
 dependent) bank LET2 in the H1 database. The structure of this
 bank is shown below

 !       BANKname BANKtype       !Comments
 !
  TABLE  LET2                    ! ET_8 acceptance parametrization
 !
 !   ATTributes:
 !   -----------
 !COL ATT-name FMT Min    Max    !Comments
 !
   1  EFF0     F    0.      1.   ! Trigger efficiency
   2  YM       F    0.      1.   ! Trigger threshold value
   3  SIGY     F    0.      1.   ! Sigma of trigger threshold
   4  PVETO    F    0.      1.   ! Gamma-arm veto level
   5  YMIN     F    0.      1.   ! Minimum y-value
   6  YMAX     F    0.      1.   ! Maximum y-value
   7  DY       F    0.      1.   ! =0.005 dy-step for parametrization
   8  Y1       F    0.      1.   ! 
   ...                           ! 
 N+8  YN       F    0.      1.   ! 
  
  END TABLE

     The simulation of the ET8 is not presently included in H1SIM
 and for this reason it is recomended to use the new ACET8(IRUN,Y,MODE)
 routine both for the analysis of the experimental data and for the 
 Monte Carlo events. This routine provides the acceptance value for
 the different run periods and for the given y-value. Chose a proper 
 option MODE the acceptance dependence on the trigger efficiency
 and on the gamma-arm veto level could be taken into account.
 
     The systematic error is formed by the next sources:

     a) precision of the electron energy scale          --> 4.5 % ,
    
     b) uncertainty in the ET-8 position with respect
        to the electron beam                            --> 4.0 % ,
     
     c) trigger efficiency determination                --> 1.0 % ,

     d) fitting procedure and averaging of the
        calibration samples                             --> 1.0 % .

     So the overall systematic error in the acceptance determination
 of the ET-8 in 1999 could be taken as 6.2 % .