The improvements done in the DCH packages, readiness for MDCII are :

• • New tracking approach in DchSimGeom
    (Ernesto Lamanna, Shahram Rahatlou| Roma)
  • Inhomogeneous material (Wire and gas medium) to evaluate the Multiple scattering
    (Ernesto Lamanna, Shahram Rahatlou| Roma)
  • DCH Misalignment in bbsim
  • Change of parameterization of dE/dx (better estimation of the resolution)
    (Mario Posocco| Padova)
  • Implementation of DchSim
    (Sumit Sen| Colorado)

• • New tracking approach in DchSimGeom

Two different tracking approaches in the crossing of the Drift Chamber cells are now available in the current version of DchSimGeom:

1. MultiStep ======== Sequence of fixed steps (1 mm) .
2. SingleStep ========Estimation of the step at the entrance on the cell to reach the exit point .

• The first method (default in the current version) was used in MDC1. It was extensively tested before the start of the production.

• The second is faster and provides a gain of around  20 % in computing time.
• • The intrinsic method used to evaluate the step provide the knowledge of the closest approach points from each wire of the current cell.
  • The multiple scattering due to the crossing of the wires can be introduced separately from the gas medium.

The relevant characteristics follow.

• The behaviour of the path distribution in the cell is similar in the two cases eventhogh 1 mm binning can be seen in method 1) and a more regular distribution is acheived  in 2);
• The  number of steps  required to cross the cell is really different. An average of  13.4 is requested in  MultiStep  while 2.8 in SingleStep. The long tail in the latter method is mainly due  to the crossing of the sense wire and very low momentum particles;
• The closest approach distance to the sense wire is similar in the two cases.
• The distributions of the differences between the Monte Carlo and the reconstructed track parameters (using only DCH and no Kalman Fit)  have been considered in the two methods.
• 
  The c²per dof and the c²probability distributions show no appreciable differences like the distributions of the 5 parameters defining the fitted helix d0, Omega, TanDip, z0, Phi0 .
   

   

 A comparison between homogeneous material,  where the medium is obtained using He, Iso, and wires, and the selection of different materials where geometric separation of wires  and gas is made, has been given using the previous  samples. 

• The 45 % of particles cross at least one wire in the SingleStep sample.
• The distribution of the scattering angle shows values up to few mrad well in agreement with the estimation  obtained using a Gaussian approximation and the radiation lenght of the crossed materials.

• The distributions of the c²per dof and the c²probability show not relevant differences.
• The distributions of  d0, Omega, TanDip, z0, Phi0  show  greater values of the Root Mean Square when at least a wire is crossed .
• The resolution in transvers momentum  as function of the Pt and the resolution difference between the homogeneous medium approach and the introduction of the wires with at least one crossed wire, indicate no differences for Pt > 1 GeV/c but  differences up to 25 % for lower Pt.