Cascades and Omegas

Analysis Algorithm

The driving routine for Cascades and Omegas reconstruction in e831/FOCUS is drvcasc.sf. The following decays are reconstructed:

First Lambda candidates are selected, then two different algorithms are used to reconstruct Cascades/Omegas according to their decay topology:

Type 1 Cascades/Omegas are those which decayed upstream of the SSD microvertex ( casc1.sf)
Type 2 Cascades/Omegas are those which decayed downstream of the SSD microvertex ( casc2.sf)

Lambda candidates are selected for Cascade/Omega reconstruction if they satisfy the following criteria:

1.100 < M(Lb) < 1.130 GeV (approximately +/- 15 MeV around Lambda nominal mass)
M1, SSD, MIC, 1-LINK SSD (vee type<=10): goodlb(vee#)>=2 (see vee skim documentation)
1-LINK PWC (vee type=11,14,15): linked prong must have bad SSD-PWC link (since the SSD prong is in actuality the Cascade/Omega which gets linked to the daughter pion/kaon)

Figure 1 : Cascades and Omegas of types 1 and 2 and combined sample (for all vee types).
Figure 2 : Type 1 Cascades for different vee types.
Figure 3 : Type 2 Cascades for different vee types.

The following analysis cuts have been imposed to clean the Cascade/Omega samples:

Type 1 Cascades/Omegas :
- M1 vees only (i.e. vee type = 1, 4, 5)
- L/sigma > 5.
- iso2 < 10%
Type 2 Cascades/Omegas :
- no SSD, MIC or 1-LINK SSD vees (i.e. vee type=1, 4, 5, 11, 14, 15)
- |dslx|<0.001, |dsly|<0.002 (dslx/y is the difference in slopes between the SSD cascade track and cascade momentum)
Type 1 and 2 Cascades: istatp(pi)!=4,8,12
Type 1 and 2 Omegas : istatp(K)=4,12

These plots were obtained from tapes 00-08 of the Vanverbilt skim (approximately 40-45 raw tapes).

Last update: 1 May 1997