E781; charged cascade particles

Lambda detected in M1 spectrometer might be a decay product of charged cascade particles: ksi- in lambda, pi- and omega- in lambda, K- decay modes. The signature for those decays is the common vertex for some track and lambda vector. The vertex position must be upstream to lambda decay vertex. A track may be either decay product of cascade particle or cascade particle itself. First (s-channel, vee-type,csi,csk,csl objects) is checked first, second (t-channel,kink type,cti,ctk,ctl objects) is checked second and only if no solution in first case was found. A track candidate must have m1 or vx segment in first, second case respectivelly. The data about track begin/end points in respect to cascade vertex Z position are not used to cut background because of frequent errors (for this case) in track link. If the momentum of the track is unknown then it is calculated from mass constrain Fit. In case of vx+m1+m2 track with foreign vx segment the momentum may be wrong. The momentum correction must be done in next Soap version. If cascade was found in s-channel, then we search in addition for initial cascade track (vx segment with total lambda+meson momentum) which could be compatible with cascade vertex (miss distance cut). So, we have several levels of confidence for cascade candidates and maybe several solutions (tracks) in v0_bk for one lambda. Are we able to find the only solution as we did with lambdas or not we will see later after Embed studies and with more statistics. I have analysed the cascade candidates from 1M sample with 3 groups of cut.
1. Omega- candidates in lambda, K- effective mass with lambdas fully measured (2p) and proton in Rich. The momentum of K- was required to be measured. The presence of vx segment in K- track was allowed. The decay length for Omega- and lambda were required to be greater than 10 cm. The K- must be in Rich with prob > 0.7 (arbitrary high cut).
2. Any cascade candidates in lambda, pi- effective mass with lambdas fully measured (2p) and proton in Rich. The momentum of the cascade's pi- was to be measured and the track was to be m1 track! We had to select appropiate pions (without vx segment) because of more soft momentum than in case of Omega (kaons in Rich) and hence more strong influence of foreign vx segment on the momentum value. The decay length for Omega- and lambda were required to be greater than 10 cm.
3. In addition to second setup, the presence of the cascade track (vx segment) was required.
The mass histograms are presented in fig.1 , fig.2 and fig.3 respectivelly, the outcome in the table below. 
     
       one million filtered interactions
       ---------------------------------
         number of events        mass mean value   GeV/cc      rms
 1. omega-    28 +- 10           1.679 +- 0.0026             0.0054
 2. ksi-     187 +- 30           1.322 +- 0.0019             0.0138
 3. ksi-     107 +- 21           1.319 +- 0.0021             0.0121


     The conclusion:

 1. We see both omega- and ksi- cascade particles in fully
    recunstructed events. The yeild of ksi- is in agreemint with
    what we did observe for neatral ksi0 -> lambda + pi0 decay.
 
 2. In the Omega- spectrum we have 175 entries when the kaon has
    vertex segment and 25 when not!
    This means that we have to recalculate the kaon momentum and
    to think haw to improve track link.
 
 3. The observed masses are in agreement with PDT but the width
    of ksi- mass peak is to big. We do have a background there.

 4. We have to increase the statistics to make final conclusions
    and we have to study strange baryons with Embed.
 
 5. We may expect to have significantly more events with all
    the candidates with soft momenta, unmeasured momenta etc
    to use them for charm analysis.

 6. With lambda in final state and with 1 Run statistics we see
    all the strange baryons: lambda, Sigma0, Ksi0, Ksi- and Omega-.
vmatveev@fnal.gov