1. K  group activities K + K - retracking features New vs Old : resolution future planning. Conclusion and outlook K + K - retracking features New vs Old : resolution future planning. Conclusion and outlook

2. KPM Reconstruction KPM Selection KPM retrackingDST production Done and working Finalized, under test Not yet addressed The KPM reconstruction has been updated/ridesigned, in particular with respect of: Track merging, T0 finding, K ± TOF correction, Multiple scattering treatment optimization, ECLO and Event selection interaction In Otranto Done and working Since August Under debugging now

3. KPM retracking:new & updated modules Kmerge T0_find atfmod Merge tracks and udpdate pattern candidates. Orders and updates K id from different ECL algos in ECLO Pattern Banks & ECLO Finds the KPM t0 globalT0GL New K TOF implementation, specific K m.s. treatment, correct hit times for T0 Fit Banks moduleNew featuresUpdated bank

4. K + K - reconstruction: merging Due to K large TOF, wrong T0 and large m.s. the “standard” rec. produces a large fraction of broken tracks (at the pattern level!). No recovery possible by the Fit The Kmerge module merge all the possible tracks (not only K + K - ) on the basis of their angle, distance and momenta and rebuild the KPM ECLO banks. After merging and T0 correction, the tracking/pass=2 (usually) splits only the correct kinks Kaon track

5. K  reconstruction: T0 finding o Applied to tagged events with K decay products with ECAL cluster associated. o From K decay vertex position, cluster times, momentum of K and charged daughter at vertex is possible to trace back the T0 of the event. t + -t - (ns) 2001 data

6. K  resolution/1 In Otranto we had switched off multiple scattering. dE/dx implementation did not distinguish in between pion and kaon. Pools (errors) were wrong for kaons! Sigma = 3.3 MeVSigma = 3.4 MeV Sigma = 2.0 MeV New Old

7. K  pulls Pools are now ok! The dE/dx for a kaon is subtracted while tracking and multiple scattering is taken into account in the error matrix Pull = 1.1 Pull = 1.15 New Old

8. K  retracking AC path use kpm_restore dcdbini raw2dtce t0meno dconvr dcprar merge atfmod/par=1 vtxfin/par=1 trclmod/par=1 eclmod/par=3 ecl_kpmfilt t0_find/par=4 clufixtin/par=2 kmerge atfmod/par=2 vtxfin/par=2 trclmod/par=2 The correct merging of the broken tracks must be done at level of pattern candidates  DTCE1 and DHRE1 banks are needed. The minimal AC path for K  retracking is reported. The red modules have been updated/written for this stream The KPM retracking is very CPU consuming. The production rate on fibm12 has been estimated to be ~ 1 pb -1 /day/CPU Now M.S. is not switched off for K  here !!! But it was switched off in Otranto.

9. New vs Old recostruction  We have tuned the retracking on MC. This work has been done on events selected by the NEW selection algorithms, reconstructed with the standard tracking (no dE/dx for K +/- and no MS corrections).  The problem is a multivariate one.. We have analized one refinement at the time.  The efficiencies have been studied in a subsample of tagged events: given a tag we look at what happen in the opposite hemisphere.

10. New vs Old : K momentum resolution/2 The distorsion induced in the OLD rec. gets more evident as far the track gets longer Kaon P rec – P true distribution at the decay vertex versus the Kaon decay path

11. Effect on data -- old recostruction -- new recostruction The new recostruction slightly improves resolution

12. New vs Old: vertex resolution New Old The vertex resolution is slightly improved. In particular tails are reduced

13. New vs Old : broken tracks Distribution of total length vs momentum of splitted kaons of the entire MC sample (1.7x10 5 ev). The merging get rid of most of the broken track  better decay length distribution ! OLD NEW

14. New vs Old : tracking eff. vs DC hits On the selected sample the tracking efficiency are similar. K  tracking efficiency

15. New vs Old : tracking eff. vs cos  K Due to the request for at least a TAG to compute any eff, large events statistic is needed. Rec.

16. New vs Old : tagging eff. vs DC hits The new reconstruction seems to behaviour better than the standard one. The tagging efficiency is sensitive to the combination of tracking and vertex eff iciency N.B. is the eff of a very clean sub-sample! Tagged/tracked eff.

17. Future planning:  The cross section: (next talk) memo by end of 2002.  Br (K +    Br ( K +      Maxim PhD thesis.  Absolute Br(K + ) by summer 2003 (2 body, semileptonic).  Br (K +        Andrea Ventura PHD thesis by summer 2003.  Br (K + e +      Andrea Ventura PHD thesis by summer 2003.

18. Conclusions The retracking code of the KPM stream is in its final shape, yet has to be tested on high statistics Sizeable (but not fantastic) improvement with respect to the standard reconstruction at first glance We now have good pulls. DST production is starting (it should last 1 month).