Status of K± p±p0 E. De Lucia

Self-tag on one side using K- (nuclear interactions) PDG fit BR(K±p±p0) = (21,13 ± 0.14)% DBR/BR = 6,6x10-3 CHIANG ’72 BR(K±p±p0) = (21,18 ± 0.28)% DBR/BR = 1,3x10-2 Self-tag on one side using K- (nuclear interactions) Vertex with 2 tracks in DC on the signal side Strategy Method: Fitting the distribution of the momentum of the secondary track (p*) in the kaon reference frame we can extract BR(K±p±p0) The selection efficiency is only related to DC reconstruction: tracking efficiency vertex efficiency

The method mn peak: p*(p mass) distribution from “m-cluster” sample pp0 peak: p*(p mass) distribution requiring the p0 3-body decays: p*(p mass) distribution from MC fit window p* cut

pp0 shape (1) p0 .and. 180 < E p0 < 230 MeV .and. cosq < -0.95 .and. (Emiss-Pmiss)< 30 .and. |tof_mass2| < 104 MeV p*(MeV)

pp0 shape (2) DATA MC Systematic uncertainty can be estimated from the fluctuation of Npp0 obtained from the shape obtained varying the previous cuts

Fit stability “run by run” : MC runs for 2002 data have been divided in 12 groups called “runs” 2) “by range” : changing the starting point of the fit window from 150 MeV up to 190 MeV using 5 MeV steps 3) “by shape” : using different shapes for the pp0 peak obtained changing the selection cuts Compare the MC true numbers with : a) Npp0/Ntag from the fit b) Npp0/Ntag from the fit corrected for p* window cut (correction from pp0 “data-like” shape …agreement with pp0 MC true shape )

Fit stability: “run by run” (I) “Run number” “Run number”

Fit stability: “run by run” (II) “Run number” “Run number”

Fit stability: “by range” (I) different fit window different fit window

Fit stability: “by range” (II) different fit window different fit window

Fit stability: “by shape” (I) different shape different shape

Fit stability: “by shape” (II) different shape different shape

Reconstruction efficiencies Kaon tracking efficiency extrapolating from tag side Vertex efficiency from neutral vtx sample thetaK pK P secondary (MeV) With MC 2002 :

Using the MC (2002) pp0 mn Stability vs fit window (lower edge from 150 to 190 MeV) pp0 mn

Using the DATA (2002) pp0 mn Stability vs fit window p*(MeV) (lower edge from 150 to 190 MeV) pp0 mn p*(MeV)

Zoom on the peaks mn pp0

To do list Concerning the fit: Finalize systematic uncertainty on the fit results using the “by shape” stability on data Concerning efficiencies: Vertex is healthy next step : use kinematic fit 2) Tracking now using overall number (all decay channels) next step: work on neutral vertex sample to get directly the efficiency for pp0 decay 3) efficiencies on run by run basis to study stability of B.R. measurements

B.R.’s vs 2002 data taking periods Using corrections for data efficiencies but mean MC corrections for each point … need MC corrections for different periods possible with the 1:1 MC production

Using DATA 2002