1. Status of K± p±p0
E. De Lucia

2. 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

3. 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

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

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

6. 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 )

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

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

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

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

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

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

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

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

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

16. Zoom on the peaks mn
pp0

17. 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

18. 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

19. Using DATA 2002