Status of K± ±0

E. De Lucia

PDG fit BR(K±) = (21,13 ± 0.14)% BR/BR = 6,6x10-3

CHIANG ’72 BR(K±) = (21,18 ± 0.28)% BR/BR = 1,3x10-2

• Self-tag on one side using K- (nuclear interactions)•Vertex with 2 tracks in DC on the signal side

Strategy

Fitting the distribution of the momentum of the secondary track (p*) in the kaon reference frame we can extract BR(K±)

The selection efficiency is only related to DC reconstruction:• tracking efficiency • vertex efficiency

Method:

The method

MCLIKE-DATA

MCTRUE

DATA εε

ε

1) peak: p*( mass) distribution from “-cluster” sample

2) peak: p*( mass) distribution requiring the

3) 3-body decays: p*( mass) distribution from MC

VTXTRKTAG

FITππ0

ε1

cut)*ε(p1

N

N)ππBR(K

fit windowp* cut

shape (1)and180 < E < 230 MeV .and. cos< -0.95 .and. (Emiss-Pmiss)< 30 .and. |tof_mass2| < 104 MeV

p*(MeV)

shape (2)

DATA

Systematic uncertainty can be estimated from the fluctuation of N obtained from the shape obtained varying the previous cuts

MC

Fit stability1)“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 0 peak

obtained changing the selection cuts

a) N0/Ntag from the fit

b) N0/Ntag from the fit corrected for p* window cut (correction from 0 “data-like” shape …agreement with 0 MC true shape )

FITTAG

0

NNππ

Compare the MC true numbers with :

)*ε(p1

NNππ

CUTFITTAG

0

Fit stability: “run by run” (I)

“Run number”

FITTAG

0

NNππ

)*ε(p1

NNππ

CUTFITTAG

0

“Run number”

Fit stability: “run by run” (II)

FITTAGNN

)*ε(p1

NN

CUTFITTAG

“Run number”

“Run number”

Fit stability: “by range” (I)

FITTAG

0

NNππ

)*ε(p1

NNππ

CUTFITTAG

0

different fit window

different fit window

Fit stability: “by range” (II)

FITTAGNN

)*ε(p1

NN

CUTFITTAG

different fit window

different fit window

Fit stability: “by shape” (I)

FITTAG

0

NNππ

)*ε(p1

NNππ

CUTFITTAG

0

different shape

different shape

Fit stability: “by shape” (II)

FITTAGNN

)*ε(p1

NN

CUTFITTAG

different shape

different shape

Reconstruction efficienciesVertex efficiency fromneutral vtx sample

Kaon tracking efficiencyextrapolating from tag side

pKthetaK

P secondary (MeV)

With MC 2002 : 0.05%39.42εMC2002

REC TRUE 0.13%38.65ε

MC2002

VTXTRK

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

0.13 21.18 )ππBR(K

0.1463.47 μν)BR(K0

0.13 21.21 )ππBR(K

0.1263.70 μν)BR(K0

Stability vs fit window(lower edge from 150 to 190 MeV)

Using the DATA (2002)

p*(MeV)

Zoom on the peaks

To do listConcerning the fit:1)Finalize systematic uncertainty on the fit results using the “by shape” stability on data

Concerning efficiencies:

1)Vertex is healthy next step : use kinematic fit2) Tracking now using overall number (all decay

channels) next step: work on neutral vertex sample to get

directly the efficiency for 0 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 fordata efficiencies but mean MC corrections for each point …

need MC corrections for different periodspossible with the 1:1MC production

Using DATA 2002