Sabino Meola Kloe meeting 10 March 2005

Status of analysisStatus of analysis400eK

Sabino Meola Kloe meeting 10 March 2005

The K± e±e decayThe K± e±e decay

1322' sec10||||8.0)4( FVeK us

• Allow the study of - scattering

• Selection rule I = ½

• Form factor F

)4( 00eK

Sabino Meola Kloe meeting 10 March 2005

at KLOE at KLOE400eK

high production cross section

possibility of -e discrimination

low efficiency for low momentum tracks

high backgrounds and Ke3300K

Sabino Meola Kloe meeting 10 March 2005

Aim is to measure a relative branching ratio Aim is to measure a relative branching ratio

4

3

3

400

00

00

00

00

00

)(

)(

eK

KObs

K

Obs

eKe

N

N

KBR

eKBR

normalized to eventsnormalized to events300K

Sabino Meola Kloe meeting 10 March 2005

Selection step 1: The neutral vertex method

Selection step 1: The neutral vertex method

Allow the selection of events with 2 0

in the final state

±X±

The neutral vertex must satisfy thefollowing requests:

• 4 neutral clusters on time(t - r/c) = (t - r/c)= (t - r/c) = (t - r/c)

• consistency with Kaon time of flight

Sabino Meola Kloe meeting 10 March 2005

300K

3Ke

Step 2: 0 associations

• Cut on of the association

• Cut on

=|best –

near|

3K 0K Knucleari

400eK

400K

Sabino Meola Kloe meeting 10 March 2005

Step 3: kinematic fitStep 3: kinematic fit

• 4-momentum conservation

• invariant mass

• cluster on time

• consistency with Kaon time of flight

• missing 4-momentum having zero mass

• invariant mass

• cluster on time

• consistency with Kaon time of flight

3 ipotesys K°°e4 ipotesys

Sabino Meola Kloe meeting 10 March 2005

400K

3Ke

0K3K Knucleari

Step 3: kinematic fitStep 3: kinematic fit

300K

400eK

Sabino Meola Kloe meeting 10 March 2005

Track to cluster associationTrack to cluster association

1

2

sec22

TrkVtxNeucl L

cttpm

Sabino Meola Kloe meeting 10 March 2005

Background analysis: K± ± Background analysis: K± ±

We require p/E < 3

)3( 00K

Sabino Meola Kloe meeting 10 March 2005

Background analisys: K± e±e (Ke3)

Background analisys: K± e±e (Ke3)

02

01

sec EEEEE Kmiss

Sabino Meola Kloe meeting 10 March 2005

Geant cluster(no accidental)

no accidental

1 accidental

Accidental clusters in Ke3 background

Accidental clusters in Ke3 background

Geant mother(no accidental)

0

K

K

Sabino Meola Kloe meeting 10 March 2005

Splitted clusters in Ke3 backgroundSplitted clusters in Ke3 background

400eK

Tridimensional clusters distance

3Ke

Sabino Meola Kloe meeting 10 March 2005

The measurement methodThe measurement methodWe consider the events distribution in the(m2,p) plane.

K°°e4 (blue region):

-900 < m2 < 3500 (MeV2)35 < p < 180 (MeV)

3 (violet region):

m2 < -1000 (MeV2)25 < p < 180 (MeV)

Sabino Meola Kloe meeting 10 March 2005

Measure of the branching ratioMeasure of the branching ratio

)1(00

300

3 KMC

KData NN

The contribution of background on data is:

23.0

Sabino Meola Kloe meeting 10 March 2005

ConclusionsConclusions

• The measurement method allow to estimate the K°°3 background contribution directly from data.

• Normalization to 3 events guarantees a cancellation of the systematics effects.

• Still Ke3 background must be better evaluated on data.

• Probably need K0 tag to increase statistics.

• Will benefit much from 2 fb-1 collection.