Sabino Meola Charged kaon group meeting 12 October 2006 Status of analysis

Sabino Meola Charged kaon group meeting 12 October 2006

Status of analysis Status of analysis400eK 400eK


The K± → e±e decay

The K± → e±e decay

132200 10||||8.0)4( sFVeK us

• Allows the study of - scattering

• Selection rule I = ½

• Form factor F

)4( 00eK

PDG value: (2.2±0.4)·10-5


The aim is to measure two relative branching ratios

The aim is to measure two relative branching ratios

4

3

3

400

00

00

00

00

00

)(

)(

eK

KObs

K

Obs

eKe

N

N

KBR

eKBR

Two normalization samples:- to events in order to obtain a cancellation of the systematic errors.- to events in order to keep under control the track-to-cluster association efficiency.

300K

3ke

4

3

3

40

00

00

00

)(

)(

eK

KeObsKe

Obs

eK

e

e

N

N

eKBR

eKBR


K00e4 VS K003K00e4 VS K003

The measurement strategy is articulated in 4 steps:1. Neutral vertex (4).2. → association.3. Kinematic fit.4. Track to cluster association.5. Background rejection.


Step 1: The neutral vertex method (4)


Allows 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)2= (t - r/c) = (t - r/c)

• consistency with Kaon time of flight


300K

3Ke

Step 2: →0 associationStep 2: →0 association

• Cut on 2 of the

association →

• Cut on

2=|2best – 2

near|

3K 0K Knucleari

400eK

400K


Step 3: kinematic fitStep 3: kinematic fit

• 4-momentum conservation

• invariant mass

• clusters on time


• missing 4-momentum having zero mass

• invariant mass

• clusters on time


3 hypotesis K00e4 hypotesis


400K

3Ke

0K3K Knucleari

Step 3: kinematic fitStep 3: kinematic fit

300K

400eK


Step 4: Track to cluster associationStep 4: Track to cluster association

1

2

sec22

TrkVtxNeucl L

cttpm


Background analysis: K± → ± Background analysis: K± → ± )3( 00K


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

ctt

L

vtxneucl

trk

sec

2

222 1

pm


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

We require p/E < 3

)3( 00K


Background analysis: K± → e±e (Ke3)

Background analysis: K± → e±e (Ke3)

02

01

sec EEEEE Kmiss

Energies constrained by a kinematic fit


Splitted clusters in Ke3 backgroundSplitted clusters in Ke3 background

400eK

3Ke

Minimum tridimensional distance

To reject Ke3 events with split clusters we cut on the minimum distance (in 3D) among each couple of clusters.

Ke3

K00e4

cm


Radiative Ke3 backgroundRadiative Ke3 background

We look at the minimum angle between the 4 photons and the secondary track.

K00e4K00e4

Ke3

K00e4


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

K00e4 (blue region):

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

3 (violet region):

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


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


Measure of the branching ratioMeasure of the branching ratio

4

400

00

00

003

003

00

)(

)(

eK

K

Obs

K

Obs

eKe

N

N

KBR

eKBR

3105.1

12471093

4

003

00KeB

KB

ObsObs

eKNNNN

1250

5105.06.2

2300 10757.1105.1)( eveKBR


K00e4 VS Ke3K00e4 VS Ke3

The measurement strategy is articulated in 3 steps:1. Neutral vertex (2).2. Track to cluster association.3. Background rejection.




Allows the selection of events with 1 0

in the final state

±→X±

The neutral vertex must satisfy thefollowing requests:

• 2 neutral clusters on time(t - r/c) = (t - r/c)2


• invariant mass


Step 2: Track-to-cluster associationStep 2: Track-to-cluster association

-900 < m2 < 3500 Mev/c2


Step 2: Track-to-cluster association (m2 cut)

Step 2: Track-to-cluster association (m2 cut)

400eK

0K

3Ke

300K


400eK

0K

Step 3: K event rejectionStep 3: K event rejection

p* < 150 Mev/c


400eK

0K

3Ke

300K

400eK

Step 3: Ke3 event rejectionStep 3: Ke3 event rejection

We look for two more neutral clusters in the calorimeter.


sec0 EEEE Kmiss sec0 PPPP Kmiss

We perform a kinematic fit to constrain the photon 4-momentum.

Step 3: Ke3 event rejectionStep 3: Ke3 event rejection

We consider the E2miss-P2

miss


3ke

400ek

Step 3: Ke3 rejectionStep 3: Ke3 rejection

We require E2m-P2

m < 104


• We have to inquire Ke3 events with two fake neutral clusters (e.g. radiative + splitting).

• Look to P/E variable to reject K00event.

To be doneTo be done


ConclusionsConclusions

• The measurement method allows to estimate the K003 background contribution directly from data.

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

• A second measurement method with normalization to Ke3 events would allow to keep under control the track-to-cluster association efficiency.

• Will benefit of 2 fb-1 statistics.

Documents

Sabino Meola Charged kaon group meeting 12 October 2006 Status of analysis