status of analysis

Sabino Meola Charged kaon group meeting 14 December 2006

Status of analysis Status of analysis400eK 400eK


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 5 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

Signal K003 Ke3

783 ~6·105 2690

S/B ratio after:~ 8·10-2

Signal PDG value: (2.2±0.4)·10-5

K00 3 PDG value: (1.757±0.024)·10-2

Ke3 PDG value: (4.98±0.07)·10-2


Step 2: →0 associationStep 2: →0 association

• Cut on 2 of the

association →

• Cut on

2=|2best – 2

near|

Signal K003 Ke3

239 ~1.8·105

326

S/B ratio after:~ 7.5·10-2


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 hypothesis K00e4 hypothesis


Step 3: kinematic fitStep 3: kinematic fit

Signal K003 Ke3

234 ~1·105 179


2

400ek

2

300K

2

400ek

2

300K


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

1

2

sec22

TrkVtxNeucl L

cttpm


The measurement methodThe measurement method

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


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

Signal K003 Ke3

81 114 77

S/B ratio after:~ 0.4


Background analysisBackground analysis

K00Is due to photon’s clusters wrongly associated to the secondary track.

Cut on P/E.

Ke3Is due to Ke3 radiative events.

02

01

sec EEEEE Kmiss

• Cut on minimum angle between the 4 photons and the secondary track

• Cut on Emiss


Background rejectionBackground rejection

Signal K003 Ke3

71 77 21

S/B ratio after background rejection cuts:~ 0.7


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

31048.1

21591663

4

003

00KeB

KB

ObsObs

eKNNNN

1586

51045.060.2

2300 10757.11048.1)( eveKBR

Relative error ~ 17%


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

Signal K003 Ke3

1859 ~1.5·106 ~5.7·106


Signal PDG value: (2.2±0.4)·10-5

K00 3 PDG value: (1.757±0.024)·10-2

Ke3 PDG value: (4.98±0.07)·10-2


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

-900 < m2 < 3500 Mev/c2

Signal K003 Ke3

229 2317 ~5.7·105

S/B ratio after:~ 2.5·10-3


sec0 EEEE Kmiss sec0 PPPP Kmiss

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

Step 3: Ke3 event rejectionStep 3: Ke3 event rejection

We consider the E2miss-P2

miss variable


3ke

400ek

Step 3: Ke3 rejectionStep 3: Ke3 rejection

We require E2m-P2

m < 2·104


Background rejectionBackground rejection

• We require two more neutral clusters in the calorimeter.• Cut on p* to reject K±→0± events.• Cut on P/E in order to reject events with a charged pion in the final state.

Signal K003 Ke3

91 214 195

S/B ratio after background rejection cuts:~ 0.2


Ke3 normalization method:• Implement a kinematic fit in Ke3 hypothesis (almost done).

To be doneTo be done

For both measurement strategy:• Tracking efficiency (already done).• TCA efficiency (almost done).• Trigger efficiency (almost done).• Tag Bias.• Systematic checks.


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.

status of analysis

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