Sabino Meola Kloe meeting 10 March 2005 Status of analysis.
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Transcript of Sabino Meola Kloe meeting 10 March 2005 Status of analysis.
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.