sabino meola kloe meeting 10 march 2005 status of analysis
TRANSCRIPT
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Sabino Meola Kloe meeting 10 March 2005
Status of analysisStatus of analysis400eK
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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
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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
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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
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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
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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
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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
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Sabino Meola Kloe meeting 10 March 2005
400K
3Ke
0K3K Knucleari
Step 3: kinematic fitStep 3: kinematic fit
300K
400eK
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Sabino Meola Kloe meeting 10 March 2005
Track to cluster associationTrack to cluster association
1
2
sec22
TrkVtxNeucl L
cttpm
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Sabino Meola Kloe meeting 10 March 2005
Background analysis: K± ± Background analysis: K± ±
We require p/E < 3
)3( 00K
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Sabino Meola Kloe meeting 10 March 2005
Background analisys: K± e±e (Ke3)
Background analisys: K± e±e (Ke3)
02
01
sec EEEEE Kmiss
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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
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Sabino Meola Kloe meeting 10 March 2005
Splitted clusters in Ke3 backgroundSplitted clusters in Ke3 background
400eK
Tridimensional clusters distance
3Ke
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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)
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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
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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.