K two body decays

B.Sciascia KLOE General Meeting - Roma - November, 14th 2003 1

K two body decays

Barbara Sciasciaon behalf of Charged Kaon Working

GroupKLOE General Meeting

Roma - November, 14th 2003

Absolute BR measurements

BR(K ) B. Sciascia BR(K ) E. De Lucia BR(K )/BR(K )

M. Martemianov, V. Kulikov


K decay:state of the art

Highest K branching ratio (63%) - A single measure exists (Chiang ‘72)

Tag for absolute BR measurements - Tag Bias - -Trigger - Correlation effects - Cosmic veto/T3 correction

2001 and 2002 Data


Event selection Reconstruction:

FilFo

Tracking 1

EvCl 1 (5 Algos)

“Kaon joining”

EvCl 2 (5 Algos)

Tracking 2

Algorithm 5th: TagDecay Preselection:

-zPCA 20cm - PCA 10cm - pK (70,130) MeV

Selection: - VTX (40,150) cm - dp (-320,-120) MeV - p(m) (180,270) MeV

Systematics: to be studied


Caveat:

K 63.46

K e 4.86

K 3.27

K 21.08

K 1.73

K 5.548

K Nuclear int. 0.04K 61.32

K e 4.69

K 3.15

K 20.36

K 1.67

K 5.345

K Nuclear int. 3.47

KLOE MC truth K

KLOE MC truth K-

Tag: K- Signal: K

K nucl. interaction not well simulated under 400-500 MeV

Measured by KLOE? (see Patera talk)


Tag and signal selection

Tag - “recover” K from EvCl2 (TagDecay) - p(m): 3 cut - Trk-to-clu for -track - 2 trigger sectors fired by the

Sig (DC only) - Look for K (TagDecay preselection) - V2 vertex - VTX (40,150) cm - p(m): 3 cut


K Tag Bias

K 0.1 0.4

K e 0.9 0.4

K 1.3 0.4

K 1.9 0.4

K 6.6 0.4

K 17.7 0.4

K 1.3 0.4

K e 0.1 0.4

K 1.3 0.4

K 0.9 0.4

K 4.5 0.4

K 19.1 0.4

DC selection (p, m mass hypothesis) Trk-to-Clu for track -cluster fires 2 trigger sectors (AutoTrigger)

Tag K Signal K Tag K Signal K

MC: 4 pb-1 for 20 pb-1 of Data

K Tag Bias at the same level


pions

on calorimeter: Data and MC

muons


Efficiency- Tag in one side- One “-cluster” different from the tag one: 0 cluster with ECLU (EA,EB) MeV 1 cluster with ECLU (EB,EC) MeV

MC: EA = 20 MeV EB = 120 MeV EC = 370 MeV

Data: EA = 20 MeV EB = 90 MeV EC = 320 MeV

MC vs MC: MC Truth = (28.9 0.1) MC-like-Data = (30.1 0.1)MC-like-Data Corr = (28.8 0.1)


“Correlation” Tracking seems to correlate Tag

and Signal emispheres Try an estimation from MC Method:

aba

abaaba

aba

p

pp

p

2

1

0

1

1

1211

b

babp

1211

Define a “kind of correlation”, :

Correction to be applied:

- from MC- from Data - typical value: 1.0460.002 (4pb-1of MC, 20pb-1 of data)

DC HW efficiency

Layer

Present MC eff.


Branching ratio MC (4pb-1) vs MC (4pb-1):

- BR(K) = (63.46 0.40) - BR(K--) = (62.44 0.40) - Remind MC truth: 63.46 and 61.32

Cosmic veto/T3 efficiency: 0.2

2001-2002 Data/MC

K+ () K- ()

NSIG/NTAG (Stat) 0.051 0.053

Efficiency (Stat) 0.059 0.062

Correlation (Stat MC) 0.050 0.051

Tag Bias (Stat MC) 0.076 0.076

Cosmic veto/T3 (Stat)

0.030 0.030

Total 0.12 0.13

BR(K) = (64.84 0.08) BR(K--) = (63.88 0.08)

Very preliminary, for K . . .

waiting for new MC:

HW DC eff. and on calo


• Self-tag on one side using K- (avoid nuclear interactions)• Vertex with 2 tracks in DC on the signal side

Strategy

Fit the distribution of the momentum of the secondary track (p*) in the kaon reference frame

The selection efficiency is only related to DC reconstruction :• tracking efficiency (see Patera’s talk) • vertex efficiency (ongoing work to be finalized)

Method:

Status of K±±

E. De Lucia


Difference between Tags

tag –

p* (MeV/c)

x10-2

p* (MeV/c)

tag tag


DATA vs MC

Clear resolution effects…two possibilities 1) work on resolutions MC wrt DATA 2) use two “clusters” sample

p* (MeV/c)p* (MeV/c)


2) Use the two”-cluster” sample

a) hp: and peaks have the same resolution function b) p*( mass) distribution for peakc) p*( mass) distribution for peak

p*( mass): peak

p* (MeV/c)

MC

peak fit with p*( mass)

MC

p* (MeV/c)


In order to extract the number of decays:

1) Estimate the background - require a in the calo and measure the efficiency2) Take into account the 3-body decays contribution - fit the distribution down to 180 MeV in order to have 3-body decays contribution only from kl3 channel

Perform the fit:

a) using the MC shapeb) parametrize it with a Fermi-Dirac distribution (first MC tuned)


DATA

a) using MC shape for 3-body decays

MC

p* (MeV/c) p* (MeV/c)

2/ndf = 1.08 2/ndf = 0.96

fit lower edge 180 MeV


b) using Fermi-Dirac shape for 3-body decays

MC

p* (MeV/c)p* (MeV/c)

MC

and populations agree within errors Work in progress

fit lower edge 180 MeV


Analysis of ratio BR(K 0)/BR(K )M. Martemianov V. Kulikov

cosK.KselKfit.Ktrg

window.exp

K

0K

K

0KR

Ktrigger - trigger efficiency,

extracted from EXP. data

Kfit - efficiency of signals and

background rejection, based on MC

data and performed of EXP data,

Ksel - selection efficiency,

from MC and EXP. data

Kvetocos - efficiency of

cosmic veto rejection, EXP. data

- hyphotesis for secondary particles

Selected - window : 190 - 220 MeV/c

Selected - window : 220 - 260 MeV/c


0.00220.00030.3346ν)μBR(K

)ππBR(K (syst.)(stat.)0

2(syst.)(stat.) 10)65.00.09(133.46

Both triggers employed

New checks on Ktrg and Kcos

Result is in good agreement with world data

Statistical error negligible due to the huge sample of kaon decays (more than 6.5 M; 2002 Data).

Systematic error ( 0.65 %) dominates.

Result can be updated by further investigation of MC/EXP uncertanties

Include calculation of K decay

Analysis of ratio BR(K 0)/BR(K )


Br(K ): measurement on a good shape Br(K ): ongoing work Br(K )/Br(K ): memo in

preparation

New MC (see M. Moulson presentation): - Small sample - HW+Tracking efficiencies (by S.Dell’agnello, ready) - on EMC (by C.Bloise, M.Testa, and T.Spadaro, ongoing work) Improve correlation study

Conclusions

Tags in a good shape for absolute BR measurements

Efficiencies: a lot of work . . .

Selection effects: - FilFo - Trk 1/Trk 2; EvCl 1/EvCl 2

Different techniques have been implemented Systematics: to be finalized. . .

Documents

K two body decays