Neutral kaon WG other activities

Volounteered Rapporteur: F. Bossi

• Coherent KS regeneration

• KL branching ratios

• KL 00 and QCAL

CP wg meeting 22 November 2002

Coherent KS regeneration

M. AntonelliA. De Santis A. Di Domenico

INFN Laboratori Nazionali di FrascatiPhysics Dept. University of Rome “La Sapienza” & INFN RM1

Coherent regeneration

Coherent regeneration occurs only in the strictly forward direction:

ScohLL KKK

2

)( ScohL KKtP

coht

coht

coht

S mteeeK LSSL cos2 2/)(222

This interference term is important for thin regenerators, i.e. when |coh| ~ |±| as for the beam pipe and inner DC walls

Event selection

Data sample : DST of 2001 and 2002integrated luminosity: 340 pb-1

Preliminary selection:• KS - sqrt(x2+y2) < 5 cm AND |z| < 10 cm - |Minv - MK| < 5 MeV

• KL - two track vertex inside a 40 cm radius sphere

- vertex inside 20 degree cone around extrapolated KL direction from PKs.

• kinematic fit to improve KS KL vertex position (the same as in interferometry study – M. Antonelli & A. Sibidanov)

)y(x 22

Event selection

Minv (MeV)

• | |PKL| - |P+-| | < 5 MeV

• |Emis + (Minv-MK0)| < 5 MeV

Emiss (MeV)

Only scalar quantities used for the selection criteria in order to avoid distortion of angular distribution of the incoherent regeneration bkg.

Beam pipe

DC inner wall

P

(rad)

cut

incoherent regeneration

incoherent regeneration

Background evaluation:• angular distribution of incoherent regeneration is assumed flat (in solid angle) in the small region• fit of incoherent regeneration background and subtraction• cut < 0.04

• K3 background negligible (checked with data)

Background

cut

(rad)

Resolution fixed

Resolution fixed

PKL

Regenerator

Background subtraction

t S

t S

Incoherent regenerationbkg smeared according to MCand with data for >cut

signal + bkgbkg

Efficiency

-Only relative variation of the efficiency are relevant. (Normalization to through |±|).

-a preliminary MC study does not shows dramatic changes in the region of interest (M. Antonelli-A. Sibidanov): more accurate studies needed !

LK

Beam pipe

fit results:

2 = 27.6/15

= (6.5 ±2.2) ·10-4

± 0.25 rad

fit results

Fit function: P(t) folded with MC resolution

DC inner wall

fit results:

2 = 14.0 / 15

= (16.6 ± 6.6) ·10-4

± 0.27 rad

fit results

fit results

DC inner wallRed curve: incoherent regeneration(only decay term)

tcoh

t SL ee22

coh

tcoh mte LS cos2 2/)(

Black curve:coherent regeneration(decay and interference term)

tinc

t SL eAe 22

fit result : phase

DC inner wall

The fit result is quite sensitiveto the coh phase, due to theinterference term

fit results: result stability vs cut

fit results as a functionof the cut parameter

For comparison:horizontal linesare the Baldini-Michettievaluations

Conclusion

- Theoretical evaluations (Baldini-Michetti) compatible with preliminary results

- more work to do on: - Efficiency evaluation - Refine and incoherent regeneration background evaluation - Complete analysis with full Kloe statistics

Our Christmas present to Paolo F. :

We will measure absolute branching ratios

Status of the measurement of

KL l,branching ratios

M. Antonelli, M. Dreucci, M. Moulson

CP meeting 16-12-2002

Introduction

Problems in both measurements:• tag bias (common to all KL BR measurements) • tracking efficiency

Additional Problems KL :• momentum calibration• momentum resolution

( semileptonic event selections needs looser kinemtic cuts)

Tag bias

Main bias is expected from trigger

require trigger from ks pions:

clusters connected to fired trigger sector no other cluster in “ks sectors” (avoid overlaps)

no splitted pion tracks (T2CL asso. quality) + ks direction far from beam line (cos()>0.9)

Ks selection: Rt<10cm ;|z|<20 cm |m-mK|<5 MeV; |p*-p*K|<10 MeV

63%

39%

25%

20%

Tag bias: MC results

Relative KS +- efficiency for various KL process

KL eKL

KL +-0

KL 000

KL All

out FVCrash included

63% standard

39% Ks trigger

25% + overlaps

20% + tracks q. Ks dir.

KLtag

in FV

+/- 1%

Tag bias: cont.

General :•Main KL decay mode can be measured with “unbiased” tag.•Rare decays can be normalized to main one

Prospects:• a <1% biased tag available • compare with data (neutral vs charged Kltag)• for more studies we need good simulation of: KL “shower”, fragments, machine bkg. inclusion (soon)

Tracking efficiency

Double tag method ( from KL analysis)

KS

Conditional efficiency N2/N1 from data

Data-MC comparison“Efficiency” dependence for about 20 variables (2000 data) just few examples efficiency definition = (# 2 tag events)/(# >0 tag events)

DATA MC

DATA MC

0 206 MeV 0 206 MeV

Data-MC comparison cont.

No clear dependencies found

BUT

Eff. vs <Hot rate>(Khz)

DATA MC

Kinematics Pm

iss

(MeV

)

Emiss (MeV)

QCAL infos and KL 0 0 search

Caterina Bloise

QCAL infos and KL 0 0 search

Can QCAL play any role in the KL 0 0 search ?

Two items have been considered :background reduction

knowledge of the distributions useful to separate signal and background

4-clusters sample ( last 115 pb-1 of the 2002 DAQ campaign) has been analyzed

Results: QCAL is marginal for the background reduction QCAL-tagged background is crucial for the knowledge of the distributions of the 30 contamination.

QCAL infos and KL 0 0 search

Likelihood Ratio - 4-clusters events (53.5 pb-1)

Eve

nts

/ 2.

Background selection: signal contamination evaluation

Plot 1 : shape of the difference between events selected with T < 20 nsand those with T < 10 ns

Plot 2 : shape of the difference between events selected with T < 10 nsand those with T < 5 ns

Plot 3 : shape of the difference between events selected with T < 5 nsand those with T < 3 ns

Black area : shape of the events selected requiring T < 3 ns

1

2

3

QCAL infos and KL 0 0 search

Background reduction is modest :

14884 events / ~66000 ~22% of the contamination is tagged by QCAL requiring at least one hit in time T < 5 ns

Black histogram : Entire sample distribution

Blue histogram : Event distribution without taggedsample by QCAL

Likelihood Ratio - 4-clusters events (115 pb-1)

Eve

nts

/ 0.

5

QCAL infos and KL 0 0 search

Black histogram : MC distribution for the entire background sample 15313 simulated events

Red points : MC distribution for the QCAL tagged background - 3598 events

Likelihood Ratio - 4-clusters events MC

Eve

nts

/ 0.

5

QCAL infos and KL 0 0 search

Black histogram : MC distribution for the entire background sample 15313 simulated events

Red points : QCAL tagged background in 115 pb-1 - 14884 events

Likelihood Ratio - 4-clusters events QCAL vs MC shape

Eve

nts

/ 0.

5

QCAL infos and KL 0 0 search

4-clusters events (black points) 59794 collected in ~ 115 pb –1

Signal shape from MC 18208 simulated events

Background shape from QCAL 14884 collected events

Fit results : Signal (red histogram): 8570 220 ev

Background: 51225 510 ev

459/356

Blue histogram is the sum of signal and background from fit results

Eve

nts

/ 0.

5

Likelihood Ratio - 4-clusters events (115 pb-1)

CONCLUSIONS

The QCAL information is crucial for the knowledge of the background behaviour

It is also important to increase its efficiency in order to achieve a better statistical accuracy on the interesting distributions