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M. Martini, INFN Frascati, for the KLOE collaboration. 7-11 June 2004. INFN, LNF. A direct search for K s  3 0 decay at KLOE. K S 3 p 0. This decay has never been observed but is allowed by SM [CP violating; CP(K S )=+1, CP(3 p 0 )=-1]. From theoretical point of view:.

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M martini infn frascati for the kloe collaboration

M. Martini, INFN Frascati,

for the KLOE collaboration.

7-11 June 2004

INFN, LNF

A direct search for Ks 3 0 decay at KLOE


KS3p0

  • This decay has never been observed but is allowed by SM

  • [CP violating; CP(KS)=+1, CP(3p0)=-1].

  • From theoretical point of view:

All KLOE statistics  0.9 signal events produced (e=100%)

Current published limit: BR(KS3p0) < 1.4x10-5 (SND, PL B459 1999)

  • The observation of this decay would confirm CP violation in KS

  • system.

  • Uncertainty on KS3p0 amplitude limits precision on CPT test

  • (Bell-Steinberger relation).


KS3p0

KLCRASH

b0.22

  • KS tagging: from KL interactions on EMC

KLCRASH(e~30%)

This algorithm searches KL which interact directly on EMC.

KLCRASH calorimetric clusters are selected using energy and b*.

  • High bkg rejection needed:

  • major expected background: KS2p0 (BR31%) + 2 fake photons either from

  • shower fragments or accidental overlap with clusters from machine

  • background.


Photons counting and kinematic fit

-- KS3p0 (MC)

-- MC BKG

 DATA

  • A kinematic fit is applied on the

  • Ks side requiring the conservation of

  • 4-momentum (NDOF=11).

  •  c2FIT

Photons counting and Kinematic fit

DATA=450pb-1 (2001+2002); MC =540pb-1 (all available statistics)

  • Preselected signal sample (KLCRASH and 6 photons): 39728 events

  • Normalization Sample (KLCRASH

  • and 4 photons): 23.5x106 events

c2FIT< 30 is not enough

(2/3 of bkg rejected)!

Other discriminating variable have to be used:

(c22p, c23p)


The c 2 2 p
The c22p

KLCRASH + 4 photons

 DATA

-- MC

The c22p is built selecting 4 out of 6 clusters

which satisfies better the kinematics of KS  2p0

  • The parameters used are:

  • mass distribution

  • opening angle between pions in

  • KS C.M. frame

  • 4-momentum conservation

The calibration is done using KS2p0sample.


The c 2 3 p
The c23p

 KS3p0

MC

 DATA

MCbg

The c23p is

based only on

the 3 “best reconstructed” pion masses


c23p

c23p

DATA-MC comparison

  • We define a signal box and 5 control boxes.


c23p

DATA-MC comparison

  • A small fraction of the background (3%) is constituted by fake KLCRASH

  • (KSp+p-) + KL3p0. Our MC well reproduces such fakes.


Analysis summary
Analysis summary

  • To increase bkg rejection we use

  • these analysis cuts:

  • Track veto:

  • to reject events with tracks

  • coming from IP.

  • DECUT:

  • After finding the four photons satisfying the kinematics

  • of KS2p0, the residual energy of the KS is measured:

  • E(KS) = EKs- Eg

  • 2 bodies decay  E(KS)~ 0 MeV

  • 3 bodies decayE(KS)~ Mp

Rejecting events with:

DE(KS)<10 MeV


c22p all

c22p>40

  • TRKveto

14<c22p<40

c22p<14

  • DECUT + c2FIT

Analysis summary

  • No Cuts


Candidates
Candidates

  • We have optimized our analysis cuts looking at MC

    • c22p

    • c23p

  • c2FIT

  • DECUT

c22p

 DATA

 MC

c23p

  • e = (22.6±0.8)%

  • We count 4 candidates with

  • 3.2±1.4±0.2

  • expected by MC

  • N3p ≤ [email protected]% CL

  • Folding the proper bkg

  • uncertainty.


Upper Limit determination

  • Using this upper limit we can calculate some parameters

  • directly related to CP and CPT test.

Using PDG values and our limit:

  • We derive from our analysis:

This improves of a factor ~70 the previous limit.


Related parameters

  • Our limitcan be compared with NA48

  • - interference term between KSKL in the

  • same final state (proportional to Re(h000)

  • and Im(h000)).

KLOE versusNA48

(hep-ph/0310152)

SND

90% CL

  • Assuming CPT invariance and ignoring

  • transition into I=3 final state:

  • Re(h000)=Re(e).

  • We can calculate the contribution of

  • 3p0 decay at Im(d) (Im(d)000) using

  • unitarity relation (eS,L=e±d):


Related parameters

  • Since these are 2 opposite values,

  • we obtain the limits:

Im(d)000

becoming negligible on the

determination of Im(d)

f000(rad)

This value is based only on unitarity and increases the precision on Im(d) of  2.5

  • The most conservative approach is to assign a phase toa000

  • which gives the minimum and maximum values of Im(d)000:


Conclusion

  • A direct search for KS3p0 decay has been performed

  • using the whole statistics collected at KLOE during 2001-

  • 2002 data taking.

  • We set an upper limit on the branching ratio to

  • 2.1x10-7 @ 90% C.L.

  • This reduce of a factor ~70 the previous limit.

  • This limit makes completely negligible the contribution of

  • this decay on Im(d) reducing of a factor~2.5 the

  • uncertainty on Im(d)



The c 2 3 p1
The c23p

 DATA

 MCbg

Due to DAFNE bkg which satisfy the trigger.

Reduced by our Splash Filter:

rmean > 70 cm

Emean > 70 MeV

“SPLASH” events

Good agreement DATA-MC in all the regions

 DATA

MCbg

 DATA

MCbg

 KS3p0

MC

c2FIT < 30

Thec23pis based only on the 3 reconstructed pion masses


Data mc comparison
DATA-MC comparison

DATA

?

FAKEKCRA

MCbg

In the data, a new category of BKG events (not simulated by the standard Kcrash MC) appears. The simulation takes into consideration only KL decaying after a cilinder bigger than DCH and smears the KL MC direction with the Kcrash resolution observed in data.


The k crash fake background
The Kcrash fake background

  • A small fraction of the background (3%) is constituted by

  • a fake Kcrash and a KL 3p0 decay.

  • The fake KLCRASH is generated mostly by KSp+p- event,

  • where the pions, spiralizing around the pipe, interact on

  • the quadrupoles creating late clusters in the event.

  • We have add the simulation of these events in the MC and

  • calibrated their quantity.


DATA-MC “fakes” comparison

  • Outside the

  • KLCRASHb*

  • windows DATA are

  • dominated by fakes

  • In the central band

  • there is also a small

  • percentage of

  • KLCRASH.

 DATA

-- MC Fake

 DATA

-- MC Fake

EKLCRA

EKLCRA

EKLCRA

b*

Comparing events with tracks from IP.

b*

 MC fakes only (i.e. no Kcrash)

 DATA dominated by fakes


The agreement between DATA and MC is better than 10% in all

the regions.

c22p

Region

Nev (Data)

Nev (MC)

SBOX

337  18

309.5  16.3

UP

Cup

UP

493  22

479.8  21.2

DOWN

382  19

426.5  14.4

CSbox

5502  74

5595.1  51.0

CSox

Cup

11249  106

11744.1  74.0

SBOX

Cdown

24396  156

23844.9  103.8

DOWN

Cdown

c23p

DATA-MC comparison


Monte carlo calibration
Monte Carlo calibration

-- DATA

-- MC

-- KCRAMC

-- FAKEKCRA

Normalized with the full sample Ng=6

(A)

(B)

Mean

KCRAMC

0.446

0.447

0.447

FAKEKCRA

1.002

0.895

0.949

c23p < 3.5

FIT data using shapes from MC:

ID(DATA) = a1 ID(MC)+ a2 ID(FAKES)

Two different regions used:

c23p < 3.5 (A)

c23p < 8.8 (B)

After removing SBOX


Data mc comparison i
DATA-MC comparison (I)

c23p all

c23p > 3.5

 DATA

-- MC

 DATA

-- MC

c23p < 3.5

c23p< 8.8

 DATA

-- MC

 DATA

-- MC

Normalization with the mean values of the coefficients


Data mc comparison ii
DATA-MC comparison (II)

c22p all

c22p > 40

 DATA

-- MC

 DATA

-- MC

14<c23p<40

c23p< 14

 DATA

-- MC

 DATA

-- MC

MC KS 3p0, BR=1.4x10-5

Normalization with the mean values of the coefficients


The track veto
The track veto

MC SignalDATAMC bkg

c22p all

c22p > 40

14<c23p<40

c23p< 14

All events with tracks from IP are rejected rPCA < 4 cm ; |zPCA| < 10 cm

MC signal, BR(KS3p0)=1.4x10-5


The topological d e cut
The topological DECUT

-- MCBG no 2fitcut

 MCBG 2fit < 30

 MCBG 2fit + TRKveto

 MCSIG

DECUT < 10 MeV

After finding the four photons satisfying the kinematics of

KS2p0, the residual energy of the KS is measured:

E(Ks) = Eks- Eg

  • Summarizing:

  • c2FIT<30

  • TRKveto

  • Sbox


Syst.error on BKG

Syst1 =  9% (Calibration)

Syst2 =  10% (Data/MC)

Systot =  14 %

Analysis efficiency and bkg systematics

Sample of 10 Kevents

KS 3p0

e3p = ( 21.30.7stat 0.3syst )


Optimization of UL cut on the kin. Fit:

  • We have optimized the UL by MC looking at 4 different

  • parameters:

    • c2FIT

    • c22p (both sides)

  • c23p

  • DECUT

  • The best choice of the cuts is the following (CUTMAX):

    • c2FIT < 31

    • 14 < c22p < 60

  • c23p < 3.7

  • DECUT > 37 MeV

  • Optimization is done by minimizing the expected 90% CL

  • upper limit (ref. J.F.Grivaz, F. Le Diberder LAL 92-37)

  • All is done varying cuts on MC only.


NA48 interference function cut on the kin. Fit:

K0 K0 Dilution factors

KL decay

KS decay

Interference KL-KS


Related parameters cut on the kin. Fit:

  • The more conservative approach is to give ata000a phase which

  • maximizeIm(D)000:

  • Because there are 2 opposite values, we obtain a range for

  • |Im(D)|[email protected] 90% C.L.:

Im(D)000 KLOE

Im(D)000 CPLEAR

Im(D)pln

This value is obtained using only unitarity, and increases the precision on CPT test.

Im(D)00

PDG 03

Im(D)+-

x10-5


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