rare decays program @kloe

Rare decays program @KLOERare decays program @KLOE

Matteo Martini

INFN Laboratori Nazionali di Frascati On behalf of the KLOE Collaboration

LNF, INFNLNF, INFNMay 26May 26thth-27-27thth 2005 2005

DANE: the Frascati - factory

ee collider @ s = M= 1019.4 MeV 2 interaction regions (KLOE –

DEAR/FINUDA)

Separate e, e rings to minimize beam-beam interactions

Crossing angle: 12.5 mrad ( px12.5

MeV )

M. Martini, K rare decaysM. Martini, K rare decays 1

KLOE: data taking

2001: 176 pb1

550×106 decays

2002: 296 pb1

920×106 decays

First published results

2000: 25 pb1

80×106 decays

Days of running

Inte

grat

ed lu

min

osit

y (p

b1 )

2002

2001

2000

Analysis

in progress

New KLOE running in progress:• Lpeak= 1.4 × 1032 cm-2s-1

• 2004: integrated Lum.: 700 pb-1

Goal: collect 2 fb-1 by Dec. 2005


The KLOE detector

Superconducting coil (B = 0.52 T)

Drift chamber Gas mixture: 90% He + 10% C4H10

4 m 3.75 m, CF frame 12582 stereo–stereo sense wires almost squared cells

Al-Be beam pipe (spherical, 10 cm , 0.5 mm thick) Instrumented permanent magnet quadrupoles (32 PMT’s)

Electromagnetic calorimeter lead/scintillating fibers (1 mm ), 15 X0

4880 PMT’s 98% solid angle coverage

p/p0.4 % (tracks with > 45°)

xhit150 m (xy), 2 mm (z)

xvertex ~1 mm

(M) ~1 MeV

E/E5.7% /E(GeV)t 54 ps /E(GeV) 50 psvtx() ~ 2 cm ( from KL )

3M. Martini, K rare decaysM. Martini, K rare decays

Kaon production and properties

S = 6 mm: KS decays near IP

L = 3.4 m: Appreciable acceptance

for KL (~0.5L)

NSL ~106 /pb-1 ; p* = 110 MeV/c

1,p , p , p ,p

2L S L Si K K K K

Tagging: observation of KS,L (K+,-) signals presence of KL,S (K-,+)

precise measurement of absolute BR’s and interference measurement of KS KL system

KSKL (KK) produced in pure JPC = 1 state:

KS (K KL (K

The meson decays at rest providing monochromatic and pure kaon beams

Contamination ~10-10

= 0.9 m: 60% acceptance for

kaon tracking

N ~ 1.5106 /pb-1 ; p* = 127 MeV/c


Tagging of KS and KL “beams”

KL tagged by KS vertex at IPEfficiency ~ 70% KL angular resolution: ~ 1°KL momentum resolution: ~ 1 MeV

KKSS

KKLL 2 2

KS tagged by KL interaction in EmCEfficiency ~ 30% KS angular resolution: ~ 1° (0.3 in )

KS momentum resolution: ~ 1 MeV

KKLL “crash”“crash”= 0.22 (TOF)= 0.22 (TOF)

KKSS ee

4 x105 tags/pb-1 3x105 tags/pb-1


Rare Kaon physics at KLOE

6

KS 30

- final results - prospects @2 fb-1

KS

- status of the analysis - prospects @2 fb-1

KS

- preliminary study

Outlook:

M. Martini, K rare decaysM. Martini, K rare decays

hep-ex/0505012 submitted to PLB

analysis inprogress

Paving theroad

Observation of KS 30 signals CP violation in mixing and/or in decay:

Uncertainty on KS 30 amplitude limits precision of CPT test from unitarity (Bell-Steinberger):

CPLEAR ’99 : Im = (2.4 5.0) x 10-5 30 uncert. dominates

after NA48 meas. : Im = (-0.2 2.0) x 10-5 error now dominated by

CPTCP

*1 tan SW S Lf

mei i A K f A K f

SM prediction: S000

= L000|+000|2, giving: BR(KS 30) = 1.9 x 109

Best limit from direct search SND ’99 : BR(KS 30) < 1.4 x 105

Interference meas. NA48 ’05: BR(KS 30) < 7.4 x 107


Search for KS 000

-- KS30 (MC)-- MC BKG DATA

A kinematic fit is applied on the Ks side requiring the conservation of 4-momentum (NDOF=11). 2

FIT

Search for KS 000

Preselected signal sample (KLCRASH and 6 photons): 39538 events

Normalization Sample (KLCRASH and 4 photons): 23.5x106 events

DATA=450pb-1 (2001+2002); MC =0.9fb-1 (all available statistics)

2FIT/NDF < 3 is not enough

(2/3 of bkg rejected)!Other discriminating variable have to be used:

(2, 3M. Martini, K rare decaysM. Martini, K rare decays 8

Search for KS 000 Rejection of bkg:

KS + 2 accidental/split ’s

Define signal box in (2, 3 plane:

3 pairing of 6 clusters with best 0 mass estimates 2 best pairing of 4’s out of 6: 0 masses, E(KS), P(KS), c.m. angle between 0’s

DataMC KS 30

In the (2 , 3) plane we define a signal and five control boxes. The agreement between DATA and MC, after each analysis step, is better than 10% in each region.

Signal generated with BR=10-5 (SND)


Search for KS 000

DataMC KS 30

Signal generated with BR=10-5 (SND)

Other analysis cuts:

-Track veto to reject events with tracks coming from IP

- Final cut on residual KS energy: E(KS)-EM. Martini, K rare decaysM. Martini, K rare decays 10

Nsel(data) = 2 events selected as signal, with efficiency = 24.5%

Nsel(bkg) = 3.130.82stat0.37sys bkg events expected from MC

Which translates into a limit on |000| @90% c.l.:

Measuring 3=24.5% from MC generated signal and normalizing signal counts to KS 00 in the same data set we obtain @90% c.l.:

Can state: N3<.45@9%CL

Search for KS 000

3

0 0 73

2

2

3 2 1.2 10S S

N

BR K BR KN

0 0

000 0 0

3 30.018

3 3

S SL

SL L

A K BR K

A K BR K

NA 48

KLOE


Search for KS 000


• Increased statistics: x 6.5 improvement– Luminosity x 5

– Add tagging by KL vertex in DC x 1.3

• Increased background rejection– Largest bkg source after all cuts is the splitting of e.m. clusters

• Merging procedure removes bkg but leaves signal untouched

• Candidates in data go from 2 to 0, in MC from 3.13 to 2

– Optimization of kinematic fit in progress

– Overall better reduction of the known background expected

If we will be able to suppress the background to a ~negligible levelUL will improve by 6.5 x 1.5 ~ 10

Search for KS +-0

Present status for the BR(KS):

• Decay amplitude is composed of CPC (3x10-7) and CPV (1.2x10-9) parts

• Direct measurement of the BR is possible using the entire KLOE data set.

• Measurement can be used to verify PT predictions. These predictions are poorly tested.

Currently, we have performed the search using a sample of 740 pb-1 of data:

- 373 pb-1 from 2001-2002 data taking

- 367 pb-1 from 2004 data taking

Assuming BR(KS) = 3 x 10-7 230 signal events produced


Search for KS +-0

Selection: KL-crash tag with 2 low momentum tracks from IP

Preselection algorithm:

- Require vertex at origin with zero net charge

- Require 2 prompt neutral clusters

- Each pair of clusters is a 0 candidate. For each:

- close 3-body kinematics using m(0), m(KS)- set t0 using pair of clusters- use p(KS) and p() to search KL-crash cluster in 20° cone

- choose 0 pair that best agrees with reconstructed KL momentum

-

KL


Search for KS +-0

Application of kinematic fit to reject bkg. Using 2 < 30 (NDOF = 8):

- Cut efficiency = 48.5% - 98.8% of bkg rejected - MC(SIG) = 3.3% 3.9 events expected

2 after preselection for MC signal and

background

MC gives 93 bkg events after kinematic fit

K+

+

The ’ bkg are due to charged kaon

events


Search for KS +-0

We studied more in detail the various background classes and developed a set of cuts to reduce them:

K± events

K± has monochromatic ± momentum at 206 MeV; cut on p*

Dalitz

dedicated MC production of Dalitz events; require TCA cuts for significant reduction of this background

After these cuts we still have 3 ’ bkg events

’

dedicated MC production of K± (Ke3 + K3 + ’), K all Cut on the energy of prompt clusters not associated to any tracks or to 0 (Efree)

±


Search for KS +-0

Compare DATA and MC:

DATA

Standard BackgroundMC

25130 eventsin the data with no cuts applied


TOF p

EFREE

Search for KS +-0

At the end of analysis signal efficiency 1.5%

Preliminary results with 740 pb-1:

- candidates: 6 events - background: ~ 3.5 events - observed events consistent with expectation within the statistical error (100%) - evaluation of systematic error in progress

Scaling the values of signal and background to 2 fb-1 we expect:

- 16 events, of which 9 background- 60% statistical accuracy on BR(KS)


BR differs from CHPT O(p4) by 30%,useful to fix one O(p6) counterterm

Projections based on– 150 pb-1 of 2001 background MC– 10K events of signal MC

With 2 + 0.5 fb-1 we expect– 500x106 KS events tagged by

Klcrash

– N(KS, tagged) = 500x106 x 2.8x10-6 = 1400 events

– acceptance 0.4

– Nsig = 560 events

2 fb-1: with good background rejection ~ 4% statistical error


Paving the road for KS

• Strategy of analysis

– No recover splitting and

large angular acceptance

– Kinematic fit to exploit two body kinematics

• Distribution of kinematic variables after fit

• Background separation

looks promising

bkg signal

A.U

.

A.U

.

bkg signal

MC distributions, no data yetN. of events in A.U.

After fit

Reco

ns.


Paving the road for KS

20

Conclusion


A direct search for KS30 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 at:

BR(KS30) < 1.2x10-7 @ 90% C.L.

We have started the direct search of the KS+-0.

For the moment we have analyzed only 740 pb-1 of data. Now we are analyzing the other 300 pb-1 already on disk. The prospects at 2 fb-1 is promising.A statistical accuracy of 60% can be reached.

We are paving the road to study KS.

With 2 fb-1 we can reach a statistical error of 4% and contributeto test the PT prediction for the branching ratio.

BackupBackup

Adding in quadrature all the sources of systematic error, we obtain:

2001 91.8 0.2 0.3 %SEL stat sys

Using these results and the efficiency on trigger and cosmic veto, we can calculate the number of events of the normalization sample:

0 62 37.8 0.2 10L SN K crash and K

This value enters directly in the upper limit calculation.


Search for KS 000

The 22 is built selecting 4 out of 6 clusters

which satisfies better the kinematics of KS 20

The parameters used are:

mass distribution

opening angle between pions in KS C.M. frame

4-momentum conservation

The calibration is done using KS20 sample (see

next slide)

The 23 is based only on the 3 “best

reconstructed” pion masses


Search for KS 000

DATA MC

DATA MC

M

EE

M

In the construction of 2 we use a different sigma

for each sample. DATA and MC

(OLDMC, NEWMC) (2001 ,2002 ).


Search for KS 000

To better calibrate data and MC, we have also questioned how well the MC reproduces the amount of double shower fragments and double accidental clusters. To understand and calibrate this we have divided the MC KL-crash events into 2 further classes:

2A: events of Ks20 in overlap with 2 accidental (~ 60% )

2S: events of Ks20 with 2 splitted clusters or 1 accidental + 1 splitted cluster (~ 35%)

To do this, we perform a 3 components fit (2S, 2A and fake events)


Search for KS 000

23

22

23

23 2

3

22

22

22

DATA 2 S

2 A Fake


Search for KS 000

Summing up 2001-2002 for each MC, we can compare DATA with the two different MC productions.

DATA data MC MC

282 17 280 17,6

5037 71 4761 59,3

452 21 424 27,1

10132 101 9993 145,6

326 18 379 13,9

22309 149 22728 269,6

DATA data MC MC

282 17 283 18,9

5037 71 4870 61,5

452 21 413 26,9

10132 101 9962 146,9

326 18 381 14,2

22309 149 22636 266,8

NEW OLD

A reasonable data-MC comparison is found for both samples at the beginning of the analysis.

SboxCSbox

UPCup

Down

CDown


BackSearch for KS 000

DATA-- MC ALL

22>40

22<14

4<22<40

ALL

23 2

3

23

23

We apply a track veto to reject events with tracks coming from IP.

We reject events with:

PCA < 4 cm|ZPCA| < 10 cm


Search for KS 000

DATA-- MC ALL

TRK veto+

E/E

23 2

3

23

23

22 down

22 up2

2central

ALL


Search for KS 000

DATA-- MC ALL 2

2 down

22 up2

2central

ALL

23 2

3

23

23

END OFANA


Search for KS 000

DATA data MC MC EV TOT tot

2 1 3,125 0,8 17 4

520 23 446,5 10,1 2402 49

0 0 0 0,0 0 0

4 2 3,2 0,8 17 4

3 2 2,45 0,8 11 3

326 18 388,5 9,6 1961 44

Comparison between DATA and MC after the optimization procedure.

Sbox

CSbox

UP

Cup

Down

CDown

Nobs = 2 Bexp = 3.13 ± 0.82


Search for KS 000

Adding in quadrature all the contribution found, we obtain:

Source Bexp/Bexp

MC calibration 1.6 %

Fakes definition 1.8 %

Track veto 4.8 %

Energy resolution 6.6 %

Energy scale 6.7 %

2FIT 5.0 %

TOTAL 11.5 %

Bexp = 3.13 ± 0.82stat ± 0.37sys


Search for KS 000

For each sample we generate 3 poissonian centered around N2S, N2A and Nfake. Weighting eachdistribution for the proper calibration factor, obtained with the 2D-fit, we sum them up to build our PDFfor the background. The obtained PDF is reasonably similar to a Gaussian with average 3.15 and with equivalent to the ext. stat.

Folding the previous PDF with a Gaussian distribution centered around 0 and with a width equivalent to the whole systematic uncertainty we obtain the PDF for bkg that we use on the upper limit calculation.

The RMS include statistic and systematic uncertainty.


Search for KS 000

THE UNIFIED APPROACH: when exp is greater than Nobs, the classical method does not provide a perfect coverage. In this condition is better to use Feldman-Cousin-Neyman method based on likelihood ratio.

Classical Neyman

N3 = 2.42 N3 = 3.45

Bexp = 3.13 ± 0.82stat± 0.37sys

We observe Nobs = 2 candidates on data and we estimate:

With this counting we obtain the following UL @ 90% C.L.:

In our case, the exp. background is greater than Nobs.


BackSearch for KS 000

Search for KS +-0

Current values for the BR

Decay amplitude is composed of CPC (3x10-7) and CPV (1.2x10-9)

Selection requiring KL-crash, 2 tracks from IP (zero net charge), 2 prompt neutral clusters

• Data 740 pb-1 (2001+2002+ some 2004 runs)• Assuming BR=3x10-7 230 signal events produced• Major bkg: charged kaons, dalitz, ’• bkg reduced using: TCA , Tcut, P*• Use kinematic fit to select events kinematically closed (2 cut)• veto events with additional neutral prompt clusters below acceptance.

The set of cuts designed grants SIG 1.38% with very high background rejection

We expect to measure this BR integrating the whole collected data so far.M. Martini, K rare decaysM. Martini, K rare decays

Search for KS +-0


Back

Search for KS +-0

Summary of signal efficiency:


Search for KS +-0

Because of Data/MC discrepancies, especially in TOF, we want to obtain Nbkg from sidebands in data after cuts on TOF and p*.

Assuming no correlation beween 2 and EFree,

Study systematics by inverting cuts, varying acceptances

A/B=C/D


Search for KS +-0


ConclusionWith the data collected during 2001-2002 data taking, KLOE has:

- determined the best upper limit on KS30

- measured the main KL BR’s with 0.5% accuracy- measured in two independent ways the KL lifetime with 0.5 % accuracy Important contribution to the measurement of Vus

Next in line:

- Direct search for BR(KS)- Final result on KSe BR- Analysis of KL semileptonic form factor slopes

KLOE expects to collect 2 fb-1 by the end of 2005:thus allowing to improve the search for rare KS decays and KSKL interference studies.


rare decays program @kloe

Documents

ks p pp0

ks decays

rare decaystagging of

ks p0p0

interference measurement

residual ks energy

p0sz3z2datamc ks 3p0in

z3z2datamc ks 3p0signal