Rare Kaon DecaysRare Kaon DecaysGiuseppina Anzivino

University of Perugia and INFN

on behalf of the

NA48/2 and KLOE Collaborations

Heavy Quarks & Leptons 08Heavy Quarks & Leptons 08

Melbourne, 5-9 June 2008Melbourne, 5-9 June 2008

6-6-2008

Giuseppina

Anzivino@HQ&L082

Overview

Mainly

Precision tests of ChPT in rare Kaon decays

In this talk:

recent results from NA48/2 and KLOE

not covered……… semileptonic decays (Vus related) (talk by P. Massarotti) leptonic decays and LFV (talk by T. Spadaro) future of very rare kaon decays (talk by M. Moulson) results from KTeV

6-6-2008

Giuseppina

Anzivino@HQ&L083

Outline

NA48/2 recent results in charged Kaon decays

K±→ ±eeBR and Form Factors (preliminary) K±→ ±BR and kinematics (preliminary) K±→ ±e+e-Branching Ratio (final)

KLOE recent results in neutral Kaon decays

KS→ Branching Ratio (final) KS→ e+e- Direct Search, Upper Limit (final) KS→ +-e+e- Branching Ratio (preliminary) KL→ eBranching Ratio (final)

6-6-2008

Giuseppina

Anzivino@HQ&L084

Experiments

LHCSPS

NA48/2NA48/2

KLOE

CERN

LNF

6-6-2008

Giuseppina

Anzivino@HQ&L085

NA48/2 @ CERN

Ke+e–

6-6-2008

Giuseppina

Anzivino@HQ&L086

Theoretical framework

(1) polynomial: W(z) = GFMK2∙f0∙(1+z)

(2) ChPT O(p6): W(z) = GFMK2∙(a++b+z) + W(z)

(3) Dubna ChPT: W(z) = W(Ma, Mρ, z)

dee/dz ~ P(z)·|W(z)|2

Form-factor models:

z=(Mee/MK)2, P(z) phase space factor

(2) D’Ambrosio et al. JHEP 8 (1998) 4 (3) Dubnickova et al. hep-ph/0611175

(f0,) or (a+,b+) or (Ma,Mρ) determine a model-dependent BR

K * l+l-

suppressed FCNC processes one-photon exchange useful test for ChPT

Parameters of models and BR in full kinematical rangeModel-independent BR (z > 0.08) in visible kinematical range

6-6-2008

Giuseppina

Anzivino@HQ&L087

Kaon flux (2003+2004) K=1.701011

K±→DK±→e+

e-

7146 events (Mee>140 MeV) (BG 0.6%)12.23 x 106 events (BG 0.15%)

Data Samples

The BR is measured normalizing to K0D e+e–

→ particle ID efficiencies cancel at first order common selection criteria for signal and normalization channel

→ 3 track vertex, electron (pion) ID with E/p > 0.95 (< 0.85) K0

D BG suppressed using a kinematical cut Mee>140 MeV

6-6-2008

Giuseppina

Anzivino@HQ&L088

Fit results (preliminary)

= 2.350.18f0 = 0.5320.016

ρ(, f0) = –0.963

a+ = –0.5790.016

b+ = –0.7980.067

ρ(a+, b+) = –0.913

Ma = (0.9650.033) GeV

Mρ = (0.7110.013) GeV

ρ(Ma, Mρ) = 0.998

(1)

(2)

(3)

polynomial: W(z) = GFMK2∙f0∙(1+z)

ChPT O(p6): W(z) = GFMK2∙(a++b+z) + W(z)

Dubna ChPT:W(z) = W(Ma, Mρ, z)

Model-Independent BR computed by integrating d/dz

BRMI (z>0.08) = (2.26±0.08)10–7

Analysis cut:z>0.08, or Mee>140MeV/c2Available data set

unable to distinguish among models

BR1 = (3.02 0.04stat) 10–7 BR2 = (3.11 0.04stat) 10–7

BR3 = (3.15 0.04stat) 10–7

6-6-2008

Giuseppina

Anzivino@HQ&L089

Results – BR in full kinematic range

BR=(3.080.04stat0.04syst0.08ext 0.07model)10–7=(3.080.12)10–7

preliminary!!

preliminary!!

Measurement BR107

Bloch et al., PL 56 (1975) B201 2.700.50

Alliegro et al., PRL 68 (1992) 278 2.750.26

Appel et al. [E865], PRL 83 (1999) 4482

2.940.15

NA48/2 preliminary (2008) 3.080.12

Including the uncertainty due to the model dependence

First measurement of CPV parameter (correlated K+/K– uncertainties excluded)

(Kee) = (BR+–BR–)/(BR++BR–)

= (–2.1 1.5stat 0.3syst)%

New

“naïv

e”

WA

NA48/2

‘75 ‘92 ‘99 ‘08

BR

(10

-7)

6-6-2008

Giuseppina

Anzivino@HQ&L0810

Results – FF slope

NA48/2 measurement of good precisioncompatible with earlier results

Contradiction of the data to VMD

further confirmed NA48/2 values of (f0, a+, b+)

in agreement with BNL E865 Measurement Process Result

Alliegro et al., PRL 68 (1992) 278 K++e+e– 1.310.48

Appel et al. [E865], PRL 83 (1999) 4482

K++e+e– 2.140.20

Ma et al. [E865], PRL 84 (2000) 2580 K+++– 2.45+1.30–0.95

NA48/2 preliminary (2008) Ke+e– 2.350.18

NA48/2

VMD models [PRD60 (1999) 053007]

‘92 ‘99 ‘00 ‘08

6-6-2008

Giuseppina

Anzivino@HQ&L0811

NA48/2 @CERN

K K e+e–

6-6-2008

Giuseppina

Anzivino@HQ&L0812

O(p4)

O(p6)

[G. D’Ambrosio and J. Portoles, Nucl., Phys. B386 (1996), 403]

[G. Ecker, A. Pich and E. de Rafael, Nucl., Phys. B303 (1988), 665]

A(z) loop diagrams contributionC(z) Wess-Zumino-Witten functional (10%)B=D=0

unitarity corrections effects can increase the BR by 30-40 %

relevant only at low m

Theoretical framework

6-6-2008

Giuseppina

Anzivino@HQ&L0813

BR dependence on ĉ

The spectrum dependence will be used to extract the ĉ value

Both decay spectrum and rate strongly depend on the single ĉ parameter The M spectrum has a pronounced cusp-like behaviour at 2 threshold.

[G. D’Ambrosio and J. Portoles, Nucl., Phys. B386 (1996), 403]

O(p4)

WDM

FM

6-6-2008

Giuseppina

Anzivino@HQ&L0814

K ±→± data sample and result

BR(O(p6),ĉ=2)=(1.070.04sta0.08sys)·10–6

1164 events in 40% of the full data

~40 times larger wrt to world sample

3.3% BG mainly from (IB)

The only previous measurement (E787),

based on 31 events (5 BG events)BR=(1.100.32)·10–6 ; ĉ=1.8±0.6

MC O(p6) and ĉ=2 comparison data shape follows ChPT prediction Model independent measurement and extraction of ĉ is ongoing

preliminary!!

6-6-2008

Giuseppina

Anzivino@HQ&L0815

K ±→±e+e- - first observation120 candidate events (6.1%

BG)

BR(±e+e−)=(1.19±0.12stat±0.04sys)·10−8

Model-independent BR (Mee> 260 MeV/c2)

[final result published, PLB659 (2008) 493]

Shape analysis [using ChPT O(p6) model, F. Gabbiani, PRD59 (1999) 094022]:

ĉ=0.90±0.45

never observed before!!

6-6-2008

Giuseppina

Anzivino@HQ&L0816

KLOE @ LNF

Mesurement of BR(KS )

6-6-2008

Giuseppina

Anzivino@HQ&L0817

Motivations

Important probe of ChPT Decay amplitude evaluated at leading order, O(p4) BR(KS ) = 2.1 x 10-6

No full O(p6) calculation exists Experimental value of the BR changed along the years, improving in precision Most recent measurement by NA48/1 BR(KS ) = (2.78±0.06±0.04) x 10-6

Differs from ChPT O(p4) by 30% possible large O(p6) contribution

In NA48, the KL background is a relevant component of the fit

In KLOE, the background from KL is reduced to zero (tagging)

D’Ambrosio and Espriu, Phys.Lett.B 175(1986) 237Kambor and Holstein, Phys.Rew.D 49(1994) 2346

6-6-2008

Giuseppina

Anzivino@HQ&L0818

Analysis strategy

Main background KS 20 with 2 photons lost in the beam-pipe and/or colliding into QCAL

veto these photons using a cut on arrival time

T = |TQCAL - RQCAL/c| < 5 ns Background reduction to 70 %

*

Full statistics (1.9 fb-1)700 x 106 KS events after KL-crash tag

count signal events by fitting M and cos *

in the KS

cms

Signal

Background

•• DATA

-- MC all

Nsig = 711 ± 35 (4.9% stat. error)

FCN/Ndof = 1.2

cos

6-6-2008

Giuseppina

Anzivino@HQ&L0819

Result

PT

O(p4) O(p6)

KLOE

There is a 3 discrepancy between KLOE and NA48 results

The NA48 measurement implies the existence of a sizeable O(p6) counterterm in ChPT

The KLOE result makes this contribution practically negligible

BR(KS → ) = (2.26 ± 0.12stat ± 0.06sys)·10−6

now published [JHEP05 (2008) 05]

NA48 Coll., Phys. Lett. B551 (2003) 7NA48 Coll., Phys. Lett. B493 (2000) 29NA31 Coll., Phys. Lett. B351 (1995) 579

6-6-2008

Giuseppina

Anzivino@HQ&L0820

Direct Search forKS e+e-

KLOE @ LNF

6-6-2008

Giuseppina

Anzivino@HQ&L0821

Search for FCNC in KS → e+e-

Exotic mediators could producetree level FCNC processes

Precise SM prediction, using ChPT, O(p4): BR(KSe+e-)=1.6 x 10-15 [Ecker and Pich, Nucl. Phys. B366, 189, 1991]

Most precise measurement by CPLEAR BR(KS e+e-) < 1.4 x 10-7 (90% C.L.)

In KLOE direct search of this decay using a pure KS beamAfter preselection: 1.1 Mevts in Data sample

Signal identification using a χ2 variable based on time of particles, E/p and cluster positionBackground rejection by kinematic cutsSignal box defined in the plane χ2 vs Minv (e

+e- hypotesis)

6-6-2008

Giuseppina

Anzivino@HQ&L0822

Result

BR(KS→e+e-) < 9.3 x 10-9 (90% C.L.)

NO events found in the signal boxUpper Limit evaluated normalizing to the number of KS→+- events

Previous result improved by more than one order of magnitude

6-6-2008

Giuseppina

Anzivino@HQ&L0823

Fit the distribution of (Emiss-Pmiss)ee

Normalize to the number of KS+-

2=117.6/92 Prob~4%

ee (E<10 MeV) bp dc+00+semil.

K+K-

Data sample (900 pb-1) N (ee) = 974 ± 53 = 0.02359 ±0.00031

Amplitude dominated by CP even IB component (needed to predict the CP violation in KL ee) CP test through measurement of angular asymmetry between and ee planes

CP test in KS → +-e+e-

BR=(4.48 ± 0.24stat ± 0.15syst)×10-5

6-6-2008

Giuseppina

Anzivino@HQ&L0824

R = (924 ± 23 ± 16) x 10-5

<X> = -2.3 ± 1.3 ± 1.4

R = (944 ± 14) x 10-5

<X> = -2.8 ± 1.8

Largely dominated by IB, negligible DEInterference IB-DE small (1%) → test of ChPT O(p6)

A 2-dimensional fit in (E*,

*) allow to measure both R and <X>

Fit results

KL → e

Adding ChPT constraintNA48 Coll., Phys.Lett. B605 (2005) 247

KTeV Coll., Phys. Rew. D71 (2005) 012001 arXiv:0710.3993

6-6-2008

Giuseppina

Anzivino@HQ&L0825

ConclusionsThe NA48/2 and KLOE experiments have produced

important experimental inputs to the Chiral Perturbation Theory,

the effective theory of strong interaction at low energy

Presented at this conference the most recent results fromNA48/2 charged kaon sector

Precise study of the Ke+e– decay (preliminary)Precise study of the K decay (preliminary)First observation of the Ke+e– decay (final)

KLOE neutral kaon sectorMeasurement of KS decay (final)Upper limit for KSe+e- (final)Measurement of KSe+e- decay (preliminary)Measurement of KLe decay (final)

Still a lot to come ……stay tuned!

6-6-2008

Giuseppina

Anzivino@HQ&L0826

SPARES

6-6-2008

Giuseppina

Anzivino@HQ&L0827

Preliminary results

BRMI

=2.26 0.03stat 0.03syst 0.06ext = (2.26 0.08) 10-7

z>0.08

= 2.35 0.15stat 0.09syst = 2.35 0.18

f0 = 0.532 0.012stat 0.008syst 0.007ext = 0.532 0.016

BR1= 3.02 0.04stat 0.04syst 0.08ext = (3.02 0.10) 10-7

a+ = –0.579 0.012stat 0.008syst 0.007ext = –0.579

0.016

b+ = –0.798 0.053stat 0.037syst 0.017ext = –0.798

0.067

BR2= 3.11 0.04stat 0.04syst 0.08ext = (3.11 0.10) 10-7

Ma = 0.965 0.028stat 0.018syst 0.002ext = 0.965 0.033 [GeV/c]

Mρ = 0.711 0.010stat 0.007syst 0.002ext = 0.711 0.013 [GeV/c]

BR3= 3.15 0.04stat 0.04syst 0.08ext = (3.15 0.10) 10-7 BR=(3.080.04stat0.04syst0.08ext 0.07model)10–7=(3.080.12)10–7

Including uncertainty due to the model dependence, (full z range)

(K±ee) = (BR+–BR–) / (BR++BR–) = (–2.1±1.5stat±0.3syst)%

CPV parameter (first measurement! correlated K+/K– uncertainties excluded):

(1)

(2)

(3)

6-6-2008

Giuseppina

Anzivino@HQ&L0828

Corrections/uncertaintiesParamete

rElectron

ID Beam

simulation

Radiativecorrection

s

Backgroundto Ke+e–

Triggerinefficiency

Fittingprocedur

e

External(PDG)

BRmi107 0.02 0.01 0.01 –0.010.01 –0.010.01 0 0.06

Model (1): linear form-factor

0.01 0.04 0.05 –0.040.04 –0.030.03 0.03 0

f0 0.001 0.006 0.004 +0.0020.002

+0.0010.001

0.003 0.007

BR1107 0.02 0.02 0.01 –0.010.01 –0.010.01 0.02 0.08

Model (2): ChPT form-factor [D’Ambrosio, Ecker, Isidori, Portoles, hep-ph/9808289]

a+ 0.001 0.005 0.004 –0.0010.001

–0.0020.002

0.004 0.007

b+ 0.009 0.015 0.022 +0.0170.017

+0.0150.015

0.010 0.017

BR2107 0.02 0.02 0.01 –0.010.01 –0.010.01 0.02 0.08

Model (3): Dubna ChPT [Dubnickova et al., hep-ph/0611175]

Ma/GeV 0.004 0.009 0.009 +0.0080.008

+0.0060.006

0.006 0.002

Mρ/GeV 0.002 0.003 0.004 +0.0030.003

+0.0030.003

0.002 0.002

BR3107 0.02 0.02 0.01 –0.010.01 –0.010.01 0.02 0.08

6-6-2008

Giuseppina

Anzivino@HQ&L0829

KS tagging

1.6 fb-1 of collisions data analyzed for KS

1.3 fb-1 of collisions data analyzed for KSe+e-

Both analyses use a clean KS beam from

KL-crash tagging based on KL interactions on EMC

KL-crash ( ~ 30%)

This algorithm searches KL interacting directly on EMC.KL-crash calorimetric clusters are selected using cuts on energy and *.

KS angular resolution: ~ 1° KS momentum resolution: ~ 2 MeV

KL-CRASH0.22

Two searches of rare KS decays :