rare kaon decay physics

August 11, 2003 LP2003, Augusto Ceccucci 1

Rare Kaon Decay Physics

Lepton Photon Symposium

Augusto Ceccucci*/CERNFermilab, August 11, 2003

*Member of the NA48 Collaboration


Why study Rare Kaon Decays

• Search for explicit violation of Standard Model – Lepton Flavour Violation

• Probe the flavour sector of the Standard Model– FCNC

• Test fundamental symmetries– CP,CPT

• Study the strong interactions at low energy – Chiral Perturbation Theory, Form Factors

•I will give a review of recent experimental results –In addition to KL and K+, also KS rare decays (BR≤10-8) start to be studied

•I will also briefly review the new initiatives that should lead to significant advance in the field by the end of this decade


Outline• Tests of the Standard Model

– KL→0 ee KTeV-E799 II (1999 data)– KS→0 ee NA48/1 CERN (2002 data)– K+→+ BNL-E787 (1997 data, region II)

• Other Tests of CP and CPT symmetry– KL→ee KTeV-E799 II (1999 data) – KS→30 NA48/1 (2000 data)– KS→ e KLOE Frascati (2001)

• Chiral Perturbation Theory– Dalitz decays: – KL→ee, KL→eeee, KL→ee KTeV-E799 II – Non-Leptonic decays– KL→ KLOE (2001+2002 data)– KS→NA48/1 (2000 data)– KS→0NA48/1 (2000 data)


Kaon Rare Decays and the SM

JCP=2(Triangle Area) is the unique measure of CP-Violation in SM

JCP = Im(Vud*VusVts

*Vtd) ~ cosc sinc Imt

In the Wolfenstein parameterisation (, A, , ): Im t = A2 5 , Re t = A2 5

CP

-Vio

lati

on

(holy grail)


Theory of KL→0ee ()

• Complete re-analysis of the decay:(Buchalla, D’Ambrosio, Isidori, hep-ph/0308008) BDI

• Short Distance (Direct CP-Violation)– From Standard Model fit: Im t = (1.36 ± 0.12) 10-4

(CKM)– B(KL→0ee)CPV-dir=(2.4 ± 0.2) ×10-12 × (Im t /10-4)2 = (3.2 ± 0.4) × 10-12

• Indirect CP-Violation– BR(KL→0 ee) CPV-ind ~1/330 BR(KS → 0 ee)– Direct and Indirect CP-Violating components interfere

• CP-Conserving contribution – Need model ind. 3 par. fit (Gabbiani, Valencia, PRD 64 2001)– BRCPC < 3 ×10-12 (conservative, BDI)

• They fix the 3 counterterms from KL→0 and KS→


KTeV-E799-II (FNAL)Pure CsI m~1 MeV

TRD

KL flux ~ 7 × 1011


Mode Upper Limit

90% CL

Ref.

KL→0 ee < 5.1 × 10-10 PRL86 (2001)

KL→ < 3.8 × 10-10 PRL84 (2000)

Experiment: KL→0ee ()Published data: E799-II (KTeV) 1997

• Irreducible background: KL→ ee()(Greenlee, 1990)

– Same final state as the signal, only mass resolution and kinematics are available to suppress these backgrounds

– To keep it to the ~1 event level the acceptance is quite reduced

– Possible future searches will be background dominated

KL→0ee KTeV 1997 data:2 events consistent with the expected background of1.06 ± 0.41 events

Augusto Ceccucci


KTeV: KL→ 0eeKL→eecrossing the signal box (BR~6 10-7 !!)

KL→000D,

e+0acc

DATA 1999preliminary

KL →000, e+acc

e+X e-X X

M(ee) computed using the neutral vertex, assuming m(=m(0) M() computed from charged vertex


KTeV: 0ee vs ee kinematics

Minimum angle between any e and

KL →ee “radiative”distribution

0 → “isotropic”distribution

cos0

0 → decay asymmetry

Expected background:

0.99 ± 0.33 events


KTeV: KL→ 0ee

• One candidate in the signal box

• Combining 1997 and 1999:

1999 data, preliminary

BR(KL → 0 ee ) < 3.5 × 10-10 @90%CL

BR(KL → 0 ee ) < 2.8 × 10-10 @90%CL


NA48/1 (CERN)

• NA48: ’/ , KL rare decays• NA48/1: KS rare decays

•Upgraded read out•High intensity short neutral beam from the CERN-SPS•Run in 2000 (only s) and 2002

Run 2002 NA48 (’/ ):•1997-1999•(2000)•2001

Liquid krypton calorimeter


NA48/1: KS →0 ee

e+-e-+ (Odd Sign) DATA e+-e-+ DATA vs. MC

Blind Control& Signal regions

mee > 0.165 GeV/c2 cut applied to reject KS → 0 0D with one missing

mee (GeV/c2)

me

e

(G

eV/c

2)


NA48/1: KS →0 ee

e+-e+- (Same Sign) DATAe+-e+- DATA vs. MC

Search region

me

e

(G

eV/c

2)

mee (GeV/c2)


NA48/1: KS →0 ee

Background from KL,S→ee : measured using NA48 KL data from 2001N(KL→ee, 2001) 10 × N(KL,S →ee, 2002)

mGeV/c2)

me

e

(GeV

/c2)


NA48/1: KS →0 ee

• DC proton beam• Read out window: ~ 200ns• Use time side band to

measure background from time-overlapping fragments from differ decays

• Major component:– e+ 00(0)– Confirmed relaxing E/P

cuts m (GeV/c2)

Accidental backgrounds

me

e

(G

eV/c

2)


NA48/1: KS →0 ee

Source Control Region

Signal region

KS→0D0

D 0.03 0.007

KL,S → ee 0.11 0.075

e+20(0) 0.19 0.069

Total 0.33+0.18-0.11 0.15+0.05

-0.04• Many other sources investigated and found to be negligible (e,g neutral cascade decays)

• Blind analysis: Control and signal region remained masked until the study of the background was finished

SUMMARY OF BACKGROUNDS:


NA48/1: KS →0 ee

•7 candidates in the signal region

•0 in control region•Background 0.15

The probability that all 7events are background is ~10-10

me

e

(G

eV/c

2)

m (GeV/c2)

First observation of KS →0 ee


The 7 KS→0ee candidates

Mee (GeV/c2)

M (GeV/c2)

t/S

Mee (GeV/c2)


NA48/1: KS →0 ee

BR(KS→0ee, mee>165 MeV/c2) = (3.0+1.5-1.2(stat) ± 0.2(syst))×10-9

• Assuming vector interaction and unity form factor:

– In remarkable agreement with L. Sehgal prediction: ~5.5 ×10-9 NP B19 (1970) – In the notation of D’Ambrosio et al. JHEP 08 (1998 004):

– BR(KS→0ee) ~ 5 |as|2

|as|=1.08+0.26-0.21

BR(KS→0ee) = (5.8 +2.8-2.3(stat) ± 0.3(syst) ± 0.8(theor))×10-9

Preliminary


Sensitivity to Im t

20 12 2

4 4

Im( ) Im( )( ) 10 15.3 6.8 2.8

10 10t t

L CPV s sB K e e a a

IF the interference is constructive some sensitivity to Im t is retained

-as


KL→ee() Perspectives

• Detector ×2 – Very ambitious, KTeV already state of the art

• KS-KL time dependent interference ×2– Position experiment between 9 and 16 KS lifetimes (hep-ph/0107046)

• KS-KL time independent interference ×3 – Assume constructive interference (theoretically preferred)

• Data Taking ×5 – Run in “factory mode”. After all E799-II run only for a few months to

collect ~7 × 1011 KL decays• Beam intensity ×4

– Need ~1012 protons/sec, slowly extracted, high energy, DC • Tot ~ ×240 → sens~ ×15

– close the gap between current upper limit and SM• Where? When?

*Admittedly aggressive Road Map*

Expect KTeV to update KL→ (1999 data) NA48/1 analysis of KS→ is in progress


As an example, within the SM, using ACP(J/KS) and k as input:

BR(K+ → ) = 7.1 ± 1.0 × 10-10

(Kettell, Nguyen, Landsberg, hep-ph/0212321 )

K+→+ (reminder)

220

411

2242

32

)(109.8

||||sin2

)()(

A

XXV

KBKB

lcctt

usW

eSD

•The hadronic matrix element can be extracted from the well measured K+→ 0 e •No long distance contributions

QCD NLOBuchalla,Buras 1999


K+→+

Region I211 < P < 229 MeV/c

Region II 150 < P < 195 MeV/c

+ in the K+ CM


Data 1995-1998Pub.1997-2002

•Stopped kaons (~6 ×1012)•Analysis of Region I: 2 events

background: 0.15 ± 0.05

AGS-E787 K+→+ Region I

BR(K+ → + , Region I) = 1.57+1.75

-0.83 × 10-10

0.29 < | t |/10-3 < 1.2 68% CL

PRL 88 2002


E787- K+→+ Region II

• 1997 (preliminary)– No new events– Background 0.5 ± 0.2

1996 data1997 dataNEW RESULT!

• 1996– One event found – Background 0.7 ± 0.2

BR(K+ → + , Region II ) < 22 × 10-10 @90%CL

PLB 537 2002


K+→+ E949

• Successor of E787– Many improvements– Better photon vetoes

• Run 12 weeks in 2002:– Expect Region I result soon – Expect much better sensitivity

than E787 in Region II– Expect from data 2002 an

overall sensitivity comparable to E787

• Approved for 60 weeks – When will the next run take

place?


Current Status

STILL A LARGE WINDOW OF OPPORTUNITY EXISTS

G. Isidori


KTeV: KL→ ee

• CPV asymmetry from the interference of IB and DE diagrams in K→ +-

• BR~3 ×10-7

• CPV asymmetry and form factors from full statistics

(5056 events)

AL= (13.3 ± 1.4 ± 1.0)% (Theory: ~14%, Sehgal et al.)• Form Factors (preliminary):

– a1/a2 = -0.75 ± 0.03 ± 0.02

– gM1 = 1.10 ± 0.10 ± 0.06

sincos

(1997+1999, preliminary):

KTeV KL

NA48 KS


NA48/1: KS → 30

• Near Beam– NA48/1 (2000) ~6.5 106 30

• Far Beam:– NA48 2000 > 107 KL→30

– To normalise the acceptance

• Analysis in bins of energy

000 000 00

1( )2 ( 2

0

)

( , )

( ) 1 2 ( ) cos sinRe ImL SL S

tt

NEARf E t

FARA E e D E e mt mt

0

000 0

( 3 )

( 3 )S

L

A K

A K

CP-Violating

In SM 000~

D(E) is the K0 K0 dilution (from NA31)

Augusto Ceccucci


NA48/1: KS → 3

From one parameter fit:BR(KS→30) < 3.0 × 10-7 90%CL BRSM ~ 3 × 10-9

From the 2 parameter fit,using BS unitarity relation:

Im CPT = (-1.2 ± 3.0) × 10-5

Assuming CPT conservation in decay:M(K0) –M(K0) = (- 1.7 ± 4.2) × 10-19 GeV/c2

Im

000

Re 000

CPT TEST: KL ~ (+CPT)K1 + K2

KS ~ K1 + (-CPT)K2


KLOE (LNF)

2002

2001

2000

Days of running

Inte

gra

ted

lu

min

osi

ty (

pb-1

)

DANE Factory:e+e- → → KSKL (K+K-)

Tagged KS and KL


KLOE: KS →e

KLOE Preliminary (2001 data):

BR(-e+) = (3.44 ± 0.09stat ± 0.06syst) × 10-4

BR(+e-) = (3.31 ± 0.08stat ± 0.05syst) × 10-4

BR(e ) = (6.76 ± 0.12stat ± 0.10syst) × 10-4


KLOE: KS → e

CPT testFirst ever measurement:

A(KS) = (1.9±1.7±0.6) ×10-2

c.f. KL w.a.

A(KL) = (3.322 ± 0.055) ×10-3

S=Q testRe (x+) = (2.2 ± 5.3 ± 3.5) ×10-3

c.f. CPLEAR

Re (x+) = (-1.8 ± 4.1 ± 4.5) ×10-3

Semileptonic asymmetries (preliminary)

PLB 535 (2002)


Kaon Dalitz decays: Motivation

• Allow to study the K-**) form factors • These form factors are related to the dispersive amplitude of

KL→ which is not under good control • Short distance contributions to KL→ are sensitive to Re t

TWO MODELS:• BMS (Bergström, Massó, Singer, 1983)

– Pseudoscalar/vector contributions: K*

• DIP (D’Ambrosio, Isidori, Portoles, 1997)

2 2 2 22 2 1 2 1 21 2 2 2 2 2 2 2 2 2

1 2 1 2

( , ) 1( )( )DIP

q q q qf q q

q m q m q m q m

*1 (3.1 0.5) K


KTeV: KL→ ee• In the 1997 data, KTeV has

identified 93,383 KL→ee over a background of less than 0.1%

• To determine the acceptance it is very Important to understand the tracking for close pairs

• Uncertainty dominated by the error on the normalisation mode:

KL→00D0

D with 0D →ee

BR(KL→ee)×106 = 10.19 ± 0.04(stat) ± 0.07(syst) ± 0.29(norm)

K3

Employ TRD to reduce background

Preliminary

Ke3 ee


KTeV: KL→ ee

K*= -0.186 ± 0.011 ± 0.009

K*=0.20

K*=-0.16

K*=0.0

K*=-0.36

Measured to ~7%Precision!


KTeV: KL→ ee ee

– Signal ~1100 events – Background: 5 events (mainly due to KL→ee+ conv)– Normalisation: KL → 00

D0D

BR(KL → ee ee) = (4.16 ± 0.13 ± 0.13 ± 0.17) ×10-8

K* = -0.03 ± 0.13 ± 0.04

1997+1999 Data (preliminary)

Theory:~3.5 10-8


DATA 1997+1999

•Signal: 132 events•Background ~0.8 event (KL → +- )

PRL 90 (2003)

KTeV: KL→ ee

BR(KL → +- e+e-)=(2.69 ± 0.24 ± 0.12)×10-9

BR(KL → -+ -+e+- e+-) < 4.12 × 10-11 90%CLLFV


KTeV KL→ ee

Combining KL → , KL → 4e, and KL→ee,

KTeV measures:

(DIP) = -1.53 ± 0.10

K*(ee)= -0.19 ± 0.11


K-(*)* Form Factor

K *

~2.6


KLOE: KL→

• Data 2001-2002• 362 pb-1, 109 • KL tagged by KS→+-

– 1.6 ×108 KL

– KL → 30 suppressed requiring 2 body kinematics

• 27375 KL→ • PL B556 2003

(KL ) / (KL ) = (2.79 ± 0.02stat ± 0.02syst) 10-3

In good agreement with the NA48 result (PL B551 2003):

(KL ) / (KL ) = (2.81 ± 0.01stat ± 0.02syst) 10-3


NA48/1: KS γ

BR ( KS γγ ) = (2.78 ± 0.06stat ± 0.03syst ± 0.02ext )×10-6

PLB 551 (2003)


KS γγ measurements

The NA48/1 result has an accuracy better than 3%

It differs by 30% from O(p4) prediction of CHPT

Used to fix one O(p6) counterterm:

8mK2/F

2 a1 = 1 ± 0.3

BDI (hep-ph/0308008)NA48/1

PL B551 2003

O(p4)

2.78 ± 0.07


NA48/1: KS PRELIMINARY: first observation

BR(KS γγ, zq0.2 ) = (4.9 ± 1.6stat ± 0.8syst )×10-8

CHPT predicts (Ecker, Pich and PLB 189 1987): BR(KS ) zq > 0.2 =3.8 10 –8

Zq=q2/MK2


NA48/2 and OKA: K+/K-

*NA48/2 is taking data*•Search for direct CP violation in Dalitz plot slope asymmetry in K± decay• Ke4 decays• Rare K± decays

Simultaneous K+ and K- beams

NA48/2Very Preliminary

K± → ± ee

Similar sensitivities expected from OKA @Protvino (2004?)


CKM@FNAL-MI (2009?)

•Proposal to measure ~100 K+→+ in flight •Make redundant measurements: spectrometer and RICH

–Built full size prototype of SCRF for 22 GeV/c separated beam–Measured inefficiency of photon vetoes @1GeV to be 5×10-6

•×6 better than needed–Demonstrated operation in vacuum of straw tubes

•Awaiting approval ratification by P5


E391a@PS-KEK

•First dedicated experiment to search for KL→ •SES~ 3 10-10

•Based on pencil kaon beam and photon vetoesScheduled for ~100 days KEK PS beam in 2004 This is a Stage I project for further study at J-PARC


KOPIO@BNL (2009?)

• Aim to collect 60 KL→ events with S/B~2 (Im t to 15%)• Measure as much as possible

– Energy, Position and Angle for each photon

• Work in the Kaon Center of Mass – Micro-bunched AGS beam– Use TOF to measure KL momentum

• Start construction in 2005?


High Energy Frontier

Rare Processes

Conclusions

•The field of kaon rare decays is quite active •New experimental initiatives are planned•Significant tests of the SM are to be expected by the end of the decade


Spare Material


NA48: KL,S→ee


CP-Violation in SM

'

'

'

ub

cb

td

ud us

cd cs

ts tb

V

V

V V

d d

s s

b b

V

V

V

V V

, , , ,

* *ij ik ji ki jki u c t i u c t

V V V V

JCP=2(Triangle Area) Is the unique measure of CP-Violation in SM

Ng=2 Nphase=0 No CP-Violation

Ng=3 Nphase=1 CP-Violation Possible

A phase in the quark-quark current leads to CP-Violation (Kobayashi, Maskawa, 1973)

6 unitarity relations( triangles in the complex plane)

* * *Im( ) Im( ) ~ sin cos Im( ) CP ud us ts td u t c c tJ V V V V


Consistency of CKM picture• Paradigm shift:

– Old question: (before the ’/ and B→J/ Ks asymmetry measurements):

• Is CKM the source of CP-violation?

– New question:• Is CKM the only source of CP-violation?

• Decisive tests must have small theoretical errors– The opportunity is to compare information

from K rare decays and B mesons


Kaon Dalitz decays: MotivationShort distance contributions to KL → sensitive to Re t

Long distance contributions:

20

492242

22

)(1051.1|ReRe|||sin

)()(

AYYV

KBKB ttcc

usWK

KLSD

L

•Absorptive part (Im A) is dominant (2 real photons) •Dispersive part (Re A) depends on the K-**) form factors that can be studied with the Dalitz decays:

•Is much less under control•Can interfere with the SD piece

Buchalla & Buras 1994


Form Factors K**

• BMS (Bergström, Massó, Singer, 1983)

42

*2

2 2 2( ,0) 1 (1 3.1 ) (( ) / )KBMS

qf q O q m

m

• DIP (D’Ambrosio, Isidori, Portoles, 1997)

2 2 2 22 2 1 2 1 21 2 2 2 2 2 2 2 2 2

1 2 1 2

( , ) 1( )( )DIP

q q q qf q q

q m q m q m q m

*1 (3.1 0.5) K


KL → 0 (reminder)

•Theoretical error ~2%:•Purely CP-Violating (Littenberg, 1989) •Totally dominated from t-quark•Computed to NLO in QCD (e.g. Buchalla Buras, 1999)•No long distance contribution SM~3 × 10-11

• Experimentally: 2/3 invisible final state !!• Best limit from KTeV using →ee decay

BR(K0 → 0) < 5.9 × 10-7 90% CL

Still far from the model independent limit: BR(K0 → 0) < 4.4 × BR(K+ → +) ~7 × 10-9 Grossman & Nir, PL B407 (1997)


NA48: KL→• Data 2000

– sub-sample of KL data

• Background:– Hadronic origin– 0.6 ± 0.3 %

• Main systematics:– calorimeter response

for the acceptance calculation

(KL ) / (KL ) = (2.81 ± 0.01stat ± 0.02syst) 10-3

4 times better precision than PDG: (2.77 ± 0.08) 10-3


Older NA48 measurement of KS γγ branching ratio based on 2 days of test-run in 1999 with high intensity KS : (2.6 ± 0.4) 10 –6 PLB 493 (2000)

NA48/1 KS γγ Decays into neutral final states : O(p2) = 0

• O(p4) unambiguosly predicted by ChPT loop diagram to better than 5% without counter terms: Theory: BR(KS→ , O(p4))=2.1 10-6

No indication of O(p6) contributions


NA48/1: KS → 0 ee

• To reject the KS → 0 0D decays that may mimic KS →0 ee if

a is lost, a cut mee>0.165 GeV/c2 is applied

KS →0 ee KS → 0 0D→ee()

MCMC


NA48/1: KS Previous limit (NA48):

BR(KS , zq > 0.2 ) < 3.310 –7 at 90% CL

ChPT predicts (Ecker, Pich, De Rafael - PLB 189 (1987)):

BR(KS ) zq > 0.2 =3.810 –8

momentum dependence

of the weak vertex Chiral structure of the weak vertex can be tested from zq = (m34 /mK)2 distribution


OKA @ Protvino - K

New RF-separated beam at U-70 PS in construction15 GeV/c kaons, alternating K+ or K-

Magnetic detector evolved from ISTRA+, GAMSIn preparation, expected 2004Measurement of 3 Dalitz plot asymmetries @ 1 10-4

T-odd correlations, search for New Physics in Kl2 decays


CKM@FNAL-MI (2009)

• SCRF 13 cell cavity – Built full size prototype

• Photon vetoes– Measured inefficiency

for 1GeV : 5×10-6 – ×6 better than needed

• Straw tubes– Demonstrated

operation in vacuum – Same preformance as

in air• Simulation of

“triggerless DAQ”• Awaiting approval

ratification by P5

From CKM proposal


OKA @ Protvino - K

New RF-separated beam at U-70 PS in construction15 GeV/c kaons, alternating K+ or K-

Magnetic detector evolved from ISTRA+, GAMSIn preparation, expected 2004Measurement of 3 Dalitz plot asymmetries @ 1 10-4

T-odd correlations, search for New Physics in Kl2 decays

rare kaon decay physics

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