rare kaon decays review and prospects

Moriond EW, March 10, 2005 A. Ceccucci, CERN 1

Rare Kaon Decays Review and Prospects

Augusto Ceccucci/CERN

•Physics•State of the Art •Prospects s d

XLth Rencontres de Moriond,EW Interactions and Unified Theories


Motivations

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

• CP-Violation and Quark Mixing– Flavour Changing Neutral Currents (FCNC)– Unique probe of s → d transitions– Small theoretical errors [for some decays!]

• Other tests of fundamental symmetries– CP,CPT (e.g. KS→30 in G. Lanfranchi’s talk, KL→ee)


Lepton Flavour Violation


Puzzling replication of generations

|G|=1

→ e x x

-e conversion

| G| = 1| G| = 0

→ eee

x

x x

x

KL→e

K+→++e-

•Foreseen in many extensions of SM:

–Generation-Changing gauge interactions (Cahn, Harari (1980))

–Left-Right symmetry–Technicolor–Compositeness–Super-symmetry


K+ ++e-AGS – E865

~108 K+ /s~3 109part /pulse PK ~6 GeV/c

New Result based on 1998 data: hep-ph/0502020BR(K+ ++e-)< 2.2 10-11 (90%CL)Combined with previous results:BR(K+ ++e-)< 1.2 10-11 (90%CL)

Backgrounds (examples):K+→→eK+→ →+e+e-K+→→ e+e-Accidentals

8 Candidates consistent withexpected background of 8.2 ±1.9 Nsig <2.4


Lower bounds for generation-changing bosons (gX/gW~1)

Further progress on LFV (charged leptons) expected in muons

• →ePSI• N →e N MECO@AGS, J-PARC

>37 TeV/c2

>80 TeV/c2

>150 TeV/c2 0 12B( ) < 4.7 10LK e

11B( )<1.2 10K e

0 0 10B( ) 3.2 10LK eKTeV

E865

E871

4 4

0 2

( ) 116

( ) sinWX

W XC

MBr K e g

g MBr K


CP-Violation and Quark Mixing


CKM matrix and CP-Violation

'

'

'

ub

cb

td

ud us

cd cs

ts tb

V

V

V V

d d

s s

b b

V

V

V

V V

Ng=2 Nphase=0 No CP-Violation

Ng=3 Nphase=1 CP-Violation Possible

Quark mixing is described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix

KM mechanism appears to be the main source of CP-violation in quarks:•Direct-CP Violation exists: ’/ 0 NA48, KTeV •CP violation in the B meson sector: ACP(J/ Ks), BaBar, Belle

Now look for inconsistencies in SM using independent observables affected by small theoretical uncertainties and different sensitivity to new physics

e.g. Im t= Im Vts*Vtd ≠ 0 CP

KM mechanism:


Kaon Rare Decays and the SM

(holy grail)

Kaons provide quantitative tests of SM independentfrom B mesons…

…and a large windowof opportunity exists!

|Vtd|

G. Isidori

Im t = A2 5 Re t = A2 5


K→ : Theory in Standard Model

2 2

5 5

20 0L L 5

Im Re Re( ) ( ) ( ) ( )

Im( ) ( )

t t ct t c

tt

B K X x X x P X

B K X x

charm

contributiontop

contributions

2 08

2 4

3 ( )

2 sinKW

Br K er

The Hadronic Matrix Element is measured and isospin rotated (~10% correction)

*

*

us

c cs cd

t ts td

VV VV V


Predictions in SM

11(latest CKM workshop)( ) (8.0 1.1) 10 BR K

Error ~ 14% Mainly parametricTheory error due to charm (Buras04):

( ) 0.389 0.033( ) 0.045( ) 0.010( )c c c sP X m Largest contributionfrom scale error. To bereduced by NNLOcalculation

0 0 11(Buras et al. 04)L( ) (3.0 0.6) 10 BR K

The error is almost purely parametric

Refer to Christopher Smith’s talkon long distance contributions


Possibly the Cleanest SM test

• In The phase derives from Z0 diagrams (S=1) whereas in A(J/ KS) originates in the box diagram (B=2)

• Any non-minimal contribution to Z0 diagrams would be signalled by a violation of the relation:

• A deviation from the predicted rates of SM would be a clear indication of new physics

• Complementary programme to the high energy frontier:– When new physics will appear at the Tevatron/LHC, the rare

decays may help to understand the nature of it

K

S/(sin 2 ) (sin 2 )K B J K

0 0d dB B


Some BSM Predictions

SM 8.0 ± 1.1 3.0 ± 0.6

MFVhep-ph/0310208

19.1 9.9

EEWPNP B697 133

7.5 ± 2.1 31 ± 10

EDSQhep-ph/0407021

15 10

MSSMhep-ph/0408142

40 50

0 0 11L( ) 10BR K 11( ) 10BR K

Compiled by S. Kettel


BR(KL ) 5.9 x 10-7 (0ee, 1997 Data) [PRD 61,072006 (2000)]

BR (KL ) 1.6 x 10-6 (0, 1997 1 Day) [PLB 447, 240 (1999)]

K0L State of the Art

DataMC BG Sumn MC MCSignal MC

KTeV 1997 Data Dalitz Analysis

Still far from the model independent limit: BR(K0 → 0) < 4.4 × BR(K++) ~ 1.4 × 10-9 Grossman & Nir, PL B407 (1997)


K+→+ : State of the art

BR(K+ → + ) = 1.47+1.30-0.89 × 10-10

•Compatible with SM within errors

hep-ex/0403036 PRL93 (2004)

Stopped K~0.1 % acceptance

AGS


Setting the bar for the next generation of K+→+ experiments

100 eventsMean=SM

100 eventsMean=E787/949

Current constraint on plane

?


0++, 2++

Direct CPV

Indirect CPV

(Measured by NA48/1 but

experimental error is

still large)

CPC

K0L→0ee and K0

L→0

Similar physics interest asK0

L→0 Complicatedby long distance contibutions and radiative backgrounds

I refer you to the talks by D. Greynat, C. Smith and L. Bellantoni


KTeV: KL→ 0ee

• One candidate in the signal box

• Combining 1997 and 1999:

1999 data

BR(KL → 0 ee ) < 3.5 × 10-10 @90%CL

BR(KL → 0 ee ) < 2.8 × 10-10 @90%CL

Expected Background 0.99 ± 0.35 events

PRL93, 021805 (2004)


KTeV: K0L

BR(K0L ) 3.8 10-10 (90% C.L.) [PRL 86, 5425 (2001)]

2 events in signal region

Background MC

Data


K0S →0 ee and K0

S →0

KS →0 eeKS →0

BR(KS→0ee) 10-9 = 5.8 +2.8

-2.3(stat) ± 0.8(syst)

|as|=1.06+0.26-0.21 (stat) ± 0.07 (syst)

PLB 576 (2003)

7 events, expected back. 0.15

BR(KS→0) 10-9 = 2.9 +1.4

-1.2(stat) ± 0.2(syst)

|as|=1.55+0.38-0.32 (stat) ± 0.05 (syst)

PLB 599 (2004)

6 events, expected back. 0.22

NA48/1 NA48/1


0 12L(K ) 10Br

0 12L( ) 10Br e e

Constructive

now favored by two independent analyses*

(Isidori, Unterdorfer, Smith,

EPJC36 (2004))

0 0L

0 0L

1.1 110.9

0.3 110.3

3.7 10

1.5 10

K e e

K

B

B

Destructive

0 0L

0 0L

0.7 110.6

0.2 110.2

1.7 10

1.0 10

K e e

K

B

B

*G. Buchalla, G. D’Ambrosio, G. Isidori, Nucl.Phys.B672,387 (2003)

*S. Friot, D. Greynat, E. de Rafael,

hep-ph/0404136, PL B 595*

K0L→0ee () in SM

Thank to the KS measurements, the KL BR can now be predicted* Interference between short- and long-distance physics*


Isidori, Unterdorfer, Smith:

Fleischer et al*:

Ratios of Bd → modes could be explained by enhanced electroweak penguins which, in turn, would enhance the KL BR’s:

•A. J. Buras, R. Fleischer, S. Recksiegel,

F. Schwab, hep-ph/0402112, NP B697 (2004)

0 0L

0 0L

1.6 111.6

0.7 110.7

9.0 10

4.3 10

NP

K e e

NP

K

B

B

0 12L(K ) 10Br

0 12L( ) 10Br e e

K0L→0ee (): Sensitivity to NP

~ SES of KTeVsearch


Prospects

• K0L

– Large window of opportunity exists.– Upper limit is 4 order of magnitude from the SM prediction– Expect results from data collected by E391a (proposed SES~3 10-10)– Next experiment KOPIO@ BNL

• K0L ee()

– Long distance contributions under better control– Measurement of KS modes has allowed SM prediction– KS rates to be better measured (KLOE?) – Background limited (study time dep. Interference?)– 100-fold increase in kaon flux to be envisaged

• K+ – The situation is different: 3 clean events are published– Experiment in agreement with SM– Next round of exp. need to collect O(100) events to be useful– Move from stopped to in flight experiments


KL→ E391a@PS-KEK

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

•Based on pencil kaon beam and photon vetoes•Collecting data now: waiting for resultsThis is a Stage I project for further study at J-PARC


KL→ KOPIO@BNL

•Proposed 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?


KOPIO@BNL

Status:Approved, Currently under cost reviewData Taking: 2011-?


Prospects on K+→+

• Decays at rest:– Window of opportunity to accumulate more data at BNL

until 2010 (before KOPIO data taking starts)– Ideas to pursue stopped kaon decays in Japan– Established technique…– …but hard to extrapolate to O(100) events

• Decays in flight– Large acceptances, good photon rejection– Separated beam: FNAL CKM (Approved but Not Ratified)

• Limited to about PK<30 GeV/c– Un-separated beam: CERN-NA48/3, FNAL-P940

• Limited by rate in beam trackers


NA48/3: SPSC-I229

• Collect 80 K+→+ events in about two years of data taking for:

– 4 1012 Kaon decays/SPS year– BR( K+→+ ~10-10

– Acceptance ~ 10%

– Absolute advantage:

High energy kaon beam: >35 GeV of EM energy deposited in the vetoes very difficult to miss 0 !!

– Disadvantage:

~1 GHz particle rate in beam tracker

Region I

P(K)=75 GeV/c

Region II

Moriond EW, March 10, 2005

A. Ceccucci, CERN 29

NA48/3 Detector Layout

800 MHz(/K/p)

Only the upstream detectors see the 800 MHz beam

10 MHz Kaon decays

K+ +

undetected


Acceptance

75 / 40 /

Assume Acceptance (Region I+II) ~ %KP GeV c P GeV c

( / )KP GeV c ( / )KP GeV c

Acceptance

Acceptance

Region I Region II

2 2 20 0.01 ( / )missm GeV c 2 2 20.026 0.068 ( / )missm GeV c

14 ( / ) 40P GeV c 14 ( / )P GeV c

14 ( / ) 30P GeV c

75 GeV/c



NA48/3 simulation

Uncorrelated non gaussian tails

Gaussian MSC (old)

Non-Gaussian MSC

P (Spectrometer 1) GeV/c P (Spectrometer 1) GeV/c

P (Spectrometer 2) GeV/c

P (Spectrometer 2)GeV/c

M(miss)2 (GeV/c2)2

New MSC

REGION I

REGION II


Beam:Present

K12(NA48/2)

New HI K+

> 2006

Factor wrt 2004

SPS protons per pulse on T10

1 x 1012 3 x 1012 3.0

Duty cycle (s./s.) 4.8 / 16.8 1.0

Solid angle (sterad) 0.40 16 40

Av. K+momentum <pK> (GeV/c)

60 75 Total : 1.35

Mom. band RMS: (p/p in %)

4 1 ~0.25

Area at Gigatracker (cm2) 7.0 20 2.8

Total beam per pulse (x 107)per Effective spill length MHz MHz/cm2 (gigatracker)

5.5182.5

25080040

~45 (~27)~45 (~27)~16 (~10)

Eff. running time / yr (pulses)

3x 105 3.1 * 105 1.0

K+ decays per year 1.0x1011 4.0x1012 40

New high-intensity K+ beam for NA48/3 AlreadyAvailable

John DaintonVillars 2004

October 7th 2004CERN seminar

SPSC@VillarsSPSC@Villars

● new rare decay frontier in K physics at CERN

● new experiments planned for Kπνν important

● support R&D now for K+π +νν results ≤ 2010


P940: Redesign of FNAL-CKM to useUnseparated beam


Conclusions

– Rare kaon decays studies are complementary to those performed at the energy frontier

– There are compelling physics cases that can be addressed with existing proton machines (SPS/MI/AGS)

– Technically challenging experiments but feasible

– Unique opportunity for you to join these efforts!


Back-up Slides



KKe3e3 KK22 ++00

S/B (hyp.)S/B (hyp.) 50 50 50

V V (hyp.)(hyp.) 5x108 (0) 5x106 () 5x108 (0)

AcceptanceAcceptance

(Flyo)(Flyo)2% (I)

12% (II)2.7% (I)13% (II)

0 (I)19% (II)

ResultResult ID < 1.5x103 (I)

1.1x103 (II)

V < 9x105

(I and II)

V < 0.2 (II)

Track Momentum: 15 – 35 GeV/c (RICH limited ?)

Signal Acceptance (Flyo estimation): 3.6% (Region I)

16% (Region II)

Legenda: V = Veto inefficiency (0 or )

Acceptance = Background acceptance (Regions I or II)

ID = Particle (electron-pion) separation inefficiency

V = Veto inefficiency of radiative photon

Formula:

or

signal signal

background V background ID V

A BR

A BR

S

B

Preliminary, G. Ruggiero



GIGATRACKER

• Specifications: – Momentum resolution to ~ 0.5 % – Angular resolution ~ 10 rad– Time resolution ~ 100 ps– Minimal material budget– Perform all of the above in

• 800 MHz hadron beam, 40 MHz / cm^2

• Hybrid Detector:– SPIBES (Fast Si micro-pixels)

• Momentum measurement • Facilitate pattern recognition in subsequent FTPC• Time coincidence with CHOD

– FTPC (NA48/2 KABES technology with FADC r/o)• Track direction



Recent lab test with 25 m gap

50 m gap 25 m gap

improvement of occupancy observed with 25m amplification gap

Width ~30 ns Width ~18

ns

KABES 25 micron amplification gap



KABES r/o with 480 MHz FADC



CompetitionNA48/3 P940

Accelerator CERN-SPS FNAL-MI

Energy (GeV) 400 120

Duty cycle (s /s ) 4.8 / 16.8 = 0.29 1.0 / 3.0 = 0.33

1 HEP year (s) 107 107

Eff. Spill. Length (s / s) 3.0 / 4.8 = 0.63 1.0 / 1.0 (?)

Total Rate (GHz) 0.8 0.23

Fraction of Kaons (%) 6 4

Flux of Kaons (MHz) 50 10

Decay fraction (%) 9 (50 m / 100 m) 17 (60 m / 67 m)

Acceptance (%) 10 5

Events/y (BR~10-10) 82 31

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