Rare Kaon Decay Physics

1
Rare Kaon Decay Physics

• Lepton Photon Symposium
• Augusto Ceccucci/CERN
• Fermilab, August 11, 2003
• Member of the NA48 Collaboration

2
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
  (BR10-8) 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

3
Outline

• Tests of the Standard Model
• KL?p0 ee KTeV-E799 II (1999 data)
• KS?p0 ee NA48/1 CERN (2002 data)
• K?p nn BNL-E787 (1997 data, region II)
• Other Tests of CP and CPT symmetry
• KL?ppee KTeV-E799 II (1999 data)
• KS?3p0 NA48/1 (2000 data)
• KS?p e n KLOE Frascati (2001)
• Chiral Perturbation Theory
• Dalitz decays
• KL?eeg, KL?eeee, KL?mmee KTeV-E799 II
• Non-Leptonic decays
• KL?gg KLOE (20012002 data)
• KS?gg NA48/1 (2000 data)
• KS?p0gg NA48/1 (2000 data)

4
Kaon Rare Decays and the SM
(holy grail)
CP-Violation
5
Theory of KL?p0ee (mm)

• Complete re-analysis of the decay
• (Buchalla, DAmbrosio, Isidori, hep-ph/0308008)
  BDI
• Short Distance (Direct CP-Violation)
• From Standard Model fit Im lt (1.36 0.12)
  10-4 (CKM)
• B(KL?p0ee)CPV-dir(2.4 0.2) 10-12 (Im lt
  /10-4)2
• (3.2 0.4)
  10-12
• Indirect CP-Violation
• BR(KL?p0 ee) CPV-ind 1/330 BR(KS ? p0 ee)
• Direct and Indirect CP-Violating components
  interfere
• CP-Conserving contribution
• Need model ind. 3 par. fit (Gabbiani, Valencia,
  PRD 64 2001)
• BRCPC lt 3 10-12 (conservative, BDI)
• They fix the 3 counterterms from KL?p0gg and
  KS?gg

6
KTeV-E799-II (FNAL)
Pure CsI mgg1 MeV
TRD
KL flux 7 1011
7
Experiment KL?p0ee (mm)
Published data E799-II (KTeV) 1997
KL?p0ee KTeV 1997 data 2 events consistent with
the expected background of 1.06 0.41 events

• Irreducible background KL? ee(mm)gg (Greenlee,
  1990)
• Same final state as the signal, only gg 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

8
KTeV KL? p0ee
KL?p0p0p0D, penp0acc
KL?eegg crossing the signal box (BR6 10-7 !!)
DATA 1999 preliminary
M(eegg) computed using the neutral vertex,
assuming m(gg)m(p0) M(gg) computed from
charged vertex
9
KTeV p0ee vs eegg kinematics
KL ?eegg radiative distribution
Minimum angle between any e and g
p0 ?gg decay asymmetry
p0 ?gg isotropic distribution
Expected background 0.99 0.33 events
cosqp0
10
KTeV KL? p0ee
1999 data, preliminary

• One candidate in the signal box
• Combining 1997 and 1999

BR(KL ? p0 ee ) lt 3.5 10-10 _at_90CL
BR(KL ? p0 ee ) lt 2.8 10-10 _at_90CL
11
NA48/1 (CERN)

• NA48 e/e , KL rare decays
• NA48/1 KS rare decays
• Upgraded read out
• High intensity short neutral
• beam from the CERN-SPS
• Run in 2000 (only gs) and 2002

Liquid krypton calorimeter

• NA48 ( e/e )
• 1997-1999
• (2000)
• 2001

Run 2002
12
NA48/1 KS ?p0 ee
e-e- (Odd Sign) DATA
e-e- DATA vs. MC
Blind Control Signal regions
meegg (GeV/c2)
mee (GeV/c2)
mee gt 0.165 GeV/c2 cut applied to reject KS ?
p0 p0D with one missing g
13
NA48/1 KS ?p0 ee
e-e- (Same Sign) DATA
e-e- DATA vs. MC
Search region
meegg (GeV/c2)
mee (GeV/c2)
14
NA48/1 KS ?p0 ee
Background from KL,S?eegg measured using NA48
KL data from 2001 N(KL?eegg, 2001) ? 10 N(KL,S
?eegg, 2002)
meegg(GeV/c2)
mgg(GeV/c2)
15
NA48/1 KS ?p0 ee
Accidental backgrounds
meegg (GeV/c2)

• DC proton beam
• Read out window 200ns
• Use time side band to measure background from
  time-overlapping fragments from differ decays
• Major component
• epn p0p0(p0)
• Confirmed relaxing E/P cuts

mgg (GeV/c2)
16
NA48/1 KS ?p0 ee
SUMMARY OF BACKGROUNDS

• 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

17
NA48/1 KS ?p0 ee

• 7 candidates in the
• signal region
• 0 in control region
• Background 0.15
• The probability that all 7
• events are background
• is 10-10

meegg (GeV/c2)
mgg (GeV/c2)
First observation of KS ?p0 ee
18
The 7 KS?p0ee candidates
Meegg (GeV/c2)
t/tS
Mgg (GeV/c2)
Mee (GeV/c2)
19
NA48/1 KS ?p0 ee
BR(KS?p0ee, meegt165 MeV/c2) (3.01.5-1.2(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 DAmbrosio et al. JHEP 08
  (1998 004)
• BR(KS?p0ee) 5 as2
• as1.080.26-0.21

BR(KS?p0ee) (5.8 2.8-2.3(stat) 0.3(syst)
0.8(theor))10-9
Preliminary
20
Sensitivity to Im lt
-as
IF the interference is constructive some
sensitivity to Im lt is retained
21
KL?p0ee(mm) Perspectives
Expect KTeV to update KL?p0 mm (1999 data)
NA48/1 analysis of KS?p0mm is in progress
Admittedly aggressive Road Map

• Detector s(gg) 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?

22
K?p nn (reminder)

• The hadronic matrix element can be extracted from
  
• the well measured K? p0 e n
• No long distance contributions

QCD NLO Buchalla, Buras 1999
As an example, within the SM, using ACP(J/?KS)
and ek as input BR(K ?
pnn) 7.1 1.0 10-10
(Kettell, Nguyen, Landsberg, hep-ph/0212321 )
23
K?p nn
Region I 211 lt P lt 229 MeV/c
Region II 150 lt P lt 195 MeV/c
p
in the K CM
24
AGS-E787 K?p nn Region I

• Stopped kaons (6 1012)
• Analysis of Region I
• 2 events
• background 0.15 0.05

Data 1995-1998 Pub.1997-2002
PRL 88 2002
BR(K ? p nn , Region I)
1.571.75-0.83 10-10 0.29 lt lt /10-3 lt
1.2 68 CL
25
E787- K?p nn Region II
PLB 537 2002
1996 data
1997 data NEW RESULT!

• 1996
• One event found
• Background 0.7 0.2

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

BR(K ? p nn , Region II ) lt 22 10-10 _at_90CL
26
K?p nn 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?

27
Current Status
G. Isidori
STILL A LARGE WINDOW OF OPPORTUNITY EXISTS
28
KTeV KL? ppee
(19971999, preliminary)
KTeV KL

• CPV asymmetry from the interference of IB and DE
  diagrams in K? pp-g
• BR3 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

sinfcos f
NA48 KS
29
NA48/1 KS ? 3p0
CP-Violating In SM h000e

• Near Beam
• NA48/1 (2000) 6.5 106 3p0
• Far Beam
• NA48 2000 gt 107 KL?3p0
• To normalise the acceptance
• Analysis in bins of energy

D(E) is the K0 K0 dilution (from NA31)
30
NA48/1 KS ? 3p0
CPT TEST KL (edCPT)K1 K2
KS K1 (e-dCPT)K2
From the 2 parameter fit, using BS unitarity
relation Im dCPT (-1.2 3.0) 10-5 Assuming
CPT conservation in decay M(K0) M(K0) (- 1.7
4.2) 10-19 GeV/c2
Im h000
From one parameter fit BR(KS?3p0) lt 3.0 10-7
90CL BRSM 3 10-9
Re h000
31
KLOE (LNF)
DAFNE f Factory ee- ? f ? KSKL (KK-)
Tagged KS and KL
32
KLOE KS ?pen

• KLOE Preliminary (2001 data)
• BR(p-en) (3.44 0.09stat 0.06syst) 10-4
• BR(pe-n) (3.31 0.08stat 0.05syst) 10-4
• BR(p e n) (6.76 0.12stat 0.10syst) 10-4

33
KLOE KS ? pen
Semileptonic asymmetries (preliminary)

• CPT test
• First ever measurement
• A(KS) (1.91.70.6) 10-2
• c.f. KL w.a.
• A(KL) (3.322 0.055) 10-3
• DSDQ test
• Re (x) (2.2 5.3 3.5) 10-3
• c.f. CPLEAR
• Re (x) (-1.8 4.1 4.5) 10-3

PLB 535 (2002)
34
Kaon Dalitz decays Motivation

• Allow to study the K-gg() form factors
• These form factors are related to the dispersive
  amplitude of KL? mm which is not under good
  control
• Short distance contributions to KL? mm are
  sensitive to Re lt
• TWO MODELS
• BMS (Bergström, Massó, Singer, 1983)
• Pseudoscalar/vector contributions aK
• DIP (DAmbrosio, Isidori, Portoles, 1997)

35
KTeV KL? eeg

• In the 1997 data, KTeV has identified 93,383
  KL?eeg 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?p0p0Dp0D with p0D ?eeg

Employ TRD to reduce background
Ke3
eeg
Kp3
BR(KL?eeg)106 10.19 0.04(stat) 0.07(syst)
0.29(norm)
Preliminary
36
KTeV KL? eeg
aK0.0
aK0.20
aK-0.36
aK-0.16
Measured to 7 Precision!
aK -0.186 0.011 0.009
37
KTeV KL? ee ee
19971999 Data (preliminary)

• Signal 1100 events
• Background 5 events (mainly due to KL?eeg
  conv)
• Normalisation KL ? p0p0Dp0D
• BR(KL ? ee ee) (4.16 0.13
  0.13 0.17) 10-8
• a K -0.03
  0.13 0.04

Theory 3.5 10-8
38
KTeV KL? mm ee

• DATA 19971999

PRL 90 (2003)

• Signal 132 events
• Background 0.8 event
• (KL ? mm- g )

BR(KL ? mm- ee-)(2.69 0.24 0.12)10-9
BR(KL ? m -m -e- e-) lt 4.12 10-11 90CL
LFV
39
KTeV KL? eemm

• Combining KL ? mmg, KL ? 4e, and KL?mmee,
• KTeV measures
• a(DIP) -1.53 0.10

aK(mmee) -0.19 0.11
40
K-g()g Form Factor
aK
2.6 s
41
KLOE KL? gg

• Data 2001-2002
• 362 pb-1, 109 f
• KL tagged by KS?pp-
• 1.6 108 KL
• KL ? 3p0 suppressed requiring 2 body kinematics
• 27375 KL? gg
• 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
42
NA48/1 KS ? ?g
BR ( KS ? ?? ) (2.78 0.06stat 0.03syst
0.02ext )10-6
PLB 551 (2003)
43
KS ? ?? measurements
O(p4)
2.78 0.07
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/Fp2 a1 1 0.3 BDI
(hep-ph/0308008)
PL B551 2003
NA48/1
44
NA48/1 KS ???? ?
PRELIMINARY first observation
Zqq2/MK2
BR(KS ? ?? ??, zq?0.2 ) (4.9 1.6stat
0.8syst )10-8
CHPT predicts (Ecker, Pich and PLB 189 1987)
BR(KS ???? ? ) zq gt 0.2 3.8 ? 10 8
45
NA48/2 and OKA K/K-

• Search for direct CP violation
• in Dalitz plot slope asymmetry
• in K ? ?? decay
• Ke4 decays
• Rare K decays

NA48/2 is taking data
NA48/2 Very Preliminary
K ? p ee
Simultaneous K and K- beams
Similar sensitivities expected from OKA _at_Protvino
(2004?)
46
CKM_at_FNAL-MI (2009?)

• Proposal to measure 100 K? p n n 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 _at_1GeV to
  be 510-6
• 6 better than needed
• Demonstrated operation in vacuum of straw tubes
• Awaiting approval ratification by P5

47
E391a_at_PS-KEK

• First dedicated experiment to search for KL? p0
  nn
• SES 3 10-10
• Based on pencil kaon beam and photon vetoes
• Scheduled for 100 days KEK PS beam in 2004
• This is a Stage I project for further study at
  J-PARC

48
KOPIO_at_BNL (2009?)

• Aim to collect 60 KL? p0 nn
• events with S/B2 (Im lt 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?

49
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

High Energy Frontier
Rare Processes
50
Spare Material
51
NA48 KL,S?ppee
52
CP-Violation in SM
A phase in the quark-quark current leads to
CP-Violation (Kobayashi, Maskawa, 1973)
Ng2 Nphase0 ? No CP-Violation Ng3
Nphase1 ? CP-Violation Possible
6 unitarity relations ( triangles in the complex
plane)
JCP2?(Triangle Area) Is the unique measure
of CP-Violation in SM
53
Consistency of CKM picture

• Paradigm shift
• Old question (before the e/e 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

54
Kaon Dalitz decays Motivation
Short distance contributions to KL ?mm sensitive
to Re lt
Buchalla Buras 1994
Long distance contributions

• Absorptive part (Im Agg) is dominant (2 real
  photons)
• Dispersive part (Re Agg) depends on the
• K-gg() form factors that can be studied with
• the Dalitz decays
• Is much less under control
• Can interfere with the SD piece

55
Form Factors Kgg()

• BMS (Bergström, Massó, Singer, 1983)

• DIP (DAmbrosio, Isidori, Portoles, 1997)

56
KL ? p0 n n (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 SM3 10-11

• Experimentally 2/3 invisible final state !!
• Best limit from KTeV using p0?eeg decay

BR(K0 ? p0nn) lt 5.9 10-7 90 CL
Still far from the model independent limit
BR(K0 ? p0nn) lt 4.4 BR(K ? pnn) 7 10-9
Grossman Nir, PL B407 (1997)
57
NA48 KL?gg

• 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
58
NA48/1 KS ? ??

• 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? gg, O(p4))2.1 10-6

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

No indication of O(p6) contributions
59
NA48/1 KS ? p0 ee
KS ? p0 p0D?ggee(g)
KS ?p0 ee
MC
MC

• To reject the KS ? p0 p0D decays that may mimic
  KS ?p0 ee if a g is lost, a cut meegt0.165 GeV/c2
  is applied

60
NA48/1 KS ???? ?

• Previous limit (NA48)
• BR(KS ???? ?, zq gt 0.2 ) lt 3.3?10 7 at
  90 CL

• ChPT predicts (Ecker, Pich, De Rafael - PLB
  189 (1987))
• 
  BR(KS ???? ? ) zq gt 0.2
  3.8?10 8

61
OKA _at_ 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 _at_ 1 ?10-4T-odd
correlations, search for New Physics in Kl2 decays
62
CKM_at_FNAL-MI (2009)
From CKM proposal

• SCRF 13 cell cavity
• Built full size prototype
• Photon vetoes
• Measured inefficiency for 1GeV g 510-6
• 6 better than needed
• Straw tubes
• Demonstrated operation in vacuum
• Same preformance as in air
• Simulation of triggerless DAQ
• Awaiting approval ratification by P5

63
OKA _at_ 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 _at_ 1 ?10-4T-odd
correlations, search for New Physics in Kl2 decays