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Rare Kaon Decay Physics

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Title: 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
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