Rare Kaon Decays Review and Prospects

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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
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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?3p0 in G. Lanfranchis talk,
  KL?pp-ee- )

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Lepton Flavour Violation
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Puzzling replication of generations

• Foreseen in many extensions of SM
• Generation-Changing gauge interactions (Cahn,
  Harari (1980))
• Left-Right symmetry
• Technicolor
• Compositeness
• Super-symmetry

m-e conversion
x
x
K?pme-
D G 0
D G 1
x
x
m? eee
KL?me
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K? pme- AGS E865
New Result based on 1998 data hep-ph/0502020 BR(K
? pme-)lt 2.2 ? 10-11 (90CL) Combined with
previous results BR(K? pme-)lt 1.2 ? 10-11
(90CL)

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

Backgrounds (examples) K?ppp- ?
pmne-n K?pp0 ?mnee-g K?mp0n?
mee-g Accidentals
8 Candidates consistent with expected background
of 8.2 1.9 Nsig lt2.4
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Lower bounds for generation-changing bosons
(gX/gW1)

• Further progress on LFV (charged leptons)
  expected in muons
• m?eg PSI
• m- N ?e- N MECO_at_AGS, J-PARC

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CP-Violation and Quark Mixing
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CKM matrix and CP-Violation
Quark mixing is described by the
Cabibbo-Kobayashi-Maskawa (CKM) matrix
KM mechanism
Ng2 Nphase0 ? No CP-Violation Ng3
Nphase1 ? CP-Violation Possible
e.g. Im lt Im VtsVtd ? 0 ? CP

• KM mechanism appears to be the main source of
  CP-violation in quarks
• Direct-CP Violation exists e/e ? 0 NA48, KTeV
  
• CP violation in the B meson sector ACP(J/y Ks),
  BaBar, Belle
• Now look for inconsistencies in SM using
  independent observables affected by small
  theoretical uncertainties and different
  sensitivity
• to new physics

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Kaon Rare Decays and the SM
(holy grail)
Vtd
Kaons provide quantitative tests of SM
independent from B mesons and a large
window of opportunity exists!
Im lt A2 l5 h Re lt A2 l5 r
G. Isidori
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K?p nn Theory in Standard Model
charm contribution
top contributions
The Hadronic Matrix Element is measured and
isospin rotated (10 correction)
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Predictions in SM
Error 14 Mainly parametric Theory error due to
charm (Buras04)
Largest contribution from scale error. To
be reduced by NNLO calculation
Refer to Christopher Smiths talk on long
distance contributions
The error is almost purely parametric
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Possibly the Cleanest SM test

• In The phase b derives
  from Z0 diagrams (DS1) whereas in A(J/y KS)
  originates in the box diagram (DB2)
• 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

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Some BSM Predictions
Compiled by S. Kettel
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K0L ? p0nn State of the Art
KTeV 1997 Data Dalitz Analysis
Still far from the model independent limit
BR(K0 ? p0nn) lt 4.4 BR(Kpnn) 1.4 10-9
Grossman Nir, PL B407 (1997)
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K?p nn State of the art
hep-ex/0403036 PRL93 (2004)
AGS
Stopped K 0.1 acceptance

• BR(K ? p nn ) 1.471.30-0.89 10-10
  
• Compatible with SM within errors

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Setting the bar for the next generation of
K?pnn experiments
Current constraint on r,h plane
?
100 events MeanSM
100 events MeanE787/949
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K0L?p0ee- and K0L?p0mm-
I refer you to the talks by D. Greynat, C. Smith
and L. Bellantoni
Similar physics interest as K0L?p0 nn .
Complicated by long distance contibutions and
radiative backgrounds
Direct CPV
Indirect CPV (Measured by NA48/1 but
experimental error is still large)
0, 2
CPC
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KTeV KL? p0ee
1999 data
PRL93, 021805 (2004)

• 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
Expected Background 0.99 0.35 events
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KTeV K0L ? p0mm
2 events in signal region

Data
Background MC
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K0S ?p0 ee- and K0S ?p0 mm-
KS ?p0 ee
KS ?p0 mm
NA48/1
NA48/1
6 events, expected back. 0.22
7 events, expected back. 0.15
BR(KS?p0ee) ? 10-9 5.8 2.8-2.3(stat)
0.8(syst) as1.060.26-0.21 (stat) 0.07
(syst) PLB 576 (2003)
BR(KS?p0mm) ? 10-9 2.9 1.4-1.2(stat)
0.2(syst) as1.550.38-0.32 (stat) 0.05
(syst) PLB 599 (2004)
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K0L?p0ee (mm) in SM
Thank to the KS measurements, the KL BR can now
be predicted Interference between short- and
long-distance physics
(Isidori, Unterdorfer, Smith, EPJC36 (2004))
Constructivenow favored by two independent
analyses
Destructive
G. Buchalla, G. DAmbrosio, G. Isidori,
Nucl.Phys.B672,387 (2003) S. Friot, D. Greynat,
E. de Rafael, hep-ph/0404136, PL B 595

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K0L?p0ee (mm) Sensitivity to NP
Isidori, Unterdorfer, Smith
Fleischer et al Ratios of Bd ? Kp modes could
be explained by enhanced electroweak penguins
which, in turn, would enhance the KL BRs
SES of KTeV search

• A. J. Buras, R. Fleischer, S. Recksiegel,
• F. Schwab, hep-ph/0402112, NP B697 (2004)

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Prospects

• K0L ? p0nn
• Large window of opportunity exists.
• Upper limit is 4 order of magnitude from the SM
  prediction
• Expect results from data collected by E391a
  (proposed SES3 10-10)
• Next experiment KOPIO_at_ BNL
• K0L ? p0ee(mm)
• 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? pnn
• 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

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KL? p0 nn E391a_at_PS-KEK

• First dedicated experiment to search for KL? p0
  nn
• Proposed SES 3 10-10
• Based on pencil kaon beam and photon vetoes
• Collecting data now waiting for results
• This is a Stage I project for further study at
  J-PARC

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KL? p0 nn KOPIO_at_BNL

• Proposed 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?

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KOPIO_at_BNL
Status Approved, Currently under cost
review Data Taking 2011-?
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Prospects on K?p nn

• 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 PKlt30 GeV/c
• Un-separated beam CERN-NA48/3, FNAL-P940
• Limited by rate in beam trackers

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NA48/3 SPSC-I229
P(K)75 GeV/c

• Collect 80 K?p nn events in about two years of
  data taking for
• 4 ? 1012 Kaon decays/SPS year
• BR( K?p nn )10-10
• Acceptance 10
• Absolute advantage
• High energy kaon beam gt35 GeV of EM energy
  deposited in the vetoes very difficult to miss p0
  !!
• Disadvantage
• 1 GHz particle rate in beam tracker

Region I
Region II
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NA48/3 Detector Layout
p
K
n
n
undetected
800 MHz (p/K/p)
10 MHz Kaon decays
Only the upstream detectors see the 800 MHz beam
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Acceptance
Region I
Region II
Acceptance
Acceptance
75 GeV/c
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NA48/3 simulation
Non-Gaussian MSC
Gaussian MSC (old)
DPp (Spectrometer 2)GeV/c
DPp (Spectrometer 2) GeV/c
DPp (Spectrometer 1) GeV/c
DPp (Spectrometer 1) GeV/c
New MSC
REGION I

• Uncorrelated non gaussian
• tails

REGION II
M(miss)2 (GeV/c2)2
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Already Available
New high-intensity K beam for NA48/3
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SPSC_at_Villars
? new rare decay frontier in K physics at CERN ?
new experiments planned for K?p?? important ?
support RD now for K?p ?? results 2010
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P940 Redesign of FNAL-CKM to use Unseparated
beam
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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!

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Back-up Slides
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Track Momentum 15 35 GeV/c (RICH limited
?) Signal Acceptance (Flyo estimation) 3.6
(Region I)
16 (Region
II) Legenda hV Veto inefficiency (p0 or m)
Acceptance Background
acceptance (Regions I or II)
hID Particle (electron-pion) separation
inefficiency hVg Veto
inefficiency of radiative photon Formula
Preliminary, G. Ruggiero
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GIGATRACKER

• Specifications
• Momentum resolution to 0.5
• Angular resolution 10 mrad
• Time resolution 100 ps
• Minimal material budget
• Perform all of the above in
• 800 MHz hadron beam, 40 MHz / cm2
• 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

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KABES 25 micron amplification gap
Recent lab test with 25 mm gap
Width 30 ns
Width 18 ns
50 mm gap
25 mm gap
improvement of occupancy observed with 25mm
amplification gap
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KABES r/o with 480 MHz FADC
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Competition