Measurement of the decay K → π νν++Douglas Bryman
University of British Columbia
JSPS Fellow

1K → πνν in the SM

Standard Model (Buras et al ., Mescia and Smith , Brod and Gorbahn ):⎛ Im λt⎞0010−B(K L → π νν ) = 1.8 x10 ⎜ 5 X ( xt ) ⎟ = 2.76 ± 0.40 x10−11λ2⎝⎠

210++−4 ⎡ 2
B(K → π νν ) ∼ 1.0 x10 A η + ρ − ρ ⎤ = 8.5 ± 0.7 x10−11⎣

Im λ =ImV V =η A λ*tst2( 0)⎦5td

Golden Relation: sin ( 2β )ψ K = sin ( 2β ) K →πννS2K → πνν
New Physics: Model-Independent Description(Buras, Isidori, et al.)
LSM ∼ Renormalizable part of an effective field theory :LEFT = LSM +ΣλΛ2Main Issues: Cutoff scale Λ [TeV], Symmetries

Rare K Decays can probe the flavor structureof the new physics at very high mass scales.
For measurement precisionσ ( B)
P== 10% :00
BSM (K L → π νν )Λ405>
TeV (90%C.L.) ⎯⎯→ Λ ≥ 1280TeV!
PIm λsd3

K →πνν : Great Discovery Potential
Two ExamplesSUSY: Rare meson decays
Minimal Flavor Violation e.g.
into light neutralinos
K → π νν → N x SM++

H. K. Dreiner et al. Bonn-TH-2009-04

Littlest Higgs Model with T-parity
B( K L0 → π 0νν ) vs. B(K + → π +νν )4 .
M. Blanke, et al.,arXiv:hep-ph/0610298

Experiments
Experiments−10E 949 : B( K + → π +νν ) = 1.73+−1.15
x10
1.05

7 events observed

5BNL E949
Measurement of

K → π νν++6

BNL E787/949

Measurement of K + → π +νν

CANADA-CHINA-JAPAN-RUSSIA-USA Collaboration:
Institute for Nuclear Research (Moscow), Institute for High Energy Physics (Protvino),
University of New Mexico, Princeton University, Brookhaven National Laboratory,TRIUMF, University of British Columbia, Tsinghua University (Beijing), Stony Brook
University, Fermilab, Kyoto University, KEK, University of Alberta, Fukui University,Osaka University, National Defense Academy (Japan)

Advanced Technologies:• Highest Efficiency Detection• Low mass central tracking
chamber - inflated cathodes• 500 MHz digitizers• Scintillating fiber target• Pure CsI calorimeter•“Blind Analysis”
7Special Features ofMeasuring

K → π νν++PNN1Background processes
exceed signal by >1010
PNN2• Determine everything possible about the K+ and π+* π+/μ+ particle ID better than 106 ( π+-μ+-e+ )• Eliminate events with extra charged particles or photons* π0 inefficiency < 10-6
• Suppress backgrounds well below the expected signal (S/N~10)* Predict backgrounds from data: dual independent cuts
* Use “Blind analysis” techniques* Test predictions with “outside-the-box” measurements• Evaluate candidate events with S/N function

8

Previous measurements E787/E949
PNN1:Above Kπ2 peak: 3 events

PNN2: Below Kπ2 peak: limit+1.30-10–0.89 ×10

B(K+→π+νν)<2.2 ×10-9
1 event observed
Bkg=1.22±0.24 events

B(K+→π+νν)=1.47

PNN2 Primary Background:
K + → π +π 0 ( K π 2 )Correlation

π0

γ

K+γLower Eπ+

9E787 Æ E949;
access to PNN2

π0 Veto power
E949
Active Degrader (AD)
E787

10

Before cuts

 Kinematics
 π→μ Extra particles
pnn2 signal region  Photon veto
 Kink cuts11

Estimating Backgrounds
Dual-Cut BLIND Analysis Method
Cut 1 vs Cut 2

Cut 1

BlindSignal Region

BADC

If Cuts 1 and 2
are uncorrelated:
A/B=C/D
Background in A:

A=B C/D

Cut 2
Blind Near-Signal Region:
Test Predictions

12

Example: Estimating the Kπ 2 Background from Data
Momentum with
Photon Veto Applied

Range vs. Energy with
Photon Veto Reversed

13

Cut-2; ‘PV threshold’

Blind Analysis
Strategy for PNN2

Mask the signal region.
• Develop the cuts andestimate the background (1/3data); use data as much as
possible in the backgroundsignalestimates.
• Bifurcated backgroundCut-1; ‘Target Cuts
analysis with (2/3) of data.
• Study correlations:
Outside the box study
Kπ2 : 1=Target scat. 2=Photon veto
• Open the “box”.
2=MC
Ke4 : 1=Tπ + Te
Kμ2 : 1=Kinematics 2=π→μ→e1415K+→π+π0 Background from ScatteringCorrelation

πγ0Scatter Cuts Suppression

K+PVγLower E

PV*scatt

π+

Excess Energy in Kaon Fiber

16

K+→π+π-e+ν (Ke4) Background
Ke4 MC Events

Ke4 candidate (data)

π+K+π-π+ννe+17Cut-2Correlation study
NSignal boxKeep signal region blinded

11M

Cut-1

Relax photon veto or target pulse shape cut
Compare predicted and observed eventsin the extended region.

Pulse shapePhoton Veto
18

PNN2 Background summary

Sensitivity

19

3 New events observed

ABC

20

21

7 events observed

Final results from E787/E949

B( K → π νν ) = 1.73+++1.15
−1.05

x10

−10

Probability thatAll 7 events are
due tobackground:
220.001

FinalGoal – notachieved!

23

Search for K → π X++X=axion
24Search for K → π XX++25

BNL E787/E949 ResultsDiscoveries
K → π νν++K + → π +γγSearches
K + → π +a
K + → π +γ
K + → π +H

K → π μμπ 0 → ννK + → μνγ ( SD)π0 →γ XK → π π γ ( DE )K + → eνμμ++++0

K + → π 0π +νν

Still to come: K + → π 0 μ +νγ , K + → π +π 0γ , K + → μν H 26

New opportunity:

K → π νν at JPARC or Fermilab:++Stopped K technique:x E9491000 events! 100
Same technique.

Lower Pk
400 MeV/c• Improved acceptance• Higher stop efficiency at low momentum• Reduced randoms and accidental spoiling of27
events (photon veto) due to low momentum.

Summary
BNL E787/E949: B ( K → π νν ) = 1.73+++1.15
−1.05

x10

−10

K → πνν experiments have come a long way
and the prospects are bright for future advancements.

K → π νν++Sensitivity or Limit vs. Yr.

K L0 → π 0νν

KTEVKEK2008

K → π νν++SMK → π νν0L0BNL

7CERN NA62 K + → π +νν
K L0 → π 0ννJ-PARC
KOTO
Fermilab,
Project-X/J-PARC?
1000 events???
28