E949

1

• Measurement of K??????
• Final Results from E949
• Steve Kettell , BNL
• September 18th, 2009
• 22nd International Workshop on Weak Interactions
  and Neutrinos

2
K?????? Motivation

• One of the Golden Modes for study of the CKM
  matrix and CP violation. The rate can be
  calculated precisely from fundamental parameters
  and any deviation in the measured rate will be a
  clear signal for new physics.

1. FCNC, hard GIM suppression
2. No long distance contribution
3. Hadronic Matrix element from Ke3 isospin
4. NNLO QCD calculation of c-quark contribution

SM 8x10-11
3
K?????? Motivation
4
K?????? Motivation
5
Outline of K?????? Experimental Method

• Problem 3-body decay (2 missing ?s) BRlt10-10
• Event signature single K in, single p out
• Basic concepts
• Precise and redundant measurement of kinematics
  e.g. Energy (E) / Momentum (P) / Range (R)
• or Velocity (V) / Momentum (P) / Range (R)
• PID p-m-e decay chain and/or P/R, P/V, dE/dx
• Hermetic veto detectors (g)
• Major backgrounds
• K?mn (Br63)
• Kinematics (monochromatic)
• PID p/m
• K?pp0 (Br21)
• Kinematics (monochromatic)
• Photon veto
• Scattered beam particles
• Timing
• PID K/p

Primary signal region
Exploit with E949 upgrades
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Outline of K?????? Experimental Method

• Measure background from data
• A priori identification of background sources.
• Suppress each background with at least two
  independent cuts.
• Measure background with data, if possible, by
  inverting cuts and measuring rejection taking any
  correlation into account.
• Automatically accounts for electronics glitches
  and variations in veto performance
• Blind Analysis
• Dont examine signal region until all backgrounds
  verified.
• To avoid bias, set cuts using 1/3 of data, then
  measure backgrounds with remaining 2/3 sample.
• Verify background estimates by loosening cuts and
  comparing observed and predicted rates.

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Measurement of backgrounds with data
Tag with ?
kinematics
Photon veto
Tag kinematics outside pnn box in Kp2 peak
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E787

• E787 was initiated by Ted Kycia and Stew Smith
  and was
• led by Laurie Littenberg, Stew Smith and Doug
  Bryman
• Engineering run in 1988
• Data runs in 19891991
• Upgrade 19911994
• Data runs in 19941999

Discovery of K??????
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E787
PRL 88, 041803 (2002)
Two events above the Kp2 (pnn1)
B(K?? ? ?) 1.571.75-0.82?10-10
1998 Event
Below Kp2 (pnn2) limit 1996 PL B537, 211 (2002)
1997 PR D70, 037102 (2004) 140ltpplt195 MeV/c 1
candidate event with an expected background of
1.22 /- 0.24 events. Background limited, with
S/Nlt0.2 Set an upper limit of B(K?? ? ?) lt 22 x
10-10
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E949 Experiment
BNL/FNAL/SBU/UNM, U.S.A IHEP/INR, Russia
Fukui/KEK/Kyoto/NDA/Osaka, Japan TRIUMF/UA/UBC,
Canada

• E949 was proposed in 1998 and approved in 1999
  (D. Bryman, S, Kettell, S. Sugimoto)
• Use entire AGS flux (65 Tp)
• high duty factor
• low K momentum
• various detector improvements
• Photon Veto (esp. for pnn2)
• Ran for 12 weeks in 2002

V.V. Anisimovsky1,A.V. Artamonov2, B.
Bassalleck3, B. Bhuyan4, E.W. Blackmore5, D.A.
Bryman6, S. Chen5, I-H. Chiang4, I.-A.
Christidi7, P.S. Cooper8, M.V. Diwan4, J.S.
Frank4, T. Fujiwara9, J. Hu5, A.P. Ivashkin1,
D.E. Jaffe4, S. Kabe10, S.H. Kettell4, M.M.
Khabibullin1, A.N. Khotjantsev1, P. Kitching11,
M. Kobayashi10, T.K. Komatsubara10, A. Konaka5,
A.P. Kozhevnikov2, Yu.G. Kudenko1, A.
Kushnirenko8, L.G. Landsberg2, B. Lewis3, K.K.
Li4, L.S. Littenberg4, J.A. Macdonald5, J.
Mildenberger5, O.V. Mineev1, M. Miyajima12, K.
Mizouchi9, V.A. Mukhin2, N. Muramatsu13, T.
Nakano13, M. Nomachi14, T. Nomura9, T. Numao5,
V.F. Obraztsov2, K. Omata10, D.I. Patalakha2,
S.V. Petrenko2, R. Poutissou5, E.J. Ramberg8, G.
Redlinger4, T. Sato10, T. Sekiguchi10, T.
Shinkawa15, R.C. Strand4, S. Sugimoto10, Y.
Tamagawa12, R. Tschirhart8, T. Tsunemi10, D.V.
Vavilov2, B. Viren4, N.V. Yershov1, Y.
Yoshimura10 and T. Yoshioka10 1. Institute for
Nuclear Research (INR), 2. Institute for High
Energy Physics (IHEP), 3. University of New
Mexico (UNM), 4. Brookhaven National Laboratory
(BNL), 5. TRIUMF, 6. University of British
Columbia, 7. Stony Brook University, 8. Fermi
National Accelerator Laboratory (FNAL), 9. Kyoto
University, 10. High Energy Accelerator Research
Organization (KEK), 11. Centre for Subatomic
Research, University of Alberta, 12. Fukui
University, 13. Research Center for Nuclear
Physics (RCNP), Osaka University, 14. Osaka
University, 15. National Defense Academy.
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E949 Overview (1)

• 700 MeV/c K beam (75)
• Active target (scintillation fibers) to stop K
• Wait at least 2ns for K decay (delayed
  coincidence)
• Drift chamber to measure p momentum
• 19 layers of scintillator, Range Stack (RS) to
  measure E and R
• Stop p in RS, waveform digitizer to record
• p-m-e decay chain
• Veto photons, charged tracks over 4p
  (BV/BVL/Endcap/)

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E949 Overview (2) Data Taking Conditions

• E787 collected NK5.9?1012 in 81 weeks over 5
  years.
• E949 proposed NK18?1012 in 60 weeks over 3
  years.
• E949 collected NK1.7?1012 in 12 weeks in 2002.
• Beam conditions were less than optimal
• broken separator more p less K
• spare M.G. lower p mom., poor duty factor
• Detector worked very well
• Smooth data taking

E787 E949 Prop. E949
AGS mom. GeV/c 25.5 25.5 21.9
Beam intensity Tp 15-35 65 65
Duty factor 41-55 63 41
K/p 3.7-4.2 4.0 3.0
NK 1012 5.9 18 1.8
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E949 Overview (3) Performance
Photon Veto
Kinematics

• Kp2 momentum, energy and range
• E949 (yellow histogram) vs. E787 (circle)

Improved PV key to pnn2 exploitation

• Goal double sensitivity while increasing s/b
  1
• 2 ? acceptance and 5 ? rejection
• Improved PV new detectors at small angles
• Improved algorithms to identify p scatters in
  target

Same or even better resolutionin 2 x higher rate
environment
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E949 pnn1 analysis
E949 observed one new event in the primary pnn1
region
PRL 93, 031801 (2004)
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E949 pnn2 analysis
Advantages

• More phase space than pnn1
• Fewer pN interactions
• Probe K?????? spectrum

After the trigger
Disadvantages

• Need photon detection near beam
• Must identify p target scattering
• kink in the pattern of target fibers
• p track that does not point back to the K decay
  point
• energy deposits inconsistent with an outgoing p
• unexpected energy deposit in the fibers traversed
  by the K

pnn1
pnn2
P vs. R of p
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K?pp0 target scattering background
Typical target pattern
Target kink transverse scatter
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Longitudinal scattering CCD pulse cut
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K?pp0 background
Photon tagged
pscat tagged
CD
Target cut
CCD pulse
Photon cut
B
C
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Beam background

• Single beam particle ID, timing

• Double beam
• redundant particle ID along beam line

• Cerenkov
• Wire chamber
• Target
• B4
• AD

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Muon background
K?mng K?mnp0

• Range momentum
• dE/dx range stack
• p?m?e chain

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Ke4 (K?pp-en) background
K?pp-en can be a background if the p- and e
have very little kinetic energy and evade
detection.
p-e energy can be very low
Ke4 MC event
signal region
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Ke4 (K?pp-en) background

• A Ke4-rich sample is tagged in data by selecting
  events with extra target energy.
• Use MC to evaluate the rejection of cuts
• The p- annihilation
• energy spectrum
• is from our
• experimental
• measurement

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Charge exchange (Kn ?K0p) background

• Characteristics
• a gap between K and p
• z info of p is not consistent with K track

• A CEX rich data sample is tagged by a gap
  between K and p
• Model KL momentum from KS monitors
• Use MC to evaluate the rejection

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Total background and sensitivity
For E787E949 pnn1 SES0.6310-10
SES is the branching ratio for a single event
observed w/o background
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Outside box study (verify bkg. est.)

• Keep signal region hidden
• Relax photon veto or CCD pulse cut
• Check the predicted events and observed events
  in the extended region A

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Inside-the-box study

• The background is not uniformly distributed in
  the signal region.
• Use the remaining rejection power of the photon
  veto, delayed coincidence, p?µ ?e and kinematic
  cuts to divide the signal region into 9 cells
  with differing levels of signal acceptance (Si )
  and background (Bi ).
• Calculate B(K????) using Si/Bi of any cells
  containing events using the likelihood ratio
  method.

Momentum (MeV/c) of
K?pp-en
Signal
p box pgt140 Tight p box pgt165
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_
Measured ????? BR of this analysis
9.26

• BR(7.89 )10-10
• The probability of all 3 events to be due to
  background alone is 0.037
• due SM signal background is 0.056
• SM prediction
• BR(0.850.07)10-10

5.10
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Combined with all E787/E949 result
1.15

• BR(1.73 )10-10
• The probability of all 7 events to be due to
  background alone is 0.001
• due to SM signal background is 0.06
• SM prediction
• BR(0.850.07)10-10

1.05
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Implications for KL?p0nn
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BR of Scalar and Tensor form factors
Trigger simulation
BR (10-10)
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Limit on the BR of ???X
The mass of X is unknown. X might have limited
lifetime We assume the detection efficiency of
decay products of X is 100 if the decay occurs
within the detector
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Summary Outlook

• Based on seven E787/E949 K?????? events the BR is
  consistent with the SM, but remains higher than
  expectedmore data is needed!
• E949 is finished, but NA62 at CERN is moving
  forward and experiments at J-PARC and FNAL are
  under consideration
• Plans are underway to move the E949 detector to
  Japan
• K???? remains an incisive test of the flavor
  structure of our physical world, whether
  described by the SM or new physics and some
  combination of experiments should go forward!
• Together K?? ?? and KL??0 ?? provide a unique
  opportunity for discovery of new physics.

E949
92
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