Search for New Physics via ? Rare Decay

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Search for New Physics via ? Rare Decay

• Liping Gan
• University of North Carolina Wilmington

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Contents

• Physics Motivation
• Why ? meson is interesting?
• ???0??
• ???0?0
• Experimental Design
• Summary

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Why ? Meson Is Interesting?

• One of the Goldstone bosons due to spontaneous
  chiral symmetry breaking
• The heaviest member in the octet pseudoscalar
  mesons
• Provide a rich program to investigate evidences
  of symmetry breaking and the new physics beyond
  Standard Model

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The Neutral ? Decay (from B.Nefkens)
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Study of the ???0?? Decay

• A stringent test of the ?PTh prediction at ?(p6)
  level
• Tree level amplitudes (both ?(p2) and ?(p4))
  vanish
• ?(p4) loop terms involving kaons are suppressed
  large mass of kaon
• ?(p4) loop terms involving pions are suppressed
  by G parity
• The first sizable contribution comes at ?(p6)
  level
• A long history that experimental results have
  large discrepancies with theoretic predictions.
• Current experimental limits in PDG is BR(???0??
  )lt4.4x10-4

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Theoretical Status on ???0??
By E. Oset et al.
Unitarized ?PTh with new PDG inputs 0.330.08

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Study of ???0 ?0 Reaction

• The Origin of CP violation is still a mystery
• CP violation is described in SM by the phase in
  the Cabibbo-Kobayashi-Maskawa quark mixing
  matrix. A recent SM calculation predicts BR(???0
  ?0)lt3x10-17
• The ???0 ?0 is one of a few available
  flavor-conserving reactions listed in PDG to test
  CP violation.
• Current experimental limit in PDG is BR(???0
  ?0)lt4.3x10-4
• Unique test of P and PC symmetries, and search
  for new physics beyond SM

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History of the ???0?? Measurements
After 1980
A long standing ? puzzle is still un-settled.
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GAMS Experiment on ???0?? at Serpukhov

• Experimental result was first published in 1981
• The ?s were produced with 30 GeV/c ?- beam in
  the ?-p??n reaction
• Decay ?s were detected by lead-glass wall

Final result (D. Alde et al.) 40 of ???0??
events BR(???0??)(7.11.4)x10-4 ?(???0??)0.840
.17 eV

• Major Background
• ?-p? ?0?0n
• ? ??0?0?0

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CB experiment on ???0?? at AGS

• About 3x107 ?s data were collected in 1998 at
  AGS, BNL
• The ?s were produced with 720 MeV/c ?- beam
  through the ?-p??n reaction
• NaI crystal ball calorimeter with 672 modules
• Decay ?s energy range 50-500 MeV

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CB Data Analysis I (by S. Prakhov et al. in 2005)
?-p? ?0?0n
? ??0?0?0

• Final result
• 1600 of ???0?? events
• BR(???0??)(3.50.9)x10-4
• ?(???0??)0.450.12 eV

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CB Data Analysis II (by N. Knecht et al. in 2004)

• Final result
• 12137 of ???0?? events
• BR(???0??)(2.70.90.8)x10-4
• ?(???0??)0.320.15 eV

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What can be improved?

• Tagged ? to reduce non-resonance ?0?0 background
• Higher beam energy to reduce the background from
  ?? ?0?0 ?0
• Lower relative threshold for ?-ray detection
• Improve calorimeter resolution
• Calorimeter with PWO4 insertion
• Higher energy resolution ? improve ?0??invariance
  mass
• Higher granularity? better position resolution
  and less pile-up clusters
• Large statistics to provide a precision
  measurement of Dalitz plot

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Experimental Design

• ? produced on LH2 target with 11 GeV tagged
  photon beam
• Tag ? by measuring recoil p with GlueX
• Forward calorimeter with PWO4 insertion to detect
  multi-photons from the ? decay

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Kinematics of Recoil Proton

• Polar angle 65o-80o
• Kinetic energy 20-300 MeV
• Momentum 200-800 MeV/c

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Acceptance
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Invariance Mass of ?0??
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Rate Estimation

• The ? production rateLH2 target length L30cm,
  ?0.0708 g/cm3

• The ?p??p cross section 1 µb
• Photon beam intensity N?1.5x107 Hz

• The ???0?? detection rate BR(???0?? )4x10-4 ,
  detection efficiency 11.4

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Summary

• High energy and high intensity tagged photon beam
• First tagged ? experiment by measuring recoil p
  with GlueX
• High resolution calorimeter with PWO4 crystal
  insertion to reduce the major backgrounds
• Precision measurement on ?(???0??) to test the
  ?PTh prediction at ?(p6) order
• Measurements of branching ratio/upper limits for
  various rare and forbidden ? decays involving
  photons in the final states to test P, PC and C
  symmetries, and search for new physics beyond
  Standard Model