Search for CP violation in t decays

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Search for CP violation in t decays

• R. Stroynowski
• SMU
• Representing CLEO Collaboration

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Symmetry

• The word symmetry derives from greek sum
  metria
• (same measure, Polykleitos 5th century BC
  describing left and
• right sides of animals).
• In Physics, it describes an invariance under a
  set of transformations.
• Continuous symmetries
• Translation invariance (homogeneity of space)
• Rotation invariance (isotropy of space)
• Boost invariance (special relativity)
• Discrete symmetries
• Space reflection (Parity, P) (x,y,z) ? (-x,-y,-z)
• Particle-antiparticle symmetry (Charge
  conjugation, C)
• Time reversal (T) t ? -t

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P and C is separately violated in weak
interactions. The violation is maximal
CP describes particle-antiparticle symmetry. In
relativistic Field Theory CPT theorem implies
that CP is equivalent to T
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• Motivation
• Particle physics
• CP violation has been observed in the quark
  sector where it is due to the structure of the
  quark mixing matrix.
• Recent observation of neutrino oscillations imply
  existence of the neutrino mixing matrix and thus
  allow for a possible CP violation in the neutrino
  sector.
• Is the analogous mixing matrix exist in the
  charged lepton sector it must be mostly diagonal,
  since there are strict limits on the lepton
  number violating decays. Such matrix if it
  exists could also lead to CP violation.
• Many extensions of the Standard Model allow for
  the CP violation in the lepton sector.

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• Cosmology
• The expectation that Big Bang should result in a
  symmetry between matter and antimatter is not
  confirmed by the astronomical observations. The
  electron-positron annihilation line is not
  observed at the rate expected even for the widely
  separate clumps of matter and antimatter. Thus
  the initial symmetry is violated. Although it is
  possible to ascribe this as due to initial
  condition, it would be much more elegant to
  describe it as due to observable processes. CP
  violating decays are natural candidates for such
  processes.
• CP violation has been observed in weak decays of
  s and b quarks but its magnitude is insufficient
  to explain cosmological problems.

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• CP Violation
• If CP symmetry is exact than there is no
  difference between a given process and its
  CP-conjugated one.
• CP violation generates a difference between the
  partial decay widths. Any kinematical variable
  associated with the decay can be described as a
  sum xxevenxodd with the corresponding
  probability density PPevenPodd
• For CP violation expect ltxgt0.
• Expected deviation is small? must optimize
  choice.
• Atwood and Soni smallest statistical error for
• xPodd/Peven
• ?must have a model for P
• ?deviation from zero independent of the model,
  but interpretation of the value (limit) is model
  dependent.

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Procedure select the model, e.g.,
multi-Higgs-doublet-model Grossman (1994),
Weinberg ((1976),Grossman,Nir,Ratazzi
(1997) calculate matrix element construct
CP-odd observable Two decay modes with similar
sensitivity to new physics t?pp0nt Scalar
coupling suppressed by isospin t?Kpnt W
coupling Cabbibo suppressed
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• Need 3 vectors to construct CP-odd variables
• For t?pp0nt use spin correlations for tau pairs
  each decays decaying to the same final state

• t direction reconstructed with 2-fold ambiguity ?
  use
• both solutions and study the bias
• Vector formfactor approximated by r(770)
  Breit-Wigner
• Scalar formfactor 1, a0(980), a0(1450)

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• Analysis
• Use 13.3 fb-1 of CLEOII data (12.2 x 106 tt-
  pairs)
• Standard CLEO selection criteria to reconstruct
  signal
• Background estimate (9.9) from MC and from the
  data
• Dominant background from other t decays.

Shape depends on formfactor NO ASYMMETRY
fs1
fsa0(980)
fsa0(1450)
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• Estimate of limits for Im(L) is model dependent.
  Since all odd powers of Im(L) are allowed, Monte
  Carlo calibration method is used to extract the
  limits. Results depend also on the choice of the
  formfactor.
• fs ltxgt Im(L)
• 1 -0.0008/-0.0014 -0.012/-0.021
• ao(980) -0.0006/-0.0024 -0.001/-0.004
• a0(1450) 0.0002/-0.0017 0.001/-0.012
• Systematics 2-fold ambiguity in reconstructing t
  direction, background contribution to the
  asymmetry, tracking ? DIm(L)0.003
• Result Limits on scalar coupling constant
• -0.046ltIm(L)lt0.022 at 90 CL

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• Search for CP violation in t?K0pnt decays

Single t decays ?spin averaged terms only No t
direction reconstruction
P2 fv2(2(qQ)(kQ)-(kq)Q2) L2fs2(qk)
2Re(L)Re(fsfv)mt(Qk) 2Im(L)Im(fsfv)mt(Qk)
q - t four-vector, k n four-vector, Q2
2mp22mK2-mhad4(mp2-mK2)2/mhad2 Obtain
(qQ),(kQ),(qk) from experimentally measured
parameters using prescription by Kuhn and
Mirkes Use fvBW (K(890)) and fsBW(K(1430))
x Podd/Peven
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• Analysis
• CLEOII data - 13.3 fb-1 .
• signal t?K0spn with K0s?pp-
• tag t?single prong, i.e., lnlnt, h(p0)nt
• background (41.3) other t decays small qq
  contribution

11970 events K(890) peak with 4.7/- MeV mass
shift no evidence for scalar K(1430)
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• Results

Monte Carlo with Im(L)1
Data
Expect enhancement due to K(890)-K(1430)
interference
Systematics background studied via Monte
Carlo tracking efficiency scalar form-factor
parametrization Overall multiplicative error -
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• Results

No CP violation observed In the range 0.85
GeV/c2 lt M(Kp) lt 1.45 GeV/c2 ltxgt -2.0/-1.8 x
10-3 Im(L) (-0.046/-0.044/-0.019)(1/-0.15)
-0.172 lt Im(L) lt 0.067 at 90 CL
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• Summary
• No CP violation has been observed
• t?pp0nt -0.046 lt Im(L) lt 0.022 at 90 CL
• t?Kpnt -0.172 lt Im(L) lt 0.067 at 90 CL
• t?pp0nt provides most restrictive limit on Im(L)
• t?Kpnt provides a limit on the lightest of
  charged Higgs in MHDM
• mH gt 2.1 GeV/c2