Search for CP violation in decays

R. Stroynowski

SMURepresenting CLEO Collaboration

Symmetry

•The word “symmetry” derives from greek “”(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

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

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.

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.

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 evenodd with the corresponding probability density P=Peven+Podd

• For CP violation expect <#0.

• Expected deviation is small must optimize choice.

• Atwood and Soni: smallest statistical error for

=Podd/Peven

must have a model for P

deviation from zero independent of the model, but interpretation of the value (limit) is model dependent.

Procedure:select the model, e.g., multi-Higgs-doublet-model

Grossman (1994), Weinberg ((1976),Grossman,Nir,Ratazzi (1997)

calculate matrix elementconstruct CP-odd observable

Two decay modes with similar sensitivity to new physics: Scalar coupling suppressed by isospin

KW coupling Cabbibo suppressed

• Need 3 vectors to construct CP-odd variables

• For use spin correlations for tau pairs each decays decaying to the same final state

direction reconstructed with 2-fold ambiguity use both solutions and study the bias

Vector formfactor approximated by (770) Breit-WignerScalar formfactor: 1, a0(980), a0(1450)

AnalysisUse 13.3 fb-1 of CLEOII data (12.2 x 106 pairs)

Standard CLEO selection criteria to reconstruct signal

Background estimate (9.9%) from MC and from the dataDominant background from other decays.

fs=1

fs=a0(980)

fs=a0(1450)

Shape depends onformfactor

NO ASYMMETRY

Estimate of limits for Im() is model dependent. Since all odd powers of Im() are allowed, Monte Carlo calibration method is used to extract the limits. Results depend also on the choice of the formfactor.

fs <> Im()

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 direction, background contribution to the asymmetry, tracking Im()=0.003

Result: Limits on scalar coupling constant

-0.046<Im()<0.022 at 90% CL

Search for CP violation in K0 decays

Single decays spin averaged terms only

No direction reconstruction

P2 ~ |fv|2(2(qQ)(kQ)-(kq)Q2) + ||2|fs|2(qk) + 2Re()Re(fsfv

*)m(Qk) – 2Im()Im(fsfv*)m(Qk)

q - four-vector, k – four-vector, Q2 = 2m

2+2mK2-[mhad

4+(m2-mK

2)2]/mhad2

Obtain (qQ),(kQ),(qk) from experimentally measured parameters using prescription by Kuhn and MirkesUse fv=BW (K*(890)) and fs=BW(K*(1430))

= Podd/Peven

AnalysisCLEOII data - 13.3 fb-1 .

• signal: K0s with K0

s+-

• tag: single prong, i.e., ll, h(0)

• background: (41.3%): other decays+ small qq contribution

11970 eventsK*(890) peak with 4.7+/- MeV mass shiftno evidence for scalar K*(1430)

Results

Data Monte Carlo with Im()=1

Expect enhancement due to K(890)-K(1430) interference

Systematics: background studied via Monte Carlotracking efficiencyscalar form-factor parametrization

Overall multiplicative error - 15%

Results

No CP violation observed

In the range: 0.85 GeV/c2 < M(K) < 1.45 GeV/c2

<> = -2.0+/-1.8 x 10-3

Im() = (-0.046+/-0.044+/-0.019)(1+/-0.15)

-0.172 < Im() < 0.067 at 90% CL

Summary

• No CP violation has been observed

: -0.046 < Im() < 0.022 at 90% CL

K : -0.172 < Im() < 0.067 at 90% CL

• provides most restrictive limit on Im()

• Kprovides a limit on the lightest of charged Higgs in MHDM

mH > 2.1 GeV/c2