CP Eigenstates Research Articles

Improved Measurement ofCPAsymmetries inB0→(cc¯)K0(*)Decays

We present results on time-dependent CP asymmetries in neutral B decays to several CP eigenstates. The measurements use a data sample of about 227 x 10(6) upsilon(4S) --> BB decays collected by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. The amplitude of the CPasymmetry, sin2beta in the standard model, is derived from decay-time distributions from events in which one neutral B meson is fully reconstructed in a final state containing a charmonium meson and the other B meson is determined to be either a B0 or B0 from its decay products. We measure sin2beta = 0.722 +/- 0.040(stat) +/- 0.023(syst) in agreement with the standard model expectation.

BELLE RESULTS ON TIME DEPENDENT CP VIOLATION IN B DECAYS

We report on measurements of time-dependent CP-violation parameters in neutral B meson systems based on a 140fb -1 data sample collected at the ϒ(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. One B meson is fully reconstructed in one of the CP eigenstate decay channels, and its flavor is identified from the decay products of the accompanying B meson. The CP-violation parameters are extracted from the asymmetries in the distributions of the proper-time intervals between the two B decays. The parameter sin 2ϕ1 is measured with the decay modes including the b→c tree and b→s penguin transitions, and sin 2ϕ2 is obtained from the decay mode B→π+π-. A brief discussion of the ϕ3 measurements with B→D(*)∓π± decays is also given.

ABOUT NEUTRAL KAONS AND SIMILAR SYSTEMS: FROM QUANTUM FIELD THEORY TO EFFECTIVE MASS MATRICES

Systems of neutral interacting mesons are investigated, concerning in particular their description by an effective Hamiltonian, with a special emphasis on discrete symmetries. Several ambiguities are pointed out. First, the connection to quantum field theory, in which the physical masses [Formula: see text] and [Formula: see text] are the poles of the full renormalized propagator, shows that, for mass-split binary systems, two mass matrices rather than a single effective one are at work; they correspond to the two values [Formula: see text] and [Formula: see text] of the momentum squared. Transformation properties of the physical eigenstates by discrete symmetries may not reflect the ones of these two mass matrices (and those of the Lagrangian at any given p2). Then, after showing that a bi-orthogonal basis has to be used to diagonalize the complex mass matrix of such unstable systems, and not a bi-unitary transformation, we turn to the ambiguity linked to the commutation of the fields of the K0 and of its charge conjugate [Formula: see text]: any constant effective mass matrix is defined, in the [Formula: see text] basis, up to arbitrary diagonal antisymmetric terms; I use this freedom to deform it in various ways, in both the [Formula: see text] and (KL,KS) basis, and I study the consequences on the spectrum. CPT symmetry is specially concerned. An effective mass matrix can always be cast into a CPT invariant form, and only T violating eigenstates can never be cast into CP eigenstates. The dual formalism of |in> and <out| states and bi-orthogonal basis, suitable for nonnormal matrices, is used. In a subsequent work, the fundamental roles played by the normality of the mass matrix and CPT symmetry in the framework of quantum field theory will be investigated in connection with experimental results.

Gold-plated mode of CP-violation in decays of Bc meson from QCD sum rules

A model-independent method based on the triangle ideology is implemented to extract the CKM-matrix angle γ in the decays of the doubly heavy long-lived meson Bc. We analyse a colour structure of diagrams and conditions to reconstruct two reference triangles by tagging the flavour and CP eigenstates of mesons in the fixed exclusive channels. The characteristic branching ratios are evaluated in the framework of QCD sum rules.

Limits on the decay-rate difference of neutralBmesons and onCP,T, andCPTviolation inB0B0oscillations

Using events in which one of two neutral B mesons from the decay of an Υ(4S) resonance is fully reconstructed, we set limits on the difference between the decay rates of the two neutral B mass eigenstates and on CP, T, and CPT violation in B0B0 mixing. The reconstructed decays, comprising both CP and flavor eigenstates, are obtained from 88 million Υ(4S)→BB¯ decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We determine six independent parameters governing oscillations (Δm,ΔΓ/Γ), CPT and CP violation (Rez,Imz), and CP and T violation (ImλCP,|q/p|), where λCP characterizes B0 and B0 decays to states of charmonium plus KS0 or KL0. The results are sgn(ReλCP)ΔΓ/Γ=−0.008±0.037(stat.)±0.018(syst.)[−0.084,0.068],|q/p|=1.029±0.013(stat.)±0.011(syst.)[1.001,1.057],(ReλCP/|λCP|)Rez=0.014±0.035(stat.)±0.034(syst.)[−0.072,0.101],Imz=0.038±0.029(stat.)±0.025(syst.)[−0.028,0.104].The values inside square brackets indicate the 90% confidence-level intervals. The values of ImλCP and Δm are consistent with previous analyses and are used as cross checks. These measurements are in agreement with standard model expectations.Received 29 February 2004DOI:https://doi.org/10.1103/PhysRevD.70.012007©2004 American Physical Society

Time-dependent CP violation in [formula omitted] decays

We note that in decays of the type B0→P0P0X0, where P0 and X0 represent any CP eigenstate spin-0 neutral particles, the final state is a CP eigenstate. We consider the possibilities for studying time-dependent CP violation in decays of this type at B factories with high luminosity, with particular attention to B0→KS0KS0KS0. We also comment on some cases where X0 has non-zero spin, and decays of the type B0→P0Q0X0, where the three final state particles are different spin-0 CP eigenstates.

Observation of large CP violation and evidence for direct CP violation in B0-->pi(+)pi(-) decays.

We report the first observation of CP violation in B0-->pi(+)pi(-) decays based on 152x10(6) gamma (4S)-->BB decays collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We reconstruct a B0-->pi(+)pi(-) CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the distribution of the time intervals between the two B meson decay points, we obtain A(pipi)=+0.58+/-0.15(stat)+/-0.07(syst) and S(pipi)=-1.00+/-0.21(stat)+/-0.07(syst). We rule out the CP-conserving case, A(pipi)=S(pipi)=0, at a level of 5.2 standard deviations. We also find evidence for direct CP violation with a significance at or greater than 3.2 standard deviations for any S(pipi) value.

Theoretical issues in b physics

Examples are given of some current questions in $b$ physics to which LHC experiments may provide answers. These include (i) the precise determination of parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix; (ii) measurements of CKM phases using B decays to CP eigenstates; (iii) the search for direct CP asymmetries in B decays; (iv) rare radiative B decays; (v) the study of $B_s$ properties and decays, (vi) excited states of $B$ and $B_s$ mesons, and (vii) the search for heavier quarks which could mix with the $b$ quark.

Correlated neutral B meson decays into CP eigenstates

In the two correlated B meson decay experiment we propose to measure intensities relating CP eigenstate (J/ψKS,L) decays on both sides, which will be measurable in future upgrades of KEK and PEP. As a CP-forbidden transition, we obtain I(J/ψKS,J/ψKS,Δt)∼sin2(2β). We calculate in a model independent way all the possible intensities relating final CP and flavour eigenstate decays. Under CPT-invariance, the asymmetries for processes related by CPΔt vanish for ΔΓ=0 and measure ΔΓ linearly. We notice the impossibility to isolate the sign of cos(2β) without an independent knowledge of the sign of ΔΓ. This exhaustion of the possible golden plate and flavour decays provides new observables which may throw light in our present understanding of CKM physics.

Possible test forCPTinvariance with correlated neutralBdecays

We study the breakdown of CPT symmetry which can occur in the decay process $B\overline{B}\ensuremath{\rightarrow}{l}^{\ifmmode\pm\else\textpm\fi{}}{X}^{\ensuremath{\mp}}f$ with f being a CP eigenstate. In this process, the standard model expectations for time-ordered semileptonic and hadronic events, i.e., which of the two decays takes place first, can be altered in the case that there is a violation of CPT symmetry. To illustrate this possibility, we identify and study several time-integrated observables. We find that an experiment with ${10}^{9}B\overline{B}$ pairs has the capability of improving the bound on the CPT violating parameter or perhaps observe CPT violation.

Impact of tag-side interference on time-dependentCPasymmetry measurements using coherentB0B0pairs

Interference between CKM-favored b {yields} c{bar u}d and doubly-CKM-suppressed {bar b} {yields} {bar u}c{bar d} amplitudes in final states used for B flavor tagging gives deviations from the standard time evolution assumed in CP-violation measurements at B factories producing coherent B{sup 0}{bar B}{sup 0} pairs. We evaluate these deviations for the standard time-dependent CP-violation measurements, the uncertainties they introduce in the measured quantities, and give suggestions for minimizing them. The uncertainty in the measured CP asymmetry for CP eigenstates is {approx} 2% or less. The time-dependent analysis of D*{pi}, proposed for measuring sin(2{beta} + {gamma}), must incorporate possible tag-side interference, which could produce asymmetries as large signal asymmetry.

Possibility of measuring the CP-violation γ-parameter in decays of Ξbc baryons

The model-independent method based on the triangle ideology is implemented to extract the CKM-matrix angle γ in the decays of doubly heavy baryons containing the charmed and beauty quarks. We analyze a color structure of diagrams and conditions for reconstructing two reference-triangles by tagging the flavor and CP eigenstates of D0↔D0 mesons in the fixed exclusive channels. The characteristic branching ratios are evaluated in the framework of a potential model setting a parametric dependence on the hadronic matrix elements for the decay rates.

Evidence forCP-violating asymmetries inB0→π+π−decays and constraints on the CKM angleφ2

We present an improved measurement of CP-violating asymmetries in B 0→π+π- decays based on a 78 fb -1 data sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider. We reconstruct one neutral B meson as a B0→π+π - CP eigenstate and identify the flavor of the accompanying B meson from inclusive properties of its decay products. We apply an unbinned maximum likelihood fit to the distribution of the time intervals between the two B meson decay points. The fit yields the CP-violating asymmetry amplitudes A ππ= +0.77 ±0.27(stat) ±0.08(syst) and S ππ=-1.23 ±0.41(stat) -0.07 +0.08(syst), where the statistical uncertainties are determined from the Monte Carlo pseudoexperiments. We obtain confidence intervals for CP-violating asymmetry parameters Aππ and Sππ based on a frequentist approach. We rule out the CP-conserving case, A ππ=Sππ=0, at the 99.93% confidence level. We discuss how these results constrain the value of the Cabibbo-Kobayashi-Maskawa (CKM) angle φ2. © 2003 The American Physical Society.

CP-violating asymmetries in B0 → π+π− decays

We present a measurement of CP-violating asymmetries in B 0 → π + π − decays based on a data sampleof 44.8 million B B pairs collected at the ϒ(4 S) resonance with the Belle detector. We fully reconstruct one neutral B meson as a B 0 → π + π − CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the distribution of time intervals between the two B meson decay points, we obtain the CP-violating asymmetry parameters S ππ = −1.21 −0.27 +0.38( stat) −0.13 +0.16( syst) and C ππ = +0.94 0.31 +0.25( stat) ± 0.09( syst).

Selected physics results from Belle

We present an updated measurement of sin 2 φ 1 in B 0 → c cW decays and first evidence for CP-violating asymmetries in B → π + π − decays. We also report the first observation of the ν c (2 S) meson. The results are based on analyses of a sample of 41.8 million B B meson pairs from the decays of the υ(4 S) resonance, collected with the Belle detector at the KEKB asymmetric-energy e + e − collider. For the B → π + π − CP-violating asymmetry measurement, we fully reconstruct one neutral B meson as a B → π + π − CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the dependence of the asymmetry on the time intervals between the two B meson decay points, we obtain the CP-violating asymmetry parameters S ππ = −1.21 −0.27 +0.38( stat) −0.13 +0.16( syst) and A gpπ = +0.94 −0.31 +0.25( stat) ± 0.09( syst). In the η c (2 S) meson search, we examined the K s K − π + invariant mass distribution in a sample of exclusive B → KK S K − π + decays. We find a narrow peak mass M = 3654 ± 6( stat) ± 8( syst) MeV/ c 2 and width Γ < 55 MeV/ c 2. The properties agree with heavy-quark potential model expectations for the η c (2 S) meson, the n = 2 singlet S-wave charmonium state.

A closer look at Bd, s→ Dfr decays and novel avenues to determine γ

Decays of neutral B mesons originating from b→ Dr ( r∈{ s, d}) processes, i.e., B d → DK S(L), B s → Dη (′), Dφ,… ( r= s) and B s → DK S(L), B d → Dπ 0, Dρ 0,… ( r= d) modes, offer valuable insights into CP violation. Here the neutral D mesons may be observed through D→ f ± or D→ f NE, where f ± and f NE are CP eigenstates and CP non-eigenstates, respectively. Recently, we pointed out that “untagged” and mixing-induced CP-violating B d, s → D ± f s observables provide a very efficient, theoretically clean determination of the angle γ of the unitarity triangle. Here we perform a more detailed analysis of the B d, s → D[→ f ±] f s channels, and focus on B d, s → D[→ f NE] f s , where interference effects between Cabibbo-favoured and doubly Cabibbo-suppressed D-meson decays lead to complications. We show that γ can nevertheless be determined in an elegant and essentially unambiguous manner from the B d, s → D[→ f NE] f s observables with the help of the corresponding “untagged” B d, s → D[→ f ±] f s measurements. Moreover, we may also extract hadronic B- and D-decay parameters. Several interesting features of decays of the kind B d, s → Df d are also pointed out.

New results from Belle

We have measured the CP violation parameters in B° decays to the following CP eigenstates: (c c)K s, J/ψK L, J/ψK −0, π +π −, θK s, η/K s and K +K −K s , using data collected with the Belle detector at the KEKB asymmetric-energy e +e − collider. One of the angles of the CKM unitality triangle, θ 1, has been determined using 78 fb −1 as sin 2 θ 1 = 0.719 ± 0.074 ± 0.035. The large A ππ is an indication of direct CP violation in B meson decay. The S θK , S η′ K are S KKK are all consistent with sin 2 θ 1 within 3σ. We also present the first measurement o the inclusive branching fraction for the electroweak penguin decay B → X s ℓ +ℓ −. The results on the branching fraction, dilepton and recoil mass spectra are in agreement with the Standard Model expectations.

Measurement of sin2β with BABAR

We present updated results on time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates containing charmonium. In the Standard Model, the amplitude of these asymmetries is proportional to sin2β. We measure sin2β = 0.741 ± 0.067 (stat) ± 0.034 (syst) from a data sample of about 88 million γ(4 S) → B B decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We have also measured CP-violating asymmetries in open charm, and penguin modes sensitive to sin2β, which provide important consistency tests of the Standard Model.

Branching fraction and properties of B meson decays to charmonium at Belle

The latest Belle results on B meson decays to charmonium are reported. The topics include the first observation of the η c (2 S) meson, which is a charmonium state so far missing; an observation of factorization-forbidden decays: B → χ C2 X and χ C0 K; and search for more CP eigenstates in both Cabibbo-favored and Cabibbo-suppressed decays.

Measurement of branching fractions for B-->eta(c)K(*) decays.

We report measurements of branching fractions for charged and neutral B-->eta(c)K decays where the eta(c) meson is reconstructed in the K(0)(S)K+/-pi(-/+), K+K-pi(0), K(*0)K-pi(+), and pp; decay channels. The neutral B0 channel is a CP eigenstate and can be used to measure the CP violation parameter sin(2phi(1). We also report the first observation of the B0-->eta(c)K(*0) mode. The results are based on an analysis of 29.1 fb(-1) of data collected by the Belle detector at KEKB.