B-meson Factories Research Articles

Model-independent analysis of B → πℓ + ℓ − decays

The results obtained by calculating, on the basis of the Standard Model, the branching fractions for the decays B → πℓ + ℓ − (ℓ ± = e ±, µ±) and the invariant-mass spectrum of dileptons for the process B + → π + ℓ + ℓ − are presented. The resulting theoretical estimates depend on the choice of model for the B → π transition form factors f +(q 2), f 0(q 2), and f T (q 2). However, one can get rid of this arbitrariness by employing experimental data or the results of QCD lattice calculations to determine the parameter dependence of the form factors. Data from B-meson factories were used to determine the dependence of the form factor f +(q 2) on the transfer momentum squared. Yet another required form factor, f T (q 2), was extracted from available lattice data on B → π and B → K transitions with allowance for nearly identical effects of the breakdown of flavor SU(3) F symmetry in the respective form factors. The resulting value of the decay branching fraction, B(B + → π +µ+µ−) = (1.88 +0.32−0.21 ) × 10−8, is in good agreement with the results of measurements of the LHCb Collaboration. The branching fraction for the isospin analog of the decay under consideration is B(B + → π +µ+µ−) = (0.94 +0.16−0.11 ) × 10−8. Therefore, this decay can be measured at the Super-B factory under construction.

Strong coupling, charm- and bottom-quark masses from electron-positron annihilation

The cross section for electron-positron annihilation into hadrons allows for a precise determination of the strong coupling constant and the charm- and bottom-quark masses. Recent theoretical and experimental results are presented with emphasis on the energy region accessible by B-meson factories and below.

Measurement and interpretation of moments in inclusive semileptonic decaysB¯→Xcℓ−ν¯

We present results for the moments of observed spectra in inclusive semileptonic B-meson decays to charm hadrons Bbar --> X_c l- nubar. Moments of the hadronic-mass and the combined mass-and-energy spectra for different minimum electron or muon momenta between 0.8 and 1.9 GeV/c are obtained from a sample of 232x10^{6} Y(4S) --> B Bbar events, collected with the BABAR detector at the PEP-II asymmetric-energy B-meson factory at SLAC. We also present a re-evaluation of the moments of electron-energy spectra and partial decay fractions BR(Bbar --> X_c e- nubar for minimum electron momenta between 0.6 and 1.5 GeV/c based on a sample of 51x10^{6} Y(4S) --> B Bbar events. The measurements are used for the extraction of the total decay fraction, the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V_cb|, the quark masses m_b and m_c, and four heavy-quark QCD parameters in the framework of a Heavy Quark Expansion (HQE). We find BR(Bbar --> X_c l- nubar) = (10.64 +/- 0.17 +/- 0.06)% and |V_cb| = (42.05 +/- 0.45 +/- 0.70) x 10^{-3}.

DIRECT TEST OF TIME REVERSAL INVARIANCE VIOLATION IN B-MESONS

In this letter we reinterpret and reanalyze the available data of the B-meson factories showing the existence of direct experimental evidence of time reversal invariance violation in B-mesons. This reinterpretation consists of using the available observables to define a new observable which, in a model-independent way and without assuming CPT invariance, compares a transition between a B0 and a here-defined Bα-state, with its time reversed transition. The observable then offers a direct way to probe time reversal invariance and it is therefore independent of any conclusion obtained from current experimental information on CP violation and CPT invariance. As far as we are concerned, this is the first direct evidence of time reversal invariance violation in B-mesons and also the first one obtained from decaying particles whose mean lifetime difference is negligible.

Development and Implementation of a Readout Module for Radiation-Sensing Field-Effect Transistors

We describe a readout module for radiation-sensing field-effect transistors. Three of these modules are currently being used for measuring the total accumulated dose in the silicon vertex detector (SVD) of the Belle experiment at KEKB B-meson factory in the High energy accelerator research organization (KEK), Japan. These modules have been in operation since August 2005

Search forB+→ϕπ+andB0→ϕπ0decays

A search has been made for the decays B+ -> phi pi+ and B0->to phi pi0 in a data sample of approximately 232 x 10^6 B Bbar pairs recorded at the Upsilon(4S) resonance with the BaBar detector at the PEP-II B-meson Factory at SLAC. No significant signals have been observed, and therefore upper limits have been set on the branching fractions: BR(B+ ->phi pi+)<2.4 x 10^{-7} and BR(B0->phi pi0)<2.8 x 10^{-7} at 90% probability.

MEASUREMENT OF CP ASYMMETRY IN $B^0 \to f_0 K^0_S$, B0 → ϕK0 AND $B^0 \to K^+K^-K^0_S$ DECAYS

We present results on time-dependent CP asymmetries in [Formula: see text] and B0 → K+K-K0. The measurements use a data sample consisting of approximately [Formula: see text] and 227(B0 → K+K-K0) million B-meson pairs recorded at the ϒ(4S) resonance with the BABAR detector at the PEP-II B-meson Factory at SLAC. From a time-dependent maximum likelihood fit, we measure for [Formula: see text]: the mixing-induced CP violation parameter [Formula: see text] and the direct CP violation parameter Cf0K = -0.24 ± 0.31 ( stat ) ± 0.15 ( syst ). From a simultaneous fit to [Formula: see text] and [Formula: see text] decays, we find: [Formula: see text] and CϕK = 0.00 ± 0.23 ( stat ) ± 0.05 ( syst ). For [Formula: see text] decays with [Formula: see text] decays excluded, we find: [Formula: see text] and [Formula: see text]. From the [Formula: see text] decays with [Formula: see text] decays excluded, we extract the fraction of CP-even final states from angular moments feven = 0.89 ± 0.08 ± 0.06.

Measurement ofCPasymmetries inB0→ϕK0andB0→K+K−Ks0decays

We measure the time-dependent CP asymmetry parameters in B0 --> K+ K- K0 based on a data sample of approximately 227 million B-meson pairs recorded at the Upsilon(4S) resonance with the BaBar detector at the PEP-II B-meson Factory at SLAC. We reconstruct two-body B0 decays to Phi(1020) K0S and Phi(1020)K0L, and the three-body decay K+ K- K0S with Phi(1020) K0S excluded. For the B0 --> Phi K0 decays, we measure sin(2 beta_{eff})(Phi K0) = +0.50 +/- 0.25(stat) +0.07/-0.04(syst). The B0 --> K+ K- K0S decays are dominated by K+ K- S-wave, as determined from an angular analysis; we measure sin(2 beta_{eff})(K+ K- K0S) = +0.55 +/- 0.22(stat) +/- 0.04(syst) +/- 0.11(CP), where the last error is due to the uncertainty in the fraction of CP-even contributions to the decay amplitude. We find no evidence for direct CP violation.

Measurement of the time-dependent CP asymmetry in the B0-->phiK0 decay.

We present a measurement of the time-dependent CP asymmetry for the neutral B-meson decay B0-->phiK0. We use a sample of approximately 114 x 10(6) B-meson pairs taken at the Upsilon(4S) resonance with the BABAR detector at the PEP-II B-meson factory at SLAC. We reconstruct the CP eigenstates phiK0S and phiK0L, where phi-->K+K-, K0S-->pi+pi-, and K0L is observed via its hadronic interactions. The other B meson in the event is tagged as either a B0 or Bbar0 from its decay products. The values of the CP-violation parameters are SphiK=0.47+/-0.34(stat)+0.08-0.06(syst) and CphiK=0.01+/-0.33(stat)+/-0.10(syst).

Measurement of the electron energy spectrum and its moments in inclusiveB→Xeνdecays

We report a measurement of the inclusive electron energy spectrum for semileptonic decays of B mesons in a data sample of 52 million Υ(4S)→BB¯ decays collected with the BABAR detector at the PEP-II asymmetric-energy B-meson factory at SLAC. We determine the branching fraction, first, second, and third moments of the spectrum for lower cutoffs on the electron energy between 0.6 and 1.5 GeV. We measure the partial branching fraction to be B(B→Xeν,Ee>0.6GeV)=[10.36±0.06(stat.)±0.23(sys.)]%. Received 23 January 2004DOI:https://doi.org/10.1103/PhysRevD.69.111104©2004 American Physical Society

Nucleon form factors, B-meson factories and the radiative return

The feasibility of a measurement of the electric and magnetic nucleon form factors at B-meson factories through the radiative return is studied. Angular distributions allow for a separation of the contributions from the two form factors. The distributions are presented for the laboratory and the hadronic rest frame, and the advantages of different coordinate systems are investigated. It is demonstrated that Q 2 values up to 8 or even 9 GeV2 are within reach. The Monte Carlo event generator PHOKHARA is extended to nucleon final states, and results are presented which include next-to-leading order radiative corrections from initial-state radiation. The impact of angular cuts on rates and distributions is investigated and the relative importance of radiative corrections is analyzed.

The radiative return at Φ- and B-factories: A status report

The measurement of the pion form factor and, more generally, of the cross section for electron–positron annihilation into hadrons through the radiative return has become an important task for high luminosity colliders such as the Φ- or B-meson factories. For detailed understanding and analysis of this reaction, the construction of a Monte Carlo program, PHOKHARA, has been undertaken. Version 2.0 was based on a next-to-leading order (NLO) treatment of the corrections from initial-state radiation (ISR) and leading order final-state radiation (FSR). The most recent extension of PHOKHARA (version 3.0), which incorporates NLO corrections to FSR and the impact of combined ISR and FSR on selected distributions, is presented.

Perspectives for the radiative return at meson factories

The measurement of the pion form factor and, more generally, of the cross section for electron-positron annihilationinto hadrons through the radiative return has become an important task for high luminosity colliders such as the Φ- or B-meson factories. This quantity is crucial for predictions of the hadronic contributions to ( g - 2) μ, the anomalous magnetic moment of the muon, and to the running of the electromagnetic coupling. But the radiative return opens the possibility of many other physical applications. The physics potential of this method at high luminosity meson factories is discussed, the last upgraded version of the event generator PHOKHARA is presented, and future developments are highlighted.

Measurements of branching fractions inB→φKandB→φπand search for directCPviolation inB±→φK±

We present measurements of branching fractions in the b→ss¯s penguin-dominated decays B+→φK+ and B0→φK0 in a sample of approximately 89 million BB¯ pairs collected by the BABAR detector at the PEP-II asymmetric-energy B-meson factory at SLAC. We determine B(B+→φK+)=(10.0−0.8+0.9±0.5)×10−6 and B(B0→φK0)=(8.4−1.3+1.5±0.5)×10−6. Additionally, we measure the CP-violating charge asymmetry ACP(B±→φK±)=0.04±0.09±0.01, with a 90% confidence-level interval of [-0.10, 0.18], and set an upper limit on the CKM- and color-suppressed decay B+→φπ+, B(B+→φπ+)<0.41×10−6 (at the 90% confidence level).Received 5 September 2003DOI:https://doi.org/10.1103/PhysRevD.69.011102©2004 American Physical Society

CP violation in B-meson decays

37 years after the discovery of CP violation in $\pi^ + \pi^-$ decays of neutral K-mesons, the experiments BABAR and BELLE have found a second system which violates CP symmetry. $\rm J/\psi K^0_S$ decays of neutral B-mesons show very large symmetry breaking. The effect has now, with the most recent data, a significance of ten standard deviations. The presentation describes the B-meson factories, the experiments, and their analyses. The results are in agreement with the Standard Model explanation of CP violation, i.e. with different couplings of the Higgs boson to quarks and antiquarks.

New re1ults on CP violation in B-meson decays

37 years after the discovery of CP violation in π + π − decays of neutral K mesons, the experiments BABAR and BELLE have found a second system which violates CP symmetry. J K S O decays of neutral B mesons show very large symmetry breaking. The effect has now, with the most recent data, a significance of about 13 standard deviations. The presentation describes the B-meson factories, the experiments, and their analyses. The results are in agreement with the Standard Model explanation of CP violation, i. e. with different couplings of the Higgs boson to quarks and antiquarks.

Possible effects of noncommutative geometry on weakCPviolation and unitarity triangles

The possible effects of noncommutative geometry on weak $\mathrm{CP}$ violation and unitarity triangles are discussed by taking into account a simple version of the momentum-dependent quark mixing matrix in the noncommutative standard model. In particular, we calculate nine rephasing invariants of $\mathrm{CP}$ violation and illustrate the noncommutative $\mathrm{CP}$-violating effect in a couple of charged D-meson decays. We also show how inner angles of the deformed unitarity triangles are related to $\mathrm{CP}$-violating asymmetries in some typical ${B}_{d}$ and ${B}_{s}$ transitions into $\mathrm{CP}$ eigenstates. B-meson factories are expected to help probe or constrain noncommutative geometry at low energies in the near future.

Radiative return at NLO and the measurement of the hadronic cross-section in electron–positron annihilation

Electron-positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for e^+ e^- annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process e^+ e^- \to \gamma +\gamma^* and the emission of two real hard photons: e^+ e^- \to \gamma + \gamma + \gamma^*. A Monte Carlo generator has been constructed, which incorporates these corrections and simulates the production of two charged pions or muons plus one or two photons. Predictions are presented for centre-of-mass energies between 1 and 10 GeV, corresponding to the energies of DAPHNE, CLEO-C and B-meson factories.

NLO QED corrections to ISR in $e^+ e^-$ annihilation and the measurement of $\sigma(e^+ e^- \rightarrow{\mathrm{hadrons}})$ using tagged photons

The leptonic tensor for the process $e^+ e^- \to \gamma+\gamma^*$, which describes the next-to-leading order virtual and soft QED corrections to initial state radiation in $e^+ e^-$ annihilation with emission of an extra virtual photon decaying into hadrons, is calculated. A Monte Carlo generator for the reaction $e^+ e^- \to \gamma + \pi^+ \pi^-$ has been set up which includes these corrections. It thus describes configurations where the invariant mass of the hadrons plus photon is very close to $\sqrt{s}$. Predictions for cms energies of 1 to 10 GeV, corresponding to the energies of DAPHNE and B-meson factories, are presented. The possibility for an accurate measurement using tagged photons of $\sigma(e^+ e^- \to hadrons)$, which plays an important role in the theoretical description of the muon anomalous magnetic moment and the running of the electromagnetic coupling, is discussed.

Bounds on sin2 β and | Vub/ Vcb| from the light-quark triangle

With the help of the light-quark triangle, which is essentially congruent to the rescaled unitarity triangle for a variety of textures of the quark mass matrices, we calculate the CP-violating quantity sin2 β and the ratio of | V ub | to | V cb |. We find that sin2 β is most likely to lie in the range 0.45⩽sin2 β⩽0.60, a result compatible very well with the present BaBar and Belle measurements. On the other hand, | V ub / V cb |⩾0.8 is disfavored. Our bounds on both sin2 β and | V ub / V cb | can soon be confronted with more precise data to be accumulated from the asymmetric B-meson factories.