B-meson Factories Research Articles

Measuring σ( e+e− → hadrons) with Tagged Photons at Electron Positron Colliders

A Monte Carlo generator has been constructed to simulate the reaction e + e − → γ + 2π and γ + 4π where the photon is assumed to be observed in the detector. Predictions are presented for cms energies of 1GeV, 3GeV and 10GeV, corresponding to the energies of DAΦNE, BEBC and of B-meson factories. The event rates are sufficiently high to allow for a precise measurement of R( Q 2) in the region of Q between approximately 1GeV and 2.5GeV. Estimates for the kinematic breaking of isospin relations between different channels as a consequence of the π ± - π 0 mass difference are given.

Four pion final states with tagged photons at electron positron colliders

A Monte Carlo generator has been constructed to simulate the reaction e^+e^- \to \gamma + 4 \pi, where the photon is assumed to be observed in the detector. Only initial state radiation is considered. Additional collinear photon radiation has been incorporated with the technique of structure functions. Predictions are presented for cms energies of 1GeV, 3GeV and 10GeV, corresponding to the energies of DAPHNE, BEBC and of B-meson factories. The event rates are sufficiently high to allow for a precise measurement of R(Q^2) in the region of Q between approximately 1GeV and 2.5GeV. For the construction of the program we employ isospin relations between the amplitudes governing tau decays into four pions and electron positron annihilation into four pions. Estimates of the kinematic breaking of these isospin relations as a consequence of the \pi^- -- \pi^0 mass difference are given.

New time distributions of D0- [formula omitted] or B0- [formula omitted] mixing and CP violation

The formulae for D 0- D ̄ 0 or B 0- B ̄ 0 mixing and CP violation at the τ-charm or B-meson factories are derived, for the case that only the decay-time distribution of one D or B meson is to be measured. In particular, we point out a new possibility to determine the D 0- D ̄ 0 mixing rate in semileptonic D decays at the Ψ(4.14) resonance; and show that both direct and indirect CP asymmetries can be measured at the ϒ(4 S) resonance without ordering the decay times of two B d mesons or measuring their difference.

The light quark sector, CP violation, and the unitarity triangle

In view of the observed strong hierarchy of quark masses, we propose a new description of flavor mixing which is particularly suited for models of quark mass matrices based on flavor symmetries. The necessary and sufficient conditions for CP violation are clarified. The emergence of CP violation is primarily linked to a large phase difference (near 90°) in the light quark sector. The unitarity triangle is determined by the mass ratios of the light quarks. We conclude that the unitarity triangle should be close or identical to a rectangular triangle, and CP violation is maximal in this sense. Instructive predictions for flavor mixing angles and CP-violating parameters, which can directly be confronted with the forthcoming data from B-meson factories, are obtained from a specific texture of quark mass matrices.

Towards determiningφ1withB→D(*)D¯(*)

We present an isospin analysis of the decay modes B\to D\bar{D}, D^*\bar{D}, D\bar{D}^* and D^*\bar{D}^*, which allows determination of the final-state interaction phases. As these transitions have branching ratios of the order 10^{-4} or larger, they could be useful in detecting the CP- violating phase \phi_1 \equiv \arg (-V^*_{cb} V_{cd} V_{tb} V^*_{td} ) in the first-round experiments of a B-meson factory. The problem of penguin pollution may still be present. Once the Kobayashi-Maskawa matrix elements are known, it is possible to obtain the magnitudes and relative phases of hadronic matrix elements for B\to D^{(*)}\bar{D}^{(*)}. This will in turn lead to some information about the penguin pollution.

D0-D¯0mixing andCPviolation in neutralD-meson decays

D^0-\bar{D}^0 mixing at the detectable level or significant CP violation in the charm system may strongly signify the existence of new physics. In view of the large discovery potential associated with the fixed target experiments, the B-meson factories and the \tau-charm factories, we make a further study of the phenomenology of D^0-\bar{D}^0 mixing and CP violation in neutral $D$-meson decays. The generic formulas for the time-dependent and time-integrated decay rates of both coherent and incoherent D^0\bar{D}^0 events are derived, and their approximate expressions up to the second order of the mixing parameters x_D and y_D are presented. Explicitly we discuss D^0-\bar{D}^0 mixing and various CP-violating signals in neutral D decays to the semileptonic final states, the hadronic CP eigenstates, the hadronic non-CP eigenstates and the CP-forbidden states. A few non-trivial approaches to the separate determination of x_D and y_D and to the demonstration of direct and indirect CP asymmetries in the charm sector are suggested.

Measurables ofCP violation in Bd→D CP 0 KS at a B-meson factory

In the context of the standard electroweak model, we emphasize that Bd→DCP0KS (DCP0 denotes aCP eigenstate of D0 or\(\overline D \)0) can compete with Bd→→π+π− in studyingCP violation and probing the Cabibbo-Kobayashi-Maskawa unitarity triangle. We discuss the measurables of direct and indirectCP asymmetries in Bd0vs.\(\overline B \)d0→DCP0KS in the circumstance of an asymmetric B-meson factory running on the γ(4S) resonance, and show that both the weak and strong phases are experimentally determinable even in the presence of unknown final-state interactions.

Soft pion emission in semileptonic B-meson decays.

An analysis of semileptonic decays of B mesons with the emission of a single soft pion is presented in the framework of the heavy-quark limit, using an effective Lagrangian which implements chiral and heavy-quark symmetries. The analysis is performed at leading order of the chrial and inverse heavy mass expansions. In addition to the ground-state heavy mesons, some of their resonances are included. The estimates of the various effective coupling constants and form factors needed in the analysis are obtained using a chiral quark model. An analysis of the decay spectrum in the squared invariant mass of the \ensuremath{\pi}${\mathit{D}}^{(\mathrm{*})}$ is carried out, showing the main effects of including the resonances. As the main result, a clear indication is found that the ${0}^{+}$ and ${1}^{+}$ resonances substantially affect the rate of the decay mode with a ${\mathit{D}}^{\mathrm{*}}$ in the final state, while a less dramatic effect is also noticed in the D mode. A peak related to the ${0}^{\mathrm{\ensuremath{-}}}$ and ${1}^{\mathrm{\ensuremath{-}}}$ radially excited D mesons is clear. The obtained rates show promising prospects for studies of soft pion emission in semileptonic B-meson decays in a B-meson factory where, modulo experimental cuts, about ${10}^{5}$ such decays in the D meson mode and ${10}^{4}$ in the ${\mathit{D}}^{\mathrm{*}}$ mode could be observed per year.

Stanford and Cornell in the frame for B-meson factory

Stanford and Cornell in the frame for B-meson factory

CP violation experiments at a B-meson factory

If the observed CP asymmetry in K 0 K 0 oscillations has its origin in the Standard charged weak interaction, large CP violating effects are expected to occur in B-meson decays. A clear and promising example is the CP asymmetry in the decays B 0 → J/ Ψ K S 0. and B 0 → J/Ψ K S 0 . The study of these decay is therefore used for optimizing experiments at a “B-Meson Factory”, a future e +e − storage ring producing boosted ϒ(4S) mesons with high rate. The luminosity requirements are discussed, and some results on feasibility studies for the storage ring and for a universal detector are presented.

Studies of helium gas mixtures for low mass tracking detectors

Helium gas mixtures can improve traciing resolution for particles below 1 GeV/ c because of the reduction in multiple scattering. We have measured the drift velocity and spatial resolution of several interesting mixtures including helium:DME and helium:CO 2:isobutane. We discuss the advantages and disadvantages of using such a gas mixture for a detector at a B-meson factory, and conclude that helium:DME (80:20) and (70:30) mixtures will give significantly improved momentum resolution. The low drift velocity in such mixtures is a disadvantage in a high rate environment, but this is partly compensated by a low sensitivity to synchrotron radiation background.

Single c- and b-quark production in charm and B-meson e +e − factories

We examine single c- and b-quark production in e +e − collisions with the standard model in charm and B-meson factories working on the ψ and the √ region respectively. Expected inclusive cross sections are estimated at resonant production closely below the threshold for associated open charm and bottom production, and in the nearby continuum.

Vetex detectors at e+ e− B meson factories

The possible applications of high-resolution vertex detectors at B-meson factories based on e+ e− collisions are discussed with special emphasis on the different possible kinematics regions (γ[4S] resonance, boosted γ[4S] resonance and e+ e− continuum at\( \sqrt s \)∼(12÷20) GeV). The observability of B0-\(\overline B ^0 \) mixing as a function of the B-meson decay length is used to define the minimal requirements on the precision of a vertex detector system. Implications on the design of the detector as well as of the collider are investigated and the technological feasibility of the required spatial resolution is discussed.