B-factory Experiments Research Articles

On measurement of photon polarization in radiative penguin B decays to baryons

A measurement of the photon polarization in radiative penguin B decays provides a test of the Standard Model and a probe for New Physics, that can lead to a deviation from the Standard Model prediction of left-handed photons in brightarrow s gamma . We propose a new method to measure the photon polarization using the baryonic decay B^- rightarrow Lambda bar{p} gamma . The P-violating Lambda -hyperon decay allows a measurement of the Lambda helicity to be performed, which can be uniquely related to the photon polarization in a model-independent way. The B^- rightarrow Lambda bar{p} gamma decay was recently measured to have a large branching fraction providing a possibility to get meaningful results with the data already available at LHC and B-factory experiments. An increase of the B-meson sample at high luminosity LHC experiments and Belle II should provide a really stringent test by using this method already in the near future.

Optimization of Geant4 for the Belle II software library

During the next decade, the SuperKEKB/Belle II experiment expects to collect almost two orders of magnitude more collision data than the previous generation B-Factory experiments. Study of this data requires monumental computing resources to process and to generate the required simulation events necessary for physics analysis. At the core of the Belle II simulation library is the Geant4 toolkit. To use the available computing resources more efficiently, the physics list for Geant4 has been optimized for the Belle II environment, and various other strategies were applied to improve the performance of the Geant4 toolkit in the Belle II software library. Following the inclusion of this newly optimized physics list in an updated version of Geant4 toolkit, we obtain much better CPU usage during event simulation and reduce the computing resource usage by ~ 44%.

Extraction of $|V_{cb}|$ from two-body hadronic B decays

We propose a method of extracting the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ from two-body hadronic decay processes of $B\to DK$ with precisely determined form factors of $B$ meson semi-leptonic decays. The amplitude $\mathcal{M}(\bar{B}^0 \to D^+ K^-)$ which does not include the effect of hadronic final state interactions can be theoretically evaluated by using factorization and form factors of semi-leptonic B decays. We can obtain all the amplitudes in an isospin relation $\mathcal{A}(B^-\to D^0K^-) =\mathcal{A}(\bar{B}^0\to D^+K^{-})+\mathcal{A}(\bar{B}^0\to D^{0}\bar{K}^0)$ including the effect of hadronic final state interactions as well as $|V_{cb}|$ using the experimental data of branching fractions of these three processes with a truncation of the states which contribute to the hadronic final state interactions. The extracted value of $|V_{cb}|$ is $(37\pm 6)\times 10^{-3}$. The decay processes of $B\to DK^{*}$ and $B\to D^{*}K$ can also be used in the same way and the extracted values of $|V_{cb}|$ are $(41\pm 7)\times 10^{-3}$ and $(42\pm 9)\times 10^{-3}$, respectively. This method becomes possible by virtue of recent precise determinations of the form factors of semi-leptonic B decays. The uncertainties of $|V_{cb}|$ by this method are expected to be reduced by the results of future B-factory experiments and lattice calculations.

Resolution of RD/[formula omitted] puzzle

One of the exciting results in flavor physics in recent times is the RD/RD⁎ puzzle. The measurements of these flavor ratios performed by the B-factory experiments, BaBar and Belle, and the LHCb experiment are about 4σ away from the Standard Model expectation. These measurements indicate that the mechanism of b→cτν¯ decay is not identical to that of b→c(μ/e)ν¯. This charge lepton universality violation is particularly intriguing because these decays occur at tree level in the Standard Model. In particular, we expect a moderately large new physics contribution to b→cτν¯. The different types of new physics amplitudes, which can explain the RD/RD⁎ puzzle, have been identified previously. In this letter, we show that the polarization fractions of τ and D⁎ and the angular asymmetries AFB and ALT in B→D⁎τν¯ decay have the capability to uniquely identify the Lorentz structure of the new physics. A measurement of these four observables will lead to such an identification.

NNLO QCD corrections to \u03b3 + \u03b7c(\u03b7b) exclusive production in electron-positron collision

Based on the NRQCD factorization formalism, we calculate the next-to-next-to-leading order QCD corrections to the heavy quarkonium ηc(ηb) production associated with a photon at electron-positron colliders. By matching the amplitudes calculated in full QCD theory to a series of operators in NRQCD, the short-distance coefficients up to NNLO QCD radiative corrections are determined. It turns out that the full set of master integrals that we obtained could be analytically expressed in terms of Goncharov Polylogarithms, integrals over polylogarithms and complete elliptic integrals, which mostly do not exist in the literature and could be employed in the analyses of other physical processes. In phenomenology, numerical calculations of NNLO K-factors and cross sections of e+e− → γ + ηc(ηb) processes in BESIII and B-factory experiments are performed, which may stand as a test of the NRQCD higher order calculation while confronting to the data.

Computing at Belle II

The existence of large matter-antimatter asymmetry (CP violation) in the b-quark system as predicted in the Kobayashi-Maskawa theory was established by the B-Factory experiments, Belle and BaBar. However, this cannot explain the magnitude of the matter-antimatter asymmetry of the universe we live in today. This indicates undiscovered new physics exists. The Belle II experiment, the next generation of the B-Factory, is expected to reveal the new physics by accumulating 50 times more data (∼50ab−1) than Belle by 2023. The Belle II computing system has to handle an amount of beam data eventually corresponding to several tens of PetaByte per year under an operation of the SuperKEKB accelerator with a designed instantaneous luminosity. Under this situation, it cannot be expected that one site, KEK, will be able to provide all computing resources for the whole Belle II collaboration including the resources not only for the raw data processing but also for the MC production and physics analysis done by users. In order to solve this problem, Belle II employed the distributed computing system based on DIRAC, which provides us the interoperability of heterogeneous computing systems such as grids with different middleware, clouds and the local computing clusters. Since the last year, we performed the MC mass production campaigns to confirm the feasibility and find out the possible bottleneck of our computing system. In parallel, we also started the data transfer challenge through the transpacific and transatlantic networks. This presentation describes the highlights of the Belle II computing and the current status. We will also present the experience of the latest MC production campaign in 2014.

Taiwan’s science miracle

In the past two decades, a flourishing economy and maturing infrastructure have Taiwanese physicists both staying home more and engaging internationally.

Hadron and quarkonium exotica

A number of charmonium-(bottomonium-)like states have been observed in B-factory experiments. Recently the BESIII experiment has joined this search with a unique data sample collected at the different center of mass energies ranging from 3.9 GeV to 4.42 GeV in which they found new charmonium-like states with non-zero electric charge. We review the status of experimental searchs for quarkonium-like states and also other types of non-[Formula: see text] meson or non-qqq baryons that are predicted by QCD-motivated models. We mainly focus on results from the B-factories and BESIII.

Results on CP violation and CKM UT angles from Belle and BaBar

We report recent results on CP violation measurements from the two B-factory experiments, Belle and BaBar.

R&D of particle identification devices with high-precision timing

We have studied micro-channel-plate photo-multiplier tubes (MCP-PMT), which realize timing measurements of the single photons with high precision of about 30ps. We investigated the timing properties of 4 different types with a magnetic field, and measured the lifetime of the gain, quantum efficiency and transit time spread.As an application, we studied the timing resolution of TOF counters by means of Cherenkov-light detection with a MCP-PMT, and attained a 6.2ps resolution using 3GeV/c pion-beams with readout electronics of 4.1ps resolution. As another application, we have developed a novel particle identification device, named TOP counter, which is a Cherenkov ring imaging counter with precise timing determination, especially for upgrading B-factory experiments. We performed beam tests with the prototype, and obtained the expected results.

A Future High Statistics Charm Mixing Experiment Using the Fermilab Tevatron

We present an idea for a future D0-D0bar mixing and CP violation experiment to run at the Fermilab Tevatron. We estimate that in three years of running, such an experiment could reconstruct an order of magnitude more flavor-tagged D0->K+pi- decays than will be reconstructed by the B-factory experiments with their full data sets. The resulting sensitivity to CP-violating parameters |q/p| and Arg(q/p) is calculated from a global fit to CP-violating observables, and it is found to be much greater than current world sensitivity.

Review of Standard Tau decays from the B-factory Experiments

B-factories have been successfully operating for more than 8 years, providing an unprecedented data sample of e{sup +}e{sup 0} {yields} hadrons events. The BABAR and Belle experiments have in fact already collected over 550 fb{sup -1} and 800 fb{sup -1} respectively at the {Upsilon}(4s) center-of-mass (CM) energy. At this energy, the cross-section for tau production is of the same order of the cross-section for b production: {sigma}(b{bar b}) {approx} 1.1 nb {approx} {sigma}({tau}{sup +}{tau}{sup -}) {approx} 0.9 nb. For this reason, B-factories can now be considered also Tau-factories. A review of the most recent results on standard tau decays from the BABAR and Belle experiments is presented in this article.

ATLAS analysis model

As we near the collection of the first data from the Large Hadron Collider, the ATLAS collaboration is preparing the software and computing infrastructure to allow quick analysis of the first data and support of the long-term steady-state ATLAS physics program. As part of this effort considerable attention has been paid to the ‘Analysis Model’, a vision of the interplay of the software design, computing constraints, and various physics requirements. An important input to this activity has been the experience of Tevatron and B-Factory experiments, one topic which was explored and discussed in the ATLAS October 2006 Analysis Model workshop. Recently, much of the Analysis Model has focused on ensuring the ATLAS software framework supports the required manipulations of event data; the event data design and content is consistent with foreseen calibration and physics analysis tasks; the event data is optimized in size, access speed, and is accessible both inside and outside the software framework; and that the analysis software may be developed collaboratively.

Radiative and Electroweak Penguin Decays of B Mesons

Radiative and electroweak penguin decays of B mesons are flavor-changing-neutral-current processes that provide powerful ways to test the Standard Model at the one-loop level, to search for the effects of new physics, and to extract Standard Model parameters such as CKM matrix elements and quark masses. The large data samples obtained by the B-factory experiments BaBar and Belle, together with an intensive theoretical effort, have led to significant progress towards understanding these rare decays. Recent experimental results include the measurements of the b → d γ decays B → ρ ( ω ) γ , the observation of B → K ( ∗ ) l + l − decays (together with studies of the associated kinematic distributions), and improved measurements of the inclusive B → X s γ rate and photon energy spectrum.

Joint extraction of [formula omitted] and [formula omitted] from hadronic τ decays

We study the simultaneous determination of ms and Vus from flavor-breaking hadronic τ decay sum rules using weights designed to bring under better control problems associated with the slow convergence of the relevant D=2 OPE series. Much improved stability and consistency is found as compared to the results of conventional analyses based on the “(k,0) spectral weights”. Results for ms are in excellent agreement with those of recent strange scalar and strange pseudoscalar sum rule analyses, as well as recent lattice analyses, while those for Vus agree within errors with the output from recent lattice-based Γ[Kμ2]/Γ[πμ2] and Kℓ3-based analyses. Very significant error reductions are shown to be expected, especially for Vus, once the improved strange spectral data from the B-factory experiments becomes available.

CP-violations in B decays

Recent results on CP-violation measurements in B decays from energy-asymmetric B-factory experiments are reported. Thanks to large accumulated data samples, CP-violations in B decays in mixing-decay interference and direct CP-violation are now firmly established. The measurements of three angles of the unitarity triangle from CP-violations of B decays are quite consistent with the Standard Model expectations. These results strongly support the validity of the Kobayashi-Maskawa prescription of CP-violation.

Probing MeV Dark Matter at Low-Energye+e−Colliders

It has been suggested that the pair annihilation of dark matter particles chi with mass between 0.5 and 20 MeV into e+e- pairs could be responsible for the excess flux (detected by the INTEGRAL satellite) of 511 keV photons coming from the central region of our Galaxy. The simplest way to achieve the required cross section while respecting existing constraints is to introduce a new vector boson U with mass M(U) below a few hundred MeV. We point out that over most of the allowed parameter space, the process e+e--->U(gamma), followed by the decay of U into either an e+e- pair or an invisible (nu(-)nu or chi(-)chi) channel, should lead to signals detectable by current B-factory experiments. A smaller, but still substantial, region of parameter space can also be probed at the Phi factory DAPhiNE.

Anticharmed Pentaquark fromBDecays

We explore the possibility of observing the anticharmed pentaquark state from the theta(c)npi(+) decay of B mesons produced in B-factory experiments. We first show that the observed branching ratio of the B(+) to lambda(-)(c)p pi(+), as well as its open histograms, can be remarkably well explained by assuming that the decay proceeds first through the pi(+) D(0) (or D(*0)) decay, and then through the subsequent decay of the virtual D(0) or D(*0) mesons to lambda(-)(c)p. We then note that the theta(c)can be similarly produced when the virtual D(0) or D(*0) decay into an antinucleon and a theta(c). Combining the present theoretical estimates for the ratio g(DNlambda(c))/g(DNtheta(c)) approximately 13 and g(D*Ntheta(c)) approximately 1/3g(DNtheta(c)), we find that the anticharmed pentaquark theta(c), which was predicted to be bound by several model calculations, can be produced via B(+)--> theta(c)npi(+), and be observed from the B-factory experiments through the weak decay of theta(c)--> pK(+) pi(-) pi(-).

Resistive plate chambers in running and future experiments

his document surveys the RPC-based detection systems of running and future collider experiments focusing on the implications of the choice of some basic detector features: number of gaps, electrode material and operating mode. The muon identification systems of the B-factory experiments BaBar and Belle is described and the RPC performance since the first operation of the detectors is briefly reported. The trigger systems of the future LHC experiments ALICE, ATLAS and CMS are discussed and some results obtained in the research and development programs carried out by the Collaborations are reported

HIGH PRECISION LATTICE QCD MEETS EXPERIMENT

We review recent results in lattice QCD from numerical simulations that allow for a much more realistic QCD vacuum than has been possible before. Comparison with experiment for a variety of hadronic quantities gives agreement to within statistical and systematic errors of 3%. We discuss the implications of this for future calculations in lattice QCD, particularly those which will provide input for B-factory experiments.