Asymmetric Collider Research Articles

Observation of radiative B-->phi K gamma decays.

The radiative decay B-->phi K gamma is observed for the first time. The branching fraction for the charged B--->phi K- gamma decay mode is measured to be B(B--->phi K- gamma)=(3.4+/-0.9+/-0.4)x10(-6). The photon energy distribution for the B--->phi K- gamma decay is presented. The signal for the neutral B(0)-->phi K(0)gamma decay mode is not statistically significant and an upper limit, B(B(0)-->phi K(0)gamma)<8.3x10(-6) at 90% C.L., is set. The analysis is based on a data set of 90 fb(-1) collected by the Belle experiment at the e(+)e(-) asymmetric collider KEKB.

B decays to baryonic final states and [formula omitted] at Belle

We report on the results for the baryonic B decays using data collected with the Belle experiment at e + e − asymmetric collider KEKB. We studied the exclusive B decays to 2-, 3- and 4-body final states with charmed baryons and observed for the first time B 0 → Σ c (2455) ++ pπ − decay. First observations and measured branching fractions are presented for the decay modes B → D (∗)0 p p, B + → p pK + and B 0 → p Λπ − . The upper limits for two-body charmless baryonic B decays to p p,Λ Λ and p Λ are improved. We also provide the measurement of Ω c 0 mass and semileptonic Ω c 0 decay at Belle.

Measurement of the cross-sections

In this paper we report the first measurement of $e^+e^- \to D^{(*)+}D^{(*)-}$ processes. The cross-sections for $e^+^e- \to D^{*+}D^{*-}$ and $e^+e^- \to D^+D^{*-}$ at $\sqrt{s}=10.58\mathrm{GeV}/c^2$ have been measured to be $0.65 \pm 0.04 \pm 0.07 \mathrm{pb}$ and $0.71 \pm 0.05 \pm 0.09 \mathrm{pb}$, respectively. We set an upper limit on the cross-section of e+e- --> D+ D- of $0.04 \mathrm{pb}$ at the 90% confidence level. In addition we have measured the fraction of the $D^{*\pm}_T D^{*\mp}_L$ final state in the e+e- --> D*+ D*- reaction to be $(97\pm 5)%$. The analysis is performed using $88.9 \mathrm{fb}^{-1}$ of data collected by the Belle detector at the $e^{+}e^{-}$ asymmetric collider KEKB.

Observation of [formula omitted] decays

The B→D (∗)K −K (∗)0 decays have been observed for the first time. The branching fractions of the B→D (∗)K −K (∗)0 decay modes are measured. Significant signals are found for the B→D (∗)K −K ∗0 and B −→ D 0 K − K 0 S decay modes. The invariant mass and polarization distributions for the K −K ∗0 and K − K 0 S subsystems have been studied. For the K −K ∗0 sybsystem these distributions agree well with those expected for two-body B→D (∗)a 1 −(1260) decays, with a 1 −(1260)→K −K ∗0 . The analysis was done using 29.4 fb −1 of data collected with the Belle detector at the e + e − asymmetric collider KEKB.

Rare B meson decays to charmed final states at Belle $(B\to D^{(*)} K^-, B^0\to D^+_s \pi^-)$

We report observations of the Cabibbo-suppressed decays B→ D(*)K and an upper limit for the decay branching fraction for [Formula: see text] using a 5.3fb-1 data sample accumulated at the ϒ(4S) resonance with the Belle detector at the KEKB e+e- asymmetric collider.

Tau physics prospects at Belle and BaBar

The new asymmetric colliders at KEK-B and SLAC PEP-II have come on line at the ϒ(4 s) and are producing luminosity at record levels. Together the experiments, Belle and BaBar, have about 25 × 10 6 tau pairs produced. Belle presented two preliminary tau-physics results at this conference. Prospects for the coming few years are for as many as hundreds of millions of tau pair events. These data sets will bring tau physics into a new regime.

The commissioning of PEP-II and its possible conversion into an asymmetric collider for measuring nucleon form factors

After reviewing the results of the commissioning of the SLAC PEP-II BFactory in the '98-'99 winter run, a parameter study is presented for a possible modification of the PEP-II facility into an asymmetric collider suitable for experiments to study the Nucleon form factors. A preliminary set of parameters is proposed for an Asymmetric Collider providing a centre-of-mass energy around 2 GeV. Operational options on the attainable performance in terms of luminosity in different modes of operation and suggestions on the way to deal with beam energies considerably lower than the PEP-II design are discussed.

Energy transparency and symmetries in the beam-beam interaction

We have modified the beam-beam simulation code CBI to handle asymmetric beams and used it to look at energy transparency and symmetries in the beam-beam interaction. We find that even a small violation of energy transparency, or of the symmetry between the two beams, changes the character of the collective (coherent) motion; in particular, period-$n$ oscillations are no longer seen. We speculate that the one-time observation of these oscillations at LEP, and the more ubiquitous observation of the flip-flop instability in colliders around the world, may be a consequence of breaking the symmetry between the electron and positron beams. We also apply this code to the asymmetric collider PEP-II, and find that for the nominal parameters of PEP-II, in particular, the nominal tune-shift parameter of ${\ensuremath{\xi}}_{0}=0.03$, there are no collective beam-beam issues. Collective quadrupole motion sets in only at ${\ensuremath{\xi}}_{0}=0.06$ and above, consistent with earlier observations for symmetric beams.

Parallel-Processing Diagnostic Program for a Transputer-Based Readout System

A parallel-processing program for system-diagnostic purposes was developed for a transputer-based readout system of a silicon vertex detector (SVD). The data-acquisition (DAQ) system for SVD was constructed as a part of research and development work for the BELLE [name of a detector for an asymmetric collider experiment at High Energy Accelerator Research Organization (KEK)] experiment consisting of data scanners (DS), slave memory modules (SMM) and direct memory access master modules (DMM). The DS, SMM and DMM have a transputer as a core processor. Each transputer was linked by a point-to-point connection with transputer serial interfaces (Inmos-link). The DAQ system was equipped with a transputer network system with the Inmos-links. The diagnostic program has the capability to detect malfunctioning readout components. To minimize the processing time during an experiment, the program runs in parallel on each transputer. For this purpose, the program was written using the programming language, occam. With the benefits of its distributed system architecture and without the need for any operating system, the program is compact with high modularity. In this paper, we report the system architecture of this diagnostic program.

ProbingCPviolation with time integrated decay rates into non-CPeigenstates

Many of the experiments proposed to look for interference $\mathrm{CP}$ violation in neutral $B$ mesons concentrate on tagged decay into $\mathrm{CP}$ eigenstates. Aleksan, Dunietz, Kayser and Le Diberder have shown that one can also look for interference $\mathrm{CP}$ violation using tagged decays into non-$\mathrm{CP}$ eigenstates. In all these methods, one must trace the time dependence of the decays. In this article we discuss a new method to search for interference $\mathrm{CP}$ violation by using only time integrated rates into non-$\mathrm{CP}$ eigenstates. The method hinges on the comparison between the decays of $\ensuremath{\Upsilon}(4S)$ into $\mathrm{ff}$, $\overline{f}\overline{f}$, and $f\overline{f}$, and also uses the rates for ${l}^{+}f$ and ${l}^{\ensuremath{-}}f$. This method does not depend on how the $\ensuremath{\Upsilon}(4S)$ is produced; provided enough statistics, one can use both symmetric and asymmetric colliders.

The B aB ar experiment and its silicon vertex tracker

The B aB ar experiment at the SLAC B-Factory is designed mainly for the study of CP violation in the B-meson system. Its silicon vertex tracker (SVT), now under construction, has an original design, sensibly different from the usual silicon strips vertex detectors, and developed to satisfy the requirements of the asymmetric collider events topologies, the background rejection and the physics measurements. The SVT characteristics and the role that its measurements play in the physics analysis are presented here.

The TRISTAN II Project

Abstract KEK plans to convert TRISTAN to an asymmetric collider B factory (TRISTAN II). An expected peak lumonisity in the initial stage is 2 × 1033cm−2sec−1. With this facility, it will become possible to carry out a definitive test of CP violation in the standard model. Our Monte Carlo studies using a modest detector design show that, while it is rather easy to measure sin2o1, measurements of sin2o2 and o3 require a best possible detector and extended theoretical studies.

The TRISTAN II project

KEK plans to convert TRISTAN to an asymmetric collider B factory (TRISTAN II). An expected peak lumonisity in the initial stage is 2 × 10 33 cm −2 sec −1. With this facility, it will become possible to carry out a definitive test of CP violation in the standard model. Our Monte Carlo studies using a modest detector design show that, while it is rather easy to measure sin2 ø 1, measurements of sin2 ø 2 and ø 3 require a best possible detector and extended theoretical studies.

A high-luminosity factory linear collider using positron recirculation and recovery

Abstract We describe an asymmetric linear collider B B factory scheme that offers a possible solution to most of the problems encountered in the design of B B factories to operate at the ϒ(4S) energy. A key feature of this collider is the recirculation and recovery of the positrons and the asymmetric energy of the collider to better achieve the search for CP violation in the B system.