E. Kikutani

Overview of the KEKB accelerators

An overview of the KEKB accelerators is given as an introduction of the following articles in this issue, first by summarizing the basic features of the machines, and then describing the improvements of the performance since the start of the physics experiment.

Observation of Large CP Violation and Evidence for Direct CP Violation in B0→π+π- 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.

Vidence for CP-violating asymmetries in B0→π +π- decays and constraints on the CKM angle φ2

We present an improved measurement of CP-violating asymmetries in B-0-->pi(+)pi(-) 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 B-0-->pi(+)pi(-) 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(pipi) = +0.77 +/-0.27(stat) +/-0.08(syst) and S-pipi = -1.23+/-0.41(stat) (+0.08)(-0.07)(syst), where the statistical uncertainties are determined from the Monte Carlo pseudoexperiments. We obtain confidence intervals for CP-violating asymmetry parameters A(pipi) and S-pipi based on a frequentist approach. We rule out the CP-conserving case, A(pipi) = S-pipi = 0, at the 99.93% confidence level. We discuss how these results constrain the value of the Cabibbo-Kobayashi-Maskawa (CKM) angle phi(2).

KEKB beam instrumentation systems

For the stable high-luminosity operation and luminosity increase, the electron and positron storage rings of the KEK B-Factory (KEKB) is equipped with various beam instrumentations, which have been working well since the start of the commissioning in December, 1998. Details and performance of the beam-position monitor system based on the spectrum analysis using DSPs, the turn-by-turn BPM with four-dimensional function available for measurements of the individual bunch position, phase and intensity, the parametric beam-DCCTs designed so as to avoid the magnetic-core-selection problems for the parametric flux modulation, the bunch-by-bunch feedback system indispensable to suppress the strong multibunch instabilities in KEKB, the various optical beam diagnostic systems, such as synchrotron radiation interferometers for precise beam-size measurement, the tune meters, the bunch length monitors and the beam-loss monitors are described. Delicate machine tuning of KEKB is strongly supported by these instrumentations.

Observation of B0→π0π0

We report the observation of the decay B0-->pi(0)pi(0), using a 253 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB e(+)e(-) collider. The measured branching fraction is B(B0-->pi(0)pi(0))=(2.3(+0.4+0.2)(-0.5-0.3))x10(-6), with a significance of 5.8 standard deviations including systematic uncertainties. We also make a measurement of the direct CP violating asymmetry in this mode.We report the observation of the decay B{sup 0}{yields}{pi}{sup 0}{pi}{sup 0}, using a 253 fb{sup -1} data sample collected at the {upsilon}(4S) resonance with the Belle detector at the KEKB e{sup +}e{sup -} collider. The measured branching fraction is B(B{sup 0}{yields}{pi}{sup 0}{pi}{sup 0})=(2.3{sub -0.5-0.3}{sup +0.4+0.2})x10{sup -6}, with a significance of 5.8 standard deviations including systematic uncertainties. We also make a measurement of the direct CP violating asymmetry in this mode.

The TRISTAN control system

The 8 GeV accumulation ring and the 30 GeV main ring of TRISTAN, an accelerator-storage ring complex at KEK, are controlled by a highly computerized control system. Twenty-four minicomputers are linked by optical fiber cables to form an N-to-N token ring network. The transmission speed on the cables is 10 Mbps. From each minicomputer, a CAMAC serial highway extends to the controlled equipment. At present, twenty minicomputers are connected to the network and are used to control the accumulation ring. The software system is based on the NODAL language devised at the CERN SPS. The KEK NODAL system retains main features of the original NODAL: the interpretive scheme, the multi-computer programming facility, and the data-module concept. In addition, it has the following features: (1) fast execution due to the compiler-interpreter method, (2) a multi-computer file system (3), a full-screen editing facility, and (4) a dynamic linkage scheme for data modules and NODAL functions. The accelerators are operated through five operator consoles, each of which is managed by one minicomputer in the network. An operator console contains two 20-inch high-resolution color graphic displays, a pair of touch-panels, and ten small TV monitors. One touch-panel is used to select a program and a piece of equipment to be controlled; the other is used mainly to perform the console actions.

Bunch by bunch feedback systems for the KEKB rings

Transverse bunch-by-bunch feedback systems for damping coupled-bunch instabilities in the KEKB rings have been working since the early stages of the commissioning of the rings. Stabilization of the beams with the system has been successful, permitting tests of higher beam currents and various filling patterns. The performance of these systems has been demonstrated under the normal physics run pattern of an 8 ns bunch spacing over long-term operation, and also under special filling patterns with a minimum bunch spacing of 2 ns.

KEK NODAL System

The KEK NODAL system, which is based on the NODAL devised at the CERN SPS, works on an optical-fiber token ring network of twenty-four minicomputers (Hitachi HIDIC 80s) to control the TRISTAN accelerator complex, now being constructed at KEK. KEK NODAL retains main features of the original NODAL: the interpreting scheme, the multi-computer programming facility, and the data-module concept. In addition, it has the following characteristics: (1) fast execution due to the compiler-interpreter method, (2) a multicomputer file system, (3) a full-screen editing facility, and (4) a dynamic linkage scheme of data modules and NODAL functions. The structure of the KEK NODAL system under PMS, a real-time multitasking operating system of HIDIC 80, is described; the NODAL file system is also explained.

Study of transverse bunch-by-bunch feedback systems based on the two tap FIR filter

Abstract A signal-processing system based on two-tap digital filters has been systematically studied considering its application to bunch feedback systems. Through studies we have found that the two-tap-filter-based system is a hopeful candidate for the signal processor used in high-speed, large-scale bunch feedback systems.

Operational Results of Optics Handling and Closed Orbit Correction in the Tristan Accumulation Ring

The optics handling system of the TRISTAN accumulation ring (AR) is facilitated by the general purpose computer of KEK as well as the machine control computers and has been dealing with many kinds of optics successfully since November 1983. Also a series of correction procedures has reduced r.m.s. values of closed orbit distortion(c.o.d.) at position monitors from 8.5mm to 0.6mm horizontally, and from 2.3mm to 0.3mm vertically in the typical optics of AR. Using the estimated errors, the pre-correction facility has been installed in AR to make an orbit correction possible in a completely new optics before beam injection.