H. Koiso

The KEKB injector linac

Abstract An 8-GeV electron/3.5-GeV positron injector for KEKB was completed in 1998 by upgrading the existing 2.5-GeV electron/positron linac. The main goals were to upgrade its accelerating energy from 2.5 to 8 GeV and to increase the positron intensity by about 20 times. This article describes not only the composition and features of the upgraded linac, but also how these goals were achieved, by focusing on an optics design and commissioning issues concerning especially high-intensity single-bunch acceleration to produce positron beams.

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.

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.

Present status and beam-stability issues of the KEKB injector linac

The KEKB injector linac was completely upgraded for the KEK B-Factory (KEKB) project in March, 1998. Many difficulties have been overcome during the elaborate commissioning of the upgraded linac since the end of 1997. The 3.5-GeV positron and 8-GeV electron beams have been injected to the KEKB rings with good performance. Much effort has also been continuing to stabilize the intensity and quality of the beams. Some experimental results on the beam stability issues am shown together with the recent operation status in this report. A beam test on a new scheme of a two-bunch injection was started in order to increase the positron intensity since March, 2001.

Optimization of dynamic aperture for the KEKB B-factory

A few methods are introduced to optimize the dynamic aperture of the KEKB B-Factory. The basic idea is to fit the linear optics around orbits with finite amplitudes in the desired acceptance. Chromaticity correction was done by this method for orbits with finite momentum offsets, and sufficient momentum acceptance, ±2.5%, was achieved. This method was extended to the transverse direction, then resulted in significant increase of the dynamic aperture. A survey on the relationship between a Taylor map and the dynamic aperture was also done.

Response of a large CsI(Tl) crystal to electrons and pions below 1.5 GeV/c

Abstract A CsI(Tl) crystal of 9.5 cm diameter and 30 cm length was tested with electrons and pions in the momentum range from 0.2 to 1.5 GeV/ c . Photodiode and photomultiplier readouts were used for comparison. In the photodiode readout, the fwhm energy resolution for electrons was 6.7% at 1 GeV in agreement with the EGS simulation. The e/π separation for momentum analyzed particles was found to be 1/1000 at 1 GeV/ c with a simple energy cut. The pulse heith nonuniformity along the longitudinal position, scanned with a pencial beam of 1 GeV/ c pions, was smaller than ±4% between 4 and 27 cm from photomultiplier.

Recent Progress at KEKB

We summarize the machine operation of KEKB during past one year focusing on progress for this period.

Increase of positrons by a high-intensity two-bunch acceleration scheme at the KEKB linac

As the accumulation current of positrons increases in the KEKB ring, the injection time is becoming longer. It will thus be one of the most important issues affecting the accumulation of the integrated luminosity. As one of the steps, we introduced a high-intensity two-bunch acceleration scheme at the KEKB linac to intensify positrons by means of doubling the primary electrons. We recently obtained test results of 0.54 nC for the first bunch and 0.49 nC for the second bunch at the linac end. This scheme increased the positron intensity by nearly 65%. Since the linac frequency is not a harmonic number of the LER frequency, the best time interval between two bunches is 96.29 ns, corresponding to 49 LER-buckets. Even with this limitation, it is undoubtedly a very useful scheme for increasing the positron injection rate. The beam test results are described.

Characteristics of the TRISTAN control computer network

Abstract Twenty-four minicomputers forming an N -to- N token-ring network control the TRISTAN accelerator complex. The computers are linked by optical fiber cables with 10 Mbps transmission speed. The software system is based on NODAL, a multicomputer interpretive language developed at the CERN SPS. The high-level services offered to the users of the network are remote execution by the EXEC, EXEC-P and IMEX commands of NODAL and uniform file access throughout the system. The network software was designed to achieve the fast response of the EXEC command. The performance of the network is also reported. Tasks that overload the minicomputers are processed on the KEK central computers. One minicomputer in the network serves as a gateway to KEKNET, which connects the minicomputer network and the central computers. The communication with the central computers is managed within the framework of the KEK NODAL system. NODAL programs communicate with the central computers calling NODAL functions; functions for exchanging data between a data set on the central computers and a NODAL variable, submitting a batch job to the central computers, checking the status of the submitted job, etc. are prepared.