Search for new particles at the alternating-gradient-synchrotron beam dump

Journal ArticleThis paper presents results of a beam-dump experiment performed at the Brookhaven alternating-gradient synchrotron to search for prompt sources of neutrinos and axionlike particles. We observe no excess of vµ or events, and no excess in neutral-current events over that expected from neutrinos from ir and K decays. We report on limits of prompt particle-production cross sections and lifetimes

Measurement of the Omega_c Lifetime

We present the measurement of the lifetime of the Omega_c we have performed using three independent data samples from two different decay modes. Using a Sigma- beam of 340 GeV/c we have obtained clean signals for the Omega_c decaying into Xi- K- pi+ pi+ and Omega- pi+ pi- pi+, avoiding topological cuts normally used in charm analysis. The short but measurable lifetime of the Omega_c is demonstrated by a clear enhancement of the signals at short but finite decay lengths. Using a continuous maximum likelihood method we determined the lifetime to be tau(Omega_c) = 55 +13-11(stat) +18-23(syst) fs. This makes the Omega_c the shortest living weakly decaying particle observed so far. The short value of the lifetime confirms the predicted pattern of the charmed baryon lifetimes and demonstrates that the strong interaction plays a vital role in the lifetimes of charmed hadrons.Comment: 15 pages, including 7 figures; gzipped, uuencoded postscrip

Observation of Two Narrow States Decaying into Ξc+γ\Xi_{c}^{+}\gamma and Ξc0γ\Xi_{c}^{0}\gamma

We report the first observation of two narrow charmed strange baryons decaying to $\Xi_c^+\gamma$ and $\Xi_c^0\gamma$, respectively, using data from the CLEO II detector at CESR. We interpret the observed signals as the $\Xi_c^{+\prime}(c{su})$ and $\Xi_c^{0\prime}(c{sd})$, the symmetric partners of the well-established antisymmetric $\Xi_c^+(c[su])$ and $\Xi_c^0(c[sd])$. The mass differences $M(\Xi_c^{+\prime})-M(\Xi_c^+)$ and $M(\Xi_c^{0\prime})-M(\Xi_c^0)$ are measured to be $107.8\pm 1.7\pm 2.5$ and $107.0\pm 1.4\pm 2.5 MeV/c^2$, respectively.Comment: 11 pages, postscript file also available through http://w4.lns.cornell.edu/public/CLN

First Observation of Inclusive BB Decays to the Charmed Strange Baryons Ξc0\Xi_{c}^{0} and Ξc+\Xi_{c}^{+}

Using data collected in the region of the Upsilon(4S) resonance with the CLEO II detector operating at the Cornell Electron Storage Ring CESR, we present the first observation of B mesons decaying into the charmed strange baryons Xi_c0 and Xi_c+. We find 79 +/- 27 Xi_c0 and 125 +/- 28 Xi_c+ candidates from B decays, leading to product branching fractions of BR(Bbar -> Xi_c0 X)BR(Xi_c0 -> Xi- pi+) = (0.144 +/- 0.048 +/- 0.021) x 10^-3 and BR(Bbar -> Xi_c+ X)BR(Xi_c+ -> Xi- pi+ pi+) = (0.453 +/- 0.096 +0.085-0.065) x 10^-3.Comment: 11 pages, postscript file also available through http://w4.lns.cornell.edu/public/CLN

Measurement of elastic νμ and ν̄μ scattering on protons

Journal ArticleWe have measured elastic vµ and vµ scattering on protons at the Brookhaven National Laboratory Alternating Gradient Synchrotron. We find RNC = σ (νµp → vµp)/σ (vµp -* vµp) = 0.44 ±0.12 and Rvµ = σ (vµp → vµp)/σ (vµn → µ-p) =0.11 ±0.03. The elastic Q2 distribution is in good agreement with present knowledge of form factors and the Weinberg-Salam model. We find sin2θw, =0.26 ±0.06

physics.nist.gov/cuu/Units/binary.html.

supercomputer As 1999 ended, IBM announced its intention to construct a onepetaflop supercomputer. The construction of this system was based on a cellular architecture—the use of relatively small but powerful building blocks used together in sufficient quantities to construct large systems. The first step on the road to a petaflop machine (one quadrillion floating-point operations in a second) is the Blue Genet/L supercomputer. Blue Gene/L combines a low-power processor with a highly parallel architecture to achieve unparalleled computing performance per unit volume. Implementing the Blue Gene/L packaging involved trading off considerations of cost, power, cooling, signaling, electromagnetic radiation, mechanics, component selection, cabling, reliability, service strategy, risk, and schedule. This paper describes how 1,024 dual-processor compute application-specific integrated circuits (ASICs) are packaged in a scalable rack, and how racks are combined and augmented with host computers and remote storage. The Blue Gene/L interconnect, power, cooling, and control systems are described individually and as part of the synergistic whole. Overview Late in 1999, IBM announced its intention to construct a one-petaflop supercomputer [1]. Blue Gene*/L (BG/L) is a massively parallel supercomputer developed at the IB

Low-Overhead, High-Speed Multi-core Barrier Synchronization

Abstract. Whereas efcient barrier implementations were once a concern only in high-performance computing, recent trends in core integration make the topic relevant even for general-purpose CMPs. While the nature of CMP applications requires low-latency, the cost of low-latency barrier implementations using hardware-based techniques can be prohibitive for CMPs, where die area represents oppor-tunities for throughput and yield. Similarly, whereas traditional multiprocessor barrier implementations were developed primarily for dedicated environments, scheduling and multi-programming on CMPs require more adaptable barrier im-plementations. In this paper, we present and evaluate three barrier implementations that are hy-brids of software and dedicated hardware barriers and are specically tailored for CMPs. The implementations leverage the unique characteristics of CMPs and provide low latency comparable to that of dedicated hardware networks at a frac-tion of the cost. The implementations also support adaptability, enabling efcient multi-programming and dynamic remapping of the barrier network.