A Performance Comparison Using HPC Benchmarks: Windows HPC Server 2008 and Red Hat Enterprise Linux 5

This document was developed with support from the National Science Foundation (NSF) under Grant No. 0910812 to Indiana University for ”FutureGrid: An Experimental, High-Performance Grid Test-bed.” Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.A collection of performance benchmarks have been run on an IBM System X iDataPlex cluster using two different operating systems. Windows HPC Server 2008 (WinHPC) and Red Hat Enterprise Linux v5.4 (RHEL5) are compared using SPEC MPI2007 v1.1, the High Performance Computing Challenge (HPCC) and National Science Foundation (NSF) acceptance test benchmark suites. Overall, we find the performance of WinHPC and RHEL5 to be equivalent but significant performance differences exist when analyzing specific applications. We focus on presenting the results from the application benchmarks and include the results of the HPCC microbenchmark for completeness

The Evidence for a Pentaquark Signal and Kinematic Reflections

Several recent experiments have reported evidence for a narrow baryon resonance with positive strangeness ($\Theta^+$) at a mass of 1.54 GeV/$c^2$. Baryons with $S=+1$ cannot be conventional $qqq$ states and the reports have thus generated much theoretical speculation about the nature of possible $S=+1$ baryons, including a 5-quark, or pentaquark, interpretation. We show that narrow enhancements in the $K^+n$ effective mass spectrum can be generated as kinematic reflections resulting from the decay of mesons, such as the $f_2(1275)$, the $a_2(1320)$ and the $\rho_3(1690)$.Comment: 4 pages, 4 figure

A Study of the \eta \pi^{0} Spectrum and Search for a J^{PC} = 1^{-+} Exotic Meson

A partial wave analysis (PWA) of the of the $\eta \pi ^0$ system (where $\eta \to \gamma \gamma$) produced in the charge exchange reaction $\pi ^-p\to \eta \pi ^0n$ at an incident momentum of 18 GeV$/c$ is presented as a function of ${\eta \pi ^0}$ invariant mass, $m_{\eta\pi^0}$, and momentum transfer squared, $t_{\pi^{-}\to\eta\pi}$, from the incident $\pi^-$ to the outgoing ${\eta\pi ^0}$ system. $S$, $P$ and $D$ waves were included in the PWA. The $a_0(980)$ and $a_2(1320)$ states are clearly observed in the overall ${\eta\pi ^0}$ effective mass distribution as well as in the amplitudes associated with $S$ wave and $D$ waves respectively after partial wave decomposition. The observed distributions in moments (averages of spherical harmonics) were compared to the results from the PWA and the two are consistent. The distribution in $t_{\pi^{-}\to\eta\pi}$ for individual $D$ waves associated with natural and unnatural parity exchange in the $t$-channel are consistent with Regge phenomenology. Of particular interest in this study is the $P$ wave since this leads to an exotic $J^{PC}=1^{-+}$ for the $\eta \pi$ system. A $P$ wave is present in the data, however attempts to describe the mass dependence of the amplitude and phase motion with respect to the $D$ wave as a Breit-Wigner resonance are problematic. This has implications regarding the existence of a reported exotic $J^{PC} = 1^{-+}$ meson decaying into $\eta \pi^0$ with a mass near 1.4 GeV$/c^2$.Comment: 19 pages, 29 figures, to appear in Phys. Rev.

A search for J^{PC}=1^{-+} exotic mesons in the pi- pi- pi+ and pi- pi0 pi0 systems

A partial wave analysis (PWA) of the pi-pi-pi+ and pi-pi0pi0 systems produced in the reaction pi- p -> (3pi)-p at 18 GeV/c was carried out using an isobar model assumption. This analysis is based on 3.0M pi-pi0pi0 events and 2.6M pi-pi-pi+ events and shows production of the a2(1320), pi2(1670) and \pi(1800) mesons. An earlier analysis of 250K pi-pi-pi+ events from the same experiment showed possible evidence for a J^{PC}=1^{-+}$ exotic meson with a mass of 1.6 GeV/c^2 decaying into rho pi. In this analysis of a higher statistics sample of the (3pi)- system in two charged modes we find no evidence of an exotic meson.Comment: 4 pages, 5 figures, added comment about the negative reflectivity exotic wave

Aspects of a0-f0 mixing in the reaction pn->da0

Some aspects of a0-f0 mixing effects in the reaction ${\vec p} n\to da^0_0$ with perpendicular polarized proton beam are discussed. An angular--asymmetry parameter $A$ is defined to study those effects. It is shown that, for energies close to the production threshold, the angular--asymmetry parameter $A(\theta, \phi)$ is proportional to the a0-f0 mixing amplitude for arbitrary polar and azimuthal angles $\theta$ and $\phi$ of the outgoing $a_0$ meson. This statement is also valid for arbitrary energies, but then only at polar angles $\theta=0^0$ and $\theta=90^0$. The mass dependence of the differential cross section $d\sigma/dm_{\pi^0\eta}$ in the reaction $pn\to d\pi^0\eta$ in the presence of \mix mixing is also discussed.Comment: 17 pages, 3 Figure

Weak Hyperon Decays: Quark Sea and SU(3) Symmetry Breaking

An explanation of the difference in the values of the apparent $f/d$ ratios for the S- and P- wave amplitudes of nonleptonic hyperon decays is proposed. The argument is formulated in the framework of the standard pole model with $(56,0^{+})$ ground-state and $(70,1^{-})$ excited baryons as intermediate states for the P- and S- waves respectively. Under the assumption that the dominant part of the deviation of $(f/d)_{P-wave}$ from $-1$ is due to large quark sea effects, $SU(3)$ symmetry breaking in energy denominators is shown to lead to a prediction for $(f/d)_{S-wave}$ which is in excellent agreement with experiment. This corroborates our previous unitarity calculations which indicated that the matrix elements $$ of the parity conserving weak Hamiltonian between the ground-state baryons are characterized by $f_{0}/d_{0} \approx -1.6$ or more. A brief discussion of the problem of the relative size of S- and P- wave amplitudes is given. Finally, implications for weak radiative hyperon decays are also discussed.Comment: 26 pages, LATEX, 1647/PH IFJ Krako