256,944 research outputs found
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 system (where ) produced in the charge exchange reaction at an incident momentum of 18 GeV is presented as a function of
invariant mass, , and momentum transfer squared,
, from the incident to the outgoing system. , and waves were included in the PWA. The
and states are clearly observed in the overall
effective mass distribution as well as in the amplitudes associated with
wave and 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
for individual waves associated with natural and
unnatural parity exchange in the -channel are consistent with Regge
phenomenology. Of particular interest in this study is the wave since this
leads to an exotic for the system. A wave is
present in the data, however attempts to describe the mass dependence of the
amplitude and phase motion with respect to the wave as a Breit-Wigner
resonance are problematic. This has implications regarding the existence of a
reported exotic meson decaying into with a mass
near 1.4 GeV.Comment: 19 pages, 29 figures, to appear in Phys. Rev.
FEWZ 2.0: A code for hadronic Z production at next-to-next-to-leading order
We introduce an improved version of the simulation code FEWZ (Fully Exclusive
W and Z Production) for hadron collider production of lepton pairs through the
Drell-Yan process at next-to-next-to-leading-order (NNLO) in the strong
coupling constant. The program is fully differential in the phase space of
leptons and additional hadronic radiation. The new version offers users
significantly more options for customization. FEWZ now bins multiple,
user-selectable histograms during a single run, and produces parton
distribution function (PDF) errors automatically. It also features a
signifcantly improved integration routine, and can take advantage of multiple
processor cores locally or on the Condor distributed computing system. We
illustrate the new features of FEWZ by presenting numerous phenomenological
results for LHC physics. We compare NNLO QCD with initial ATLAS and CMS
results, and discuss in detail the effects of detector acceptance on the
measurement of angular quantities associated with Z-boson production. We
address the issue of technical precision in the presence of severe phase-space
cuts.Comment: 29 pages, 13 figure
Color Difference Makes a Difference: Four Planet Candidates around Ï„ Ceti
The removal of noise typically correlated in time and wavelength is one of the main challenges for using the radial-velocity (RV) method to detect Earth analogues. We analyze τ Ceti RV data and find robust evidence for wavelength-dependent noise. We find that this noise can be modeled by a combination of moving average models and the so-called "differential radial velocities." We apply this noise model to various RV data sets for τ Ceti, and find four periodic signals at 20.0, 49.3, 160, and 642 days, which we interpret as planets. We identify two new signals with orbital periods of 20.0 and 49.3 days while the other two previously suspected signals around 160 and 600 days are quantified to a higher precision. The 20.0 days candidate is independently detected in Keck data. All planets detected in this work have minimum masses less than 4M⊕ with the two long-period ones located around the inner and outer edges of the habitable zone, respectively. We find that the instrumental noise gives rise to a precision limit of the High Accuracy Radial Velocity Planet Searcher (HARPS) around 0.2 m s−1. We also find correlation between the HARPS data and the central moments of the spectral line profile at around 0.5 m s−1 level, although these central moments may contain both noise and signals. The signals detected in this work have semi-amplitudes as low as 0.3 m s−1, demonstrating the ability of the RV technique to detect relatively weak signals
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