26,422 research outputs found
Instanton Effects in QCD Sum Rules for the Hybrid
In this paper, we study instanton contributions to the correlator of the
hybrid current . These contributions
are then included in a QCD sum-rule analysis of the isoscalar hybrid
mass. We find a mass at 1.83 GeV for the hybrid.
However, for the hybrid, we find the sum rules are unstable. We also
study non-zero width effects, which affect the mass prediction. The mixing
effects between these two states are studied and we find QCD sum rules support
the existence of a flavor singlet hybrid with mass at around 1.9 GeV. Finally,
we study the mixing effects between hybrid and glueball currents. The mixing
between the () and the glueball causes
two states, one in the region 1.4-1.8 GeV(1.4-2.2 GeV), and the other in the
range 1.8-2.2 GeV(2.2-2.6 GeV).Comment: 12 pages, revised versio
Design and implementation of wire tension measurement system for MWPCs used in the STAR iTPC upgrade
The STAR experiment at RHIC is planning to upgrade the Time Projection
Chamber which lies at the heart of the detector. We have designed an instrument
to measure the tension of the wires in the multi-wire proportional chambers
(MWPCs) which will be used in the TPC upgrade. The wire tension measurement
system causes the wires to vibrate and then it measures the fundamental
frequency of the oscillation via a laser based optical platform. The platform
can scan the entire wire plane, automatically, in a single run and obtain the
wire tension on each wire with high precision. In this paper, the details about
the measurement method and the system setup will be described. In addition, the
test results for a prototype MWPC to be used in the STAR-iTPC upgrade will be
presented.Comment: 6 pages, 10 figues, to appear in NIM
Generation of multiple plasmons in strontium niobates mediated by local field effects
Recently, an anomalous generation of multiple plasmons with large spectral
weight transfer in the visible to ultraviolet range (energies below the band
gap) has been experimentally observed in the insulating-like phase of
oxygen-rich strontium niobium oxides (SrNbO). Here, we investigate
the ground state and dielectric properties of SrNbO as a function
of by means of extensive first principle calculations. We find that in
the random phase approximation by taking into account the local field effects
(LFEs), our calculations are able to reproduce both the unconventional multiple
generations of plasmons and spectral weight transfers, consistent with
experimental data. Interestingly, these unconventional plasmons can be tuned by
oxygen stoichiometry as well as microscopic superstructure. This unusual
predominance of LFEs in this class of materials is ascribed to the strong
electronic inhomogeneity and high polarizability and paves a new path to induce
multiple plasmons in the untapped visible to ultraviolet ranges of
insulating-like oxides
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