7,353 research outputs found

### Rates for the reactions antiproton-proton --> pi phi and gamma phi

We study antiproton-proton annihilation at rest into $\pi\phi$ and
$\gamma\phi$. Rescattering by $\overline{K^*}K+K^*\overline{K}$ and
$\rho^{+}\rho^{-}$ for $\overline{p}p\rightarrow\pi\phi$ states is sizable, of
order $(0.90\, {\rm to}\,2.6)\times 10^{-4}$ in the branching ratio, but
smaller than experiment. For $\overline{p}p\rightarrow\gamma\phi$ the
rescattering contributions are negligible, but the $\gamma\phi$ channel is well
explained by a $\rho\phi$ intermediate state combined with vector meson
dominance.Comment: 12 pages, plain latex, 2 postscript figures available upon request,
PSI-PR-93-2

### Scalar Quarkonium Masses and Mixing with the Lightest Scalar Glueball

We evaluate the continuum limit of the valence (quenched) approximation to
the mass of the lightest scalar quarkonium state, for a range of different
quark masses, and to the mixing energy between these states and the lightest
scalar glueball. Our results support the interpretation of $f_0(1710)$ as
composed mainly of the lightest scalar glueball.Comment: 14 pages of Latex, 5 PostScript figure

### Instanton Effects in the Decay of Scalar Mesons

We show that instanton effects may play a crucial role in the decay of scalar
mesons into two pseudoscalars. Particularly the branching ratios of two meson
decays of the $f_0(1500)$, which is considered as a glue-ball candidate, are
then compatible with an ordinary $q \bar{q}$-structure of this resonance and a
small positive SU(3) mixing angle, close to a result recently calculated with
the same instanton-induced force.Comment: 9 pages, uuencoded latex including two figure

### Chiral field theory of $0^{-+}$ glueball

A chiral field theory of $0^{-+}$ glueball is presented. By adding a $0^{-+}$
glueball field to a successful Lagrangian of chiral field theory of
pseudoscalar, vector, and axial-vector mesons, the Lagrangian of this theory is
constructed. The couplings between the pseodoscalar glueball field and mesons
are via U(1) anomaly revealed. Qualitative study of the physical processes of
the $0^{-+}$ glueball of $m=1.405\textrm{GeV}$ is presented. The theoretical
predictions can be used to identify the $0^{-+}$ glueball.Comment: 29 page

### Study of nuclear recoils in liquid argon with monoenergetic neutrons

For the development of liquid argon dark matter detectors we assembled a
setup in the laboratory to scatter neutrons on a small liquid argon target. The
neutrons are produced mono-energetically (E_kin=2.45 MeV) by nuclear fusion in
a deuterium plasma and are collimated onto a 3" liquid argon cell operating in
single-phase mode (zero electric field). Organic liquid scintillators are used
to tag scattered neutrons and to provide a time-of-flight measurement. The
setup is designed to study light pulse shapes and scintillation yields from
nuclear and electronic recoils as well as from {\alpha}-particles at working
points relevant to dark matter searches. Liquid argon offers the possibility to
scrutinise scintillation yields in noble liquids with respect to the
populations of the two fundamental excimer states. Here we present experimental
methods and first results from recent data towards such studies.Comment: 9 pages, 8 figures, proceedings of TAUP 2011, to be published in
Journal of Physics: Conference Series (JCPS

### Luminescence quenching of the triplet excimer state by air traces in gaseous argon

While developing a liquid argon detector for dark matter searches we
investigate the influence of air contamination on the VUV scintillation yield
in gaseous argon at atmospheric pressure. We determine with a radioactive
alpha-source the photon yield for various partial air pressures and different
reflectors and wavelength shifters. We find for the fast scintillation
component a time constant tau1= 11.3 +- 2.8 ns, independent of gas purity.
However, the decay time of the slow component depends on gas purity and is a
good indicator for the total VUV light yield. This dependence is attributed to
impurities destroying the long-lived argon excimer states. The population ratio
between the slowly and the fast decaying excimer states is determined for
alpha-particles to be 5.5 +-0.6 in argon gas at 1100 mbar and room temperature.
The measured mean life of the slow component is tau2 = 3.140 +- 0.067 microsec
at a partial air pressure of 2 x 10-6 mbar.Comment: 7 pages submitted to NIM

### Digital computer design of compensation for linear control systems

If a control system is to be synthesized, it is inferred that a plant or process is present which must be controlled, and the problem of how to design the control system then arises. The first step is to decide on performance specifications to which the complete system must conform. These specifications may involve such things as the system steady state response, transient response, or frequency response. Any of several synthesis methods may then be applied to complete the system design.
In this study a synthesis method is developed for single-loop linear feedback systems. First, the number of compensating poles and zeros and the approximate location of each is determined by conventional methods. A set of functions, one for each specification and one involving each plant pole, is written in terms of the system singularities with the compensation singularity positions as variables and each such function is equated to zero. linear approximations of each of these generally non-linear functions are obtained by expanding each function with a multivariable Taylor series and retaining only linear terms. Expansion is about a point described by the approximate singularity values. This linear set of equations is solved by the Gauss-Jordan elimination method. Due to truncation of the Taylor series, this does not give an exact solution to the original specification equations but will serve as a second approximation which is used as a new point of Taylor series expansion. This iterative process is repeated until a satisfactory solution is found.
This entire iterative technique is adapted for digital computer programming and flow charts for such a program are drawn --Abstract, page ii

### Performance of the CMS cathode strip chambers with cosmic rays

The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device in the CMS endcaps. Their performance has been evaluated using data taken during a cosmic ray run in fall 2008. Measured noise levels are low, with the number of noisy channels well below 1%. Coordinate resolution was measured for all types of chambers, and fall in the range 47μm to 243μm. The efficiencies for local charged track triggers, for hit and for segments reconstruction were measured, and are above 99%. The timing resolution per layer is approximately 5 ns

### Single photo and electroproduction of pions at EBAC@JLAB

Within the Excited Baryon Analysis Center we have performed a dynamical
coupled-channels analysis of the available $p(e,e' \pi)N$ data in the region of
$W \leq$ 1.6 GeV and $Q^2 \leq$ 1.45 (GeV/c)$^2$. The channels included are
$\gamma^* N$, $\pi N$, $\eta N$, and $\pi\pi N$ which has $\pi\Delta$, $\rho
N$, and $\sigma N$ components. With the hadronic parameters of the model
determined in our previous investigations of $\pi N\to \pi N$ reaction, we have
found that the available data in the considered $W \leq$ 1.6 GeV region can be
fitted well by only adjusting the bare $\gamma^* N \to N^*$ helicity amplitudes
for the lowest $N^*$ states in $P_{33}$, $P_{11}$, $S_{11}$ and $D_{13}$
partial waves. The meson cloud effect, as required by the unitarity conditions,
on the $\gamma^* N \to N^*$ form factors are examined.Comment: 6 pages, invited talk at NSTAR 2009, Beijing (China), 2009, to appear
in the proceeding

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