536 research outputs found
A study of the pi^0pi^0 system produced in charge exchange and central collisions
A study of the system produced in charge exchange
collisions at 38 and 100 GeV/c and in central interactions at 450 GeV/c
has been carried out. The wave has rather a complicated structure in both
processes indicating the existence of several scalar resonances. The
and appear as dips at 1 and 1.5 GeV in the wave for charge
exchange reaction, and as shoulders at these masses in the wave for central
production. The production of the , and in
the reaction as a function of the
kinematical filter shows the behaviour differed from what has been observed for
the undisputed mesons. An extra state is seen in the
wave for charge exchange reaction as a dip at 2 GeV. Resonances with higher
spins, , and , have also been studied. All
the three mesons are produced in the reaction mainly
via an one-pion exchange for small , whereas a natural-parity exchange
domimates for large . The behaviour of the centrally produced
as a function of the is consistent with what has been observed for
other states.Comment: 6 pages, 6 figures, use file stwol.sty, presented at International
High-Energy Physics Euroconference in Quantum Chromodynamics, 2-8 July 1998,
Montpellier, France on behalf of the GAMS and WA102 Collaboration
Nonet Classification of Scalar/Isoscalar Resonances in the Mass Region below 1900 MeV: Observation of the Lightest Scalar Glueball
We summarize the results of the investigation of the wave
which is devoted to the search for the lightest scalar glueball. In the
framework of the K-matrix formalism, the -nonet classification of the
scalar/isoscalar states is performed in the mass region below 1900 MeV basing
on the following data: GAMS data for , ,
; CERN-M\"unich data for ; Crystal Barrel
data for , , ; BNL
data for . It is shown the existence of an extra state
for classification: this state is a good candidate for the lightest
scalar glueball. Analysis of the glueball/ mixing shows that the
glueball state has mainly dispersed over three real resonances: ,
and . The broad resonance with complex mass
MeV is descendant of the pure glueball. The
restored mass of the pure glueball is equal to 1695 MeV. This value agrees well
with the results of lattice gluodynamics.Comment: LaTex, 5 pages and 7 figures. Talk given by V.V.Anisovich at LEAP96,
Dinkelsbuhl, German
exotic meson at light quark masses
The mass of the exotic meson, created with hybrid interpolating
fields, is explored at light quark masses approaching 25 MeV (). Access to such light quark masses is facilitated by the use of
the Fat-Link Irrelevant Clover (FLIC) fermion action. Additionally, we make use
of large () lattices to obtain good control of statistical and
finite volume errors. Our results indicate that the exotic exhibits
significant curvature close the chiral limit, indicating previous linear
extrapolations, far from the chiral regime, have overestimated the mass of the
. We find for the first time in lattice studies a mass in
agreement with the candidate. We also find a strangeness 1
state with a mass close to 2 GeV.Comment: 8 pages, 11 figures, 3 tables, published versio
Experimental Status of Exotic Mesons and the GlueX Experiment
One of the unanswered and most fundamental questions in physics regards the
nature of the confinement mechanism of quarks and gluons in QCD. Exotic hybrid
mesons manifest gluonic degrees of freedom and their spectroscopy will provide
the data necessary to test assumptions in lattice QCD and the specific
phenomenology leading to confinement. Within the past two decades a number of
experiments have put forth tantalizing evidence for the existence of exotic
hybrid mesons in the mass range below 2 GeV. This talk represents an overview
of the available data and what has been learned. In looking toward the future,
the GlueX experiment at Jefferson Laboratory represents a new initiative that
will perform detailed spectroscopy of the light-quark meson spectrum. This
experiment and its capabilities will be reviewed.Comment: 10 pages, 8 figures, 2nd Meeting of the APS Topical Group on Hadron
Physics GHP06, Nashville, TN (10/22-10/24/06
Mechanisms of the production in the reaction
The model of the pure one-pion exchange mechanism, which gives a good
description of the GAMS results on the alteration of the -wave
mass spectrum in the region in the reaction
with increasing , is compared with the recent detailed data on the and
distributions of the events obtained by the BNL-E852
Collaboration. It is shown that the predictions of this model are not confirmed
by the BNL data. Therefore the observed phenomenon should be explained by the
different exchange mechanism. It is most likely to be the exchange
mechanism.Comment: 11 pages including 3 figure
Nonet Classification of Scalar/Isoscalar Resonances below 1900 MeV: the Existence of an Extra Scalar State in the Region 1200-1600 MeV
A classification of the mesons is performed on the basis of
the K-matrix analysis of meson spectra in the reactions: (i) GAMS data on , , ; (ii) Crystal Barrel data on
, , ;
(iii) CERN-M\"unich data on ; (iiii) BNL data on . The analysis points to the existence of four comparatively
narrow scalar resonances which correspond to the following poles of the
scattering amplitude (in MeV): , , and .
The scattering amplitude also has a fifth pole at the
complex mass . The masses of the K-matrix
poles (bare states) are at MeV, MeV,
MeV, MeV and MeV. The quark content of the bare
states is analyzed using the values of their couplings to the , , and . It is shown that one of the bare states in the
mass region 1200-1600 MeV is superfluous for the classification and
should be considered as the lightest glueball.Comment: LaTex 26 pages and 8 figure
Simulation of the shape memory effect in a NiTi nano model system
The shape memory behavior of a NiTi nanoparticle is analyzed by molecular
dynamics simulations. After a detailed description of the equilibrium
structures of the used model potential, the multi variant martensitic ground
state, which depends on the geometry of the particle, is discussed. Tensile
load is applied, changing the variant configuration to a single domain state
with a remanent strain after unloading. Heating the particle leads to a shape
memory effect without a phase transition to the austenite, but by variant
reorientation and twin boundary formation at a certain temperature. These
processes are described by stress-strain and strain-temperature curves,
together with a visualization of the microstructure of the nanoparticle.
Results are presented for five different Ni concentrations in the vicinity of
50%, showing for example, that small deviations from this ideal composition can
influence the critical temperature for shape recovery significantly.Comment: 7 pages, 4 figures; accepted for publication in the "Journal of
Alloys and Compounds
On the microstructure and properties of Nb-12Ti-18Si-6Ta-5Al-5Cr-2.5W-1Hf (at.%) silicide-based alloys with Ge and Sn additions
The microstructures and properties of the alloys JZ3 (Nb-12.4Ti-17.7Si-6Ta-2.7W-3.7Sn-4.8Ge-1Hf-4.7Al-5.2Cr) and JZ3+(Nb-12.4Ti-19.7Si-5.7Ta-2.3W-5.7Sn-4.9Ge-0.8Hf-4.6Al-5.2Cr) were studied. The densities of both alloys were lower than the densities of Ni-based superalloys and many of the refractory metal complex concentrated alloys (RCCAs) studied to date. Both alloys had Si macrosegregation and the same phases in their as cast and heat treated microstructures, namely βNb5Si3, αNb5Si3, A15-Nb3X (X = Al, Ge, Si, Sn), C14-Cr2Nb and solid solution. W-rich solid solutions were stable in both alloys. At 800 °C only the alloy JZ3 did not show pest oxidation, and at 1200 °C a thin and well adhering scale formed only on JZ3+. The alloy JZ3+ followed parabolic oxidation with rate constant one order of magnitude higher than the single crystal Ni-superalloy CMSX-4 for the first 14 h of oxidation. The oxidation of both alloys was superior to that of RCCAs. Both alloys were predicted to have better creep at the creep goal condition compared with the superalloy CMSX-4. Calculated Si macrosegregation, solid solution volume fractions, chemical compositions of solid solution and Nb5Si3, weight changes in isothermal oxidation at 800 and 1200 °C using the alloy design methodology NICE agreed well with the experimental results
K-Matrix Analysis of the () Amplitude in the Mass Region up to 1550 MeV
K-matrix analysis of the wave is performed in the channels
and in the mass region up to 1550 MeV. The
fit is based on the following data: ,
[1,2], [3,4], [5] and the inelastic cross section of the interaction [6].
Simultaneous analysis of these data confirms the existence of the scalar
resonances: and , the poles of the amplitude
being at the following complex masses (in MeV): ,
, and . The fourth pole has
sunk deeply into the complex plane: . Positions
of the K-matrix poles (which are referred to the masses of bare states) are at
MeV, MeV, MeV and MeV.
Coupling constants of the K-matrix poles to the , and channels are found that allow us to analyze the quark and gluonic content of
bare states. It is shown that and (which
are strongly related to ) can be considered as good candidates for
scalar glueball.Comment: 19 pages, LATEX, 6 figures in one uu-fil
- …