2,187 research outputs found
Structure for the breathing mode of the nucleon from high energy p-p scattering
Spectra of p-p and pi-p scattering at beam momenta between 6 and 30 GeV/c
have been reanalysed. These show strong excitation of N* resonances, the
strongest one corresponding to the "scalar" P11 excitation (breathing mode) at
m_o= 1400+-10 MeV with Gamma= 200+-25 MeV. The result of a strong scalar
excitation is supported by a large longitudinal amplitude S_1/2 extracted from
e-p scattering. From exclusive data on p+p=>p p pi+ pi- a large 2pi-N decay
branch for the P_11 resonance of B_2pi= 75+-20 % has been extracted.
The differential cross sections were described in a double folding approach,
assuming multi-gluon exchange as the dominant part of the effective interaction
between the constituents of projectile and target. First, the parameters of the
interaction were fitted to elastic scattering; then with this interaction the
inelastic cross sections were described in the distorted wave Born
approximation. A good description of the data requires a surface peaked
transition density, quite different from that of a pure radial mode. In
contrast, the electron scattering amplitude S_1/2 is quite well described by a
breathing mode transition density with radial node. This large difference
between charge and matter transition density suggests, that in p-p scattering
the coupling to the multi-gluon field is much more important than the coupling
to the valence quarks. A multi-gluon (or sea-quark) transition density is
derived, which shows also breathing, indicating a rather complex multi-quark
structure of N and N* including multi-glue (or q^2n qbar ^-2n) creation out of
the g.s. vacuum.Comment: 18 pages with 7 figure
Observation of photon-assisted tunneling in optical lattices
We have observed tunneling suppression and photon-assisted tunneling of
Bose-Einstein condensates in an optical lattice subjected to a constant force
plus a sinusoidal shaking. For a sufficiently large constant force, the ground
energy levels of the lattice are shifted out of resonance and tunneling is
suppressed; when the shaking is switched on, the levels are coupled by
low-frequency photons and tunneling resumes. Our results agree well with
theoretical predictions and demonstrate the usefulness of optical lattices for
studying solid-state phenomena.Comment: 5 pages, 3 figure
Excitation and damping of collective modes of a Bose-Einstein condensate in a one-dimensional lattice
The mode structure of a Bose-Einstein condensate non-adiabatically loaded
into a one-dimensional optical lattice is studied by analyzing the visibility
of the interference pattern as well as the radial profile of the condensate
after a time-of-flight. A simple model is proposed that predicts the short-time
decrease of the visibility as a function of the condensate parameters. In the
radial direction, heavily damped oscillations are observed, as well as an
increase in the condensate temperature. These findings are interpreted as a
re-thermalization due to dissipation of the initial condensate excitations into
high-lying modes.Comment: 5 pages; submitted to PR
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