191 research outputs found
Electron Scattering on 3He - a Playground to Test Nuclear Dynamics
The big spectrum of electron induced processes on 3He is illustrated by
several examples based on Faddeev calculations with modern nucleon-nucleon and
three-nucleon forces as well as exchange currents. The kinematical region is
restricted to a mostly nonrelativistic one where the three-nucleon c.m. energy
is below the pion production threshold and the three-momentum of the virtual
photon is sufficiently below the nucleon mass. Comparisons with available data
are shown and cases of agreement and disagreement are found. It is argued that
new and precise data are needed to systematically check the present day
dynamical ingredients.Comment: 27 pages, 24 figure
Size of Isospin Breaking in Charged K(L4) Decay
We evaluate the size of isospin breaking corrections to form factors and
of the decay process which
is actually measured by the extended NA48 setup at CERN. We found that, keeping
apart the effect of Coulomb interaction, isospin breaking does not affect
modules. This is due to the cancelation between corrections of electromagnetic
origin and those generated by the difference between up and down quark masses.
On the other hand, electromagnetism affects considerably phases if the infrared
divergence is dropped out using a minimal subtraction scheme. Consequently, the
greatest care must be taken in the extraction of phase shifts from
experiment.Comment: 29 pages, LaTeX, 7 postscript figure
Anisotropic field dependence of the magnetic transition in Cu2Te2O5Br2
We present the results of measurements of the thermal conductivity of
Cu2Te2O5Br2, a compound where tetrahedra of Cu^{2+} ions carrying S=1/2 spins
form chains along the c-axis of the tetragonal crystal structure. The thermal
conductivity kappa was measured along both the c- and the a-direction as a
function of temperature between 3 and 300 K and in external magnetic fields H
up to 69 kOe, oriented both parallel and perpendicular to the c-axis. Distinct
features of kappa(T) were observed in the vicinity of T_N=11.4 K in zero
magnetic field. These features are unaltered in external fields which are
parallel to the c-axis, but are more pronounced when a field is applied
perpendicularly to the c-axis. The transition temperature increases upon
enhancing the external field, but only if the field is oriented along the
a-axis.Comment: 5 pages, 3 figure
Coherence length of an elongated condensate: a study by matter-wave interferometry
We measure the spatial correlation function of Bose-Einstein condensates in
the cross-over region between phase-coherent and strongly phase-fluctuating
condensates. We observe the continuous path from a gaussian-like shape to an
exponential-like shape characteristic of one-dimensional phase-fluctuations.
The width of the spatial correlation function as a function of the temperature
shows that the condensate coherence length undergoes no sharp transition
between these two regimes.Comment: 8 pages, 6 figure, submitted to EPJ
LUX Cryogenics and Circulation
We report the effciency of a thermosyphon-based cooling system for a liquid xenon (LXe) time projection chamber (TPC), as well as the effciency of a unique internal heat exchanger with standard gas phase purification using a heated getter, which allows for very high flow purification without requiring large cooling power.Peer Reviewe
On kaonic hydrogen. Quantum field theoretic and relativistic covariant approach
We study kaonic hydrogen, the bound K^-p state A_(Kp). Within a quantum field
theoretic and relativistic covariant approach we derive the energy level
displacement of the ground state of kaonic hydrogen in terms of the amplitude
of K^-p scattering for arbitrary relative momenta. The amplitude of low-energy
K^-p scattering near threshold is defined by the contributions of three
resonances Lambda(1405), Lambda(1800) and Sigma^0(1750) and a smooth elastic
background. The amplitudes of inelastic channels of low-energy K^-p scattering
fit experimental data on near threshold behaviour of the cross sections and the
experimental data by the DEAR Collaboration. We use the soft-pion technique
(leading order in Chiral Perturbation Theory) for the calculation of the
partial width of the radiative decay of pionic hydrogen A_(pi p) -> n + gamma
and the Panofsky ratio. The theoretical prediction for the Panofsky ratio
agrees well with experimental data. We apply the soft-kaon technique (leading
order in Chiral Perturbation Theory) to the calculation of the partial widths
of radiative decays of kaonic hydrogen A_(Kp) -> Lambda^0 + gamma and A_(Kp) ->
Sigma^0 + gamma. We show that the contribution of these decays to the width of
the energy level of the ground state of kaonic hydrogen is less than 1%.Comment: 33 pages, 1 figure, latex, References are adde
K Kbar photoproduction and S-P wave interference
Results of a new analysis of the photoproduction at two photon
energies and with a particular emphasis on the
-wave production are presented. We show that the proper treatment of all the
helicity components of the - and -waves enables one to eliminate the
reported discrepancies in extraction of the -wave photoproduction cross
section from experimental data.Comment: 25 pages, 5 figures, new predictions at 8 GeV added in Fig.
Evidence for an Excess of Soft Photons in Hadronic Decays of Z^0
Soft photons inside hadronic jets converted in front of the DELPHI main
tracker (TPC) in events of qqbar disintegrations of the Z^0 were studied in the
kinematic range 0.2 < E_gamma < 1 GeV and transverse momentum with respect to
the closest jet direction p_T < 80 MeV/c. A clear excess of photons in the
experimental data as compared to the Monte Carlo predictions is observed. This
excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/-
0.27) x 10^{-3} gamma/jet in the specified kinematic region, while the expected
level of the inner hadronic bremsstrahlung (which is not included in the Monte
Carlo) is (0.340 +/- 0.001 +/- 0.038) x 10^{-3} gamma/jet. The ratio of the
excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8),
which is similar in strength to the anomalous soft photon signal observed in
fixed target experiments with hadronic beams.Comment: 37 pages, 9 figures, Accepted by Eur. Phys. J.
Measurement of the Strong Coupling alpha s from Four-Jet Observables in e+e- Annihilation
Data from e+e- annihilation into hadrons at centre-of-mass energies between
91 GeV and 209 GeV collected with the OPAL detector at LEP, are used to study
the four-jet rate as a function of the Durham algorithm resolution parameter
ycut. The four-jet rate is compared to next-to-leading order calculations that
include the resummation of large logarithms. The strong coupling measured from
the four-jet rate is alphas(Mz0)=
0.1182+-0.0003(stat.)+-0.0015(exp.)+-0.0011(had.)+-0.0012(scale)+-0.0013(mass)
in agreement with the world average. Next-to-leading order fits to the
D-parameter and thrust minor event-shape observables are also performed for the
first time. We find consistent results, but with significantly larger
theoretical uncertainties.Comment: 25 pages, 15 figures, Submitted to Euro. Phys. J.
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