8,108,483 research outputs found
New result on the measurement of the direct photon emission in K+ --> pi^+ pi^0 gamma decay
We present a new result on the K^+ --> pi^+ pi^0 gamma decay measurement
using stopped kaons. The best fit to the decay spectrum comprised of 10k events
gives a branching ratio for the direct photon emission of
[3.8+-0.8(stat)+-0.7(syst)] times 10^{-6} in the pi^+ kinetic energy region of
55 to 90 MeV. This result has been obtained with the assumption that there is
no component due to interference with the inner bremsstrahlung.Comment: 14 pages, 7 figures, 3 tables (Fig.1 which had problems with
uploading first time is replaced. Besides introduction is changed to bring
into accordance with the version published in Eur.Phys.J.C.
Geometric Phase of a qubit interacting with a squeezed-thermal bath
We study the geometric phase of an open two-level quantum system under the
influence of a squeezed, thermal environment for both non-dissipative as well
as dissipative system-environment interactions. In the non-dissipative case,
squeezing is found to have a similar influence as temperature, of suppressing
geometric phase, while in the dissipative case, squeezing tends to counteract
the suppressive influence of temperature in certain regimes. Thus, an
interesting feature that emerges from our work is the contrast in the interplay
between squeezing and thermal effects in non-dissipative and dissipative
interactions. This can be useful for the practical implementation of geometric
quantum information processing. By interpreting the open quantum effects as
noisy channels, we make the connection between geometric phase and quantum
noise processes familiar from quantum information theory.Comment: Accepted for publication in Eur. Phys. J. D; slightly abridged
version of v2; 10 pages, 12 figure
Bragg spectroscopy of discrete axial quasiparticle modes in a cigar-shaped degenerate Bose gas
We propose an experiment in which long wavelength discrete axial
quasiparticle modes can be imprinted in a 3D cigar-shaped Bose-Einstein
condensate by using two-photon Bragg scattering experiments, similar to the
experiment at the Weizmann Institute [J. Steinhauer {\em et al.}, Phys. Rev.
Lett. {\bf 90}, 060404 (2003)] where short wavelength axial phonons with
different number of radial modes have been observed. We provide values of the
momentum, energy and time duration of the two-photon Bragg pulse and also the
two-body interaction strength which are needed in the Bragg scattering
experiments in order to observe the long wavelength discrete axial modes. These
discrete axial modes can be observed when the system is dilute and the time
duration of the Bragg pulse is long enough.Comment: 5 pages, 3 figures, title, abstract, results changed, references
added. to appear in The European Physical Journal
Geometric Phase in Entangled Bipartite Systems
The geometric phase (GP) for bipartite systems in transverse external
magnetic fields is investigated in this paper. Two different situations have
been studied. We first consider two non-interacting particles. The results show
that because of entanglement, the geometric phase is very different from that
of the non-entangled case. When the initial state is a Werner state, the
geometric phase is, in general, zero and moreover the singularity of the
geometric phase may appear with a proper evolution time. We next study the
geometric phase when intra-couplings appear and choose Werner states as the
initial states to entail this discussion. The results show that unlike our
first case, the absolute value of the GP is not zero, and attains its maximum
when the rescaled coupling constant is less than 1. The effect of
inhomogeneity of the magnetic field is also discussed.Comment: 5 pages and to be published in Euro. Phys. J.
Diffractive gamma-gamma production at hadron colliders
We compute the cross section for exclusive double-diffractive gamma-gamma
production at the Tevatron, , and
the LHC. We evaluate both the gluon-gluon and quark-antiquark t-channel
exchange contributions to the process. The observation of exclusive gamma-gamma
production at the Tevatron will provide a check on the model predictions, and
offer an opportunity to confirm the expectations for exclusive
double-diffractive Higgs production at the LHC.Comment: 16 pages, 7 figure
Probing dense and hot matter with low-mass dileptons and photons
Results on low-mass dileptons, covering the very broad energy range from the
BEVALAC up to SPS are reviewed. The emphasis is on the open questions raised by
the intriguing results obtained so far and the prospects for addressing them in
the near future with the second generation of experiments, in particular HADES,
NA60 and PHENIX.Comment: 6 pages, 8 figures, Proceedings of Hard Probes 2004 Conference,
Ericeira, November 4-10, 2004. Caption of Figure 2 corrected. To be published
in Eur. Phys. J. C. The orginal version is available at www.springerlink.co
Modelling nucleon-nucleon scattering above 1 GeV
Motivated by the recent measurement of proton-proton spin-correlation
parameters up to 2.5 GeV laboratory energy, we investigate models for
nucleon-nucleon (NN) scattering above 1 GeV. Signatures for a gradual failure
of the traditional meson model with increasing energy can be clearly
identified. Since spin effects are large up to tens of GeV, perturbative QCD
cannot be invoked to fix the problems. We discuss various theoretical scenarios
and come to the conclusion that we do not have a clear phenomenological
understanding of the spin-dependence of the NN interaction above 1 GeV.Comment: 36 pages, 8 figure
Transport of a quantum degenerate heteronuclear Bose-Fermi mixture in a harmonic trap
We report on the transport of mixed quantum degenerate gases of bosonic 87Rb
and fermionic 40K in a harmonic potential provided by a modified QUIC trap. The
samples are transported over a distance of 6 mm to the geometric center of the
anti-Helmholtz coils of the QUIC trap. This transport mechanism was implemented
by a small modification of the QUIC trap and is free of losses and heating. It
allows all experiments using QUIC traps to use the highly homogeneous magnetic
fields that can be created in the center of a QUIC trap and improves the
optical access to the atoms, e.g., for experiments with optical lattices. This
mechanism may be cascaded to cover even larger distances for applications with
quantum degenerate samples.Comment: 7 pages, 8 figure
Strange particle production in proton-proton collisions at TeV with ALICE at the LHC
The production of mesons containing strange quarks (K, ) and both
singly and doubly strange baryons (, Anti-, and
+Anti-) are measured at central rapidity in pp collisions at
= 0.9 TeV with the ALICE experiment at the LHC. The results are
obtained from the analysis of about 250 k minimum bias events recorded in 2009.
Measurements of yields (dN/dy) and transverse momentum spectra at central
rapidities for inelastic pp collisions are presented. For mesons, we report
yields () of 0.184 0.002 stat. 0.006 syst. for K and
0.021 0.004 stat. 0.003 syst. for . For baryons, we find
= 0.048 0.001 stat. 0.004 syst. for , 0.047
0.002 stat. 0.005 syst. for Anti- and 0.0101 0.0020 stat.
0.0009 syst. for +Anti-. The results are also compared with
predictions for identified particle spectra from QCD-inspired models and
provide a baseline for comparisons with both future pp measurements at higher
energies and heavy-ion collisions.Comment: 33 pages, 21 captioned figures, 10 tables, authors from page 28,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/387
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
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