2,143 research outputs found

### Coulomb-nuclear interference in pion-nucleus bremsstrahlung

Pion-nucleus bremsstrahlung offers a possibility of measuring the structure
functions of pion-Compton scattering from a study of the
small-momentum-transfer region where the bremsstrahlung reaction is dominated
by the single-photon-exchange mechanism. The corresponding cross-section
distribution is characterized by a sharp peak at small momentum transfers. But
there is also a hadronic contribution which is smooth and constitutes an
undesired background. In this communication the modification of the
single-photon exchange amplitude by multiple-Coulomb scattering is investigated
as well as the Coulomb-nuclear interference term.Comment: 21 pages, 5 figures. Eqs.(51,52) corrected; some new figure

### A remark on the Primakoff effect

The coherent-nuclear reaction a + A -> a* + A is in the small-angle region
dominated by the one-photon-exchange mechanism, often referred to as the
Primakoff effect. In this region information about the electromagnetic decay a*
-> a + gamma can be obtained. Well-known examples are the two-photon decays of
the pi- and eta-mesons. Also decays of charged hadrons can be studied. For
charged hadrons the one-photon-exchange amplitude comes with a Coulomb-phase
factor and a Coulomb-form factor, which depend on the ratio between transverse-
and logitudinal-momentum transfers, the latter being fixed. At the peak of the
cross-section distribution, where the two momentum transfers are equal, the
form factor could cut down the cross-section value by as much as 40 %.
Consequently, a determination of a radiative-decay rate that relies on the peak
value becomes sensitive to a proper treatment of the Coulomb-form factor.Comment: 5 pages, 2 figure

### Slow Proton Production in Semi-Inclusive Deep Inelastic Scattering off Deuteron and Complex Nuclei: Hadronization and Final State Interaction Effects

The effects of the final state interaction in slow proton production in semi
inclusive deep inelastic scattering processes off nuclei, A(e,e'p)X, are
investigated in details within the spectator and target fragmentation
mechanisms; in the former mechanism, the hard interaction on a nucleon of a
correlated pair leads, by recoil, to the emission of the partner nucleon,
whereas in the latter mechanism proton is produced when the diquark, which is
formed right after the visrtual photon-quark interaction, captures a quark from
the vacuum. Unlike previous papers on the subject, particular attention is paid
on the effects of the final state interaction of the hadronizing quark with the
nuclear medium within an approach based upon an effective time-dependent cross
section which combines the soft and hard parts of hadronization dynamics in
terms of the string model and perturbative QCD, respectively. It is shown that
the final state interaction of the hadronizing quark with the medium plays a
relevant role both in deuteron and complex nuclei; nonetheless, kinematical
regions where final state interaction effects are minimized can experimentally
be selected, which would allow one to investigate the structure functions of
nucleons embedded in the nuclear medium; likewise, regions where the
interaction of the struck hadronizing quark with the nuclear medium is
maximized can be found, which would make it possible to study non perturbative
hadronization mechanisms.Comment: 35 pages, 12 figures, accepted for pubblication in Phys. Rev.

### Hanbury-Brown and Twiss Intensity Correlations of Parabosons

This paper shows that in intensity correlation measurements there will be
clear and unambiguous signals that new-physics particles are, or aren't,
parabosons. For a parabosonic field in a dominant single-mode, there is a
diagonal P-representation in the "even and odd coherent states" basis. It is
used to analyze zero-time-interval intensity correlations of parabosons in a
maximum-entropic state. As the mean number of parabosons decreases, there is a
monotonic reduction to (2/p) of the constant bosonic ``factor of two''
proportionality of the second-order versus the squared first-order intensity
correlation function.Comment: 16 pages; version 4 to add simple p-independent recursion relatio

### Quantum Surveying: How Entangled Pairs Act as Measuring Rods on Manifolds of Generalized Coherent States

Generalized coherent states arise from reference states by the action of
locally compact transformation groups and thereby form manifolds on which there
is an invariant measure. It is shown that this implies the existence of
canonically associated Bell states that serve as measuring rods by relating the
metric geometry of the manifold to the observed EPR correlations. It is further
shown that these correlations can be accounted for by a hidden variable theory
which is non-local but invariant under the stability group of the reference
state.Comment: 14 pages, 0 figures, plain te

### Yoctosecond metrology through HBT correlations from a quark-gluon plasma

Expansion dynamics at the yoctosecond timescale affect the evolution of the
quark gluon plasma (QGP) created in heavy ion collisions. We show how these
dynamics are accessible through Hanbury Brown and Twiss (HBT) intensity
interferometry of direct photons emitted from the interior of the QGP. A
detector placed close to the beam axis is particularly sensitive to early polar
momentum anisotropies of the QGP. Observing a modification of the HBT signal at
the proposed FoCal detector of the LHC ALICE experiment would allow to measure
the isotropization time of the plasma and could provide first experimental
evidence for photon double pulses at the yoctosecond timescale.Comment: 5 pages, 3 figure

### Consequences of energy conservation in relativistic heavy-ion collisions

Complete characterization of particle production and emission in relativistic
heavy-ion collisions is in general not feasible experimentally. This work
demonstrates, however, that the availability of essentially complete
pseudorapidity distributions for charged particles allows for a reliable
estimate of the average transverse momenta and energy of emitted particles by
requiring energy conservation in the process. The results of such an analysis
for Au+Au collisions at sqrt{s_{NN}}= 130 and 200 GeV are compared with
measurements of mean-p_T and mean-E_T in regions where such measurements are
available. The mean-p_T dependence on pseudorapidity for Au+Au collisions at
130 and 200 GeV is given for different collision centralities.Comment: 8 pages, 8 figures, Submitted to Phys. Rev.

### Self-organizing, two-temperature Ising model describing human segregation

A two-temperature Ising-Schelling model is introduced and studied for
describing human segregation. The self-organized Ising model with Glauber
kinetics simulated by M\"uller et al. exhibits a phase transition between
segregated and mixed phases mimicking the change of tolerance (local
temperature) of individuals. The effect of external noise is considered here as
a second temperature added to the decision of individuals who consider change
of accommodation. A numerical evidence is presented for a discontinuous phase
transition of the magnetization.Comment: 5 pages, 4 page

### Fermion- and spin-counting in strongly correlated systems in and out of thermal equilibrium

Atom counting theory can be used to study the role of thermal noise in
quantum phase transitions and to monitor the dynamics of a quantum system. We
illustrate this for a strongly correlated fermionic system, which is equivalent
to an anisotropic quantum XY chain in a transverse field, and can be realized
with cold fermionic atoms in an optical lattice. We analyze the counting
statistics across the phase diagram in the presence of thermal fluctuations,
and during its thermalization when the system is coupled to a heat bath. At
zero temperature, the quantum phase transition is reflected in the cumulants of
the counting distribution. We find that the signatures of the crossover remain
visible at low temperature and are obscured with increasing thermal
fluctuations. We find that the same quantities may be used to scan the dynamics
during the thermalization of the system.Comment: 10 pages, 7 figure

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