100 research outputs found
Quantum Communication Countermeasures
Quantum communication, particularly quantum key distribution, is poised to
play a pivotal role in our communication system in the near future.
Consequently, it is imperative to not only assess the vulnerability of quantum
communication to eavesdropping (one aspect of quantum hacking), but also to
scrutinise the feasibility of executing a denial-of-service attack,
specifically, stopping quantum communication from working. Focusing primarily
on the free-space quantum channel, the investigation of possible
denial-of-service attacks from a strategic perspective is performed. This
encompasses the analysis of various scenarios, numerical modelling, risk
estimation and attack classification. The out-of-FOV (field of view) attack
emerges as a particularly severe threat across nearly all scenarios. This is
accompanied by proposed counter-countermeasures and recommendations
Drell-Yan process in collisions: the exact treatment of coherence effects
In this work, we investigate production of Drell-Yan (DY) pairs in
proton-nucleus collisions in kinematic regions where the corresponding
coherence length does not exceed the nuclear radius, , and the quantum
coherence effects should be treated with a special care. The results for the
nucleus-to-nucleon production ratio available in the literature so far are
usually based on the assumption of a very long coherence length (LCL) . Since the onset of coherence effects is controlled by the coherence
length , we estimated its magnitude in various kinematic regions of the DY
process and found that the LCL approximation should not be used at small and
medium c.m. collision energies ( GeV) as well as at
large dilepton invariant masses. In order to obtain realistic predictions, we
computed for the first time the DY cross section using the generalised color
dipole approach based on the rigorous Green function formalism, which naturally
incorporates the color transparency and quantum coherence effects and hence
allows to estimate the nuclear shadowing with no restrictions on the CL. In
addition to the shadowing effect, we studied a complementary effect of initial
state interactions (ISI) that causes an additional suppression at large values
of the Feynman variable. Numerical results for the nuclear modification factor
accounting for the ISI effect and the finite are compared to the data
available from the fixed-target FNAL measurements and a good agreement has been
found. Besides, we present new predictions for the nuclear suppression as a
function of dilepton rapidity and invariant mass in the kinematic regions that
can be probed by the RHIC collider as well as by the planned AFTER@LHC and LHCb
fixed-target experiments.Comment: 14 pages, 10 figure
Theoretical uncertainties in exclusive electroproduction S-wave heavy quarkonia
In this work, we revise the conventional description of J/Psi(1S), Y(1S),
Psi'(2S) and Y'(2S) elastic photo- and electroproduction off a nucleon target
within the color dipole picture and carefully study various sources of
theoretical uncertainties in calculations of the corresponding
electroproduction cross sections. For this purpose, we test the corresponding
predictions using a bulk of available dipole cross section parametrisations
obtained from deep inelastic scattering data at HERA. Specifically, we provide
the detailed analysis of the energy and hard-scale dependencies of quarkonia
yields employing the comprehensive treatment of the quarkonia wave functions in
the Schroedinger equation based approach for a set of available c-\bar{c} and
b-\bar{b} interquark interaction potentials. Besides, we quantify the effect of
Melosh spin rotation, the Q^2-dependence of the diffractive slope and an
uncertainty due to charm and bottom quark mass variations.Comment: 43 pages of Latex including 29 figure
Spin rotation effects in diffractive electroproduction of heavy quarkonia
In this work we present for the first time the comprehensive study of the
Melosh spin rotation effects in diffractive electroproduction of S-wave heavy
quarkonia off a nucleon target. Such a study has been performed within the
color dipole approach using, as an example and a reference point, two popular
parametrizations of the dipole cross section and two potentials describing the
interaction between Q and bar{Q} and entering in the Schroedinger equation
based formalism for determination of the quarkonia wave functions. We find a
strong onset of spin rotation effects in 1S charmonium photoproduction which is
obviously neglected in present calculations of corresponding cross sections.
For photoproduction of radially excited Psi'(2S) these effects are even
stronger leading to an increase of the photoproduction cross section by a
factor of 2-3 depending on the photon energy. Even in production of radially
excited Y'(2S) and Y"(3S) they can not be neglected and cause the 20-30%
enhancement of the photoproduction cross section. Finally, we predict that the
spin effects vanish gradually with photon virtuality Q^2 following universality
properties in production of different heavy quarkonia as a function of Q^2 +
M_V^2.Comment: 23 pages of Latex including 10 figures. The version for resubmission
to European Physical Journal
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