207 research outputs found
The role of heavy quarks in light hadron fragmentation
We investigate the role of heavy quarks in the production of light flavored
hadrons and in the determination of the corresponding non perturbative
hadronization probabilities. We define a general mass variable flavor number
scheme for fragmentation functions that accounts for heavy quark mass effects,
and perform a global QCD analysis to an up-to-date data set including very
precise Belle and BaBar results. We show that the mass dependent picture
provides a much more accurate and consistent description of data.Comment: 5 pages, 3 eps figure
Massive relic neutrinos in the galactic halo and the knee in the cosmic ray spectrum
Despite many efforts to find a reasonable explanation, the origin of the
"knee" in the cosmic ray spectrum at energy around 10**15.5 eV remains
mysterious. In this letter we suggest that the "knee" may be due to a GZK-like
effect of cosmic rays interacting with massive neutrinos in the galactic halo.
Simple kinematics connects the location of the "knee" with the mass of the
neutrinos, and, while the required interaction cross section is larger than
that predicted by the Standard Model, it can be accommodated by a small
neutrino magnetic dipole moment. The values for the neutrino parameters
obtained from the analysis of existing experimental data are compatible with
present laboratory bounds.Comment: 8 pages, 1 figure, uses RevTe
Global extraction of the parton-to-pion fragmentation functions at NLO accuracy in QCD
In this review, we discuss the results on the parton-to-pion fragmentation
functions obtained in a combined NLO fit to data of single-inclusive hadron
production in electron-positron annihilation, proton-proton collisions, and
lepton-nucleon deep-inelastic scattering. A more complete discussion can be
found in Ref. [1].Comment: 6 pages, 1 figure. To be published in Journal of Physics Conference
Series (IOP). Joint Proceedings of the XV Mexican Workshop on Particles and
Fields & the XXX Annual Meeting of the Division of Particles and Fields of
the Mexican Physical Societ
Quark-Antiquark Potential and Generalized Borel Transform
The heavy quark potential and particularly the one proposed by Richardson to
incorporate both asymptotic freedom and linear confinement is analyzed in terms
of a generalized Borel Transform recently proposed. We were able to obtain, in
the range of physical interest, an approximate analytical expression for the
potential in coordinate space valid even for intermediate distances. The
deviation between our approximate potential and the numerical evaluation of the
Richardson's one is much smaller than of QCD. The
and quarkonia energy levels agree reasonably well with
experimental data for and masses in good agreement with the values
obtained from experiments.Comment: 9 pages, 3 Tabl
Hadronic interactions models beyond collider energies
Studies of the influence of different hadronic models on extensive air
showers at ultra-high energies are presented. The hadronic models considered
are those implemented in the well-known QGSJET and SIBYLL event generators. The
different approaches used in both codes to model the underlying physics is
analyzed using computer simulations performed with the program AIRES. The most
relevant observables for both single collisions and air showers are studied for
primary energies ranging from eV up to eV. In addition,
the evolution of lateral and energy distributions during the shower development
is presented. Our analysis seems to indicate that the behaviour of shower
observables does not largely reflect the strong differences observed in single
collisions.Comment: 31 RevTex pages - 14 ps figure
Right handed currents and FSI phases in B^0 --> \phi K^{*0}
We consider possible effects of New Physics (NP) on the angular distributions
of the decay B^0 --> \phi K^{*0}, showing how these effects depend on the
nature of nonstandard interactions. In a general framework based on
factorization, we show that triple products can be used to probe the chirality
of NP currents. In this analysis we take into account the presence of
non-vanishing strong phases, which is motivated by recent experimental
evidence. It is seen that the observability of right-handed NP is strongly
dependent on the relation between the relative magnitude of these phases and
the ratio of Standard Model and NP scales. As an application we estimate the
expected values of relevant observables in a particular Left Right Symmetric
Model.Comment: 16 pages, no figures. Comments and references added, conclusions
unchanged. Final version to appear in Phys. Rev.
Comment on "On the Origin of the Highest Energy Cosmic Rays"
We show that the photodisintegration of heavy cosmic ray nuclei with energies
above 10^20 eV is dominated by interactions with photons from the cosmic
microwave background radiation, rather than from infrared ones. This implies
that the observed air shower events with energies 2-3 10^20 eV cannot originate
from Fe nuclei coming from distances beyond 10 MpcComment: 1 page, 2 figure
Tensor-force effects and a new N-N separable potential in the 3-N system
The considerable amount of work already done in connection with the three-nucleon problem allows us to assert that the low-energy properties of this system can be reasonably well described using separable two-body interactions.Facultad de Ciencias Exacta
Bound-state energy of a three-boson system
We are reporting here the results of some calculations made with Faddeev equations for the simplest three-body system: the nonrelativistic three-boson system. Our aim is to study the J= 0 bound-state energy spectrum of the system formed by three structureless alpha-particles (α) and compare it as a reference with the low-lying J = 0 states of the nucleus 12C(2). The nuclear interaction between the alphas is represented by pair-wise (Vαα) nonlocal separable potentials. We are, therefore, mainly concerned with the comparison of the different descriptions of the low-energy properties of the 3α system as obtained with different nuclear potentials Vαα.Facultad de Ciencias Exacta
Generalized Borel Transform Technique in Quantum Mechanics
We present the Generalized Borel Transform (GBT). This new approach allows
one to obtain approximate solutions of Laplace/Mellin transform valid in both,
perturbative and non perturbative regimes. We compare the results provided by
the GBT for a solvable model of quantum mechanics with those provided by
standard techniques, as the conventional Borel sum, or its modified versions.
We found that our approach is very efficient for obtaining both the low and the
high energy behavior of the model.Comment: 13 pages, 2 figure
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