2,864 research outputs found
Anomaly and Condensate in the Light-Cone Schwinger Model
The axial anomaly and fermion condensate in the light cone Schwinger model
are studied following path integral methods. This formalism allows for a simple
and direct calculation for these and other vacuum dependent phenomena.Comment: 10pp, Revte
On the dependence of the wave function of a bound nucleon on its momentum and the EMC effect
It is widely discussed in the literature that the wave function of the
nucleon bound in a nucleus is modified due to the interaction with the
surrounding medium. We argue that the modification should strongly depend on
the momentum of the nucleon. We study such an effect in the case of the
point-like configuration component of the wave function of a nucleon bound in a
nucleus A, considering the case of arbitrary final state of the spectator A-1
system. We show that for non relativistic values of the nucleon momentum, the
momentum dependence of the nucleon deformation appears to follow from rather
general considerations and discuss the implications of our theoretical
observation for two different phenomena: i) the search for medium induced
modifications of the nucleon radius of a bound nucleon through the measurement
of the electromagnetic nucleon form factors via the A(e,e'p)X process, and ii)
the A-dependence of the EMC effect; in this latter case we also present a new
method of estimating the fraction of the nucleus light-cone momentum carried by
the photons and find that in a heavy nuclei protons loose about 2% of their
momentum.Comment: 38 pages, 1 figure; changed references and text in Section I
(Introduction
High-Energy QCD Asymptotics of Photon-Photon Collisions
The high-energy behaviour of the total cross section for highly virtual
photons, as predicted by the BFKL equation at next-to-leading order (NLO) in
QCD, is discussed. The NLO BFKL predictions, improved by the BLM optimal scale
setting, are in good agreement with recent OPAL and L3 data at CERN LEP2. NLO
BFKL predictions for future linear colliders are presented.Comment: Latex, 7 pages, 4 figure
On BLM scale fixing in exclusive processes
We discuss the BLM scale fixing procedure in exclusive electroproduction
processes in the Bjorken regime. We show that in the case of vector meson
production the usual way to aplly the BLM method fails due to singularities
present in equations fixing the BLM scale. We argue that the BLM scale should
be extracted from the squared amplitudes which are directly related to
observables.Comment: accepted for the publication in Eur.Phys.J.
Propagation in the atmosphere of ultrahigh-energy charmed hadrons
Charmed mesons may be produced when a primary cosmic ray or the leading
hadron in an air shower collide with an atmospheric nucleon. At energies \ge
10^8 GeV their decay length becomes larger than 10 km, which implies that they
tend to interact in the air instead of decaying. We study the collisions of
long-lived charmed hadrons in the atmosphere. We show that (\Lambda_c,D)-proton
diffractive processes and partonic collisions of any q^2 where the charm quark
is an spectator have lower inelasticity than (p,\pi)-proton collisions. In
particular, we find that a D meson deposits in each interaction just around 55%
of the energy deposited by a pion. On the other hand, collisions involving the
valence c quark (its annihilation with a sea cbar quark in the target or
c-quark exchange in the t channel) may deposit most of D meson energy, but
their frequency is low (below 0.1% of inelastic interactions). As a
consequence, very energetic charmed hadrons may keep a significant fraction of
their initial energy after several hadronic interactions, reaching much deeper
in the atmosphere than pions or protons of similar energy.Comment: 13 pages, version to appear in PR
Vector meson - mixing and their form factors in light-cone quark model
The vector meson - mixing is studied in two alternative
scenarios with different numbers of mixing angles, i.e., the one-mixing-angle
scenario and the two-mixing-angle scenario, in both the octect-singlet mixing
scheme and the quark flavor mixing scheme. Concerning the reproduction of
experimental data and the behavior of transition form factors,
one-mixing-angle scenario in the quark flavor scheme performs better than that
in the octet-singlet scheme, while the two-mixing-angle scenario works well for
both mixing schemes. The difference between the two mixing angles in the
octet-singlet scheme is bigger than that in the quark flavor scheme.Comment: 16 pages, 7 figures, final version to appear in PR
High Energy Photon-Photon Collisions at a Linear Collider
High intensity back-scattered laser beams will allow the efficient conversion
of a substantial fraction of the incident lepton energy into high energy
photons, thus significantly extending the physics capabilities of an
electron-electron or electron-positron linear collider. The annihilation of two
photons produces C=+ final states in virtually all angular momentum states. The
annihilation of polarized photons into the Higgs boson determines its
fundamental two-photon coupling as well as determining its parity. Other novel
two-photon processes include the two-photon production of charged lepton pairs,
vector boson pairs, as well as supersymmetric squark and slepton pairs and
Higgstrahlung. The one-loop box diagram leads to the production of pairs of
neutral particles. High energy photon-photon collisions can also provide a
remarkably background-free laboratory for studying possibly anomalous
collisions and annihilation. In the case of QCD, each photon can materialize as
a quark anti-quark pair which interact via multiple gluon exchange. The
diffractive channels in photon-photon collisions allow a novel look at the QCD
pomeron and odderon. Odderon exchange can be identified by looking at the heavy
quark asymmetry. In the case of electron-photon collisions, one can measure the
photon structure functions and its various components. Exclusive hadron
production processes in photon-photon collisions test QCD at the amplitude
level and measure the hadron distribution amplitudes which control exclusive
semi-leptonic and two-body hadronic B-decays.Comment: Invited talk, presented at the 5th International Workshop On
Electron-Electron Interactions At TeV Energies, Santa Cruz, California, 12-14
December 200
New nuclear three-body clusters \phi{NN}
Binding energies of three-body systems of the type \phi+2N are estimated. Due
to the strong attraction between \phi-meson and nucleon, suggested in different
approaches, bound states can appear in systems like \phi+np (singlet and
triplet) and \phi+pp. This indicates the principal possibility of the formation
of new nuclear clusters
- …