1,881 research outputs found
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.
Partonic calculation of the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer
We estimate the two-photon exchange contribution to elastic electron-proton
scattering at large momentum transfer through the scattering off a parton in
the proton. We relate the process on the nucleon to the generalized parton
distributions which also enter in other wide angle scattering processes. We
find that when taking the polarization transfer determinations of the form
factors as input, adding in the 2 photon correction, does reproduce the
Rosenbluth data.Comment: 4 pages, 4 figure
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
Theoretical Uncertainties in Gamma_sl(b->u)
I review the existing theoretical uncertainties in relating the semileptonic
decay width in b->u transitions to the underlying Kobayashi-Maskawa mixing
element |V_ub|. The theoretical error bars are only a few percent in |V_ub|,
with uncertainties from the impact of the nonperturbative effects nearly
negligible.Comment: 12 pages, LaTeX; discussion of 1/m_b^3 effects is expanded.
Contribution to Workshop on the Derivation of |V_cb| and |V_ub|: Experimental
Status and Theory Uncertainties, CERN, May 28 - June 2, 199
The half-filled Landau level - composite fermions and dipoles
The composite-fermion approach as formulated in the fermion Chern-Simons
theory has been very successful in describing the physics of the lowest Landau
level near Landau level filling factor 1/2. Recent work has emphasized the fact
that the true quasiparticles at these filling factors are electrically neutral
and carry an electric dipole moment. In a previous work, we discussed at length
two formulations in terms of dipolar quasiparticles. Here we briefly review one
approach - termed electron-centered quasiparticles - and show how it can be
extended from 1/2 to nearby filling factors where the quasiparticles carry both
an electric dipole moment and an overall charge.Comment: 10 pages, minor improvements of notation and referencin
Gluon Virtuality and Heavy Sea Quark Contributions to the Spin-Dependent g_1 Structure Function
We analyze the quark mass dependence of photon gluon fusion in polarized deep
inelastic scattering for both the intrinsic and extrinsic gluon distributions
of the nucleon. We calculate the effective number of flavors for each of the
heavy and light quark photon gluon fusion contributions to the first moment of
the spin-dependent structure function .Comment: LaTex, 19 page
Non-Abelian Dipole Radiation and the Heavy Quark Expansion
Dipole radiation in QCD is derived to the second order in . A
power-like evolution of the spin-singlet heavy quark operators is obtained to
the same accuracy. In particular, relation between a
short-distance low-scale running heavy quark mass and the \barMS mass is
given. We discuss the properties of the effective QCD coupling \aw(E) which
governs the dipole radiation. This coupling is advantageous for heavy quark
physics.Comment: 12 pages, Late
Ultimate parameters of the photon collider at the ILC
At linear colliders, the e+e- luminosity is limited by beam-collision
effects, which determine the required emittances of beams in damping rings
(DRs). While in gamma-gamma collisions at the photon collider, these effects
are absent, and so smaller emittances are desirable. In present damping rings
designs, nominal DR parameters correspond to those required for e+e-
collisions. In this note, I would like to stress once again that as soon as we
plan the photon-collider mode of ILC operation, the damping-ring emittances are
dictated by the photon-collider requirements--namely, they should be as small
as possible. This can be achieved by adding more wigglers to the DRs; the
incremental cost is easily justified by a considerable potential improvement of
the gamma-gamma luminosity. No expert analysis exists as of yet, but it seems
realistic to obtain a factor five increase of the gamma-gamma luminosity
compared to the ``nominal'' DR design.Comment: Talk at LCWS06, Bangalore, India, March 2006, to be published in
Indian Journal of Physics, 5 pp, Latex, 1 .eps figur
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