243 research outputs found
Neutrino Dimuon Production and the Strangeness Asymmetry of the Nucleon
We have performed the first global QCD analysis to include the CCFR and NuTeV
dimuon data, which provide direct constraints on the strange and anti-strange
parton distributions, and . To explore the strangeness
sector, we adopt a general parametrization of the non-perturbative functions satisfying basic QCD requirements. We find that the
strangeness asymmetry, as represented by the momentum integral , is sensitive to the dimuon data provided the
theoretical QCD constraints are enforced. We use the Lagrange Multiplier method
to probe the quality of the global fit as a function of and find
. Representative parton distribution sets spanning this
range are given. Comparisons with previous work are made.Comment: 23 pages, 4 figures; expanded version for publicatio
Tau Polarization in Tau-Neutrino Nucleon Scattering
We investigate the spin polarization of \tau^{\pm} leptons produced in
\nu_{\tau} and \bar{\nu}_{\tau} nucleon scattering via charged currents.
Quasi-elastic scattering, \Delta resonance production and deep inelastic
scattering processes are studied. The polarization information is essential for
measuring the \tau^{\pm} appearance rate in long baseline neutrino oscillation
experiments, because the decay particle distributions depend crucially on the
\tau^{\pm} spin. In this article, we calculate the spin density matrix of each
process and estimate the spin polarization vector in medium and high neutrino
energy interactions. We find that the produced \tau^{\pm}'s have high degree of
polarization, and their spin direction depends non-trivially on the energy and
the scattering angle of \tau^{\pm} in the laboratory frame.Comment: 23 pages, 35 figures; compile errors corrected; notation errors in
Eq.(30) and (31) corrected, typo error in Eq.(40) corrected, references and
comments in footnote adde
Heavy Quark Production and PDF's Subgroup Report
We present a status report of a variety of projects related to heavy quark
production and parton distributions for the Tevatron Run II.Comment: Latex. 8 pages, 7 eps figures. Contribution to the Physics at Run II
Workshops: QCD and Weak Boson Physic
On The Injection Spectrum of Ultrahigh Energy Cosmic Rays in the Top-Down Scenario
We analyze the uncertainties involved in obtaining the injection spectra of
UHECR particles in the top-down scenario of their origin. We show that the
DGLAP evolution of fragmentation functions (FF) to (mass of the X
particle) from their initial values at low is subject to considerable
uncertainties. We therefore argue that, for x\lsim 0.1 (the region of
interest for most large values of interest, being the
scaled energy variable), the FF obtained from DGLAP evolution is no more
reliable than that provided, for example, by a simple Gaussian form (in the
variable ) obtained under the Modified Leading Log Approximation
(MLLA). Additionally, we find that for x\gsim0.1, the evolution in of
the singlet FF, which determines the injection spectrum, is ``minimal'' -- the
singlet FF changes by barely a factor of 2 after evolving it over 14
orders of magnitude in . We, therefore, argue that as long as the
measurement of the UHECR spectrum above \sim10^{20}\ev is going to remain
uncertain by a factor of 2 or larger, it is good enough for most practical
purposes to directly use any one of the available initial parametrisations of
the FFs in the region x\gsim0.1 based on low energy data even without
evolving them to the requisite value.Comment: Minor changes, added a reference, version to appear in Phys. Rev.
Microcanonical Jet-fragmentation in proton-proton collisions at LHC Energy
In this paper, we show that the distribution of the longitudinal momentum
fraction of charged hadrons inside jets stemming from proton-proton
collisions at = 7 TeV center of mass energy can be described by a
statistical jet-fragmentation model. This model combines microcanonical
statistics and super-statistics induced by multiplicity fluctuations. The
resulting scale dependence of the parameters of the model turns out to be
similar to what was observed in electron-positron annihilations in Urmossy,
Barnaf\"oldi, and Bir\'o.Comment: 7 pages, 8 figure
Variation of jet quenching from RHIC to LHC and thermal suppression of QCD coupling constant
We perform a joint jet tomographic analysis of the data on the nuclear
modification factor from PHENIX at RHIC and ALICE at LHC. The
computations are performed accounting for radiative and collisional parton
energy loss with running coupling constant. Our results show that the observed
slow variation of from RHIC to LHC indicates that the QCD coupling
constant is suppressed in the quark-gluon plasma produced at LHC.Comment: 9 pages, 2 figure
Can the polarization of the strange quarks in the proton be positive ?
Recently, the HERMES Collaboration at DESY, using a leading order QCD
analysis of their data on semi-inclusive deep inelastic production of charged
hadrons, reported a marginally positive polarization for the strange quarks in
the proton. We argue that a non-negative polarization is almost impossible.Comment: 6 pages, latex, minor changes in the discussion after Eq. (9
Higher Twist, Scaling, and Effective for Lepton Scattering in the Few GeV Region
We use a new scaling variable , and add low modifications to
GRV98 leading order parton distribution functions such that they can be used to
model electron, muon and neutrino inelastic scattering cross sections (and also
photoproduction) at both very low and high energies.Comment: 6 pages, 3 figures. To be published in J. Phys. G (Conf. Proceedings)
based on two talks by Arie Bodek at the NuFact conference, Imperial
College, London, England, July 200
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