1,291 research outputs found
A model for the parton distributions in hadrons
A simple model is presented for the parton distributions in hadrons. The
parton momenta in the hadron rest frame are derived from a spherically
symmetric, Gaussian, distribution having a width motivated by the Heisenberg
uncertainty relation applied to the hadron size. Valence quarks and gluons
originate from the `bare' hadron, while sea partons arise mainly from pions in
hadronic fluctuations. Starting from a low Q^2 scale, the distributions are
evolved with next-to-leading order DGLAP and give the proton structure function
F2(x,Q^2) in good agreement with deep inelastic scattering data.Comment: 12 pages, Latex, 5 figures. Added discussion on the applicability of
the model at small Q^2. Figure 3 modified to show smaller Q^
The Photon Structure Function at Small-x
It is shown that recent small-x measurements of the photon structure function
F_2^{\gamma}(x,Q^2) by the LEP-OPAL collaboration are consistent with
parameter-free QCD predictions at all presently accessible values of Q^2.Comment: 7 pages, LaTeX, 2 figure
Leading logarithm calculation of the e^+ e^- -> e^+ \nu_e \bar{u} d cross section
We analytically evaluate in the leading logarithm approximation the
differential cross section for e^+ e^- -> e^+ \nu_e \bar{u} d. We compare our
order \alpha^4 \alpha_s^0 leading-log result to the order \alpha^4 \alpha_s^0
exact result obtained from the GRC4F Monte Carlo program. Finally we use the
Gluck, Reya, Schienbien distribution of partons in a virtual photon, which
incorporates both evolution and nonperturbative strong interaction
contributions, to obtain better estimates of the differential cross section.Comment: 10 pages including 9 figure
Has the QCD RG-Improved Parton Content of Virtual Photons been Observed?
It is demonstrated that present and DIS ep data on the structure of
the virtual photon can be understood entirely in terms of the standard `naive'
quark--parton model box approach. Thus the QCD renormalization group (RG)
improved parton distributions of virtual photons, in particular their gluonic
component, have not yet been observed. The appropriate kinematical regions for
their future observation are pointed out as well as suitable measurements which
may demonstrate their relevance.Comment: 24 pages, LaTeX, 5 figure
Heavy Quark Initiated Contributions to Deep Inelastic Structure Functions
We present O(alpha_s^1) corrections to deep inelastic scattering amplitudes
on massive quarks obtained within the scheme of Aivazis, Collins, Olness and
Tung (ACOT). After identifying the correct subtraction term the convergence of
these contributions towards the analogous coefficient functions for massless
quarks, obtained within the modified minimal subtraction scheme (MSbar), is
demonstrated. Furthermore, the quantitative relevance of the contributions to
neutral current (NC) and charged current (CC) structure functions is
investigated for several choices of the factorization scale.Comment: 29 pages, 6 figures; uses epsfig.sty, amssymb.sty, axodraw.sty; minor
changes for publication in Phys. Rev.
Longitudinally Polarized Photoproduction of Inclusive Hadrons Beyond the Leading Order
We present a complete next-to-leading order QCD calculation for
single-inclusive large-pT hadron production in longitudinally polarized
lepton-nucleon collisions, consistently including ``direct'' and ``resolved''
photon contributions. This process could be studied experimentally at a future
polarized lepton-proton collider like eRHIC at BNL. We examine the sensitivity
of such measurements to the so far completely unknown parton content of
circularly polarized photons.Comment: 15 pages, 7 eps figure
Models for Photon-photon Total Cross-sections
We present here a brief overview of recent models describing the
photon-photon cross-section into hadrons. We shall show in detail results from
the eikonal minijet model, with and without soft gluon summation.Comment: 7 pages, 5 figures, laTeX, requires espcrc2.sty. To appear in the
Proceedings of Photon-99, Freiburg, 23 -27 May 99, labels in the figures
1,3,4,5 corrected, one typo in an equation correcte
Impact of Neutron Decay Experiments on non-Standard Model Physics
This paper gives a brief overview of the present and expected future limits
on physics beyond the Standard Model (SM) from neutron beta decay, which is
described by two parameters only within the SM. Since more than two observables
are accessible, the problem is over-determined. Thus, precise measurements of
correlations in neutron decay can be used to study the SM as well to search for
evidence of possible extensions to it. Of particular interest in this context
are the search for right-handed currents or for scalar and tensor interactions.
Precision measurements of neutron decay observables address important open
questions of particle physics and cosmology, and are generally complementary to
direct searches for new physics beyond the SM in high-energy physics. Free
neutron decay is therefore a very active field, with a number of new
measurements underway worldwide. We present the impact of recent developments.Comment: 13 pages, 6 figures; Proceedings of the 5th International BEYOND 2010
Conference, Cape Town, South Africa (2010), World Scientific, accepted for
publication; Corrected typo
Threshold resummation for the prompt-photon cross section revisited
We study the resummation of large logarithmic perturbative corrections to the
partonic cross sections relevant for the process pp->gamma X at high transverse
momentum of the photon.These corrections arise near the threshold for the
partonic reaction and are associated with soft-gluon emission. We especially
focus on the resummation effects for the contribution to the cross section
where the photon is produced in jet fragmentation. Previous calculations in
perturbation theory at fixed-order have established that this contribution is a
subdominant part of the cross section. We find, however, that it is subject to
much larger resummation effects than the direct (non-fragmentation) piece and
therefore appears to be a significant contribution in the fixed-target regime,
not much suppressed with respect to the direct part. Inclusion of threshold
resummation for the fragmentation piece leads to some improvement in
comparisons between theoretical calculations and experimental data.Comment: 12 pages, 5 figure
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