1,181 research outputs found
Testing Color Evaporation in Photon-Photon Production of J/Psi at CERN LEP II
The DELPHI Collaboration has recently reported the measurement of J/Psi
production in photon-photon collisions at LEP II. These newly available data
provide an additional proof of the importance of colored c bar{c} pairs for the
production of charmonium because these data can only be explained by
considering resolved photon processes. We show here that the inclusion of color
octet contributions to the J/Psi production in the framework of the color
evaporation model is able to reproduce this data. In particular, the
transverse-momentum distribution of the J/Psi mesons is well described by this
model.Comment: 10 pages, 5 Figures, Revtex
Interaction of small size wave packet with hadron target
We calculate in QCD the cross section for the scattering of an energetic
small-size wave packet off a hadron target. We use our results to study the
small- behaviour of , the distribution over cross
section for the pion, in the leading -order.Comment: Revised version of the report CEBAF-TH-96-0
Leading Chiral Contributions to the Spin Structure of the Proton
The leading chiral contributions to the quark and gluon components of the
proton spin are calculated using heavy-baryon chiral perturbation theory.
Similar calculations are done for the moments of the generalized parton
distributions relevant to the quark and gluon angular momentum densities. These
results provide useful insight about the role of pions in the spin structure of
the nucleon, and can serve as a guidance for extrapolating lattice QCD
calculations at large quark masses to the chiral limit.Comment: 8 pages, 2 figures; a typo in Ref. 7 correcte
A GLOBAL QCD STUDY OF DIRECT PHOTON PRODUCTION
A global QCD analysis of the direct photon production process from both fixed
target and collider experiments is presented. These data sets now completely
cover the parton range from 0.01 to 0.6, thereby providing a stringent test
of perturbative QCD and parton distributions. Previous detailed studies of
direct photons emphasized fixed target data. We find most data sets have a
steeper distribution than the QCD prediction. Neither global fits with
new parton distributions nor improved photon fragmentation functions can
resolve this problem since the deviation occurs at different values for
experiments at different energies. A more likely explanation is the need for
additional broadening of the of the initial state partons. The magnitude
and the possible physical origin of this effect are investigated and discussed.Comment: 8 page Latex file using epsf.sty for figures. 6 eps figures submitted
separately in uuencoded file
Comparison of -Factorization Approach and QCD Parton Model for Charm and Beauty Hadroproduction
We compare the numerical predictions for heavy quark production in high
energy hadron collisions of the conventional QCD parton model and the
-factorization approach (semihard theory). The total production cross
sections, one-particle rapidity and distributions as well as two-particle
correlations are considered. The difference in the predictions of the two
approaches is not very large, while the shapes of the distributions are
slightly different.Comment: 16 pages, LaTeX, + 16 PostScript figure
Asymptotics and local constancy of characters of p-adic groups
In this paper we study quantitative aspects of trace characters
of reductive -adic groups when the representation varies. Our approach
is based on the local constancy of characters and we survey some other related
results. We formulate a conjecture on the behavior of relative to
the formal degree of , which we are able to prove in the case where
is a tame supercuspidal. The proof builds on J.-K.~Yu's construction and the
structure of Moy-Prasad subgroups.Comment: Proceedings of Simons symposium on the trace formul
The Leading Particle Effect from Heavy-Quark Recombination
The leading particle effect in charm hadroproduction is an enhancement of the
cross section for a charmed hadron D in the forward direction of the beam when
the beam hadron has a valence parton in common with the D. The large D+/D-
asymmetry observed by the E791 experiment is an example of this phenomenon. We
show that the heavy-quark recombination mechanism provides an economical
explanation for this effect. In particular, the D+/D- asymmetry can be fit
reasonably well using a single parameter whose value is consistent with a
recent determination from charm photoproduction.Comment: Revtex file, 4 pages, 3 figure
Small representations of finite classical groups
Finite group theorists have established many formulas that express
interesting properties of a finite group in terms of sums of characters of the
group. An obstacle to applying these formulas is lack of control over the
dimensions of representations of the group. In particular, the representations
of small dimensions tend to contribute the largest terms to these sums, so a
systematic knowledge of these small representations could lead to proofs of
important conjectures which are currently out of reach. Despite the
classification by Lusztig of the irreducible representations of finite groups
of Lie type, it seems that this aspect remains obscure. In this note we develop
a language which seems to be adequate for the description of the "small"
representations of finite classical groups and puts in the forefront the notion
of rank of a representation. We describe a method, the "eta correspondence", to
construct small representations, and we conjecture that our construction is
exhaustive. We also give a strong estimate on the dimension of small
representations in terms of their rank. For the sake of clarity, in this note
we describe in detail only the case of the finite symplectic groups.Comment: 18 pages, 9 figures, accepted for publications in the proceedings of
the conference on the occasion of Roger Howe's 70th birthday (1-5 June 2015,
Yale University, New Haven, CT
ExTrA: Exoplanets in Transit and their Atmospheres
The ExTrA facility, located at La Silla observatory, will consist of a
near-infrared multi-object spectrograph fed by three 60-cm telescopes. ExTrA
will add the spectroscopic resolution to the traditional differential
photometry method. This shall enable the fine correction of color-dependent
systematics that would otherwise hinder ground-based observations. With both
this novel method and an infrared-enabled efficiency, ExTrA aims to find
transiting telluric planets orbiting in the habitable zone of bright nearby M
dwarfs. It shall have the versatility to do so by running its own independent
survey and also by concurrently following-up on the space candidates unveiled
by K2 and TESS. The exoplanets detected by ExTrA will be amenable to
atmospheric characterisation with VLTs, JWST, and ELTs and could give our first
peek into an exo-life laboratory.Comment: 15 pages, 11 figures, SPIE 201
Next-to-leading order QCD corrections to one hadron-production in polarized pp collisions at RHIC
We calculate the next-to-leading order QCD corrections to the spin-dependent
cross section for single-inclusive hadron production in hadronic collisions.
This process will be soon studied experimentally at RHIC, providing a tool to
unveil the polarized gluon distribution . We observe a considerably
improvement in the perturbative stability for both unpolarized and polarized
cross sections. The NLO corrections are found to be non-trivial, resulting in a
reduction of the asymmetry.Comment: 8 pages, RevTeX4, 9 figures include
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