5,480 research outputs found
Fragmentation, NRQCD and Factorization in Heavy Quarkonium Production
We discuss factorization in heavy quarkonium production in high energy
collisions using NRQCD. Infrared divergences at NNLO are not matched by
conventional NRQCD matrix elements. However, we show that gauge invariance and
factorization require that conventional NRQCD production matrix elements be
modified to include Wilson lines or non-abelian gauge links. With this
modification NRQCD factorization for heavy quarkonium production is restored at
NNLO.Comment: 3pages Latex, 3eps figures, Talk given by G. C. Nayak at PANIC05
Santa Fe, NM, USA, October 24-28, 200
NRQCD Factorization and Velocity-dependence of NNLO Poles in Heavy Quarkonium Production
We study the transition of a heavy quark pair from octet to singlet color
configurations at next-to-next-to-leading order (NNLO) in heavy quarkonium
production. We show that the infrared singularities in this process are
consistent with NRQCD factorization to all orders in the heavy quark relative
velocity v. This factorization requires the gauge-completed matrix elements
that we introduced previously to prove NNLO factorization to order v ^2.Comment: 23pages latex, 2 figure
Probing Gluonic Spin-Orbit Correlations in Photon Pair Production
We consider photon pair production in hadronic collisions at large mass and
small transverse momentum of the pair, assuming that factorization in terms of
transverse momentum dependent parton distributions applies. The unpolarized
cross section is found to have azimuthal angular dependencies that are
generated by a gluonic version of the Boer-Mulders function. In addition, the
single-transversely polarized cross section is sensitive to the gluon Sivers
function. We present simple numerical estimates for the Boer-Mulders and Sivers
effects in diphoton production at RHIC and find that the process would offer
unique opportunities for exploring transverse momentum dependent gluon
distributions.Comment: 5 pages, 2 figures, minor changes, final version, to be published in
PR
Toolbox for entanglement detection and fidelity estimation
The determination of the state fidelity and the detection of entanglement are
fundamental problems in quantum information experiments. We investigate how
these goals can be achieved with a minimal effort. We show that the fidelity of
GHZ and W states can be determined with an effort increasing only linearly with
the number of qubits. We also present simple and robust methods for other
states, such as cluster states and states in decoherence-free subspaces.Comment: 5 pages, no figures, v3: final version, to appear as a Rapid
Communication in PR
k_T factorization is violated in production of high-transverse-momentum particles in hadron-hadron collisions
We show that hard-scattering factorization is violated in the production of
high-p_T hadrons in hadron-hadron collisions, in the case that the hadrons are
back-to-back, so that k_T factorization is to be used. The explicit
counterexample that we construct is for the single-spin asymmetry with one beam
transversely polarized. The Sivers function needed here has particular
sensitivity to the Wilson lines in the parton densities. We use a greatly
simplified model theory to make the breakdown of factorization easy to check
explicitly. But the counterexample implies that standard arguments for
factorization fail not just for the single-spin asymmetry but for the
unpolarized cross section for back-to-back hadron production in QCD in
hadron-hadron collisions. This is unlike corresponding cases in e^+e^-
annihilation, Drell-Yan, and deeply inelastic scattering. Moreover, the result
endangers factorization for more general hadroproduction processes.Comment: 10 pages. V. 2: Title change, misprints and minor corrections, as in
journal versio
One-dimensional Ising model built on small-world networks: competing dynamics
In this paper, we offer a competing dynamic analysis of the one-dimensional
Ising model built on the small-world network (SWN). Adding-type SWNs are
investigated in detail using a simplified Hamiltonian of mean-field nature, and
the result of rewiring-type is given because of the similarities of these two
typical networks. We study the dynamical processes with competing Glauber
mechanism and Kawasaki mechanism. The Glauber-type single-spin transition
mechanism with probability p simulates the contact of the system with a heat
bath and the Kawasaki-type dynamics with probability 1-p simulates an external
energy flux. By studying the phase diagram obtained in the present work, we can
realize some dynamical properties influenced by the small-world effect.Comment: 5 pages, one figure, accepted for publication in Physical Review
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