Dennis Sivers

Kane-Pumplin-Repko Factorization: its application to precision measurements of transverse spin asymmetries and to the study of TMD evolution.

This article presents a summary of overlapping presentations by the author to the QCD Evolution 2013 Workshop (Jefferson Lab, May 6-10, 2013) and to the Opportunities for Polarized Physics at Fermilab workshop (Fermilab, May 20-22, 2013). It contains an introduction to the concept of Kane-Pumplin-Repko (KPR) factorization and describes how this concept can be used in the analysis of high precision measurements of parity-conserving transverse single-spin asymmetries. The discussion demonstrates that such measurements can not only probe directly for specific mechanisms that enhance our fundamental understanding of nonperturbative QCD dynamics but, because transverse spin asymmetries are unambiguously parameterized by a spin-directed momentum shift, 2 (, ) TN kx δ μ , such measurements can also be used to calibrate other phenomenological applications of transverse momentum dependent distributions (TMD’s) and of TMD evolution. The calibration supplied by these measurements can thus enable the use of TMD factorization for the exploration of a broad range of other aspects of hadronic structure. KPR factorization ensures that 2 (, ) TN kx δ μ remains invariant under TMD evolution and this invariance can be used in the precision comparison of transverse single-spin asymmetries in the Drell-Yan process with those in Semi-inclusive deep inelastic scattering.

Fractured Boer-Mulders effect in the production of polarized baryons

The fractured Boer-Mulders functions, {Delta}{sup N}M{sub B{up_arrow}/(q,q){up_arrow}:p}{sup q}(x,p{sub TN};z,p-vector{sub T{center_dot}}k-vector{sub T};Q{sup 2}), describe an intriguing class of polarization effects for the production of baryons in the target fragmentation region of deep-inelastic processes. These functions characterize transverse momentum asymmetries related to the spin orientation for different flavors of axial-vector diquarks,(q{sub i},q{sub j}){up_arrow}, in an unpolarized ensemble of protons just as the familiar Boer-Mulders functions characterize transverse momentum asymmetries connected to the spin orientation of quarks in unpolarized targets. The asymmetries in p{sub TN} of the fractured Boer-Mulders effect originating in the proton distribution function can be separated kinematically, both in semi-inclusive deep-inelastic scattering and in the Drell-Yan process, from the asymmetries in k{sub TN} of the polarizing fracture functions, {Delta}{sup N}M{sub B{up_arrow}/(q,q):p}{sup q}(x,p{sub T}{sup 2};z,k{sub TN};Q{sup 2}), generated during the soft color rearrangement of the fragmentation process. The experimental requirements for this separation are presented in this article and it is shown that the fractured Boer-Mulders effect should change sign between Drell-Yan and semi-inclusive deep-inelastic scattering while the polarizing fracture functions remain the same. Simple isospin arguments indicate the two polarization mechanisms should give significantly different results for the production of polarized {Lambda}s and {Sigma}s.

Factorization prescriptions and phenomenological applications of the parton model

Abstract We discuss the arbitrary conventions involved in formulating the QCD-aided parton model. The precise definition of constituent distribution and decay functions is seen to involve the choice of a factorization prescription. Just as in the case of a renormalization prescription, the choice of a factorization prescription can have phenomenological impact in that it can dramatically affect the size of higher-order corrections to calculations of physical observables. We present criteria based on next-to-leading order calculations for defining nonsinglet quark distributions. These can be seen to agree, in the appropriate limits, with speculations based on the resumming of certain “large” logarithmic corrections. We give a form of the Altarelli-Parisi equation suitable for directly calculating the evolution of a measurable structure function such as F2(x, Q2).

Quantum Number Density Asymmetries Within QCD Jets Correlated With Lambda Polarization

The observation of jets in a variety of hard-scattering processes has allowed the quantitative study of perturbative quantum chromodynamics (PQCD) by comparing detailed theoretical predictions with a wide range of experimental data. This paper examines how some important, nonperturbative, facets of QCD involving the internal dynamical structure of jets can be studied by measuring the spin orientation of Lambda particles produced in these jets. The measurement of the transverse polarization for an individual Lambda within a QCD jet permits the definition of spin-directed asymmetries in local quantum number densities in rapidity space (such as charge, strangeness and baryon number densities) involving neighboring hadrons in the jet. These asymmetries can only be generated by soft, nonperturbative dynamical mechanisms and such measurements can provide insight not otherwise accessible into the color rearrangement that occurs during the hadronization stage of the fragmentation process.

Quark mobility in extended nuclear matter

Abstract The propagation of an energetic quark through extended nuclear matter is analyzed in terms of a simple model in which localization of color is imposed through chromoelectric flux tubes. A mobile quark in the nuclear medium creates a disturbance which affects neighboring nucleons. The model suggests that the spatial properties of the disturbance involve a competition among different dynamical mechanisms. Experimental measurements involving the target fragmentation region in deep-inelastic leptoproduction on large nuclei may help specify some of the important features of nuclear dynamics.

High‐PT theory in a spin

The role of measurements using polarized hadron beams or polarized targets is discussed. Future experiments can be compared with explicit calculations to provide tests of QCD.

Transverse spin observables in hadron‐hadron and hadron‐nucleus collisions*

Transverse, single‐spin asymmetries offer a chance to test QCD at the level of ‘‘twist‐3’’ observables. Early suggestions that such asymmetries necessarily vanish as mq→0 or involve an extra power of αs can be refuted with a simple example. Recent experimental results support the interpretation of these data in hard‐scattering QCD. The asymmetry in the scattering on nuclear targets can provide new, nontrivial information the space‐time structure of the interaction.

RITES OF SPIN

Some simple examples which deal with spin degrees of freedom in gauge theories are examined for clues concerning the role of spin in formulating new theoretical ideas.

Classical behavior in high temperature chromodynamics

A classical chromodynamic approach to the description of high temperature hadronic matter is discussed. (AIP)

Polarizable Media in Classical Gluodynamics and the SU2 Vacuum

The description of a polarizable medium, interacting with non-Abelian gauge fields can be formulated in a simple, gaugeinvariant manner. Working with a Euclidean-space version of an SU2 gauge-theory, we find a solution to the resulting field equations with “vacuun-like” properties: 1. E i a B i a =0 2. E i a E i a + B i a B i a constant 3. Area law behavior for Wilson loops formed from the classical fields.