Spin in Particle Physics

Abstract

Motivated by recent dramatic developments in the field, this book provides a thorough introduction to spin and its role in elementary particle physics. Starting with a simple pedagogical introduction to spin and its relativistic generalisation, the author successfully avoids the obscurity and impenetrability of traditional treatments of the subject. The book surveys the main theoretical and experimental developments, as well as discussing exciting plans for the future. Emphasis is placed on the importance of spin-dependent measurements in testing QCD and the Standard Model. This book will be of value to graduate students and researchers working in all areas of quantum physics and particularly in elementary particle and high energy physics. It is suitable as a supplementary text for graduate courses in theoretical and experimental particle physics.

Azimuthal and single spin asymmetries in hard scattering processes

“…The interested reader may fortunately find complete and comprehensive accounts on this subject in Refs. [1,2,9,13]. Whenever possible we will refer to published work.…”

“…frame; in this frame, hadron A, B, move respectively along the ±Z cm -axis direction and the final hadron C is produced in the (XZ) cm plane, with (p C ; notice that the helicity density matrix always describes the polarization state of the particle in its helicity rest frame; for a massless particle no rest frame exists and the helicity frame is defined as the standard frame, reached from the hadronic c.m. frame, in which the particle four-momentum is p µ = (p, 0, 0, p) [13]; (vii)f a/A,S A (x a , k ⊥a ) is the spin and TMD distribution function of the unpolarized parton a inside the polarized hadron A, and similarly for parton b inside hadron B; these leading-twist TMD distributions generalize the usual partonic distributions in the collinear configuration; notice that in this paper, for the sake of clarity, we adopt the following convention: for all k ⊥ dependent distribution and fragmentation functions and soft amplitudes we will use a "hat" to indicate full, vectorial dependence on k ⊥ , while we will not use it for dependence on k ⊥ = |k ⊥ |, with factorized azimuthal dependence; notice also that this notation is partially at variance with those adopted in the papers where the original formulation of the GPM was developed, which by the way slightly differ from paper to paper; (viii) TheM λ c ,λ d ;λ a ,λ b 's are the helicity amplitudes for the elementary process ab → cd, opportunely normalized according to the kinematical phase-space factors explicitly shown in Eq. (33);…”

“…The rich, low-energy aspects of topics iii) and iv), which may be confronted only with nonperturbative approaches, will also remain uncovered. A comprehensive overview on these subjects and on related topics can be found in several review papers, addressing both their theoretical and experimental aspects [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Here we will focus on the high-energy regime and the treatment in the context of pQCD approaches of transverse SSA's and, marginally, of the transverse polarization of spin 1/2 particles in unpolarized processes.…”

Angular momentum conservation law in light-front quantum field theory

“…There are three popular choices of Lorentz transformations in the literature which give rise to different definitions of relativistic spin states [2] [3] [14][15]:…”

Tau polarization in quasielastic charged-current neutrino(antineutrino)–nucleus scattering

“…The large mass of the tau in contrast to electron and muon implies that it can be partially polarized [2,3]. The degree of polarization of tau is one of the parameters which describe its decay products distributions [4,5]. Therefore, the discussion the tau polarization in the neutrino-matter scattering can play an important role in the analysis of the experimental data and is also of theoretical interest.…”