scholarly journals HERMES AND THE SPIN OF THE PROTON

2002 ◽  
Vol 17 (25) ◽  
pp. 3551-3570 ◽  
Author(s):  
H. E. JACKSON
Keyword(s):  
Spin Structure ◽  
Total Angular Momentum ◽  
Virtual Compton Scattering ◽  
Gluon Polarization ◽  
Spin Asymmetries ◽  
Single Spin ◽  
Double Spin ◽  
Azimuthal Asymmetries ◽  
Deep Virtual Compton Scattering ◽  
Hadron Pairs

HERMES is a second generation experiment to study the spin structure of the nucleon, in which measurements of the spin dependent properties of semi-inclusive deep-inelastic lepton scattering are emphasized. Data have been accumulated for semi-inclusive pion, kaon, and proton double-spin asymmetries, as well as for high-pT hadron pairs, and single-spin azimuthal asymmetries for pion electroproduction and deep virtual Compton scattering. These results provide information on the flavor decomposition of the polarized quark distributions in the nucleon and a first glimpse of the gluon polarization, while the observation of the azimuthal asymmetries show promise for probing the tensor spin of the nucleon and isolating the total angular momentum carried by the quarks.

MEASUREMENTS WITH POLARIZED HADRONS

2004 ◽  
Vol 19 (07) ◽  
pp. 1089-1098
Author(s):  
T.-A. SHIBATA
Keyword(s):  
Compton Scattering ◽  
Spin Structure ◽  
Recent Progress ◽  
Deeply Virtual Compton Scattering ◽  
Virtual Compton Scattering ◽  
Nucleon Spin ◽  
Parton Distributions ◽  
Single Spin ◽  
Generalized Parton Distributions ◽  
Azimuthal Asymmetries

Recent progress in physics with polarized hadrons is described with the emphasis on the spin structure of the nucleon. The nucleon spin problem, which was discovered by EMC in 1988, is now being studied in various experiments. Flavor separation of the quark helicity distributions has been made. Recent observations of asymmetries in deeply virtual Compton scattering (DVCS) and exclusive meson productions provide possibilities to access the total angluar momentum carried by quarks in the framework of generalized parton distributions. Single spin azimuthal asymmetries observed in semi-inclusive measurements provide a new handle to determine the transverse quark distributions which are basic but have never been measured so far.

LONGITUDINALLY POLARIZED HADRO- AND PHOTOPRODUCTION OF HEAVY QUARKS

2009 ◽  
Vol 24 (35n37) ◽  
pp. 3045-3051
Author(s):  
JOHANN RIEDL
Keyword(s):  
Spin Structure ◽  
Heavy Quarks ◽  
Monte Carlo Code ◽  
Heavy Flavor ◽  
Gluon Polarization ◽  
Order Accuracy ◽  
Spin Asymmetries ◽  
Double Spin ◽  
Heavy Flavor Production ◽  
Phenomenological Studies

Measurements of double-spin asymmetries for single-inclusive heavy flavor production and for heavy quark correlations are expected to provide valuable information about the spin structure of the nucleon, in particular, the elusive gluon polarization. We discuss progress towards a versatile parton-level Monte-Carlo code for the production and decay of heavy quarks in longitudinally polarized hadron-hadron and photon-hadron collisions at next-to-leading order accuracy of QCD. Phenomenological studies are presented for BNL-RHIC and COMPASS.

scholarly journals SPIN PHYSICS WITH STAR

2003 ◽  
Vol 18 (08) ◽  
pp. 1335-1342 ◽  
Author(s):  
◽  
JOANNA KIRYLUK
Keyword(s):  
Star Collaboration ◽  
Gluon Polarization ◽  
Proton Proton ◽  
Spin Asymmetries ◽  
Single Spin ◽  
Double Spin ◽  
Single Spin Asymmetries ◽  
Polarized Proton ◽  
First Time ◽  
Proton Proton Collisions

The STAR collaboration aims to study polarized proton-proton collisions at RHIC. The emphasis of the spin run this year is on transverse single spin asymmetries. Beyond 2001, we aim to determine directly and precisely the gluon polarization, as well as the polarizations of the u, [Formula: see text], d and [Formula: see text] quarks in the proton by measuring in addition longitudinal and double spin asymmetries. Furthermore, we aim to measure for the first time the quark transversity distributions. These measurements will improve substantially the knowledge and understanding of the spin structure of the nucleon.

scholarly journals Physics Opportunities at a Photon–Photon Collider

2003 ◽  
Vol 18 (16) ◽  
pp. 2871-2892 ◽  
Author(s):  
Stanley J. Brodsky
Keyword(s):  
Deeply Virtual Compton Scattering ◽  
Virtual Compton Scattering ◽  
High Energy ◽  
Quadrupole Moments ◽  
Spin Asymmetries ◽  
Polarized Beams ◽  
Single Spin ◽  
Single Spin Asymmetries ◽  
Photon Collider ◽  
Electron Photon

The advent of back-scattered laser beams for e±e-colliders will allow detailed studies of a large array of high energy γγ and γe collision processes with polarized beams. These include tests of electroweak theory in photon-photon annihilation such as γγ → W+W-, γγ → Higgs bosons, and higher-order loop processes, such as γγ → γγ, Zγ, H0Z0and ZZ. Methods for measuring the anomalous magnetic and quadrupole moments of the W and Z gauge bosons to high precision in polarized electron-photon and photon-photon collisions are discussed. Since each photon can be resolved into a W+W-pair, high energy photon-photon collisions can also provide a remarkably background-free laboratory for studying WW collisions and annihilation. I also review high energy γγ and eγ tests of quantum chromodynamics, including the production of two gluon jets in photon-photon collisions, deeply virtual Compton scattering on a photon target, and leading-twist single-spin asymmetries for a photon polarized normal to a production plane. Exclusive hadron production processes in photon-photon collisions provide important tests of QCD at the amplitude level, particularly as measures of hadron distribution amplitudes which are also important for the analysis of exclusive semi-leptonic and two-body hadronic B-decays.

scholarly journals Azimuthal single- and double-spin asymmetries in semi-inclusive deep-inelastic lepton scattering by transversely polarized protons

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
A. Airapetian ◽  
◽  
N. Akopov ◽  
Z. Akopov ◽  
E. C. Aschenauer ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Photon Exchange ◽  
Spin Asymmetries ◽  
Single Spin ◽  
Double Spin ◽  
Polarized Protons ◽  
Charged Pions ◽  
Exchange Approximation ◽  
Polarization Orientation ◽  
The One

Abstract A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing cos (ϕ−ϕS) modulations provide evidence for a sizable worm-gear (II) distribution, $$ {g}_{1\mathrm{T}}^q\left(x,{\mathrm{p}}_T^2\right) $$ g 1 T q x p T 2 . Most of the other modulations are found to be consistent with zero with the notable exception of large sin (ϕS) modulations for charged pions and K+.

scholarly journals Two-Photon Exchange in Elastic Electron Scattering on Hadronic Systems

2021 ◽  
Vol 66 (1) ◽  
pp. 3
Author(s):  
D. Borisyuk ◽  
A. Kobushkin
Keyword(s):  
Charge Asymmetry ◽  
Form Factors ◽  
Photon Exchange ◽  
Spin Asymmetries ◽  
Single Spin ◽  
Two Photon ◽  
Double Spin ◽  
Theoretical Approaches ◽  
Single Spin Asymmetries ◽  
Proton Form Factors

In the present review, we discuss different aspects of the two-photon exchange (TPE) physics in elastic ep scattering at high Q2, as well as at low Q2. The imaginary part of the TPE amplitude gives rise to beam and target single-spin asymmetries. Different theoretical approaches to the calculation of these observables are considered. The real part of the TPE amplitude influences the unpolarized cross-section and double-spin observables and is, most likely, responsible for the discrepancy between two methods of measurements of the proton form factors. We review different methods of calculations of the TPE amplitudes in the framework of the “hadron” and “quark-gluon” approaches. We discuss the dispersion approach suitable for low and intermediate Q2, which includes elastic and inelastic intermediate hadronic states, as well as the connection of TPE with the proton radius puzzle. The present situation with direct experimental searches for the TPE amplitude in the e+p/e−p charge asymmetry is also discussed, as well as attempts to extract the TPE amplitudes from existing experimental data obtained by the Rosenbluth and double polarization techniques. The TPE physics in other processes such as elastic мp, e-nucleus, and еп scattering is also reviewed.

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