Spin physics at COMPASS

Results for the spin structure of the nucleon from the COMPASS data taking periods 2002 to 2004 are presented. The quark contribution to the nucleon spin, following from a QCD fit to the new data, turns out to be significantly larger than it was derived from the previous world data. The new data favour, on the other side, a comparatively small gluon polarisation in the range x _g ≈ 0.1. In the data taken with the deuteron target polarised transversely the related asymmetries are found to be small on the level of accuracy reached so far, indicating a cancellation of the proton and neutron contributions. This is in agreement, for both the Collins and the Sivers asymmetry, with recent theoretical calculations. Also, a step towards the understanding of angular-momentum contributions with COMPASS is taken by the evaluation of asymmetries in exclusive vector meson production.     

Spin physics and more with HERMES

A review of recent results obtained by the HERMES experiment is given. Inclusive measurements on polarized and unpolarized targets provide precise information on the polarized structure functions g₁^d and g₁^p and the isoscalar unpolarized structure function ratio F₂^A/F₂^d. The geometrical acceptance of the HERMES detector and the good particle identification capabilities allow the study of semi-inclusive reactions as well. Using polarized targets, the polarized quark distribution functions can be extracted as well as a first indication of the transversity distributions . On unpolarized heavy targets, hadron formation in a nuclear environment is studied. Finally, data on Deeply Virtual Compton Scattering, the hard exclusive electroproduction of real photons, are presented, which are closely linked to the novel framework of Generalised Parton Distributions. For this reaction HERMES has measured the asymmetry main beam charge as well as in-beam spin.Received: 1 November 2002, Published online: 15 July 2003PACS: 13.60.Hb Total and inclusive cross-sections (including deep-inelastic processes) - 13.60.Le Meson production - 24.85.+p Quarks, gluons, and QCD in nuclei and nuclear processes - 25.30.Mr Muon scattering (including the EMC effect)B. Seitz: For the HERMES Collaboration     

Spin physics at IHEP

IHEP has rich program devoted to the spin physics studies. New experimental program will significantly increase the number of reaction investigated at large kinematic region. The experiment will measure different polarization variables in inclusive and exclusive reactions, including single- and double-spin asymmetry, polarization, spin transfer parameters. One of the most important task is the creation of the polarized beam and especially polarized anti-proton beam.     

Spin physics at HERMES

The primary goal of the HERMES experiment is the study of the spin structure of the nucleon. Results on the measured inclusive and semi-inclusive hadron asymmetries using a polarized positron beam on polarized ³He, hydrogen and deuterium targets are here presented. In the covered kinematic range, 0.023<x _Bj <0.6 and 1 GeV²<Q ²<10GeV² the polarized quark distribution were determined for all up (u+?u) and down (d+?) quarks, and separately for valence and sea quarks. The up quark polarization is positive, and the down quark polarization is negative. The polarization of the sea is consistent with zero in the measured range. A first indication of a positive gluon polarization is presented, based on the measured spin asymmetry in the photo-production of hadron pairs with high transverse momentum p _T . This asymmetry is negative, which is in contrast to the measured positive asymmetry for inclusive experiments.     

Spin physics through unpolarized processes

This article presents a review of our present understanding of the spin structure of the unpolarized hadron. Particular attention is paid to the quark sector at leading twist, namely, the quark Boer–Mulders function, which describes the transverse polarization of the quark inside an unpolarized hadron. After introducing the operator definition of the Boer–Mulders function, a detailed treatment of different non-perturbative calculations of the Boer–Mulders functions is provided. The phenomenology in Drell–Yan processes and semi-inclusive leptoproduction, including the extraction of the quark and antiquark Boer–Mulders functions from experimental data, is presented comprehensively. Finally, prospects for future theoretical studies and experimental measurements are presented in brief.     

The Spin Structure of the Nucleon; A COMPASS Perspective

The COMPASS experiment at CERN is carrying on an experimental investigation of the spin structure of the nucleon, covering both longitudinal and transverse spin phenomena. In the first case, the central topic is the direct measurement of the gluon polarisation with the hope to solve the spin crisis first observed by EMC. The result shows that Δg/g is small around x _g ≃0.1, and its first moment should not be larger than 0.2—0.3 in absolute value. About transverse spin effects, evidence is given for new phenomena, associated with transverse momentum dependent distribution and fragmentation functions.     

Spin physics with internal targets and the blast detector

The aim of this paper is to give a set of central elements of the algebras U_q(so_m) and U _q(iso _m ) when q is a root of unity. They are surprisingly arise from a single polynomial Casimir element of the algebra U_q(so₃). It is conjectured that the Casimir elements of these algebras under any values of q (not only for q a root of unity) and the central elements for q a root of unity derived in this paper generate the centers of U_q(so_m) and U _q(iso _m ) when q is a root of unity.     

Spin physics in high-energy hardon interaction

Data on single-spin asymmetry (A_N) in high-energy hadron-hadron collisions are discussed. The data are classified according to the beamand target types. The single-spin asymmetry A_N is considered as a function of kinematical variables and the sort of participant particles. Data from the PROZA and FODS facilities operating in beams of the IHEP accelerator are presented. The origin of a large single-spin asymmetry is briefly considered.     

Spin physics in Jefferson Lab's Hall C

Jefferson Lab's Hall C is highly flexible and well suited to take advantage of the facility's polarized electron beam. Using standard and custom equpment, a number of experiments have been staged here studying spin dependent observables and investigating allarge range of physical properties. More promising measurements are planned.     

Spin physics at JINR: Present and future

A short review of spin physics program at JINR is presented. The proposals on spin program at the NICA collider are discussed. The main purpose of this program is to study the nucleon spin structure and other phenomena with polarized proton and deuteron beams.     

Spin physics at RHIC: Present and future

In 2001–2002 the relativistic heavy-ion collider (RHIC) at the Brookhaven National Laboratory (BNL) was first commissioned for polarized proton collisions. Polarized protons were injected into the RHIC, accelerated to 100 GeV, stored and the two beams were made to collide in four interaction regions. I will review the progress made by the RHIC spin program, followed by the physics goals for the next few years. After that I will present a brief overview of a proposal to build a high intensity polarized electron/positron beam facility at BNL which would enable deep inelastic scattering (DIS) experiments to be pursued at BNL by its collisions with the RHIC hadron beams.     

Spin physics in few body systems at Nuclotron

The review of the recent results on spin effects in few nucleon systems obtained at LHEP-JINR are presented. The data on the deuteron analyzing powers in different reactions in the wide energy range demonstrate the sensitivity to the spin structure of the light nuclei. The future plans on the studies with polarized deuterons from new polarized ion source at Nuclotron will be reported.     

Spin physics in solid helium: Experimental results and applications

We have observed optical pumping signals from Cs atoms trapped in solid⁴He. While the longitudinal electronic spin relaxation timeT ₁ is found to be in the range of 1–2 s, the transverse relaxation timeT ₂, as inferred from magnetic resonance linewidths has a lower bound of 150 s, and is determined by magnetic field inhomogeneities. We present a quantitative discussion of how paramagnetic species trapped in solid He might be used in a highly sensitive search for permanent atomic electric dipole moments.     

Spin physics at a fixed-target experiment at the LHC (AFTER@LHC)

We outline the opportunities for spin physics which are offered by a next generation and multipurpose fixed-target experiment exploiting the proton LHC beam extracted by a bent crystal. In particular, we focus on the study of single transverse spin asymetries with the polarisation of the target.     

Measurement of the gluon polarisation with COMPASS

The COMPASS experiment at CERN is investigating the nucleon spin structure in polarised deep inelastic muon scattering, mainly the gluon polarisation .     

Study of SAR imaging with COMPASS signal

A concept of space-surface bistatic synthetic aperture radar (SS-BSAR) passive imaging system is proposed,which is parasitic on the signal of COMPASS Navigation Satellite System (CNSS).The feasibility is demonstrated by analyzing the signal ambiguity function and the range resolution as well as the system topology.Due to the multiple peaks of signal in the auto-correlation function,a new correlation is used to remove the side-peaks.A double-channel receiver is employed to receive the direct satellite signal...     

Hadron program at COMPASS

The fixed target COMPASS experiment at CERN offers the opportunity to search for exotic mesons and glueball candidates in the light quark sector with unprecedented statistics.Preliminary results from the2008 data taken with an incoming negative hadron beam(190 GeV/c,mainly pions)on a liquid hydrogen target are presented.New detectors dedicated to hadron beam measurements have been added.These give access to rare neutral and kaonic channels.An amplitude analysis which will allow to fit simultaneously diffractively and/or centrally produced resonances will be described and compared with those used in the CERN WA102and BNL E852 experiments.     

Hadron program at COMPASS

The fixed target COMPASS experiment at CERN offers the opportunity to search for exotic mesons and glueball candidates in the light quark sector with unprecedented statistics.Preliminary results from the 2008 data taken with an incoming negative hadron beam （190 GeV/c,mainly pions） on a liquid hydrogen target are presented.New detectors dedicated to hadron beam measurements have been added.These give access to rare neutral and kaonic channels.An amplitude analysis which will allow to fit simultaneously diffractively and/or centrally produced resonances will be described and compared with those used in the CERN WA102 and BNL E852 experiments.