Conveners
Helicity: Parallel II
- Gerhard Mallot (CERN)
Helicity: Parallel III
- Emanuele Roberto Nocera (University of Oxford)
Helicity: Parallel IV
- Gerhard Mallot (CERN)
Helicity: Parallel V
- Emanuele Roberto Nocera (University of Oxford)
Helicity: Parallel VI
- Gerhard Mallot (CERN)
Description
Nucleon helicity structure
The COMPASS experiment at the CERN SPS has taken data with a polarised muon beam scattering off a polarised NH3 target in 2007 and 2011 and scattering off a 6LiD target from 2002-2004 and 2006. The 2006 measurement increases the statistics from 2002-2004 by roughly a factor of two. For the measurement in 2011 the beam energy has been increased from 160 GeV to 200 GeV thus higher values of Q2...
There exist new polarized structure functions b1−4 for spin-one hadrons such as the deuteron. These functions probe very different nature of hadron spin physics from the longitudinally polarized distributions measured by g1 for the nucleon. The twist-two structure functions b1 and b2 are expressed by tensor polarized parton distribution functions, which indicate unpolarized parton...
Tensor-polarized parton distribution functions are new quantities in spin-one hadrons such as the deuteron, and they could probe new quark-gluon dynamics in hadron and nuclear physics. In charged-lepton deep inelastic scattering (DIS), they are studied by the twist-two structure functions b1 and b2 [1, 2]. The HERMES collaboration found unexpectedly large b1 values than a naive theoretical...
To obtain sensible information about hadronization in the current region from experiment, it is essential to understand the kinematical range of applicability of the formalism of fragmentation functions, which is often overlooked in phenomenological applications. In this talk, I will describe how one may identify the current region and argue that at low Q2 the distinction between current and...
We present COMPASS results on the longitudinal double-spin asymmetry, Ap1, and the spin dependent structure function of the proton, gp1, in the quasi-real photoproduction regime. Data were collected by scattering a longitudinally polarised
muon beam off a longitudinally polarised proton target. Two data sets with a beam energy of respectively 160 and 200 GeV were taken, which improve, once...
Measurements of the nucleon spin-dependent structure functions have provided powerful tools to test the validity of effective theories of Quantum Chromodynamics (QCD). The neutron spin structure functions, gn1 and gn2, and the proton spin structure function, gp1, have been measured over a wide kinematic range. However, the proton spin structure function, gp2, is mostly unknown. Recently an...
The Gerasimov-Drell-Hearn (GDH) sum rule, as a fundamental sum rule for real photon absorption, relates the anomalous magnetic moment to the spin structure of the nucleon. The generalized form of GDH sum rule extends this relation to finite four-momentum transfer squared (Q2). Jefferson Lab experiment E97-110 was performed with a High Resolution Spectrometer (HRS) and a septum magnet in Hall A...
Proton spin is investigated in chiral effective field theory through an examination of the singlet axial charge, a0, and the two non singlet axial charges, a3 and a8. Finite-range regularization is considered as it provides an effective model for estimating the role of disconnected sea-quark loop contributions to baryon observables. Baryon octet and decuplet intermediate states are included to...
The contribution to the spin of the proton from its constituents has been one of the unresolved questions in nuclear physics. The longitudinal spin program at STAR is exploring a wide range of measurements to determine the gluon helicity distribution inside the proton. The inclusive jets and pions in the kinematic range accessed by RHIC are dominated by quark-gluon and gluon-gluon scattering...
Understanding the proton spin structure in terms of quark and gluon degrees of freedom is one of the key open questions in the field of hadron physics. Gluon helicity, ∆g(x), related measurements play an important role in solving this “Spin Puzzle”. The polarized proton+proton collisions at the Relativistic Heavy Ion Collider provide unique opportunities for studying ∆g(x) by accessing it via...
One of the main goals of the RHIC spin program is the determination of the gluon helicity contribution to the proton spin. This can be accessed by measuring double spin asymmetries (ALL) of pion production at mid-rapidity in longitudinally polarized proton collisions with the PHENIX experiment. The ordering of the asymmetries with the charge of the final state pions can in addition directly...
Starting with the discovery of EMC that quarks are not the only building blocks of the nucleon spin its structure has been a topic of intense studies for numerous experiments. With precision measurements of quark and gluon polarisations by SMC, HERMES, COMPASS, STAR and PHENIX collaborations we are closing to an answer. The quark contribution is already determined with good accuracy and...
The STAR experiment at RHIC has provided significant contributions to our understanding of the structure of the proton. The STAR experiment is well equipped to measure W± → e± +ν in √s = 510 GeV longitudinally polarized p + p collisions at mid rapidity (|η| < 1). The longitudinal single spin asymmetry in W production, AL, measured as a function of decay positron (electron) pseudo-rapidity η...
The measurement of the single spin asymmetry of parity violating W boson production in longitudinally polarized proton collisions provides unique and clean access to the light sea quark helicity distributions. The W boson couples only to left handed quark and right-handed anti quark, and hence one can directly relate the charge of the W with initial state quark flavors. The PHENIX experiment...
The net contribution of the strange quark spins to the proton spin, ∆s, can be determined from neutral current elastic neutrino-proton interactions at low momentum transfer combined with data from electron-proton scattering. This is because the probability of neutrino-proton interactions depends on the axial form factor, which represents the spin structure of the proton and can be separated...
The existence of intrinsic quark and antiquark in the nucleon and their asymmetric distribution were suggested some time ago, but there is still no convinced evidence. We investigate the difference between quark to Λ and Λ longitudinal spin transfers in the light-cone quark-spectator diquark model at COMPASS, E665 and HERMES kinematic domains. Such a difference can provide additional...
Longitudinal spin asymmetries have been a prime source of information on the nucleon’s spin structure for several decades. In order to match the precision of currently available and future data taken at Compass, JLab, RHIC and a future EIC, it is of great importance to understand higher order corrections in QCD. We review the current status of higher order QCD corrections for longitudinally...
In recent years, the NNPDF Collaboration has developed a new methodology to determine the parton distribution functions (PDFs) of the proton. This is based on a Monte Carlo sampling and representation of PDFs, a parametrization of PDFs based on neural networks, and closure tests for a full characterization of procedural uncertainties. The aim is to provide minimally biased parton sets in which...
The HERMES Collaboration has measured charge-separated pion and kaon multiplicities in semi- inclusive deep-inelastic scattering using a 27.6 GeV electron or positron beam scattering off a hydrogen or deuterium target. The results are presented as functions of the Bjorken variable x, the negative squared four momentum transfer Q2, the hadron fractional energy, and the hadron’s transverse...
Final results on the measurement of charged pion, kaon and unidentified hadron multiplicities in semi-inclusive deep inelastic scattering at the COMPASS experiment at CERN are presented and discussed. Measurements are performed using data collected in 2006 by scattering a 160 GeV muon beam off an isoscalar target, and cover a wide kinematic range defined by Q2 > 1 (GeV/c)2, 0.1 < y < 0.7 and...
Based on both the constituent quark picture and the instanton model for QCD vacuum, I will talk about the latest results about gluon distributions inside the constituent quark generated by the perturbative quark-gluon interaction, the non-perturbative quark gluon interaction, and the non-perturbative quark-gluon pion anomalous chromomagnetic interaction. The non-perturbative interactions are...
