2010 # Quark helicity distributions from longitudinal spin asymmetries in muon–proton and muon–deuteron scattering

**Abstract:** Double-spin asymmetries for production of charged pions and kaons in semi-inclusive deep-inelastic muon scattering have been measured by the COMPASS experiment at CERN. The data, obtained by scattering a 160 GeV muon beam off a longitudinally polarised NH 3 target, cover a range of the Bjorken variable x between 0.004 and 0.7. A leading order evaluation of the helicity distributions for the three lightest quarks and antiquark flavours derived from these asymmetries and from our previous deuteron data is presen…

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(91 citation statements)

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“…We note that small strange-quark charges have also been observed in recent studies [15,16]. Within the present uncertainty, our results for the axial charges, g A and g s A , are consistent with the experimental values [17,18]. The suppression compared to the simple quark model estimate, g s A = 1 and g A = 5/3, was argued by one of the authors in Schwinger-Dyson analyses [19,20].…”

confidence: 93%

“…We note that small strange-quark charges have also been observed in recent studies [15,16]. Within the present uncertainty, our results for the axial charges, g A and g s A , are consistent with the experimental values [17,18]. The suppression compared to the simple quark model estimate, g s A = 1 and g A = 5/3, was argued by one of the authors in Schwinger-Dyson analyses [19,20].…”

confidence: 93%

“…In this case, there will be no strangeness contribution, Ás to ÁAE ¼ Áu þ Ád þ Ás þÁÁÁ, where, in our notation, Áq ¼ ÁAE q contains both the spin of the quarks q and of the antiquarks " q. Experimentally, Ás is obtained by integrating the strangeness contribution ÁsðxÞ to the spin structure function g 1 over the momentum fraction x. The integral over the range in which data exist agrees with zero; see, e.g., new COMPASS data [2,3] for x ! 0:004 or HERMES data [4] for x !…”

mentioning

confidence: 88%

“…This fact has surprised many physicists, and many theoretical studies trying to explain this "proton spin crisis" have been done [15,[17][18][19][20] with no definitive consensus between them. Currently the experimental studies continue [21], and the recent experimental data of the sum of the quark spin contribution to the nucleon spin is given by [22] ∆Σ = 0.32 ± 0.03 ± 0.03 .…”

confidence: 99%