Role Of Strange Quarks Research Articles

IMPORTANCE OF STRANGE QUARKS IN HADRONS, NUCLEI AND DENSE MATTER

We review recent progress in our understanding of the role of strange quarks in the structure of the nucleon. For the contribution to its mass the result is remarkably small, an order of magnitude smaller than commonly assumed. This has profound consequences for the searches for dark matter which are currently underway. There has also been remarkable progress in the understanding of hypernuclei. In particular, there is a very natural explanation at the quark level of why Λ-hypernuclei are bound whereas Σ-hypernuclei are not. The consequences for dense matter, for example in neutron stars, are not yet fully understood but we know they are significant.

New results from the HAPPEX Experiments at Q2 = 0.1GeV/c2

The nucleon’s strange electric and magnetic form factors G E s and G M s can be probed via parity-violating electron scattering. The HAPPEX Collaboration has made new measurements of the parity-violating asymmetry A PV in elastic scattering of 3 GeV electrons off hydrogen and 4He targets with ≈ 6.0°. For 4He the preliminary result is A PV = (+6.43 ± 0.23 (stat) ± 0.22 (syst)) × 10−6. For hydrogen the preliminary result is A PV = (−1.60 ± 0.12 (stat) ± 0.05 (syst)) × 10−6. From these values we extract G E s = 0.004 ± 0.014 ± 0.013 at = 0.077 GeV/c 2, and G E s + 0.09G M s = 0.004 ±0.011 ± 0.005 at = 0.109 GeV/c 2, both consistent with zero, providing stringent new limits on the role of strange quarks in the vector structure of the nucleon.

Precision Measurements of the Nucleon Strange Form Factors atQ2∼0.1 GeV2

We report new measurements of the parity-violating asymmetry APV in elastic scattering of 3 GeV electrons off hydrogen and He4 targets with ⟨θlab⟩≈6.0°. The He4 result is APV=(+6.40±0.23(stat)±0.12(syst))×10−6. The hydrogen result is APV=(−1.58±0.12(stat)±0.04(syst))×10−6. These results significantly improve constraints on the electric and magnetic strange form factors GEs and GMs. We extract GEs=0.002±0.014±0.007 at ⟨Q2⟩=0.077 GeV2, and GEs+0.09GMs=0.007±0.011±0.006 at ⟨Q2⟩=0.109 GeV2, providing new limits on the role of strange quarks in the nucleon charge and magnetization distributions.Received 6 September 2006DOI:https://doi.org/10.1103/PhysRevLett.98.032301©2007 American Physical Society