Measurement of the proton and deuteron spin structure functions g and asymmetry A 12 2 E 155 Collaboration

A We B have measured the spin structure functions g C p D and E g C d F and E the virtual photon asymmetries A p D and E A F over G the 2 2 2 2 2 H I 2 kinematic range 0.02 J x K L 0.8 M and 1.0 N Q O P 30 Q GeV R c S by scattering 38.8 GeV longitudinally polarized electrons from 6 T U transversely V polarized NH and LiD targets. The absolute value of A is significantly smaller than the R positivity W limit 3 2 over G the measured range, while g C is consistent with the twist-2 Wandzura-Wilczek calculation. We obtain results for the 2 p d D n X Y twist-3 V reduced matrix elements d Z , [ d Z and E d Z . The Burkhardt-Cottingham sum rule integral \ g x C dx is reported for the 2 2 ] 2 2 range ^ 0.02 _ x K ` 0.8. M a 1999 Elsevier Science B.V. All rights reserved. PACS: 13.60.Hb; 13.88. b e; 24.70. c s; 25.30.Fj The d deep inelastic spin structure functions of the nucleons, e g f and g g f , depend on the spin distribution 1 2 of h the partons and their correlations. The function g f 1 can i be primarily understood in terms of the quark j k parton l model QPM and perturbative QCD with higher m twist terms at low Q. There exists no such n o picture l for g f . Feynman 1 claimed that the trans2 p verse q structure function g f r g f s g f had m a simple T 1 2 parton l interpretation in terms of the transverse polarization t of the quark spins which is proportional to quark u masses. However, g f is t sensitive to higher 2 v w twist x effects such as quark-gluon correlations 2 and is t not easily interpreted in pQCD where such effects are g not included. By interpreting g f using y the opera2 p z { | } tor x product expansion OPE 2,3 , it is possible to study contributions to the nucleon spin structure beyond ~ the simple QPM. The virtual photon-nucleon 1 Work  supported by the National Science Foundation and the Department of Energy contract DE–AC03–76SF00515. 2 € Present address: College of William and Mary, Williamsburg, Virginia 23187. 3  Permanent Address: Institut des Sciences Nucleaires, ́ IN2P3‚ CNRS, 38026 Grenoble Cedex, France. 4 ƒ Present Address: Duke University, TUNL, Durham, NC 27708. 5 „ Present Address: St. Norbert College, De Pere, WI 54115. 6 … Present Address: DESY, D-22603, Hamburg, Germany. 7 † Present Address: Lawrence Livermore National Laboratory, Livermore, CA 94551. asymmetry g A is proportional to g f ‡ F where ˆ F is 2 p T 2 2 p the x unpolarized structure function. ‰ Š The structure function g f can i be written 4 : 2 p 2 p W W 2 2 p g x f ,Q ‹ g x f ,Q Œ g x f ,Q , 1  Ž   ‘ ’ “ ”