Drell - Yan Scaling in Semi - Inclusive Electroproduction ”

The scaling behavior of deep inelastic single-particle inclusive electroproduction (or neutrino production) expected from the parton model has been given by Drell and Yan as v 3 g&2 when the observed hadron has a finite fraction of the virtual photon’s laboratory momentum. Although Drell and Yan give the correct scaling behavior with their choice of variables, we show that with variables more appropriate experimentally, the proper scaling is v2”;“v2. Recent data previously thought inconsistent with the parton model are now found to be in agreement, which is especially important since scaling in this kinematic region cannot be predicted from a light-cone analysis. (Submitted to Comments and Addenda, Phys. Rev.) *Work supported by the U. S. Atomic Energy Commission. LIBRARY l/l/O/ SLAC 82 Single particle inclusive electroproduction (or neutrino production) in the deep inelastic region provides several interesting features: (i) an extra variable (Q2) not found in hadronic reactions, (ii) a combination of the Bjorken scaling limit with Feynman scaling or limiting fragmentation, and (iii) a kinematic region accessible to parton and not light-cone anglysis. In the parton model, the scaling behavior has been derived by Drell and Y an’ using field theory with a transverse momentum cut-off. The kinematic variables and structure functions for spin-averaged inelastic electron scattering with the detection of the final electron plus one hadron (P,) are given by Drell and Yan as follows: Q2=-q2 > 0 v =P.q/M v1 = PI* q/M1 K~ = P* P,/M d4 (T 2 dQ dv d KIdvI 9e2 cos2 ( 8 /2) + 2 “3/i sin2 (0 /2) 1 (1) where E is the incident energy and E ‘, 8 are the energy and angle of the scattered electron in the laboratory system. (The azimuthal angle of the hadron is integrated over. ) The kinematic region of deep inelastic scattering where the observed hadron in the laboratory system has a finite fraction (denoted as z) of the virtual photon’s momentum (equal to laboratory energy in the Bj limit) is best described as the parton fragmentation region, l-5 i e . . , v,Q2 2Mv 1 K1 Mu 1 1 1 -00, w =Q2 finite, zify finite, u1 = ~lv = -+ol 9 WW 1 0 v (The Feynman scaling variable z is also the ratio of momentum of the hadron to that of the parton struck by the photon in the parton-photon Breit frame2 or of the hadron to its maximum momentum in the center-of-mass frame. )