yscaling

Y scaling, or y-scaling, is a concept in nuclear physics describing the behavior of inclusive quasielastic electron-nucleus scattering. In the impulse approximation at sufficiently high momentum transfer q, the measured cross section, when divided by the appropriate single-nucleon cross section and kinematic factors, depends primarily on a single scaling variable y rather than on q and the energy transfer ω separately. The scaling variable y is defined from energy conservation and represents the minimum initial momentum of the struck nucleon along the direction of the momentum transfer.

A scaling function F(y) can be formed from the reduced cross section and, ideally, is independent of q (scaling of the first kind) and independent of the target nucleus (scaling of the second kind). When both occur, the phenomenon is called superscaling. In its simplest interpretation, F(y) is related to the one-nucleon momentum distribution in the nucleus, providing information about high-momentum components and short-range correlations.

Observations and limitations: data from inclusive electron scattering show approximate y-scaling at sufficiently large q, with violations arising from final-state interactions, meson-exchange currents, and inelastic processes such as delta resonance excitation. Y-scaling has been used to extract nucleon momentum distributions and to test nuclear models, and it informs neutrino-nucleus scattering by providing constraints on cross sections in similar kinematic regimes.

See also: impulse approximation, inclusive electron scattering, scaling function, short-range correlations.