2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/122724Recent simulations have predicted that near jamming for collections of spherical particles, there will be a discontinuous increase in the mean contact number, Z, at a critical volume fraction, phi_c. Above phi_c, Z and the pressure, P are predicted to increase as power laws in phi-phi_c. In experiments using photoelastic disks we corroborate a rapid increase in Z at phi_c and power-law behavior above phi_c for Z and P. Specifically we find power-law increase as a function of phi-phi_c for Z-Z_c with an exponent beta around 0.5, and for P with an exponent psi around 1.1. These exponents are in good agreement with simulations. We also find reasonable agreement with a recent mean-field theory for frictionless particles.4 pages, 4 figures, 2 pages supplement; minor changes and clarifications, 2 addtl. refs., accepted for publication in Phys. Rev. LettSoft Condensed MatterDisordered Systems and Neural NetworksStatistical Mechanicstext