We probe the Ioffe-Regel limits of glasses with repulsions near the zero-temperature jamming transition by measuring the dynamical structure factors. At zero temperature, the transverse IoffeRegel frequency vanishes at the jamming transition with a diverging length, but the longitudinal one does not, which excludes the existence of a diverging length associated with the longitudinal excitations. At low temperatures, the transverse and longitudinal Ioffe-Regel frequencies approach zero at the jamming-like transition and glass transition, respectively. As a consequence, glasses between the glass transition and jamming-like transition, which are hard sphere glasses in the low temperature limit, can only carry well-defined longitudinal phonons and have an opposite pressure dependence of the ratio of the shear modulus to the bulk modulus from glasses beyond the jamminglike transition.PACS numbers: 63.50. Lm,64.70.pv,61.43.Bn Upon compression, colloidal systems undergo the glass transition when the relaxation time (or the viscosity) exceeds the measurable value [1][2][3]. In the absence of the thermal energy, the compression leads to the jamming transition of packings of repulsive particles with the sudden formation of rigidity and static force networks [4,5]. Although the initial jamming phase diagram [4] proposes that the glass transition of purely repulsive systems collapses with the jamming transition in the zero temperature (T = 0) limit, or equivalently in the hard sphere limit [6], recent studies have evidenced that the T = 0 or hard sphere glass transition happens at a packing fraction φ g0 lower than the critical value φ j0 of the T = 0 jamming transition at the so-called point J [7][8][9][10][11][12].The departure of φ g0 from φ j0 leaves φ ∈ (φ g0 , φ j0 ) a special region. At T = 0, the systems in this region are unjammed and unable to sustain the shear or compression. However, they are by definition glasses when being thermally excited, because particles are unable to diffuse freely. While glasses are believed to be mechanically rigid solids, it seems perplexing that the systems in (φ g0 , φ j0 ) are rigid in the glass perspective but not in the T = 0 jamming perspective, which makes T = 0 singular.For soft and repulsive spheres, recent simulations have indicated that the glass transition temperature T g is proportional to the pressure p and vanishes at φ g0 [6][7][8][9]. Both colloidal experiments and simulations have also shown that inside the glass regime, at fixed temperature, there exists a crossover pressure p j at which the first peak of the pair distribution function reaches the maximum height g max 1 [7,8,[13][14][15], reminiscing the structural signature of the T = 0 jamming transition [16]. At such a crossover, the pressure dependence of the temperatureand vanishes at φ j0 [7,8]. In other words, when compressed at a fixed low temperature, the system undergoes the glass transition first and then the emergence of g max 1 .The whole picture is reproduced here as well in Fig. 3.A recent study ha...