Deep sub-threshold {\phi} production and implications for the K+/K- freeze-out in Au+Au collisions

Understand

We present data on charged kaons (K+-) and {\phi} mesons in Au(1.23A GeV)+Au collisions.

• It is the first simultaneous measurement of K and {\phi} mesons in central heavy-ion collisions below a kinetic beam energy of 10A GeV.
• The {\phi}/K- multiplicity ratio is found to be surprisingly high with a value of 0.52 +- 0.16 and shows no dependence on the centrality of the collision.
• Consequently, the different slopes of the K+ and K- transverse-mass spectra can be explained solely by feed- down, which substantially softens the spectra of K- mesons.