Energy dependence of $K\pi$, $p\pi$, and $Kp$ fluctuations in Au + Au collisions from $\sqrt{s_{NN}}=7.7$ to 200 GeV

A search for the quantum chromodynamics (QCD) critical point was performed by the STAR experiment at the BNL Relativistic Heavy Ion Collider, using dynamical fluctuations of unlike particle pairs. Heavy ion collisions were studied over a large range of collision energies with homogeneous acceptance and excellent particle identification, covering a significant range in the QCD phase diagram where a critical point may be located. Dynamical $K\pi$, $p\pi$, and $Kp$ fluctuations as measured by the STAR experiment in central 0–5% Au + Au collisions from center-of-mass collision energies $\sqrt{s_{NN}}=7.7$ to 200 GeV are presented. The observable ${\nu }_{\mathrm{dyn}}$ was used to quantify the magnitude of the dynamical fluctuations in event-by-event measurements of the $K\pi$, $p\pi$, and $Kp$ pairs. The energy dependences of these fluctuations from central 0–5% Au + Au collisions all demonstrate a smooth evolution with collision energy.

Figure 1

$p\pi$ fluctuations as a function of collision energy, expressed as ${\nu }_{\mathrm{dyn},p\pi }$. Shown are data from central (0–5%) Au + Au collisions at energies from $\sqrt{s_{NN}}=7.7$ to 200 GeV from the STAR experiment (black stars), predictions from UrQMD and HSD filtered through the same experimental acceptance (open stars and open triangles, respectively), and data from central (0–3.5%) Pb + Pb collisions at energies from $\sqrt{s_{NN}}=6.3$ to 17.3 GeV from the NA49 experiment (blue squares) [27].

Figure 2

$Kp$ fluctuations as a function of collision energy, expressed as ${\nu }_{\mathrm{dyn},\mathrm{Kp}}$. Shown are data from central (0–5%) Au + Au collisions at energies from $\sqrt{s_{NN}}=7.7$ to 200 GeV from the STAR experiment (black stars), predictions from UrQMD and HSD filtered through the same experimental acceptance (open stars and open triangles, respectively), and data from central (0–3.5%) Pb + Pb collisions at energies from $\sqrt{s_{NN}}=6.3$ to 17.3 GeV from the NA49 experiment (blue squares) along with charge-separated $K^{+}p$ fluctuations (open squares). [28].

Figure 3

$K\pi$ fluctuations as a function of collision energy, expressed as ${\nu }_{\mathrm{dyn},K\pi }$. Shown are data from central (0–5%) Au + Au collisions at energies from $\sqrt{s_{NN}}=7.7$ to 200 GeV from the STAR experiment (black stars), predictions from UrQMD and HSD filtered through the same experimental acceptance (open stars and open triangles, respectively), and data from central (0–3.5%) Pb + Pb collisions at energies from $\sqrt{s_{NN}}=6.3$ to 17.3 GeV from the NA49 experiment (blue squares) [27].