Higher-order cumulants and correlation functions of proton multiplicity distributions in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi>N</mml:mi><mml:mi>N</mml:mi></mml:mrow></mml:msub></mml:msqrt><mml:mo>=</mml:mo><mml:mn>3</mml:mn><mml:mo> </mml:mo><mml:mi>GeV</mml:mi><mml:mo> </mml:mo><mml:mi>Au</mml:mi><mml:mtext>+</mml:mtext><mml:mi>Au</mml:mi></mml:mrow></mml:math> collisions at the RHIC STAR experiment

Various models of the QCD phase diagram favor a first-order phase transition to quark-gluon plasma, and therefore a critical endpoint which could manifest itself in measurable fluctuations and correlations. The authors report measurements of the moments of the net proton multiplicity fluctuations (cumulants) and correlation functions from the RHIC beam energy scan. They establish that at $\sqrt{{s}_{N\phantom{\rule{0}{0ex}}N}}=3$ GeV the produced system is dominated by hadronic rather than thermal interactions. This puts a limit on the search for the elusive critical point in the QCD phase diagram to energies higher than 3 GeV.