Precision Measurement of Net-Proton-Number Fluctuations in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Au</mml:mi><mml:mo>+</mml:mo><mml:mi>Au</mml:mi></mml:mrow></mml:math> Collisions at RHIC
B. E. Aboona, J. Adam, L. Adamczyk, I. Aggarwal, M. M. Aggarwal, Z. Ahammed, A. K. Alshammri, E. C. Aschenauer, Saba Aslam, Jennifer Atchison, V. Bairathi, Xinhe Bao, K. N. Barish, S. Behera, R. Bellwied, P. Bhagat, A. Bhasin, S. Bhatta, S. R. Bhosale, J. Bielcik, J. Bielcikova, J. D. Brandenburg, C. Broodo, X. Z. Cai, H. Caines, M. Calderón de la Barca Sánchez, D. Cebra, J. Ceska, I. Chakaberia, P. Chaloupka, B. K. Chan, Z. Chang, Arindam Chatterjee, D. Chen, J. Chen, J. H. Chen, Q. Chen, Z. Chen, J. Cheng, Yin Cheong Cheng, W. Christie, X. Chu, Seth J. Corey, H. J. Crawford, M. Csanád, G. Dale-Gau, Arkaprava Das, I. M. Deppner, A. Deshpande, A. Dhamija, A. P. Dimri, P. Dixit, X. Dong, J. L. Drachenberg, E. Duckworth, J. C. Dunlop, J. Engelage, G. Eppley, S. Esumi, O. Evdokimov, O. Eyser, R. Fatemi, S. Fazio, Yanting Feng, E. Finch, Y. Fisyak, F. A. Flor, C. Fu, Taotao Fu, C. A. Gagliardi, T. Galatyuk, Tong Gao, F. J. M. Geurts, N. Ghimire, A. Gibson, K. Gopal, X. Gou, D. Grosnick, A. Gu, A. Gupta, W. Guryn, A. Hamed, Richard Hamilton, Xiang Han, S. Harabasz, M. D. Harasty, J. W. Harris, H. Harrison-Smith, L. B. Havener, X. H. He, M. He, N. Herrmann, L. Holub, C. Hu, Qingyuan Hu, Y. Hu, H. Z. Huang, H. Z. Huang, S. L. Huang, Tao Huang
Abstract
We report precision measurements on cumulants (C_{n}) and factorial cumulants (κ_{n}) of (net) proton number distributions up to fourth order in Au+Au collisions over center-of-mass energies sqrt[s_{NN}]=7.7-27 GeV from phase II of the Beam Energy Scan program at RHIC. (Anti)protons are selected at midrapidity (|y|<0.5) within a transverse momentum range of 0.4<p_{T}<2.0 GeV/c. Relative to various noncritical-point model calculations and peripheral collision 70%-80% data, the net proton C_{4}/C_{2} measurement in 0%-5% collisions shows a minimum around 19.6 GeV for significance of deviation at ∼2-5σ. A minimum in C_{4}/C_{2} with respect to a noncritical baseline is expected to be a characteristic feature of the signature associated with a critical point in the QCD phase diagram. In addition, deviations from noncritical baselines around the same collision energy region are also seen in proton factorial cumulant ratios, especially in κ_{2}/κ_{1} and κ_{3}/κ_{1}. Dynamical model calculations including a critical point are called for in order to understand these precision measurements.