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Measurement of fifth- and sixth-order fluctuations of (net-)proton number in Au + Au collisions from phase II of the beam energy scan program at RHIC

Aboona, B. E. [Texas A&M University]·Adam, J. [Czech Technical University in Prague]·Adamczyk, L. [AGH University of Krakow]·Aggarwal, I. [Panjab University]·Aggarwal, M. M. [Panjab University]·Ahammed, Z. [Variable Energy Cyclotron Centre]·Alshammri, A. K. [Kent State University]·Aschenauer, E. C. [Brookhaven National Laboratory]·Aslam, S. [Fudan University]·Atchison, J. [Abilene Christian University]·Bairathi, V. [Instituto de Alta Investigación]·Bao, X. [Shandong University]·Barik, P. [Indian Institute of Science Education and Research (IISER)]·Barish, K. [University of California]·Behera, S. [Indian Institute of Science Education and Research (IISER) Tirupati]·Bellwied, R. [University of Houston]·Bhagat, P. [University of Jammu]·Bhasin, A. [University of Jammu]·Bhatta, S. [State University of New York]·Bhosale, S. R. [AGH University of Krakow]·Bielcik, J. [Czech Technical University in Prague]·Bielcikova, J. [Czech Technical University in Prague; Nuclear Physics Institute of the CAS]·Brandenburg, J. D. [The Ohio State University]·Broodo, C. [University of Houston]·Cai, X. Z. [Shanghai Institute of Applied Physics]·Caines, H. [Yale University]·Sánchez, M. Calderón de la Barca [University of California]·Cebra, D. [University of California]·Ceska, J. [Czech Technical University in Prague]·Chakaberia, I. [Lawrence Berkeley National Laboratory]·Chaloupka, P. [Czech Technical University in Prague]·Chang, Y. S. [Purdue University]·Chang, Z. [Indiana University]·Chatterjee, A. [National Institute of Technology Durgapur]·Chen, D. [University of California]·Chen, J. H. [Fudan University]·Chen, L. [Central China Normal University]·Chen, Q. [Guangxi Normal University]·Chen, W. [Fudan University]·Chen, Z. [Shandong University]·Cheng, J. [Tsinghua University]·Cheng, Y. [University of California]·Christie, W. [Brookhaven National Laboratory]·Chu, X. [Brookhaven National Laboratory]·Corey, S. [The Ohio State University]·Crawford, H. J. [University of California]·Csanád, M. [ELTE Eötvös Loránd University]·Dale-Gau, G. [Czech Technical University in Prague]·Das, A. [Czech Technical University in Prague]·Lemos, D. De Souza [Brookhaven National Laboratory]·Deppner, I. M. [University of Heidelberg]·Deshpande, A. [State University of New York]·Dhamija, A. [Panjab University]·Dimri, A. [State University of New York]·Dixit, P. [Fudan University]·Dong, X. [Lawrence Berkeley National Laboratory]·Drachenberg, J. L. [Abilene Christian University]·Duckworth, E. [Kent State University]·Dunlop, J. C. [Brookhaven National Laboratory]·El-Feky, Y. S. [American University in Cairo]·Engelage, J. [University of California]·Eppley, G. [Rice University]·Esumi, S. [University of Tsukuba]·Evdokimov, O. [University of Illinois at Chicago]·Eyser, O. [Brookhaven National Laboratory]·Fan, B. [Central China Normal University]·Fang, Y. [Tsinghua University]·Fatemi, R. [University of Kentucky]·Fazio, S. [University of Calabria & INFN-Cosenza]·Feng, H. [Central China Normal University]·Feng, Y. [Central China Normal University]·Finch, E. [Southern Connecticut State University]·Fisyak, Y. [Brookhaven National Laboratory]·Flor, F. A. [Yale University]·Fu, B. [Central China Normal University]·Fu, C. [Institute of Modern Physics]·Fu, T. [Shandong University]·Gagliardi, C. A. [Texas A&M University]·Galatyuk, T. [Technische Universität Darmstadt]·Gao, T. [Shandong University]·Gao, Y. [Fudan University]·Garcia, G. [Brookhaven National Laboratory]·Geurts, F. [Rice University]·Gibson, A. [Valparaiso University]·Giri, A. [University of Houston]·Gopal, K. [Indian Institute of Science Education and Research (IISER) Tirupati]·Gou, X. [Shandong University]·Grosnick, D. [Valparaiso University]·Gu, A. [Huzhou University]·Gu, J. [Fudan University]·Gupta, A. [University of Jammu]·Guryn, W. [Brookhaven National Laboratory]·Hamed, A. [American University in Cairo]·Hamilton, R. J. [Yale University]·Han, J. [Central China Normal University]·Han, X. [The Ohio State University]·Harabasz, S. [Technische Universität Darmstadt]·Harasty, M. D. [University of California]·Harris, J. W. [Yale University]·Harrison-Smith, H. [University of Kentucky]
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Abstract

We report high-statistics measurements of fifth- and sixth-order factorial cumulants and cumulant ratios of (net-)proton multiplicity distributions in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7–27GeV, using data from the STAR experiment collected during the Beam Energy Scan Phase II at RHIC. Protons and antiprotons are identified at midrapidity (|𝑦| < 0.5) with transverse momentum 0.4 < 𝑝 𝑇 < 2.0GeV/𝑐. The proton factorial cumulants 𝜅 4 , 𝜅 5 , and 𝜅 6 increase with order but exhibit no sign alternation within current uncertainties, offering no evidence for a two-component structure in the proton multiplicity distribution, as might be expected near a first-order phase transition. The cumulant ratios 𝐶 5 /𝐶 1 and 𝐶 6 /𝐶 2 fluctuate around zero in collisions at 0–40% centrality. The results are consistent with both the negative predictions from lattice QCD and the positive trends obtained from the ultrarelativistic quantum molecular dynamics (UrQMD) model. At $\sqrt{s_{NN}}$ ≳ 27GeV, the 𝐶 4 /𝐶 2 and 𝐶 5 /𝐶 1 results are compatible with predictions from lattice QCD, functional renormalization group (FRG), and hadron resonance gas (HRG) models, while UrQMD describes the data better at lower energies. Here, these measurements place constraints on baryon number fluctuations and offer valuable insights into the QCD phase structure.

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73 NUCLEAR PHYSICS AND RADIATION PHYSICSCharged-particle multiplicityLattice QCDQCD phase transitionsQuantum chromodynamicsQuark-gluon plasmaRelativistic heavy-ion collisionsStrong interactionThermal & statistical models

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Aboona, B. E. [Texas A&M University], Adam, J. [Czech Technical University in Prague], Adamczyk, L. [AGH University of Krakow], Aggarwal, I. [Panjab University], Aggarwal, M. M. [Panjab University], Ahammed, Z. [Variable Energy Cyclotron Centre], Alshammri, A. K. [Kent State University], Aschenauer, E. C. [Brookhaven National Laboratory], Aslam, S. [Fudan University], Atchison, J. [Abilene Christian University], Bairathi, V. [Instituto de Alta Investigación], Bao, X. [Shandong University], Barik, P. [Indian Institute of Science Education and Research (IISER)], Barish, K. [University of California], Behera, S. [Indian Institute of Science Education and Research (IISER) Tirupati], Bellwied, R. [University of Houston], Bhagat, P. [University of Jammu], Bhasin, A. [University of Jammu], Bhatta, S. [State University of New York], Bhosale, S. R. [AGH University of Krakow], Bielcik, J. [Czech Technical University in Prague], Bielcikova, J. [Czech Technical University in Prague; Nuclear Physics Institute of the CAS], Brandenburg, J. D. [The Ohio State University], Broodo, C. [University of Houston], Cai, X. Z. [Shanghai Institute of Applied Physics], Caines, H. [Yale University], Sánchez, M. Calderón de la Barca [University of California], Cebra, D. [University of California], Ceska, J. [Czech Technical University in Prague], Chakaberia, I. [Lawrence Berkeley National Laboratory], Chaloupka, P. [Czech Technical University in Prague], Chang, Y. S. [Purdue University], Chang, Z. [Indiana University], Chatterjee, A. [National Institute of Technology Durgapur], Chen, D. [University of California], Chen, J. H. [Fudan University], Chen, L. [Central China Normal University], Chen, Q. [Guangxi Normal University], Chen, W. [Fudan University], Chen, Z. [Shandong University], Cheng, J. [Tsinghua University], Cheng, Y. [University of California], Christie, W. [Brookhaven National Laboratory], Chu, X. [Brookhaven National Laboratory], Corey, S. [The Ohio State University], Crawford, H. J. [University of California], Csanád, M. [ELTE Eötvös Loránd University], Dale-Gau, G. [Czech Technical University in Prague], Das, A. [Czech Technical University in Prague], Lemos, D. De Souza [Brookhaven National Laboratory], Deppner, I. M. [University of Heidelberg], Deshpande, A. [State University of New York], Dhamija, A. [Panjab University], Dimri, A. [State University of New York], Dixit, P. [Fudan University], Dong, X. [Lawrence Berkeley National Laboratory], Drachenberg, J. L. [Abilene Christian University], Duckworth, E. [Kent State University], Dunlop, J. C. [Brookhaven National Laboratory], El-Feky, Y. S. [American University in Cairo], Engelage, J. [University of California], Eppley, G. [Rice University], Esumi, S. [University of Tsukuba], Evdokimov, O. [University of Illinois at Chicago], Eyser, O. [Brookhaven National Laboratory], Fan, B. [Central China Normal University], Fang, Y. [Tsinghua University], Fatemi, R. [University of Kentucky], Fazio, S. [University of Calabria & INFN-Cosenza], Feng, H. [Central China Normal University], Feng, Y. [Central China Normal University], Finch, E. [Southern Connecticut State University], Fisyak, Y. [Brookhaven National Laboratory], Flor, F. A. [Yale University], Fu, B. [Central China Normal University], Fu, C. [Institute of Modern Physics], Fu, T. [Shandong University], Gagliardi, C. A. [Texas A&M University], Galatyuk, T. [Technische Universität Darmstadt], Gao, T. [Shandong University], Gao, Y. [Fudan University], Garcia, G. [Brookhaven National Laboratory], Geurts, F. [Rice University], Gibson, A. [Valparaiso University], Giri, A. [University of Houston], Gopal, K. [Indian Institute of Science Education and Research (IISER) Tirupati], Gou, X. [Shandong University], Grosnick, D. [Valparaiso University], Gu, A. [Huzhou University], Gu, J. [Fudan University], Gupta, A. [University of Jammu], Guryn, W. [Brookhaven National Laboratory], Hamed, A. [American University in Cairo], Hamilton, R. J. [Yale University], Han, J. [Central China Normal University], Han, X. [The Ohio State University], Harabasz, S. [Technische Universität Darmstadt], Harasty, M. D. [University of California], Harris, J. W. [Yale University], Harrison-Smith, H. [University of Kentucky]. 2026-05-15. Measurement of fifth- and sixth-order fluctuations of (net-)proton number in Au + Au collisions from phase II of the beam energy scan program at RHIC. https://doi.org/10.1103/lq8c-9fr6

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