Tracking the baryon number with nuclear collisions
Abstract
Baryon quantum number is found to be conserved since baryogenesis in the early Universe. Conventionally, each fractionally charged valence quark is understood to carry one-third of a baryon number. An alternative hypothesis posits that baryon number is instead carried by a baryon junction—a nonperturbative, Y-shaped gluonic configuration. Neither scenario has been verified experimentally. The STAR Collaboration reports measurements at mid-rapidity of baryon number ( B ) over the electric charge number difference (∆ Q ) in isobar nuclear collisions, and the net-proton yield along rapidity in photonuclear collisions. A larger B /∆ Q ratio and less asymmetric net-proton yield are observed than predicted from models assigning baryon number to valence quarks. These findings, corroborated by previous measurements in Au+Au collisions, disfavor the valence quark picture.
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Authors: B.E. Aboona, J. Adam, L. Adamczyk, I. Aggarwal, M. M. Aggarwal, Z. Ahammed, A. K. Alshammri, E. C. Aschenauer, S. Aslam, J. Atchison, V. Bairathi, X. Bao, P. Barik, K. 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. Calderon De La Barca Sanchez, D. Cebra, J. Ceska, I. Chakaberia, P. Chaloupka, Y. S. Chang, Z. Chang, A. Chatterjee, D. Chen, J. H. Chen, L. Chen, Q. Chen, W. Chen, Z. Chen, J. Cheng, Y. Cheng, W. Christie, X. Chu, S. Corey, H. J. Crawford, M. Csanad, G. Dale-Gau, A. Das, D. De Souza Lemos, I. M. Deppner, A. Deshpande, A. Dhamija, A. Dimri, P. Dixit, X. Dong, J. L. Drachenberg, E. Duckworth, J. C. Dunlop, Y. S. El-Feky, J. Engelage, G. Eppley, S. Esumi, O. Evdokimov, O. Eyser, B. Fan, Y. Fang, R. Fatemi, S. Fazio, H. Feng, Y. Feng, E. Finch, Y. Fisyak, F. A. Flor, B. Fu, C. Fu, T. Fu, C. A. Gagliardi, T. Galatyuk, T. Gao, Y. Gao, G. Garcia, F. Geurts, A. Gibson, A. Giri, K. Gopal, X. Gou, D. Grosnick, A. Gu, J. Gu, A. Gupta, W. Guryn, A. Hamed, R. J. Hamilton, J. Han, X. Han, S. Harabasz, M. D. Harasty, J. W. Harris
Institutions: University of California, Los Angeles, Chinese Academy of Sciences, University of Tsukuba, Fudan University, The Ohio State University, Heidelberg University, Yale University, University of Houston, University of Illinois Chicago, Czech Technical University in Prague, Huzhou Normal University, Tsinghua University, AGH University of Krakow, University of California, Berkeley, University of Kentucky, University of California, Riverside, Purdue University West Lafayette, University of California, Davis, University of Calabria, Texas A&M University, Guangxi Normal University, Rice University, Shandong University of Science and Technology, Indiana University Bloomington, Brookhaven National Laboratory, State University of New York, Indian Institute of Science Education and Research Berhampur, Technische Universität Darmstadt, Central China Normal University, University of Jammu, Eötvös Loránd University, University of Tarapacá, Panjab University, Lawrence Berkeley National Laboratory, Krakow University of Economics, National Institute of Technology Durgapur, Czech Academy of Sciences, Nuclear Physics Institute, Shanghai Institute of Applied Physics, Valparaiso University, American University in Cairo, Institute of Modern Physics, Southern Connecticut State University, Indian Institute of Science Education and Research, Tirupati, Variable Energy Cyclotron Centre, Kent State University, Abilene Christian University