Upper limit on the chiral magnetic effect in isobar collisions at the Relativistic Heavy-Ion Collider
M. I. Abdulhamid, B. E. Aboona, J. Adam, J. R. Adams, G. Agakishiev, I. Aggarwal, M. M. Aggarwal, Z. Ahammed, A. Aitbaev, I. Alekseev, E. Alpatov, A. Aparin, S. Aslam, Jennifer Atchison, G. S. Averichev, V. Bairathi, J. Ball, K. N. Barish, P. Bhagat, A. Bhasin, S. Bhatta, S. R. Bhosale, I. G. Bordyuzhin, J. D. Brandenburg, A. V. Brandin, C. Broodo, X. Z. Cai, H. Caines, M. Calderón de la Barca Sánchez, D. Cebra, J. Ceska, I. Chakaberia, B. K. Chan, Z. Chang, A. Chatterjee, D. Chen, J. Chen, J. H. Chen, Z. Chen, Jianping Cheng, Y. Cheng, S. Choudhury, W. Christie, X. Chu, H. J. Crawford, G. Dale-Gau, Arkaprava Das, Т. Г. Дедович, I. M. Deppner, A. A. Derevschikov, A. Dhamija, 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, C. Feng, Yanting Feng, E. Finch, Y. Fisyak, F. A. Flor, Changbo Fu, T. Gao, F. J. M. Geurts, N. Ghimire, S. M. Gibson, K. Gopal, X. Gou, D. Grosnick, A. Gupta, A. Hamed, Y. F. Han, M. D. Harasty, J. W. Harris, H. Harrison-Smith, W. He, X. H. He, Yayun He, C. Hu, Qiang Hu, Y. Hu, Handong Huang, H. Z. Huang, S. L. Huang, T. Huang, X. Huang, Y. Huang, Y. Huang, T. J. Humanic, M. Isshiki, W. W. Jacobs, A. Jalotra, C. Jena
Abstract
The chiral magnetic effect (CME) is a phenomenon that arises from the QCD anomaly in the presence of an external magnetic field. The experimental search for its evidence has been one of the key goals of the physics program of the Relativistic Heavy-Ion Collider. The STAR Collaboration has previously presented the results of a blind analysis of isobar collisions (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mmultiscripts><a:mi>Ru</a:mi><a:mprescripts/><a:mn>44</a:mn><a:mn>96</a:mn></a:mmultiscripts><a:mo>+</a:mo><a:mmultiscripts><a:mi>Ru</a:mi><a:mprescripts/><a:mn>44</a:mn><a:mn>96</a:mn></a:mmultiscripts></a:mrow><a:mo>,</a:mo><a:mo> </a:mo><a:mrow><a:mmultiscripts><a:mi>Zr</a:mi><a:mprescripts/><a:mn>40</a:mn><a:mn>96</a:mn></a:mmultiscripts><a:mo>+</a:mo><a:mmultiscripts><a:mi>Zr</a:mi><a:mprescripts/><a:mn>40</a:mn><a:mn>96</a:mn></a:mmultiscripts></a:mrow></a:math>) in the search for the CME. The isobar ratio (<b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>Y</b:mi></b:math>) of CME-sensitive observable, charge separation scaled by elliptic anisotropy, is close to but systematically larger than the inverse multiplicity ratio, the naive background baseline. This indicates the potential existence of a CME signal and the presence of remaining nonflow background due to two- and three-particle correlations, which are different between the isobars. In this postblind analysis, we estimate the contributions from those nonflow correlations as a background baseline to <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mi>Y</c:mi></c:math>, utilizing the isobar data as well as Heavy Ion Jet Interaction Generator simulations. This baseline is found consistent with the isobar ratio measurement, and an upper limit of 10% at 95% confidence level is extracted for the CME fraction in the charge separation measurement in isobar collisions at <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:msqrt><d:msub><d:mi>s</d:mi><d:mi mathvariant="normal" mathsize="small">NN</d:mi></d:msub></d:msqrt><d:mo>=</d:mo><d:mn>200</d:mn></d:mrow></d:math> GeV. Published by the American Physical Society 2024