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Observation of the Electromagnetic Field Effect via Charge-Dependent Directed Flow in Heavy-Ion Collisions at the Relativistic Heavy Ion Collider

M. I. Abdulhamid⁴, B. E. Aboona⁵⁵, J. Adam¹⁵, J. R. Adams⁴⁰, G. Agakishiev³⁰, I. Aggarwal⁴¹, M. M. Aggarwal⁴¹, Z. Ahammed⁶¹, A. Aitbaev³⁰ et al. (STAR Collaboration)

A. Aitbaev³⁰, I. Alekseev^2,37, E. Alpatov³⁷, A. Aparin³⁰, S. Aslam²⁶, J. Atchison¹, G. S. Averichev³⁰, V. Bairathi⁵³, J. G. Ball Cap²², K. Barish¹¹, P. Bhagat²⁹, A. Bhasin²⁹, S. Bhatta⁵², S. R. Bhosale¹⁷, I. G. Bordyuzhin², J. D. Brandenburg⁴⁰, A. V. Brandin³⁷, X. Z. Cai⁵⁰, H. Caines⁶⁴, M. Calderón de la Barca Sánchez⁹, D. Cebra⁹, J. Ceska¹⁵, I. Chakaberia³³, B. K. Chan¹⁰, Z. Chang²⁷, A. Chatterjee¹⁶, D. Chen¹¹, J. Chen⁴⁹, J. H. Chen ¹⁹, Z. Chen⁴⁹, J. Cheng⁵⁷, Y. Cheng¹⁰, S. Choudhury¹⁹, W. Christie⁶, X. Chu⁶, H. J. Crawford⁸, G. Dale-Gau¹³, A. Das¹⁵, A. P. Dash¹⁰, M. Daugherity¹, T. G. Dedovich³⁰, I. M. Deppner²¹, A. A. Derevschikov⁴², A. Dhamija⁴¹, P. Dixit²⁴, X. Dong³³, J. L. Drachenberg¹, E. Duckworth³¹, J. C. Dunlop⁶, J. Engelage⁸, G. Eppley⁴⁴, S. Esumi⁵⁸, O. Evdokimov¹³, O. Eyser⁶, R. Fatemi³², S. Fazio⁷, C. J. Feng³⁹, Y. Feng⁴³, E. Finch⁵¹, Y. Fisyak⁶, F. A. Flor⁶⁴, C. Fu²⁸, T. Gao⁴⁹, F. Geurts⁴⁴, N. Ghimire⁵⁴, A. Gibson⁶⁰, K. Gopal²⁵, X. Gou⁴⁹, D. Grosnick⁶⁰, A. Gupta²⁹, A. Hamed⁴, Y. Han⁴⁴, M. D. Harasty⁹, J. W. Harris⁶⁴, H. Harrison-Smith³², W. He¹⁹, X. H. He²⁸, Y. He⁴⁹, C. Hu⁵⁹, Q. Hu²⁸, Y. Hu³³, H. Huang³⁹, H. Z. Huang¹⁰, S. L. Huang⁵², T. Huang¹³, X. Huang⁵⁷, Y. Huang⁵⁷, Y. Huang¹², T. J. Humanic⁴⁰, D. Isenhower¹, M. Isshiki⁵⁸, W. W. Jacobs²⁷, A. Jalotra²⁹, C. Jena²⁵, Y. Ji³³, J. Jia^6,52, C. Jin⁴⁴, X. Ju⁴⁶, E. G. Judd⁸, S. Kabana⁵³, D. Kalinkin³², K. Kang⁵⁷, D. Kapukchyan¹¹, K. Kauder⁶, D. Keane³¹, A. Kechechyan³⁰, A. Kiselev⁶, A. G. Knospe³⁴, H. S. Ko³³, L. Kochenda³⁷, A. A. Korobitsin³⁰, A. Yu. Kraeva³⁷, P. Kravtsov³⁷, L. Kumar⁴¹, M. C. Labonte⁹, R. Lacey⁵², J. M. Landgraf⁶, A. Lebedev⁶, R. Lednicky³⁰, J. H. Lee⁶, Y. H. Leung²¹, N. Lewis⁶, C. Li⁴⁹, H-S. Li⁴³, W. Li⁴⁴, X. Li⁴⁶, Y. Li⁴⁶, Y. Li⁵⁷, Z. Li⁴⁶, X. Liang¹¹, Y. Liang³¹, T. Lin⁴⁹, Y. Lin²⁰, C. Liu²⁸, F. Liu¹², G. Liu⁴⁷, H. Liu¹², L. Liu¹², T. Liu⁶⁴, X. Liu⁴⁰, Y. Liu⁵⁵, Z. Liu¹², T. Ljubicic⁶, O. Lomicky¹⁵, R. S. Longacre⁶, E. M. Loyd¹¹, T. Lu²⁸, N. S. Lukow⁵⁴, X. F. Luo¹², V. B. Luong³⁰, L. Ma¹⁹, R. Ma⁶, Y. G. Ma¹⁹, N. Magdy⁵², D. Mallick⁶², S. Margetis³¹, H. S. Matis³³, G. McNamara⁶³, K. Mi¹², N. G. Minaev⁴², B. Mohanty³⁸, M. M. Mondal³⁸, I. Mooney⁶⁴, D. A. Morozov⁴², A. Mudrokh³⁰, M. I. Nagy¹⁷, A. S. Nain⁴¹, J. D. Nam⁵⁴, M. Nasim²⁴, E. Nedorezov³⁰, D. Neff¹⁰, J. M. Nelson⁸, D. B. Nemes⁶⁴, M. Nie⁴⁹, G. Nigmatkulov¹³, T. Niida⁵⁸, L. V. Nogach⁴², T. Nonaka⁵⁸, G. Odyniec³³, A. Ogawa⁶, S. Oh⁴⁸, V. A. Okorokov³⁷, K. Okubo⁵⁸, B. S. Page⁶, R. Pak⁶, A. Pandav³³, Y. Panebratsev³⁰, T. Pani⁴⁵, P. Parfenov³⁷, A. Paul¹¹, C. Perkins⁸, B. R. Pokhrel⁵⁴, M. Posik⁵⁴, A. Povarov³⁷, T. Protzman³⁴, N. K. Pruthi⁴¹, J. Putschke⁶³, Z. Qin⁵⁷, H. Qiu²⁸, A. Quintero⁵⁴, C. Racz¹¹, S. K. Radhakrishnan³¹, A. Rana⁴¹, R. L. Ray⁵⁶, H. G. Ritter³³, C. W. Robertson⁴³, O. V. Rogachevsky³⁰, M. A. Rosales Aguilar³², D. Roy⁴⁵, L. Ruan⁶, A. K. Sahoo²⁴, N. R. Sahoo²⁵, H. Sako⁵⁸, S. Salur⁴⁵, E. Samigullin², S. Sato⁵⁸, B. C. Schaefer³⁴, W. B. Schmidke^6,*, N. Schmitz³⁵, J. Seger¹⁴, R. Seto¹¹, P. Seyboth³⁵, N. Shah²⁶, E. Shahaliev³⁰, P. V. Shanmuganathan⁶, T. Shao¹⁹, M. Sharma²⁹, N. Sharma²⁴, R. Sharma²⁵, S. R. Sharma²⁵, A. I. Sheikh³¹, D. Shen⁴⁹, D. Y. Shen¹⁹, K. Shen⁴⁶, S. S. Shi¹², Y. Shi⁴⁹, Q. Y. Shou¹⁹, F. Si⁴⁶, J. Singh⁴¹, S. Singha²⁸, P. Sinha²⁵, M. J. Skoby^5,43, Y. Söhngen²¹, Y. Song⁶⁴, B. Srivastava⁴³, T. D. S. Stanislaus⁶⁰, D. J. Stewart⁶³, M. Strikhanov³⁷, B. Stringfellow⁴³, Y. Su⁴⁶, C. Sun⁵², X. Sun²⁸, Y. Sun⁴⁶, Y. Sun²³, B. Surrow⁵⁴, D. N. Svirida², Z. W. Sweger⁹, A. C. Tamis⁶⁴, A. H. Tang⁶, Z. Tang⁴⁶, A. Taranenko³⁷, T. Tarnowsky³⁶, J. H. Thomas³³, D. Tlusty¹⁴, T. Todoroki⁵⁸, M. V. Tokarev³⁰, S. Trentalange¹⁰, P. Tribedy⁶, S. K. Tripathy⁶², O. D. Tsai^10,6, C. Y. Tsang^31,6, Z. Tu⁶, J. Tyler⁵⁵, T. Ullrich⁶, D. G. Underwood^3,60, I. Upsal⁴⁶, G. Van Buren⁶, A. N. Vasiliev^42,37, V. Verkest⁶³, F. Videbæk⁶, S. Vokal³⁰, S. A. Voloshin⁶³, F. Wang⁴³, G. Wang ¹⁰, J. S. Wang²³, J. Wang⁴⁹, X. Wang⁴⁹, Y. Wang⁴⁶, Y. Wang¹², Y. Wang⁵⁷, Z. Wang⁴⁹, J. C. Webb⁶, P. C. Weidenkaff²¹, G. D. Westfall³⁶, H. Wieman³³, G. Wilks¹³, S. W. Wissink²⁷, J. Wu¹², J. Wu²⁸, X. Wu¹⁰, X. Wu⁴⁶, B. Xi¹⁹, Z. G. Xiao⁵⁷, G. Xie⁵⁹, W. Xie⁴³, H. Xu²³, N. Xu³³, Q. H. Xu⁴⁹, Y. Xu⁴⁹, Y. Xu¹², Z. Xu³¹, Z. Xu¹⁰, G. Yan⁴⁹, Z. Yan⁵², C. Yang⁴⁹, Q. Yang⁴⁹, S. Yang⁴⁷, Y. Yang³⁹, Z. Ye⁴⁴, Z. Ye³³, L. Yi⁴⁹, K. Yip⁶, Y. Yu⁴⁹, W. Zha⁴⁶, C. Zhang¹⁹, D. Zhang⁴⁷, J. Zhang⁴⁹, S. Zhang⁴⁶, W. Zhang⁴⁷, X. Zhang²⁸, Y. Zhang²⁸, Y. Zhang⁴⁶, Y. Zhang⁴⁹, Y. Zhang¹², Z. J. Zhang³⁹, Z. Zhang⁶, Z. Zhang¹³, F. Zhao²⁸, J. Zhao¹⁹, M. Zhao⁶, C. Zhou¹⁹, J. Zhou⁴⁶, S. Zhou¹², Y. Zhou¹², X. Zhu⁵⁷, M. Zurek^3,6, and M. Zyzak¹⁸ (STAR Collaboration)

¹Abilene Christian University, Abilene, Texas 79699
²Alikhanov Institute for Theoretical and Experimental Physics NRC ”Kurchatov Institute,” Moscow 117218
³Argonne National Laboratory, Argonne, Illinois 60439
⁴American University in Cairo, New Cairo 11835, Egypt
⁵Ball State University, Muncie, Indiana, 47306
⁶Brookhaven National Laboratory, Upton, New York 11973
⁷University of Calabria and INFN-Cosenza, Rende 87036, Italy
⁸University of California, Berkeley, California 94720
⁹University of California, Davis, California 95616
¹⁰University of California, Los Angeles, California 90095
¹¹University of California, Riverside, California 92521
¹²Central China Normal University, Wuhan, Hubei 430079
¹³University of Illinois at Chicago, Chicago, Illinois 60607
¹⁴Creighton University, Omaha, Nebraska 68178
¹⁵Czech Technical University in Prague, FNSPE, Prague 115 19, Czech Republic
¹⁶National Institute of Technology Durgapur, Durgapur-713209, India
¹⁷ELTE Eötvös Loránd University, Budapest, Hungary H-1117
¹⁸Frankfurt Institute for Advanced Studies FIAS, Frankfurt 60438, Germany
¹⁹Fudan University, Shanghai, 200433
²⁰Guangxi Normal University, Guilin
²¹University of Heidelberg, Heidelberg 69120, Germany
²²University of Houston, Houston, Texas 77204
²³Huzhou University, Huzhou, Zhejiang 313000
²⁴Indian Institute of Science Education and Research (IISER), Berhampur 760010, India
²⁵Indian Institute of Science Education and Research (IISER) Tirupati, Tirupati 517507, India
²⁶Indian Institute Technology, Patna, Bihar 801106, India
²⁷Indiana University, Bloomington, Indiana 47408
²⁸Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, Gansu 730000
²⁹University of Jammu, Jammu 180001, India
³⁰Joint Institute for Nuclear Research, Dubna 141 980
³¹Kent State University, Kent, Ohio 44242
³²University of Kentucky, Lexington, Kentucky 40506-0055
³³Lawrence Berkeley National Laboratory, Berkeley, California 94720
³⁴Lehigh University, Bethlehem, Pennsylvania 18015
³⁵Max-Planck-Institut für Physik, Munich 80805, Germany
³⁶Michigan State University, East Lansing, Michigan 48824
³⁷National Research Nuclear University MEPhI, Moscow 115409
³⁸National Institute of Science Education and Research, HBNI, Jatni 752050, India
³⁹National Cheng Kung University, Tainan 70101
⁴⁰The Ohio State University, Columbus, Ohio 43210
⁴¹Panjab University, Chandigarh 160014, India
⁴²NRC ”Kurchatov Institute,” Institute of High Energy Physics, Protvino 142281
⁴³Purdue University, West Lafayette, Indiana 47907
⁴⁴Rice University, Houston, Texas 77251
⁴⁵Rutgers University, Piscataway, New Jersey 08854
⁴⁶University of Science and Technology of China, Hefei, Anhui 230026
⁴⁷South China Normal University, Guangzhou, Guangdong 510631
⁴⁸Sejong University, Seoul, 05006, South Korea
⁴⁹Shandong University, Qingdao, Shandong 266237
⁵⁰Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800
⁵¹Southern Connecticut State University, New Haven, Connecticut 06515
⁵²State University of New York, Stony Brook, New York 11794
⁵³Instituto de Alta Investigación, Universidad de Tarapacá, Arica 1000000, Chile
⁵⁴Temple University, Philadelphia, Pennsylvania 19122
⁵⁵Texas A&M University, College Station, Texas 77843
⁵⁶University of Texas, Austin, Texas 78712
⁵⁷Tsinghua University, Beijing 100084
⁵⁸University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
⁵⁹University of Chinese Academy of Sciences, Beijing, 101408
⁶⁰Valparaiso University, Valparaiso, Indiana 46383
⁶¹Variable Energy Cyclotron Centre, Kolkata 700064, India
⁶²Warsaw University of Technology, Warsaw 00-661, Poland
⁶³Wayne State University, Detroit, Michigan 48201
⁶⁴Yale University, New Haven, Connecticut 06520

^*Deceased.

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Phys. Rev. X 14, 011028 – Published 23 February, 2024

DOI: https://doi.org/10.1103/PhysRevX.14.011028

Abstract

The deconfined quark-gluon plasma (QGP) created in relativistic heavy-ion collisions enables the exploration of the fundamental properties of matter under extreme conditions. Noncentral collisions can produce strong magnetic fields on the order of $10^{18} G$ , which offers a probe into the electrical conductivity of the QGP. In particular, quarks and antiquarks carry opposite charges and receive contrary electromagnetic forces that alter their momenta. This phenomenon can be manifested in the collective motion of final-state particles, specifically in the rapidity-odd directed flow, denoted as $v_{1} (y)$ . Here, we present the charge-dependent measurements of $d v_{1} / d y$ near midrapidities for $π^{\pm}$ , $K^{\pm}$ , and $p (\bar{p})$ in $Au + Au$ and isobar ( ${}_{44}^{96}{Ru} + {}_{44}^{96}{Ru}$ and ${}_{40}^{96}{Zr} + {}_{40}^{96}{Zr}$ ) collisions at $\sqrt{s_{NN}} = 200 GeV$ , and in $Au + Au$ collisions at 27 GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The combined dependence of the $v_{1}$ signal on collision system, particle species, and collision centrality can be qualitatively and semiquantitatively understood as several effects on constituent quarks. While the results in central events can be explained by the $u$ and $d$ quarks transported from initial-state nuclei, those in peripheral events reveal the impacts of the electromagnetic field on the QGP. Our data put valuable constraints on the electrical conductivity of the QGP in theoretical calculations.

Physics Subject Headings (PhySH)

Relativistic heavy-ion collisions

Focus

Colossal Magnetic Field Detected in Nuclear Matter

Published 23 February, 2024

Collisions of heavy ions briefly produced a magnetic field $1 0^{18}$ times stronger than Earth’s, and it left observable effects.

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Popular Summary

In ultrarelativistic nuclear collisions, heavy ions such as gold and lead are accelerated close to the speed of light and pass through each other via collisions to create a deconfined quark-gluon plasma. When the collision is noncentral, an extremely intense electromagnetic field can be generated in the interaction region. This electromagnetic field has the highest strength ever achieved on Earth, but an extremely short lifetime. That hinders its direct observations by experiments. We examine the collective motion of charged hadrons emitted from the plasma to uncover the characteristic pattern imprinted by that electromagnetic field.

In this work, we analyze data on ion collisions collected at Brookhaven’s Relativistic Heavy Ion Collider in 2014 and 2016 as part of the STAR experiment. We measure, with unprecedented precision, the charge-dependent sideward motion of $π$ mesons, $K$ mesons, and protons emitted from those collisions. These motions provide, for the first time, a clear signature in glancing collisions of both Faraday induction—an electric field induced by the fast decay of the magnetic field in the quark-gluon plasma—and the Coulomb effect—acceleration due to the electric fields of other protons in the vicinity. This combination confirms the interaction between the strong electromagnetic field and the quark-gluon plasma.

These results pave the way for investigation of the properties of the plasma and other novel phenomena that are fundamental to our understanding of the strong nuclear interaction.

Article Text

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Phys. Rev. X 14, 011028– Published 23 February, 2024

Vol. 14, Iss. 1 — January - March 2024

Received 10 April 2023
Revised 14 December 2023
Accepted 11 January 2024

DOI: https://doi.org/10.1103/PhysRevX.14.011028

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physical Review X

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Observation of the Electromagnetic Field Effect via Charge-Dependent Directed Flow in Heavy-Ion Collisions at the Relativistic Heavy Ion Collider

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Colossal Magnetic Field Detected in Nuclear Matter

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