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Phys Rev Lett. 2018 Sep 28;121(13):132301. doi: 10.1103/PhysRevLett.121.132301.

Low-p_{T} e^{+}e^{-} Pair Production in Au+Au Collisions at sqrt[s_{NN}]=200  GeV and U+U Collisions at sqrt[s_{NN}]=193  GeV at STAR.

Adam J1, Adamczyk L2, Adams JR3, Adkins JK4, Agakishiev G5, Aggarwal MM6, Ahammed Z7, Ajitanand NN8, Alekseev I9,10, Anderson DM11, Aoyama R12, Aparin A5, Arkhipkin D13, Aschenauer EC13, Ashraf MU14, Atetalla F15, Attri A6, Averichev GS5, Bai X16, Bairathi V17, Barish K18, Bassill AJ18, Behera A8, Bellwied R19, Bhasin A20, Bhati AK6, Bielcik J21, Bielcikova J22, Bland LC13, Bordyuzhin IG9, Brandenburg JD23, Brandin AV10, Brown D24, Bryslawskyj J18, Bunzarov I5, Butterworth J23, Caines H25, Calderón de la Barca Sánchez M26, Campbell JM3, Cebra D26, Chakaberia I13,15,27, Chaloupka P21, Chang FH28, Chang Z13, Chankova-Bunzarova N5, Chatterjee A7, Chattopadhyay S7, Chen JH29, Chen X30, Chen X31, Cheng J14, Cherney M1, Christie W13, Contin G32, Crawford HJ33, Das S16, Dedovich TG5, Deppner IM34, Derevschikov AA35, Didenko L13, Dilks C36, Dong X32, Drachenberg JL37, Dunlop JC13, Efimov LG5, Elsey N38, Engelage J33, Eppley G23, Esha R39, Esumi S12, Evdokimov O40, Ewigleben J24, Eyser O13, Fatemi R4, Fazio S13, Federic P22, Federicova P21, Fedorisin J5, Filip P5, Finch E41, Fisyak Y13, Flores CE26, Fulek L2, Gagliardi CA11, Galatyuk T42, Geurts F23, Gibson A43, Grosnick D43, Gunarathne DS44, Guo Y15, Gupta A20, Guryn W13, Hamad AI15, Hamed A11, Harlenderova A21, Harris JW25, He L45, Heppelmann S36, Heppelmann S26, Herrmann N34, Hirsch A45, Holub L21, Horvat S25, Huang X14, Huang B40, Huang SL8, Huang HZ39, Huang T28, Humanic TJ3, Huo P8, Igo G39, Jacobs WW46, Jentsch A47, Jia J13,8, Jiang K30, Jowzaee S38, Judd EG33, Kabana S15, Kalinkin D46, Kang K14, Kapukchyan D18, Kauder K38, Ke HW13, Keane D15, Kechechyan A5, Kikoła DP48, Kim C18, Kinghorn TA26, Kisel I49, Kisiel A48, Klein SR32, Kochenda L10, Kosarzewski LK48, Kraishan AF44, Kramarik L21, Krauth L18, Kravtsov P10, Krueger K50, Kulathunga N19, Kumar S6, Kumar L6, Kvapil J21, Kwasizur JH46, Lacey R8, Landgraf JM13, Lauret J13, Lebedev A13, Lednicky R5, Lee JH13, Li X30, Li C30, Li W29, Li Y14, Liang Y15, Lidrych J21, Lin T11, Lipiec A48, Lisa MA3, Liu F16, Liu P8, Liu H46, Liu Y11, Ljubicic T13, Llope WJ38, Lomnitz M32, Longacre RS13, Luo X16, Luo S40, Ma GL29, Ma YG29, Ma L51, Ma R13, Magdy N8, Majka R25, Mallick D17, Margetis S15, Markert C47, Matis HS32, Matonoha O21, Mayes D18, Mazer JA52, Meehan K26, Mei JC27, Minaev NG35, Mioduszewski S11, Mishra D17, Mohanty B17, Mondal MM53, Mooney I38, Morozov DA35, Nasim M39, Negrete JD18, Nelson JM33, Nemes DB25, Nie M29, Nigmatkulov G10, Niida T38, Nogach LV35, Nonaka T12, Nurushev SB35, Odyniec G32, Ogawa A13, Oh K54, Oh S25, Okorokov VA10, Olvitt D44, Page BS13, Pak R13, Panebratsev Y5, Pawlik B55, Pei H16, Perkins C33, Pluta J48, Porter J32, Posik M44, Pruthi NK6, Przybycien M2, Putschke J38, Quintero A44, Radhakrishnan SK32, Ramachandran S4, Ray RL47, Reed R24, Ritter HG32, Roberts JB23, Rogachevskiy OV5, Romero JL26, Ruan L13, Rusnak J22, Rusnakova O21, Sahoo NR11, Sahu PK53, Salur S52, Sandweiss J25, Schambach J47, Schmah AM32, Schmidke WB13, Schmitz N56, Schweid BR8, Seck F42, Seger J1, Sergeeva M39, Seto R18, Seyboth P56, Shah N29, Shahaliev E5, Shanmuganathan PV24, Shao M30, Shen WQ29, Shen F27, Shi SS16, Shou QY29, Sichtermann EP32, Siejka S48, Sikora R2, Simko M22, Singha S15, Smirnov N25, Smirnov D13, Solyst W46, Sorensen P13, Spinka HM50, Srivastava B45, Stanislaus TDS43, Stewart DJ25, Strikhanov M10, Stringfellow B45, Suaide AAP57, Sugiura T12, Sumbera M22, Summa B36, Sun Y30, Sun X16, Sun XM16, Surrow B44, Svirida DN9, Szymanski P48, Tang Z30, Tang AH13, Taranenko A10, Tarnowsky T58, Thomas JH32, Timmins AR19, Tlusty D23, Todoroki T13, Tokarev M5, Tomkiel CA24, Trentalange S39, Tribble RE11, Tribedy P13, Tripathy SK53, Tsai OD39, Tu B16, Ullrich T13, Underwood DG50, Upsal I3, Van Buren G13, Vanek J22, Vasiliev AN35, Vassiliev I49, Videbæk F13, Vokal S5, Voloshin SA38, Vossen A46, Wang G39, Wang Y16, Wang F45, Wang Y14, Webb JC13, Wen L39, Westfall GD58, Wieman H32, Wissink SW46, Witt R59, Wu Y15, Xiao ZG14, Xie G40, Xie W45, Xu QH27, Xu Z13, Xu J16, Xu YF29, Xu N32, Yang S13, Yang C27, Yang Q27, Yang Y28, Ye Z40, Ye Z40, Yi L27, Yip K13, Yoo IK54, Yu N16, Zbroszczyk H48, Zha W30, Zhang Z29, Zhang L16, Zhang Y30, Zhang XP14, Zhang J31, Zhang S29, Zhang S30, Zhang J32, Zhao J45, Zhong C29, Zhou C29, Zhou L30, Zhu Z27, Zhu X14, Zyzak M49; STAR Collaboration.

Author information

1
Creighton University, Omaha, Nebraska 68178.
2
AGH University of Science and Technology, FPACS, Cracow 30-059, Poland.
3
Ohio State University, Columbus, Ohio 43210.
4
University of Kentucky, Lexington, Kentucky 40506-0055.
5
Joint Institute for Nuclear Research, Dubna 141 980, Russia.
6
Panjab University, Chandigarh 160014, India.
7
Variable Energy Cyclotron Centre, Kolkata 700064, India.
8
State University of New York, Stony Brook, New York 11794.
9
Alikhanov Institute for Theoretical and Experimental Physics, Moscow 117218, Russia.
10
National Research Nuclear University MEPhI, Moscow 115409, Russia.
11
Texas A&M University, College Station, Texas 77843.
12
University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
13
Brookhaven National Laboratory, Upton, New York 11973.
14
Tsinghua University, Beijing 100084.
15
Kent State University, Kent, Ohio 44242.
16
Central China Normal University, Wuhan, Hubei 430079.
17
National Institute of Science Education and Research, HBNI, Jatni 752050, India.
18
University of California, Riverside, California 92521.
19
University of Houston, Houston, Texas 77204.
20
University of Jammu, Jammu 180001, India.
21
Czech Technical University in Prague, FNSPE, Prague 115 19, Czech Republic.
22
Nuclear Physics Institute AS CR, Prague 250 68, Czech Republic.
23
Rice University, Houston, Texas 77251.
24
Lehigh University, Bethlehem, Pennsylvania 18015.
25
Yale University, New Haven, Connecticut 06520.
26
University of California, Davis, California 95616.
27
Shandong University, Jinan, Shandong 250100.
28
National Cheng Kung University, Tainan 70101.
29
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800.
30
University of Science and Technology of China, Hefei, Anhui 230026.
31
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, Gansu 730000.
32
Lawrence Berkeley National Laboratory, Berkeley, California 94720.
33
University of California, Berkeley, California 94720.
34
University of Heidelberg, Heidelberg 69120, Germany.
35
Institute of High Energy Physics, Protvino 142281, Russia.
36
Pennsylvania State University, University Park, Pennsylvania 16802.
37
Lamar University, Beaumont, Texas 77710.
38
Wayne State University, Detroit, Michigan 48201.
39
University of California, Los Angeles, California 90095.
40
University of Illinois at Chicago, Chicago, Illinois 60607.
41
Southern Connecticut State University, New Haven, Connecticut 06515.
42
Technische Universitat Darmstadt, Darmstadt 64289, Germany.
43
Valparaiso University, Valparaiso, Indiana 46383.
44
Temple University, Philadelphia, Pennsylvania 19122.
45
Purdue University, West Lafayette, Indiana 47907.
46
Indiana University, Bloomington, Indiana 47408.
47
University of Texas, Austin, Texas 78712.
48
Warsaw University of Technology, Warsaw 00-661, Poland.
49
Frankfurt Institute for Advanced Studies FIAS, Frankfurt 60438, Germany.
50
Argonne National Laboratory, Argonne, Illinois 60439.
51
Fudan University, Shanghai 200433.
52
Rutgers University, Piscataway, New Jersey 08854.
53
Institute of Physics, Bhubaneswar 751005, India.
54
Pusan National University, Pusan 46241, Korea.
55
Institute of Nuclear Physics PAN, Cracow 31-342, Poland.
56
Max-Planck-Institut fur Physik, Munich 80805, Germany.
57
Universidade de Sao Paulo, Sao Paulo 05314-970, Brazil.
58
Michigan State University, East Lansing, Michigan 48824.
59
United States Naval Academy, Annapolis, Maryland 21402.

Abstract

We report first measurements of e^{+}e^{-} pair production in the mass region 0.4<M_{ee}<2.6  GeV/c^{2} at low transverse momentum (p_{T}<0.15  GeV/c) in noncentral Au+Au collisions at sqrt[s_{NN}]=200  GeV and U+U collisions at sqrt[s_{NN}]=193  GeV. Significant enhancement factors, expressed as ratios of data over known hadronic contributions, are observed in the 40%-80% centrality of these collisions. The excess yields peak distinctly at low p_{T} with a width (sqrt[⟨p_{T}^{2}⟩]) between 40 and 60  MeV/c. The absolute cross section of the excess depends weakly on centrality, while those from a theoretical model calculation incorporating an in-medium broadened ρ spectral function and radiation from a quark gluon plasma or hadronic cocktail contributions increase dramatically with an increasing number of participant nucleons. Model calculations of photon-photon interactions generated by the initial projectile and target nuclei describe the observed excess yields but fail to reproduce the p_{T}^{2} distributions.

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