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.

J Adam,O Eyser,Y Yang,S Trentalange,A Attri,J Engelage,M Cherney,L Yi,R Esha,D Mishra,K Yip,P Seyboth,S Heppelmann,R Bellwied,R Sikora,L Ruan,Y Panebratsev,G Odyniec,T Ullrich,C Li,A Gibson,I Alekseev,Y Liang,M Sergeeva,S Horvat,I Chakaberia,L He,S Mioduszewski,L Ma,J Kvapil,A Aparin,N Shah,S Luo,G Eppley,S Siejka,J Lidrych,L Wen,A Lipiec,D Tlusty,S Kumar,C Zhou,P Chaloupka,D Cebra,Z Ahammed,E Shahaliev,N Xu,R Seto,W Solyst,I Bunzarov,H Wieman,J Schambach,P Filip,S Das,D Arkhipkin,Z Xu,P Sorensen,R Fatemi,R Reed,Y Sun,R Majka,X Dong,M Strikhanov,D Kapukchyan,S Ramachandran,D Grosnick,J Sandweiss,Z Ye,Y Wu,M Lomnitz,D Smirnov,A Gupta,S Singha,W Christie,B Stringfellow,T Tarnowsky,R Aoyama,L Kumar,A Harlenderova,G Contin,D Mallick,A Chatterjee,O Evdokimov,N Schmitz,B Srivastava,H Caines,T Todoroki,N Elsey,J Pluta,M Posik,N Chankova-Bunzarova,R Pak,T Huang,S Zhang,L Holub,F-H Chang,A Quintero,I Vassiliev,D Kalinkin,Q Yang,K Jiang,J Zhang,P Huo,O Rusnakova,A Kechechyan,B Tu,B Summa,C Dilks,A Vossen,B Pawlik,L Krauth,R Witt,A Lebedev,A Hirsch,G Igo,S Fazio,Y Li,H Zbroszczyk,F Seck,X Huang,J Lauret,L Zhang,X Chen,T Galatyuk,J Jia,P Federic,L Adamczyk,Y Zhang,K Krueger,P Tribedy,Y Guo,M Shao,M Zyzak,F Shen,F Videbæk,S Jowzaee,N Magdy,S Chattopadhyay,D Keane,M Calderón De La Barca Sánchez,M Simko,W Xie,A Ogawa,K Kang,I Kisel,P Federicova,A Behera,O Matonoha,A Hamed,Y Wang,C Perkins,M Nie,G Van Buren,W Li,K Kauder,S Esumi,A Jentsch,J Seger,A Kisiel,P Liu,L Didenko,Z Chang,T Niida,J Zhao,Y Fisyak,J Putschke,W Zha,J Cheng,F Liu,B Mohanty,G Nigmatkulov,T Sugiura,C Markert,X Zhu,F Wang,G Xie,Md Nasim,D Olvitt,L Kochenda,I Mooney,J Porter,N Herrmann,M Tokarev,N Yu,W Guryn,X Li,R Lacey,Y Liu,Z Zhang,H Liu,G Agakishiev,S Kabana,B Surrow,J Bryslawskyj,K Meehan,S Yang,N Smirnov,K Oh,A Taranenko,I Upsal,Z Tang,S Salur,B Huang,E Finch,N Kulathunga,H Pei,T Nonaka,S Margetis,V Bairathi,J Ewigleben,G Wang,A Bhasin,C Kim,J C Webb ,I K Yoo ,Y G ,J Mazer ,N Sahoo ,D S Brown ,G L ,Jing Xu ,Q Shou ,S K Tripathy ,L Kramárik ,T A Kinghorn ,A Schmah ,R L Ray ,L K Kosarzewski ,L G Efimov ,T D S Stanislaus ,O D Tsai ,S B Nurushev ,K N Barish ,M A Lisa ,E P Sichtermann ,J C Dunlop ,F J M Geurts ,W J Llope ,J M Landgraf ,P Szymański ,V Okorokov ,P K Sahu ,J L Drachenberg ,D N Svirida ,J W Harris ,П Кравцов ,M M Mondal ,E G Judd ,A V Brandin ,D G Underwood ,J M Nelson ,S K Radhakrishnan ,L C Bland ,Q Xu ,B S Page ,J M Campbell ,P V Shanmuganathan ,W B Schmidke ,G S Averichev ,A I Hamad ,J Vaněk ,S W Wissink ,F G Atetalla ,J H Chen ,T J Humanic ,Ł Fulek ,H W Ke ,J D Negrete ,A H Tang ,T G Dedovich ,David G Mayes ,M M Aggarwal ,J H Kwasizur ,D S Gunarathne ,H M Spinka ,O V Rogachevskiy ,J Fedorišin ,David J Stewart ,J Bielčíková ,J L Romero ,W W Jacobs ,N N Ajitanand ,S Vokál ,J D Brandenburg ,R E Tribble ,Д А Морозов ,D P Kikoła ,Z H Zhu ,M Przybycień ,R Ma ,C A Tomkiel ,A J Bassill ,H J Crawford ,D M Anderson ,L V Nogach ,G D Westfall ,B R Schweid ,Zhong Chen ,R Lednický ,J Rusňák ,R S Longacre ,A F Kraishan ,I M Deppner ,X M Sun ,Y Xu ,S R Klein ,A A P Suaide ,H G Ritter ,Zhou Liu ,C G Yang ,M U Ashraf ,D B Nemes ,Xiaozhi Bai ,S K Oh ,C A Gagliardi ,Xuan Luo ,Xiao Zhang ,A A Derevschikov ,C Flores ,J Roberts ,I G Bordyuzhin ,E C Aschenauer ,A Vasiliev ,S Voloshin ,M Šumbera ,J R Adams ,H S Matis ,X P Zhang ,A R Timmins ,S S Shi ,H Z Huang ,T Ljubičić ,J K Adkins ,Jincheng Mei ,J Bielčík ,N K Pruthi ,J H Thomas ,N G Minaev ,W Q Shen ,A K Bhati ,J H Lee ,J M Butterworth ,S Huang ,Tongyan Lin

doi:10.1103/physrevlett.121.132301

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.

Highlights

UlowþWteUrarncesopvloelrirstsiefoinrmsstoammt eepnastffisffiuuffiNffimrffiNffieffiffim(1⁄4peTn1t9
Previous dilepton measurements over a wide pT region at the Super Proton Synchrotron (SPS) [3,4] and Relativistic Heavy-Ion Collider (RHIC) [5,6,7] showed a significant enhancement with respect to known hadronic sources in the mass region below ∼0.7 GeV=c2
Virtual photons emitted by one nucleus can interact either with the other whole nucleus or with individual nucleons in the other nucleus to produce vector mesons (γ þ A → V þ A), which decay into dileptons [11]

Summary

GeV and

J. Adam,9 L. Adamczyk,1 J. R. Adams,31 J. K. Adkins,21 G. Agakishiev,19 M. M. Aggarwal,33 Z. Ahammed,56 N. N. Ajitanand,44 I. Alekseev,17,28 D. M. Anderson,46 R. Aoyama,50 A. Aparin,19 D. Arkhipkin,3 E. C. Aschenauer,3 M. U. Ashraf,49 F. Atetalla,20 A. Attri,33 G. S. Averichev,19 X. Bai,7 V. Bairathi,29 K. Barish,52 A. J. Bassill,52 A. Behera,44 R. Bellwied,48 A. Bhasin,18 A. K. Bhati,33 J. Bielcik,10 J. Bielcikova,11 L. C. Bland,3 I. G. Bordyuzhin,17 J. D. Brandenburg,38 A. V. Brandin,28 D. Brown,25 J. Bryslawskyj,52 I. Bunzarov,19 J. Butterworth,38 H. Caines,59 M. Calderón de la Barca Sánchez,5 J. M. Campbell,31 D. Cebra,5 I. Chakaberia,3,20,42 P. Chaloupka,10 F-H. Chang,30 Z. Chang,3 N. Chankova-Bunzarova,19 A. Chatterjee,56 S. Chattopadhyay,56 J. H. Chen,43 X. Chen,41 X. Chen,23 J. Cheng,49 M. Cherney,9 W. Christie,3 G. Contin,24 H. J. Crawford,4 S. Das,7 T. G. Dedovich,19 I. M. Deppner,53 A. A. Derevschikov,35 L. Didenko,3 C. Dilks,34 X. Dong,24 J. L. Drachenberg,22 J. C. Dunlop,3 L. G. Efimov,19 N. Elsey,58 J. Engelage,4 G. Eppley,38 R. Esha,6 S. Esumi,50 O. Evdokimov,8 J. Ewigleben,25 O. Eyser,3 R. Fatemi,21 S. Fazio,3 P. Federic,11 P. Federicova,10 J. Fedorisin,19 P. Filip,19 E. Finch,51 Y. Fisyak,3 C. E. Flores,5 L. Fulek,1 C. A. Gagliardi,46 T. Galatyuk,12 F. Geurts,38 A. Gibson,55 D. Grosnick,55 D. S. Gunarathne,45 Y. Guo,20 A. Gupta,18 W. Guryn,3 A. I. Hamad,20 A. Hamed,46 A. Harlenderova,10 J. W. Harris,59 L. He,36 S. Heppelmann,34 S. Heppelmann,5 N. Herrmann,53 A. Hirsch,36 L. Holub,10 S. Horvat,59 X. Huang,49 B. Huang,8 S. L. Huang,44 H. Z. Huang,6 T. Huang,30 T. J. Humanic,31 P. Huo,44 G. Igo,6 W. W. Jacobs,16 A. Jentsch,47 J. Jia,3,44 K. Jiang,41 S. Jowzaee,58 E. G. Judd,4 S. Kabana,20 D. Kalinkin,16 K. Kang,49 D. Kapukchyan,52 K. Kauder,58 H. W. Ke,3 D. Keane,20 A. Kechechyan,19 D. P. Kikoła,57 C. Kim,52 T. A. Kinghorn,5 I. Kisel,13 A. Kisiel,57 S. R. Klein,24 L. Kochenda,28 L. K. Kosarzewski,57 A. F. Kraishan,45 L. Kramarik,10 L. Krauth,52 P. Kravtsov,28 K. Krueger,2 N. Kulathunga,48 S. Kumar,33 L. Kumar,33 J. Kvapil,10 J. H. Kwasizur,16 R. Lacey,44 J. M. Landgraf,3 J. Lauret,3 A. Lebedev,3 R. Lednicky,19 J. H. Lee,3 X. Li,41 C. Li,41 W. Li,43 Y. Li,49 Y. Liang,20 J. Lidrych,10 T. Lin,46 A. Lipiec,57 M. A. Lisa,31 F. Liu,7 P. Liu,44 H. Liu,16 Y. Liu,46 T. Ljubicic,3 W. J. Llope,58 M. Lomnitz,24 R. S. Longacre,3 X. Luo,7 S. Luo,8 G. L. Ma,43 Y. G. Ma,43 L. Ma,14 R. Ma,3 N. Magdy,44 R. Majka,59 D. Mallick,29 S. Margetis,20 C. Markert,47 H. S. Matis,24 O. Matonoha,10 D. Mayes,52 J. A. Mazer,39 K. Meehan,5 J. C. Mei,42 N. G. Minaev,35 S. Mioduszewski,46 D. Mishra,29 B. Mohanty,29 M. M. Mondal,15 I. Mooney,58 D. A. Morozov,35 Md. Nasim,6 J. D. Negrete,52 J. M. Nelson,4 D. B. Nemes,59 M. Nie,43 G. Nigmatkulov,28 T. Niida,58 L. V. Nogach,35 T. Nonaka,50 S. B. Nurushev,35 G. Odyniec,24 A. Ogawa,3 K. Oh,37 S. Oh,59 V. A. Okorokov,28 D. Olvitt, Jr.,45 B. S. Page,3 R. Pak,3 Y. Panebratsev,19 B. Pawlik,32 H. Pei,7 C. Perkins,4 J. Pluta,57 J. Porter,24 M. Posik,45 N. K. Pruthi,33 M. Przybycien,1 J. Putschke,58 A. Quintero,45 S. K. Radhakrishnan,24 S. Ramachandran,21 R. L. Ray,47 R. Reed,25 H. G. Ritter,24 J. B. Roberts,38 O. V. Rogachevskiy,19 J. L. Romero,5 L. Ruan,3 J. Rusnak,11 O. Rusnakova,10 N. R. Sahoo,46 P. K. Sahu,15 S. Salur,39 J. Sandweiss,59 J. Schambach,47 A. M. Schmah,24 W. B. Schmidke,3 N. Schmitz,26 B. R. Schweid,44 F. Seck,12 J. Seger,9 M. Sergeeva,6 R. Seto,52 P. Seyboth,26 N. Shah,43 E. Shahaliev,19 P. V. Shanmuganathan,25 M. Shao,41 W. Q. Shen,43 F. Shen,42 S. S. Shi,7 Q. Y. Shou,43 E. P. Sichtermann,24 S. Siejka,57 R. Sikora,1 M. Simko,11 S. Singha,20 N. Smirnov,59 D. Smirnov,3 W. Solyst,16 P. Sorensen,3 H. M. Spinka,2 B. Srivastava,36 T. D. S. Stanislaus,55 D. J. Stewart,59 M. Strikhanov,28 B. Stringfellow,36 A. A. P. Suaide,40 T. Sugiura,50 M. Sumbera,11 B. Summa,34 Y. Sun,41 X. Sun,7 X. M. Sun,7 B. Surrow,45 D. N. Svirida,17 P. Szymanski,57 Z. Tang,41 A. H. Tang,3 A. Taranenko,28 T. Tarnowsky,27 J. H. Thomas,24 A. R. Timmins,48 D. Tlusty,38 T. Todoroki,3 M. Tokarev,19 C. A. Tomkiel,25 S. Trentalange,6 R. E. Tribble,46 P. Tribedy,3 S. K. Tripathy,15 O. D. Tsai,6 B. Tu,7 T. Ullrich,3 D. G. Underwood,2 I. Upsal,31 G. Van Buren,3 J. Vanek,11 A. N. Vasiliev,35 I. Vassiliev,13 F. Videbæk,3 S. Vokal,19 S. A. Voloshin,58 A. Vossen,16 G. Wang,6 Y. Wang,7 F. Wang,36 Y. Wang,49 J. C. Webb,3 L. Wen,6 G. D. Westfall,27 H. Wieman,24 S. W. Wissink,16 R. Witt,54 Y. Wu,20 Z. G. Xiao,49 G. Xie,8 W. Xie,36 Q. H. Xu,42 Z. Xu,3 J. Xu,7 Y. F. Xu,43 N. Xu,24 S. Yang,3 C. Yang,42 Q. Yang,42 Y. Yang,30 Z. Ye,8 Z. Ye,8 L. Yi,42 K. Yip,3 I.-K. Yoo,37 N. Yu,7 H. Zbroszczyk,57 W. Zha,41 Z. Zhang,43 L. Zhang,7 Y. Zhang,41 X. P. Zhang,49 J. Zhang,23 S. Zhang,43 S. Zhang,41 J. Zhang,24 J. Zhao,36

Published by the American Physical Society

Findings

Excess Yield