Measurements of Dielectron Production in Au$+$Au Collisions at $\sqrt{s_{NN}}$= 27, 39, and 62.4 GeV from the STAR Experiment
24 Oct 2018 · STAR Collaboration, Adam J., Adamczyk L., Adams J. R., Adkins J. K., Agakishiev G., Aggarwal M. M., Ahammed Z., Alekseev I., Anderson D. M., Aoyama R., Aparin A., Arkhipkin D., Aschenauer E. C., Ashraf M. U., Atetalla F., Attri A., Averichev G. S., Bai X., Bairathi V., Barish K., Bassill A. J., Behera A., Bellwied R., Bhasin A., Bhati A. K., Bielcik J., Bielcikova J., Bland L. C., Bordyuzhin I. G., Brandenburg J. D., Brandin A. V., Brown D., Bryslawskyj J., Bunzarov I., Butterworth J., Caines H., Sánchez M. Calderón de la Barca, Cebra D., Chakaberia I., Chaloupka P., Chan B. K., Chang F-H., Chang Z., Chankova-Bunzarova N., Chatterjee A., Chattopadhyay S., Chen J. H., Chen X., Cheng J., Cherney M., Christie W., Contin G., Crawford H. J., Csanad M., Das S., Dedovich T. G., Deppner I. M., Derevschikov A. A., Didenko L., Dilks C., Dong X., Drachenberg J. L., Dunlop J. C., Edmonds T., Efimov L. G., Elsey N., Engelage J., Eppley G., Esha R., Esumi S., Evdokimov O., Ewigleben J., Eyser O., Fatemi R., Fazio S., Federic P., Fedorisin J., Filip P., Finch E., Fisyak Y., Flores C. E., Fulek L., Gagliardi C. A., Galatyuk T., Geurts F., Gibson A., Grosnick D., Gunarathne D. S., Guo Y., Gupta A., Guryn W., Hamad A. I., Hamed A., Harlenderova A., Harris J. W., He L., Heppelmann S., Heppelmann S., Herrmann N., Hirsch A., Holub L., Hong Y., Horvat S., Huang B., Huang H. Z., Huang S. L., Huang T., Huang X., Humanic T. J., Huo P., Igo G., Jacobs W. W., Jentsch A., Jia J., Jiang K., Jowzaee S., Ju X., Judd E. G., Kabana S., Kagamaster S., Kalinkin D., Kang K., Kapukchyan D., Kauder K., Ke H. W., Keane D., Kechechyan A., Kelsey M., Kikoła D. P., Kim C., Kinghorn T. A., Kisel I., Kisiel A., Kocan M., Kochenda L., Kosarzewski L. K., Kraishan A. F., Kramarik L., Krauth L., Kravtsov P., Krueger K., Kulathunga N., Kumar L., Elayavalli R. Kunnawalkam, Kvapil J., Kwasizur J. H., Lacey R., Landgraf J. M., Lauret J., Lebedev A., Lednicky R., Lee J. H., Li C., Li W., Li X., Li Y., Liang Y., Licenik R., Lidrych J., Lin T., Lipiec A., Lisa M. A., Liu F., Liu H., Liu P., Liu P., Liu X., Liu Y., Liu Z., Ljubicic T., Llope W. J., Lomnitz M., Longacre R. S., Luo S., Luo X., Ma G. L., Ma L., Ma R., Ma Y. G., Magdy N., Majka R., Mallick D., Margetis S., Markert C., Matis H. S., Matonoha O., Mazer J. A., Meehan K., Mei J. C., Minaev N. G., Mioduszewski S., Mishra D., Mohanty B., Mondal M. M., Mooney I., Moravcova Z., Morozov D. A., Nasim Md., Nayak K., Negrete J. D., Nelson J. M., Nemes D. B., Nie M., Nigmatkulov G., Niida T., Nogach L. V., Nonaka T., Odyniec G., Ogawa A., Oh K., Oh S., Okorokov V. A., Olvitt D. Jr., Page B. S., Pak R., Panebratsev Y., Pawlik B., Pei H., Perkins C., Pinter R. L., Pluta J., Porter J., Posik M., Pruthi N. K., Przybycien M., Putschke J., Quintero A., Radhakrishnan S. K., Ray R. L., Reed R., Ritter H. G., Roberts J. B., Rogachevskiy O. V., Romero J. L., Ruan L., Rusnak J., Rusnakova O., Sahoo N. R., Sahu P. K., Salur S., Sandweiss J., Schambach J., Schmah A. M., Schmidke W. B., Schmitz N., Schweid B. R., Seck F., Seger J., Sergeeva M., Seto R., Seyboth P., Shah N., Shahaliev E., Shanmuganathan P. V., Shao M., Shen F., Shen W. Q., Shi S. S., Shou Q. Y., Sichtermann E. P., Siejka S., Sikora R., Simko M., Singh J, Singha S., Smirnov D., Smirnov N., Solyst W., Sorensen P., Spinka H. M., Srivastava B., Stanislaus T. D. S., Stewart D. J., Strikhanov M., Stringfellow B., Suaide A. A. P., Sugiura T., Sumbera M., Summa B., Sun X. M., Sun Y., Surrow B., Svirida D. N., Szymanski P., Tang A. H., Tang Z., Taranenko A., Tarnowsky T., Thomas J. H., Timmins A. R., Tlusty D., Todoroki T., Tokarev M., Tomkiel C. A., Trentalange S., Tribble R. E., Tribedy P., Tripathy S. K., Tsai O. D., Tu B., Ullrich T., Underwood D. G., Upsal I., Van Buren G., Vanek J., Vasiliev A. N., Vassiliev I., Videbæk F., Vokal S., Voloshin S. A., Vossen A., Wang F., Wang G., Wang P., Wang Y., Wang Y., Webb J. C., Wen L., Westfall G. D., Wieman H., Wissink S. W., Witt R., Wu Y., Xiao Z. G., Xie G., Xie W., Xu J., Xu N., Xu Q. H., Xu Y. F., Xu Z., Yang C., Yang Q., Yang S., Yang Y., Ye Z., Ye Z., Yi L., Yip K., Yoo I. -K., Zbroszczyk H., Zha W., Zhang D., Zhang J., Zhang L., Zhang S., Zhang S., Zhang X. P., Zhang Y., Zhang Z., Zhao J., Zhong C., Zhou C., Zhu X., Zhu Z., Zurek M. K., Zyzak M. ·
We report systematic measurements of dielectron ($e^{\pm}e^{\pm}$) invariant-mass $M_{ee}$ spectra at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}}$ = 27, 39, and 62.4 GeV taken with the STAR detector at the Relativistic Heavy Ion Collider. For all energies studied, a significant excess yield of dielectrons is observed in the low-mass region (0.40$ < M_{ee} < 0.75$ MeV/$c^2$) compared to hadronic cocktail simulations at freeze-out. Models that include an in-medium broadening of the $\rho$-meson spectral function consistently describe the observed excess. In addition, we report acceptance-corrected dielectron-excess spectra for Au+Au collisions at mid-rapidity ($\left|y_{ee}\right|$ $<$ 1) in the 0$-$80% centrality bin for each collision energy. The integrated excess yields for $0.4 < M_{ee} < 0.75\ \textrm{GeV}/c^{2}$, normalized by the charged particle multiplicity at mid-rapidity, are compared with previously published measurements for Au+Au at $\sqrt{s_{NN}}$ = 19.6 and 200 GeV. The normalized excess yields in the low-mass region show no significant collision energy dependence. The data, however, are consistent with model calculations that demonstrate a modest energy dependence.
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