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arXiv · 1501.05341

Energy dependence of acceptance-corrected dielectron excess mass spectrum at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}} = 19.6$ and 200 GeV

STAR Collaboration·L. Adamczyk·J. K. Adkins·G. Agakishiev·M. M. Aggarwal·Z. Ahammed·I. Alekseev·J. Alford·A. Aparin·D. Arkhipkin·E. C. Aschenauer·G. S. Averichev·A. Banerjee·R. Bellwied·A. Bhasin·A. K. Bhati·P. Bhattarai·J. Bielcik·J. Bielcikova·L. C. Bland·I. G. Bordyuzhin·J. Bouchet·A. V. Brandin·I. Bunzarov·T. P. Burton·J. Butterworth·H. Caines·M. Calder'on de la Barca S'anchez·J. M. campbell·D. Cebra·M. C. Cervantes·I. Chakaberia·P. Chaloupka·Z. Chang·S. Chattopadhyay·J. H. Chen·X. Chen·J. Cheng·M. Cherney·W. Christie·M. J. M. Codrington·G. Contin·H. J. Crawford·S. Das·L. C. De Silva·R. R. Debbe·T. G. Dedovich·J. Deng·A. A. Derevschikov·B. di Ruzza·L. Didenko·C. Dilks·X. Dong·J. L. Drachenberg·J. E. Draper·C. M. Du·L. E. Dunkelberger·J. C. Dunlop·L. G. Efimov·J. Engelage·G. Eppley·R. Esha·O. Evdokimov·O. Eyser·R. Fatemi·S. Fazio·P. Federic·J. Fedorisin·Feng·P. Filip·Y. Fisyak·C. E. Flores·L. Fulek·C. A. Gagliardi·D. Garand·F. Geurts·A. Gibson·M. Girard·L. Greiner·D. Grosnick·D. S. Gunarathne·Y. Guo·S. Gupta·A. Gupta·W. Guryn·A. Hamad·A. Hamed·R. Haque·J. W. Harris·L. He·S. Heppelmann·A. Hirsch·G. W. Hoffmann·D. J. Hofman·S. Horvat·H. Z. Huang·X. Huang·B. Huang·P. Huck·T. J. Humanic
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Abstract

The acceptance-corrected dielectron excess mass spectra, where the known hadronic sources have been subtracted from the inclusive dielectron mass spectra, are reported for the first time at mid-rapidity $|y_{ee}|<1$ in minimum-bias Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6 and 200 GeV. The excess mass spectra are consistently described by a model calculation with a broadened $\rho$ spectral function for $M_{ee}<1.1$ GeV/$c^{2}$. The integrated dielectron excess yield at $\sqrt{s_{NN}}$ = 19.6 GeV for $0.4<M_{ee}<0.75$ GeV/$c^2$, normalized to the charged particle multiplicity at mid-rapidity, has a value similar to that in In+In collisions at $\sqrt{s_{NN}}$ = 17.3 GeV. For $\sqrt{s_{NN}}$ = 200 GeV, the normalized excess yield in central collisions is higher than that at $\sqrt{s_{NN}}$ = 17.3 GeV and increases from peripheral to central collisions. These measurements indicate that the lifetime of the hot, dense medium created in central Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV is longer than those in peripheral collisions and at lower energies.

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STAR Collaboration, L. Adamczyk, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, A. Aparin, D. Arkhipkin, E. C. Aschenauer, G. S. Averichev, A. Banerjee, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, A. V. Brandin, I. Bunzarov, T. P. Burton, J. Butterworth, H. Caines, M. Calder'on de la Barca S'anchez, J. M. campbell, D. Cebra, M. C. Cervantes, I. Chakaberia, P. Chaloupka, Z. Chang, S. Chattopadhyay, J. H. Chen, X. Chen, J. Cheng, M. Cherney, W. Christie, M. J. M. Codrington, G. Contin, H. J. Crawford, S. Das, L. C. De Silva, R. R. Debbe, T. G. Dedovich, J. Deng, A. A. Derevschikov, B. di Ruzza, L. Didenko, C. Dilks, X. Dong, J. L. Drachenberg, J. E. Draper, C. M. Du, L. E. Dunkelberger, J. C. Dunlop, L. G. Efimov, J. Engelage, G. Eppley, R. Esha, O. Evdokimov, O. Eyser, R. Fatemi, S. Fazio, P. Federic, J. Fedorisin, Feng, P. Filip, Y. Fisyak, C. E. Flores, L. Fulek, C. A. Gagliardi, D. Garand, F. Geurts, A. Gibson, M. Girard, L. Greiner, D. Grosnick, D. S. Gunarathne, Y. Guo, S. Gupta, A. Gupta, W. Guryn, A. Hamad, A. Hamed, R. Haque, J. W. Harris, L. He, S. Heppelmann, A. Hirsch, G. W. Hoffmann, D. J. Hofman, S. Horvat, H. Z. Huang, X. Huang, B. Huang, P. Huck, T. J. Humanic. 2015-01-21. Energy dependence of acceptance-corrected dielectron excess mass spectrum at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}} = 19.6$ and 200 GeV. https://doi.org/10.1016/j.physletb.2015.08.044

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