Observation of Strong Nuclear Suppression in Exclusive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> Photoproduction in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Au</mml:mi><mml:mo stretchy="false">+</mml:mo><mml:mi>Au</mml:mi></mml:mrow></mml:math> Ultraperipheral Collisions at RHIC
M. I. Abdulhamid, B. E. Aboona, J. Adam, L. Adamczyk, J. R. Adams, I. Aggarwal, M. M. Aggarwal, Z. Ahammed, E. C. Aschenauer, Saba Aslam, Jennifer Atchison, V. Bairathi, J. Ball, K. N. Barish, R. Bellwied, P. Bhagat, A. Bhasin, S. Bhatta, S. R. Bhosale, J. Bielčík, J. Bielčíková, J. D. Brandenburg, C. Broodo, X. Z. Cai, X. Z. Cai, M. Calderón de la Barca Sánchez, D. Cebra, J. Ceska, I. Chakaberia, P. Chaloupka, B. K. Chan, Z. Chang, A. Chatterjee, D. Chen, Jian Chen, J. H. Chen, Z. Chen, J. Cheng, Y. Cheng, S. Choudhury, W. Christie, X. Chu, H. J. Crawford, M. Csanád, G. Dale-Gau, Arkaprava Das, I. M. Deppner, A. Dhamija, P. Dixit, X. Dong, J. L. Drachenberg, E. Duckworth, J. C. Dunlop, J. Engelage, G. Eppley, S. Esumi, O. Evdokimov, O. Eyser, R. Fatemi, S. Fazio, C. Feng, Y. Feng, E. Finch, Y. Fisyak, F. A. Flor, C. Fu, C. A. Gagliardi, T. Galatyuk, Tong Gao, F. J. M. Geurts, N. Ghimire, S. M. Gibson, K. Gopal, X. Gou, D. Grosnick, A. Gupta, W. Guryn, A. Hamed, Y. Han, S. Harabasz, M. D. Harasty, J. W. Harris, H. Harrison-Smith, W. He, X. H. He, Y. He, N. Herrmann, L. Holub, C. Hu, Q. Hu, Y. Hu, H. Z. Huang, H. Z. Huang, S. L. Huang, T. Huang, X. Huang, Y. Huang, Y. Huang, T. J. Humanic, M. Isshiki
Abstract
We report a measurement of exclusive $J/\ensuremath{\psi}$ and $\ensuremath{\psi}(2s)$ photoproduction in $\mathrm{Au}+\mathrm{Au}$ ultraperipheral collisions at $\sqrt{{s}_{\mathrm{NN}}}=200\text{ }\text{ }\mathrm{GeV}$ using the STAR detector. For the first time, (i) the $\ensuremath{\psi}(2s)$ photoproduction in midrapidity at the Relativistic Heavy-Ion Collider has been experimentally measured; (ii) nuclear suppression factors are measured for both the coherent and incoherent $J/\ensuremath{\psi}$ production. At average photon-nucleon center-of-mass energy of 25.0 GeV, the coherent and incoherent $J/\ensuremath{\psi}$ cross sections of Au nuclei are found to be $71\ifmmode\pm\else\textpm\fi{}10%$ and $36\ifmmode\pm\else\textpm\fi{}7%$, respectively, of that of free protons. The stronger suppression observed in the incoherent production provides a new experimental handle to study the initial-state parton density in heavy nuclei. Data are compared with theoretical models quantitatively.