J/ψ azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2009-06, Vol.61 (4), p.853-858
• Main Authors: Prino, F., Alessandro, B., Alexa, C., Arnaldi, R., Atayan, M., Beolè, S., Boldea, V., Bordalo, P., Borges, G., Castanier, C., Castor, J., Chaurand, B., Cheynis, B., Chiavassa, E., Cicalò, C., Comets, M. P., Constantinescu, S., Cortese, P., De Falco, A., De Marco, N., Dellacasa, G., Devaux, A., Dita, S., Fargeix, J., Force, P., Gallio, M., Gerschel, C., Giubellino, P., Golubeva, M. B., Grigoryan, A. A., Grigoryan, S., Guber, F. F., Guichard, A., Gulkanyan, H., Idzik, M., Jouan, D., Karavicheva, T. L., Kluberg, L., Kurepin, A. B., Le Bornec, Y., Lourenço, C., Mac Cormick, M., Marzari-Chiesa, A., Masera, M., Masoni, A., Monteno, M., Musso, A., Petiau, P., Piccotti, A., Pizzi, J. R., Puddu, G., Quintans, C., Ramello, L., Ramos, S., Riccati, L., Santos, H., Saturnini, P., Scomparin, E., Serci, S., Shahoyan, R., Sigaudo, F., Sitta, M., Sonderegger, P., Tarrago, X., Topilskaya, N. S., Usai, G. L., Vercellin, E., Villatte, L., Willis, N., Wu, T.
• Format: Article
• Language: English
• Subjects: Anisotropy; Astronomy; Astrophysics and Cosmology; Atomic collisions; Elementary Particles; Hadrons; Heavy Ions; Ionic collisions; Measurement Science and Instrumentation; Mesons; Nuclear Energy; Nuclear Physics; Nucleons; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Regular Article - Experimental Physics; String Theory; Transverse momentum
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-009-0907-4

The J / ψ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed J / ψ mesons at SPS energies. Hence, the measurement of J / ψ elliptic anisotropy, quantified by the Fourier coefficient v 2 of the J / ψ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous J / ψ suppression observed in Pb-Pb collisions. We present the measured J / ψ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient v 2 as a function of the collision centrality and of the J / ψ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or p T sub-samples. The extracted v 2 values are significantly larger than zero for non-central collisions and are seen to increase with p T .