J/psi production in sqrt s_NN=200 GeV Cu+Cu collisions

Area of Science:

• High-energy nuclear physics
• Quantum chromodynamics
• Quark-gluon plasma studies

Background:

• J/psi meson production is a key probe for studying the properties of hot and dense nuclear matter.
• Previous measurements in gold-gold and proton-proton collisions provide a baseline, but data in smaller systems are needed to probe the transition region.
• Copper-copper collisions offer a system size intermediate between proton-proton and gold-gold, crucial for understanding the onset of quark-gluon plasma formation.

Purpose of the Study:

• To precisely measure J/psi production yields in copper-copper collisions at a center-of-mass energy of 200 GeV per nucleon.
• To compare these yields with existing data from proton-proton and gold-gold collisions to investigate system-size dependencies.
• To test theoretical models, including cold nuclear matter effects, in the regime relevant to the predicted quark-gluon plasma transition.

Main Methods:

• Utilized the Relativistic Heavy Ion Collider (RHIC) to perform copper-copper collisions at sqrt s_NN = 200 GeV.
• Measured J/psi meson production over a pseudo-rapidity range of |y|<2.2.
• Analyzed data to extract production yields and compared them with theoretical calculations and data from other collision systems.

Main Results:

• Precise measurements of J/psi yields in copper-copper collisions were obtained, offering improved precision over previous gold-gold data for small to intermediate numbers of participants.
• The data cover the collision energy regime where the quark-gluon plasma transition is theoretically predicted.
• Cold nuclear matter effects, estimated using fits to d+Au data, successfully describe the measured J/psi production up to approximately 50 participants, corresponding to a Bjorken energy density of at least 1.5 GeV/fm^3.

Conclusions:

• Copper-copper collision data provide crucial insights into J/psi production in the critical region for quark-gluon plasma formation.
• The results suggest that cold nuclear matter effects play a significant role in J/psi suppression at lower collision energies and system sizes.
• Further studies are needed to fully disentangle the contributions of cold nuclear matter effects and the formation of the quark-gluon plasma.