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In this document the PHENIX collaboration proposes a major upgrade to the PHENIX detector at the Relativistic Heavy Ion Collider. This upgrade, sPHENIX, enables an extremely rich jet and beauty quarkonia physics program addressing fundamental questions about the nature of the strongly coupled quark-gluon plasma (QGP), discovered experimentally at RHIC to be a perfect fluid. The startling dynamics of the QGP on fluid-like length scales is an emergent property of quantum chromodynamics (QCD), seemingly implicit in the Lagrangian but stubbornly hidden from view. QCD is an asymptotically free theory, but how QCD manifests as a strongly coupled fluid with specific shear viscosity near $T_C$, as low as allowed by the uncertainty principle, is as fundamental an issue as that of how confinement itself arises.
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The PHENIX collaboration presents a concept for a major upgrade to the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). This upgrade, referred to as sPHENIX, brings exciting new capability to the RHIC program by opening new and important channels for experimental investigation and utilizing fully the luminosity of the recently upgraded RHIC facility. sPHENIX enables a compelling jet physics program that will address fundamental questions about the nature of the strongly coupled quark-gluon plasma discovered experimentally at RHIC to be a perfect fluid. The upgrade concept addresses specific questions whose answers are necessary to advance our understanding of the quark-gluon plasma: (1) How to reconcile the observed strongly coupled quark-gluon plasma with the asymptotically free theory of quarks and gluons? (2) What are the dynamical changes to the quark-gluon plasma in terms of quasiparticles and excitations as a function of temperature? (3) How sharp is the transition of the quark-gluon plasma from the most strongly coupled regime near Tc to a weakly coupled system of partons known to emerge at asymptotically high temperatures? In three Appendices, we detail the additional physics capabilities gained through further upgrades: (A) two midrapidity detector additions, (B) a forward rapidity upgrade, and (C) an evolution to an ePHENIX detector suitable for a future Electron Ion Collider at RHIC.
The PHENIX Experiment at the Relativistic Heavy Ion Collider has made measurements of event-by-event fluctuations in the net charge, the mean transverse momentum, and the charged particle multiplicity as a function of collision energy, centrality, and transverse momentum in heavy ion collisions. The results of these measurements will be reviewed and discussed.
The PHENIX MPC-EX detector is a Si-W preshower extension to the existing PHENIX Muon Piston Calorimeters (MPC). The MPC-EX will consist of eight layers of alternating W absorber and Si mini-pad sensors and will be installed in time for RHIC Run-15. Covering a large pseudorapidity range, 3.1 < eta < 3.8, the MPC-EX and MPC access high-x partons in the projectile nucleon (and low-x partons in the target nucleon) in p+A and transversely polarized proton-proton collisions at 200 GeV. With the addition of the MPC-EX, the neutral pion reconstruction range extends to energies > 80 GeV, a factor of four improvement over current capabilities. Not only will the MPC-EX strengthen PHENIXs existing forward neutral pion and jet measurements, it also provides the necessary neutral pion rejection to make a prompt photon measurement feasible in both p+A and p+p collisions. With this neutral pion rejection, prompt (direct + fragmentation) photon yields at high p_T, p_T > 3 GeV, can be statistically extracted using a double ratio method. In p+A collisions direct photons at forward rapidities are optimally sensitive to the gluon distribution because, unlike pions, direct photons are only produced by processes that are directly sensitive to the gluon distribution at leading order. A measurement of the forward prompt photon R_pA will cleanly access and greatly expand our understanding of the gluon nuclear parton distribution functions and provide important information about the initial state in heavy ion collisions. In transversely polarized p+p collisions the MPC-EX will make possible a measurement of the prompt photon single spin asymmetry A_N, and will help elucidate the correlation of valence partons in the proton with the proton spin.
Quarkonia suppression in nucleus-nucleus collisions is a powerful tool to probe the density and temperature of the medium created in heavy ion collisions. Forward rapidity measurements in $p(d)$+Au collisions are essential to understand how quarkonia states are affected by initial state effects, formation time, and local particle multiplicity. Earlier measurements in Au+Au collisions showed a stronger suppression of forward $J/psi$ compared to mid-rapidity results, indicating the possibility of a smaller contribution of regenerated quarkonia states at forward rapidity. These proceedings report on the latest quarkonia studies performed by the PHENIX collaboration in the rapidity range $1.2<|y|<2.2$.
The first results from Au-Au collisions at $sqrt{s_{NN}}$=130 GeV obtained with the PHENIX detector in the Year 2000 run at RHIC are presented. The mid-rapidity charged particle multiplicity and transverse energy per participating nucleon rise steadily with the number of participants, such that transverse energy per charged particle remains relatively constant as a function of centrality. Identified charged hadron spectra as well as $bar{p}/p$ and $K^+/K^-$ ratios are discussed. Charged particle and neutral pion transverse momentum distributions in peripheral nuclear collisions are consistent with point-like scaling. The spectra at high $p_t$ from central collisions are significantly suppressed when compared to a simple superposition of binary nucleon-nucleon collisions.
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