ORNL Physics Division
Managed by UT-Battelle for the Department of Energy
Search     Go!
  Heavy Ions
The PHENIX Experiment at RHIC

General Description

Work associated with the RHIC PHENIX experiment is a central part of the ORNL group's program since the early 1990s (see the PHENIX experiment homepage for more info). PHENIX concentrates on detection of lepton pairs, photons, and identified hadrons emitted in heavy-ion collisions produced by RHIC. The central idea of the PHENIX experiment is to focus on electromagnetic and high Q2 probes of the system formed in a relativistic heavy-ion collision, since these probes should provide the best way to view these collisions' early-time behavior when quark deconfinement, large gluon density, and direct radiation from the ensemble of partons should be most visible. PHENIX addresses this by having a wide kinematical coverage (in rapidity, transverse momentum, and mass) combined with excellent particle identification, stressing excellent detection of electrons, muons, and photons in particular. The experiment had its first major data-taking run during June-August 2000, with the muon arms starting operation in 2001.

PHENIX has now successfully recorded data for 12 Runs over the past 13 years, with a wide variety of colliding species and energies, including d+Au, Cu+Cu, Cu+Au, and U+U at √sNN = 200 GeV/u, Au+Au over the range √sNN = 7.7-200 GeV/u, and polarized p+p up to √s = 500 GeV. In 2005 each of the RHIC experiments released a White Paper summarizing the current evidence of a quark-gluon plasma. You can find the PHENIX White Paper online at ScienceDirect. In addition, please visit this link to see a recent video describing some of the discoveries made at RHIC.

Detailed Description

ORNL initiated and led the effort within WA80/93/98 to develop an event-mixing algorithm for use in analyzing photon data. The algorithm allows us to extract cross sections for π0 and η mesons, even in the presence of 100 times larger combinatoric background. The π0 and η cross sections are essential input to determining what fraction of the total photon cross section observed in heavy-ion collisions is of hadronic origin and, thus, not due to direct radiation from a deconfined system. This algorithm is a necessary development to analyze photon results without being overwhelmed by combinatoric background in the high multiplicity environment that is encountered at RHIC. The tools developed for this effort are also used to estimate signal/noise, counting rates, and detection limits for direct photons at RHIC. This effort culminated in the present design of the photon part of the PHENIX spectrometer.

Our major development effort for new spectrometer design and construction for PHENIX has been in the area of the PHENIX Muon Arm. The North and South MuID arrays were constructed and installed in 1998 at BNL. All the readout electronics for the MuID has been designed at ORNL. In support of this detector design and construction, we have determined signal rates and expected counts distributions for the muon arm and took lead responsibility for performing trigger selectivity simulations, signal-to-noise estimates, hadron absorber design, and parametric studies of various spectrometer designs. We also performed the mechanical engineering design for the muon identifier (MuID). We earlier carried out, between 1990 and 1994, an R&D program at the BNL AGS test beam to optimize hadron absorber and muon identifier design for the Muon Arm. This culminated in construction of a 1.2-meter-square by 8-interaction-length-deep mockup of a MuID sector instrumented with limited streamer tubes and scintillator arrays; this had final tests during the 1993 AGS run and has since been decommissioned. The data from it were used to size the PHENIX MuID. Data from it and a subsequent device at RIKEN have been used to prepare simulation code and fast trigger algorithms for the PHENIX MuID.

Technical Description

ORNL headed the on-line effort within PHENIX from inception through construction. This included front-end electronics, trigger, data acquisition, and computing systems plus software. We carried out an R&D program on monolithic electronics development from 1989 to 1998 under the auspices of RHIC. The development in support of the CERN program described above has provided us with experience that was directly transportable to PHENIX and has informed the architecture, design, performance specifications, and costing efforts for the PHENIX on-line system. ORNL designed and constructed the monolithic front-end electronics for the silicon strip, pad chamber, ring-imaging Cerenkov EM calorimeters, and muon tracker for PHENIX (some six custom-mixed analog and digital ASICs in all). ORNL handled design and construction of the entire front-end chain for the EM calorimeters and muon identifier. ORNL also provided the system architecture and circuit board designs and manufacture for the entire signal processing chain for the silicon strip detector and the control board design and manufacture for the pad chamber. In addition, we contributed the system architecture for the RICH and MuTR subsystems. Around the start of RHIC, ORNL also designed trigger boards for use with the EM Calorimeter, RICH, and MuID system.

More recent hardware efforts include work on the electronics for the new vertex detector (VTX), using the SVX4 chip developed at FNAL. The VTX detector have so far been taking data successfully during the runs in 2011 and 2012.

ORNL staff have contributed to the management of PHENIX in various ways. G.R. Young was Deputy Spokesman for many years and headed the on-line system from inception up until commissioning in 1999. F. Plasil served on the Executive Council, drafted most of the governing agreements for PHENIX, and served as the first chair of the PHENIX Speakers Bureau. K. Read is the Detector Council member for the MuID, and V. Cianciolo headed the MuID front-end electronics effort. T. C. Awes headed the lead-glass calorimeter effort, and P. W. Stankus is in charge of all electromagnetic calorimeter electronics. S. P. Sorensen headed the off-line effort during its initial years.

ORNL staff have also led important physics analysis work; Awes, Cianciolo, Silvermyr, and Stankus have all been PHENIX Physics Working Group conveners, and all current group members active on PHENIX have been members of numerous PHENIX Paper Preparation Groups and Internal Review Committees, coordinating the analysis and publication of important results, particularly on photons, correlations and heavy flavor (more detailed information available on request)

For More Information

The following links will let you learn more about this topic:

PHENIX public homepage
PHENIX internal homepage


Vince Cianciolo, cianciolotv at ornl.gov
David Silvermyr, silvermy at ornl.gov