The primary physics direction of the Yale RHI Group focuses on measurements of heavy flavor production, high transverse momentum particles, jets and correlations to probe the QGP (quark-gluon plasma). Measurements are made in STAR at RHIC at BNL and in ALICE at the LHC at CERN. The range of beam energies and systems available at RHIC and LHC allow detailed investigation of the properties of the QGP, with potential sensitivity of observables to the collision energy and initial temperature of the system. This research is at the frontier of relativistic heavy ion physics.
The STAR experiment searches for signatures of QGP formation and investigates the behavior of strongly interacting matter at high energy density by focusing on measurements of hadron production over a large solid angle. STAR is one of the two large–scale experiments at the Relativistic Heavy Ion Collider (RHIC) at BNL, which began operation in 2000. It was designed to focus primarily on hadronic observables and features a large acceptance for high precision tracking and momentum analysis at center of mass (c.m.) rapidity.
The STAR experiment utilizes colliding beams of various nuclei from protons to gold at center of mass energies ranging from 7–200 GeV per nucleon pair in nucleus–nucleus collisions. The experiment utilizes a large volume Time Projection Chambers (TPC) and a state–of–the–art inner silicon tracking system, for tracking and particle identification in a high track density environment. STAR measures many observables simultaneously to study signatures of a QGP phase transition and the space–time evolution of the collision. The goal is to obtain a fundamental understanding of the microscopic structure of hadronic interactions, at the level of quarks and gluons, at high energy densities. STAR measures the bulk properties of the matter formed in the most violent (near–) head–on collisions at RHIC, for example entropy, baryochemical potential, strangeness chemical potential, temperature, fluctuations, and particle and energy flow. It also measures high transverse momentum (pT) processes representing hard scattered partons in the form of high pT single particles, azimuthal correlations of high pT particles, and jets.
The ALICE experiment is the dedicated heavy-ion experiment at the LHC with precision tracking, particle identification and electromagnetic calorimeter detectors similar in concept to those of STAR. The physics research interests of the Yale group in ALICE are to establish through experiment the underlying mechanisms of parton energy-loss in the QGP and to investigate its response to the energy deposition by parton energy–loss. At the LHC the energies and energy densities (and temperatures) are several times that at RHIC. The research focuses on jet physics, large transverse momentum (pT) particle production and correlations, similar to those in the STAR experiment. Heavy ions became available in 2010 in the LHC; ALICE has accumulated data with protons and heavy ions.
The Yale Group has contributed significantly to ALICE analyses and papers involving full jet reconstruction, to open heavy flavor production at large pT, and analyses involving high–pT triggered multi–particle correlations. The group continues to analyze jets and their correlations, with emphasis on the collision centrality dependence of jet spectra and spectral shapes in p+Pb and Pb+Pb collisions. The p+Pb collisions are studied to investigate initial state nuclear effects for comparison and better understanding of the parton energy-loss observed in Pb+Pb collisions.
The LHC will re-commence operation in 2015 with higher energies and luminosities. A newly-installed di-jet calorimeter in ALICE will make available more detailed triggers, increased statistics and the added ability to measure correlations of di-jets, π0–jets and γ0–jets and jets with heavy flavor electrons. At RHIC the group continue its high pT analyses of the STAR Beam Energy Scan data, including helping to incorporate particle identification into the studies and comparisons to theoretical models. In addition the group is studying di–jet energy balance measurements in the top energy Au+Au collisions.
The Yale RHI Group also continues to utilize its experience in detector R&D, design and testing. Before the start-up of the LHC, the group focused on assembly, testing, calibration and installation of the electromagnetic calorimeter (EMCal) in ALICE. Much of this work was undertaken at Yale during 2008–2010, with shipment to CERN and installation and operation in ALICE. The Group is engaged in simulations, R&D, design and prototyping of future detectors for STAR, ALICE, and a possible future Electron Ion Collider detector. The detector construction effort of the Group is focused presently on construction of the inner readout chambers for the ALICE TPC Upgrade with planned completion in 2018.
Group Presentations for Students 2014John Harris
Recreating the Primordial QGP
Using Hard Probes to Study the QGP
Detectors in Nuclear and High Energy Physics
Introduction to Jets