Experimental Study of the Strongly-Coupled

Experimental Study of the Strongly-coupled

Quark Gluon Plasma via Heavy Quark Production at RHIC

Xin Dong, Staff Scientist

Lawrence Berkeley National Laboratory

510-486-4121,

Year Doctorate Awarded: 2005

DOE National Laboratory Announcement Number: LAB 12-751

Quantum ChromoDynamics (QCD) calculations predict that a new state of matter, the Quark Gluon Plasma (QGP), exists at extremely high temperature and/or high density. Relativistic heavy ion collisions allow us to create and study this type of matter in the laboratory. The study of this matter is the primary mission of the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National laboratory. So far, we learned at RHIC that hot, opaque, and strongly interacting matter with partonic collectivity is formed in Au+Au collisions at a center-of-mass energy of 200 GeV per nucleon pair. The next important task of relativistic heavy ion collisions is to quantify the properties of this novel QCD matter, the strongly-coupled quark gluon plasma (sQGP).

At RHIC, heavy quarks, charm and bottom, are expected to create in initial hard scatterings. Their production rates are calculable usingthe well-established techniques of perturbative QCD.Heavy quark masses are not easily modified by the QCD medium, therefore serving as a clean and penetrating probe. Their interactions with the hot QCD medium provideunique and sensitive measurements of the medium properties. Studying the flavor dependence of the parton energy loss in the medium will providekey information for us to understand the detail of energy loss mechanism that is one of the unsolved puzzles in hot/dense QCD. The interacting strength between heavy quarks and the medium will be sensitive to the medium transport properties, which can be revealed from the experimental observables. The collective behavior of heavy quarks in the medium will also shed light on the mechanism of thermalization in such collisions. The medium properties can also be assessed via charm-charm correlations. Studying the behavior of heavy flavor jets traversing the medium via heavy flavor tagged events will strongly enhance the QCD energy loss program. Such measurements will be unique at RHIC, since the leading order process of heavy flavor production is dominant, while heavy flavor event tagging is achievable by utilizing both the high luminosity deliverable by the RHIC machine, as well as the electron and muon triggering capability within the large acceptance of STAR. In addition, understanding the charm-charm correlations will aid the research of intermediate mass dilepton spectra (1< Mll < 3 GeV/c2) to study the thermal radiations from the medium.

Measuring the heavy flavor hadron production spectra and correlations is a DOE milestone in 2016.

I propose to carry out an experimental study of the sQGP through precision measurements of heavy quark production and correlations at RHIC utilizing the heavy flavor tracker (HFT) at the STAR experiment. The STAR HFT upgrade is a DOE funded project, and is scheduled to complete in STAR by fall of 2013. The key component of the HFT system uses the CMOS active pixel sensor technology, which will provide pointing resolution to the collision vertex that is better than 30 microns. The HFT, together with other STAR tracking and particle identification subsystems is covering full azimuth at mid-rapidity. Therefore STARis well suited for precision measurements of the production of charmed hadrons via the reconstruction of the secondary decay vertices.

My study will be focusing on the following experimental measurements:

1)Production yields on various charm hadrons to address the energy loss mechanism.

2)Charm hadron elliptic flow over a large momentum region to address the issue of medium thermalization.

3)Charm-charm correlations to further address the medium response to the heavy quark jet, as well as to aid the understanding of dilepton spectra in the STAR experiment.

I will carry out the proposed research in collaboration withpostdocs and students funded in this project within the STAR experiment. The research will start with the simulation studies, detector commissioning and calibrations. After the HFT is installed into STAR, the STAR collaboration will collect the necessary data samples from the RHIC beam collisions, and we will carry out the data analysis for the measurements proposed above.

The proposed project described is critical, highly interesting, feasible, and fully aligned with the2007 NSAC Long Range Plan as well as the supported directions in the funding announcement. If funded, the proposed research will address fundamental questions, such as “what are the phases of strongly interacting matter?”, and will significantly impact our understandings of the strongly coupled quark gluon plasma by measuring “its physical properties with controlled accuracy” [1].

Reference:

[1]: 2007 NSAC Long Range Plan. http://science.energy.gov/np/nsac/