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star focus: Baryon Number Fluctuations to look for the QCD Critical Point
Highlights from the STAR papers
Higher Moments of Net-proton Multiplicity Distributions at RHIC Published in Physical Review Letters 105 (2010) 022302




















A recent paper from the STAR Collaboration published in Physical Review Letters proposes using the higher moments of net-proton multiplicity distributions produced in high energy heavy-ion collisions as an observable for locating the QCD Critical Point. It has been shown that a careful choice of the products of the moments of the net-proton distributions form observables that can be related to the ratios of various order baryon number susceptibilities computed in QCD (basic theory of strong interactions) calculations. Thus the measurements provide a way for comparisons of heavy-ion collision data to first principle QCD calculations on lattice. Since susceptibilities diverge at critical point, these products of moments of net-proton distributions are also expected to take up larger values at the critical point. Thus the measurements reported provide a unique and new observable to search for landmark QCD critical point in QCD phase diagram of Temperature vs. Baryon chemical potential,in high energy heavy-ion collisions.

The measurements (product of kurtosis times the variance of net-proton distribution is shown in the figure) carried out at three different beam energies have been used to rule out the presence of QCD critical point below 200 MeV baryon chemical potential in the QCD phase plane. In high energy heavy-ion collisions the moments of net-protons, related to baryon number susceptibilities, have been shown to be independent of the system volume. QCD calculations on lattice have shown such a case happens when the system undergoes a cross over transition between hadronic and quark-gluon phases. In the near future these measurements (as indicated by the arrows at the bottom of the figure) will be carried out at varying collision energies or baryon chemical potential at the Relativistic Heavy Ion Collider to locate the QCD critical point. This is one of the physics goals of the RHIC Beam Energy Scan Program, moving towards that direction the STAR experiment has collected a good data set at beam energies of 7.7, 11.5 and 39 GeV this year.

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August 26, 2010
Congratulations to Lokesh Kumar, from Panjab University, for successfully defending the phd thesis titled "Identified particle production, fluctuations and correlations studies in heavy-ion collisions at RHIC energies".

August 16, 2010
Congratulations to Muhammad Elnimr from Wayne State University for successfully defending his phd thesis titled "Dihadron Fragmentation Functions in p+p collisions at sqrt{s} of 200 GeV"

August 12, 2010
Congratulations to Priscilla Kurnadi from UCLA, for the successful defense of the phd thesis titled: "Measurements of non-photonic electron cross section and double longitudinal spin asymmetry, ALL , in polarized p+p collisions at [sNN]1/2 = 200 GeV".

August 12, 2010
Congratulations to Bertrand Helmut Josef Biritz from UCLA, for the successful defense of the phd thesis titled: "Electron-hadron azimuthal correlations in Au+Au collisions at [sNN]1/2 = 200 GeV".

August 12, 2010
Congratulations to David Staszak, from UCLA, for the successful defense of the phd thesis titled: "Measurements of the Jet Cross Section and Spin Asymmetry ALL Using Polarized Proton Beams at RHIC"

July 17, 2010
Congratulations to Michael Skoby from Purdue University for successfully defending his thesis titled "Forward-Backward Multiplicity correlations for identified particles in Au+Au collisions at sqrt_{NN} = 200 GeV".

May 26, 2010
Congratulating Fu Jin, from SINAP, for successfully defending his phd thesis. The thesis title is: "Measurement of the Non-Photonic Electrons and Study of Phase Transition in Heavy Ion Collisions".

May 26, 2010
Congratulating Jian Tian, from SINAP, for successfully defending his phd thesis. The thesis title is: "Study of the Fluctuations in Particle Production and GP Phase Transition in Relativistic Heavy Ion Collisions".


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