Identified Particle Measurements RHIC Beam Energy Scan

1. STAR Identified Particle MeasurementsRHIC Beam Energy Scan Abhilash Nair STAR Collaboration University of Illinois at Chicago

2. Beam Energy Scan at RHIC • Properties of matter created at 200 GeV are consistent with an expected2nd order phase transition • Beam Energy Scan (BES) at RHIC looks to experimentally find the critical point of 1st order phase transition predicted to exist at lower energies • STAR has collected data from the following collision energies (in decreasing energy order) : • 200, 130, 62.4, 39, 19.6, 11.5, 9, 7.7 GeV • This presentation aims to show the work-in-progress analysis of the 39 GeV data sample • Spectra shapes and particle ratios help connect collected data to observables that are expected to change in such a phase transition Simply a cartoon, does not represent actual experiential data

3. Time Projection Chamber (TPC) • The TPC is a barrel shaped detector consisting of a gas-filled chamber, magnet providing a strong uniform magnetic field, and an electric field between the center and endplates • We use measurements of the ionization energy loss (dE/dx) and momentum to identify particles

4. Event Selection • From Min-Bias Trigger • |Vz| < 30 cm • |Vr| < 2 cm • 10 M events pass cuts Track-Quality Cuts • |Dca| < 3 cm • NHitFits > 25 • NHitFits/NHitPoss > 0.51 Vertex Z Vertex Y [cm] Vertex X [cm]

5. 2-D Particle-Centered Histograms dE/dx (Arb Units) p (GeV/c) π p K pT (GeV) pT (GeV/c) pT (GeV/c) Zπ Zk Zp Where superscript BB represents the expectation of dE/dx for a given particle i = ( π, K, p )

6. Gaussian Peak Fitting & Electron Contamination π+ π- K+ p K- e+ e- pbar Zk Zk Without constraints, e-/e+ peak positions will jump sharply over a relatively small pT range e-/e+ peak overlaps with nearby peaks in certain pT ranges During crossover, e-/e+ peak is not reliable without further constraints Zk

7. Estimate of E-/E+ Contamination dE/dx p K • For overlap areas we rely on extrapolated centroid positions and yields • This is done independently in each particle-centered histogram, and across different rapidity bins e π p (Gev/c) e+ Centroids e+ Yields [-0.1 < y < 0.1) [-0.1 < y < 0.1) dE/dx STAR Preliminary STAR Preliminary pT (GeV/c) pT (GeV/c)

8. Uncorrected Yields vs. mT-m0 [-0.1 < y < 0.1) [-0.1 < y < 0.1) [-0.1 < y < 0.1) π+ p Arbitrary Units Arbitrary Units Arbitrary Units K+ Arbitrary Units STAR Preliminary STAR Preliminary STAR Preliminary mT-m0 (GeV) mT-m0 (GeV) mT-m0 (GeV) [-0.1 < y < 0.1) [-0.1 < y < 0.1) [-0.1 < y < 0.1) Arbitrary Units π- K- pbar Arbitrary Units Arbitrary Units STAR Preliminary STAR Preliminary STAR Preliminary mT-m0 (GeV) mT-m0 (GeV) mT-m0 (GeV)

9. Uncorrected Antiparticle to Particle Ratios • Cannot make a physics conclusions without corrections, which include: • Single Particle Efficiency • Energy Loss Correction • Acceptance • Proton Background [-0.1 < y < 0.1) [-0.1 < y < 0.1) [-0.1 < y < 0.1) π- / π+ K- / K+ pbar / p Arbitrary Units Arbitrary Units Arbitrary Units Efficiency, absorption, &background uncorrected Efficiency, absorption, &background uncorrected Efficiency, absorption, &background uncorrected STAR Preliminary STAR Preliminary STAR Preliminary mT-m0 (GeV) mT-m0 (GeV) mT-m0 (GeV)

10. Proton Background: DCA Plots dN/d(dca) [cm^-1] Phys. Rev. C 79 (2009) 34909 200 MeV < pT < 300 MeV STAR Preliminary Phys. Rev. C 79 (2009) 34909 Dca [cm] DCA plot courtesy of Alex Brown (UIC)

11. Future Outlook • Our work-in-progress min-bias π+/π- ratio at 39 GeV is similar to results from 19 GeV & 200 GeV • Plans for the future include: • Efficiency Corrections • Proton Background • Energy Loss Corrections • Investigate Rapidity Dependence • K/Pi, p/Pi • Integrated Yields & Ratios [-0.1 < y < 0.1) π+ / π- Arbitrary Units Efficiency, absorption, &background uncorrected STAR Preliminary mT-m0 (GeV)