Status of 20 GeV Au+Au Analysis Overview: 20 GeV run’s details 2 centrality bins analyzed PID method efficiency correction results: yields, ratios, dN/dy Roppon Picha 23 Oct 2002 UCD NPG meeting

RHIC Runs Overview Au + Au @ 130 GeV 2 weeks p + p @ 130 GeV (3) weeks Refs: K. Schweda, HS02 RHIC BUR 2002 Year 2000: Au + Au @ 130 GeV 2 weeks p + p @ 130 GeV (3) weeks Year 2001: (Silicon Vertex Tracker installed) Au + Au @ 200 GeV 15 weeks Au + Au @ 20 GeV 1 day p + p @ 200 GeV 5 weeks Year 2002: 1st of November d + Au @ 200 GeV 16 weeks p + p @ 200 GeV 8 weeks 9/22/2018 NPG Meeting

20 GeV Au+Au at STAR # good minbias events = 172,202 Au+Au at E = 19.6 GeV per nucleon; 0.25 Tesla magnetic field Trigger: ZDC e&w and CTB > 15 [RHIC BUR 2002] Details: Production: /auto/stardata/pDST/flow_pDST_production/reco/minBias/22GeVZDC/ReversedHalfField/P02ge/2001/ 12 runs: 2329: 88, 89, 91, 92, 93, 94, 100, 101 2330: 2, 3, 4, 5 # minbias events = 278,452 # events with (Nch = 0) = 106,250 # good minbias events = 172,202 9/22/2018 NPG Meeting

Selections: Events Vertex locations vY vZ vX |vZ| < 30 (center of TPC, which has uniform acceptance) (vX+0.246)2+(vY-0.378)2 < 1 (eliminates interactions with beam pipe material) 9/22/2018 NPG Meeting

Selections: Events Multiplicity: 2 centrality bins are studied more central collisions more central collisions 0-10% central: Nch >= 237 10-30% central: 117 <= Nch < 237 9/22/2018 NPG Meeting

Selections: Tracks Fit points DCA (cm) Tracking % Chi squared The distance of closest approach between the track and the main event vertex has a built-in cut at 3 cm to eliminate background protons. The c2 of the helix fit to the found points was limited to 2.5. The total number of points used in the fit was required to be greater than 25 (out of a maximum of 45) to eliminate short tracks. And the fraction of points used in the fit was required to be greater than half the possible number to avoid split tracks. rapidity: |y| < 0.5, 5 bins, bin’s width = 0.2 DCA (cm) Tracking % Chi squared 9/22/2018 NPG Meeting

Particle ID: finding dE/dx Bethe-Bloch parametrization: Particles to identify: +, -, K+, K-, p, and pbar p- masses : 139.570 MeV K: 493.677 MeV p: 938.272 MeV K- e- - 9/22/2018 NPG Meeting

PID: Fitting dE/dx distribution From the parameters, 4 Gaussians are constructed in each mt-m0 slices. mt-m0 range: 0-1 GeV/c2, divided into 40 slices (bins), bin’s width = 0.025 GeV/c2. The integrations of the fits then give the raw yields of the particles (d2N/(2pi mt dmt dy) as a function of mt-m0). - e- K- p- 9/22/2018 NPG Meeting

Efficiency Method: O. Barannikova and J. Romero Plot pt distribution of Monte-Carlo embedded tracks (mMcTracks.mPtMc) and the reconstructed tracks (mMatchedPairs.mPtMc) from /auto/pdsfdv41/starprod/QA/MiniDst/20GeV/RevHalfField/ Plot the ratio of the two Fit the ratio to: eff = m1*exp(-(m2/pt)^m3) Efficiency depends on particle type, rapidity, and impact parameter. The higher the track density, the lower the efficiency. The embedding was run for -, K-, and pbar. We apply the same corrections for their positive counterparts. 9/22/2018 NPG Meeting

Corrected yields corrected yield = raw yield/eff Fit the yields to distribution functions: use Bose-Einstein for pions and kaons (bosons); Fermi-Dirac for protons and antiprotons (fermions) … obtain dN/dy and temperatures from the fits 9/22/2018 NPG Meeting

Pion Spectra, Au+Au 20 GeV |y| < 0.1 Au + Au --> + + X 9/22/2018 NPG Meeting

Kaon Spectra, Au+Au 20 GeV |y| < 0.1 Au + Au --> K+ + X 9/22/2018 NPG Meeting

p, pbar Spectra, Au+Au 20 GeV |y| < 0.1 low statistics for pbar Au + Au --> p+ + X Au + Au --> p- + X 9/22/2018 NPG Meeting

Spectra shape h+ h- h+ h- 0-10% central 10-30% central 9/22/2018 NPG Meeting

dN/dy distributions + K+ p+ p- - K- dN/dy increases with centrality, nearly doubles in some cases more uniform as a function of rapidity in peripheral collisions p- - K- 9/22/2018 NPG Meeting

Particle ratios K- u K+ - d - u s + d u d u d + u s + p- d K- + From the yields --> particle ratios can be obtained. The ratios give us basic information about the collision dynamics and the nuclear matter produced. K/ ratios (not studied here) --> strangeness production (70% of strange quarks go into producing kaons) K-/K+ ratios --> kaon medium modification pbar/p ratios --> baryon transport Refs: STAR Coll., nucl-ex/0206008 F. Wang, nucl-ex/9911004 C. Roy, nucl-ex/0111017 K- u K+ - d - u s + up’s and down’s d up’s and down’s u d u d + u s + quarks’ masses u: 1.5 - 4.5 MeV d: 5 - 8.5 MeV s: 80 - 155 MeV p- d K- + 1 Au ion = 79 p, 118 n - 9/22/2018 NPG Meeting

Ratios: Pions As the lightest mesons, pions are the most abundant particles produced. Unlike K and p ratios, the +/- ratio is not constant over mt-m0. We found a slight excess of negative pions. This is due to the isospin dependence in the branching ratios. There are more neutrons (118+118) than protons (79+79) in a collision. The direct + are produced in pp, while direct - are produced in nn collisions. [J. Klay, Ph.D. thesis 2001] 0-10% y ---> -0.4 -0.2 0.0 0.2 0.4 const 0.9375 0.9941 0.9307 0.9554 0.9044 slope 0.0696 0.5118 0.116 0.4505 0.1624 The +/- ratio also allows us to calculate the Coulomb potential (q1q2/r). We find that the potential decreases as the energy increases. [D. Cebra, QM 2002] 10-30% * errors omitted y ---> -0.4 -0.2 0.0 0.2 0.4 const 0.9337 0.9406 0.981 0.9315 0.9327 slope 0.1031 0.0968 -0.030 0.08674 0.1309 9/22/2018 NPG Meeting

Ratios: Kaons and Protons K-/K+ pbar/p both vary very little as a function of rapidity not a big difference between the two centrality bins 9/22/2018 NPG Meeting

Ratios: Kaons and Protons Both (us)/(us)and (uud)/(uud) increase with collisions energy, with the kaon’s ratio increasing faster (more s quarks). They approach unity at E = 200 GeV. K-/K+ Sources: E866/917 nucl-ex 0008010 WA97 JPhys G25 (1999) 171 NA44 JPhys G23 (1997) 1865 NA49 NP A661 (1999) 45c 9/22/2018 NPG Meeting

Summary yields increase with centrality; similar shape in 2 centrality bins; uniform over |y| < 0.5 dN/dy increases with centrality; uniform over |y| < 0.5, although some have curious shapes Both K-/K+ and pbar/p ratios uniform over |y| < 0.5; dramatically increases with energy K ratio - no strong dependence on impact parameter pbar/p ratio slightly higher in peripheral collisions * To do - antiproton absorption in detector material; analysis of other centrality bins; better understanding of the physics involved 9/22/2018 NPG Meeting