1.  production in p+p and Au+Au collisions at 200 GeV in STAR Rosi Reed UC Davis

2. Rosi Reed - SJSU 9/16/20102 Some Relevant Terms Standard Model – Theory that combines 3 out of the 4 fundamental forces Quantum Chromo-dynamics (QCD) – The strong force which holds the nucleus together Quark Gluon Plasma (QGP) – A hot, dense form of matter with free quarks Heavy Ion – Gold ions eV – Electron Volt = 1.6 x 10 -19 Joules

3. Rosi Reed - SJSU 9/16/20103 Goals for this talk Introduce Relativistic Heavy Ion physics Explain the physics behind the Quark Gluon Plasma (QGP) Show how the  meson can be used to probe the (QGP) –Measure the temperature

4. Rosi Reed - SJSU 9/16/20104 Standard Model Fermions Bosons Describes interactions due to 3 out of 4 of the fundamental forces Predicted the existence of the W, Z, gluons, top and charm before these particles were observed http://bccp.lbl.gov/Academy/workshop08/08%20PDFs/chart_2006_4.jpg Higgs is the only particle predicted that has not be found Does not include gravity, dark matter, or dark energy

5. Rosi Reed - SJSU 9/16/20105 Electro-Magnetic Force Quantum Electro-dynamics (QED) 2 charges, + and – Perturbation theory Calculations done via Feynman diagrams Allows QED calculations to be truncated with very few diagrams ? e-e- e-e- e+e+ e+e+ 1st Order Contributions2nd Order Contributions + Each multiplies result by 1/137

6. Rosi Reed - SJSU 9/16/20106 Strong Force Quantum-Chromodynamics (QCD) 3 charges called “colors” All known stable particles are colorless –Mesons have a quark and an anti-quark (ex.  ) –Baryons have 3 quarks, 1 of each color (ex. protons) Only quarks and gluons can feel the QCD force Mediated by gluons –Color+anti-color but not colorless! –Spin 1 –Mass 0 –Can interact with each other! g Feynman diagram

7. Rosi Reed - SJSU 9/16/20107 Confinement in QCD: a cartoon At high energy and small distances, the strength of this force decreases! “Asymptotic freedom” Nobel Prize 2004 http://nobelprize.org/nobel_prizes/physics/laureates/2004/illpres/index.html

8. Rosi Reed - SJSU 9/16/20108 Heavy Ion Collisions At STAR we use Gold Ions Gold is nearly spherical 197 protons and neutrons Allows us to study the energy range > deconfinement but < Asymptotic freedom Ions look like “pancakes” due to relativistic length contraction!

9. Rosi Reed - SJSU 9/16/20109 Generating a deconfined state Nuclear Matter (confined) Hadronic Matter (confined) Quark Gluon Plasma deconfined ! Melting protons and neutrons: Hot quarks and gluons in (QCD) heating compression  deconfined color matter !

10. Rosi Reed - SJSU 9/16/201010 QCD Phase diagram

11. Rosi Reed - SJSU 9/16/201011 Room Temperature: 300 K = 0.025 eV Fire: 1000-2000 K: ~0.12 eV Sun : –Surface: 5000 K: ~0.4 eV –Corona: 5 x 10 6 K ~ 400 eV –Core: 15 x 10 6 K ~ 1 keV Heavy ion collision : –T c ~ 173 MeV : 2 x 10 12 K –Initial T of QGP at STAR = ? > T c Heavy ion collisions = HOT matter

12. Rosi Reed - SJSU 9/16/201012 RHIC BRAHMS PHOBOS PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC) 2 km v = 0.99995  c = 186,000 miles/sec

13. Rosi Reed - SJSU 9/16/201013 RHIC: Some key results Goal: Produce matter in the hot phase of QCD. –What are its properties? –Is the system made up of quarks and gluons? Results and interpretation. –Temperature is high. All estimates > T c –Observation of collective fluid-like behavior of quarks –High momentum particles are suppressed Matter produced is nearly opaque to quarks and gluons Sci Am May 2006. by W. Zajc. STAR White Paper: Nuc Phys A 757 (2005) 102

14. Rosi Reed - SJSU 9/16/201014  : a probe of the QGP How hot is the matter formed at RHIC? –Is there a way to quantitatively measure the temperature of the produced matter? Yes!  Upsilon) production –bb quark Mesons –Measure production in Heavy Ion collisions compared to proton-proton collisions

15. Rosi Reed - SJSU 9/16/201015 Heavy quark bound states Non-relativistic Quantum Mechanics –Schr ö dinger equation –Two particles bound by a linearly rising potential V(r) ~ kr. Bound state of charm-anticharm –Charmonium –J/ ,  ’ (ground state 1s, and excited state 2s state) –Excited states have different Bottom-antibottom –Bottomonium –  (1S, 2S, 3S)

16. Rosi Reed - SJSU 9/16/201016 Suppression of  (1S+2S+3S) Quarkonia = heavy quark+anti-quark meson (bb,cc) b+c quarks are produced early in the collision –Makes them an excellent probe Quantifying suppression requires: –Baseline p+p measurement Sequential Suppression of the  (1S+2S+3S) gives a model dependent temperature –Each state has a different “melting” temperature

17. Rosi Reed - SJSU 9/16/201017 Melting of Quarkonia

18. Rosi Reed - SJSU 9/16/201018 Measuring Temperature Sequential disappearance of states: QCD thermometer  QGP Properties A.Mocsy, 417th WE-Heraeus-Seminar,2008 A. Mocsy and P.Petreczky, PRL 99, 211602 (2007) Theoretical Expectations in 200 GeV Au+Au Collisions:  (1S) does not melt  (2S)+J/  are likely to melt  (3S)+  (2S) will melt A. Mocsy and P. Petreczky PRD 77 014501 (2008)

19. Rosi Reed - SJSU 9/16/201019 Measuring  at STAR  (1S) –m = 9.46 GeV –  = 54 keV – BR(e + e - ) = 2.5%  (2S) –m = 10.02 GeV –  = 32 keV – BR(e + e - ) = 2.0%  (3S) –m = 10.35 GeV –  = 20 keV – BR(e + e - ) = 2.2% Decay channel:   e + e − PDG  Values BR = Branching Ratio = How often  decays in that manner  = mass width due to finite lifetime Why look at di-elelectron channel? Di-lepton channel is clean STAR can only measure electrons out of e, ,  M proton = 0.938 GeV M electron = 0.511 MeV

20. Rosi Reed - SJSU 9/16/201020 Measuring  at STAR Using Einstein’s famous equation (c  1) –unlike-sign electron pairs  Signal + Background –like-sign electron pairs  Background Widths are larger than PDG values due to detector resolution M is the invariant mass

21. Rosi Reed - SJSU 9/16/201021 STAR Detectors Tracker (TPC) Tracking  momentum ionization energy loss  electron ID Calorimeter (BEMC) Measures Energy magnet beam E/p  electron ID

22. Rosi Reed - SJSU 9/16/201022 A STAR  Event

23. Rosi Reed - SJSU 9/16/201023 A STAR  Event

24. Rosi Reed - SJSU 9/16/201024 E 2 Cluster  E 1 Cluster STAR  Trigger pp Data AuAu Rejection ~10 5 in p+p Can sample full luminosity pp Data One in 10 9 p+p collisions will have a  !

25. Rosi Reed - SJSU 9/16/201025 Electron ID E/p and ionization energy loss (dE/dx) of tracks are used to select e + and e - tracks Combination allows greater purity e p K  arXiv: 1001.2745v2 [nucl-ex] Contamination Electrons from  will be here

26. Rosi Reed - SJSU 9/16/201026 Analysis Techniques Track pairs combined into: e + e - = N +- = Signal + Background Unlike-Sign e - e -,e + e + = N --,N ++ = Background Like-Sign Signal calculated as: S = N +- -2√N -- N ++ arXiv: 1001.2745v2 [nucl-ex]

27. Rosi Reed - SJSU 9/16/201027  in p+p 200 GeV arXiv:1001.2745v2 [nucl-ex] 3σ Signal Significance N  (total)= 67±22(stat.) 1 b = 10 -28 m 2 Barn  probability of an interaction between particles At 200 GeV the total inelastic p+p cross-section is 42 mb

28. Rosi Reed - SJSU 9/16/201028 STAR  vs. theory and world data STAR 2006 √s=200 GeV p+p  +  +  →e + e - cross section consistent with pQCD and world data trend arXiv:1001.2745v2 [nucl-ex]

29. Rosi Reed - SJSU 9/16/201029 Measuring  in Au+Au How many p+p collisions = 1 Au+Au collision? This will allow us to compare p+p and Au+Au  yields directly! 0-60% Centrality RefMult  # charged particles  # collisions RefMult is the observable # collisions per centrality based on model Bright Colors = collision

30. Rosi Reed - SJSU 9/16/201030  in Au+Au 200 GeV 4 Million Events 4.6  significance 95 Signal counts

31. Rosi Reed - SJSU 9/16/201031  1S+2S+3S) Ratio 0-60% Centrality Yield of  (1S+2S+3S) –78±15(stat:)+17/-22(sys.) –Evidence that  can be measured in heavy ion collisions Ratio of Observed/Expected –0.920±0.35(stat.)+0.06/-0.18 –Indicates little suppression at RHIC energies

32. Rosi Reed - SJSU 9/16/201032 Temperature!  (1S) = 69.0% of  e + e - yield in p+p  (2S) = 18.3% of  e + e - yield in p+p  (3S) = 12.7% of  e + e - yield in p+p Assume Ratio of Observed/Expected > 0.2 Ratio of  (1S+2S+3S) = 0.92 = Some suppression of the  (3S) state  T < T c Ratio = 0.53 (lower bound) = Complete suppression of the  (2S+3S) state  T < 2T c Ratio = 1.28 (upper bound)  T << T c and some new physics T = T c +T c /-0 = 170 MeV +170/-0 MeV

33. Rosi Reed - SJSU 9/16/201033 Conclusions  (1S+2S+3S) peak measured in p+p collisions  (1S+2S+3S) peak observed in Au+Au collisions –Proof that  can be measured in Heavy Ion collisions! Temperature is 170 +170/-0 MeV –Indicates we will be able to set an upper limit! Future Measurements –3x more p+p data from 2009 –4x more Au+Au data from 2010 –Improve Temperature Precision

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