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

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 for STAR eV – Electron Volt = 1.6 x Joules

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

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 Higgs is the only particle predicted that has not been found Does not include gravity, dark matter, or dark energy

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 = 1/4  0 ħc

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 Each multiplies result by ~1 –QCD is not perturbative at low energies Mediated by gluons –Color+anti-color but not colorless! –Spin 1 –Mass 0 –Can interact with each other! g Feynman diagram

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

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 E > E deconfinement E < E Asymptotic freedom Ions look like “pancakes” due to relativistic length contraction!

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 !

Rosi Reed - SJSU 9/16/ QCD Phase diagram

Rosi Reed - SJSU 9/16/ Room Temperature: 300 K = eV Fire: 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 K Temperature of deconfinement –Initial T of QGP at STAR = ? > T c Heavy ion collisions = HOT matter

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

Rosi Reed - SJSU 9/16/ 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 by W. Zajc. STAR White Paper: Nuc Phys A 757 (2005) 102

Rosi Reed - SJSU 9/16/  : 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

Rosi Reed - SJSU 9/16/ 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)

Rosi Reed - SJSU 9/16/ Suppression of  (1S+2S+3S) Quarkonia = heavy quark+anti-quark meson 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

Rosi Reed - SJSU 9/16/ Melting of Quarkonia

Rosi Reed - SJSU 9/16/ Measuring Temperature Sequential disappearance of states: QCD thermometer  QGP Properties A.Mocsy, 417th WE-Heraeus-Seminar,2008 A. Mocsy and P.Petreczky, PRL 99, (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 (2008)

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

Rosi Reed - SJSU 9/16/ Measuring  at STAR  (1S) –m = 9.46 GeV –  = 54 keV – BR(e + e - ) = 2.5%  (2S) –m = GeV –  = 32 keV – BR(e + e - ) = 2.0%  (3S) –m = GeV –  = 20 keV – BR(e + e - ) = 2.2% PDG  Values Decay channel:   e+e− 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 = GeV M electron = MeV

Rosi Reed - SJSU 9/16/ 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

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

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

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

Rosi Reed - SJSU 9/16/ 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  Contamination Electrons from  will be here Phys. Rev. D 82 (2010) 12004

Rosi Reed - SJSU 9/16/ 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 ++ Phys. Rev. D 82 (2010) 12004

Rosi Reed - SJSU 9/16/  in p+p 200 GeV 3σ Signal Significance N  (total)= 67±22(stat.) 1 b = m 2 Barn  probability of an interaction between particles At 200 GeV the total inelastic p+p cross-section is 42 mb Phys. Rev. D 82 (2010) 12004

Rosi Reed - SJSU 9/16/ STAR  vs. theory + world data STAR 2006 √s=200 GeV p+p  +  +  →e + e - cross section consistent with pQCD and world data trend Phys. Rev. D 82 (2010) 12004

Rosi Reed - SJSU 9/16/ Measuring  in Au+Au How many p+p collisions = 1 Au+Au collision? 0-60% Centrality RefMult  # charged particles  # collisions RefMult is the observable # collisions per centrality based on model Bright Colors = collision

Rosi Reed - SJSU 9/16/  in Au+Au 200 GeV 4 Million Events 4.6  significance 95 Signal counts First Heavy Ion  Measurement!

Rosi Reed - SJSU 9/16/  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

Rosi Reed - SJSU 9/16/ Temperature! Ratio of  (1S+2S+3S) = 0.92  Some suppression of  (3S)  T =0.8 T c 0.53 (lower bound)  Suppression of  (2S+3S)  T = 1.2 T c 1.28 (upper bound)  T << T c not physical 140 < T < 210 MeV S. Digal, P. Petreczky, and H. Satz, Phys. Rev. D 64, (2001) Phys. Rev. D 64, (2001)

Rosi Reed - SJSU 9/16/ 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 140 < T < 210 MeV –Indicates we will be able to set an upper limit with more statistics! Future Measurements –3x more p+p data from 2009 –4x more Au+Au data from 2010 –Improve Temperature Precision Phys. Rev. D 82 (2010) 12004

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