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Beam Energy Scan at RHIC HighlightsHighlights fromfrom thethe STARSTAR experimentexperiment Hanna Zbroszczyk for the STAR Collaboration Faculty of Physics, Warsaw University of Technology MESON 2018, Kraków, 9th June 2018 1 IntroductionIntroduction 2 RRelativisticelativistic HHeavyeavy IIonon CColliderollider (RHIC)(RHIC) BrookhavenBrookhaven NationalNational LaboratoryLaboratory (BNL),(BNL), NewNew YorkYork PHOBOS BRAHMS PHENIX RHIC STAR AGS TANDEMS • 2 concentric rings of 1740 superconducting magnets 3 • 3.8 km circumference TheThe SSolenoidalolenoidal TTrackerracker AAtt RRHICHIC .1 4 IntroductionIntroduction RHIC Top Energy p+p, p+Al, p+Au, d+Au, 3He+Au, Cu+Cu, Cu+Au, Ru+Ru, Zr+Zr, Au+Au, U+U QCD at high energy density/temperature Properties of QGP, EoS Beam Energy Scan Au+Au 7.7-62 GeV QCD phase transition Search for critical point Turn-off of QGP signatures Fixed-Target Program Au+Au =3.0-7.7 GeV High baryon density regime with 420-720 MeV 5 IntroductionIntroduction 1. Open heavy flavor - D0 v , D0 R and R , 1 AA CP ΛC 2. Quarkonium – R Υ AA 3. Jet modification and high-pT hadrons - di-jet imbalance, di-hadron correlation 4. Chirality, vorticity and polarization effects - Λ polarization, Φ polarization, CME, CMW 5. Initial state physics and approach to equilibrium - v and v fluctuations 2 3 6. Collectivity in small systems - v in p+Au and d+Au 2 7. Collective dynamics - longitudinal decorrelation, identified particle v 1 8. High baryon density and astrophysics - v from fixed target 1 9. Correlations and fluctuations – femtoscopy 10. Phase diagram and search for the critical point - net Λ and off-diagonal cumulants 11. Thermodynamics and hadron chemistry - triton, hypertriton mass 6 12. Upgrades - BES-II and forward upgrades IntroductionIntroduction 1. Open heavy flavor - D0 v , D0 R and R , 1 AA CP ΛC 2. Quarkonium – R Υ AA 3. Jet modification and high-pT hadrons - di-jet imbalance, di-hadron correlation 4. Chirality, vorticity and polarization effects - Λ polarization, Φ polarization, CME, CMW 2. Initial state physics and approach to equilibrium - v and v fluctuations 2 3 3. Collectivity in small systems - v in p+Au and d+Au 2 7. Collective dynamics - longitudinal decorrelation, identified particle v 1 4. High baryon density and astrophysics - v from fixed target 1 5. Correlations and fluctuations – femtoscopy 10. Phase diagram and search for the critical point - net Λ and off-diagonal cumulants 6. Thermodynamics and hadron chemistry - triton, hypertriton mass 7 7. Upgrades - BES-II and forward upgrades (as summary) ResultsResults 8 1)1) DD0 –– OpenOpen heavyheavy flavorflavor First evidence of non-zero D0 v is measured. 1 Probe the initial tilt of the source and the initial EM field 9 2)2) InitialInitial statestate physicsphysics Q-cumulant method (traditional) Φ - azimuthal angle Two-subevent method Sensitive to flow fluctuations10 11 2)2) InitialInitial statestate physicsphysics Strong dependence of v {k} on collision 2 energy. Weak dependence of v {4}/v {2} on collision 2 2 centrality 11 2)2) InitialInitial statestate physicsphysics Strong dependence of v {2} and v {4} on 2 2 collision centrality. Weak dependence of v {2}/v {4} on collision 2 2 centrality 12 2)2) InitialInitial statestate physicsphysics Weak dependence of v {2}/v {4} on transverse momentum 2 2 13 2)2) InitialInitial statestate physicsphysics Significant dependence of v {2}, v {4} 2 2 and v {2}/v {4} on <N > among 2 2 ch different systems 14 2)2) InitialInitial statestate physicsphysics Anisotropic flow magnitude is sensitive to: - initial-state spatial anisotropy - flow fluctuations and correlations - viscous attenuation ( ∝ η/s (T) ) Weak dependence of v {2}/ {2} 2 ε2 on collision centrality among different systems. Are dynamical final-state fluctuations significantly less than the initial-state fluctuations? 15 2)2) InitialInitial statestate physicsphysics Strong dependence of v {2}, v {4} on collision centrality, 2 2 collision energy, transverse momentum Weak dependence of v {4}/v {2} and v {2}/ {2} (elliptic flow 2 2 2 ε2 fluctuations) on the size of colliding system and: collision centrality, collision energy, transverse momentum Flow flucuations are dominated by the fluctuations of the initial state eccentricity Similar viscous coefficient for different colliding systems 16 3)3) SmallSmall systemssystems Near-side ridge observed in High Multiplicity (HM) of d+Au collisions 17 3)3) SmallSmall systemssystems Low multiplicity subtraction scaled by short-range near-side (|Δη|<0.5) jet yield Short-range near-side jet modification = long-range away-side jet modification Template fit A new method by ATLAS Collaboration away-side jet shape can be measured in Low Multiplicity (LM) events scaled by ”F” parameter (due to jet modification) 18 3)3) SmallSmall systemssystems v without subtraction is larger than that 2 with subtraction for both methods. The subtraction of non-flow contributions are very important for STAR results are comparable with PHENIX results. At lowet p v from Low Multiplicity T 2 subtraction is 35% lower than from template fit At intermediate p they agree with each T other STAR results are comparable with PHENIX ones. 19 3)3) SmallSmall systemssystems v in p+Au collisions without 2 subtraction is larger than v in 2 d+Au collisions that with subtraction for both methods. v in p+Au collisions from Low 2 Multiplicity subtraction is lower than from template fit. STAR results are comparable with PHENIX results, except at high pT. The STAR data is clearly lower than PHENIX for p >1.5 GeV/c T 20 3)3) SmallSmall systemssystems Large difference between subtraction method and template fit v from subtraction method is negative at lower collision energies 2 (different kinematics between near-side and away-side jet-like correlations?) v from template fit increases with collision centrality 21 2 c 3)3) SmallSmall systemssystems v becomes negative at 2 high transverse momentum in d+Au collisions at low collision energy The correlation from away-side jet is stronger at high transverse momentum 22 3)3) SmallSmall systemssystems Large difference between v from two methods has been 2 observed at low energy → large uncertainties in the non-flow subtraction in small systems. We do see similar v between p+Au and d+Au collisions for 2 same multiplicity → v is not only driven by initial geometry. 2 The integral v extracted by a template fit shows an universal 2 trend as a function of <dN/dη> for different small systems at different energies → multiplicity plays an important role in small systems. 23 4)4) FixedFixed targettarget modemode BES goals: Collider mode is unusable - Search for 1st order phase for s <7.7 GeV ⎷ NN transition - Search for existance of the Fix target mode is able to Critical Point cover ⎷s from 3.0 GeV to - Search for turn-off QGP NN 7.7 GeV signatures 24 4)4) FixedFixed targettarget modemode (1) Detector’s scheme (2a) (2b) Spectra corrections: Detector efficiency Detector acceptance (each rapidity window) Energy loss 25 4)4) FixedFixed targettarget modemode π- spectra are consistent with AGS results. 26 4)4) FixedFixed targettarget modemode Directed flow for pions and protons with fit describing mid- rapidity region. 27 Directed flow of protons agrees with AGS results. 4)4) FixedFixed targettarget modemode Directed flow for and K0 particles and their fits describing mid-rapidity Λ S region. 28 4)4) FixedFixed targettarget modemode Directed flow for identified particles agrees with AGS results. 29 4)4) FixedFixed targettarget modemode HBT radii for pions are consistent with AGS results. 30 4)4) FixedFixed targettarget modemode - STAR is ready to operate with the Fixed Target mode - Spectra and particle yields agree with AGS results - Proton directed flow and elliptic flow (v and v ) agree with AGS 1 2 results - HBT radii agree with AGS results High-baryon density regime will be accessible with the Fix Target mode in STAR! 31 5)5) FemtoscopyFemtoscopy Single- and two- particle distributions dN 4 S(x,p) – emission function: the distribution P1( p)=E 3 =∫ d x S(x , p) d p of source density probability of finding particle with x and p dN 4 4 P2( p1 , p2)=E1 E 2 3 3 =∫ d x1 S (x1 , p1)d x2 S (x2 , p2)Φ(x2, p2∣x1, p1) d p1 d p2 The correlation function P2( p1, p2) C( p1 , p2)= P1( p1)P1( p2) 32 Pair Rest Frame reference 5)5) FemtoscopyFemtoscopy UrQMD Au+Au Identical baryon- baryon - Quantum Statistics- QS - Final State Interactions- FSI - Coulomb 0.1 0.05 k* [GeV/c] - Strong Non-identical baryon- (anti)baryon - Final State Interactions- FSI - Coulomb UrQMD - Strong Au+Au 33 5)5) FemtoscopyFemtoscopy proton-proton @39 GeV antiproton-antiproton @39 GeV STAR Preliminary STAR Preliminary QM 2018 QM 2018 No significant difference between proton-proton and antiproton-antiproton correlation functions 34 5)5) FemtoscopyFemtoscopy Radii from proton-proton and STAR Preliminary antiproton-antiproton systems QM 2018 differ from those from proton- antiprootn system → Residual Correlations. Residual feed-down correction needs to be applied. proton-proton @39 GeV proton-antiproton @39 GeV STAR Preliminary QM 2018 35 5)5) FemtoscopyFemtoscopy proton-proton, centrality 0-10% proton-antiproton, centrality 0-10% QM 2018 QM 2018 Energy dependence more significant for proton-proton than for proton-antiproton system. 36 38 5)5) FemtoscopyFemtoscopy STAR Preliminary 0-10% QM 2018 10-30% 30-70% Feed-down correction may decrease significance of centrality dependence. 37 5)5) FemtoscopyFemtoscopy - Clear centrality dependence of source size at BES energies - Visible energy dependence of source size at BES energies - No visible difference between proton-proton and antiproton-antiproton correlation functions at √s = 39 GeV NN - Correlation functions contaminated by residual correlations – residual correction required 403 8 6)6) HypertritonHypertriton Hyperon-Nucleon: - play an important role in neutron star and QCD theory - measurements of masses of hypertriton and anti-hypertriton provide insight into H-N interactions and the CPT symmetry - measurements sensitive to the temperature and nucleon phase-space of the system freeze- out.
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