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Chiral Magnet Effect, where are we? 1. Measure Charge Separation Zhangbu Xu For the STAR Collaboration QCD Topology Charge 2. Signal vs background study (final-stage v2, initial colliding systems, rapidity, PID) 3. Dissect the necessary conditions • • Chiral Symmetry Restoration Strong Magnetic Field 4. Future Plans Rencontres de Moriond: QCD and High Energy Interactions LA THUILE, March 25- April 1, 2017 Particle Identification at STAR TPC TP C K π p TOF TPC d e, μ TOF Log10(p) Charged hadrons Hyperons & Hyper-nuclei EM particles MTD HFT EMC Jets Jets & Correlations High pT muons Heavy-flavor hadrons Forward protons Forward photons Multiple-fold correlations for identified particles! 2 Observing Topological Charge Transitions To observe in the lab - add massless fermions - apply a magnetic field Paul Sorensen: QM2017 CME task force report: arXiv: 1608.00982 PRC 81 (2010) 54908 PRL 103 (2009) 251601 A required set of Extraordinary Phenomena: QCD Topological Charge + Chiral Symmetry Restoration + Strong Magnetic Field Observable: Chirally restored quarks separated along magnetic field Experimental strategy: Measure 2 particle correlations (++,--,+-) WRT reaction plane Derek Leinweber, University of Adelaide 3 3 P. Tribedy, QM2017 4 (gOS-gSS) ´ 10 Obs 0.3 0.25 Charge separation depends on final-stage shape v•2 Str 0.2 0.15 P. Tribedy, UCLA Chirality Workshop 2016 0.1 0 (gOS-gSS) ´ 104 0.05 0.025 0.5 ce STAR U+U 193 GeV 0-10% Dh>0.025 Multiplicity binning Spectator binning 0.035 0.045 STAR Au+Au 200 GeV v2 {2} Year 2004 (0909.1717) Year 2007 (1302.3802) Year 2011 (0-1%) STAR Dominancepreliminary of fluctuations of particip 0 Number of participants Azimuthal anisotropy (v2) contributes to background (could be very large); PRC89(2014) magnetic field which drives the signal, Qualitatively have similar centrality dependence. Most comparisons and disentangle tools have to be quantitative. 0 0.01 0.02 0.03 v2 {2} 0.04 14 0.05 U+U and Au+Au central data: different dependence on v2; Not just driven by final-stage background correlations? P.Tribedy, QCD chirality 5 Charge Separation depends on initial systems Same-sign Peripheral A+A p+Au and d+Au qualitatively similar 0.002 same-sign 30-40% U+U 193 GeV 0 ácos(f1 + f2 - 2f3)ñ ´ Npart magnitude of charge separation dependence on correlation conditions (rapidity gaps) Qualitatively different rapidity distribution from central to peripheral A+A (p+A) -0.002 STAR preliminary 70-80% U+U 193 GeV 0.004 0.002 0 -0.002 fit Short-range-positive Residual 0.004 0.002 0 -0.002 0-100% p+Au 200 GeV 0.4 0.8 1.2 1.6 Dh12 6 P.Tribedy, Separation appears in many forms PRL113(2014) peak between 10-200GeV Has a predicted dependence on Global charge excess: Chiral Magnetic Wave 7 Strangeness (PID) distinguish models STAR Preliminary “… We demonstrate that the STAR results can be understood within the standard viscous hydrodynamics without invoking the CMW…” “… the slope r for the kaons should be negative, in contrast to the pion case, and the magnitude is expected to be larger… Note that in these predictions are integrated over 0 < pT < ∞. In order to properly test them, a wider pT coverage is necessary…” — Y. Hatta et al. Nuclear Physics A 947 (2016) 155 Measured kaon slope is positive: contradict the conventional model prediction without CMW 8 Chiral Symmetry & Magnetic Field Two other Extraordinary phenomena to make this possible (QCD topology reflects in charge separation) Chiral Symmetry Restoration Disentangle and assess necessary conditions low-mass dilepton excess (change of vector meson r spectral function) Strong Magnetic Field Global Hyperon Polarization Coherent photo-production of J/Ψ and low-mass dilepton in non-central A+A collisions A required set of Extraordinary Phenomena: QCD Topological Charge + Chiral Symmetry Restoration + Strong Magnetic Field Observable: Chirally restored quarks separated along magnetic field 9 QCD phase transition is a chiral phase transition Golden probe of chiral symmetry restoration: change vector meson (r→e+e-) spectral function STAR data (RHIC and SPS): Consistent with continuous QGP radiation and broadening of vector meson in-medium PRL113(2014) PLB750(2015) 10 Global Hyperon Polarization new tool to study QGP and relativistic Quantum fluid Vorticity in general arXiv:1701.06657 Non-zero global angular momentum transfer to hyperon polarization 11 QCD fluid responds to external field • Positive Global Hyperon Polarization indicating a spin-orbit (Vortical) coupling • Current data not able to distinguish Lambda/AntiLambda polarization difference, • (potentially) Direct measure of Magnetic Field effect • Need >x10 more data sum STAR Preliminary difference 12 Coherent photoproduction in violent non-central A+A collisions? 10−1 • Non-central but not UPC photoproduction • Large enhancement of dilepton and J/Ψ production at very low pT (<150MeV) d2N/(dtdy) ((GeV/c)-2) Shower the nucleus with electromagnetic field • Consistent with strong electromagnetic field interacting with nucleus target collectively AuAu@200 GeV, 0.4< M ee <0.76 GeV/c 2 −2/ndf: 3.07/4 Slope: 371 ± 31 (GeV/c)-2 10−2 AuAu@200 GeV, 1.2< M ee <2.6 GeV/c 2 −2 /ndf: 0.55/3 Slope: 287 ± 37 (GeV/c)-2 STAR preliminary −3 10 10−4 Centrality: 60-80% 10−1 UU@193 GeV, 0.4< Mee <0.76 GeV/c 2 T Slope: 506 ± 53 (GeV/c) 10−2 10 UU@193 GeV, 1.2< Mee <2.6 GeV/c 2 2 2 t = p2 −((GeV/c) /ndf: 5.08/4 ) 2 2 t = p2 −((GeV/c) /ndf: 1.26/4 ) T -2 Slope: 411 ± 81 (GeV/c)-2 −3 10−4 0 0.01 0.02 0.03 t = p2 ((GeV/c)2) T 0 0.01 0.02 0.03 t = p2 ((GeV/c)2) T 13 A decisive test with Isobars 96 40 Zr + 4096 Zr vs. 96 44 Ru + 4496 Ru 1.2B minbias events RHIC run in 2018: Zr and Ru same geometry and mass; charge different by 10% (20% signal difference) 5s effect with 20% (signal)+80% (background) • • • Dilepton and J/Ψ: Coherent photoproduction: Z2 Photon-photon fusion: Z4 Hadronic interaction: Z0 14 Summary Observed charge separation was examined in Au+Au, U+U, p+Au and d+Au Investigation of two major necessary phenomena: scaled with final-stage v2 in peripheral Chiral Symmetry Restoration: and mid-central and close to zero with observation of large excess of different v2 in Central U+U and Au+Au low-mass dilepton, consistent with vector r in-medium Qualitatively different rapidity distribution from central to peripheral A+A (p+A) Strong Magnetic Field: Values depend on correlation conditions in Suggestive difference between p+Au and d+Au Global Hyperon (antihyperon) polarization); Correct kaon ”sign” in Chiral Magnetic need more statistics Wave Photoproduction in non-central Largest at beam energies (10-200GeV) collisions, a good probe of Background (v2) and signal (B field) electromagnetic field interacts with nucleus collectively predicted to have similar centrality (geometry) dependence Isobar collisions will provide a decisive test 15 backup 16 -1 -0.5 0 0.5 1 1.4 1.2 1 0.8 0.6 0.4 0.2 0 ´10-3 a,b PbPb sNN = 5.02 TeV CMS Cent. 60-70% 1.5 |h | < 2.4, 4.4 < |hc| < 5.0 a,b |h | < 0.8, |hc| < 0.8 1 CMS 0.5 ´10-3 |Dh| ´10-3 PbPb sNN = 5.02 TeV 0.5 0 -0.5 -1 SS OS PbPb offline pPb sNN = 5.02 TeV (b) offline (a) SS OS fc(Pb-going) fc(p-going) Dh 185 £ Ntrk < 220 0 17 185 £ Ntrk < 220 1 -0.4 -0.2 b b 17 0 1 2 3 4 0 1 2 3 4 Dh ácos(fa +f -2fc)ñ/v 2,c b ácos(fa+f -2fc)ñ/v 2,c (OS-SS) ácos(fa +f -2fc)ñ/v 2,c