The long-range pseudo-rapidity correlations in high-energy collisions 王福强 Purdue University

Proton, neutron, meson (hadron)Quark Gluon Plasma (QGP) The Big Bang and the Little Bang 7/1/20132

Nuclear Phase Diagram 7/1/20133

Heavy-Ion Collisions simulation Hadron cascade 7/1/20134

CMS STAR ALICE 7/1/20135 PHENIX

Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) STAR and PHENIX experiments New York BNL － RHIC 7/1/20136

Two types of discoveries Theoretically predicted, and experimentally verified, e.g. – J/  – W, Z bosons Surprises, e.g. – Parity violation – Microwave background radiation Long-range pseudo-rapidity correlations 7/1/20137

Variables, observables  = fm STAR: Solenoidal Tracker At RHIC y x   z p pTpT pzpz 7/1/2013

x y z coordinate space anisotropy pypy pxpx momentum space anisotropy Hydrodynamic bulk collectivity, elliptic flow   particle  R.P. (rad) 7/1/20139

Collective expansion of QGP - elliptic (2 nd order) and higher order event anisotropic collectivity and its N quark scaling - hydro-dynamic properties of QGP PHENIX Preliminary, QM12 7/1/201310

Elliptic expansion during the partonic (quark-gluon) phase Hadron formation via quark recombination / coalescence Hadron 7/1/201311

jet pp Au Energy loss (jet quenching) in QGP Phys. Rev. Lett. 91, (2003) PRL109, (2012) arXiv: central Au+Au  q 7/1/201312

Novel phenomena in heavy-ions Double-peak away-side correlations Odd harmonics Long-range ridge correlations Ridge in small systems … Au+Au ridge   7/1/201313

14 Jet Correlations Jet event in e  e   collision STAR Au+Au collision Jet produces high p T particles  Select a high pT particle to trigger on jet. NB: trigger = off-line trigger  trigger particle p T > 3 GeV/c associated particle 7/1/2013

Dihadron correlations STAR, PRL 95 (2005); PRC82 (2010) STAR, PRL91 (2003) Clear evidence of jet-quenching, and it’s a final-state effect Low p T enhancement and broadening Away-side double peak; Large-  small-  ridge correlation v 2 subtracted but not higher harmonics Away-side trigger jet 0  1  p T trig =4-6 GeV/c p T assoc = GeV/c 7/1/201315

Relative to the Event Plane Ep-dep correl 7/1/ v 2 max {2,  gap =0.7} v 2 max {2,  gap =0.7}, v 3 {2,  gap =0.7} STAR, arXiv: v1 Todoroki (PHENIX) Trigger Associated  EP SS Evolution of structure seems to remain from in-plan to out-of-plane. Single away-side peak in-plane, double-peak out-of-plane. Jet interactions with QGP medium. Physics mechanisms? |  | > 0.7

Three-particle correlations v2 and v4 subtracted. Does v3 remove all of the off-diag. peak strength? Need further study. Deflected jets contributions (to diag. peaks) must be present. Need to be followed up with v3 subtraction. 7/1/ Δ1Δ1 Trigger Δ2Δ2

18  trigger particle p T > 3 GeV/c assoc. particle p T =1-2 GeV/c d+Au Au+Au ridge   The longitudinal ridge  ~ 1  ~ 0 trigger particle p T > 3 GeV/c  assoc. particle p T =1-3 GeV/c |  |< 0.7 7/1/2013

Ridge vs trigger angle v 2 max {2,  gap =0.7} v 2 max {2,  gap =0.7}, v 3 {2,  gap =0.7}   7/1/201319

Ridge yield vs trigger angle v 2 max {2,  gap =0.7} v 2 max {2,  gap =0.7}, v 3 {2,  gap =0.7} Subtract v 3 7/1/201320

LHC-CMS usual p-p collisionhigh multiplicity p-p collision 7/1/ Ridge in small systems

Why wasn’t it discovered long ago by HEP? Two types of discoveries: – Theoretically predicted, and experimentally verified – Surprises HEP moved on to more exclusive processes There may be still important physics that were missed in last half century. 7/1/201322

p-p collision (high Mul.) p-Pb collision (high Mul.) 7/1/ Physical origin unclear

CGC/Glasma Dusling & Venugopalan Dusling and Venugopalan, arXiv: /1/201324

Another explanation: Hydro flow In heavy-ions, large  small  correlations: subtract v2  non-zero finite correlation (ridge) In pp, pA, dA systems, large  small  correlations: subtract flat pedestal  non-zero finite correlation (ridge) 7/1/201325

d+Au ridge? Jet contribution within PHENIX acceptance LHC+RHIC more stringent test on theoretical models. 7/1/ PHENIX, arXiv: GeV/c Bozek, PRC85 (2012) PHENIX acceptance

Straight difference No ZYAM involved  projections in different  (TPC mult. |  |<1 as centrality) 27 ZYAM syst. error from different sizes of  region for ZYAM. Efficiency corrected: 85 ± 5% < p T trig < 3 GeV/c, 1 < p T assoc < 2 GeV/c ZYAM-ed 7/1/2013

 projections in different  (TPC mult. |  |<1 as centrality) 28 ZYAM syst. error from different sizes of  region for ZYAM. Efficiency corrected: 85 ± 5%. ZYAM-ed 0.15 < p T trig < 3 GeV/c 1 < p T assoc < 2 GeV/c 7/1/2013

Central – Peripheral 29 ZYAM syst. error from different sizes of  region for ZYAM. Efficiency corrected: 85 ± 5% < p T trig < 3 GeV/c, 1 < p T assoc < 2 GeV/c FTPC 0-20% % TPC 0-20% % Minimal ridge 7/1/2013

Very forward correlations 7/1/201330

TPC-FTPC correlations 31  triangle acceptance 7/1/2013

Sanity check 32 PHOBOS, PRC 72 (2005) (R) TPC-FTPC TPC-TPC All charged hadrons 7/1/2013

ZYAM’ed  Correlations (TPC mult. as centrality) 33 Discontinuity because it’s  not  distribution. At  =2, TPC-TPC and TPC-FTPC pairs come form different  ’s. Raw correl. ZYAM’ed 7/1/2013

Fourier fit results 34 TPC-TPC Au-side TPC-TPC d-side TPC-FTPC d-side TPC-FTPC Au-side 7/1/2013

Fourier fit results (replot of previous slide) Summary Correlations have v1 and v2 components v1 appears ~1/N. v2 ~constant over multiplicity Even at very forward d-side, v2 component is large (maybe even larger than Au-side). Not sure what the data mean. 35 Au-side d-side 7/1/2013

Conclusions Particle correlations in heavy-ions – Novel phenomenon of v3 – After v3 subtraction, features of jet-medium interactions remain Ridge in small systems – Intriguing – May contain important physics 7/1/201336

The question of v 1 In the pt=1-2 GeV/c region, directed flow fluctuation effect may be negligible. 37 Pandit (STAR), arXiv: /1/2013

Have to rethink about inclusive dihadron 387/1/2013

ZYAM’ed  Correlations (ZDC as centrality) 397/1/2013