QCD Experimental status of the CME search Fuqiang

QCD 物 理 研 � � 基 金 委 重 大 � 目 交 流 会 Experimental status of the CME search Fuqiang Wang Purdue University, Huzhou University

Outline • What is CME? Why is CME important? • Background issue • New progresses • Summary Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 2 / 32

What is CME? • QCD vacuum fluctuations – Non-zero topological charge gluon field – Chirality imbalance, quantum anomaly – Local P, CP violations • Chiral symmetry restoration Derek Leinweber Diakonov, PPNP 51 – Current quark degrees of freedom • Strong magnetic field u. RL u. R Kharzeev, et al. NPA 803 (2008) 227 u. R u. LR u. R B B Local C, CP violations QW<0 Electric charge separation d. R Fuqiang Wang d. RL d. LR d. R QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 d. R 3 / 32

Why is CME important? Kharzeev, Pisarski, Tytgat, PRL 81 (1998) 512; Kharzeev, et al. NPA 803 (2008) 227 CP QGP c-sym. Vacuum fluctuations Topological gluon field in local domains Local C and CP violations Weak interaction No B ~ 1015 T Fuqiang Wang CP CP too small is observed in strong interaction The strong CP problem • Strong magnetic field • Quark degree of freedom, c-symmetry • QCD vacuum fluctuations, Topological gluon field, Qw≠ 0. • Local P, CP violations • Strong CP problem, matter-antimatter asymmetry QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 4 / 32

To measure CME: the g observable p+ p+ RP p. Voloshin, PRC 70 (2004) 057901 Fuqiang Wang p- Lead to BNL Press Release in 2010 QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 5

The Background Issue: It’s big! OS CME + momentum conserv. OS + charge conserv. OS SS SS Use OS-SS SS Signal is ambiguous π+ + ρ π π- π- Next slide Background: nonflow coupled with flow FW, Jie Zhao, PRC 95 (2017) 051901 FW 2009, Bzdak, Koch, Liao 2010, Pratt, Schlichting 2010, … 20/1002*0. 65 ~ 10 -3 Fuqiang Wang 0. 1 Pratt, Schlichting QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 6

The resonance background in g correlator Voloshin 2004; FW 2009; Bzdak, Koch, Liao 2010; Pratt, Schlichting 2010; … Y π+ π+ π- ρ π+ ρ ρ π- π- X π+ ψRP πBackground: nonflow coupled with flow Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 7 / 32

Handling background • When background is small – Can be a bit sloppy in background estimation. Imprecision can be afforded by systematic uncertainty. – Can be somewhat model-dependent (theo. syst. uncertainties). • When background is large – Have to cleanly remove background. – Extreme care should be taken. Small error in background can result in big mistake in signal. – Should not rely on theory/model/trends (unless theory is very precise). – Better be data-driven, often involving new observables and methods. Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 8 / 32

The infamous k parameter * k STAR, PRL 113 (2014) 052302 DH Dg - kv 2 d • k=1 is a misconception • Background size assumed! • No new info beyond the original Dg measurement. Over-sold. Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 9 / 32

CMS clarification * k k 2 = k 3 accidental? Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 10 / 32

To eliminate background Make v 2 zero… STAR Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 11 / 32

Here D is similar to cos(a+b-2 y) correlator Make v 2 “zero” – Eby. E technique Event-by-event v 2 technique STAR PRC 89(2014)044908 Still has residual background, because background ~ v 2, r not v 2, p FW, Jie Zhao, PRC 95 (2017) 051901(R) STAR PRC 89 (2014) 044908 Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 12 / 32

Here D is similar to cos(a+b-2 y) correlator Make v 2 “zero” – Eby. E technique Event-by-event v 2 technique STAR PRC 89(2014)044908 Still has residual background, because background ~ v 2, r not v 2, p FW, Jie Zhao, PRC 95 (2017) 051901(R) v 2, r STAR PRC 89 (2014) 044908 v 2, p final state Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 13 / 32

Here D is similar to cos(a+b-2 y) correlator Make v 2 “zero” – Eby. E technique Event-by-event v 2 technique STAR PRC 89(2014)044908 Still has residual background, because background ~ v 2, r not v 2, p FW, Jie Zhao, PRC 95 (2017) 051901(R) v 2, r STAR PRC 89 (2014) 044908 v 2, p final state Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 14 / 32

Here D is similar to cos(a+b-2 y) correlator Make v 2 “zero” – Eby. E technique Event-by-event v 2 technique STAR PRC 89(2014)044908 Still has residual background, because background ~ v 2, r not v 2, p FW, Jie Zhao, PRC 95 (2017) 051901(R) v 2, r STAR PRC 89 (2014) 044908 v 2, p Be self-critical! final state Sciences often progress thru self-denials. Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 15 / 32

Event-by-event q 2 technique Wen, Bryon, Wen, Wang, CPC 42 (2018) 014001 Similar to event-by-event v 2 technique v 3 v 2 Intercept = (7. 51 ± 0. 75)*10 -3 Fuqiang Wang Intercept = (8. 32 ± 1. 92)*10 -3 QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 16

To eliminate background Three methods on the market that I think are hopeful to eliminate the backgrounds… 1. Event-shape engineering 2. Invariant mass 3. RP vs. PP comparison Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 17 / 32

Here D is similar to cos(a+b-2 y) correlator 1) Event-shape-engineering technique STAR PRC 89(2014)044908 ALICE PLB 777(2018)151 CMS PRC 97(2018)044912 ESE displaced from a, b phase space Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 18

Here D is similar to cos(a+b-2 y) correlator 1) Event-shape-engineering technique STAR PRC 89(2014)044908 ALICE PLB 777(2018)151 CMS PRC 97(2018)044912 ESE displaced from a, b phase space v 2, r v 2, p final state Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 19

2) The invariant mass method Get rid of resonances, or utilize them… Identify the backgrounds by invariant mass ar. Xiv: 1705. 05410 Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 20 / 32

Get away from resonances Jie Zhao (STAR) Quark Matter 2018, ar. Xiv: 1807. 09925 Resonance structure in Dg as function of minv Major background High mass Dg: Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 22

Can CME survive to high mass? Kinematics ced Directly produ ate t Final s Shi et al. , 1711. 02496, Ann. Phys. 394(2018)50 • minv > 2 Ge. V/c 2 contains appreciable low p. T pions • CME signal may not be limited only to low p. T • High mass should still contain CME Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 23 / 32

Indulge into the resonance region Jie Zhao (STAR), QM 18, 1807. 09925 STAR Preliminary Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 STAR Preliminary 26

Indulge into the resonance region Jie Zhao (STAR), QM 18, 1807. 09925 STAR Preliminary Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 STAR Preliminary 27

3) RP vs PP comparison measurement H. Xu, J. Zhao, X. Wang, H. Li, Z. -W. Lin, C. Shen, F. Wang, CPC 42 (2018) 084103, ar. Xiv: 1710. 07265 RP Intra-event “CME-v 2 Filter” BKG×a CME CME and BKG are entangled in AA PP BKG CME×a measured input SAME EVENT Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 28 / 32

“CME-v 2 Filter” results from STAR BKG RP CME BKG CME Fuqiang Wang BKG×a CME PP BKG CME×a QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 29 / 32

Summary of Possible CME Signal Jie Zhao (STAR) Quark Matter 2018 ar. Xiv: 1807. 09925 • Major physics backgrounds • Possible CME signal ~ a few %, 1 -2 s from zero. Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 30 / 32

A day-1 prediction for isobar 96 44 Ru Ru+Ru vs. Zr+Zr 96 40 Zr Multiplicity sensitive to nuclear structure Our prediction Woods-Saxon prediction Haojie Xu et al. PRL 121 (2018) 022301 Haojie Xu et al. CPC 42 (2018) 084103 Hanlin Li et al. PRC 98 (2018) 054907 Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 31 / 32

Summary • Very important physics • Background dominate in inclusive Dg. Rigorous treatment of background is critical. • Three viable methods so far: – Event-shape engineering – Invariant mass – RP vs. PP comparison • Possible CME signal is small, a few % of the inclusive Dg, current precision 1 -2 s from zero. Fuqiang Wang QCD物理研讨暨基金委重大项目交流会 -- 山东大学, 威海, 2019/7 32 / 32