Globally Polarized Quark Gluon Plasma in Non-Central A+A Collisions - PowerPoint PPT Presentation

The 9th Workshop on Hadron physics in China and Opportunities Worldwide Globally Polarized Quark Gluon Plasma in Non-Central A+A Collisions at High Energies 梁作堂 (Liang Zuo-tang) 山东大学物理学院 (School of physics, Shandong University) 201 7年 7 月 25 日，南京 July 25, 2017, NanJing 1 Hadron2017 2017 年 7 月 24-28 日，南京

The 9th Workshop on Hadron physics in China and Opportunities Worldwide STAR Collaboration, arXiv:1701.06657[nucl-exp] to appear in Nature (2017). 2 Hadron2017 2017 年 7 月 24-28 日，南京

Outline Ø Introduction Ø Orbital angular momentum of QGP in non-central AA collisions Ø Global polarization of QGP in non-central AA collisions Ø Direct consequences: Hyperon polarization & vector meson spin alignment Ø Measurements and results Ø Further discussions and developments Ø Summary and out look ZTL & Xin-Nian Wang, PRL 94 (2005), Phys. Lett. B629 (2005); Jian-Hua Gao, Shou-Wan Chen, Wei-Tian Deng, ZTL, Qun Wang, Xin-Nian Wang, PRC77 (2008). ZTL, plenary talk at the 19th Inter. Conf. on Ultra-Relativistic Nucleus-Nucleus Collisions (QM2006). 3 Hadron2017 2017 年 7 月 24-28 日，南京

Introduction Spin effects usually provide us with useful information and often surprises. Nuclear physics: Nuclear shell model and L-S-coupling Examples: Condensed matter physics: Spintronics High energy physics: proton’s spin crisis Much more …....... Ø Since 1970s: Transverse polarization of hyperon in unpolarized pp or pA collisions; Ø Since 1970s: Single-spin left-right asymmetry in inclusive production p ( ↑ ) + p → π + X Ø Since 1970s: Spin analyzing power in pp elastic scattering p ( ↑ ) + p → p + p p + p / A → Λ + X p ( ↑ ) + p → p + p Hadron2017 2017 年 7 月 24-28 日，南京 4

Introduction Hadron2017 2017 年 7 月 24-28 日，南京 5

Introduction Nuclear dependence two important aspects in QCD physics Spin dependence heavy ion heavy ion collider physics RHIC spin physics in heavy ion collisions ? polarized pp spin physics collider Do spin physics in AA collisions without polarizing A ? Hadron2017 2017 年 7 月 24-28 日，南京 6

Global Orbital Angular Momentum Huge orbital angular momentum of the colliding system. reaction plane: can be determined by measuring v 2 and v 1 . - L y in unit of 10 5 � � � b/R A × b � p b = � n in Y � impact parameter re × | p b | in normal of the reaction plane 7 Hadron2017 2017 年 7 月 24-28 日，南京

Global orbital angular momentum Gradient in p z -distribution along the x -direction x � impact z parameter b 8 Hadron2017 2017 年 7 月 24-28 日，南京

Gradient in p z -distribution along x -direction p z ( x,b ) in unit of p 0 Au+Au at 200AGeV = ≈ p s / 2 c ( s ) 2 . 22 GeV 0 dp z \dx in unit of 2 p 0 \R A ≈ 2 p / R 0 . 68 GeV/fm 0 A ZTL & X.N. Wang, PRL 94, 102301(2005), PLB 629, 20(2005); J.H. Gao, S.W. Chen, W.T. Deng, ZTL, Q. Wang, X.N. Wang, PRC77, 044902 (2008). 9 Hadron2017 2017 年 7 月 24-28 日，南京

Local Orbital Angular Momentum dp Δ = Δ z p x z dx Δ = − Δ Δ ≈ − L p x 1 . 7 y z for b =R A , Δ x =1fm � � has a preferred direction ( ) ! impact parameter of � Δ x b x x the two partons T T 10 Hadron2017 2017 年 7 月 24-28 日，南京

Question Can such a local orbital angular momentum be transferred to the polarization of quark or anti-quark through the interactions between the partons in a strongly interacting QGP? q 1 + q 2 → q 1 + q 2 take a collision as an example. 2017 年 7 月 24-28 日，南京 Hadron2017 11

Quark scattering with fixed reaction plane � Scattering amplitude in momentum space M ( q , E ) λ λ , T i a 2-dimensional Fourier transformation to impact parameter space � x Differential cross section w.r.t. the impact parameter T � d σ unp + λ d Δ σ σ 2 2 d d q d k � 1 � � � ∑ ∫ = − ⋅ = λ i ( k q ) x * T T e M ( k , E ) M ( q , E ) T T T λ λ λ λ , T , T 2 π 2 π 2 d 2 x T d x ( 2 ) ( 2 ) 2 d 2 x T i i λ T i spin independent part � average over the preferred directions x spin dependent part T Quark polarization after the scattering: ≡ Δ σ / σ P q unp 12 Hadron2017 2017 年 7 月 24-28 日，南京

Qualitative results Static potential model with “small angle approximation” σ d Bessel functions unp 2 = α 2 µ 4 c K ( x ), � T s 0 D T 2 d x T Δ σ µ d � � � p 2 = − ⋅ × α µ µ D n ( p x ) 4 c K ( x ) K ( x ) � λ T + T s 0 D T 1 D T 2 d x E ( E m ) T q spin direction of the quark after the scattering QCD at finite temperature with HTL(hard thermal loop) gluon propagator σ scalar functions of x T d σ σ d d unp 2 ≡ + + − = α c F ( x ) � � � qq s T 2 2 2 d x d x d x T T T Δ σ σ σ d d d � � � 2 ≡ + − − = − ⋅ × α Δ n ( p x ) c F ( x ) � � � λ T qq s T 2 2 2 d x d x d x T T T Both have exactly the same form ! 13 Hadron2017 2017 年 7 月 24-28 日，南京

Qualitative results d Δ σ ∝− ! n λ ⋅ ( ! p × ! x T ) normal of the d 2 x T AA -reaction plane p × ! ! ! x T x T has a preferred ! has a preferred ! − ! n re ∝ ! direction b p in × b direction ⎛ ⎞ d Δ σ = d Δ σ at ! n λ = − ! n re ⎜ ⎟ d 2 x T d 2 x T ⎝ ⎠ max a polarization of quark in the direction opposite to the normal of the reaction plane! 14 Hadron2017 2017 年 7 月 24-28 日，南京

Quantitative results with QCD at finite temperature - Quark polarization q ∼ 0.02 − 0.25 P P q Δ p / T T : temperature ZTL & X.N. Wang, PRL 94, 102301(2005), PLB 629, 20(2005); J.H. Gao, S.W. Chen, W.T. Deng, ZTL, Q. Wang, X.N. Wang, PRC77, 044902 (2008). 15 Hadron2017 2017 年 7 月 24-28 日，南京

A new picture of QGP in non-central AA collisions � n re � p � f p � x T The scattered quark acquires a negative polarization in the normal direction of the reaction plane! “global polarization” 16 Hadron2017 2017 年 7 月 24-28 日，南京

Direct consequences In a non-central AA collision: global polarization of polarization hadronization quarks & anti-quarks of hadrons ! e + e − → Z 0 → ! Compare to: q + q → H (or V ) + X ρ 00 : probability for the third component of Lambda polarization the spin of K* 0 to take zero. OPAL e + e − → K *0 + X Vector meson spin alignment ρ 00 =1/3: unpolarized Hadron2017 17 2017 年 7 月 24-28 日，南京

Consequence I: Hyperon polarization ↑ + q 2 ↑ + q 3 ↑ → H ↑ q 1 Recombination scenario u = P d = P u = P d ≡ P s = P P q , P s . We expect Λ Σ Ξ Ω Hyperon s − P q − 3 P 2 s (5 + P q − P s − 3 P 2 4 P s P P 2 ) 4 P s P q P H P s q s 3 − 4 P s + P 2 q P 3(1 + P 2 ) 3 − 4 P s + P 2 q P q s s P H in the case P q P q P q P q that P q = P s In the case that u = P d = P u = P d = P s = P P s H = P P q for all H ' s and H ' s . 18 Hadron2017 2017 年 7 月 24-28 日，南京

Consequence I: Hyperon polarization q ↑ → H + X Fragmentation scenario Λ Σ Ξ Ω Hyperon q − n s P s − f s P 4 f s P 4 n s P n s P P H P s q s s n s + 2 f s 3( n s + 2 f s ) 3(2 n s + f s ) 3 P H in the case of 4 f s − n s 4 n s − f s n s P P 3( n s + 2 f s ) P 3(2 n s + f s ) P s P q =P s n s + 2 f s q q q 3 P H in the case of P P P P q q q q P q =P s and n s =f s 3 3 3 3 N u : N d : N s = 1:1: n s for quarks in QGP N u : N d : N s = 1:1: f s for quarks produced in fragmentation 19 Hadron2017 2017 年 7 月 24-28 日，南京

Consequence I: Hyperon polarization Some of the expected qualitative features n The same for hyperons and anti-hyperons. n (Approximately) the same for different hyperons. n No polarization at b=0 , increases approximately linearly with b . 20 Hadron2017 2017 年 7 月 24-28 日，南京

Consequence II: Vector meson spin alignment ↑ + q 2 ↑ → V Recombination scenario q 1 1 − P 2 1 − P q P ρ ( rec ) = K *( rec ) = q ρ 00 2 , ρ 00 s , 3 + P 3 + P q P q s V ( rec ) < 1/3 for q ↑ + q ↑ → V ρ 00 q ↑ → V + X or q ↑ → V + X Fragmentation scenario ! e + e − → Z 0 → ! q → K * + + X In analog to (parameterization) q + 1 + β P 2 1 + β P 2 f s n s 1 + β P 2 K *( rec ) = ρ ( frag ) = q ρ 00 q ρ 00 2 + 2 , 2 , β ≈ 0.5 s 3 − β P n s + f s n s + f s 3 − β P 3 − β P q q s ρ V ( frag ) > 1/3 for q ↑ → V + X or q ↑ → V + X 21 Hadron2017 2017 年 7 月 24-28 日，南京

Measurements Hyperon: Spin self-analyzing parity violating decay H → N + M d Ω * = N dN 4 π (1 + α P H cos θ * ) V → M 1 + M 2 Vector meson: Strong decay d Ω * = 3 N dN V − 1)cos 2 θ * ]. V ) + (3 ρ 00 4 π [(1 − ρ 00 22 Hadron2017 2017 年 7 月 24-28 日，南京

Earlier Measurements by STAR on global polarization STAR Collaboration 23 Hadron2017 2017 年 7 月 24-28 日，南京