Experimental results on quark-gluon correlations Anselm Vossen - PowerPoint PPT Presentation

GHP Meeting, Denver 2019 Experimental results on quark-gluon correlations Anselm Vossen Thanks for helpful discussions and slides to Research supported by the Daniel Pitonyak • Andreas Metz • • Chris Dilks

Outline • Motivation: transverse spin phenomena in hard scattering • Recent theoretical progress in unifying twist3 functions and connections to TMD framework • Recent results in single hadron channels • Toward better specificity à Di-hadron channels • Recent results and plans at CLAS12 to access twist3 PDFs 2

D. Pitonyak • Since 40+ years L • P, T- invariance à TSSAs should vanish! R ! " ($$ → &') 1976

Interference of QCD amplitudes + ,% ∝ • Explanation: Phase shifts due to interference on the QCD amplitude level • Qiu, Sterman 1991: (Colinear) Twist3: measurement of direct QCD quantum interference � Single scale process ! " , $ % ≫ Λ ()* 4

Slide from D. Pitonyak CT3 FF ( z ) CT3 FF ( z, z 1 ) CT3 PDF ( x ) CT3 PDF ( x, x 1 ) Hadron Pol. intrinsic kinematical dynamical dynamical intrinsic kinematical h ⊥ (1) U H ⊥ (1) H < , = ˆ e H F U E, H 1 1 F U h ⊥ (1) L H ⊥ (1) H < , = h L ˆ H F L H L , E L 1 L 1 L F L f ⊥ (1) D ⊥ (1) , , T 1 T D < , = G < , = 1 T ˆ F T , ˆ F F T , G F T g T D T , G T F T g ⊥ (1) G ⊥ (1) 1 T 1 T

Slide from D. Pitonyak D. Pitonyak All kinematical and intrinsic functions can be written in terms of dynamical functions (multi-parton correlators)! (Kanazawa, Koike, Metz, Pitonyak, Schlegel, PRD 93 (2016))

Interference of QCD amplitudes e – e – current quark jet γ * quark final state interaction S spectator system proton 11-2001 8624A06 From Brodsky, Schmidt, Hwang • Explanation: Phase shifts due to interference on the QCD amplitude level • Qiu, Sterman 1991: (Colinear) Twist3: measurement of direct QCD quantum interference � Single scale process ! " , $ % ≫ Λ ()* • TMD picture, Sivers (1990), Collins (1992), (e.g. model calculations by Brodsky, Schmidt, Hwang (2002) � Two scale process: ! " ≫ + % ≈ Λ ()* • Recent Developments: Strong relation between TMD and Twist3 picture à can be treated in same framework on same footing • All transverse spin phenomena are driven my multi-parton correlations! 7

What can we learn from Twist3 PDFs/FFs (non-exhaustive list) • Fundamentally the result of quark gluon correlations • Interference between single and two parton amplitude • OPE: Fundamental to study Proton Wave function • Connection to TMD framework via EoMR and LIR à On same footing as TMDs! • Interpretation in terms of forces of the gluon fields on the struck quark à See M. Burkardt’s talk • Twist3 FF E à Connection to hadronic mass generated in fragmentation (Accardi, Signori arXiv:1903.04458) • … • Last but not least: Large effects! (see ! " ) 8

The ‘classic’ !! → #$ STAR, Talk by C. Dilks (DIS 2016) PHENIX, Talk by J. Bok (DIS 2018) PHENIX shows A 1/3 suppression STAR shows no suppression with A (neutral pions, larger x F region) (charged hadrons, smaller x F region) *,, Sensitive to % &' and ( &) 9

Fit shows leading contribution by FF piece (Kanazawa, Koike, Metz, Pitonyak,PRD 89 (RC) (2014)) STAR Data at ! = 200 %&' from :Phys. Rev. D86, 051101 (2012) 10

A N in ep -> π X From PRD 90 (2014)) • HERMES ! " Hermes data from PLB 728 183 (2014) (,* • Sensitive to # $% and & $' 11 11

$%&' ( in SIDIS: Access to ) ! "# * • Compass +,-. / modulation ˜ 2 M h H a ( z ) F sin φ S X e 2 h a 1 ( x ) ∝ a UT Q z a See Mulders, Tangerman Nucl.Phys. B461 (1996) 197-237, Erratum : Nucl.Phys. B484 (1997) 538-540 12

$%&' ( in SIDIS: Mix of Twist2/Twist3 PDF, FFs ! "# From B Parsamyan at DIS 2018 13

#$%& ' in SIDIS: Mix of Twist2/Twist3 PDF, FFs ! "" From B Parsamyan at DIS 2018 14

Planned at STAR: ! " for direct # (Gamberg, Kang, Prokudin (2013), Kanazawa, Koike, Metz, Pitonyak (2015)) d ∆ σ π ∼ H ⊗ f 1 ⊗ F F T ( x, x ) 15

So.. That sounds interesting, what are the experimental challenges? • Single scale observable è Less degrees of freedom in typical inclusive ! production measurement � "# → !% � ## → !% • Solution: Use more final states with more degrees of freedom ! + � Di-hadrons (here) � Polarized Λ à See M. Schlegel’s talk / 0 1 • (or processes with only PDFs, or only FFs) 2 � E.g. ' ( ## → )% (not discussed here) ! , � Unclear how to access twist3 FFs in * + * , • OTOH: Inclusive observables can have twist3 contributions, e.g. - . à See W. Armstrong’s talk 16

Di-hadron fragmentation Functions Additional Observable: < = > # − > @ : The relative momentum of the hadron pair is an additional degree of freedom: the orientation of the two hadrons w.r.t. each other and the jet direction can be an indicator of the quark transverse spin Parton polarization à Spin averaged longitudinal transverse Hadron Polarization ⇣ spin averaged $/& ((, *) " # longitudinal G 1 ⊥ (z,M,P h , q )= H 1 ∢ (z,M)= Transverse Type eq Ty equat ation he here. T -odd, chiral-even T -odd, chiral-odd à jet handedness Colinear QCD vaccum strucuture • Relative momentum of hadrons can carry away angular momentum Partial wave decomposition in q • • Relative and total angular momentum à In principle endless tower of FFs 17

Dihadron Production in SIDIS ● Dihadron degrees of freedom: ● Reaction plane is spanned by q and the incoming/outgoing lepton momenta ● Φ h is the angle between the reaction plane and plane Figure from arXiv:1702.07317 spanned by P h and q ● Φ R is the angle between the reaction plane and the plane spanned by R and q ● M h denotes dihadron invariant mass Dihadron Spin asymmetries depend on momentum combinations P h and R Modulations in Φ h and Φ R are sensitive to different fragmentation and parton distributions 18

Accessing Twist-3 PDFs via SIDIS Dihadrons in Longitudinal Beam/Target Spin Asymmetries Beam Spin Asymmetry Target Spin Asymmetry Twist-3 PDFs Twist-3 DiFFs PDFs P 1 IFF Dihadron CoM frame (likely small) θ P h P 2 Twist-3 PDFs are accessible in the sin(Φ R ) modulation in longitudinal single spin asymmetries Pereira, PoS (DIS2014) 231 Bacchetta and Radici, Phys.Rev. D67 (2003) 094002 Bacchetta and Radici, Phys.Rev. D69 (2004) 074026 19

Twist-3 PDF Interpretations Nucleon Polarization Collinear PDFs e(x) U L T – Twist-2 – Twist-3 U f 1 e Decomposable in terms of: ● Unpolarized PDF f 1 (x) [twist-2] L g 1 h L ● Pure twist-3 part T g T h 1 1 st moment → pion-nucleon σ term, representing the contribution to the nucleon mass from the finite quark masses Quark Polarization 2 nd moment → proportional to quark mass and number of valence quarks 3 rd moment → transverse polarization dependence of the transverse color-Lorentz force experienced by a struck quark, in an unpolarized nucleon h L (x) Decomposable in terms of: Bacchetta and Radici, Phys.Rev. D69 (2004) 074026 ● Helicity PDF g 1 (x) [twist-2] Jaffe and Ji, Nucl.Phys. B375 (1992) 527-560 Efremov and Schweitzer, JHEP 0308 (2003) 006 ┴(1) [twist-2] ● Wormgear TMD moment h 1L Courtoy, arXiv:1405.7659 Burkardt, Phys.Rev. D88 (2013) 114502 Pereira, PoS (DIS2014) 231 ● Pure twist 3 part Mulders, Tangerman, Nucl.Phys. B461 (1996) 197-237 Sirtl, PhD Thesis Related to the distribution of transversely polarized quarks in a longitudinally polarized nucleon 20 Nu

e(x) and h L (x) Predictions • Chiral Quark Soliton Model • Similar � Light Front Const. Quark. Mod. (Lorcé , Pasquini, Schweitzer, JHEP 1501 (2015) 103) � Bag Model (Jaffe and Ji, Nucl.Phys. B375 (1992) 527-560) � Spectator Model (Jakob, Mulders, Cebulla et al., Acta Phys.Polon. B39 (2008) 609-640 and Rodrigues, Nucl.Phys. A626 (1997) 937-965) 21

Dihadron Asymmetries from CLAS and COMPASS Beam Spin Asymmetries A LU CLAS6 < ] ● [ e H 1 Target Spin Asymmetries A UL CLAS6 COMPASS, !" # < ] ● [ h L H 1 Pereira, PoS(DIS2014)231 5.5 GeV electrons scattered on: 1 < Q 2 < 6 GeV 2 ● ● Longitudinally Polarized solid NH 3 (compared to BSAs with H 2 target) SinΦ R modulation, sensitive to e(x) ● ● 85% beam polarization, 80% target polarization (see aforementioned extraction) ● ● 22

CLAS12 Forward Detector : - TORUS magnet - HT Cherenkov Counter - Drift chamber system - LT Cherenkov Counter - Forward ToF System - Preshower calorimeter - E.M. calorimeter (EC) Central Detector: MM - SOLENOID magnet - Barrel Silicon Tracker CND FT - Central Time-of-Flight Implemented Upgrades: Number of readout channels ~100,000 - Micromegas (CD) RICH - Neutron detector (CD) - RICH detector (FD) https://www.jlab.org/Hall-B/clas12-web/ - Forward Tagger (FD) 23

CLAS12 Kinematic Reach Beam energy at 10.6 GeV Torus current 3770 A, electrons in-bending, Solenoid magnet at 2416 A. p(e,e’)X Θ max e’ minimum energy threshold 24

CLAS12 Data Acquisition Status Run Group Target Period Observable Sensitivity ┴ A Liquid H 2 Spring 2018 A LU e(x), G 1 (Unpolarized) Autumn 2018 Spring 2019 ┴ B Liquid D 2 Spring 2019 A LU e(x), G 1 (Unpolarized) Autumn 2019 C Solid NH 3 Possibly A UL h L (x), G 1 ┴ Solid ND 3 Autumn 2020 (and A LU , A LL ) (and e(x), also Longitudinal or later twist-3 DiFFs) Polarization 25