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

SLIDE 1

Experimental results on quark-gluon correlations

GHP Meeting, Denver 2019 Anselm Vossen

Research supported by the Thanks for helpful discussions and slides to

Daniel Pitonyak
Andreas Metz
Chris Dilks

SLIDE 2

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

SLIDE 3

!" ($$ → &')

1976

D. Pitonyak
Since 40+ years
P, T- invarianceà TSSAs should vanish!

L R

SLIDE 4

Interference of QCD amplitudes

4

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()*

+

,% ∝

SLIDE 5

Hadron Pol.

U L T

intrinsic kinematical intrinsic kinematical dynamical dynamical

CT3 PDF (x) CT3 PDF (x, x1) CT3 FF (z) CT3 FF (z, z1)

e

hL

gT

E, H

HL, EL DT , GT

h⊥(1)

1

h⊥(1)

1L

f ⊥(1)

1T

, g⊥(1)

1T

D⊥(1)

1T

, G⊥(1)

1T

H⊥(1)

1L

H⊥(1)

1

HF U HF L FF T , GF T ˆ H<,=

F U

ˆ D<,=

F T , ˆ

G<,=

F T

ˆ H<,=

F L

Slide from D. Pitonyak

SLIDE 6

D. Pitonyak

(Kanazawa, Koike, Metz, Pitonyak, Schlegel, PRD 93 (2016)) Slide from D. Pitonyak

All kinematical and intrinsic functions can be written in terms of dynamical functions (multi-parton correlators)!

SLIDE 7

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()*

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 pictureàcan be treated in same

framework on same footing

All transverse spin phenomena are driven my multi-parton correlations!

7

11-2001 8624A06

S

current quark jet final state interaction spectator system proton e– γ* e– quark

From Brodsky, Schmidt, Hwang

SLIDE 8

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 LIRàOn 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 EàConnection to hadronic mass generated in

fragmentation (Accardi, Signori arXiv:1903.04458)

…
Last but not least: Large effects! (see !")

8

SLIDE 9

The ‘classic’ !! → #$

9

STAR shows no suppression with A (neutral pions, larger xF region)

PHENIX, Talk by J. Bok (DIS 2018) STAR, Talk by C. Dilks (DIS 2016)

PHENIX shows A1/3 suppression (charged hadrons, smaller xF region)

Sensitive to %&' and (&)

*,,

SLIDE 10

Fit shows leading contribution by FF piece

STAR Data at ! = 200 %&' from :Phys. Rev. D86, 051101 (2012)

10

(Kanazawa, Koike, Metz, Pitonyak,PRD 89(RC) (2014))

SLIDE 11

HERMES !"
Sensitive to #$% and &$'

(,*

11

AN in ep -> π X

11

From PRD 90 (2014)) Hermes data from PLB 728 183 (2014)

SLIDE 12

!"#

$%&'( in SIDIS: Access to )

*

Compass +,-./ modulation

12

F sin φS

UT

∝ X

a

e2

a

2Mh Q ha

1(x)

˜ Ha(z) z

See Mulders, Tangerman Nucl.Phys. B461 (1996) 197-237, Erratum: Nucl.Phys. B484 (1997) 538-540

SLIDE 13

!"#

$%&'(in SIDIS: Mix of Twist2/Twist3 PDF, FFs

13

From B Parsamyan at DIS 2018

SLIDE 14

14

From B Parsamyan at DIS 2018

!""

#$%&'in SIDIS: Mix of Twist2/Twist3 PDF, FFs

SLIDE 15

Planned at STAR: !" for direct #

15

(Gamberg, Kang, Prokudin (2013), Kanazawa, Koike, Metz, Pitonyak (2015))

d∆σπ ∼ H ⊗ f1 ⊗ FF T (x, x)

SLIDE 16

So.. That sounds interesting, what are the experimental challenges?

Single scale observableèLess 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

(or processes with only PDFs, or only FFs)

E.g. '( ## → )% (not discussed here) Unclear how to access twist3 FFs in *+*,

OTOH: Inclusive observables can have twist3 contributions, e.g.
.àSee W. Armstrong’s talk

16

/0 1

2

!+ !,

SLIDE 17

Parton polarization à Hadron Polarization⇣ Spin averaged longitudinal transverse spin averaged

"#

$/&((, *)

longitudinal Transverse Ty Type eq equat ation he here.

G1⊥(z,M,Ph,q)=

T

odd, chiral-even

àjet handedness QCD vaccum strucuture

H1∢(z,M)=

T

odd, chiral-odd

Colinear

Di-hadron fragmentation Functions

17

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

Relative momentum of hadrons can carry away angular momentum
Partial wave decomposition in q
Relative and total angular momentum àIn principle endless tower of FFs

SLIDE 18

Dihadron Production in SIDIS

Reaction plane is spanned by q and the

incoming/outgoing lepton momenta

Φh is the angle between the reaction plane and plane

spanned by Ph and q

ΦR is the angle between the reaction plane and the

plane spanned by R and q

Mh denotes dihadron invariant mass

18

Dihadron degrees of freedom:

Figure from arXiv:1702.07317

Dihadron Spin asymmetries depend on momentum combinations Ph and R Modulations in Φh and ΦR are sensitive to different fragmentation and parton distributions

SLIDE 19

Accessing Twist-3 PDFs via SIDIS Dihadrons in Longitudinal Beam/Target Spin Asymmetries

19

Beam Spin Asymmetry

Twist-3 PDFs

IFF PDFs

Pereira, PoS (DIS2014) 231 Bacchetta and Radici, Phys.Rev. D67 (2003) 094002 Bacchetta and Radici, Phys.Rev. D69 (2004) 074026

θ Ph P2 P1

Dihadron CoM frame

Twist-3 DiFFs (likely small) Target Spin Asymmetry Twist-3 PDFs are accessible in the sin(ΦR) modulation in longitudinal single spin asymmetries

SLIDE 20

Twist-3 PDF Interpretations

20

Decomposable in terms of:

Unpolarized PDF f1(x) [twist-2]
Pure twist-3 part

1st moment → pion-nucleon σ term, representing the contribution to the nucleon mass from the finite quark masses 2nd moment → proportional to quark mass and number of valence quarks 3rd moment → transverse polarization dependence of the transverse color-Lorentz force experienced by a struck quark, in an unpolarized nucleon

Bacchetta and Radici, Phys.Rev. D69 (2004) 074026 Jaffe and Ji, Nucl.Phys. B375 (1992) 527-560 Efremov and Schweitzer, JHEP 0308 (2003) 006 Courtoy, arXiv:1405.7659 Burkardt, Phys.Rev. D88 (2013) 114502 Pereira, PoS (DIS2014) 231 Mulders, Tangerman, Nucl.Phys. B461 (1996) 197-237 Sirtl, PhD Thesis

e(x)

Decomposable in terms of:

Helicity PDF g1(x) [twist-2]
Wormgear TMD moment h1L

┴(1) [twist-2]

Pure twist 3 part

Related to the distribution of transversely polarized quarks in a longitudinally polarized nucleon

hL(x)

U L T U

f1 e

L

g1 hL

T

gT h1

Nu Quark Polarization

Collinear PDFs – Twist-2 – Twist-3

Nucleon Polarization

SLIDE 21

e(x) and hL(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, and Rodrigues, Nucl.Phys. A626 (1997) 937-965)

21

Cebulla et al., Acta Phys.Polon. B39 (2008) 609-640

SLIDE 22

Dihadron Asymmetries from CLAS and COMPASS

1 < Q2 < 6 GeV2
SinΦR modulation, sensitive to e(x)
(see aforementioned extraction)

22

Beam Spin Asymmetries ALU Target Spin Asymmetries AUL

Pereira, PoS(DIS2014)231

5.5 GeV electrons scattered on:
Longitudinally Polarized solid NH3 (compared to BSAs with H2 target)
85% beam polarization, 80% target polarization

COMPASS, !"# CLAS6 CLAS6

[ hL H1

< ]

[ e H1

< ]

SLIDE 23

CLAS12

23

Forward Detector:

TORUS magnet
HT Cherenkov Counter
Drift chamber system
LT Cherenkov Counter
Forward ToF System
Preshower calorimeter
E.M. calorimeter (EC)

Central Detector:

SOLENOID magnet
Barrel Silicon Tracker
Central Time-of-Flight

Implemented Upgrades:

Micromegas (CD)
Neutron detector (CD)
RICH detector (FD)
Forward Tagger (FD)

MM CND FT RICH https://www.jlab.org/Hall-B/clas12-web/

Number of readout channels ~100,000

SLIDE 24

CLAS12 Kinematic Reach

24

Beam energy at 10.6 GeV Torus current 3770 A, electrons in-bending, Solenoid magnet at 2416 A.

e’ minimum energy threshold

p(e,e’)X

Θmax

SLIDE 25

CLAS12 Data Acquisition Status

25

Run Group Target Period Observable Sensitivity A Liquid H2 (Unpolarized) Spring 2018 Autumn 2018 Spring 2019 ALU e(x), G1

┴

B Liquid D2 (Unpolarized) Spring 2019 Autumn 2019 ALU e(x), G1

┴

C Solid NH3 Solid ND3 Longitudinal Polarization Possibly Autumn 2020

r later

AUL (and ALU, ALL) hL(x), G1

┴

(and e(x), also twist-3 DiFFs)

SLIDE 26

First results on di-hadron correlations

26

Use about 10% of spring run (~3% of

approved running time)

Select !" → $%$& + (
Calculate fR, fh angles of hadron pair

)* = )

, % + ) , &,

. = )

, % − ) , &

2D fit to asymmetries 01%02

01%02(fR, fh)à345 6789:

Correct with kinematic factor and Pbeam~86%

Particle selection

Q2>1.0 GeV2
W>2.0 GeV/c2
zi>0.1
z<0.95
Mmiss>2.05

GeV/c2

xF>0
y<0.8
ppi>1 GeV/c

pp

SLIDE 27

Projections for ! " sensitive di- hadron correlations at CLAS12

120/30 days of running are approved with unpolarized liquid

H2/liquid D2 targets (underway!)

120 + 50 days of running are approved with longitudinally

polarized NH3/ND3 targets (targets ready ~2020)

27

Projections using 54 days of unpolarized proton

SLIDE 28

Summary

Twist3 functions encapsulate fundamental quark-gluon

correlations in the nucleon

Integration of Twist3 picture and TMD picture exciting!

Global fits on the horizon

Di-hadron observables are a great tool to isolate twist3 PDFs
Exciting program at CLAS12 ahead

28

SLIDE 29

BACKUP

29

SLIDE 30

Flavor Separation

30

Flavor separation can be achieved with different targets:

Proton Target: Deuteron Target:

SLIDE 31

e(x) extraction

31

Extraction: Courtoy, arXiv:1405.7659 LFCQM Model: Lorcé , Pasquini, Schweitzer, JHEP 1501 (2015) 103 [ figure from Pisano, Radici, Eur.Phys.J. A52 (2016) no.6, 155 ]

Extracted from CLAS6 preliminary ALU and AUL Consistent with LFCQM model prediction (black curve)

SLIDE 32

e(x) and hL(x) Predictions

32

Jaffe and Ji, Nucl.Phys. B375 (1992) 527-560

Figures from JLab Proposal E12-06-112B/E12-09-008B

Jakob, Mulders, and Rodrigues, Nucl.Phys. A626 (1997) 937-965

Bag Model Spectator Model

SLIDE 33

C. Dilks

33

Twist-3 Dihadron Fragmentation Function

Pereira, PoS(DIS2014)231

is very small, since cosΦR as is also likely very small Double spin asymmetries can help: – a pure twist-3 DiFF

~0 under Wandzura-Wilzcek approximation What can we learn from data?

Extracting e(x) and hL(x) involves is expected to be larger than

SLIDE 34

C. Dilks

34

Twist-3 Dihadron Fragmentation Function

Extraction of e(x) is more difficult if this is not the case
Higher-precision data from CLAS12 will help address this

SLIDE 35

e(x) and hL(x) Predictions

35

Solid: LFCQM model Dot-Dashed: spectator model Dashed: bag model

Relatively larger magnitude partly d

Lorcé , Pasquini, Schweitzer, JHEP 1501 (2015) 103

Light Front Constituent Quark Model

SLIDE 36

C. Dilks

36

Twist-3 Dihadron Fragmentation Function

Leading order term of is <0.5% of that of the leading-twist DiFF

Partial Wave Expansions

W. Yang , X. Wang, Y. Yang, Z. Lu

Phys.Rev. D99 (2019) no.5, 054003

Spectator Model Calculation:

SLIDE 37

C. Dilks

37

Dihadron Asymmetries from CLAS6

Beam Spin Asymmetries ALU Target Spin Asymmetries AUL

5.5 GeV electrons scattered on:
Longitudinally Polarized solid NH3 (compared to BSAs with H2 target)
85% beam polarization, 80% target polarization
1 < Q2 < 6 GeV2
SinΦR modulation, sensitive to e(x)
(see aforementioned extraction)

Pereira, PoS(DIS2014)231

SLIDE 38

Access of e(x) in SIDIS x-section

One of only three colinear twist-3 parton distribution functions in

the nucleon

Interference of quark-gluon with quark amplitude
∫ "#$ " %" à⊥ force on ⊥ polarized quarks in an unpolarized

nucleon, “Boer-Mulders force” (Burkardt)

Sizable model predictions

38

Jaffe, Ji, Nucl. Phys. B375, 527-560 (1992).

SLIDE 39

!"# $% → '(') + +: Clean access to e(x)

See e.g. Aurore Courtoy, arXiv:1405.7659

39

Solid: points hydrogen E.P .J. Web of Conf. 73(2014) 02008 Open points: NH3 PoS DIS2014 (2014) 231

0.04 xB

z M

Evidence for non-zero BSA

,-.

/0123 = 5

67 89: ;3

577 from CLAS6:

<

= = < > ( + < > ),

@ = <

> ( − < > )

SLIDE 40

CLAS12

40

Forward Detector:

TORUS magnet
HT Cherenkov Counter
Drift chamber system
LT Cherenkov Counter
Forward ToF System
Preshower calorimeter
E.M. calorimeter (EC)

Central Detector:

SOLENOID magnet
Barrel Silicon Tracker
Central Time-of-Flight

Implemented Upgrades:

Micromegas (CD)
Neutron detector (CD)
RICH detector (FD)
Forward Tagger (FD)

MM CND FT RICH https://www.jlab.org/Hall-B/clas12-web/

Number of readout channels ~100,000

SLIDE 41

Spring 2018: CLAS12 installation complete for first run with H2 target

41

SLIDE 42

CLAS12 Kinematic Reach

42

Beam energy at 10.6 GeV Torus current 3770 A, electrons in-bending, Solenoid magnet at 2416 A.

e’ minimum energy threshold

p(e,e’)X

Θmax

SLIDE 43

Performance plots

43

Forward Calorimeter sampling fraction for electrons

TOF particle identification π+ K+ p

SLIDE 44

First results on di-hadron correlations

44

Use about 10% of spring run (~3% of

approved running time)

Select !" → $%$& + (
Calculate fR, fh angles of hadron pair

)* = )

, % + ) , &,

. = )

, % − ) , &

2D fit to asymmetries 01%02

01%02(fR, fh)à345 6789:

Correct with kinematic factor and Pbeam~86%

Particle selection

Q2>1.0 GeV2
W>2.0 GeV/c2
zi>0.1
z<0.95
Mmiss>2.05

GeV/c2

xF>0
y<0.8
ppi>1 GeV/c

pp

SLIDE 45

Using only pairs with Mpp

pp> 0.9 GeV/c2

45

Enhanced asymmetries
Rise with x

pp

SLIDE 46

Summary

First Beam Spin Asymmetries of Di-hadrons shown
Indications of signal consistent with previous measurement
120/30 days of running are approved with unpolarized liquid

H2/liquid D2 targets (underway!)

120 + 50 days of running are approved with longitudinally

polarized NH3/ND3 targets (targets ready ~2020)

46

Projections using 54 days of unpolarized proton

SLIDE 47

47

SLIDE 48

What can we learn?

48

Andrea Signori at FF2019

SLIDE 49

Twist-3 Parton Distribution Functions

49

The sin(ΦR) modulation of ALU and AUL in dihadrons is sensitive to Twist-3 PDFs: e(x) and

Figure from arXiv:1702.07317

Twist-3 PDFs

Image from Gamberg, FF2019 Workshop

SLIDE 50

AN in pp -> π X – PUZZLE FOR 40+ YEARS! PHENIX (2014) STAR (2012) PHENIX, Talk by J. Bok (DIS 2018)

D. Pitonyak

SLIDE 51

Fds !" ! =

$% & ' ( ! − 2+ ∫

(

( ./0123 /,/0 /-/0

/

5 ℎ7 = $ & 8( ! − ℎ(7 9 ( ! − 2+ ∫

(

( ./012: /,/0 /-/0

4/10/19

51

From: Phys.Rev. D93 (2016) no.5, 054024

SLIDE 52

Spring 2018: CLAS12 installation complete for first run with H2 target

52

SLIDE 53

Enter polarization in the final States

Analogue àsimilar to PDFs encoding spin/orbit correlations
Determining final state polarization needs self analyzing decay (Λ)
Gluon FFs similar but with circular/linear polarization (not as relevant for e+e-)

53 Parton polarization à Hadron Polarization⇣ Spin averaged longitudinal transverse spin averaged

$%

&/((*, ,-)

.%

/&/((*, ,-)

longitudinal Transverse (here L) 012

/3/4(5, 62)

Observables: z: fractional energy of the quark carried by the hadron ph,T: transverse momentum of the hadron wrt the quark direction: TMD FFs

SLIDE 54

D. Pitonyak
Similar: !" in SIDIS …
Since 40+ years
P, T- invarianceà TSSAs should vanish!

F

x

4

10

3

10

2

10

1

10 1 P

0.4
0.3
0.2
0.1

0.1 = 7 TeV s ATLAS = 42 GeV s HERA-B = 39 GeV s E799 = 29 GeV s NA48 = 27 GeV s M2

)* → ,↑.

FNAL 1977

Phys.Rev. D91 (2015) no.3, 032004

SLIDE 55

Enter polarization in the final States

Analogue àsimilar to PDFs encoding spin/orbit correlations
Determining final state polarization needs self analyzing decay (Λ)
Gluon FFs similar but with circular/linear polarization (not as relevant for e+e-)

55 Parton polarization à Hadron Polarization⇣ Spin averaged longitudinal transverse spin averaged

$%

&/((*, ,-)

.%

/&/((*, ,-)

longitudinal Transverse (here L) 012

/3/4(5, 62)

Observables: z: fractional energy of the quark carried by the hadron ph,T: transverse momentum of the hadron wrt the quark direction: TMD FFs

See M. Schlegel’s talk

SLIDE 56

56

Flavor Separation

Flavor separation can be achieved with different targets:

Proton Target: Deuteron Target:

SLIDE 57

Extras

57