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Exploring Proton Structure with Drell-Yan Scattering Hadron Physics Seminar Darmstadt, December 13, 2017 M. Grosse Perdekamp, University of Illinois Overview o Exploring Proton Structure Drell Yan vs Deep Inelastic Scattering o Quark and

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  • M. Grosse Perdekamp, University of Illinois

Exploring Proton Structure with Drell-Yan Scattering

Hadron Physics Seminar

Darmstadt, December 13, 2017

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SLIDE 2

Overview

  • Exploring Proton Structure

Drell Yan vs Deep Inelastic Scattering

  • Quark and Gluon Structure of the Proton

Momentum distributions Spin (helicity) distributions

  • Transverse momentum dependent proton structure

A challenge to QCD? Drell-Yan measurements

  • Meson Structure from Drell-Yan

Exploring Proton Structure with Drell-Yan 2

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Motivation: The Proton as QCD Laboratory

The proton is the fundamental bound state of QCD; Quarks and gluons are the Constituents: Can we understand the wave function of the proton from first principles QCD ? Present (modest) status: Description of proton in hard scattering processes with parton distribution functions.

Exploring Proton Structure with Drell-Yan 3

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  • n

distributi momentum quark

  • anti

(x) q

  • n

distributi momentum quark ) ( = = x q

  • n

distributi momentum gluon = G(x)

proton quark

p p x =

Proton Structure: Momentum Distributions

Constituents: quarks = u, d, s and gluons

Exploring Proton Structure with Drell-Yan 4

small x ~ sea quarks, gluons medium - high x valence quarks

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SLIDE 5

5

DIS

DF ⊗ FF

electron- electron collisions

FF ⊗ FF

Drell-Yan (DY)

DF ⊗ DF

Probing the Quark Structure of Hadrons

mapping of sea quarks

space-like virtual photon time-like virtual photon

time

time-like virtual photon

mapping of valence quarks

Exploring Proton Structure with Drell-Yan

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SLIDE 6

Both DIS and Drell-Yan processes are tools for probing the quark and anti-quark structure of hadrons. The data stretch over a wide range in Q2 and test evolution.

CTEQ Fits to DIS and Drell-Yan CTEQ Phys.Rev. D 93, 033006 (2016)

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SLIDE 7

7

Quark and Gluon Momentum Distributions from CTEQ

CTEQ Phys. Rev. D 93, 033006 (2016)

for example: d(x,Q 2 = 2 GeV 2) is the number density for down quarks up-quark uncertainties

Exploring Proton Structure with Drell-Yan

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8

Quark and Gluon Momentum Distributions from CTEQ

CTEQ Phys. Rev. D 93, 033006 (2016)

for example: d(x,Q 2 = 2 GeV 2) is the number density for down quarks up-quark uncertainties anti-up uncertainties

Exploring Proton Structure with Drell-Yan

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SLIDE 9

9

Quark and Gluon Momentum Distributions from CTEQ

CTEQ Phys. Rev. D 93, 033006 (2016)

for example: d(x,Q 2 = 2 GeV 2) is the number density for down quarks up-quark uncertainties anti-up uncertainties ATLAS Drell-Yan cross section vs invariant mass

Exploring Proton Structure with Drell-Yan

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E866: Isospin Broken in the Anti-Quark Sea

10

Fermilab E866/NuSea 1998

?

  • Inclusion of E866 σpd/σpp into global

fits: dramatic impact of sea-quark

  • dis. from QCD analysis of hard

scattering data!

}

}

parameterizations excluding E866 data parameterization including E866 data

Exploring Proton Structure with Drell-Yan

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SLIDE 11

Current Fermilab E906/SeaQuest

extending sea-quark measurements to larger x by using 120 GeV protons from Fermilab Main Injector.

11

25% of total expected beam current

Exploring Proton Structure with Drell-Yan

from Paul Reimer’s ECT talk, 10-2017

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SLIDE 12
  • n

distributi quark dependent spin (x) q

  • (x)

↑↓ ↑↑

= ∆ q q(x)

  • n

distributi momentum quark ) ( = x q

  • n

distributi gluon dependent spin (x) G

  • (x)

↑↓ ↑↑

= ∆ G G(x)

proton quark

p p x =

Proton Structure: Spin (Helicity) Distributions

Constituents: quarks = u, d, s and gluons

(x) : Spin Quark Total

, 1

∑ ∫

= =

∆ = ∑ ∆ ⇒

q q x x

q

(x) : Spin Gluon Total

1

∫

= =

∆ = ∆ ⇒

x x

G G

Exploring Proton Structure with Drell-Yan 12

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SLIDE 13

proton quark

p p x =

Proton Structure: Helicity Sumrule

De-composition of the Proton Spin

z

L G + ∆ + ∑ ∆ = 2 1 2 1

Quark Spin Orbital Angular momentum Gluon Spin

Exploring Proton Structure with Drell-Yan 13

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Quark and Gluon Helicity Distributions from NNPDF

  • E. Nocera et. Al. Nucl.Phys. B887 (2014) 276-308

For example:

Up and down quark helicity distributions are known. Still large uncertainties for gluon and anti-quarks. RHIC: evidence for non-zero gluon spin contribution!

Exploring Proton Structure with Drell-Yan 14

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Transverse degrees

  • f freedom:

Transverse proton/quark spin Intrinsic transverse momentum of quarks kT Transverse momentum in hadron fragmentation pT

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Quark Helicity Distributions from Deep Inelastic Lepton-Nucleon Scattering

electron or muon probe

spin

proton target

spin

Magnetic Spectrometer

  • eg. COMPASS to measure

Momentum of final state Leptons and hadrons

Spectator System

d

Exploring Proton Structure with Drell-Yan 16

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Quark Helicity Distributions from Deep Inelastic Lepton-Nucleon Scattering

electron or muon probe

spin

proton target

spin e- e-

proton spectator system current quark jet

Spectator System

d factorize processes in the high energy lepton-quark scattering from target related processes

Exploring Proton Structure with Drell-Yan 17

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How is Transverse Spin Different?

electron or muon probe proton target

spin

Spectator System

d Are the quark distributions changed by a spin rotation? At high probe energy: yes! boosts and rotations do not commute!

Exploring Proton Structure with Drell-Yan 18

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Optical Theorem in Hard Scattering

Cross Section Forward Elastic Scattering Amplitude

Optical Theorem q(x,Q2), G(x,Q2) photon, gluon proton pQCD, hard scattering quark Process independent quark and gluon distri- butions initial state final state Factorization

∑

− = − ν µ ν µ

ν µ

σ

... 2 2 /

| | ) ( 1 ~

...

p O p Q C Q

... n d t t

Wilson coefficients Operator matrix element Operator product expansion in twist parameter t, t=d-nu..v

e- e-

proton spectator system current quark jet Exploring Proton Structure with Drell-Yan 19

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Helicity Amplitudes in Hard Scattering

proton, Hf

Forward Scattering Amplitude

proton, Hi

initial state final state hard probe: gluon, photon

Quark, hf Quark, hi ) , ( 2 1 2 1

  • 2

1

  • 2

1 ), , ( , ) , ( 2 1

  • 2

1 2 1

  • 2

1 2 1 2 1 2 1 2 1

2 2 1 2 2 2 1 2

Q x q ) (x,Q g Q x q ) (x,Q F Q x q

,

δ ⇒ → ∆ ⇒ → →

h: quark helicity H: proton helicity In initial and final state

Hi hi Hf hf

Helicity is conserved helicity average helicity difference helicity flip transverse spin distributions for quarks: transversity

Exploring Proton Structure with Drell-Yan 20

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Decomposition of Helicity Flip Amplitudes at Leading Twist

Transverse Momentum Dependent (TMD) TMD independent

Exploring Proton Structure with Drell-Yan 21

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Transversity : correlation between transverse proton spin and quark spin Sivers : correlation between transverse proton spin and quark transverse momentum Boer/Mulders: correlation between transverse quark spin and quark transverse momentum

) (x q δ

) , (

2 1 ⊥ ⊥

k x f

q T

) , (

2 1

⊥

⊥

k x h

q

Sp– Sq – coupling ? Sp-- Lq– coupling ? Sq-- Lq– coupling ?

Proton Transverse Spin Structure: Transversity, Sivers and Boer-Mulders

Insight in spin-orbit structure

  • f quarks in the proton …
  • r

) , (

2 1 ⊥

k x h T

Exploring Proton Structure with Drell-Yan 22

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First Experiment: Single Transverse Spin Asymmetries (SSA) in Hadron-Hadron Collisions

23

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Single Transverse Spin Asymmetries (SSA) AN in Polarized Proton-Proton Scattering

sp π p p π sp

⊥ π

p 

⊥ π

p 

= 0 ? AN = NL - NR NL + NR

NL : pions to the left NR : pions to the right

X p p + →  +

↑

π

Example: Inclusive π production in polarized p-p Correlation proton spin Sp vs pπ⊥ π transverse momentum Single transverse spin asymmetries AN

  • ne proton

is polarized!

Exploring Proton Structure with Drell-Yan 24

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For High Energy Reactions: AN  0 QCD Test ! (Kane, Pumplin, Repko, 1978)

4 q

10 , 20 , 3 m example,

−

≈ = = ∝

N q s N

A GeV s MeV s m A α

Exploring Proton Structure with Drell-Yan 25

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Experiment: Large SSA Observed

  • ver Large Range of Scales !

Experiment: AN >> 10-4 for 4 GeV < √s < 200 GeV for charged pions !

from Christine Aidala, Spin 2008 and Don Crabb & Alan Krisch in then Spin 2008 Summary, CERN Courier, 6-2009

ZGS √s=4.7 GeV AGS √s=6.5 GeV FNAL √s = 20 GeV RHIC √s = 200 GeV

π+ π-

Soft effects due to QCD dynamics in hadrons remain relevant up to scales where pQCD can be used to describe the scattering process!

Exploring Proton Structure with Drell-Yan 26

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Origin of Large SSA  Inspect Factorized Components of Cross Section

2

P

) ( 1 x qi δ ) (

2

x G

1 1P

x

2 2P

x

ij LL

a

1

p

s 

+

π

Jet

proton ton struct cture hard s scatte tterin ring react ction ion

frag ragmen mentat tation proce

  • cess

( )

) , ( ) ( ˆ ) ( ) , (

, 2 1 3 2 , 1 2 1 3

.

T h q l k j i T q i

p z FF dx dx q q q q d x G k x q dz dx dx X pp d

l k

× → × ⋅ ∝ →

↑ ↑ + ↑ ↑

σ π σ

Final state – hadron fragmentation pQC pQCD Init nitia ial s l state – pr proto ton s stru tructu ture Kane, Pumplin, Repko  aLL~10-4 Can initial and/or final state effects generate large transverse spin asymmetries? (AN ~10

  • 1)

Exploring Proton Structure with Drell-Yan 27

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Transverse Spin in QCD: Two Solutions

(I) “Transversity” quark-distributions and Collins fragmentation

Correlation between proton- und quark-spin and spin dependent fragmentation

) , ( ) (

2 2 1

T

p z H x q

⊥

⋅ ∝ δ

(II) Sivers quark-distribution+

Correlation between proton-spin and transverse quark momentum

) ( ) , (

2 1

z D k x f

h q q T

⋅ ∝

⊥ ⊥

Collins FF Quark transverse spin distribution Sivers distribution STAR, PRL-92:171801, 2004

Exploring Proton Structure with Drell-Yan 28

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Sivers: Connection to Orbital Angular Momentum?

  • M. Burkardt

) (

1

x x f right δ − ) (

1

x x f left δ +

xq is blue/red shifted!

Exploring Proton Structure with Drell-Yan 29

from Matthias Burkhardt

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30

Sivers Effect: Final State Interaction

Final state soft gluons ? What happens to factorization and universality ? Gauge link formalism, process dependence of Sivers effect!

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Theoretical Description: Include soft Gluon Exchange in the Initial and Final State of Hard Scattering Processes

∑

− = − ν µ ν µ

ν µ

σ

... 2 2 /

| | ) ( 1 ~

...

p O p Q C Q

... n d t t

Sum initial state gluon exchange: gauge link and insert gauge link in hard scattering matrix element Sum final state gluon exchange: gauge link and insert gauge link integral in hard scattering matrix element

Exploring Proton Structure with Drell-Yan 31

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Sign Change of Sivers- and Boer-Mulders Functions Between SIDIS and DY

Direction of the gauge-link integrals of kT

  • dep. pdfs is process-dependent and

changes its sign between SIDIS and DY

Need to confirm sign reversal in polarized Drell-Yan! NSAC performance Milestone HP13

TEST “modified” universality of TMD pdfs! Sivers Boer-Mulders SIDIS DY

Exploring Proton Structure with Drell-Yan 32

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TMD Modulations in the SIDIS and Drell-Yan Cross Sections

 '  Exploring Proton Structure with Drell-Yan 33

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Modulation Amplitudes vs TMDs

Avoids dependence on FFs !

Exploring Proton Structure with Drell-Yan 34

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COMPASS: TMD Observables

COMPASS at CERN: unique capability of measuring TMD

  • bservables with lepton beams (SIDIS)

and hadron beams (Drell-Yan) Transverse Momentum Dependent PDFs Single Spin Asymmetries in SIDIS from COMPASS Constraining Boer Mulders-, Sivers- and Transversity- distributions Drell-Yan at COMPASS

Set-up Data taking in 2014 and 2015 Plans for 2018 First Steps towards the future: COMPASS 2020

Exploring Proton Structure with Drell-Yan 35

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COMPASS at the CERN SPS

Exploring Proton Structure with Drell-Yan 36

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COMPASS – Important Instrumentation Features

1.Muon, electron or hadron secondary beams with the momentum range 20-250 GeV and intensities up to 108 particles per second.

  • 2. Solid state polarized targets, NH3
  • r 6LiD, as well as liquid hydrogen

target and nuclear targets. 3.Powerful tracking system – 350 planes.

  • 4. Versatile PID – RICH, Muon Walls,

Calorimeters.

Two stage large acceptance spectrometers with high rate capability:

RHIC based hadron ID

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COMPASS – Important Instrumentation Features

1.Muon, electron or hadron secondary beams with the momentum range 20-250 GeV and intensities up to 108 particles per second.

  • 2. Solid state polarized targets, NH3
  • r 6LiD, as well as liquid hydrogen

target and nuclear targets. 3.Powerful tracking system – 350 planes.

  • 4. Versatile PID – RICH, Muon Walls,

Calorimeters.

Two stage large acceptance spectrometers with high rate capability:

RHIC based hadron ID

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SLIDE 39

COMPASS – Important Instrumentation Features

Solenoid 2.5T Dipole magnet 0.6T

3He – 4He dilution refrigerator (T~50mK)

d (6LiD) p (NH3) Polarization 50% 90% Dilution factor 40% 16% Opposite polarization in different target segments reversed frequently

Vertex distribution for SIDIS

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Kinematic Coverage: SIDIS vs Drell-Yan

The phase space for Drell-Yan and SIDIS processes partially overlap in the x-Q2 plane In the region of overlap in x, the average Q2 in Drell-Yan is about two times larger compared to SIDIS

Exploring Proton Structure with Drell-Yan 40

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COMPASS and HERMES Sivers Asymmetries for π+ vs K+

COMPASS Phys.Lett. B744:250(2015)

Combined 2007 and 2010 COMPASS proton data samples analyzed.

Exploring Proton Structure with Drell-Yan 41

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Sivers – Global Analysis of HERMES & COMPASS Data

Leading order analysis Full QCD analysis including TMD evolution Still significant errors, no data for x>0.35 Sign Change  COMPASS Drell-Yan (NSAC Milestone …)

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Sivers Result from 35,000 Dimuons

Released by Barkur Parsamyan at DIS 2017 and Marcia Quaresma at IWHSS 2017 PRL 119, 112002 (2017)

Exploring Proton Structure with Drell-Yan 43

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SLIDE 44

First Results on Sign Change in DY: AN for W-Production in STAR

Comparison of AN

W to Sivers from SIDIS by Anselmino,

Boglione, D’Alesio, Murgia, JHEP 1704 (2017) 046

AN W+ in STAR AN W- in STAR AN

W+/- slightly better

compatible with sign change

χ2 between MC variations

  • f Sivers PDF and STAR AN

W.

Exploring Proton Structure with Drell-Yan 44

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SLIDE 45

COMPASS Transversity Asymmetry

Exploring Proton Structure with Drell-Yan 45

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Active & Future Experimental Facilities: with Drell-Yan Experiments

BNL

JPARC FNAL

RHIC is running with STAR remaining as active experiment. E906 running: SeaQuest Drell-Yan: 2014, 2015 & 208 + future with RF separated beams Drell-Yan physics proposals pending. Drell-Yan + J/ψ in preparation Drell-Yan physics in PANDA

Exploring Proton Structure with Drell-Yan 46

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TMD Drell-Yan Asymmetries with PANDA

Projections for 5 months of PANDA: Two bins of qT: 1<qT< 2 GeV 2<qT< 3 GeV Transversity Boer Mulders Pretzelosity  Precision measurement of Boer Mulders, Transversity, Sivers asymmetries without FFs !  Testing qT dependence! From M. Destefanis, EPJ 73,

Exploring Proton Structure with Drell-Yan 47

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Test Unified Picture: TMD (Sivers & Collins) vs Collinear at Twist 3

Use TMD description (Sivers & Collins) if pT << Q Use collinear description at Twist 3 if pT ~< Q Origin of TSA (I) Transversity (II) Sivers (III) Initial or final state twist-3+

Qiu/Sterman and Koike

+ unified picture: Ji, Qiu, Vogelsang and Yuan in PRL-97:082002, 2006

Exploring Proton Structure with Drell-Yan 48

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Unpolarized Cross Section: Precision Measurement of the Lam-Tung Relation  Boer Mulders

Exploring Proton Structure with Drell-Yan 49 Discussion of Lam-Tung Relation from Vincent Andrieux, UIUC

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SLIDE 50

Precision Measurement of the Lam-Tung Relation  Boer Mulders

PANDA, RF separated beams at CERN?

Exploring Proton Structure with Drell-Yan 50

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Drell-Yan with RF Separated Kaon and Anti-Proton Beams at CERN

Discussion of RF upgrade from Vincent Andrieux, UIUC Exploring Proton Structure with Drell-Yan 51

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Kaon Structure: Flavor Separation

First measurement of kaon sea!

Exploring Proton Structure with Drell-Yan 52

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Anti-Proton Beams for COMPASS

(1) measure Sivers asymmetries without uncertainty from pion pdf (2) use transversity modulation, sin(2ϕCS-ϕS) for Boer Mulders measurement (less QCD radiative effects):  extract transversity from SIDIS and e+e- measurements  measure Drell Yan A sin(2ϕCS-ϕS)  combine with SIDIS transversity to

  • btain proton Boer Mulders

Exploring Proton Structure with Drell-Yan 53

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SLIDE 54

Summary

Several experiments with complementary kinematics Will cleanly measure TSAs and for the first time kaon structure

Exploring Proton Structure with Drell-Yan 54