1

Nucleon Sea Structure and the

Five-Quark Components

Wen-Chen ChangInstitute of Physics, Academia Sinica, Taiwan

Jen-Chieh Peng University of Illinois at Urbana-Champaign, USA

Baryons2013International Conference on the Structure of

Baryons June 24th - 28th 2013

Outline• Evidences of nucleon sea• Flavor Asymmetry of light sea quarks• Structure of strange quarks• Intrinsic sea quarks in light-front 5q model• Sea quarks in lattice-QCD• Prospect• Conclusion

2

Deep Inelastic Scattering

3

Q2 :Four-momentum transferx : Bjorken variable (=Q2/2Mn)n : Energy transferM : Nucleon massW : Final state hadronic mass

22

'2 2

1

2 22 1

2

2[ 2 * tan ( / 2)]

[

( , ) ( ,

/ 2 / * tan ( / 2

)

( , ) , )( ])

Mott

Mott

W Q W Q

F x Q F x Q

dd dE

M

n

n n

•Scaling•Valence quarks•Quark-antiquark pairs

Sum Rules

4J.I. Friedman, Rev. Mod. Phys. Vol. 63, 615 (1991)

: expectation value of number of quarks.N

Gottfried Sum Rule

2 2

1

2 20

1 1

0 0

[( ( ) ( )) / ]

1 2( ) ( ( ) ( ))3

13

)

3

(

p nG

p n

p p p pv

p

v

p

S I I

F x F x x dx

dx u d u x d

if u d

x dx

5

Assume a symmetric quark-antiquark sea,GSR is only sensitive to valance quarks.J.I. Friedman, Rev. Mod. Phys. Vol. 63, 615 (1991)

6

Gottfried Sum Measured by NMC

SG = 0.235 ± 0.026

New Muon Collaboration (NMC), Phys. Rev. D50 (1994) R1

SG is significantly lower than 1/3 !

Explanations for the NMC result

7

• Uncertain extrapolation for 0.0 < x < 0.004• Charge symmetry violation • in the proton

,( )n p n pu d d u

( ) ( )u x d x1

0( ( ) ( )) 0.148 0.04d x u x dx

Need independent methods to check the asymmetry, and to measure its x-dependence !

d u

224 1 [ ( ) ( ) ( ) ( )]

9 t b t bb t b t

d e q x q x q x q xdx dx x x s

( )11 ( ) 1 ( )4 ( )| 1 1

2 2 2( ) ( ) ( ) ( )14 ( ) ( )

b t

bpd

t tbx xppb t t t

b t

d xd x d xu x

d x d x u x u xu x u x

Drell-Yan Process

8

Acceptance in Fixed-target Exps.

Light Anti-quark Flavor Asymmetry

Naïve Assumption:

9

NA51 (Drell-Yan, 1994)

NMC (Gottfried Sum Rule)

NA 51 Drell-Yan confirms d(x) > u(x)

Light Anti-quark Flavor Asymmetry

Naïve Assumption:

10

NA51 (Drell-Yan, 1994)

E866/NuSea (Drell-Yan, 1998)

NMC (Gottfried Sum Rule)

Origin of u(x)d(x): Perturbative QCD effect?• Pauli blocking

• guu is more suppressed than gdd in the proton since p=uud (Field and Feynman 1977)

• pQCD calculation (Ross, Sachrajda 1979)

• Bag model calculation (Signal, Thomas, Schreiber 1991)

• Chiral quark-soliton model (Pobylitsa et al. 1999)• Instanton model (Dorokhov, Kochelev 1993)• Statistical model (Bourrely et al. 1995; Bhalerao 1996)• Balance model (Zhang, Ma 2001)

11

The valence quarks affect the gluon splitting.

G 𝑞𝑞

Origin of u(x)d(x): Non-perturbative QCD effect?• Meson cloud in the nucleons (Thomas 1983, Kumano 1991):

Sullivan process in DIS.

• Chiral quark model (Eichten et al. 1992; Wakamatsu 1992): Goldstone bosons couple to valence quarks.

12Pion cloud is a source of antiquarks in the protons and it lead to d>u.

0; : : 4 : 3 : 2q q

0; : : 2 :1: 0p N

n

13

( ) ( ) vs. Theoretical Modelsd x u x

Strange Quark in the Nucleon:Deep-Inelastic Neutrino Scattering

14

;

;

s c X c s

s c X c s

n n

n

n

15

)(*5.0)( duss

)()( xsxs

Strange Quark in the Nucleon

CCFR, Z. Phys. C 65, 189 (1995)

16

Strange Quark AsymmetryNuTeV, PRL 99, 192001 (2007)

2 216 GeVQ

• Meson Cloud Model (Signal and Thomas, 1987)

• Chiral Field (Burkardt and Warr , 1992)

• Baryon-Meson Fluctuation (Brodsky and Ma , 1996)

• Perturbative evolution (Catani et al., 2004)

17

s(x)=s(x)?

( ) ( ) at large s x s x x

( ) ( ) at large s x s x x

( ) ( ) at large s x s x x

( ) ( ) at large s x s x x

Strange Content from Semi-Inclusive Charged-Kaon DIS Production

18

( ( ) ( )) ( ( ) ( ))Restoration of SU(3) symmetrys x s x u x d x

2 22.5 GeVQ

HERMES, PLB 666, 446 (2008)

19

W and Z production at LHC

0.250.28

0.5( ) 1.00ss srd

ATLAS, PRL 109, 012001 (2012)

Parton Distribution Functions of Protons

20

Short Range Structure of HadronExtrinsic Sea Intrinsic SeaGluon splitting in leading twist Gluon fusion & light quark

scattering (higher-twist)Perturbative radiation Non-perturbative dynamicsCP invariant Possible CP non-invariantFast fluctuation With a longer lifetimeOf small x Of large x (valence-like)Strong Q2 dependent Small Q2 dependent

21Hoyer and Brodsky, AIP Conf. Proc. 221, 238 (1990)

22

Intrinsic Sea Quarks in Light-Front 5q Fock States

25 52 2

1 5 51 1

3 5

The "intrinsic"-cha

| |

rm from | is "valence"-like and peak at large unl

( ,..., ) (1 ) / [

ike the "extrinsic" sea (

]

)

|q

ii p

i i

q

i

uudcc

p P uud P uudQQ

mP x x

x c

N

g c

x mx

“intrinsic”

“extrinsic”The | intrinsic-charmcan lead to large contribution to charm production at large

uudcc

x

Brodsky, Hoyer, Peterson, Sakai (BHPS) PLB 93,451 (1980); PRD 23, 2745 (1981)

23

Experimental Evidences of Intrinsic Charm

Gunion and Vogt, hep-ph/9706252

24

Global Fit by CTEQ

No Conclusive Evidence…..

Pumplin, Lai, Tung, PRD 75, 054029 (2007)

25

Search for the lighter “intrinsic” quark sea

No conclusive experimental evidence for intrinsic-charm so far

Are there experimental evidences for the intrinsic

| , | , | 5-quark states ?uuduu uuddd uudss 2

5 /1~ Qq mP

The 5-quark states for lighter quarks have larger probabilities!

3 5| | |q qp P uud P uudQQ

26

How to separate the “intrinsic sea” from the “extrinsic sea”?• Select experimental observables which have no

contributions from the “extrinsic sea”• “Intrinsic sea” and “extrinsic sea” are expected to

have different x-distributions.• Intrinsic sea is “valence-like” and is more abundant at

larger x.• Extrinsic sea is more abundant at smaller x.

27

How to separate the “intrinsic sea” from the “extrinsic sea”?• Select experimental observables which have no

contributions from the “extrinsic sea”• Investigate the x distribution of flavor non-singlet

quantities: , .

only sea" intrinsic" tosensitive is and )(sea extrinsic from oncontributi no has qqgud

d u d u s s

28

Data of d(x)-u(x) vs. Light-Front 5q Fock States

• The data are in good agreement with the 5q model after evolution from the initial scale μ to Q2=54 GeV2

• The difference of these two 5-quark components could be determined.

5 5 0.118uuddd uuduuP P

Chang and Peng, PRL 106, 252002 (2011)

29

How to separate the “intrinsic sea” from the “extrinsic sea”?

• “Intrinsic sea” and “extrinsic sea” are expected to have different x-distributions

• Intrinsic sea is “valence-like” and is more abundant at larger x

• Extrinsic sea is more abundant at smaller x

ondistributi )()( theis example An xsxs

30

Data of x(s(x)+s(x)) vs. Light-Front 5q Fock States

• The x(s(x)+s(x)) are from HERMES kaon SIDIS data at <Q2>=2.5 GeV2.

• The data seem to consist of two components.

• Assume data at x>0.1 are originated from the intrinsic |uudss> 5-quark state.

5 0.024uudssP

Chang and Peng, PLB 704, 197 (2011)

31

only sea" intrinsic" tosensitive is and )(sea extrinsic from oncontributi no has qqgssud

How to separate the “intrinsic sea” from the “extrinsic sea”?• Select experimental observables which have no

contributions from the “extrinsic sea”• Investigate the x distribution of flavor non-singlet

quantities: , .d u d u s s

32

Data of x(d(x)+u(x)-s(x)-s(x)) vs. Light-Front 5q Fock States • The d(x)+u(x) from

CTEQ 6.6.• The s(x)+s(x) from

HERMES kaon SIDIS data at <Q2>=2.5 GeV2.

5 5 52 0.314uuduu uuddd uudssP P P

5 5 5~ 2(not sensitive to extrinsic sea)

uuduu uuddd uudss

u d s s

P P P

Chang and Peng, PLB 704, 197 (2011)

33

Extraction of various 5q-components for light quarks

5 5 50.240; 0.122; 0.024uuddd uuduu uudssP P P

314.02 555 suudsduudduuudu PPP024.05 suudsP5 5 0.118uuddd uuduuP P

34

Constituent 5q model

proton = uud + [uuds] s

Axial Form Factor uud

s

s

s

s

sA E M

P

G G

P

G sAG

2q

Riska and Zou, PLB 636, 265 (2006)

30Dominate configuration of [uuds] s [4] [22] [2

1

2 ]is

0 15%FS F S

ssP

P

35

Constituent 5q model

proton = uud + [uuds] s

Axial Form Factor uud

s

s

s

s

sA E M

P

G G

P

G

2q

Kiswandhi, Lee, Yang, PLB 704, 373 (2011)

3 30 0[4] [22] [22]

Two dominate configurations of [uuds] s are

and [31] [211] [22]0.025 0.058

.%

FS F S FS F

ss

SP PP

36

Extended Chiral Constituent 5q model(complete configurations)

30Use version for the transition

coupling between 3q and 5q states.P

An and Saghai, PRC 85, 055203 (2012); 1306.3041 (2013)

Strong interplays among different components with (very) large cancellations.

37

Comparison of 5q ProbabilitiesP(uu) P(dd) P(ss) P(cc) References

0.198 0.148 0.093 0.011 Bag model; Donoghue and Golowich, PRD15, 3421 (1977)

0.003 Light-cone 5q model;Hoffmann and Moore, ZPC 20, 71 (1983)

0.250 0.250 0.050 0.009 Meson cloud model; Navarra et al., PRD 54, 842 (1996)

0.10 -0.15

Constituent 5q model;Riska and Zou, PLB 636, 265 (2006)

0.122 0.240 0.024 Light-front 5q model;Chang and Peng, this work (2011)

0.098 0.216 0.057 Extended chiral constituent quark model;An and Saghai, PRC 85, 055203 (2012)

Diagrams of Nucleon Hadronic Tensor in Path-Integral Formalism

38

Connected Diagram Disconnected Diagram

3

1 21 ( , ) (0, )

2 2iq x

vN

d xW N e J x t J t NM V

n

Connected and Disconnected Sea• qds(x)=qds(x), where q=u, d, s; s(x)=s(x)• uds(x)=dds(x)• qcs(x)=qcs(x), where q=u, d• Origin of u(x)d(x): ucs(x)dcs(x)• Small-x behaviors:

• qvalence(x) , qcs(x) x-1/2

• qds(x) x-1

39

How do we separate these two components?

Liu and Dong, PRL 72, 1790 (1994)

Ratio of Momentum Fraction between s and u in DI by Lattice QCD

40

Doi, et al. PoS LATTICE2008:163, 2008Connected Insertion (CI)

Disconnected Insertion (DI)

Connected Sea

41

( ) ( )CS CSu x d x

HERMESCT10

( ) ( )

( ( ) ( )) ( ( ) ( ))1( ( ) ( )) ( ( ) ( ))

CS CS

DS DS

u x d x

u x d x u x d x

u x d x s x s xR

( ) ( )

( ( ) ( )) ( ( ) ( ))

( ( ) ( ))

CS CS DS DS

CS CS

d x u x

d x u x d x u x

d x u x

Liu, Chang, Cheng and Peng, PRL 109, 252002 (2012)

Small-x Behaviors of CS and DS

42

Small-x behavior:•Valence and CS x-1/2

•DS x-1

Liu, Chang, Cheng and Peng, PRL 109, 252002 (2012)

Moments of Nucleon Sea

43

2 22.5 GeVQ

Momentum fraction of u+d is about equally divided between CS and DS.

Liu, Chang, Cheng and Peng, PRL 109, 252002 (2012)

“Connected, Disconnected Sea” VS.“Intrinsic, Extrinsic sea”

44

Connected Sea(u, d quarks only)

Intrinsic Sea:•Non-perturbative•Origin of flavor asymmetry of light sea quarks•With x^-1/2 small-x behavior from the Reggeon exchange

Disconnected Sea(u, d quarks and heavy quarks)

Intrinsic Sea:•Non-perturbative•Peaked at medium x (~ 0.1)•Meson cloud or the Reggeon exchangeExtrinsic Sea:•Perturbative•At small x•With x^-1 small-x behavior from the Pomeron exchange

45

Future Prospect (Experimental) • Light sea quarks:

• E906/SeaQuest at FNAL: flavor asymmetry of d-bar/u-bar at large x region.

• MINERνA at FNAL: x-dependence of nuclear effects for sea quarks.• JLAB-12 GeV: transverse spatial distribution of sea quarks.• Kaon-induced DY experiment at J-PARC: s and s-bar.• Electron-Ion Collider (EIC): sea quark distributions and their spin

structure.• Heavy sea quarks:

• Open-charm production at forward rapidity, e.g. fixed-target experiment at LHC.

• Higgs production at large xF at LHC.

d/u From E906/SeaQuest at FNAL

Ratio of Drell-Yan cross sections

(in leading order—E866 data analysis confirmed in NLO)

Global NLO PDF fits which include E866 cross section ratios agree with E866 results

Fermilab E906/Drell-Yan will extend these measurements and reduce statistical uncertainty.

E906 expects systematic uncertainty to remain at approx. 1% in cross section ratio.

46

47

Future Prospect (Theoretical) • Intrinsic sea for hyperons and mesons? • Intrinsic gluons in the nucleons? • Connection between the 5-quark model and the

meson-cloud model? • Connection between the 5-quark model and lattice

QCD? • Spin-dependent observables of intrinsic sea?

48

Conclusion• Using DIS, Drell-Yan and SIDIS processes, the

structure of sea quarks in the nucleon are explored.• The measured x distributions of (d-u), (s+s) and

(u+d-s-s) could be reasonably described by the light-front 5q Fock states. The probabilities of the intrinsic 5q states of light sea quarks are extracted.

• The intrinsic or valence-like sea quarks are deeply connected with the non-perturbative QCD. More accurate data will be available in the coming experiments at FNAL, JLAB, LHC, J-PARC and EIC.