Generalized Parton Distributions in the Chiral Odd …...1 Generalized Parton Distributions in the...

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Generalized Parton Distributions in the Chiral Odd Sector

& Their Role in Neutral Meson Leptoproduction

Gary R. Goldstein !Tufts University!

Simonetta Liuti,!

Osvaldo Gonzalez-Hernandez!

University of Virginia!

!

Presentation for QCD Evolution Workshop II!Jefferson Lab - May, 2012!

These ideas were developed in Trento ECT*, INT, Jlab, DIS2011, Frascati INF, etc. & in consultation with many of you !

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Exploring Transversity!!•  “I’ve been to the zoo! Do you know what I did before I

went to the zoo today? I walked all the way up Fifth Avenue from Washington Square; all the way . . . I took the subway down to the Village so I could walk all the way up Fifth Avenue to the zoo. It’s one of those things a person has to do; sometimes a person has to go a very long distance out of his way to come back a short distance correctly.”!

Zoo Story, Edward Albee (1958) !

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Outline !   Some history of Transversity!!   “Flexible” parameterization for Chiral Even GPDs!

! Regge ✖ diquark spectator model!!   Satisfies all constraints!

!   Results for DVCS (transverse γ* à transverse γ)!!   cross sections & asymmetries!

!   Extend to Chiral Odd GPDs via diquark spin relations!!   Some relations between Chiral even & odd helicity amps!

!   π0, η, η’ production data involve sizable γ*Transverse

(factorization shown at leading twist for γ*Longitudinal

[Collins, Franfurt, Strikman])!! γ*

T requires chiral odd GPDs!!   Q2 dependence for π0 depends on γ*+(ρ, b1)àπ0!

!   π0 cross sections & asymmetries!

! Transversity Amplitudes, GPDs & TMDs!

QCDII 2012 GR.Goldstein

Transversity •  Early history – 4 decades ago!SSA πp⇑ ⇒ πp elastic – single ρ Regge pole exchange !

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But…

Nucl. Phys. B56 (1973)

Transversity •  Early history – 4 decades ago!SSA πp⇑ ⇒ πp elastic – single ρ Regge pole exchange !Need interference & helicity flip!Regge + fsi !!•  Spin is not an unnecessary complication! Polarized target experiments pp⇑ ⇒ π X! Polarized hyperon production pp ⇒ Λ⇑ X!•  Amplitude analyses !•  How to parameterize? Define Transversity Amplitudes !(“Optimally Simple Connection Between the Reaction Matrix and the Observables”.!G. R. Goldstein and M. J. Moravcsik, Ann. Phys. (N.Y.) 98, 128 (1976); 142, 219 (1982); 195, 213 (1989).)!

•  QCD & SSAs? Kane, Pumplin & Repko, PRL41, 1889 (1978).!

Pol or Asym ∝!

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!(s)mq/ s

SSA’s cont’d •  Several SSA directions!

§  Λ (WGD Dharmaratna & GG,PRD 41, 1731 (1990); PRD 53, 1073 (1996)) & ΛC,B !

§  Heavy quark⇑ fragmentation (A.Adamov and GG, PRD56, 7381 (1997).!•  Jaffe & Ji PRL67,552 (1991) introduce h1(x) – transversity transfer! “Chiral-Odd Parton Distributions and Polarized Drell-Yan Process”!

§  How to measure chiral odd? DY or SIDIS !§  or Fragmentation version Λ⇑ + antiΛ⇑ (Chen, GG, Jaffe, Ji NPB 445, 380

(1995))! New Millennium !•  Transversity → tensor current Ψbar-q σμν Ψq → δq (L.Gamberg & GG, PRL 87,

242001 (2001))!

•  Leptoproduction: SIDIS & TMDs (S.Liuti & GG . . . )!

•  Leptoproduction: Exclusives & GPDs (π0 electroproduction)!•  Λ in e p scattering, target fragmentation & fracture functions!•  Λ in p+p at LHC !

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9 9

t

DVCS & DVMP γ*(Q2)+P→(γ or meson)+P’ partonic picture

P'+=(1-ζ)P+

P’T=-Δ

k+=XP+ k'+=(X-ζ)P+

q q+Δ k'T=kT-Δ kT

P+

} {

ζ→0 Regge Quark-spectator

quark+diquark

Factorized “handbag” picture

}

X>ζ DGLAP ΔT -> bT transverse spatial X<ζ ERBL x=(X-ζ/2)/(1-ζ/2); x=ζ/(2-ζ) see Ahmad, GG, Liuti, PRD79, 054014, (2009) for first chiral odd GPD parameterization focused on pseudoscalar production

GPD

QCDII 2012 GR.Goldstein

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Momentum space nucleon matrix elements of quark field correlators see, e.g. M. Diehl, Eur. Phys. J. C 19, 485 (2001).

Chiral even GPDs -> Ji sum rule

Chiral odd GPDs -> transversity

QCDII 2012 GR.Goldstein

Jqx= 1

2 dx H (x, 0, 0)+ E(x, 0, 0)[ ]x!

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How to determine GPDs? Flexible Parameterization è Recursive Fit

CHIRAL EVENS: O. Gonzalez Hernandez, G. G., S. Liuti, PRD84, 034007 (2011)

Constraints from Form Factors Dirac

Pauli, etc. including Axial & Pseudoscalar

How can these be independent of ξ? Constraints from Polynomiality

dx x nH(x,!, t) = An ,kk = 0, 2,..

n"#1

+ 1

$ ( t)! k +1# (#1)

n

2Cn(t)! n +1

dxH(x,!, t)0

1

" = F1 (t)

dxE (x,!,t)0

1

" = F2( t)

dx x n E (x,!,t)"1

1

# = Bn ,k (t)!

k k= 0,2,...

n

$ - 1- (-1)

n

2Cn(t)!n +1

Result of Lorentz invariance & causality. Not necessarily built into models

Constraints from pdf’s:H(x,0,0)=f1(x),H~(x,0,0)=g1(x), HT(x,0,0)=h1(x)

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Helicity amps (q’+N->q+N’) are linear combinations of GPDs

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In diquark spectator models A++;++, etc. are calculated directly. Inverted -> GPDs

T-reversal at ξ =0

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Spectator inspired model of GPDs •  2 directions – !

§  1. getting good parameterization of H, E & ~H, ~E ! satisfying many constraints!

(see O. Gonzalez-Hernandez, GG, S. Liuti - Phys.Rev. D84, 034007 (2011))!

§  2. getting 8 spin dependent GPDs!•  Chiral Odd GPDs π0 production is testing ground (Ahmad, GG, Liuti, PRD79,054014 (2009),

Gonzalez, GG, Liuti, arXiv:1201.6088 [hep-ph] )!

•  Simple Spectator -- scalar diquark – ! helicity amps for Pàq ::::: q’àP’ ! Spin simplicity - Pàq+diq and q’+diqàP’ are spin disconnected! => Chiral even related to Chiral odd GPDs!

! !H, E, . . ß helicity amp relations à HT, ET, . . !•  Axial diquark: more complex linear relations ! & distinction between u & d flavors !•  Small x & Regge behavior!•  Bridge through GPD in helicity or transversity to TMDs?!

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Invert to obtain model for GPDs

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A++,-+= - A++,+- A-+,++ = - A+-,++ A++,++ = A++,--

double flip

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k+=XP+ k’+=(X-ζ)P+

P’+=(1- ζ)P+ PX+=(1-X)P+

Vertex Structures

P+ PX+=(1-X)P+

λ

Λ

S=0 or 1

E !"++

*(k ',P ')"

+ # (k,P) +" + #

*(k ', P ')"

+ +(k,P)

First focus e.g. on S=0 pure spectator

H !"+ +

*(k ', P ')"

++(k, P) + "

#+

*(k ',P ')" #+ (k, P)

Vertex functions

λ’

Λ’

QCDII 2012 GR.Goldstein

!H !"++

*(k ',P ')"

++(k,P) #"

#+

*(k ',P ')"#+ (k,P)

!E!"++

*(k ',P ')"

+# (k,P) #"+#

*(k ',P ')"

++(k,P)

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Fitting Procedure e.g. for H and E ✔  Fit at ζ=0, t=0 => Hq(x,0,0)=q(X)

✔  3 parameters per quark flavor (MXq, Λq, αq) + initial Qo

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✔  Fit at ζ=0, t≠0 ⇒

✔  2 parameters per quark flavor (β, p)

✔  Fit at ζ≠0, t≠0 ⇒ DVCS, DVMP,… data (convolutions of GPDs with Wilson coefficient functions) + lattice results (Mellin Moments of GPDs)

✔  Note! This is a multivariable analysis ⇒ see e.g. Moutarde, Kumericki and D. Mueller, Guidal and Moutarde

Regge factor

Quark-Diquark

R = X![!+! '(1!X )p t+" (# )t ]

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Reggeized diquark mass formulation

Where does the Regge behavior come from?

Following DIS work by Brodsky, Close, Gunion (1973)

Diquark spectral function

ρ

MX2

∝ (MX2)α

∝δ(MX2-MX

2)

“Regge”

+ Q2 Evolution

QCDII 2012 GR.Goldstein

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Flexible Parametrization of Generalized Parton Distributions from Deeply Virtual Compton Scattering Observables Gary R. Goldstein, J. Osvaldo Gonzalez Hernandez , Simonetta Liuti arXiv:1012.3776

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Compton Form Factors Real & Imaginary Parts

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Observables

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Note GPD & Bethe-Heitler separate amplitudes -> interference linear in GPD

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Hall B data ALU(90o)

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Hermes data

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-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

10-2

10-1

1 1

Hermes kinematics

x=0.097Q

2=2.5 GeV

2-t=0.118 GeV

2

x=0.097-t=0.118 GeV

2

Q2=2.5 GeV

2

Hermes kinematics

no DVCS

-t (GeV2) Q

2 (GeV

2) x

Bj

10-1

ALU(90o)

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Interference contribution to cos(φ) term in DVCS cross section

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-0.20

0.20.40.60.8

11.2 H+E

HE

Nucleon

J(x,

Q2 =2

GeV

2 )

JD(x)/JN(x)

HD(x)/HN(x)

x

Rat

io D

/N

0.850.9

0.951

1.051.1

1.15

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-0.5-0.25

00.250.5

0.751

1.251.5

u Q2=µ2 Q2=4 GeV2

d Q2=µ2 Q2=4 GeV2

J q(x)

x

L q(x)

-0.6-0.4-0.2

00.20.40.60.8

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Deuteron Spin Sum Rule Taneja, Katuria, Liuti, GG arXiV 2012

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N N

πo

+1,0

+1/2 -1/2

+1/2

+1/2

+1/2

-1/2

-1/2

e.g. f+1+,0-(s,t,Q2)

+1,0

g+1+,0- A++,- -

HT

q nos of C-odd 1- - exchange

1+- exchange b1 & h1

What about coupling of π to q→q′ ? Assumed γ5 vertex Then for mquark=0 has to flip helicity for q→π+q′ and q×q′ ≠ 0. Naïve twist 3 ψbar γ5 ψ Rather than γµγ5 – does not flip twist 2. But q’ γµγ5q will not contribute to transverse γ *. Differs from t-channel approach to Regge factorization

N N

πo

+1/2 -1/2

+1,0 b1 & h1

Exclusive Lepto-production of πo or η, η’ to measure chiral odd GPDs

QCDII 2012 GR.Goldstein

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k+=XP+ k’+=(X-ζ)P+

P’+=(1- ζ)P+ PX+=(1-X)P+

Vertex Structures

P+ PX+=(1-X)P+

Λ

S=0 or 1

E !"++

*(k ',P ')"

+ # (k,P) +" + #

*(k ', P ')"

+ +(k,P)

First focus e.g. on S=0 pure spectator

H !"+ +

*(k ', P ')"

++(k, P) + "

#+

*(k ',P ')" #+ (k, P)

Vertex function

Note that by switching λè- λ & Λ è -Λ (Parity) will have chiral evens go to ± chiral odds giving relations – before k integrations A(Λ’λ’;Λλ)è ±A(Λ’,λ’;-Λ,-λ) but then (Λ’-λ’)-(Λ-λ) ≠(Λ’-λ’)+(Λ-λ) unless Λ=λ

λ’

Λ’

QCDII 2012 GR.Goldstein

!H !"++

*(k ',P ')"

++(k,P) #"

#+

*(k ',P ')"#+ (k,P)

!E!"++

*(k ',P ')"

+# (k,P) #"+#

*(k ',P ')"

++(k,P)

λ

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S=0 Chiral even <-> odd

Invert to get GPDs

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S=1 Chiral even <-> odd

Invert to get GPDs

Chiral odd amplitudes

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-

Which GPDs involved in π0 • Consider t-channel γ* π0 à N+antiN!

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Axial Vector operators (S;L)

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Hence only E~ will enter in p0 but will be suppressed by Dx or x2. Tables: See Lebed & Ji, PRD63,076005 (2001); Diehl & Ivanov, Eur. Phys. Jour. C52, 919 (2007)

}S=1 crossing even

←S=1 crossing odd S=0 crossing even

& S=1 crossing odd

}S=1 crossing odd

S=1 crossing even

S=0 crossing odd & S=1 crossing even

5/15/12 JLab Excl2010 Goldstein

•  2 series for each GPD, space-space or time-space tensor from σµν. µ-> + in light front frame.!

•  Indices become (+,1) or (+,2), so mixtures. !•  see P. Haegler, PLB 594 (2004) 164–170; Z.Chen & X.Ji, PRD 71, 016003 (2005)!

lowest J values have lowest L for N-Nbar states & are nearest meson singularities

5/15/12 36 JLab Excl2010 Goldstein !

HT , ET , ˜ H T ˜ E T

GPDs & JPC • Even and odd under crossing!

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Chiral even ⇔ odd relations •  Helicity amps from ϕ∗q’N’ × ϕqN !

»  With ϕ-q –N = ±ϕ*qN!

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τ = (t0-t)/2M2

HT, ET, !ET, ET

5/15/12

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TotalHT!"#(2H

~T+ET)

H~

T

xBj=0.37 Q2= 2.35 GeV2

T + L

-t (GeV2)

Cro

ss S

ectio

n (n

b/G

eV2 )

10-1

1

10

10 2

0 0.2 0.4 0.6 0.8 1 1.2 1.4

data

h1=HTh1T

perp=H~

TBoer Mulders=2H

~T+ET

x

1st m

omen

t TM

D v

s. G

PDs

-1.5

-1

-0.5

0

0.5

1

10-3

10-2

10-1

1

Hall B data, Kubarovsky& Stoler, PoS ICHEP 2010

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How well do the parameters fixed with DVCS data reproduce πo

electroproduction data?

Hall B data, Kubarovsky& Stoler, PoS ICHEP 2010

5/15/12 41

Transversity amplitudes •  HT(x,0,0) = h1(x) “measures” transfer of transversity!•  | p,+(-)>Ty=[|p,+> +(-)i |p,->]/√2 (y-normal to scattering plane)!•  Or | p,+(-)>Tx=[|p,+> +(-)|p,->]/√2 (x-in plane)!•  Or | p,+(-)>Tx=[|p,+> +(-)eiφ |p,->]/√2 (in transverse plane)!•  ATy

N’,q’;N,q = linear combination of Ahelicity!•  HT ∝ ATy

++,++ - Aty+-,+- - Aty

-+,-+ + Aty--,-- !

•  Diagonal in transversities ⇒ probabilistic interpretation ! w/o b-space!•  Same spin form as TMD h1T(x,kT

2)! h1T (x,kT

2) compare HT(x,0,ΔT2) !

or unintegrated HT(x,0, ΔT2,k) !

!

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TMDs & GPDs

•  f1 !∝ A++,++ + A+−,+− + A−−,−− + A−+,−+! = ATY

++,++ + ATY+-,+- + ATY

--,-- + ATY-+,-+ ~ H !

•  g1L !∝ A++,++ − A+−,+− + A−−,−− − A−+,−+! = ATY

++,-- + ATY+-,+- + ATY

--,++ + ATY-+,-+ ~ H~

!

•  h1T⊥ ∝ A+-,-+ + A-+,+- ~ HT

~ mixture of TY & TX!

•  “T”-odd TMD vs. GPD !•  f1T

⊥ ∝ ATY++,++ + ATY

+-,+- - ATY--,-- - ATY

-+,-+ ~ E!•  h1

⊥ ∝ ATY++,++ - ATY

+-,+- + ATY--,-- + ATY

-+,-+ ~ 2HT~+ET!

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!ET

2 !HT + ET

d

u

(h1T)

A++,+! ! A+!,++ " 2 !HT + ET

A++,!+ ! A!+,++ " E

!m F"+,"#"$ % h1& (x,kT

2 )

!m F+!,#!!$ % f1T& (x,kT

2 )

5/15/12 44

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Conclusions [ Flexible Model GPDs → phenomenology (DVCS & DVMP) [ Spectator models relate Chiral even to Chiral odd GPDs. How far broken? Regge behavior [ Exclusive π0 electroproduction observables (depend on axial vector 1+- exchange quantum numbers) [ GPD HT yield values of δu & δd also have κT

u & κTd

. [  dσT/dt, dσTT/dt, AUT, beam asymmetry, beam-target correlations, dσL/dt, dσLT/dt [  FUTURE: DVCS & π0 along with η, ρ, ω production will narrow range of basic parameters of GPDs, transversity & hadronic spin. [  GPD ⇔ TMDs through transversity

QCDII 2012 GR.Goldstein

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backup slides

QCDII 2012 GR.Goldstein

DVCS Cross Section (Belitsky, Kirchner, Muller, 2002)

Amplitude

y =(P1q)

(P1k1)

! = 2xB

M

Q2

Azimuthal angle between planes

Angle between transverse spin and final state plane

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Comtpon Scattering and Bethe Heitler Processes

Dynamics

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Look for instance at DVCS-BH Interference

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Observables

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more observables

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All GPDs Ahmad, GRG, Liuti, PRD79, 054014 (2009)

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Q2 dependent form factors t-channel view

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see Belitsky, Ji, Yuan (2007) & Ng (2007)

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All GPDs Ahmad, GRG, Liuti, PRD79, 054014 (2009)

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•  delicate interplay among amps, GPDs & Compton Form factor phases. very sensitive to physical parameters – tensor charges, “anomalous transversity”!

•  AUT (sin(Φ-Φs)) AUT’ (sinΦs) α (beam pol’z’n) AUL (“long.”)!

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-0.08!-0.06!-0.04!-0.02!

0!0.02!0.04!0.06!0.08!

0.1!0.12!

0! 0.5! 1! 1.5! 2!

Asymmetries Q^2=3.5, x=0.36!

A_UT!

A_UT'!

alpha!

A_UL!

-0.06!

-0.04!

-0.02!

0!

0.02!

0.04!

0.06!

0.08!

0! 0.5! 1! 1.5! 2!

Asymmetries Q^2=2.5, x=0.25!

A_UT!

A_UT'!

alpha!

A_UL!

QCDII 2012 G.R.Goldstein