1Ralf W. Gothe

Basic Tools: Experiment and Theory Goals: Unveil the dynamics of the strong interaction Connections: Not everything is difficult that sounds difficult

Ralf W. Gothe

Users Group Workshop and Annual MeetingJune 8-10, 2009

Jefferson Lab, Newport News, VA

Roadmap to the CLAS12 Physics Program

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A B C

Jefferson Lab Today

Two high-resolution 4 GeV spectrometers

Large acceptance spectrometer electron/photon beams

7 GeV spectrometer 1.8 GeV spectrometer

Hall A Hall B

Hall C

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6 GeV CEBAF11

CHL-2CHL-2

12

Upgrade magnets Upgrade magnets and power and power suppliessupplies

Two 0.6 GeV linacs1.1

Enhanced capabilities in existing Halls

1.1

4Ralf W. Gothe

Overview of Upgrade Technical Performance Requirements

Hall D Hall B Hall C Hall A4 hermetic detector

GlueExluminosity 1035

CLAS12High Momentum

Spectrometer SHRSHigh Resolution

Spectrometer HRS

polarized photons hermeticity precision space

E~ 8.5-9.0GeV 11 GeV beamline

108 photons/s target flexibility

good momentum/angle resolution excellent momentum resolution

high multiplicity reconstruction luminosity up to 1038

.

5Ralf W. Gothe

CLAS12

Luminosity > 1035 cm-2s-1

Baryon Spectroscopy N and N* Form Factors GPDs and TMDs DIS and SIDIS Nucleon Spin Structure Color Transpareny …

Central Detector

Forward Detector

1m

CLAS12

6Ralf W. Gothe

CLAS12 Approved ExperimentsProposal Contact Person Physics Energy

(GeV)PAC days Parallel

RunningRun Group days Comment

E12-09-103 Gothe, Mokeev N* at high Q2 11 60

80

20

20

120

E12-06-119(a) Sabatie DVCS pol. beam 11 80

E12-06-112 Avakian ep→eπ+/-/0 X 11 60

E12-06-108 Stoler DVMP in π0,η prod

L/T separation

11 80

8.8

6.6

20

20

E12-06-119(b) Sabatie DVCS pol. target 11 120 120

50

5

175

Assume polarized

experiments run 50% of

time w/ reversed field

E12-06- 109 Kuhn Long. Spin Str. 11 82

E12-07-107 Avakian TMD SSA 11 103

E12-09-007(b) Hafidi Partonic SIDIS 11 103

E12-09-009 Avakian Spin-Orbit Corr. 11 103

E12-06-106 Hafidi Color Trans. ρ0 11 40 40 40

E12-06-117 Brooks Quark Hadronizat. 11 60 60 60

E12-06-113 Bültman Neutron Str. Fn. 11 40 40 40 cond. appr.

E12-07-104 Gilfoyle Neutron mag. FF 11 56 56

26

82

007/008 need 26d reversed

fieldE12-09-007(a) Hafidi Partonic SIDIS 11 56

E12-09-008 Contalbrigo Boer-Mulders w/ Kaons 11 56

Total 1139 517

7Ralf W. Gothe

quar

k m

ass

(GeV

)

Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asqtad action.

… resolution

low

high

q

e.m. probe

LQCD (Bowman et al.)

Physics Goals

N,N*,*…

3q-core+MB-cloud

3q-core

pQCD

LQCD, DSE and …

Study the structure of the nucleon spectrum in the domain where dressed quarks are the major active degree of freedom.

Explore the formation of excited nucleon states in interactions of dressed quarks and their emergence from QCD.

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Hadron Structure with Electromagnetic Probes

v N

p

p

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Hadron Structure with Electromagnetic Probes

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Cross Section Decomposition

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What do we really know?

Spectroscopy

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Quark Model Classification of N*

(1232)

D13(1520)S11(1535)

Roper P11(1440)

+ q³g

+ q³qq

+ N-Meson

+ …

16Ralf W. Gothe

“Missing” Resonances?

fewer degrees-of-freedom open question: mechanism for q2 formation?

Problem: symmetric CQM predicts many more states than observed (in N scattering) Possible solutions: 1. di-quark model

2. not all states have been found

possible reason: decouple from N-channel model calculations: missing states couple to N, N, N, KY

3. coupled channel dynamicsall baryonic and mesonic excitations beyond the groundstate octets and decuplet are generated by coupled channel dynamics (not only (1405), (1520), S11(1535) or f0(980))

old but always young

new

17Ralf W. Gothe

Process described by 4 complex, parity conserving amplitudes 7 well-chosen measurements are needed to determine amplitude. For hyperon finals state 16 observables will be measured in CLAS huge ➠redundancy in determining the photo-production amplitudes allows many ➠cross checks. 7 observables measured in reactions without recoil polarization.

weak decay has large analyzing power

γp→K+Λ

FROST/HD N N’, N, K, K, N

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Quasi-Real Electroproduction

Meson spectroscopy:exotic, high t, coherent, J/

Baryon spectroscopy:heavy mass N*, hyperons

Time-like Compton scattering: GPDs, …

20Ralf W. Gothe

Quasi-Real Electroproduction

Meson spectroscopy:exotic, high t, coherent, J/

Baryon spectroscopy:heavy mass N*, hyperons

Time-like Compton scattering: GPDs, …

DDVCS?

pXeeep

Missing momentum analysis

of all final state particles

Double Deep Virtual Compton scattering

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Photoproduction of Lepton Pairs

’e+e-

Mee > 1.2 GeV for TCS analysis

CLAS/E1-6 CLAS/G7

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Color Transparency Color Transparency is a spectacular prediction of QCD: under the right

conditions, nuclear matter will allow the transmission of hadrons with reduced attenuation.

Unexpected in a hadronic picture of strongly interacting matter, but straightforward in quark gluon basis.

Small effects observed at lower energy. Expect significant effects at higher energy.

CLAS12 projected

A

e+

e-

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Dynamical Mass of Light Dressed Quarks

DSE and LQCD predict the dynamical generation of the momentum dependent dressed quark mass that comes from the gluon dressing of the current quark propagator.

These dynamical contributions account for more than 98% of the dressed light quark mass.

The data on N* electrocouplings at 0<Q2<12 GeV2 will allow us to chart the momentum evolution of dressed quark mass, and in particular, to explore the transition from dressed to almost bare current quarks as shown above.

Q2 = 12 GeV2 = (p times number of quarks)2 = 12 GeV2 p = 1.15 GeV

per dressed quark DSE: lines and LQCD: triangles

24Ralf W. Gothe

S11 Q3A1/2

F15 Q5A3/2

P11 Q3A1/2

D13 Q5A3/2

F15 Q3A1/2

D13 Q3A1/2

Constituent Counting Rule

A1/2 1/Q3

A3/2 1/Q5

GM 1/Q4*

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N → Multipole Ratios REM , RSM

New trend towards pQCD behavior does not show up.

CLAS12 can measure REM and RSM up to Q²~12 GeV².

REM +1

M. Ungaro

GM 1/Q4*

GD = 1

(1+Q2/0.71)2

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Electrocouplings of N(1440)P11 from CLAS Data

N (UIM, DR)PDG estimation N, N combined analysis N (JM)

The good agreement on extracting the N* electrocouplings between the two exclusive channels (1/2) – having fundamentally different mechanisms for the nonresonant background – provides evidence for the reliable extraction of N* electrocouplings.

27Ralf W. Gothe

Electrocouplings of N(1520)D13 from the CLAS 1/2 data

world data

10-3 G

eV-1

/2

N (UIM, DR)PDG estimation N, N combined analysis N (JM)

Ahel = A1/2

2 – A3/22

A1/22 + A3/2

2

A1/2

A3/2

L. Tiator

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Kinematic Coverage of CLAS12

60 daysL= 1035 cm-2 sec-1, W = 0.025 GeV, Q2 = 0.5 GeV2

Genova-EG (e’,p) detected

W GeV

Q2 G

eV2 2 limit > 1 limit >

2 limit > 1 limit >

1 limit >

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Proton Electromagnetic Form Factors

green : Rosenbluth data (SLAC, JLab)

Pun05Gay02

JLab/HallA recoil polarization data

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Quark Transverse Charge Densities in Nucleons

longitudinally polarized nucleon

q+ = q0 + q3 = 0

photon only couples to forward moving quarks

quark charge density operator

p’p

z

Light-Front Formalism

Miller

(2007)

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transversely polarized nucleon

transverse spin

e.g. along x-axis :

dipole field pattern Carlson, Vanderhaegen (2007)

Quark Transverse Charge Densities in Nucleons

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data : Arrington, Melnitchouk, Tjon (2007)

densities : Miller (2007); Carlson, Vdh (2007)

induced EDM : dy = F2p (0) . e / (2 MN)

ρ0

ρT

Quark Transverse Charge Densities in the Proton

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p nn p -> + (1232) p -> N* (1440)

quadrupole pattern Tiator, Vdh (2008)Carlson, Vdh (2007)

Transverse Transition Densities

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p -> D13(1520)

Tiator, Vdh (2009)

ρ0

ρT

Transverse Transition Densities

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Elastic Scatteringtransverse quark distribution

in coordinate space

DISlongitudinal quark distribution

in momentum space

DES (GPDs)fully-correlated quark

distribution in both coordinate and momentum space

3-dim quark structure of nucleon3-dim quark structure of nucleonBurkardt (2000,2003)

Belitsky,Ji,Yuan (2004)

GGeneralizedeneralized P Partonarton D Distributionsistributions

37Ralf W. Gothe

Fourier transform of GPDs gives simultaneous distributions of quarks w.r.t. longitudinal momentum x P and transverse position b

P + Δ/2

*Q2 >>

x + ξ

x - ξP - Δ/2

t = Δ2

ξ = 0

GGeneralizedeneralized P Partonarton D Distributionsistributions

H,H,E,E (x, ξ ,t)~ ~

GPDs

38Ralf W. Gothe

DVCS Kinematics Coverage of the 12 GeV Upgrade

H1, ZEUS

JLab Upgra

de

11 GeV

H1, ZEUS

JLab @

12 G

eV11 GeV27

GeV

200 G

eV

W =

2 G

eV

Study of high xB domain requires high luminosity

HERMES

COMPASS

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Unpolarized beam, longitudinal target:

ULUL~~ sinsin {F {F11HH++ξξ(F(F11+F+F22)()(HH ++ξξ/(1+/(1+ξξ))EE) -) -

… … }d}d

~~

Kinematically suppressed

H(ξ,t)~

A =

=ξ ~ xB/(2-xB)

k = t/4M2

Unpolarized beam, transverse target:UTUT~ cos~ cossin(sin(ss--)){k(F{k(F22HH – – FF11EE) ) + …+ … }d}d

Kinematically suppressed

E(ξ,t)

How to Extract GPDs ?How to Extract GPDs ?

H(ξ,t)

Polarized beam, unpolarized target:

LULU~~ sinsin {F {F11HH++ξξ(F(F11+F+F22))HH ++kFkF2EE))}d}d ~~

Kinematically suppressed

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DVCS Polarized Beam Asymmetry

2/25/092/25/09 4040Volker Burkert, CLAS12 Workshop, GenoaVolker Burkert, CLAS12 Workshop, Genoa

e p ep

A =

=

LU~sin{F1H+…}d

Extract H(ξ,t)

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DVCS Longitudinal Target Asymmetry

e p ep

UL~sinIm{F1H+ξ(F1+F2)H...}d~

Extract H(ξ,t)~

2/25/092/25/09 4141Volker Burkert, CLAS12 Workshop, GenoaVolker Burkert, CLAS12 Workshop, Genoa

e p ep

A =

=

42Ralf W. Gothe

Transverse Momentum Distributions

TMDs are complementary to GPDs in that they allow to construct TMDs are complementary to GPDs in that they allow to construct 3-D images of the nucleon in of the nucleon in momentum space space

TMDs can be studied in TMDs can be studied in SIDISSIDIS experiments measuring azimuthal experiments measuring azimuthal asymmetries or moments.asymmetries or moments.

Semi Inclusive Deep Inelastic Scattering

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TMDs in SIDIS Land

Many spin asymmetries

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TMDs in SIDIS Land

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The cos2 moment of the azimuthal asymmetry gives access to the Boer-Mulders function, which measures the momentum distribution of transversely polarized quarks in unpolarized nucleons..

4 <Q2< 5 GeV2

TMDs in SIDIS Land

46Ralf W. Gothe

The sin2 moment gives access to the Kotzinian-Mulders function, which measures the momentum distribution of transversely polarized quarks in the longitudinally polarized nucleon.

TMDs in SIDIS Land

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per dressed quark

Summary and Outlook