Exclusive Meson ProductionCLAS and CLAS11

Paul Stoler-RPI

Measure electroproduction of mesons above theresonance region (W > 2 GeV) over a large range ofof Q2 and t in the valence quark region of x

Goals of the DVMP Experimental Program

Explore transition from “hadronic” to “partonic” regime by testing model-independent features of reaction mechanisms

Obtain mapping of nucleon structure in terms of quarks and gluons through application of phenomenological models (e.g. handbag).

Physics IssuesQ2 : Size of interaction region probed by virtual photon.

t: Size of interaction region for emission of meson (DVMP) or photon(DVCS)

low Q2 high -t

low -tlow Q2

high Q2 high -t

W>2 GeV High Q2 Low -t Complement DVCS experiment. Unique access to spin dependent GPDs.

W>2 GeV Low Q2 High -t New form factors related to 1/x moments of GPDs

W>2 GeV High Q2 High -t Region never before accessed. Small initial configurations and small reaction size.

W<2 GeV High Q2 - High -t Resonance form factors.

Kinematic regions in electroproduction

ep en

ep ep 0 , 0 ep ep,

Pseudoscalar

CLAS6: lots of data.CLAS12: Exp. # ****

ep en, 0

ep ep0 , 0

ep en , 0

ep en, K K

CLAS6: lots of data.CLAS12: New proposal being preparedfor PAC 38

Vector

No published CLAS6 papersLarge program planned for CLAS12 by RICH group..

ep eY (K ,K 0 ,K ,K*, K1    g g)Strangeness

Scaling of t slopes with Q2

Gluon GPD

Dynamical Mass of Light Dressed Quarks

per dressed quark

Q2 12 GeV➙ 2 p 1.15 GeV➙

LQCD

DSE and LQCD

Pq

Q2 ~ 11 GeV

P. Stoler, Ohio, Jan 8, 2008

Cross sections vs t for different Q2

___ 1.75___ 2.25___.75 2___ 3.25___ 4.75___ 5.25

Q2 (GeV2)

epe’p

~0eBt

B~1 GeV-2 0.2 fm

rho t slope small for low Q2 –larger for large Q2large size to small size

eta same large for all Q2, thereforealways small size

????? New experiment extend t Q2

Structure Functions

GM Laget Regge model-t

ddtd

dT

dt

d L

dt

dTT

dtcos2 2( 1)

d LT

dtcos

*p p 0

Flavor separationAccess to polarized GPDs

EH ~,~

H , E

GPD’s

d LM

dt d( )R(t, )

0

1

        R(t) RVM RV

MgRAM RV

M

RVM (t)

q dx

x 1

1

H q (x, t ) RTM (t)

q dx

x 1

1

Eq (x, t ) RAM (t )

q dx

x 1

1

Hq

(x, t )

s W 2 6.5 GeV2

Q2 1.75 GeV2

ep ep

d/d

sdtd

Q2 (n

b/G

eV6 )

-t (GeV2)

Pseudoscaler Meson Production(Analog to WACS)

(Huang and Kroll)

Factorization of short range hard and long range softonly works for longitudinal photons.

d LM

dt d( )R(t, )

0

1

R(t, ) 1 M f q ( )RVM (t) 1

CFf g ( )RV

Mg (t)

1 M f q ( )RA

M (t)

RVM (t )

q dx

x 1

1

H q (x, t ) RTM (t)

q dx

x 1

1

Eq (x, t ) RAM (t)

q dx

x 1

1

H q(x, t )

s W 2 6.5 GeV2

Q2 1.75 GeV2

ep ep

d/d

sdtd

Q2 (n

b/G

eV6 )

-t (GeV2)

Large angle (high -t) relatively small Q2

(Analog to WACS where handbag works very well)

(Huang and Kroll)

Vector mesons Separate Long Through angular distriburion of the decay products in helicity frame.

Gluon and Quark GPDs

VGG VGG+``D term”

world dataL* p p0

Compare an

GPD n ≈ 2.0

•Kinematics Q2 from 3 – 10 GeV2

•t from .5 to 10 Gev2 W from 2-4 GeV2

•W from 2-4 GeV2

•Run simultaneously with *******

•Simulations for f and r are beginning

•(Isolating K’s over entire kinematic range.)

ep en, K K             ep ep0 , 0

ep en, 0

New PAC38 Proposal (August 2011)

Vector Meson Deep Virtual Exclusive Electroproduction

Conclusion

• We have a very rich program of pseudoscalar meson production which will provide unique information about the transition between soft long-range phenomena and hard short range.

• It will serve as a complementary component of the deep exclusive program at CLAS12, providing

unique access to axial/spin distributions in the nucleon.

• The goal would then be to get a picture of the quark momentum and spin distributions of the nucleons.

Experiments Already Completed

Electroproduction of pat 0.2<0.6, 1.3<1.57GeV Fedotov PRC 79, 015204 (2009)

Measurement of semi-inclusive + electroproduction off the proton Osipenko PRD 80, 032004 (2009)

Exclusive 0 electroproduction on the proton at CLAS, S.Morrow, EPJ A 39, 5 (2009)

Electroproduction of 1020 mesons at 1.4<=Q2<=3.8 GeV^2 measured with the CLAS spectrometer SantoroPRC 78, 025210 (2008) Measurement of ep-->ep0 beam spin asymmetries above the resonance region De Masi PRC 77, 042201 (R) (2008)

Separated Structure Functions for the Exclusive Electroproduction of KL and K0 Final States Ambrozewicz Phys.Rev.C75:045203

Deeply virtual and exclusive electroproduction of omega mesons Morand EPJA 24, 445 (2005)

Exclusive rho0 meson electroproduction from hydrogen at CLAS Hadjidakis PLB 605, 256 (2005)

First Measurement of Transferred Polarization in the Exclusive e(pol)p -> e'K+Lambda (pol) Reaction Carman PRL 90, 131804 (2003)

Measurement of ep -> e'p and baryon resonance analysis Ripani PRL 91, 022002, (2003)

Exclusive electroproduction of F mesons at 4.2 GeV Lukashin PRC 63, 065205 (2001); Err. 64, 059901 (2001)

Electroproduction of the L1520 Hyperon Barrow PRC 64, 044601 (2001)

Measurement of Single and Double Spin Asymmetries in Deep Inelastic Pion Electroproduction with Longitudinally Polarized Target Avakian PRL 105, 262002 (2010)