nov. 25-26, 2010 annual meeting of gdr nucleon - k. park

Nov. 25-26, 2010 Annual Meeting of GDR Nucleon - K. Park

Pert.

hard part

soft part

Successful factorization@ Q2 ∞ , t << fixed


Pert. Pert.

hard part

soft part

What about u <<, DVCS ?

Non-pert. Part does not describe the Hadron Hadron transitionNeed a Transition DA (TDAs)

???

???


Non-pertubative transition between pion and baryon in backward angleInvestigation of Transition Distribution

Amplitude B. Pire, L. Szymanowski PRD71, 111501 (2005)Pert. Pert.

Amplitude = Correlation between meson → transition

Mesonic TDA

pp @ GSI

e+e- B-factories

Large Q2 would provide hard scale with pert. expansion

pp J/ @ GSI

pp t << @ GSI


Non-pertubative transition between pion and baryon in backward angleInvestigation of Transition Distribution

AmplitudeJ.P. Lansberg, B. Pire, PRD75,074004 (2007)

GPD can not describe Non-perturbative part Baryon →π transition

Pert. Pert.

Amplitude = Meson almost stay at rest in the target(baryon) rest frame

Pert.Baryonic TDA

e’n u << , t >> @ CLAS

at 180o @ Hall-C

e’pe’po @ CLAS

JLAB 12GeV

*p pJ/@ COMPASS


• The kinematics imposes the exchange of 3 quarks in the u -channel

• Factorization in the generalized Bjorken limit:

• The object factorized from the hard part is a Transition Distribution Amplitude

• Interpretation at the amplitude

Amplitude of probability to find a meson within the proton

Baryonic TDA


2 2TQ 2 2TQ

2W GeV 2W GeV


Kinematical variables Unpol. CRS w/ one-photon exchange approx.


The CLAS Collaboration

Old Dominion University, Norfolk, VARensselaer Polytechnic Institute, Troy, NY

Rice University, Houston, TXUniversity of Richmond, Richmond, VA

University of Rome Tor Vergata, ItalyUniversity of South Carolina, Columbia, SC

Thomas Jefferson National Accelerator Facility, Newport News, VAUnion College, Schenectady, NY

Virginia Polytechnic Institute, Blacksburg, VAUniversity of Virginia, Charlottesville, VA

College of William and Mary, Williamsburg, VAYerevan Institute of Physics, Yerevan, Armenia

Brazil, Germany, Morocco and Ukraine, , have individuals or groups involved with CLAS,

but with no formal collaboration at this stage.

Arizona State University, Tempe, AZUniversity Bari, Bari, ItalyUniversity of California, Los Angeles, CACalifornia State University, Dominguez Hills, CACarnegie Mellon University, Pittsburgh, PACatholic University of AmericaCEA-Saclay, Gif-sur-Yvette, FranceChristopher Newport University, Newport News, VAUniversity of Connecticut, Storrs, CTEdinburgh University, Edinburgh, UKUniversity Ferrara, Ferrara, ItalyFlorida International University, Miami, FLFlorida State University, Tallahassee, FLGeorge Washington University, Washington, DCUniversity of Glasgow, Glasgow, UK

University of Grenoble, Grenoble, France Idaho State University, Pocatello, Idaho

INFN, Laboratori Nazionali di Frascati, Frascati, ItalyINFN, Sezione di Genova, Genova, Italy

Institut de Physique Nucléaire, Orsay, FranceITEP, Moscow, Russia

James Madison University, Harrisonburg, VAKyungpook University, Daegu, South KoreaUniversity of Massachusetts, Amherst, MA Moscow State University, Moscow, Russia

University of New Hampshire, Durham, NHNorfolk State University, Norfolk, VA

Ohio University, Athens, OH


CLAS

Emax 6 GeV Imax 200 A

Duty Factor 100% E/E 2.5 10-5

Beam P ~ 85%Eg(tagged) ~ 0.8-5.5GeV

e-

π+

e-


Kinematical variables Unpol. CRS w/ one-photon exchange approx.


Particle Identification

Acceptance Calculation

Radiative Correction

Background Subtraction

Kinematical Correction

Extract CRS & structure functionsAcceptance cross check after more simulation in backward angle with Modification of GENEV vs. FSGEN

Bin corrections

Systematic error studies

E1-6 data set was used.

E0=5.754GeV, B =3375A, LH2

…….


1. No (s-) resonance access (= no event below 2GeV of W)

2. No missing mass cut


1. No (s-) resonance access (= no event below 2GeV of W)

2. No missing mass cut

3. Automatically, accessible small -u large –t

u

t


Requirement

W>2GeV


Requirement

W>2GeVcos* <0.0T

2 <0.5GeV 2


Requirement

W>2GeVcos* <0.0T

2 <0.5GeV 2

TOF mass 3sigma cut


Requirement

W>2GeVcos* <0.0T

2 <0.5GeV 2

TOF mass 3sigma cut : 2sigma cut


Blue bullets : _T2 < 0.5GeV2 cut

Red hist. : _T2 < 1.0GeV2 cut

u

t

cos *Nov. 25-26, 2010 Annual Meeting of GDR Nucleon - K.

Park

Black bullets : exp. Data before BG subtraction

Red bullets : exp. Data before BG subtraction

Blue solid lines : nominal MMx 3 cut


Blue bullets : exp. Data after BG subtraction

Red hist. : GPP + w/o (left) & with (right) correction applied MC


1. Two event generators were tested

2. cos cut was applied on top of T

2 cut


1. Two event generators were tested

2. cos cut was applied on top of T

2 cut

Nov. 12, 2010 DPWG K. Park

W>2GeVMMx cutcos* <0.0T

2 <0.5GeV 2


W>2GeV

T2 <1.0GeV

2

+ GPP+corr.T

2 <0.5GeV 2

MMx cut


Blue square : data with stat. err. only

Red triangle : fit with cos2

Average Chi2 ~ 1.74

except last Q2 bin


σT+εσL σT+εσL


σT+εσL σT+εσL

J.P. Lansberg, B. Pire, PRD75,074004 (2007)But 0 – calculation for

=0.8, =180o


σT+εσL σT+εσL

< 1/2 < 1/2

~1

- range is about 0.4-0.7


• Hard exclusive process of meson in the backward angle opens a new window in the understand of hadronic physics in the framework of the collinear-factorization approach of QCD.

• Measurement of cross sections and asymmetries are crucial to develop a realistic model for the TDAs.

• Careful study has been performed by communicating with theory group (kinematic binning, corrections, acceptance(GENEV/FSGEN), cuts, etc.)

• We measured the differential cross sections on backward angle in the kinematic range of W > 2GeV, high “t” and low “u”.

• We extracted the structure functions from differential cross sections,

TT has a similar amplitude of LT

T+ L is ~2x larger than TT and LT . Open questions ?


Thank you ! Questions/comments ?


Black bullets : exp. Data before BG subtraction

Red bullets : exp. Data before BG subtraction

Blue solid lines : nominal MMx 3sigma cut


W>2GeV

T2 <0.5GeV

2

+ 18 bins of

MMx cut

T2 <0.5GeV

2

+ 9 bins of


W>2GeVT

2 <0.5GeV 2

MMx : +/- 4 cut MMx : +/- 2 cut


nov. 25-26, 2010 annual meeting of gdr nucleon - k. park

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