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Pert.
hard part
soft part
Successful factorization@ Q2 ∞ , t << fixed
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Pert. Pert.
hard part
soft part
What about u <<, DVCS ?
Non-pert. Part does not describe the Hadron Hadron transitionNeed a Transition DA (TDAs)
???
???
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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
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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
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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
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• 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
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2 2TQ 2 2TQ
2W GeV 2W GeV
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2 2TQ 2 2TQ
2W GeV 2W GeV
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Kinematical variables Unpol. CRS w/ one-photon exchange approx.
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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
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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
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e-
π+
e-
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Kinematical variables Unpol. CRS w/ one-photon exchange approx.
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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
…….
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1. No (s-) resonance access (= no event below 2GeV of W)
2. No missing mass cut
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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
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Requirement
W>2GeV
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Requirement
W>2GeVcos* <0.0T
2 <0.5GeV 2
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Requirement
W>2GeVcos* <0.0T
2 <0.5GeV 2
TOF mass 3sigma cut
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Requirement
W>2GeVcos* <0.0T
2 <0.5GeV 2
TOF mass 3sigma cut : 2sigma cut
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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
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Black bullets : exp. Data before BG subtraction
Red bullets : exp. Data before BG subtraction
Blue solid lines : nominal MMx 3 cut
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Blue bullets : exp. Data after BG subtraction
Red hist. : GPP + w/o (left) & with (right) correction applied MC
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1. Two event generators were tested
2. cos cut was applied on top of T
2 cut
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1. Two event generators were tested
2. cos cut was applied on top of T
2 cut
Nov. 12, 2010 DPWG K. Park
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W>2GeVMMx cutcos* <0.0T
2 <0.5GeV 2
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W>2GeV
T2 <1.0GeV
2
+ GPP+corr.T
2 <0.5GeV 2
MMx cut
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Blue square : data with stat. err. only
Red triangle : fit with cos2
Average Chi2 ~ 1.74
except last Q2 bin
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σT+εσL σT+εσL
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σT+εσL σT+εσL
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σT+εσL σT+εσL
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σT+εσL σT+εσL
J.P. Lansberg, B. Pire, PRD75,074004 (2007)But 0 – calculation for
=0.8, =180o
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σT+εσL σT+εσL
< 1/2 < 1/2
~1
- range is about 0.4-0.7
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• 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 ?
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Thank you ! Questions/comments ?
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Black bullets : exp. Data before BG subtraction
Red bullets : exp. Data before BG subtraction
Blue solid lines : nominal MMx 3sigma cut
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Black bullets : exp. Data before BG subtraction
Red bullets : exp. Data before BG subtraction
Blue solid lines : nominal MMx 3sigma cut
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Black bullets : exp. Data before BG subtraction
Red bullets : exp. Data before BG subtraction
Blue solid lines : nominal MMx 3sigma cut
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Black bullets : exp. Data before BG subtraction
Red bullets : exp. Data before BG subtraction
Blue solid lines : nominal MMx 3sigma cut
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Black bullets : exp. Data before BG subtraction
Red bullets : exp. Data before BG subtraction
Blue solid lines : nominal MMx 3sigma cut
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W>2GeV
T2 <0.5GeV
2
+ 18 bins of
MMx cut
T2 <0.5GeV
2
+ 9 bins of
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W>2GeVT
2 <0.5GeV 2
MMx : +/- 4 cut MMx : +/- 2 cut
Nov. 25-26, 2010 Annual Meeting of GDR Nucleon - K. Park