Transcript Baryon Resonances

Transition Form Factors at JLab:
The Evolution of Baryonic Degrees of Freedom
Ralf W. Gothe
University of South Carolina
Workshop on Partial Wave Analysis and Dalitz Plot Analysis
January 25-26, 2007
Beijing, China
 Introduction
 N D, N Roper, and N N* Transitions
 1p and 2p Production
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
1
Physics Goals
0.1 – 1.0 fm
<< 0.1fm
?
pQCD
q, g, qq
!
? !
Models
Quarks and Gluons
as Quasiparticles
> 1.0 fm
? !
! ?
ChPT
Nucleon and
Mesons
 Understand QCD in the full strong coupling regime
 transition form factors to nucleon excited states
allow us to study
 relevant degrees-of-freedom
 wave function and interaction of the constituents
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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N
D(1232) Transition Form Factors
Need data at
low Q2
Lattice QCD indicates a
small oblate deformation
of the D(1232) and that the
pion cloud makes E1+ /M1+
more negative at small Q2.
Data at low Q2 needed to
study effects of the pion
cloud.
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Low-Q2 Mutipole Ratios for REM, RSM
C. Alexandrou et al., PRL, 94, 021601 (2005)
REM (%)
Need data at
low Q2
RSM (%)
 Quenched LQCD describes REM within
error bars, but shows discrepancies with
RSM at low Q2 . Pion cloud effects?
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Low-Q2 Mutipole Ratios for REM, RSM
C. Smith
C. Alexandrou et al., PRL, 94, 021601 (2005)
 Significant discrepancy between CLAS
and Bates/MAMI results for RSM.
Ralf W. Gothe
 Quenched LQCD describes REM within
error bars, but shows discrepancies with
RSM at low Q2 . Pion cloud effects?
Nucleon Transition Form Factors
Beijing 2007
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Preliminary Multipole Ratios REM, RSM
Need data at
low Q2
 Data at even lower Q2 are
needed to investigate the pion
cloud further.
 Data at high Q2 are needed to
study the transition to pQCD.
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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(GeV )
Constituent Counting Rule
S11 Q3A1/2
Bowman et al.
F15 Q5A3/2
(LQCD) P11 Q35A1/2
D13 Q A3/2
A1/2 a 1/Q3
A3/2 a 1/Q5
F15 Q3A1/2
* a 1/Q4
GM
D13 Q3A1/2
Quark mass extrapolated to the chiral limit, where q is the momentum variable of
the tree-level quark propagator using the Asquat action.
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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N → D Multipole Ratios REM , RSM
M. Ungaro
 New trend towards pQCD behavior
does not show up.
 REM +1
 G*M
1/Q4
 CLAS12 can measure REM and RSM
up to Q²~12 GeV².
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Roper Electro-Coupling Amplitudes A1/2, S1/2
nr |q3>
LF |q3>
LF |q3>
|q3+qq>
LF |q3>
LF |q3>
|q3+g>
|q3+g>
nr |q3>
|q3+qq>
nr |q3>
PDG estimation
electro-production (UIM,
(UIM, DR)
DR)
pp electro-production
p, 2p combined analysis
Ralf W. Gothe
K. Park (Data)
I. Aznauryan (UIM)
Nucleon Transition Form Factors
Beijing 2007
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S11(1535) Electro-Coupling Amplitudes A1/2, S1/2
LF
LF
LF |q3>
nr |q3>
|q3>
|q3>
nr |q3>
LF |q3>
nr |q3>
nr |q3>
PDG estimation
h production (UIM, DR)
p electro-production (UIM, DR)
K. Park (Data)
I. Aznauryan (UIM)
S11, D13 combined analysis (SQTM)
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Energy-Dependence of p+ Multipoles for P11, S11
I. Aznauryan (UIM)
Q2 = 0 GeV2
Q2 = 2.05 GeV2
The study of some
baryon resonances
becomes easier at
higher Q2.
real part
Ralf W. Gothe
Nucleon Transition Form Factors
imaginary part
Beijing 2007
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Legendre Moments of Structure Functions
CLAS
Q2=2.05GeV2
K. Park
M1- = 0
I. Aznauryan
UIM fit
M1- = 0
The dominating final state
multipole amplitude M1- of
the P11(1440) resonance is at
high Q2 are much more
prominent than at small Q2.
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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J /  pp  n
and
J /  pp  n
BES
Bing-Song Zou
N*(1440): M = 1358 m 17
G = 179 m 56
N*(2050): M = 2068 1540
G = 165 m 42
pN invariant mass / MC phase space
BES/BEPC, Phys. Rev. Lett. 97 (2006)
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Fermion Helicity Conservation
Helicity Conservation
l=l´ for q >> M
(GeV)
Bowman et al.
(LQCD)
Quark mass extrapolated to the chiral limit, where q is the momentum variable of
the tree-level quark propagator using the Asquat action.
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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D13(1520) Helicity Asymmetry
A1/22 – A3/22
Ahel =
A1/22 + A3/22
A1/2
A3/2
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Nucleon Resonances in 2p Electroproduction
Q2 < 4.0GeV2
Trigger
p(e,e’)X
2p channel is sensitive
to N*’s heavier than
1.4 GeV
p(e,e’p)p0
Provides complementary
information to the 1p
channel
p(e,e’p+)n
Many higher lying N*’s
decay preferably to ppN
final states
p(e,e’pp+)p
W in GeV
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Contributing Mechanisms to g p → pp+p(*)
JM05
Isobar Model JM05
Full calculations
gpp-D++
gpp+D0
gpp+D13(1520)
gprp
gpp-P++33(1600)
gpp+F015(1685)
direct 2p production
 Combined fit of various single
differential cross sections allowed to
establish all significant mechanisms
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Resonances in g p → pp+p(*)
CLAS
photo-production
M. Ripani
electro-production
Full calculation
no 3/2+
Background
Resonances
W(GeV)
3/2+(1720)
P?3(1720)
W(GeV)
 N* contributions are much smaller
than non-resonant mechanisms
Ralf W. Gothe
 Full JM05 calculation with and
without the 3/2+(1720) state
Nucleon Transition Form Factors
Beijing 2007
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Resonances and Background in g(*)p → pp+p
CLAS
JM05
Background
Resonances
photo-production
electro-production
Full JM05
no 3/2+
3/2+(1720)
P?3(1720)
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Combined 1p-2p Analysis of CLAS Data
D33(1700)
JM05
D33(1700)
 PDG at Q2=0
 Previous world data
 2p analysis
P13(1720)
P13(1720)
 1p-2p combined at
////Q2=0.65 GeV2
 Many more examples:
////P11(1440), D13(1520), S31(1650),
////S11(1650), F15(1685), D13(1700),
////…
 EBAC at JLab:
////Full coupled channel analysis
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Combined 1p-2p Analysis of CLAS Data
PDG at Q2=0
2p analysis
1p-2p combined at
Q2=0.65 GeV2
Previous world data
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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1p Data Description by N* Electro-Couplings of the Combined Analysis
CLAS
W=1.52 GeV Q2=0.65 GeV2
W=1.68 GeV Q2=0.65 GeV2
JM05
gvp → p0p
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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2p Data Description by N* Electro-Couplings of the Combined Analysis
CLAS
W=1.54 GeV Q2=0.65 GeV2
W=1.66 GeV Q2=0.65 GeV2
JM05
The successful description of all 1p and 2p observables measured with CLAS at
Q2=0.65 GeV2 demonstrates the credibility of the N* background separation.
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
23
Roper Electro-Coupling Amplitudes A1/2, S1/2
CLAS
 PDG at Q2=0
 1p analysis (UIM)
 1p-2p combined at
////Q2=0.65 GeV2
 Newest 2p analysis
////at low Q2 (JM 06)
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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Conclusion: Do Exclusive Electron Scattering
D13(1520)
Q2 = 2.05 GeV2
D13(1520)
... to
Learn QCD!
Ralf W. Gothe
Nucleon Transition Form Factors
Beijing 2007
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