i. g. aznauryan jefferson lab yerevan physics institute october 13, 2008, jlab
DESCRIPTION
Electroexcitation of P 11 (1440), D 13 (1520), and S 11 (1535) from CLAS data and quark model predictions. On the definitions of the g * p N * helicity amplitudes. I. G. Aznauryan Jefferson Lab Yerevan Physics Institute October 13, 2008, Jlab - PowerPoint PPT PresentationTRANSCRIPT
I. G. Aznauryan
Jefferson Lab Yerevan Physics Institute
October 13, 2008, Jlab Electromagnetic N-N* Transition Form Factors Workshop
Electroexcitation of P11(1440), D13(1520), and S11(1535)
from CLAS data and quark model predictions.On the definitions of the p N* helicity
amplitudes
Results on the pP11(1440), D13(1520), S11(1535) helicity amplitudes extracted from CLAS andelectroproduction data, comparison with earlier data
Correct definition of the amplitudes : very important as Q2 dependence of the NN* amplitudes extracted in wide region of Q2 is highly sensitive to different description of N and N* : - 3q picture - additional qq components - hybrid q3G states - resonances dynamically generated in N interaction - results of lattice QCD Comparison with quark model predicions Summary
Outline
CLAS: the eNeN data
Q2 = 0.4, 065 GeV2
epeN 14 863 data points:
K. Joo et al., PRL 88 (2002) 122001 PR C68 (2003) 032201 PR C70 (2004) 042201H.Egiyan et al., PR C73(2006) 025204
Analysis: DR, UIM
I.Aznauryan et al., PR C71 (2005) 015201 PR C72 (2005) 045201
Q2 = 1.72, 2.05, 2.44, 2.91, 3.48, 4.16 GeV2
epeN 36 300 data points:
K. Park et al., PR C77 (2008) 015208
Analysis: DR, UIM
I.Aznauryan et al., nucl-exp/0804.0447, will appear in PRC
CLAS: the epep data
Q2 = 0.65 GeV2
Combined analysis of epepepepdata:
I.Aznauryan, V.Burkert, V.Mokeev et al., PR C72 (2005) 045201
Q2 = 0.275, 0.325, 0.375, 0.425, 0.475, 0.525, 0.575 GeV2
Data:
G.Fedotov,V.Mokeev, V.Burkert,… nucl-ex/0809.1562
Analysis:
V.Mokeev, V.Burkert, J.Phys. Conf.Ser. 69 (2007) 012019;Proc. of NSTAR2007, p. 76
Helicity amplitudes of the p P11 (1440) transition
N
CLAS data :
PDG
First measurements of A1/2 at Q2 > 0
NNcombined
Npreliminary
pp M.Dugger et al.,PR C76 025211,2007
First measurements of S1/2
Helicity amplitudes of the p S11 (1535) transition
N
CLAS data :
PDG
pp M.Dugger
First measurements of S1/2 :
Results for A 1/2 obtained in and production agree with each other with PDG:
N
it is difficult to extract S1/2 in electroproduction
Slow falloff of A1/2 observed in production is confirmed by data
Helicity amplitudes of the p D13(1520) transition
N
CLAS data :
NNcombined
Npreliminary
Old data:Bonn, DESY, NINA
PDG
pp M. Dugger
First definite results for A 1/2 , A 3/2 in wide range of Q2
First measurements of S1/2
Definitions: common sign of the p N* amplitudes
In the analyses of N N data, the p N* helicity amplitudes are defined through reaction multipole amplitudes. For example, for p P11(1440) in p p
we have:
This definition contains information on signs of two vertices NN* and N*N :
gN*N)
N*N1/2N* NN
Common sign of the p N* amplitudes (con-d)
Definition of A1/2 in theoretical approaches :
N* NN
N*N*)
*
Depends on the phase of N*
Contains information on the N N* vertex only
Common sign of the p N* amplitudes (con-d)
Commonly used definition of A1/2 in quark model
is :
A1/2 sign NN*
R.L.Walker, Proc. of IV Int. Symp. on Electron-Photon Inter. at High Energies, Liverpool (1969), p. 21.
In QM, traditionally, the sign NN* was chosen to describe the sign of the experimental A1/2 amplitude for Q2=0; sometimes this can bring to confusing and wrong results
Possibly, it will be right to make some changes in conventions to avoid this confusion, for example, to reflect in the amplitude extracted from experiment the final state: A AN, …?
Common sign of the p N* amplitudes (con-d)
We need explicit formulas, how to account for the relativesign of the contributions :
Res.:
Bornterms:
I.Aznauryan, V.Burkert, H.Lee, nucl-th/0810.0997
Through covariant calculations, we have obtained the relations:
For example, for P11 (1440) :
, if
Definition of the p N* amplitudes (con-d)
In this way, we have also checked, which definition ofgives the sign consistent with the relative sign of the amplitudesextracted from experiment, i.e. S1/2 relatively to A1/2, A3/2
We have presented different definitions of A1/2, A3/2, S1/2 : Through the N N multipole amplitudes
Through the N N* electromagnetic current
Through the N N* form factors
In nonrelativistic quark model
These definitions are consistent with each other, and may be useful in theoretical calculations
Common sign of the p N* amplitudes (con-d)
For the resonances of [70,1- ] –plet, common signs of the
p N* amplitudes in quark model were found
(using PCAC for the N N* vertex) by Aznauryan, Bagdasaryan, Sov.J.Nucl.Phys. 41 (1985) 158
For all resonances, except D13(1700), traditionally used sign is right
For P11(1440), sign of the p N* amplitudes was found
using 3Po model for the N N* vertex by
Capstick, Keister, PR D51 (1995) 3598
using PCAC for the N N* vertex by Aznauryan, PR C76 (2007) 025212
Signs forp P11 (1440)
Light-front RQM Capstick, Keister (1995) Weber, PR C41 (1990)2783 Simula… PL B397 (1997)13 NRQM Warns… Z.Phys. C45 (1990)627 Giannini… J.Phys. G24 (1998)753
1. strong model dependence 2. for some models strong disagreement with experiment
Corrected signs1. less model dependence 2. better agreement with exp.
Signs taken in ‘traditional way’
p P11 (1440): 3q picture with P11 (1440) as [56,0+]r
LF RQM:
Weber, PR C41 (2783) 1990
Capstick, Keister, PR D51 (1995) 3598
Pace, Simula et.al., PR D51 (1995) 3598
Aznauryan, PR C76 (2007) 025212
All LF RQM describe
sign change of A1/2 the amplitude S1/2 Strong evidence
in favor of P11 (1440) as a firstradial excitation of3q ground state
All LF RQM fail to describe
the amplitude A1/2 at Q2 < 1 GeV2
P11 (1440): Additional components and contributions
Pion cloud
EBAC (preliminary)
Julia-Diaz et.al.,
PR C77(2008)045205
30% admixture of qqqqq components in the Roper resonance (theory) = (exp) :
Li, Riska, PR C74(2006)015202
Pion cloud contributions and additional qqqqq components in the Roper resonance can improve the description at small Q2
P11 (1440) as a q3G hybrid state
Supression of S1/2 has its origin in the form of the vertex *q qG; it is practically independent ofrelativistic effects
P11 (1440) as qG:Li, Burkert,Li, PR D46 (1992) 70
P11 (1440) as q3Ghybrid state is ruled out !!!
p D13 (1520): 3q picture + pion cloud
Pion cloud: EBAC (preliminary)
Significant contribution at small Q2 for A3/2
In 3q picture, the signsof all amplitudes are described; however, this picture fails to describe A3/2 at small Q2
Nonrelativistic approaches: Warns et al., Z.Phys.C45(1990)627
Aiello et.al., J.Phys.G24 (1998)753
Merten…, Eur.Phys.J.A14 (2002)477
p S11 (1535): 3q picture
Opposite sign
of S1/2!!!
LF RQM:
Capstick, Keister,
PR D51 (1995) 3598
Pace, Simula et.al.,
PR D51 (1995) 3598
Combined with the difficultiesin the description of large width of S11(1535) N and largeS11(1535) N,K couplings, this shows that 3q picture for S11(1535) should be complemented
Impossible to change in quark
model !!!
S11 (1535): Additional components and contributions
Pion cloud: EBAC (preliminary), MAINZ
qq (mostly ss) : An,Zou , nucl-th/0802.3996
sign should be consistent with the interference of (uu,dd) and ss components in (S11 (1535)p)
It is possible that agreement of 3q picture with experimental data will be achieved by taking into account pion cloud contribution and additional qqqqq components in S11(1535)
Summary
For the first time transverse and longitudinal amplitudes of the p P11(1440) transition are extracted from experiment for Q2 > 0 in wide range of Q2 For the first time longitudinal amplitudes of the p D13(1520), S11(1535) transitions are extracted from
experiment, and in wide range of Q2
For the first time definite results are obtained for the transverse amplitudes of the p D13(1520) transition in wide range of Q2 The results for the p S11(1535) transverse
amplitude extracted from and electroproduction data are consistent with each other
Summary: P11(1440)
The results for p P11(1440) available in wide region
of Q2 allow us to make conclusions on the nature of P11(1440):
Comparison with quark model predictions provides strong evidence in favor of P11(1440) as a first radial excitation of the 3q ground state
Presentation of P11(1440) as a q3G hybrid state is ruled outQuark model predictions underestimate the value of A1/2
at small Q2 Pion cloud contributions and additional qq components
in the Roper resonance can improve description of A1/2
at small Q2
Summary: D13(1520), S11(1535)
Quark models describe the signs of all amplitudes for the p D13(1520) transition
There is significant underestimation at small Q2 for A3/2 which apparently is related to the pion cloud contribution Quark models predict opposite sign for the S1/2
amplitude of the p S11(1535) transition !!! Combined with the difficultiesin the description of couplings to hadronic channels, this shows that 3q picture for S11(1535) should be complemented
Apparently, agreement of 3q picture with experimental data can be achieved by taking into account pion cloud contribution, and additional qqqqq components in S11(1535)
Summary: definitions of the N N* amplitudes
The N N* amplitudes extracted from the experimental data on the N Nreaction are related to the N N* amplitudes calculated in theoretical approaches through the sign of the NN* vertexPossibly, it makes sense to introduce new conventions in orderto avoid confusion caused by this fact
S11 (1535) as a dynamically generated resonance
Dynamically generated S11 (1535):Oset… , nucl-th/0712.0038
sign should be checked via calculation of the vertex S11 (1535)N in addition to p S11 (1535)
For both signs, presentation of S11 (1535) as only dynamicallygenerated resonance is ruled out.However, it is interesting to investigate the possibility of the dynamically generated resonance as a component additional to 3q state.