The strange properties of the nucleon are investigated within the framework
of the SU(3) chiral quark-soliton model assuming isospin symmetry and applying
the symmetry conserving SU(3) quantization. We present the form factors
$G^0_{E,M}(Q^2)$, $G^Z_M(Q^2)$ and the electric and magnetic strange form
factors $G^s_{E,M}(Q^2)$ incorporating pion and kaon asymptotics. The results
show a fairly good agreement with the recent experimental data from the SAMPLE
and HAPPEX collaborations. We also present predictions for future measurements
including the A4 experiment at MAMI (Mainz).Comment: 10 pages with four figures. RevTeX4 is used. Few lines are changed.
  Accepted for publication in Phys.Rev. 

António Silva

B. Mueller

B.-Q. Ma

C.V. Christov

D. Diakonov

D.B. Kaplan

D.B. Leinweber

D.E. Groom

H. Forkel

H. Weigel

H.-Ch. Kim

H.-W. Hammer

Hyun-Chul Kim

K.A. Aniol

Klaus Goeke

L. Hannelius

M. Praszalowicz

M.J. Musolf

N. Mathur

N.W. Park

R. Alkofer

R. Hasty

R.L. Jaffe

S. Hong

T.R. Hemmert

Ulf-G. Meißner

English

arXiv

We present the recent results of the strange vector form factors of the nucleon within the framework of the SU(3) chiral quark-soliton model. We compare our results with the recent experimental data of the SAMPLE and HAPPEX collaborations and find that they are in a good agreement with the data. We also predict the future experiments of the A4, HAPPEX-II and G0 collaborations.http://www.sciencedirect.com/science/article/B6TVB-49H6B0H-2T/1/933b74771f888904c55d466516e9522

Silva, Antonio

Kim, Hyu-Chul

Goeke, Klaus

Estudo Geral

Strange vector form factors in the context of the SAMPLE, A4, HAPPEX and G0 experiments

ELSEVIER Nuclear Physics A72 1 (2003) 4 17c-420~ 
www.elsevier.com/locate/npe 
Strange vector form factors in the context of the SAMPLE, A4, 
HAPPEX and GO experiments 
Antonio Silvaab, Hyun-Chul Kim” and Klaus Goeke” 
a Institut fur Theoretische Physik II, Ruhr-Universitlt Bochum, 
D-44780 Bochum, Germany 
b Departamento de Fisica and Centro de Fisica Computational, 
Universidade de Coimbra, P-3000 Coimbra, Portugal 
CDepartment of Physics, Pusan National University, 
609-735 Pusan, Republic of Korea 
We present the recent results of the strange vector form factors of the nucleon within 
the framework of the SU(3) chiral quark-soliton model. We compare our results with 
the recent experimental data of the SAMPLE and HAPPEX collaborations and find that 
they are in a good agreement with the data. We also predict the future experiments of 
the A4, HAPPEX-II and GO collaborations. 
The strange vector form factors of the nucleon have been a hot issue recently, as their 
first measurement was conducted by the SAMPLE collaboration [l-3] at MIT/Bates, 
parity-violating electron scattering being used. The HAPPEX collaboration at JLAB also 
announced the measurement of the strange vector form factors [4]. The A4 collaboration 
at MAMI in Mainz will soon bring out new measurements and the HAPPEX-II and GO 
experiments at JLAB are being preprared. 
There has been a great deal of theoretical attempts to predict the strange vector form 
factors, differing by the methods employed to investigate the non-perturbative physics 
behind them. In a recent review [5], many of theoretical works were reviewed. 
We shall use the chiral quark-soliton model (xQSM) as our theoretical framework. 
It is an effective quark theory based on the instanton vacuum of QCD and results in 
a Lagrangian for valence and sea quarks interacting via a static self-consistent pseudo- 
Goldstone background field. The xQSM has been successful in describing the electromag- 
netic and axial-vector form factors [6] in SU(2) and the forward and generalized parton 
distributions [7-91. 
Recently, we have studied the strange form factors in the context of the SAMPLE, 
HAPPEX, HAPPEX-II, A4 and GO experiments within the framework of this xQSM [lo, 
111, employing symmetry-conserving quantization [12] and taking into account kaonic 
effects. In this talk, we want to present the recent results on the strange form factors and 
discuss their aspects in comparison with those experiments. 
0375-9474/03/$ - see front matter 0 2003 Elsevier Science B.V. All rights reserved 
doi:lO.l016/S0375-9474(03)01086-8 
418~ A. Siloa et al. /Nuclear Physics A721 (2003) 417cd2Oc 
0.10 I I I 1  
,_-----__ 
0.08 I’ 
-.._ 
-. 
/’ --._ 
--.\ 
Q2 [GeV’] 
Figure 1. The strange electric form factor G& as a function of Q2 with the kaon (b = 490 
MeV) and pion (p = 140 MeV) asymptotic tails. The constituent quark mass is M  = 420 
MeV. 
0.15 2.0 
--p=490Me” 
1.5. *’ ----@=140Me” - 
2 1.0. 
“u” 
0.5 
0.0. 8 ’ I 0.2 0.4 0.6 0.8 1.0 
Q2 [GeV’] 
Figure 2. The strange magnetic form factor GS, and the neutral vector form factor in 
units of PN as a function of Q2. Conventions and model parameter as in Fig. 1. The 
experimental data are taken from the SAMPLE experiment [3]. 
The results for the strange electric form factor G& are shown in Fig. 1 and for the 
strange magnetic form factor Gb in the left panel of Fig. 2. The neutral vector form 
factor is drawn in the right panel of Fig. 2. As shown in Fig. 2, the model results are 
very close to the SAMPLE data, but the experimental error is too large to draw any 
conclusion as yet. These figures show a general effect due to the influence of the Yukawa 
mass p, governing the asymptotic behavior of the profile function at large T, exp(-pr)/r, 
on the form factors. It is expected that the kaon influence on the asymtotics of the meson 
fields play an important role in the description of the strange vector form factors, since 
strange quarks in the nucleon may be excited in the form of virtual kaons and hyperons. 
Keeping this in mind, we implement a heavier mass asymptotic behavior of the profile 
function of the pseudo-Goldstone soliton field. We shall regard the difference arising from 
A. Siloa et al. /Nuclear Physics A721 (2003) 417c-420~ 419c 
(G% + 0.392G’iMW~rJ Gg + 0.392Gs, 
1.433 N 1.695 (/J = m, N mx) 0.103 w 0.071 (p = m, N rnk) 
1.527 f- 0.048 f 0.027 f O.Oll(HAPPEX) 0.025 f 0.020 zt 0.014 (HAPPEX) 
Table 1 
The combinations (GO, + 0.392G~)/(G~/~~) and G& + 0.392GS, for the HAPPEX kine- 
matics Q2 = 0.477 GeV2. The model parameters as in Fig. 1. The experimental data are 
taken from HAPPEX [4]. 
two different profile functions as our systematic uncertainty of the model. 
The results for the strange electric and magnetic radii are: (r2)g = -0.220(7r) N 
-0.095(K) fm and (r2)h = 0.303(7r) N 0.631(K) f m, respectively. Those for the strange 
magnetic moment are: ps = 0.074(r) N 0.115(K) pjv. 
In Table 1 we present the results relevant for the HAPPEX experiments. While the 
model result of the flavor-singlet form factor is in a fairly good agreement with the 
HAPPEX data, that of the strange vector one shows a little bit higher value than the 
experimental one. In Tables 2-4, we list the predictions of the future experiments. 
Table 2 
Strange form factors: The prediction for the GO experiment. The model parameters as in 
Fig. 1. 
I I 8=lW I 8 = 108" 
Gk+PG$ (p=m,~m) 
0.11 N 0.09 
0.24 0.20 
0.325 0.26 
0.435 0.35 
0.576 0.47 
0.751 0.61 
0.951 0.81 
Gk + PG”, = m, - mK) p 
0.09 N 0.05 0.63 
0.10 N 0.06 0.99 
0.11 N 0.07 1.31 
0.11 N 0.07 1.81 
0.10 N 0.07 2.49 
0.08 N 0.06 3.35 
0.07 N 0.06 4.62 
0.14 - 0.11 
0.14 - 0.13 
0.15 N 0.14 I 0.14 - 0.14 0.12 - 0.13 0.11 N 0.12 
Table 3 
Strange form factors: The prediction for the A4 experiment. The model parameters as in 
Fig. 1. 
I e = 35" I9 =145" 
Q”[GeV’] p jG~+,BG~(~=rn,+~rnx) p ]G~+,BG~(~=m,~rnk) 
0.10 0.099 1 0.07 r-4 0.04 - - 
0.227 0.22 0.10 N 0.06 4.07 0.28 N 0.32 
0.47 - - 8.963 0.33 N 0.42 
420~ A. Silva et al. /Nuclear Physics A721 (2003) 417c-420~ 
Table 4 
Strange form factors: The prediction for the HAPPEX II experiment. The model param- 
eters as in Fig. 1. 
c9 = 6” 
Q2 [GeV’l P  1 GSE + PGL (P = m  N mK) 
0.11 0.09 1 0.07 N 0.04 
In this talk, our aim has been to present the recent results of the strange form factors 
of the nucleon within the framework of the SU(3) chiral quark-soliton model. We have 
taken into account the new scheme of the SU(3) quantization. We also have considered two 
different Yukawa asymptotic tails, that is, the pion and kaon tails. The difference between 
the results with the pion and kaon tails is regarded as the uncertainty which is inherent 
in the present model. The results are in a fairly good agreement with the SAMPLE and 
HAPPEX results. We also predict the future experiments of the A4, HAPPEX-II and GO 
experiments. 
AS acknowledges partial financial support from Praxis XXI/BD/15681/98. The work of 
HCK is supported by the KOSEF (ROl-2001-00014). The work has also been supported 
by the BMBF, the DFG, the COSY-Project (Jiilich) and POCTI (MCT-Portugal). 
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8. V. Y. Petrov, P. V. Pobylitsa, M. V. Polyakov, I. Bornig, K. Goeke and C. Weiss, 
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Strange form factors in the context of SAMPLE, HAPPEX, and A4 experiments

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