Transcript GDR-PH-QCD, IPNO 7/XII/2012

Modelling Hadron Form
Factors
Egle Tomasi-Gustafsson
IRFU, SPhN-Saclay,
and
IN2P3- IPN Orsay
GDR-PH-QCD, IPNO
7/XII/2012
IPNO, 7-XII-2012
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IPNO, 7-XII-2012
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Polarization experiments - Jlab
A.I. Akhiezer and M.P. Rekalo, 1967
GEp collaboration
1) "standard" dipole function for
the nucleon magnetic FFs
GMp and GMn
2) linear deviation from the
dipole function for the
electric proton FF Gep
3) QCD scaling not reached
3) Zero crossing of Gep?
4) contradiction between
polarized and unpolarized
measurements
A.J.R. Puckett et al, PRL (2010)
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Issues
• Some models (IJL 73, Diquark, soliton..) predicted
such behavior before the
data appeared
BUT
• Simultaneous description of
the four nucleon form
factors...
• ...in the space-like and in the
time-like regions
• Consequences for the light
ions description
• When pQCD starts to apply?
• Source of the discrepancy
IPNO, Kolomna,
7-XII-201211-VI-2010
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Proton form factors at large q2
L = 2  10 32 cm-2 s-1
Connection with QCD
asymptotics?
100 days
Applies to NN and NN
Interaction
(Pomeranchuk theorem)
t=0 : not a QCD regime!
E. T-G. and M. P. Rekalo, Phys. Lett. B 504, 291 (2001)
IPNO, 7-XII-2012
E. T-G. e-Print: arXiv:0907.4442 [nucl-th]
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The nucleon: homogenous, symmetric sphere?
Analogy with Gravitation
Coulomb Potential ~
Gravitational Potential
Mass~charge
1/r
• Spherical symmetric distributed
mass density,
• A point at a distance r<R from the
center feels only the matter inside
works for the SCALAR part,
NOT for the
→
VECTOR part of A=(Φ, A)
R=
r~0.7 fm → Q= 0.29 GeV
R~1/Q3 is NOT the experimental behavior
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The nucleon
3 valence quarks and
a neutral sea of qq pairs
antisymmetric state of
colored quarks
Main assumption
Does not hold in the spatial center of the
nucleon: the center of the nucleon is
electrically neutral, due to strong gluonic field
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The nucleon
Inner region: gluonic condensate of clusters with
randomly oriented chromo-magnetic field (Vainshtein,
1982):
Intensity of the gluon field in vacuum:
In the internal region of strong chromo-magnetic field,
the color quantum number of quarks does not play any
role, due to stochastic averaging
didj
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proton
neutron
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Model
Antisymmetric state
of colored quarks
Colorless quarks:
Pauli principle
1) uu (dd) quarks are repulsed from the inner region
2) The 3rd quark is attracted by one of the identical
quarks, forming a compact di-quark
3) The color state is restored
Formation of di-quark: competition between
attraction force and stochastic force of the gluon
field
proton: (u) Qq=-1/3
neutron: (d) Qq=2/3
attraction force >stochastic force of the gluon field
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Model
attraction force >
stochastic force of the
gluon field
Proton: r0=0.22 fm, p02 = 1.21 GeV2
Neutron: r0=0.31 fm, p02 = 2.43 GeV2
Applies to the scalar
part of the potential
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Model
Quark counting rules apply
to the vector part of the potential
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Model
Additional suppression for the scalar part
due to colorless internal region:
“charge screening in a plasma”:
Neutrality condition:
Additional suppression
(Fourier transform)
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Boltzmann constant
fitting parameter
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Fourier Transform
Root mean square radius
Perugia, 18-XII-2012
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Model: generalized form factors
Definition:
space-time distribution of the
electric charge in the space-time volume
In SL- Breit frame (zero energy transfer):
In TL-(CMS):
: time evolution of the charge distribution
in the domain
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The annihilation channel:
1) Creation of a pp state through
intermediate state with
2) The vacuum state transfers all the released
energy to a state of matter consisting of:
• 6 massless valence quarks
• Set of gluons
• Sea of current qq pairs of quarks with
energy q0>2Mp, J=1, dimensions
3)
Pair of p and p formed by three bare quarks:
•Structureless
•Colorless
pointlike FFs !!!
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The annihilation channel:
•
The point-like hadron pair expands and cools down:
the current quarks and antiquarks absorb
gluon and transform into constituent quarks
• The residual energy turns into kinetic energy
of the motion with relative velocity
• The strong chromo-EM field leads to an effective
loss of color. Fermi statistics: identical quarks are
repulsed. The remaining quark of different flavor
is attracted to one of the identical quarks,
creating a compact diquark (du-state)
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The annihilation channel:
The neutral plasma acts on the distribution of the
electric charge (not magnetic).
Prediction: additional suppression due to the neutral
plasma
similar behavior in SL and TL regions
• Implicit normalization at q2=4Mp2: |GE|=|GM| =1
• No poles in unphysical region
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The annihilation channel:
The repulsion of p and p with kinetic energy
is balanced by the confinement potential
•
•
The long range color forces create a stable
colorless state of proton and antiproton
The initial energy is dissipated from current
to constituent quarks originating on shell
separated by R.
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The annihilation channel:
At larger distances, the inertial force exceeds
the confinement force: p and p start to move
apart with relative velocity 
p and p leave the interaction region: at large
distances the integral of Q(t) must vanish.
For very small values of the velocity
FSI lead to the creation of a bound NN system .
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Space-Like region
GEp polarization
GEp dipole
GEn
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Proton Form Factors
GEp polarization
GEp dipole
|GMp|=|GEp|
GMp
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Neutron TL region
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Time-Like region
R=|GEp|/|GMp|
Not a fit
Ps178
BaBar
Dafne
E835
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Point-like form factors?
S. Pacetti
IPNO, 7-XII-2012
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Point-like form factors?
S. Pacetti
IPNO, 7-XII-2012
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Point-like form factors?
S. Pacetti
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Hadron Form Factors: Conclusions
New, interesting results in Space-like and Timelike regions
VEPP-Novosibirsk
IHEP
Unified model in SL and TlL regions
•
pointlike behavior at threshold
•
complex FFs due to to FSI , vanishing at
asymptotics
•
spin one intermediate state
dynamical polarization of p and p?
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