Download Egle Tomasi Gustafsson

Fp
Peculiar Features of
Electromagnetic Proton Form Factors
10- 1
10- 1
10- 2
4
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8
10
10- 3
20
Fp
10
30
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q2 [GeV2]
Egle Tomasi-Gustafsson
CEA, IRFU,SPhN,
Saclay, France
(a)
0.3
0.2
In collaboration with A. Bianconi (Univ. di Brescia)
and Wang Ying(IPN Orsay)
0.1
0.04
(b)
D
0.02
0
-0.02
-0.04
0
1
2
3
p [GeV]
Varenna, 15-VI2015
4th INTERNATIONAL CONFERENCE
ON NUCLEAR REACTION MECHANISMS
Varenna (Italy), Villa Monastero
June 15 - 19 , 2015
Egle Tomasi-Gustafsson
1
Proton Charge and Magnetic Distributions
e-
GE(0)=1
GM(0)=mp
p
Space-like
FFs are real
e+p  e+p
Varenna, 15-VI2015
Unphysical region
p+p ↔ e+e-+p0
q2<0
p
Asymptotics
- QCD
- analyticity
e-
0 q2=4mp2
e+
p
q2>0
e-
p
_
_ Time-Like
FFs are complex
p+p ↔ e++e-
q2
GE=GM
Egle Tomasi-Gustafsson
2
Hadron Electromagnetic Form Factors
GE
2<0 unpolarized
q
GE(0)=1
GM(0)=mp
GMp
p
Space-like
FFs are real
e+p  e+p
Varenna, 15-VI2015
Unphysical region
p+p ↔ e++e- +p0
e- eGE Polarized
Asymptotics
- QCD
- analyticity
+
e
q2>0
GE=GM
q2=4mp2
GE=GM
Egle Tomasi-Gustafsson
p
p
e_
_Time-Like
FFs are complex
p+p ↔ e++e-
q2
3
Hadron Electromagnetic Form Factors
GE Polarized
GE unpolarized
GE=GM
GM
e+p  e+p
Varenna, 15-VI2015
GE=GM
Egle Tomasi-Gustafsson
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Polarization Experiments
A.I. Akhiezer and M.P. Rekalo, 1967
Jlab-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), PRC (2012)
Varenna, 15-VI-2015
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Time-like observables: | GE| 2 and | GM| 2 .
A. Zichichi, S. M. Berman, N. Cabibbo, R. Gatto, Il Nuovo Cimento XXIV, 170 (1962)
B. Bilenkii, C. Giunti, V. Wataghin, Z. Phys. C 59, 475 (1993).
G. Gakh, E.T-G., Nucl. Phys. A761,120 (2005).
As in SL region:
- Dependence on q2 contained in FFs
- Even dependence on cos2q (1g exchange)
- No dependence on sign of FFs
- Enhancement of magnetic term
but TL form factors are complex!
Varenna, 15-VI2015
Egle Tomasi-Gustafsson
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Time-like observables: | GE| 2 and | GM| 2
A. Zichichi, S. M. Berman, N. Cabibbo, R. Gatto, Il Nuovo Cimento XXIV, 170 (1962)
B. Bilenkii, C. Giunti, V. Wataghin, Z. Phys. C 59, 475 (1993).
G. Gakh, E.T-G., Nucl. Phys. A761,120 (2005).
IHEP
Varenna, 15-VI2015
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VMD: Iachello, Jakson and Landé (1973)
g*
,ρ,
Isoscalar and isovector FFs
Varenna, 15-VI2015
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The Time-like Region
The Experimental Status
•
•
•
•
Fp
•
GE=GM
No individual determination 10-1
of GE and GM
10- 1
TL proton FFs twice larger
than in SL at the same Q2 10-2
Steep behaviour at
threshold
4
6
8
10
10-3
Babar:Structures?
Resonances?
10
20
30
40
q2 [GeV ]
2
S. Pacetti, R. Baldini-Ferroli, E.T-G , Physics Reports, 514 (2014) 1
Panda contribution: M.P. Rekalo, E.T-G , DAPNIA-04-01, ArXiv:0810.4245.
Varenna, 15-VI2015
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Fp
The Time-like Region
Expected QCD scaling (q2)2
-1
10
GE=GM
10- 1
10-2
4
6
8
10
10-3
10
20
30
40
q [GeV ]
2
Varenna, 15-VI2015
Egle Tomasi-Gustafsson
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Oscillations : regular pattern in PLab
Fp
The relevant variable is pLab associated to the relative
motion of the final hadrons.
(a)
0.3
0.2
0.1
0.04
(b)
D
0.02
A: Small perturbation B: damping
C: r < 1fm
D=0: maximum at p=0
0
-0.02
-0.04
0
1
2
3
p [GeV]
Simple oscillatory behaviour
Small number of coherent sources
A. Bianconi, E. T-G. Phys. Rev. Lett. 114,232301 (2015)
Varenna, 15-VI2015
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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
E.A. Kuraev, E. T-G, A. Dbeyssi, Phys.Lett. B712 (2012) 240
Varenna, 15-VI2015
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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
Varenna, 15-VI2015
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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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Fourier Transform
3
3
M(r) (1/fm )
M0(r) (1/fm )
0.15
102
F0 ==
10
0.1
1
0.05
10-1
10-2
0
10-3
-0.05
10-4
0
0.5
1
1.5
2
r (fm)
0.6
0.8
1
1.2
1.4
1.6
r (fm)
• Rescattering processes
• Large imaginary part
• Related to the time evolution of the charge density?
(E.A. Kuraev, E. T.-G., A. Dbeyssi, PLB712 (2012) 240)
• Consequences for the SL region?
• Data expected at BESIII, PANDA
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Conclusions
• Recent and precise data on the proton time-like form
factors measured by the BABAR collaboration show a
systematic sinusoidal modulation in the near-threshold
region.
• The relevant variable is the momentum p associated to the
relative motion of the final hadrons.
• The periodicity and the simple shape of the oscillations
point to a unique interference mechanism, which occurs
when the hadrons are separated by about 1 fm.
• At some stage of the hadronic matter, is distributed in a
non-trivial way: the formation evolves along alternative
interfering channels.
• The oscillation period corresponds to hadronic-scale
 scaling-violating parameter
 origin ?
A. Bianconi, E. Tomasi-Gustafsson
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A. Bianconi, E. Tomasi-Gustafsson
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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.
Varenna, 15-VI2015
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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
Varenna, 15-VI2015
proton
neutron
Egle Tomasi-Gustafsson
Colorless quarks:
Pauli principle
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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
Varenna, 15-VI2015
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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
Varenna, 15-VI2015
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Model
Quark counting rules apply
to the vector part of the potential
Varenna, 15-VI2015
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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)
Varenna, 15-VI2015
Egle Tomasi-Gustafsson
Boltzmann constant
fitting parameter
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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 !!!
Varenna, 15-VI2015
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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)
Varenna, 15-VI2015
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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 .
Varenna, 15-VI2015
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Point-like form factors?
S. Pacetti
Varenna, 15-VI2015
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Radiative return (ISR)
e+ +e-  p + p + g
2
2
E
d( e  e -  ppg ) 2m
m
g

W ( s , x , q )( e  e -  pp )( m ), x 
 1,
dm d cos q
s
s
s
me
  2 - 2 x  x 2 x 2 
W ( s , x ,q ) 
, q 
.
2


px
2
s
 sin q

B. Aubert ( BABAR Collaboration) Phys Rev. D73, 012005 (2006)
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