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1Egle Tomasi-Gustafsson
Peculiar Features of Electromagnetic Proton Form Factors
Varenna, 15-VI-2015
Egle Tomasi-GustafssonCEA, IRFU,SPhN,
Saclay, France
In collaboration with A. Bianconi (Univ. di Brescia)and Wang Ying(IPN Orsay)
4th INTERNATIONAL CONFERENCEON NUCLEAR REACTION MECHANISMS
Varenna (Italy), Villa MonasteroJune 15 - 19 , 2015
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2Egle Tomasi-Gustafsson
__
q2<0
e-e-
p p
q2>0
e-
e+p
p
q2q2=4mp2
Time-LikeFFs are complex
Space-likeFFs are real
GE=GM
GE(0)=1
GM(0)=mp
Asymptotics- QCD- analyticity
p+p ↔ e++e-e+p e+p
Unp
hysi
cal r
egio
n
p+p
↔ e
+e- +
p0
0
Proton Charge and Magnetic Distributions
Varenna, 15-VI-2015
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3Egle Tomasi-GustafssonVarenna, 15-VI-2015
GE=GM p+p ↔ e++e-e+p e+p
__
q2<0
e-e-
p p
q2>0
e-
e+ p
p
q2q2=4mp2
Time-LikeFFs are complex
Space-likeFFs are real Unp
hysi
cal r
egio
nGE(0)=1
GM(0)=mp
Asymptotics- QCD- analyticity
p+p
↔ e
++
e- +
p0
Hadron Electromagnetic Form Factors
GE=GMGE unpolarized
GM
GE Polarized
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4Egle Tomasi-GustafssonVarenna, 15-VI-2015
GE=GMe+p e+p
Hadron Electromagnetic Form Factors
GE=GMGE unpolarized
GM
GE Polarized
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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 reached3) Zero crossing of Gep?4) contradiction between
polarized and unpolarized measurements
Egle Tomasi-GustafssonVarenna, 15-VI-2015 5
A.J.R. Puckett et al, PRL (2010), PRC (2012)
Polarization Experiments
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6
Time-like observables: | GE| 2 and | GM| 2 .
Egle Tomasi-GustafssonVarenna, 15-VI-2015
As in SL region:- Dependence on q2 contained in FFs- Even dependence on cos2 q (1g exchange)- No dependence on sign of FFs- Enhancement of magnetic term
but TL form factors are complex!
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).
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7
Time-like observables: | GE| 2 and | GM| 2
Egle Tomasi-Gustafsson
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-VI-2015
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Egle Tomasi-Gustafsson 8
VMD: Iachello, Jakson and Landé (1973)
Isoscalar and isovector FFs* ,ρ,
Varenna, 15-VI-2015
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• The Experimental Status
• No individual determination of GE and GM
• TL proton FFs twice larger than in SL at the same Q2
• Steep behaviour at threshold
• Babar:Structures? Resonances?
Egle Tomasi-Gustafsson 9
The Time-like Region
GE=GM
Panda contribution: M.P. Rekalo, E.T-G , DAPNIA-04-01, ArXiv:0810.4245.
S. Pacetti, R. Baldini-Ferroli, E.T-G , Physics Reports, 514 (2014) 1
Varenna, 15-VI-2015
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Egle Tomasi-Gustafsson 10
The Time-like Region
Expected QCD scaling (q2)2
Varenna, 15-VI-2015
GE=GM
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Egle Tomasi-Gustafsson 11
Oscillations : regular pattern in PLab
A: Small perturbation B: damping C: r < 1fm D=0: maximum at p=0
Varenna, 15-VI-2015
The relevant variable is pLab associated to the relative motion of the final hadrons.
Simple oscillatory behaviourSmall number of coherent sources
A. Bianconi, E. T-G. Phys. Rev. Lett. 114,232301 (2015)
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The nucleon
Egle Tomasi-GustafssonVarenna, 15-VI-2015
12
antisymmetric state of colored quarks
3 valence quarks anda neutral sea of qq pairs
Does not hold in the spatial center of the nucleon: the center of the nucleon is electrically
neutral, due to strong gluonic field
Main assumption
E.A. Kuraev, E. T-G, A. Dbeyssi, Phys.Lett. B712 (2012) 240
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The annihilation channel:
Egle Tomasi-GustafssonVarenna, 15-VI-2015
13
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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space-time distribution of the electric charge in the space-time volume
Model: generalized form factors
Egle Tomasi-GustafssonVarenna, 15-VI-2015
14
Definition:
In SL- Breit frame (zero energy transfer):
In TL-(CMS):
: time evolution of the charge distribution in the domain
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Egle Tomasi-Gustafsson 15
Fourier Transform
• Rescattering processes• Large imaginary part • Related to the time evolution of the charge
density?
• Consequences for the SL region?• Data expected at BESIII, PANDA
(E.A. Kuraev, E. T.-G., A. Dbeyssi, PLB712 (2012) 240)
Varenna, 15-VI-2015
F0 ==
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A. Bianconi, E. Tomasi-Gustafsson 16
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 ?
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A. Bianconi, E. Tomasi-Gustafsson 17
Thank you for attention
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Egle Tomasi-GustafssonVarenna, 15-VI-2015
18
• 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.
The annihilation channel:
The repulsion of p and p with kinetic energy
is balanced by the confinement potential
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The nucleon
Egle Tomasi-GustafssonVarenna, 15-VI-2015
19
In the internal region of strong chromo-magnetic field, the color quantum number of quarks does not play any role, due to stochastic averaging
Intensity of the gluon field in vacuum:
Inner region: gluonic condensate of clusters with randomly oriented chromo-magnetic field (Vainshtein, 1982):
didjprotonneutron
Colorless quarks: Pauli principle
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Model
Egle Tomasi-GustafssonVarenna, 15-VI-2015
20
1) uu (dd) quarks are repulsed from the inner region2) The 3rd quark is attracted by one of the identical quarks, forming a compact di-quark3) The color state is restoredFormation of di-quark: competition between attraction force and stochastic force of the gluon field
Antisymmetric state of colored quarks
Colorless quarks: Pauli principle
attraction force >stochastic force of the gluon field
proton: (u) Qq=-1/3
neutron: (d) Qq=2/3
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Egle Tomasi-GustafssonVarenna, 15-VI-2015
21
Proton: r0=0.22 fm, p02 = 1.21 GeV2
Neutron: r0=0.31 fm, p02 = 2.43 GeV2
Model
attraction force >stochastic force of the gluon field
Applies to the scalar part of the potential
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Egle Tomasi-GustafssonVarenna, 15-VI-2015
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Quark counting rules apply to the vector part of the potential
Model
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Egle Tomasi-GustafssonVarenna, 15-VI-2015
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Additional suppression for the scalar part due to colorless internal region: “charge screening in a plasma”:
Additional suppression(Fourier transform)
fitting parameter
Model
Neutrality condition:Boltzmann constant
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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
The annihilation channel:
Egle Tomasi-Gustafsson
Varenna, 15-VI-2015
24
3) Pair of p and p formed by three bare quarks:
• Structureless• Colorless pointlike FFs !!!
1) Creation of a pp state through intermediate state with
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The annihilation channel:
Egle Tomasi-GustafssonVarenna, 15-VI-2015
25
• 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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At larger distances, the inertial force exceeds the confinement force: p and p start to move apart with relative velocity
The annihilation channel:
Egle Tomasi-GustafssonVarenna, 15-VI-2015
26
For very small values of the velocityFSI lead to the creation of a bound NN system .
p and p leave the interaction region: at large distances the integral of Q(t) must vanish.
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Egle Tomasi-GustafssonVarenna, 15-VI-2015
27
Point-like form factors?
S. Pacetti
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Egle Tomasi-Gustafsson 28
.s
m,
x
sin
xx
x),x,s(W
,s
m
s
Ex),m)(ppee(),x,s(W
s
m
cosddm
)ppee(d
e
2
22
122
2
2
2
2
Varenna, 15-VI-2015
e+ +e- p + p +
B. Aubert ( BABAR Collaboration) Phys Rev. D73, 012005 (2006)
Radiative return (ISR)