egle tomasi-gustafsson 1 peculiar features of electromagnetic proton form factors varenna, 15-vi-...

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

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

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

4Egle Tomasi-GustafssonVarenna, 15-VI-2015

GE=GMe+p e+p

Hadron Electromagnetic Form Factors

GE=GMGE unpolarized

GM

GE Polarized

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

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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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

Egle Tomasi-Gustafsson 8

VMD: Iachello, Jakson and Landé (1973)

Isoscalar and isovector FFs* ,ρ,

Varenna, 15-VI-2015

• 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?


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


The Time-like Region

Expected QCD scaling (q2)2

Varenna, 15-VI-2015

GE=GM


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)

The nucleon


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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

The annihilation channel:


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

space-time distribution of the electric charge in the space-time volume

Model: generalized form factors


14

Definition:

In SL- Breit frame (zero energy transfer):

In TL-(CMS):

: time evolution of the charge distribution in the domain


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 ==

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 ?

A. Bianconi, E. Tomasi-Gustafsson 17

Thank you for attention


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• 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 repulsion of p and p with kinetic energy

is balanced by the confinement potential

The nucleon


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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

Model


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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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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


22

Quark counting rules apply to the vector part of the potential

Model


23

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

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


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 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)

At larger distances, the inertial force exceeds the confinement force: p and p start to move apart with relative velocity



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.


27

Point-like form factors?

S. Pacetti


.s

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sin

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x),x,s(W

,s

m

s

Ex),m)(ppee(),x,s(W

s

m

cosddm

)ppee(d

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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)

egle tomasi-gustafsson 1 peculiar features of electromagnetic proton form factors varenna, 15-vi-...

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