Electromagnetic form factors of the proton in
the time-like region with the PANDA detector
GDR/LQCD Autrans, 6-7 Juin 2005
IPN Orsay and UPJV Amiens
Layout of the detector (top view)
Charmonium (narrow charmonium and charmonium above open
Hybrid Charmonium and Gluballs
Exotics (tetra and pentaquark up to 2.7 GeV/c2)
Charm in Nuclei (charmonium absorption and mass shift of
charmed mesons in Nuclei)
Open charm physics
Crossed-channel Compton scattering
Transverse quark distribution and Drell-Yan processes
Electromagnetic FF of the proton in the time-like region
S.K. Choi et al., Phys. Rev. Lett. 94, 182002 (2005)
Observation of a hybrid meson at the KEK Laboratory (Belle
The new meson is known as the Y(3940).
It may be a hybrid meson containing a charm quark, a charm
antiquark and a gluon . It decays into omega and J/psi
LQCD predicts the presence of about 15 glueballs in the mass
range accessible to the HESR (< 5.4 GeV/C2)
See for details : C. Morningstar and M. Peardon, Phys. Rev. D60,
(350 physicists, 47 lnstitutions of 15 Countries ).
We (IPNO group) propose to measure the
electromagnetic FF of the proton in the time-like region.
L 2.10 cm s
p _ 1.5 15.GeV / c
p / p 10 10 5 6
Electromagnetic form factors of hadrons in the space-
like and time-like regions provide fundamental
informations on their structure and internal dynamics.
Till now, the available data in the time-like-region are
limited by low statistics. The |Ge| and |Gm|
separation could not be done without assumptions.
The numerical values of |Gm| in the region explored
by Fermilab (E760, E835) are approximately twice as
large as those in the corresponding space-like region.
The space-like FF are reals, The time-like form
factors have a phase structure reflecting the final or
initial state interaction of the hadrons.
The JLab results show us that the Pauli/Dirac ratio is
not observed to fall with the nominal expected power
and make critical to carefully measure and separate
the time-like Gm and Ge form factors
With polarized proton-antiproton reactions, the
measurement of the proton FF in the time-like region
should strongly discriminate between the different
models suggested to fit the proton FF in the space-
M. Ambrogiani et al., Phys. Rev D60,032002(1999)
O. Gayou et al.,Phys. Rev. Lett. 88, 092301
E. Tomasi-Gustaffson, Proc. of the “Baryons 04”
Spokepersons: Ch. Perdrisat,
V. Punjabi, M. Jones, E. Brash
20 Laboratories, 80 people
Cross section ( pp e e )
A. Zichichi, SM. Berman, N. Cabibbo, R. Gatto, Nuovo Cimento 24,
[ GM (1 cos ) GE sin 2 ]
2 2 2
d (cos ) 2 s s
Lint 2.10 cm
S (GeV2) σ (pb) N(events)
8.84 10.8 21600
10.78 2.82 5643
14.36 0.8 1617
30. 0.021 42
The analysis of the data is based on the
identification of the coplanar e+e- pairs
tracks collinear in the CMS with an invariant
mass compatible with the center of mass
energy of the p barp system.
Simulations of the signal and backgrounds
are in progress.
B. Ramstein and J. Van de Wiele (private communication)
MP. Rekalo and E. Tomasi-Gustafsson, EPJ A22, 331 (2004)
1g-2g interference in the annihilation channel ?
pp e e
1) Photon conversions and
2) Hadronic two body decays
3) J/ψ (γ) or Inclusive J/Ψ
pp J / e e
pp J / X
Energy deposit in ECAL @ 0.5GeV
Th. Zerguerras (private communication)
90% e- incident energy measured
Need for another independant
identification (TPC, Kinematics,
DIRC, Scint. …)
Kinematical separation of and e+ e-
at 5 GeV p_bar p (T. Hennino, private communication)
P(-)–P(e-) = 10 MeV/c !
[0o,20o] [20o,40o] [40o,60o] independant of angle and
170 70 34
Below 90 degrees,
identification by ECAL is
[60o,80o] [80o,100o] [100o,120o] sufficient
17 10 7.5
[120o,140o] [140o,160o] [160o,180o] Might be of help in the
6.5 6.5 13 Other criteria for a better
separation have to be
worked out (TPC, DIRC,
Resolution in momentum (MeV/c) for 9 angular intervals
FAIR-ESAC/Pbar/Technical Progress Report, January 2005.
TPC Option for tracking particles
Antiproton-proton scattering with polarization
PAX Collaboration (www.fz-juelich.de/ikp/pax)
Ay the transverse single
spin asymmetry (SSA) p pe e
in annihilation (beam or
sin 2 Im GE GM
Q 2 / 4m 2
D [(1 cos ) GM sin GE / ] /
2 2 2 2
Py is the normal polarization to the scattering
plane of the outgoing hadron in annihilation
e+e- to p barp
The polarization Py does
not require polarization
in the initial state.
The measurement of the
SSA would strongly
the models suggested
to fit the proton Ge/Gm
data in the space like
A. Z. Dubnickova, S. Dubnicka, M. P. Rekalo, Nuovo Cim.
A109, 241 (1996).
S.J. Brodsky et al., Phys. Rev. D69, 054022 (2004) and
Separation of |Ge| and |Gm| in the time-like
region with the detector PANDA up to
S > 15 GeV2.
With a transversely polarized proton target
or polarized beam, we would determine the
relative phase between Ge and Gm by
measuring the transverse single spin