Electromagnetic form factors of the proton in the time-like region with the PANDA detector

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GDR/LQCD Autrans, 6-7 Juin 2005

Saro OngIPN Orsay and UPJV Amiens

http//www.gsi.de/panda

PANDA detector

Layout of the detector (top view)

Main Topics

Charmonium (narrow charmonium and charmonium above open charm threshold)

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) Hypernuclei

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) and hep-ex/0408126

Observation of a hybrid meson at the KEK Laboratory (Belle Collaboration).

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 (< 4.5 GeV/C2)

See for details : C. Morningstar and M. Peardon, Phys. Rev. D60, 034509 (1999)

Panda Collaboration (350 physicists, 47 lnstitutions of 15 Countries ).We (IPNO group) propose to measure the electromagnetic FF of the proton in the time-like region.

/.155.1

Physics Motivation

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-like region.

M. Ambrogiani et al., Phys. Rev

D60,032002(1999)

O. Gayou et al.,Phys. Rev. Lett. 88, 092301 (2002).E. Tomasi-Gustaffson, Proc. of the “Baryons 04” Palaiseau, France.

Jlab E01-109 approved 07/2001-07/2004

scheduled 2006 Spokepersons: Ch. Perdrisat, V. Punjabi, M. Jones, E. Brash 20 Laboratories, 80 people

Cross section ( )A. Zichichi, SM. Berman, N. Cabibbo, R. Gatto, Nuovo Cimento 24, 170 (1962)

)cos1([2)(cos

6.0cos

10.2 239int

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

Events selection

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) 1-2 interference in the annihilation channel ?

Backgrounds processes

1) Photon conversions and Dalitz decays

2) Hadronic two body decays

3) J/ψ (γ) or Inclusive J/Ψ production

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 ! independant of angle and incident energy

[0o,20o]

Resolution in momentum (MeV/c) for 9 angular intervals

[160o,180o][140o,160o][120o,140o]

[100o,120o][80o,100o][60o,80o]

[40o,60o][20o,40o]

170 70

6.56.5

Below 90 degrees, identification by ECAL is sufficient

CONCLUSION:

Might be of help in the backward region

Other criteria for a better separation have to be worked out (TPC, DIRC, Scint. )

(PANDA Collaboration)FAIR-ESAC/Pbar/Technical Progress Report, January 2005. TPC Option for tracking particles

Antiproton-proton scattering with polarizationPAX Collaboration (www.fz-juelich.de/ikp/pax)

Ay the transverse single spin asymmetry (SSA) in annihilation (beam or target polarized):

/]/sin)cos1[(

Im2sin

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 discriminate between the models suggested to fit the proton Ge/Gm data in the space like region

A. Z. Dubnickova, S. Dubnicka, M. P. Rekalo, Nuovo Cim. A109, 241 (1996).S.J. Brodsky et al., Phys. Rev. D69, 054022 (2004) and References therein

Conclusion

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, we would determine the relative phase between Ge and Gm by measuring the transverse single spin asymmetry.

Electromagnetic form factors of the proton in the time-like region with the PANDA detector

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