Electromagnetic form factors of the proton in the time-like region with the PANDA detector
description
Transcript of Electromagnetic form factors of the proton in the time-like region with the PANDA detector
Electromagnetic form factors of the proton in the time-like region with the PANDA detector
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.
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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
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Cross section ( )A. Zichichi, SM. Berman, N. Cabibbo, R. Gatto, Nuovo Cimento 24, 170 (1962)
]sin4
)cos1([2)(cos
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222
EM G
s
mG
sd
d
eepp
S
m241
cm
6.0cos
10.2 239int
cmL
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 ?
eepp
Backgrounds processes
1) Photon conversions and Dalitz decays
2) Hadronic two body decays
3) J/ψ (γ) or Inclusive J/Ψ production
pp
pp
pp0
00
pp
XJpp
eeJpp
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Energy deposit in ECAL @ 0.5GeV Th. Zerguerras (private communication)
e-
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
17
34
7.5
6.56.5
10
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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):
eepp
/]/sin)cos1[(
4/
Im2sin
2222
22
*
EM
MEyy
GGD
mQ
D
GGPA
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.