Abstract
This paper reports on Monte Carlo simulation results for future measurements of the moduli of time-like proton electromagnetic form factors, |G_{E}| and |G_{M}|, using the bar{p} p rightarrow mu ^{+} mu ^{-} reaction at overline{text {P}}text {ANDA} (FAIR). The electromagnetic form factors are fundamental quantities parameterizing the electric and magnetic structure of hadrons. This work estimates the statistical and total accuracy with which the form factors can be measured at overline{text {P}}text {ANDA}, using an analysis of simulated data within the PandaRoot software framework. The most crucial background channel is bar{p} p rightarrow pi ^{+} pi ^{-}, due to the very similar behavior of muons and pions in the detector. The suppression factors are evaluated for this and all other relevant background channels at different values of antiproton beam momentum. The signal/background separation is based on a multivariate analysis, using the Boosted Decision Trees method. An expected background subtraction is included in this study, based on realistic angular distributions of the background contribution. Systematic uncertainties are considered and the relative total uncertainties of the form factor measurements are presented.
Highlights
Electromagnetic form factors (FFs) are fundamental quantities, which describe the internal structure of hadrons
The proton structure at leading order in α (α, being the electromagnetic fine structure constant), can be described by the electric (G E ) and the magnetic (G M ) FFs. Experimental access to these FFs is possible via the measurement of differential and total cross sections for elastic electronproton scattering in the space-like region (momentum transfer squared q2 < 0 (GeV/c)2), while in the time-like region (q2 > 0 (GeV/c)2) proton FFs can be accessed in annihilation processes of the type pp → + − with = e, μ, τ
The polarization transfer method showed that the ratio μpG E /G M decreases linearly from unity to zero with increasing values of Q2
Summary
Electromagnetic form factors (FFs) are fundamental quantities, which describe the internal structure of hadrons. The proton structure at leading order in α (α, being the electromagnetic fine structure constant), can be described by the electric (G E ) and the magnetic (G M ) FFs. The proton structure at leading order in α (α, being the electromagnetic fine structure constant), can be described by the electric (G E ) and the magnetic (G M ) FFs Experimental access to these FFs is possible via the measurement of differential and total cross sections for elastic electronproton scattering in the space-like region (momentum transfer squared q2 < 0 (GeV/c)2), while in the time-like region (q2 > 0 (GeV/c)2) proton FFs can be accessed in annihilation processes of the type pp → + − with = e, μ, τ (or the time-reversed process in case of electrons).
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