Electromagnetic Processes (EMP)

This release note reports about feasibility studies for the measurement of time-like proton electromagnetic form factors (FF's) using reactions of the type $\bar{p} p \rightarrow \mu^{+} \mu^{-}$ at the PANDA experiment at FAIR. Electromagnetic form factors are fundamental quantities which parameterize the electric and magnetic structure of hadrons. In the time-like region, the FF's can be accessed through reactions of the type $p\bar{p}\rightarrow l^{+} l^{-}$, where l = e, $\mu$, under the assumption of one photon exchange. It will be the first time that muon pairs in the final state will be used for the individual measurement of the TL em FF's of the proton. One advantage of using this channel is that radiative corrections due to final state radiation are suppressed by the heavy mass of the muon. Measuring $\bar{p} p \rightarrow \mu^{+} \mu^{-}$ will also serve as a consistency check of the TL em FF data from $\bar{p} p \rightarrow e^{+} e^{-}$. In frame of the PANDARoot software, which encompasses full detector simulation and event reconstruction, the statistical precision at which the proton FF's will be determined at PANDA is estimated for the signal reaction $p \bar{p} \rightarrow \mu^{+} \mu^{-}$ at different antiproton beam momenta. The signal identification and the suppression of the main background process ($p\bar{p} \rightarrow \pi^{+} \pi^{-}$) are studied. In addition, the expected statistical precision of the effective TL proton FF is presented at different beam momenta. Possible systematic error sources are considered for the estimation of the total uncertainties.

The feasibility of measuring pi0+J/psi production in pbar+p reaction in PANDA is investigated. The study is based on a TDA model for the description of the signal and uses a combination of available data and established hadronic event generator DPM for the description of the background. Events generated using these two approaches were simulated and reconstructed using PANDAroot, and the output was analyzed to check if the input spectra can be reconstructed with the currently proposed PANDA. Results on the s/b ratio and expected accuracy on differential cross-section measurements are given.

This note reports on the latest status of the feasibility studies for the measurement
of time-like, proton electromagnetic form factors (TL EM FFs) at the PANDA
experiment at FAIR. Electromagnetic FFs are fundamental quantities parameterizing
the electric and magnetic structure of hadrons. In the time-like region proton
FFs can be accessed experimentally with the aid of annihilation processes of the type
pbar p -> l+l− (l = e, μ), assuming that the interaction takes place through the exchange of
one virtual photon. The individual determination of the time-like electric and magnetic
proton FFs was limited in the past by the low luminosity available at colliders. In frame
of the PANDARoot software, which encompasses full detector simulation and event reconstruction,
the statistical precision at which the proton FFs will be determined at
PANDA is estimated for the signal channel pbar p -> μ+μ-. The signal identification and suppression
of the main background process (pbar p -> π+π−) is studied. Different methods have
been used to generate and analyse the processes of interest. The results show that TL EM FFs can be measured at PANDA with unprecedented statistical accuracy.

The results of simulations for future measurements of electromagnetic form factors at PANDA
(FAIR) in frame of the PANDARoot software are reported. The statistical precision at which the proton form factors can be determined is estimated. The suppression of the main background (pbar p -> pi+pi-) process versus the signal (pbar p -> e+e-) efficiency, the extraction of the information from the relevant spectra and the evaluation of the statistical errors on the extracted proton form factors from the events of the reaction pbar p -> e+e- have been done on the basis of two different but consistent procedures. The procedure developed here will be directly applied to the experimental data. The comparison with older predictions based on old framework shows consistency of the results and a slightly better precision achieved in a large range of momentum transfer, assuming the nominal conditions of beam and detector performances.