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This paper reports on Monte Carlo simulation results for future measurements of the moduli of time-like proton electromagnetic form factors, |GE | and |GM|, using the ¯pp → μ+μ− reaction at PANDA (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 PANDA, using an analysis of simulated data within the PandaRoot software framework. The most crucial background channel is ¯pp → π+π−,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 distribuations of the background contribution. Systematic uncertainties are considered and the relative total uncertainties of the form factor measurements are presented.
In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπ±pdpTdy distributions of correlated π±p pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1<Minv(GeV/c2)<1.4, the yield is found to be similar for π+p and π−p pairs, and to follow a power law 〈Apart〉α, where 〈Apart〉 is the mean number of participating nucleons. The exponent α depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is α=1.5±0.08st±0.2sy.