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A. Hoefer

Publications and source records attributed to A. Hoefer.

4 recordsLinked to original sources
arXiv2002

Measuring the FSR--inclusive pi+pi- cross section

Final state radiation (FSR) in pion--pair production cannot be calculated reliably because of the composite structure of the pions. However, FSR corrections have to be taken into account for a precise evaluation of the hadronic contribution to g-2 of the muon. The role of FSR in both energy scan and radiative return experiments is discussed. It is shown how FSR influences the pion form factor extraction from experimental data and, as a consequence, the evaluation of a_mu^had. In fact the O(alpha) FSR corrections should be included to reach the precision we are aiming at. We argue that for an extraction of the desired FSR--inclusive cross section sigma^(gamma)_had a photon--inclusive scan measurement of the ``e+e- to pi+pi- + photons'' cross section is needed. For exclusive scan and radiative return measurements in contrast we have to rely on ad hoc FSR models if we want to obtain either sigma^(gamma)_had or the FSR--exclusive cross section sigma^(0)_had. We thus advocate to consider seriously precise photon--inclusive energy scan measurements at present and future low energy e+e- facilities. Then together with radiative return measurements from DAFNE and BABAR and forthcoming scan measurements at VEPP-2000 we have a good chance to substantially improve the evaluation of a_mu^had in the future.

hep-ph↗
arXiv2002

Pion Pair Production with Higher Order Radiative Corrections in Low Energy e+e- Collisions

The complete one-loop QED initial state, final state and initial--final state interference corrections to the process e+e- -> pi+pi- are presented. Analytic formulae are given for the virtual and for the real photon corrections. The total cross section, the pion angular distribution and the pi+pi- invariant mass distribution are investigated in the regime of experimentally realistic kinematical cuts. It is shown that in addition to the full one-loop corrections also two-loop initial state corrections and even the resummation of higher order soft photon logarithms can be necessary if at least per cent accuracy is required. For the data analysis we focus on an inclusive treatment of all photons. The theoretical error concerning our treatment of radiative corrections is then estimated to be less than 2 per mille for both the measurement of the total cross section and the pi+pi- invariant mass distribution. In addition we discuss the model uncertainty due to the pion substructure. Altogether the precision of the theoretical prediction matches the requirements of low energy e+e- experiments like the ones going on at DAFNE or VEPP-2M.

hep-ph↗