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Antiproton-proton elementary cross sections: lack of data at low momentum

Antiproton-proton elementary cross sections: lack of data at low momentum. pp total cross section. Total cross section Measurements exist down to 220 MeV/c Annihilation cross section Measurements by OBELIX exist even below 100 MeV/c Elastic cross section Measurements down to 181 MeV/c

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Antiproton-proton elementary cross sections: lack of data at low momentum

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  1. Antiproton-proton elementary cross sections: lack of data at low momentum pp total cross section • Total cross section • Measurements exist down to 220 MeV/c • Annihilation cross section • Measurements by OBELIX exist even below 100 MeV/c • Elastic cross section • Measurements down to 181 MeV/c • No way to determine el below this value • Lack of measurements in the low momentum region • Why is the elastic cross section so interesting? pp annihilation cross section Evidences of an anomaly observed in np interactions

  2. Total vs annihilation np cross sections An odd dimp-bump effect is observed in (np)TOT close to 65-80 MeV/c • Regular and smooth trend of (np)ANN in the same momentum region • Impossible to find a set of parameters able to describe correctly at the same time both T and ann • Bad fits of T with ER expansions, of different kinds • The elastic cross section is most likely responsible for the unexpected irregular trend of T Total cross section Annihilation xsec: smooth Due to a NN bound state close to threshold?

  3. I=0 vs I=1 interactions • From the ratio between T(pp) and T(np) one can deduce the contribution to annihilation of the I=0 and I=1 sources of the NN interaction: • Strong dominance of the I=0 component at low momentum: • T(I=0)/T(I=1): • (2.50.4) @ 70 MeV/c • (1.10.1) @ 300 MeV/c • Effect explained as a manifestation of the coherence of meson exchanges in the central and tensor terms of the NN medium range force (Dover et al.) • For ann the same rule is valid: ann(np) < ann(pp) • ann(I=0)/ann(I=1): • (2.4 0.4) @ 70 MeV/c • (I=1) always lower than (I=0)BUT 1.5 @ ~ 700 MeV/c!

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