Antiproton slowing Down in H2 and He and evidence of nuclear stopping power

We report stopping powers of hydrogen and helium for antiprotons of kinetic energies ranging from about 0.5 keV to 1.1 MeV. The Barkas effect, i.e., a difference in the stopping power for antiprotons and protons of the same energy in the same material, shows up clearly in either of the gases. Moreover, below ≈0.5 keV there is indirect evidence for an increase of the antiproton stopping power. This "nuclear" effect, i.e., energy losses in quasimolecular interactions, shows up in fair agreement with theoretical predictions

Experimental antiproton nuclear stopping power in H2 and D2

Data about antiprotons slowing down in gaseous targets at very low energies (E<1 keV) show that the stopping power in D2 is lower than in H2; the right way to explain this behavior seems to be through a nuclear stopping power derived from the classical Rutherford formula

A STUDY OF PONTECORVO REACTIONS IN ANTIPROTON DEUTERIUM ANNIHILATIONS AT REST

The results of the analysis of a new data sample of (p) over bar annihilations at rest on deuterium and hydrogen, taken at the CERN LEAR by the OBELIX spectrometer, are presented. The (p) over bar d --> pi(-)p channel has been measured with a noticeable reduction of both the statistical and the systematic errors with respect to the previous OBELIX measurement and the branching ratio turns out to be (1.29 +/- +/- 0.07(stat) +/- 0.05(syst)).10(-5), in good agreement with the previous result. The (p) over bar d --> rho(-)p --> pi(-) pi(0)p channel has been investigated for the first time and the branching ratio is evaluated to be (2.9 +/- 0.4(stat) +/- 0.5(syst)).10(-5). Finally, as a check of the spectrometer absolute calibration, the (p) over bar p --> pi(+) pi(-) channel was also studied with a measured branching ratio of (4.27 +/- 0.15(stat) +/- 0.17(syst)).10(-3), in good agreement with the ASTERIX result. RI Galli, Domenico/A-1606-2012; Iazzi, Felice/F-4490-2012; Botta, Elena/G-9742-2012; Villa, Mauro/C-9883-2009; Fontana, Andrea/I-4375-2012; Filippi, Alessandra/I-9530-201

Measurement of the frequency of the annihilation reaction anti-p p -> pi0 pi0 at rest in a NTP hydrogen target

The annihilation frequency of the reaction has been measured, for the first time by stopping antiprotons in a NTP hydrogen target. The obtained result is discussed in the frame of the study of the initial angular momentum of the p̄p system

Phi and omega-meson production in (N)-OVER-BAR-P annihilation and the ozi rule

The phipi+/omegapi+ ratio from npBAR annihilations on a liquid hydrogen target, for nBAR momenta between 64 and 297 MeV/c, was measured using the OBELIX spectrometer at LEAR. The ratio R(phipi/omegapi) = sigma(npBAR --&gt; phipi+)/sigma(npBAR --&gt; omegapi+) turned out 0.110 +/- 0.015(stat) +/- 0.006syst. Implications of this result on the OZI rule are discussed. RI Galli, Domenico/A-1606-2012; Iazzi, Felice/F-4490-2012; Botta, Elena/G-9742-2012; Villa, Mauro/C-9883-2009; Fontana, Andrea/I-4375-201

φπ0 and φη production in antiproton annihilation at rest in a hydrogen gas target at NTP

Data of antiproton annihilation at rest in a hydrogen gas target at NTP have been collected with the Obelix spectrometer exposed to the beam extracted from the LEAR accelerator of CERN. The reactions and have been studied. The analysis of the angular distribution of the kaons emitted by the φ decay has shown that the reaction occurs essentially from 3S1 states with a production rate RNTP = (2.46 ± 0.23 ± 0.07) × 10−4, while the rate from 1P1 states is compatible with zero. Because of acceptance limitations, 3S1 and 1P1 contributions to the reaction could not be resolved and lower and upper limits for the production rate have been measured with the middle value RNTP = (0.87 ± 0.21) × 10−4. Also, for the phase-space K+K−η events the production rate RNTP = (4.67 ± 0.35) × 10−4 has been measured. The φπ0 and φη branching ratios in S- and P-waves (defined in the text) have been estimated in a model dependent way. For the evaluation of the φη rate, a combination of our production rate and of data obtained with a liquid target has been used. The φπ0 production rate, compared to our preliminary value for the ωπ0 production, confirms the strong violation of the OZI rule observed in other experiments. No violation is apparent in the φη production

Protonium annihilation into KSKL at three different target densities

The frequency of the protonium annihilation channel has been measured at three different target densities: liquid hydrogen (LH), gaseous hydrogen at NTP conditions and gaseous hydrogen at low pressure (5 mbar). The obtained results are: .... . Since the KSKL final stat and be originated only from the 3S1 initial state, these values give direct information on the scaling of the protonium spin-triplet S-wave annihilation probability with the density