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

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

Measurements of the anti-p d annihilation at rest

The measurement of different reactions of d annihilation at rest in a gaseous target has been performed using the OBELIX spectrometer at LEAR (CERN). A strong deviation from the OZI-rule prediction was found from the measurement of the ratio in two regions of proton momenta, P < 200 MeV/c and P > 400 MeV/c: and (113 ± 30) × 10−3, respectively. These values are about 30 times greater than the theoretical prediction. For the first time the excitation of the †-resonance was observed among the final-state products of d annihilation. The existence of a broad enhancement in the 4π invariant mass at m ≈ 1480 MeV, seen in previous experiments, was confirmed. A ≈ 100 MeV downward shift of the bump position, when the proton momentum increased up to P > 400 MeV/c, was also observed, while the positions of ω, ϱ and f2(1270) did not change with the proton momentum. The following branching ratios were measured: .

EVIDENCE OF A NEW STATE AT SIMILAR-TO-1660-MEV/C(2) OBSERVED IN NP-ANNIHILATIONS

A study of up in-night annihilations is presented. The 4 pi invariant mass spectrum resulting from the analysis of the five-prong exclusive events, following the annihilation of similar to(100-297) MeV/c ($) over bar n, reveals, besides a large structure centred at similar to 1500 MeV/c(2), some evidences for a new state around 1660 MeV/c(2). 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

First results from obelix on reactions with detected neutral pions in the final state

We describe some results obtained by the OBELIX experiment at LEAR by exploiting the whole spectrometer, including the electromagnetic calorimeter, to study the antiproton-proton annihilation at rest in an NTP hydrogen target. In particular, we give some information on the calibration of the calorimeter, as obtained from the analysis of two-prong events, and we describe the status of the analysis of the first sample of ''all neutrals'' events collected in gaseous hydrogen. A preliminary result on the branching ratio of the annihilation reaction ($) over bar pp-->pi(0) pi(0) is reported. 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

MESON SPECTROSCOPY WITH S-WAVE AND P-WAVE DOMINANT INITIAL-STATE SELECTION IN (P)OVER-BAR-P-ANNIHILATION

The possibility of selecting the initial angular-momentum state from which antiproton-proton annihilation at rest can occur can be a fundamental tool in meson spectroscopy. With the OBELIX detector different target systems have been employed, ranging from S-wave to P-wave dominance. The preliminary results both on meson spectroscopy and branching ratio measurements 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-4375-2012; Filippi, Alessandra/I-9530-201