K. Kirsebom

Search for the 1P1 charmonium state in pp annihilations at the CERN intersecting storage rings

Abstract This experiment has been performed at the CERN Intersecting Storage Rings to study the direct formation of charmonium states in antiproton-proton annihilations. The experimental program has partly been devoted to an inclusive scan for p p → J /ψ + X in the range 3520–3530 MeV/c2. A cluster of five events has been observed in a narrow energy band, centred on the centre of gravity of the 3PJ states where the 1P1 is expected to be. When interpreted as a new resonace, these data yield a mass m = 3525.4±0.8 MeV/c2.

Direct observation and partial-width measurement of γγ decay of charmonium states

As part of the charmonium formation experiment at the CERN Intersecting Storage Rings, we studied the reaction pp→cc→γγ in an antiproton momentum scan through the ηc, χ1, and χ2 regions. We report events observed in the ηc and χ2 regions, whilst no event was observed in the χ1 region, as expected for a spin-1 state.

J/Ψ resonant formation and mass measurement in antiproton-proton annihilations

Abstract Experiment R704, the last to be performed at the CERN-ISR, has successfully applied a new method to study ( c c ) states formed directly in antiproton-proton annihilations. The novelty of the method rests on the capability to build a highly performing annihilation source by letting a cold

Formation of the χ1 and χ2 charmonium resonances in antiproton-proton annihilation and measurements of their masses and total widths

In an experiment performed at the CERN-ISR the direct formation is observed of the χ1 and χ2 charmonium states in proton-antiproton annihiliation. A novel technique provided excellent energy resolution together with small background and reduced systematics. The following values for the masses and total widths of the states were obtained: Λχ1 <3 MeV (95% CL); mχ1 = (3511.3±0.4±0.4) MeV; Λχ2=(2.6 +1.4−1.0) MeV; mξ2=(3556.9±0.4±0.5) MeV. First measurements of the partial widths to antiproton-proton are also reported: Λ(χ1→pp)=57+13-11±11) and Λ(χ2→pp)=(233 +51-45±48) eV.

Upper limits of the proton magnetic form factor in the time-like region from p̄p→ e+e- at the CERN-ISR

Abstract From the measurement of e + e - pairs from the reaction pp→e + e - at the CERN-ISR, using an antiproton beam and a hydrogen jet target, we derived upper limits for the proton magnetic form factor in the time-like region at Q 2 ⋍8.9( GeV c ) 2 and Q 2 ⋍12.5( GeV c ) 2 .

Measurement of the φφ cross section in pp annihilations at ECM≈3 GeV

In an experiment performed at the CERN Intersecting Storage Rings as a part of an energy scan to detect the ηc formation in pp annihilation, we studied the reaction pp→φφ→K+K−K+K−. The total cross section has been determined to be 25.0± 7.4±3.8 nb.

Precision measurements of the antiproton-proton elastic scattering cross section at 90° in the incident momentum range between 3.5 GeV/c and 5.7 GeV/c

Abstract The high antiproton-proton luminosity obtained by using a target system consisting of a hydrogen gas-jet crossing a coasting beam of cooled antiproton circulating in one of the rings of CERNs ISR provides the possibility to measure low cross section reactions with very high precision. We present measurements of the antiproton-proton elastic cross section at 90° CM at incident momenta between 3.5 GeV/ c and 5.7 GeV/ c . The precision of these measurements is much higher than previously reported results. The data show that the cross section of this reaction decreases faster than s −12 over this momentum range.

Study of the reaction anti-p p ---> phi phi from 1.1-GeV/c to 2.0-GeV/c

A study has been performed of the reaction pbar p -> 4K using in-flight antiprotons from 1.1 to 2.0 GeV/c incident momentum interacting with a hydrogen jet target. The reaction is dominated by the production of a pair of phi mesons. The pbar p -> phi phi cross section rises sharply above threshold and then falls continuously as a function of increasing antiproton momentum. The overall magnitude of the cross section exceeds expectations from a simple application of the OZI rule by two orders of magnitude. In a fine scan around the xi/f_J(2230) resonance, no structure is observed. A limit is set for the double branching ratio B(xi -> pbar p) * B(xi -> phi phi) < 6e-5 for a spin 2 resonance of M = 2.235 GeV and Width = 15 MeV.

Study of the reaction pbar p -> phi phi from 1.1 to 2.0 GeV/c

A study has been performed of the reaction pbar p -> 4K using in-flight antiprotons from 1.1 to 2.0 GeV/c incident momentum interacting with a hydrogen jet target. The reaction is dominated by the production of a pair of phi mesons. The pbar p -> phi phi cross section rises sharply above threshold and then falls continuously as a function of increasing antiproton momentum. The overall magnitude of the cross section exceeds expectations from a simple application of the OZI rule by two orders of magnitude. In a fine scan around the xi/f_J(2230) resonance, no structure is observed. A limit is set for the double branching ratio B(xi -> pbar p) * B(xi -> phi phi) < 6e-5 for a spin 2 resonance of M = 2.235 GeV and Width = 15 MeV.

Measurement of the

Abstract Data collected in the experiment R704 at the CERN ISR are used to study the annihilation process p p → π 0 π 0 at several centre-of-mass energies between 2.97 and 3.56 GeV. A total sample of 7359 events has been identified, from which cross sections and angular distributions in the interval 0 cos θ ∗ | have been measured.