A. Lundby

Elastic scattering and two-body annihilations at 5 GeV/c

We present results of measurements of K±p and pp elastic scattering and of the annihilation reactions pp→π+π− and pp→K+K− at an incident laboratory momentum of 5 GeV/c. Nearly complete angular distributions were obtained. Results are also presented for π-meson proton elastic scattering in the momentum transfer ranges 2 < −t < 8 (GeV/c)2 (for π+) and 0.16 < −t < 7 (GeV/c)2 (for π−). All measurements were done in one experimental geometry. The measured differential cross sections range from 10 to 10−5 mb/(GeV/c)2. For the first time, backward peaks have been observed in K−p and pp elastic scattering. In K+p elastic scattering the forward peak shows a break at −t ≈ 0.8 (GeV/c)2 and the backward peak shows a structure at −u ≈ 1.2 (GeV/c)2. Large angle πp scattering oscillates around an average differential cross section of 0.1 μb/(GeV/c)2. In addition to the well-known dip at −t ≈ 3 (GeV/c)2, we observe further dips at −t ≈ 4.6 and 5.7 (GeV/c)2. The annihilation reactions show both forward and backward peaks.

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.

K±p elastic scattering at 5 GeV/c. Evidence for a K−p backward peak

The elastic scattering of K± mesons on protons has been studied at 5 GeV/c. A total of about 500 000 events have been measured in the c.m. angular range 17° < θcm < 165° corresponding to 0.2 < −t < (GeV/c)2. We observed a K−p backward peak which we have parametrized as dσ/du = (0.6 ± 0.2) exp [(3.3 ± 0.6)u] μb/(GeV/c)2, while for the K+p backward peak we find dσ/du = (17.5 ± 1) exp [(3.6 ± 0.2)u] μb/(GeV/c)2. The K−p cross-section falls to about 0.03 μb(GeV/c)2 around −t = 5 (GeV/c)2, while the K+p cross-section stays in the vicinity of 0.3 μb(GeV/c)2 in the same t-region. The K+p and K−p differential cross-sections have cross-over points at −t = 0.2, 1.1 and about 3.5 (GeV/c)2.

Elastic forward and backward scattering of π− and K-mesons at 5.2 and 7.0 GeV/c

Abstract We present results of measurements of the differential cross sections for the following elastic-scattering reactions: (i) π + p at 5.2 and 7.0 GeV/ c in the range −1 u c ) 2 , (ii) π − p at 7.0 GeV/ c in the range −0.7 u c ) 2 , (iii) K + p at 5.2 and 7.0 GeV/ c in the ranges −1 t c ) 2 and −1 u c ) 2 , and K − p at 7.0 GeV/ c in the range −1 u c ) 2 . Backward peaks were observed in K + p scattering with an energy dependence s −4 . No event was found in backward K − p scattering. The anglar distributions of forward K + p elastic scattering show no structure. Backward π + p elastic scattering shows the known dip at u ≈ −0.15 (GeV/ c ) 2 , which in this experiment was covered in one geometry.

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.

Kp and πp backward elastic scattering at 5.2 and 6.9 GeV/c

Abstract The angular distributions of K + p and π + p backward elastic scattering have been measured at 5.2 and 6.9 GeV/ c . Backward π - p and K - p elastic scattering were studied at 6.9 GeV/ c . Backward peaks are observed in K + p scattering with an energy dependence of the form s −4 .

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.

Disc: Compteur Cherenkov a selection de vitesse

Abstract A class of differential Cerenkov counters with liquids or gases as radiators is described, which makes use of the essential characteristic features of Cerenkov light. The counters are directional, isochronous and self-collimating, thus called DISC. The optical system has been designed so as to extract the maximum information from the Cerenkov light in the most efficient way, thus minimizing the radiator thickness.

K±p elastic scattering at 3.55 GeV/c

Abstract We present results of measurements of K±p elastic scattering at 3.55 GeV/c in the c.m. angular ranges from 10° to 70° (0.16