D. Dibitonto

Diffractive production of the charmed baryon Λ+c at the CERN ISR☆

Abstract In a sample of diffractive events of high multiplicity a sharp five standard deviation signal is observed at M = 2255 MeV/c2 in the K−pπ+ mass distribution and, although with less statistical strength, at the same mass in the Λ0π+π+π− channel. These signals are identified as being due to the decay of the charmed baryon Λ+c which is produced with a cross section times branching ratio σcB in the range 0.7−1.8 μb for the K−π+p decay and 0.3−0.7 μb for the Λ-π+π+ π− system.

Experimental observation of a copious yield of electrons with small transverse momenta in pp collisions at high energies

Abstract Inclusive electron and positron emission have been observed for θcm = 30° and s = 2800 GeV2 at the CERN Intersecting Storage Rings (ISR). Over the transverse momentum interval 0.2 GeV/c

Further evidence for production of electrons with small transverse momenta in pp collisions

A new measurement of prompt lepton production at small transverse momenta in pp collisions at the ISR, for s = 53 GeV, is presented. The cπ ratio, which is about 10−4 for pT > 1 GeV/c, rises rapidly as pT goes to smaller values, confirming our original results. The data are consistent with equality between the numbers of e+ and e− produced in each transverse momentum interval.

Search for D0-meson production in p-p interactions at a centre-of-mass energy of 53 GeV

Abstract A search for D(1.87) mesons produced at x ∼ 0.1 at the CERN ISR gave a null result. Cross-section upper limits of 9 μb and 8 μb at the 95% confidence level were measured for the processes p + p → D 0 + X, D 0 → K − + π + , and p + p → D 0 + X , D 0 → K + + π − , respectively. Producton of f 0 (1270) was observed with a cross-section of 1.9 ± 0.4 mb.

Production of charmed particles at the CERN intersecting storage rings in events triggered by an electron

Abstract Production of charmed particles has been investigated at √ s = 63 GeV usi ng the Lampshade Magnet detector triggered by electrons and positrons emitted at 30% from the ISR beam axis. The results of a search for Λ c and Λ c signals in the K − pπ + and K + p π − channels are presented. Cross sections for the reactions pp → D Λ c X and pp → Λ c Λ c X, and upper limits. for pp → D D X, are evaluated under various models and compared with other values obtained at the ISR.

Limits on e±μ∓ production in pp collisions at the CERN ISR

Abstract A search for the reaction p+p → e ± μ ± +X at the CERN ISR gave no evidence for this process. Upper limits for e ± μ ∓ /e +- are presented and are related to the branching fraction for leptonic decay of D(1.87).

Upper limit for DD production in pp interactions at C.M. energy of 55 GeV

Abstract From a search for e ± μ ± production at the CERN ISR an upper limit of 0.92 μ b (95% confidence limit) has been inferred for σ · B e · B μ for the reaction p + p → D + D + X at √s of 55 GeV .