We present new precision measurements of the ψ (2 S) total and partial widths from excitation curves obtained in antiproton-proton annihilations by Fermilab experiment E835 at the Antiproton Accumulator in the year 2000. A new technique of complementary scans was developed to study narrow resonances with stochastically cooled antiproton beams. The technique relies on precise revolution-frequency and orbit-length measurements, while making the analysis of the excitation curve almost independent of machine lattice parameters. We study the ψ (2 S) meson through the processes over(p, ̄) p → e+ e- and over(p, ̄) p → J / ψ + X → e+ e- + X. We measure the width to be Γ = 290 ± 25 (sta) ± 4 (sys) keV and the combination of partial widths Γe+ e- Γover(p, ̄) p / Γ = 579 ± 38 (sta) ± 36 (sys) meV, which represent the most precise measurements to date.
|Original language||English (US)|
|Number of pages||6|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - Oct 11 2007|
Bibliographical noteFunding Information:
We gratefully acknowledge the support of the Fermilab staff and technicians and especially the Antiproton Source Department of the Accelerator Division and the On-line Department of the Computing Division. We also wish to thank the INFN and University technicians and engineers from Ferrara, Genoa, Turin and Northwestern for their valuable work. This research was supported by the Italian Istituto Nazionale di Fisica Nucleare (INFN) and the US Department of Energy.