Search Results (4 total)

The Tevatron in Collider Run II (2001–present) is operating with 6 times more bunches, many times higher beam intensities and luminosities than in Run I (1992–1995). Electromagnetic long-range and head-on interactions of high intensity proton and antiproton beams have been significant sources of beam loss and lifetime limitations. We present observations of the beam-beam phenomena in the Tevatron and results of relevant beam studies. We analyze the data and various methods employed in operations, predict the performance for planned luminosity upgrades, and discuss ways to improve it.

The cross section of the process e⁺e^-→π⁺π^-π⁰ was measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2M collider in the energy region sqrt[s] below 980 MeV. This measurement was based on about 1.2×10⁶ selected events. The obtained cross section was analyzed together with the SND and DM2 data in the energy region sqrt[s] up to 2 GeV. The ω-meson parameters m_ω=782.79±0.08±0.09 MeV, Γ_ω=8.68±0.04±0.15 MeV, and σ(ω→3π)=1615±9±57 nb were obtained. It was found that the experimental data cannot be described by a sum of only ω, φ, ω^′, and ω^″ resonance contributions. This can be interpreted as a manifestation of ρ→3π decay, suppressed by G parity, with a relative probability B(ρ→3π)=(1.01_-0.36^+0.54±0.034)×10^-4.

Analytic calculation and numerical simulations reveal a multiline structure in the spectrum of coherent dipole oscillations in the colliding beam system due to coupled synchrobetatron beam-beam modes. The model employed in the analysis involves linearization of the beam-beam kick and takes into account the fact that the length of the colliding bunches is finite. In the present paper, we discuss the behavior of the synchrobetatron beam-beam modes, obtained both analytically and numerically, and compare it with the experimental results for the VEPP-2M collider. A particular case of the betatron tune close to the half-integer resonance is considered on the basis of the presented models.

A numerical simulation of a possible coherent beam-beam instability of the head-tail type is presented. The studied model employs a linearized coherent beam-beam interaction and takes complete account of the bunch length, including the deformation of the colliding bunches during their overlap. Measured head-tail mode spectra from the VEPP-2M collider are compared with the results of the analytical model and tracking. A computer code for evaluation of the coherent mode increments, which was used for analysis of possible ways to stabilize the beam-beam system, is described.