Search

Measurements were made to detect differences in the velocity of propagation of $\ensuremath{\gamma}$ rays and electrons in the energy range 15-20 GeV, by using a time-of-flight technique with 1-psec sensitivity and a flight path of \ensuremath{\sim} 1 km. A relative velocity difference larger than $1\ensuremath{-}{\ensuremath{\beta}}_{e}$ (\ensuremath{\sim} 5\ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$) would imply a breakdown of special relativity. No significant difference in the velocities of light and electrons was observed to within \ensuremath{\sim} 2 parts in ${10}^{7}$.

A design for a secondary electron beam suitable for electron scattering experiments at the National Accelerator Laboratory is presented. Using standard NAL beam transport magnets it will operate at up to 300 GeV/c with the following properties: acceptance 9.5μsr%Δp/p(fw), momentum bite ±2%, momentum resolution of momentum hodoscope Δp/p=±0.30% (hw at base), final spot size ≤±3.0mm×±5.5mm(hw at base). Hodoscopes are also included for measuring the angles at which electrons pass through the experimental target with resolutions in both planes of better than ±0.1 mr. These properties are achieved by a periodic beam structure which includes correction of 2nd order aberrations by means of sextupoles. The yield of electrons is estimated to be ∽108/1013 incident protons when the energy of the electrons is about one half the energy of the protons. It is emphasized that synchrotron radiation by electrons in the beam transport magnets is very significant in reducing pion contamination of the final beam spot. It is shown that superconducting magnets to enhance this effect are superfluos. Pion impurity is ≤0.01% at every energy and may be made essentially zero at energies greater than 160 GeV. The beam is designed with four focussing stages, the first two of which provide a beam spot of sufficient quality for tagged photon experiments.

We present the analysis of the reaction π−p →π−π+n at 16 GeV/c. The total cross section for this channel was measured to be 0.40 ± 0.08 mb and production cross sections of 52 ± 13 ωb and 38 ± 9 ωb were determined for the ϱo and fo resonances, respectively. A comparison with the one-pion-exchange model of Wolf shows good agreement with our data.

The production of $\ensuremath{\Delta}(1236)$ by linearly polarized photons at 2.8 and 4.7 GeV was studied using a hydrogen bubble chamber. At 2.8 GeV the cross sections for $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\Delta}}^{++}{\ensuremath{\pi}}^{\ensuremath{-}}(\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\Delta}}^{0}{\ensuremath{\pi}}^{+},{\ensuremath{\Delta}}^{0}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{\ensuremath{-}})$ were found to be 3.7 \ifmmode\pm\else\textpm\fi{} 0.4 \ensuremath{\mu}b (0.5 \ifmmode\pm\else\textpm\fi{} 0.2 \ensuremath{\mu}b); at 4.7 GeV, 1.0 \ifmmode\pm\else\textpm\fi{} 0.1 \ensuremath{\mu}b (0.16 \ifmmode\pm\else\textpm\fi{} 0.09 \ensuremath{\mu}b). Measurement of the parity asymmetry, ${P}_{\ensuremath{\sigma}}$, for ${\ensuremath{\Delta}}^{++}$ production with $|t|l0.5$ Ge${\mathrm{V}}^{2}$ yielded the values -0.27 \ifmmode\pm\else\textpm\fi{} 0.12 and -0.53 \ifmmode\pm\else\textpm\fi{} 0.15 at 2.8 and 4.7 GeV, respectively, whereas pure one-pion exchange would lead to ${P}_{\ensuremath{\sigma}}=\ensuremath{-}1$.

The vector-dominance model predictions are used on the measurement of u -channel π − p → ϱ o n cross sections and a complete transversality system analysis on the ϱ o spin density matrix elements. The photon isovector part in γ p → π + n is isolated using the u -channel cross-section measurements and a specific Regge-pole fit for the Δ, N α and N γ trajectory exchanges. Both results are compared to examine their consistency.

A picosencond time measurement method is described based on the microwave properties of beams from electron linear accelerators or from possible remodulated external proton beams at proton synchrotrons. A conventional RF separator (RFS) is used operating at the same frequency as the microwave structure of beams and driven by the same master oscillator which modulates the beam. For example, the 2856 MHz microwave at SLAC corresponds to 350 psec between beam RF buckets; accelerated electrons with an RF phase bite of about 5 degrees are time structured and correspondingly have about 5 psec time spread in every 350 psec interval. Charged particles produced in interactions or decays originate with this time structure. An RFS is placed at the last stage of a double focussing spectrometer, providing a lever arm between it and the final (few mm) small spot size focus. Reference calibration charged particles are timed by setting the RFS relative phase to null deflections. Other observed particles arriving at different times than this standardare deflected a few tenths ofa anm per psec of delay. A multi-wire proportional chamber (IMPC) having a 0.05 mm space resolution can provide time measurements with sub-picosecond resolution. The technique is used in an experiment to search for changes in the velocity of light with high energy photons at SLAC. The devised timing method is presented and the properties of a new, fine space resolution MWPC is demonstrated.