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This paper describes some of the system features of a large array of instrumentation to be used for data collection in an experiment utilizing multi-wire proportional chambers (MWPC) of both the amplifierper-wire and the delay-line types. The system is designed to uniquely meet special functional requirements for background reduction and dead-time reduction in high counting-rate experiments at FERMILAB.

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 ${10}^{7}$.

Author(s): Chung, Suh Urk; Neveu-Rene, Monique; Dahl, Orin X.; Kirz, Janos; Miller, Donald H.; Guiragossian, Zaven T.

An analysis was made of the decay angular distribution of rho mesons produced via $\ensuremath{\gamma}p\ensuremath{\rightarrow}p{\ensuremath{\rho}}^{0}$ by linearly polarized photons at 2.8 and 4.7 GeV. The reaction proceeds almost completely through natural-parity exchange, the contribution from unnatural-parity exchange for momentum transfers $|t|l1$ Ge${\mathrm{V}}^{2}$ being (3.1\ifmmode\pm\else\textpm\fi{}2.2)% at 2.8 GeV and (-1.1\ifmmode\pm\else\textpm\fi{}1.9)% at 4.7 GeV. The behavior of the density-matrix elements shows that the rho-production mechanism conserves $s$-channel c.m. system helicity for $|t|l0.4$ Ge${\mathrm{V}}^{2}$.

In ${\ensuremath{\pi}}^{\ensuremath{-}}p$ single-pion-production reactions near 4 GeV/c, we observe several interesting features. Backward ${\ensuremath{\rho}}^{0}$ production is seen to occur with $\frac{d\ensuremath{\sigma}}{\mathrm{du}}=63\ifmmode\pm\else\textpm\fi{}21$ \ensuremath{\mu}b/${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ at 180\ifmmode^\circ\else\textdegree\fi{}. Backward ${\ensuremath{\rho}}^{\ensuremath{-}}$ production is less prominent. We see evidence for production at small $u$ of ${N}^{*0}$ ($p{\ensuremath{\pi}}^{\ensuremath{-}}$ near 1700 MeV) and ${\ensuremath{\Delta}}^{\ensuremath{-}}$ ($n{\ensuremath{\pi}}^{\ensuremath{-}}$ at 1236 MeV), and possible evidence for other $n{\ensuremath{\pi}}^{\ensuremath{-}}$ structure at about 1800 MeV. The density-matrix elements for peripheral ${\ensuremath{\rho}}^{0}$ production are presented in the Jackson and in the helicity frame. The ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ elastic cross section is obtained by extrapolation of the data to the mass shell. The $S$-wave $\ensuremath{\pi}\ensuremath{\pi}$ phase shifts are calculated by two methods and compared with previous results. We find evidence in the dipion decay angular distribution for the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decay mode of the ${S}^{*}(1070)$.

The total hadronic $\ensuremath{\gamma}p$ cross section has been measured using 7.5-GeV positron-electron annihilation radiation in a hydrogen bubble chamber. A value of 126 \ifmmode\pm\else\textpm\fi{} 17 \ensuremath{\mu}b is found, excluding reactions with only one charged particle (\ensuremath{\sim}3 \ensuremath{\mu}b).

Agreement with the Vector Dominance Model predictions are obtained in a system where the pion produced vector mesons are described in the Donohue-Hogaasen frame. generalized to account for the presence of s-wave contributions. In this system the admixture of polarizations from the element ϱ 10 V are suppressed by a dynamical unitary transformation on the helicity frame spin density matrix. The tests are applied to pion photoproduction data by polarized and unpolarized photons; also an independent search is made for the γ-ϱ coupling constant at q 2 = 0, yielding a value of γ ϱ 2 /4 π = 0.40 ± 0.03.

A multi-GeV monochromatic photon beam is operational at SLAC. The energy spectrum consists of a monochromatic part, derived from the in-flight annihilation of positrons, superimposed on the usual thin target bremsstrahlung. The beam has been successfully utilized in the study of photoproduction processes by both bubble chamber and spark chamber techniques.

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.

A nearly monochromatic high-energy photon beam produced by Compton backscattering of ruby laser light has been used to study photoproduction in a hydrogen bubble chamber. The total hadronic γp cross sections at 1.44, 2.8, and 4.7 GeV are found to be 145.1 ± 5.7, 131.3 ± 4.3, and 124.2 ± 3.9 μb, respectively. Partial cross sections are presented also. © 1969 The American Physical Society.

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.

pi/sup -/ + p yields mas teractions. SU/sub 3/ validity is shown by application to baryonThaler phase shifts as a starting point. The polarization, polarization contour map, and phase-shifts are presented. (C.E.S.)

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 orbital angular momentum of the ${A}_{1}$ meson produced from ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}p$ at 16 GeV/c was studied by analyzing the decay angular distributions in the ${\ensuremath{\rho}}^{0}{\ensuremath{\pi}}^{\ensuremath{-}}$ state. A completely Bose-symmetrized formalism was used to measure the ratio $\frac{{g}_{1}}{{g}_{0}}$ of the helicity states of the $\ensuremath{\rho}$ from the ${A}_{1}$ decay. The value obtained, $|\frac{{g}_{1}}{{g}_{0}}|=0.48\ifmmode\pm\else\textpm\fi{}0.13$, indicates a substantial $d$-wave contribution in the ${A}_{1}$ decay.

Photoproduction of resonances has been studied using positron annihilation radiation at 5.25 GeV in the SLAC 40-inch hydrogen bubble chamber. Results are presented on the nonstrange particle events and related to the vector dominance model.

We have observed a resonance in the ${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ final state with $I=0$, $M=1.06\ifmmode\pm\else\textpm\fi{}0.015$ GeV, and $\ensuremath{\Gamma}l0.07$ GeV; our analysis favors $lg~2$. It is produced primarily at a four-momentum transfer squared less than 0.1 Ge${\mathrm{V}}^{2}$, and observed most clearly in the region where the cosine of the $\ensuremath{\pi}\ensuremath{\pi}$ scattering angle is less than -0.75.

Author(s): Barbaro-Galtieri, A.; Matison, M.J.; Rittenberg, A.; Chadwick, G.B.; Guiragossian, Z.G.T.; Pickup, E.

A Vector Dominance Model relation, free of interference terms, has been tested to discriminate for values of the γϱ coupling constant in favor of γϱ24π = 0.52. The diffractive part of Compton scattering is examined under a ϱ-dominance assumption and compared with ϱO photoproduction, and the behavior of σtot(γp) at high energies is shown.

We have examined the reaction γp → π+π−p for evidence of ϱo − ω interference. Assuming the ratio of the ϱo and ω-photoproduction amplitudes to be |Aϱ/Aω|2 = 7.1 ± 0.7, we find that the Re(δeiβ) = 2.3 ± 0.9 MeV and Im (δeiβ) = −0.4 ± 0.9 MeV, where δ(≈ 2.3 MeV) is the mass mixing parameter and β(≈ −9o) is the relative phase of the ϱo −ω amplitudes. Our result, obtained using a hydrogen bubble chamber, agrees with the high-statistics Daresbury result using photoproduction on carbon.

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.

Data from the reactions ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}p$ and ${\ensuremath{\pi}}^{+}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}p$ have been obtained at 16 GeV/c in approximately equal samples from the BNL 80-in. hydrogen bubble chamber. We have studied both reactions for resonance production and compared our results with predictions of the one-pion-exchange model (OPEM) calculated by Wolf. The four-body longitudinal phase-space (LPS) plot suggested by Van Hove was used to analyze the data from both reactions. The events were separated according to distinct regions of the LPS plot in order to study the following classes of quasi-two-body final states: (1) diffractively produced three-pion states, (2) diffractively produced $\ensuremath{\pi}\ensuremath{\pi}p$ states, (3) double-resonance production such as ${\ensuremath{\rho}}^{0}{\ensuremath{\Delta}}^{++}$, (4) single-resonance production such as ${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\Delta}}^{++}$. The Van Hove analysis provided a much cleaner separation of resonances from background effects than the usual techniques. We observe production of the ${A}_{1}$ and ${A}_{2}$ mesons as well as the ${N}^{*}(1470)$ and ${N}^{*}(1700)$ isobars in the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}p$ system for both reactions. There is strong formation of the doubly resonant states ${\ensuremath{\rho}}^{0}{\ensuremath{\Delta}}^{++}$ and ${f}^{0}{\ensuremath{\Delta}}^{++}$ and the general features of the nondiffractive events are all in good agreement with one-pion exchange. Detailed comparisons between the data and the OPEM in each LPS plot region show that Van Hove analysis provides a sensitive test for the OPE model.

Signal shaping properties are demonstrated with a large NaI(Tl) crystal assembly, 20 in. thick and 30 in. in diameter. Correlated energy resolution responses are shown for total energy absorption in the crystal from 580 MeV electrons. Light collection optics by diffuse reflection most likely determined the 10% to 90% rise-time of signals of 80 nsec, connected with the transit time of trapped light, before it reaches a photocathode surface. Using a signal clipping technique, the trailing edge of pulses are shaped to have base-lines entirely restored to zero. Providing good energy resolution, signals are obtained which are shaped to have 200 nsec full-width at base. The energy resolution responses from signal pulse-height measurement are demonstrated. Further improvements to obtain shorter pulse-widths are discussed and the capability of these crystals to handle several types of background is shown.

The Hazard Inspector is a CAMAC module which divides a MWPC delay line into 8 independent signal monitor and control segments. Independent control effectively reduces delay line occupation time and cuts the number of background and non-trigger particles accepted by the 4XQT charge-time-pulse-width digitizer, a device presented in a separate communication. Only segments containing legitimate information are digitized. Non-trigger related events are gated out at the digitizer, and contaminating hits are noted for computer correction.

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.

We observe production of the ${A}_{2}$ meson in the reaction $\ensuremath{\gamma}p\ensuremath{\rightarrow}n{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ at 4.3 and 5.25 GeV. The data are consistent with a one-pion-exchange production mechanism and we give an estimate of $\ensuremath{\Gamma}({A}_{2}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\pi})\ensuremath{\approx}0.5$ MeV. A similar value for $\ensuremath{\Gamma}({A}_{2}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\pi})$ is also obtained using a vector dominance model.

A discriminator has been developed for digitizing both intercepted total charge and location of electromagnetic shower and particle trajectories in multiwire proportional chambers read by delay lines. Determination of shower trajectory is aided by video signal integration followed by centroid-locating discrimination. Calibrated run-down of the signal integrating capacitor gives the charge information above a given threshold level. The discriminator is designed to handle up to four shower-induced video signals per event by incorporating steering circuits within the module. Each video signal is examined for time over an adjustable threshold. Video pulses with separation of less than 20 nsec are treated as a single pulse. Counter-logic circuits indicate the number of video signals digitized. These signal processing circuits provide a first level of data sifting which otherwise must be carried out with additional discriminator channels and added complexity in data recognition.