Zaven G. T. Guiragossian

γp interactions at 5.25 GeV

Abstract 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.

A study of the reaction π−p → π−π+n at 16 GeV/c

Abstract 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 γ- ρO coupling constant, compton scattering, and total hadronic γ-p cross sections

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.

A MWPC Instrumentation System with Small Dead-Time and with Provision for Automatic Testing and Calibration

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.

THE SLAC MONOCHROMATIC PHOTON BEAM.

Abstract 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.

Delay Line MWPC Hazard Signals Inspector

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.

Four-Deep Charge-Time and Pulse-Width Scaling Discriminator for Delay Line MWPC's

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.

Picosecond Time Measuremnts with a Linear Accelerator and RF Separator

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.

Study ofγp→pωwith Linearly Polarized Photons at 2.8 and 4.7 GeV

1. Vertical scales for the density matrix elements p:O, Re p;O and piwl * are incorrectly labeled in Fig. 4. Change 0.4 to 0.2 and -0.4 to -0.2. Other density matrix elements and Pa are correctly labeled. 2. There are two typographical errors in Table IV: In IV-a (2.8 GeV Gottfried-Jackson system) for 0.06 5 It I I 0.15 GeV2, the value of 0 Re PlO is given as -0.14 f 0.04; it should be +O. 14 f 0.04. In IV-e (4.7 GeV helicity system) for 0.014 5 It I ,< 0.06 the value of pi-l should be -0.04 f 0.12; it is shown correctly in Fig. 4.

The ρO − ω interference parameters in diffractive photoproduction of vector mesons on hydrogen

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.