Photoproduction of the Psi Particles *

The s and t dependence of incoherent +(3100) photoproduction from deuterium has been measured at the Stanford Linear Accelerator Center. $(3'700) photoproduction and #(3100) photoproduction from hydrogen have also been measured,Two narrow resonances have recently been discovered, the $(3100) and the zjJ(3700). l Since the original discovery, the $(3100) has been observed in photo-production by 100-200 GeV photons from a Beryillium target at Fermilab. 2 This paper reports the results of photoproduction *measurements of psi particles at the Stanford Linear Accelerator Center (SLAC). Both psi particles were detected by observing the decays into lepton pairs. The experiment was carried out using the 8 CeV and 20 GeV spectrometers instrumented to detect both electron and muon pairs from psi decay. A brems-r. strahlung beam from a 5% radiator was incident on 30.3 cm liquid hydrogen or liquid deuterium targets. Identical empty target cells were available for background studies. The beam intensity was monitored with the SLAC 1.6 GeV spectrometer, which was periodically calibrated against a secondary emission quantame ter e The overall accuracy of beam intensity monitoring was better than 3%. Typical beam intensities were 2 x 10 lo equivalent quanta (EQ) per 1.6 psec SLAC beam pulse. The detection system was essentially identical in each spectrometer. Electrons were identified by a threshold gas Cerenkov counter, a lead'glass preradiator, and a lead-lucite shower counter. The measured single arm electron yields were principally due to electrons produced directly in the target , and from electrons produced by r "-my decays with subsequent conversion of one of the photons in the target material. Muons were identified with an iron-scintillation counter range telescope.. The single arm muon yields, primarily due to muons from pion decay, were typically 3-40/o of the pion flux and a factor of 20-30 higher than the single arm electron yields. The trigger pulses were used to strobe momentum and angle defining hodo-scopes. These hodoscopes consisted of proportional wire chambers in the 20-3-GeV spectrometer, and scintillation counter hodoscopes in the 8 GeV spectrometer. The hodoscope information was used to determine the invariant mass of the electron or muon pair and this information, as well as relative coincidence times between the spectrometers and various puls6 height information, was logged on magnetic tape and displayed online by an SDS 9300 computer. The resolution of the hodoscopes was approximately .15% in momentum and 0.3 mrad in production angle, giving an invariant mass resolution of-20 …