Low Mass and Low Transverse Momentum Direct Electron-Positron Production in Proton Beryllium Interactions

Amrit Yegneswaran

Interest in the production of direct leptons in hadronic interactions dates back to the early sixties. Over the years, data on the production of direct single-leptons and direct lepton-pairs have been accumulated. The lepton pair data, however, suffers from low statistics. Production of direct single-lepton and direct lepton-pairs are assumed to be connected even though the nature of this relationship is not clear. The low mass and low transverse-momentum behaviour of the data are not understood. Further, a proton proton interaction experiment, at 800 [MeV] laboratory beam kinetic energy, observed no direct signals.

Low-mass direct lepton-pair production is the simplest of all hadronic interactions and an understanding of this process should be helpful in understanding more complicated processes. Understanding the hadronic case will in turn be useful in extracting the signature of the quark-gluon plasma which is conjectured to be formed at higher center of mass energies. This is one of the main reasons for the renewed interest in this field. Leptons are ideal probes for such experiments because they are not affected by strong interactions. These factors taken together make the study of direct lepton-pairs essential.

This thesis reports on the production of direct electron-positron pairs in proton-Beryllium interactions. For these interactions, proton beams with laboratory kinetic energies of 4.90 [GeV], 2.10 [GeV], and 1.04 [GeV] were used to bombard segmented Beryllium targets. The electron-positron pairs were identified with the aid of a two arm spectrometer known as the Di-Lepton-Spectrometer. Each arm of the spectrometer consisted of two hodoscope planes, three drift chambers, two gas Cerenkov counters and an array of lead glass blocks. Analysis of the data involved the identification and the extraction of relevant physical quantities of the direct electron-positron pairs.

This series of experiments for the first time established the existence and determined the production cross-sections of direct electron-positron pairs in proton-Beryllium interactions.

Return to list of theses