Why is it interesting?

Layman

Student

This is how phenomenology works:

Which of these new particles—the hypothetical neutral heavy lepton or the hypothetical charmed quark—was the progenitor of the dimuons? The test would lie in the distribution of their speeds. The relative speeds of the positively and negatively charged muons would depend on whether the heavy lepton or the charmed quark had been their parent. In the former case, both muons arose from the decay of the heavy lepton and, because both had a similar origin, they tended to emerge with similar speeds; in the latter, the positively charged muon arose from the decay of a charmed quark and would have a very different speed. Much as each brand of water gun produces its own characteristic spray of water, so the different particles, when they decay,produce their own characteristic dimuon distribution. Together with my colleagues Lay Nam Chang and John Ng, I began to investigate the properties of the dimuon distribution that resulted from heavy lepton production in order to compare it with the muonspeeds reported by Mann and his collaborators. It was a classic phenomenology problem, the comparison of theory and experiment, closely related to my thesis work, and so I knew how to calculate the distributions of the final speeds and angles of muons. Lay Nam, John, and I checked each other’s analytical calculations, and I wrote the computer program to evaluate the distribution of the muons. Suddenly I was involved again, and it was simply thrilling to be working on something new and relevant in close proximity to the experimentalists. I entered aperiod of great mental stimulation which resuscitated me. Spontaneously, I began to rise early in the morning; as soon as I awoke I rushed into work to calculate and program. I participated in long, intoxicating lybuoyant arguments and discussions on blackboards, where Lay Nam,John, and I took turns scribbling and talking, one of us seizing the chalk from the other. Rivalries and self-doubt disappeared as we pushed for-ward, working keenly late into the night. The exact nature of the hypothetical weak force responsible for the decay of the putative heavy lepton was not known—it had to be conjectured, and there were a variety of forms it could reasonably take. LayNam, John, and I calculated the relative speeds of the muons for a wide(but not exhaustive) range of forces.We showed that for all the cases we considered, the predicted disparity between the speeds of the positive and negative muon, when both were produced by the decay of a heavy lepton, was much smaller than the disparity observed by Mann and his collaborators. Therefore, we claimed, it was highly unlikely that the dimuon events signaled the production of a new heavy neutral lepton. We circulated our work as a “preprint,” a mimeographed prepublication report sent out to other physicists in the field, and it drew a gratifying spurt of attention. Now, almost down to the wire, I had completed a piece of research that would get me my next postdoc position, just as my two-year stint at Penn trailed off into its last few months. I sent out my letters of application and, late in the spring of 1975, in the nick of time, I received postdoctoral offers from the University of Wisconsin at Madisonand from Oxford University in England. The work we did on heavy leptons was topical and timely, but not quite thorough enough.Though we had shown that it was unlikely that a heavy lepton had produced the dimuons, we had not proved it truly impossible—we had not calculated the asymmetry for every possible form of the hypothetical weak force that caused its decay.A few months later, Bram Pais (one of the few Columbia seminar speakers I had seen stand up to T. D. Lee) and his long-time collaborator, Sam Treiman of Princeton, entered the scene. Both of them old hands at analyzing weak interactions, they derived a very general upper bound to the asymmetry between the speeds of the positive and negative muons produced in the decay of a heavy lepton, no matter what the form of its still unknown weak force. They showed that the maximum value of the asymmetry under any circumstances was smaller than the one observed by Mann and his collaborators, and so truly excluded heavy leptons as asource of the dimuons. What we had shown to be unlikely Pais and Treiman had then demonstrated to be impossible. More experienced and professional than Lay Nam, John, and me, they received the lion’s share of the credit, but we got a little, too; it was more than enough to get me that second postdoc offer from Oxford.

From My Life As A Quant by Emanuel Derman

Researcher

Common Question 1

Common Question 2

Examples

Example1

Example2:

History