This is the fifth and final part of Chapter 3 of the book "Anomaly! Collider Physics and the Quest for New Phenomena at Fermilab". (the beginning of the chapter was omitted since it described a different story). The chapter recounts the pioneering measurement of the Z mass by the CDF detector, and the competition with SLAC during the summer of 1989.  The title of the post is the same as the one of chapter 3, and it refers to the way some SLAC physicists called their Fermilab colleagues, whose hadron collider was to their eyes obviously inferior to the electron-positron linear collider. For part 1, see here. For part 2, see here. For part 3, see here. For part 4, see here.



On August 9, Mark II released their paper as a laboratory preprint, numbered SLAC-5037, and sent it to PRL. The measurement consisted in a fit to the number of events collected as a function of the center-of-mass energy of the electron-positron collisions. This allowed Mark II to "see" the resonance shape, obtaining the Z mass as the location of the peak rate. The Z boson mass was determined to be 91.11 ± 0.23 GeV, a 35% reduction in uncertainty from the CDF result. But it had come out two weeks later! Scooped by CDF by two weeks, the Mark II collaborators had to content themselves with scooping LEP. The four CERN experiments would start collecting data five days later and soon produce results 10 times more accurate than those of Mark II. As for the CDF and the Mark II articles, they ended up in print in the same issue of PRL, which got published on August 14. Below the abstract, the Mark II paper reads "Received July 24th 1989". This is in mismatch with the preprint cited above, dated August 9. Regardless, one is left wondering why the CDF article had to appeal to the special 1976 rule of APS, whereas the Mark II one, which did not, still made it in the next issue of the magazine. Evidently, the Mark II paper benefited from the very same treatment of the CDF one - no external refereeing. The editor-in-chief Lazarus probably decided to avoid favoring Fermilab against SLAC. This was the correct decision; besides, rather than one against the other the two laboratories were really both competing against CERN. The LEP results would soon come in and send the American measurements to eternal oblivion.

91.11 ± 0.23 GeV is a very accurate measurement, as we know today that the Z weighs 91.19 GeV. But the alert reader will notice that the Mark II estimate lays a whole GeV and a half below the value that Arthur showed to Ragan before his talk! Did Mark II revise in a rush their measurement, finding a mistake at the last moment, after the events of July 19? That is extremely unlikely: a 1.5-GeV shift in the measured Z mass is an enormous one given the 0.23 GeV uncertainty quoted in the final Mark II article. But the alternative is almost as startling: it involves imagining that Arthur had purposely produced a fake draft with a bogus number in the abstract, in order to puzzle the CDF speaker - maybe in the attempt of convincing him to remove the Z measurement from his talk.

One may imagine that if, in place of Ken Ragan, CDF had sent to give the talk one of the slimeballs that some scientists at SLAC claimed populated in large supply the CDF author list, the outcome of the topical conference would have been a much sweeter one for Mark II. That fact alone was enough to raise some bad feelings in the CDF collaborators. Several of them received by electronic mail a summary of the events, where Ken included a mention of the pre-talk incident with Arthur. Worse still, a few Mark II collaborators reportedly let go with inflammatory statements. They openly complained to the Fermilab management, arguing that the escamotage of using the Fermilab director's signature to speed up the review process of their paper was an act of belligerence against SLAC. Some of them went as far as to speculate that CDF had used leaked information on the Z mass that Mark II was fitting, in order to ascertain that their own measurement was in the right ballpark! Of course, the SLAC scientists were either getting the story of Arthur's leak wrong or were being bad losers. The inflammatory accusation against CDF could also be read between the lines in an article by David Perlman on the San Francisco Chronicle, which was evidently embargoed by SLAC and got published on July 21:

"What particularly annoyed the SLAC group, according to physicist Michael Riordan, is the fact that "Fermilab has very actively tried to scoop us by press release, even though their uncertainties are under serious challenge and they knew our measurements even before they released theirs." Reluctantly, however, Fermilab's Shochet conceded in a phone interview yesterday that Stanford's calculation was in fact predictably the more accurate."

This was only an inch short of accusing the CDF researches of scientific fraud, as it both questioned the uncertainty of their measurement and suggested that CDF might have used the knowledge of the "correct" Z mass - the one Mark II had estimated - to fine-tune their result! Many CDF members were shocked by the Chronicle article, and even more so by seeing that the Fermilab management did nothing to react to that absolute lack of fair play by the scientists of the other laboratory.

In retrospect, Arthur's trick and the allegations of the Mark II scientists leave a bad flavor to the whole story. Yet, it makes sense to try and discern a deeper meaning behind such petty behavior. Those reactions had their deepest roots in the strong belief that the SLAC scientists held about the impossibility of doing precision physics with hadron collisions. That was the gospel they had heard for years, as well as their motivation for planning a career in electron–positron machines and experiments. That gospel had brought them to sink in a groupthink black hole, one from which they were unable to get out. To them, a hadron collider could never be capable of reaching a 300-MeV precision on the mass of the Z, because! Because it was obviously impossible. Given this belief, their syllogism was immediate: if CDF had managed to produce such an accurate determination of the Z mass (they knew it was accurate since they measured the same value!), it meant CDF had cheated. The above syllogism explains the name-calling as well as Arthur's juvenile trick, yet the Mark II scientists were badly wrong: the hadron collider result was as genuine as theirs, and it was actually a groundbreaking scientific accomplishment.

As for the methods that allowed CDF to reduce the systematic uncertainties on electron energy scale, muon momentum scale, and all the other small nuisances that one has to worry about when performing sub-percent measurements, they have become cherished standards in hadron collisions and have enabled CDF to hold the world's best measurement on the W boson mass before and after the LEP II electron-positron collider, CERN's "W factory," got in that game. At the time of writing, the W boson mass is known with 0.02% precision thanks to the final CDF result, which is still the world's best.


Tommaso Dorigo is an experimental particle physicist, who works for the INFN at the University of Padova, and collaborates with the CMS experiment at the CERN LHC. He coordinates the European network AMVA4NewPhysics as well as research in accelerator-based physics for INFN-Padova, and is an editor of the journal Reviews in Physics. In 2016 Dorigo published the book “Anomaly! Collider physics and the quest for new phenomena at Fermilab”. You can purchase a copy of the book by clicking on the book cover in the column on the right.