Tuesday, January 31, 2017 ... /////

Anomaly! by Tommaso Dorigo, a review

A guest blog: a review by Tristan du Pree of CMS at CERN

Anomaly! Collider Physics and the Quest for New Phenomena at Fermilab
World Scientific Publishing

Book by Tommaso Dorigo, 2016

To the outside world, Italian particle physicist Tommaso Dorigo is best known for his blogs, not afraid to express his personal thoughts about particle physics research. His new book, ‘Anomaly!’, describes this research from the inside – it covers the parts of the field that one normally does not hear about: the history, the sociology, and everything usually happening behind the screens.

Dorigo

In the world of Big Science, nowadays performed at CERN in collaborations of thousands of particle physicists, press releases have become as common as reconstruction algorithms. Of course, any personal opinion will be carefully hidden and controversial statements should be avoided at all costs. Dorigo’s new book, about the research at the American Tevatron collider at the end of the 20th century, is his latest piece that goes against this trend.

Within the CMS Collaboration at CERN, where the INFN physicist performs his research nowadays, Dorigo is mostly known as a statistics expert. Professionally, I have interacted with Dorigo as reviewer of some of my own searches at CMS for physics beyond the Standard Model, where I encountered him as a thorough, sometimes pedantic, but usually very efficient reviewer. Unsurprisingly, his role in this book is also one of a reviewer – a young researcher who has the important role of validating the claims of one of the CDF collaborators in this book.

But this book is not about Tommaso himself. Like the extensive lists of authors of experimental particle physics papers, the main character in this book is the CDF Collaboration.

CDF

The CDF experiment was located at one of the interaction points of the Tevatron collider at Fermilab, near Chicago. This book illustrates, after starting from a collaboration of the order of hundred people in the mid eighties, how the CDF collaboration had successfully constructed a silicon tracker, advanced the identification of heavy-flavor quarks, and discovered the top quark. In many senses, they did pioneering work for the research that we, together with my thousands of colleagues, are currently doing at the LHC at CERN.

The discovery at the Tevatron of the top quark, the sixth, and surprisingly heavy quark, was one of the major discoveries of CDF, confirming the Standard Model of particle physics. While reading about the 1990’s research in the US, the similarity of the top quark discovery with the later discovery of the Higgs boson at CERN is easily seen. Some people are quickly convinced this to be a real effect, whereas others needed more evidence. In the end, the first group turned out to be right, but the latter group wasn’t wrong either.

The internal reviews of such anomalous events, events that could possibly be the first signs of a new discovery, lead to lively internal discussions. Those are the main subject of this book.

BSM

Whereas confirming in further detail the Standard Model is a great achievement, truly finding something beyond would be the ultimate scientific jackpot. And apparently, people inside CDF were convinced some unexpected events were the first hints of such new physics. In ‘Anomaly!’, various of such events pass by: anomalous Higgs-like events, events with “superjets”, possible hints of bottom squarks, dimuon bumps, etcetera... Even though we now know these claims were all premature, these discussions are very entertaining and useful to read.

Do we really understand all detector effects? Does it harm our image if we later have to retract a claim? Will the media misrepresent our claims, which could possibly negatively influence our funding? Should experimentalists just provide data, or should we go one step further and provide interpretations? Will people misinterpret our interpretation as a claim for discovery? Is it unscientific to keep a result for ourselves? These are just some of the questions being discussed.

All of these are valid questions, leading to a multidimensional discussion with opposite conclusions. Agreeing how (if at all) to present the results is a topic of various conversations in this book. These time-consuming, but very important, discussions are the reason why experimental particle physicists spend so many days, evenings, and weekends in meetings, phone calls, and video conferences.

3 sigma

In the end, collider experimentalists are a funny bunch. As our collaborations have become so large, we will never be able to win a Nobel Prize for our individual work. Also, constructing a gigantic detector requires close collaboration with various colleagues. But still, curiosity and pride push us to be the first to have the histogram with new events on our own computer.

And whenever a 3 sigma’ish excess appears, some people will claim this might be something not understood, whereas others are convinced that it must be a statistical fluctuation. And one person (usually the first investigator) will claim with certainty this to be the first signs of new physics. Optimists and pessimists are everywhere, and most of the time both sides do have valid arguments.

With so many clever (and stubborn) people, simultaneously collaborating to develop a good experiment while competing on making a first discovery, converging on the final result, and its presentation, can be tough or even impossible. Why, in some cases, this can take so much time – that’s the one thing that Dorigo makes totally clear from this book.

Theorists

What makes the book so interesting and special is the way the discussions are described.

The description of the dialogues and the researchers are often recognizable and hilarious. For example, we hear Michelangelo Mangano (now CERN theorist) in a restaurant asking “Are you crazy?” (while almost spilling his beer on his freshly ironed Yves Saint Laurent shirt) and we see Claudio Campagnari (currently CMS Susy convener) saying in a meeting: “As long as I’m alive, this stuff will not make it out of here!”. In a collaboration with hundreds (and nowadays thousands) of such people with strong opinions, finding agreement will often take time.

And this brings me to the audience that could most benefit from reading this book: theorists! How often do it not hear, at conferences, on social media, and blogs the question from theorists, wondering why the experiments don’t publish faster. Just to quote a very recent post from Luboš at The Reference Frame:
“Don't you find it a bit surprising that now, in early 2017, we are still getting preprints based on the evaluation of the 2012 LHC data? The year was called "now" some five years ago. Are they hiding something? And when they complete an analysis like that, why don't they directly publish the same analysis including all the 2015+2016 = 4031 data as well? Surely the analysis of the same channel applied to the newer data is basically the same work.”
Well, this book gives the answer! Sometimes data is not yet sufficiently understood in order to become public. Often, further studies and crosschecks are needed, for example if the research reveals differences between different periods of data taking. And, finally, despite the large amount of automatization, all this work is in the end done by humans, and the collaboration has to convinced of the soundness of the obtained result.

Read this book, once, and you’ll never be surprised why some experimental particle physics publications appear to take long from the outside.

Comment

It’s a great read, but if I would have to mention one comment on the book, it’s that parts are written for the non-expert reader. I personally think that the book is mostly readable and interesting for professionals (in experiment and theory) and possibly also for an additional audience with a relatively large knowledge of the field. But, in the end, it is a niche market (which also explains the price of the book).

Dorigo has tried to make the book readable for a wider audience, and he is certainly great in trying to explain fundamental concepts in a clear way, using original analogies. His two-page long slow-motion description of a ppbar-collision generating an “anomalous” dielectron-diphoton-met event was actually quite amazing! But I doubt it’s sufficient to clarify our research to the non-expert reader. To me, those descriptions could’ve been dropped, or maybe formatted differently, to distinguish them from the main story line.

Anomaly

But all in all, it’s certainly a unique inside view in the history of particle physics.

This book really makes you experience the research atmosphere during the nineties at Fermilab. The situation around the Fermilab top discovery reminds one of the CERN Higgs discovery. The Tevatron dilepton-diphoton discussion reminds one of the excited discussion around the LHC diphoton events in 2015. And the discussions about internal results that have never been published… well, you know…

After finishing this description focusing on CDF Run-1, I was immediately curious to read more about the stories of CDF Run-2. Not just the measurements, but the everyday research inside a large experimental collaboration.

Beyond

This week, I will attend CMS Week for the last time. After >6 years in this collaboration, I move to the ATLAS experiment. I will take all the stories of eventful internal meetings with me, as I also did in 2010, after >4 years in the LHCb collaboration. I won’t write a book about it now, this would certainly be too early. Maybe someone else will do it, in like twenty years from now.

If you want to know how experimental particle physics is really done behind the screens, read this book! In all those years, the technology has advanced, as has our knowledge of particle physics, but the sociology is still very much the same.

Tristan du Pree

PS: Thanks to Orange, my provider in France, for recently cutting my telephone, tv, and internet (for no reason). It allowed me to quickly read this paper book without modern disturbance.