A Neutrino Buzz in the Air

Today is a special day for those who have been working in the area of neutrino oscillations.

We were still celebrating the recent awarding of the Nobel Prize to Drs Art McDonald and Takaaki Kajita, who are leaders of the SNO and Super-K experiments respectively—it is a fantastic feeling to know that colleagues in the area of physics we study have been recognised in one of the most visible ways possible.

But a different award was announced today—or rather on the evening of Sunday 8th November in California where a flashy presentation ceremony was held, with Seth Macfarlane as the host—the 2016 Breakthrough Prize in Fundamental Physics.

From the official announcement page:

The 2016 Breakthrough Prize in Fundamental Physics to be Awarded to Seven Leaders and 1370 Members of Five Experiments Investigating Neutrino Oscillation: Daya Bay (China); KamLAND (Japan); K2K / T2K (Japan); Sudbury Neutrino Observatory (Canada); and Super-Kamiokande (Japan)"

The Nobel Prize is famously awarded to up to only three individuals per prize, and there is always much discussion before and after as to who ought to receive the prize, and, inevitably, who missed out unfairly. There is usually no controversy about whether the actual recipients deserved their prizes, but there are cases where many of us feel that it would have been fairer to relax the three-winner requirement a little, a constraint that was only officially introduced in the late 1960s.

One of the many differences between the Nobel Prize and the Breakthrough Prize is that the latter not only allows more than three people to win the prize, but that it acknowledges the important role that collaborative work plays in modern science. Therefore, the $3M prize goes not just to the top few leaders of an experiment (although such leaders are also recognised explicitly; with seven physicists in this year's case being honoured his way), but is shared by all those who worked together to produce the seminal journal papers in which these experiments reported their findings.

At Imperial, we are delighted that many past and present HEP group members are laureates for the T2K experiment, and as it happens I also receive the prize for my work with KamLAND when at Stanford University.

In our field, collaborations can be all-consuming parts of our lives; in the early days of T2K, I vividly remember my colleagues working day and night, week after week, to help design the detectors we would be building, and long hours spent in the lab, testing and assembling detector components; we would discuss and argue over and over again about how best to do things, and toiled to make sure that the fruits of our work in 2005 would still be worthwhile in 2015 (and now, we are hoping they will continue to be useful in 2025).

Collaborations can continue working together for many years, with individuals receiving their PhDs, becoming postdocs and obtaining academic positions, and generally growing old together, all while pursuing the same common goal—to make their experiment successful. Of course many people will move on to different things, be they jobs in industry or work at other experiments (and in new collaborations), but I think the bond between people who have worked on these experiments together during the most intense times is quite unique and long-lasting.

Today I received an email that was sent out to the roughly 100 prize recipients of the KamLAND Collaboration who worked on the papers from early 2000s where we demonstrated that neutrinos actually oscillate, rather than disappearing in other ways. The list of names on its own brings back memories to me of stressful, but also exhilarating, days and nights spent deep in a mine—in fact all of the experiments which received the prize today involve some kind of underground part to their set-ups—trying to get the experiment to perform as well as it needed to, and arguing over how to analyse the data. Yes, we do spend a lot of time arguing with each other!

Super-K and SNO, whose leaders received the Nobel Prize, showed definitively how neutrinos change identity as the travel; but one needs to put together the discoveries made by all five experiments which won the Breakthrough Prize to form the current picture that we have of neutrino oscillations, and it is an interesting distinction that has been made by the respective prize committees.

All the buzz that surrounds our field is made even more exciting by the fact that the discoveries we have made point to more possible progress in the next several years, and here at Imperial we are working on the future Hyper-K and LBNF/DUNE experiments as well as other neutrino projects, all as part of international collaborations. As proof of this, this month we are hiring three postdoctoral researchers (we are currently going through the selection process) to join the T2K and Hyper-K effort, and we hope that some of the new cohort of PhD students that have just arrived at Imperial will also join us (but that is up to them!).

So while these prizes do help us look back to savour the amazing physics discoveries that we have made in this field over the last couple of decades, it is the future that really excites us—not only in neutrinos, but in all the other areas in which we are building experiments that have the ability to make breakthrough discoveries that tell us more about the universe we live in.

Decommissioning SciBooNE

We have just done something on SciBooNE that has become somewhat rare in the field these days: we turned off the detector intentionally! On 18 August 2008, the SciBooNE neutrino beam data run offically ended at 08:00 in the morning (CDT). It seems like only yesterday that we put SciBooNE together and observed the first neutrino events in the detector, but we have now finished all the data-taking and have decommissioned the detector. Many of the detector components will be returned to their respective owners, but the main bulky parts will remain the detector hall until someone else decides to use the parts or the hall.

When most people learn that we decided to end the run, they are puzzled and ask why, apparently in the belief that we must have been forced to end the run. In fact, we ended the run mainly because we have already collected all the data we need to achieve the physics goals we set out to achieve, and it's now time to concentrate on the analysis of the data. Far from being a sad occasion, it was actually rather triumphant. (You can see how happy our Run Coordinator Hidekazu Tanaka, Columbia University, was to end the run in the photo at right. Also shown in the photo is Zelimir Djurcic, Columbia, who was the last SciBooNE shifter. (Photo courtesy of Hideyuki Takei.)

We spent a couple of weeks dismantling everything in the detector hall and sorting out all the parts for shipment back to their places of origin. As usual for us, most of that work was done ahead of schedule. To help out with the work, many of our collaborators came to the lab, and we had a large influx of young students as well. In the photo at left you can see several SciBooNErs working on removing the multi-anode photomultipliers from the top side of SciBar. From left to right are Yuki Kobayashi and Shunsuke Masuike, Tokyo Institute of Technology, co-spokesperson Tsuyoshi Nakaya, Kyoto University, Joan Catala Perez, University of Valencia, and in front is Katsuki Hiraide, Kyoto University. (Photo courtesy of Reidar Hahn.)

Yuki and Shunsuke are two M.S. students who came to Fermilab (and America) for the first time just to help with the decommissioning, and Joan and Katsuki are two of our PhD students and they've both been out at Fermilab for years building and operating the detector and of course working on data analysis. Actually, Katsuki recently presented our first preliminary physics result at the ICHEP08 conference in Philadelphia, PA. You can see him in front of a pretty large audience of neutrino physicists presenting the result in the photo at right. (Photo courtesy of Herman White.)

To commemorate and celebrate the end of the run we threw a big party at Fermilab on 22 Aug. You can see the invitation to the party up at the top of this entry. (The photo in the

invitation is courtesy of Reidar Hahn.) We had a nice simple cookout and a friendly game of volleyball which, unfortunately, the SciBooNE team lost to the MiniBooNE team. I guess we can't win them all...

(Photo courtesy of Joan Catala Perez.)

Opened Box

Well, the big moment is about to arrive. More than a decade ago, the LSND collaboration shook up the particle physics world by announcing a neutrino (actually, antineutrino) oscillation result whose interpretation requires physics beyond the standard model. As I wrote in a previous entry, I am on MiniBooNE which has been working on a blind analysis to confirm or refute the LSND result for the past ten years. We have been pushing very hard to "open the box" and see what the answer is for quite a while and it has finally happened.

Our box opening procedure was a four step process in which each step was designed to reveal enough information that we could decide if things were working correctly, but not enough information to tell us the answer. Thus blindness was preserved until the final step. Our procedure was designed so that if a problem were to be found in one of the early steps, we could stop the procedure and try to fix the problem, before starting over again. Doing that would be OK as long as we did not reveal any information about the contents of the box.

Today at Fermilab, our first oscillation result will finally be announced, and tomorrow I will give a seminar on the result myself here at Imperial. I can't say what the answer is yet, so you'll have to come to my seminar to find out!

As an interesting side note, we did have to stop the box opening procedure and start over again, so it was a very good thing that we had this procedure. We attempted a box opening in February, over the weekend when I wrote my blind analysis blog entry, and discovered a reason to abort the process and regroup. But a full entry about that will have to wait until the result is announced to the world. Right now, I have to complete my seminar!

Blind Analysis

I'm a member of the MiniBooNE collaboration, and we are doing a blind analysis in our search for neutrino oscillations. The idea is that we wish to prevent biasing ourselves before we complete the analysis of the data. We are doing a "closed box" blind analysis, which means that we sequester the events that appear to be signal-like and do not perform any analyses on them before the analysis chain is complete.

Our analysis is a search for electron neutrino events in a muon neutrino beam, which is the signature of neutrino oscillations seen by the LSND experiment. We are performing the experiment to confirm or rule out the LSND neutrino oscillation result. Effectively, the blind analysis means that we use other data samples, like the muon neutrino data and cosmic muon decay electron events, to understand our event reconstruction and analysis algorithms. We do not use electron neutrino events that might come from neutrino oscillations in the development of the analysis, but only after the algorithms are complete. We are currently in the final stages of the analysis, and are hoping to open the box soon, although we have been saying that for a while!

We chose to do a blind analysis for many reasons, but one of the key reasons is that the LSND result, if it is due to oscillations, would be inconsistent with the Standard Model's prediction of only three families of neutrinos. Thus, the LSND result has huge ramifications if it is confirmed and we deemed it necessary to use the most strict methods in our search for these oscillations.

As a MiniBooNE collaborator, I am often asked if we will see a signal, which is to say: do I think the LSND signal is real? I've come to realize I don't care if we see a signal. All that matters to me is getting it right. Frankly, I think it would be scientifically irresponsible for me to hold a strong opinion about it one way or the other. I think that the beauty of science comes from the idea that Nature can reveal her secrets if we ask the right questions and are open to the answers. Approaching this analysis with a strong bias one way or the other would be tantamount to closing one's mind to a certain type of answer, and to me that would be a failure.

A lot of people in the field feel that the signal is false, and that we will rule out LSND-type oscillations, with almost religious conviction. It belies their bias in what should be an objective pursuit. I think part of it stems from the saga of the 17 keV neutrino. In that case the scientific method was vindicated (although I am sure that there was plenty of subjective chatter amongst the participants, especially at conferences) but I think the experience left a lot of people in the field uncomfortable with new and different experimental results in neutrino physics. We will shortly learn whether or not the LSND result was a false alarm, or whether Nature is a lot more complex than we thought.

And I can't wait to know the answer, whatever it might be!