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Sarah Demers | USLHC | USA

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Making ATLAS Results Public

Monday, May 2nd, 2011

Any large collaboration like ATLAS needs a process for allowing members to communicate their work to each other and to the public. There have been some recent questions about how this process works, so I’m going to address the topic in this post.

We particle physicists are a bit unusual, though not unique, among scientific disciplines in that our authors sign official papers in alphabetical order as opposed to being ranked by how much they contributed to the work. We are also famous for our long author lists, which for the large LHC experiments include up to a few thousand people since all members of the collaboration sign each paper unless individuals request that their names be removed.

There has been some debate in the field about whether our author lists should be more exclusive and include only those people who worked directly on the physics analysis being published. I have always appreciated the lack of squabbling over author lists and the way our inclusive list gives a nod to the fact that our detector is incredibly complex and could only be built, maintained and interpreted for physics results with a large team. There are also many people who have contributed to the upstream work of an analysis, which makes the final result possible. The counter-argument is that it is nearly impossible for people outside the field to know who did the actual analysis work for any particular result. I think that people inside the field can usually find out who did what, even at other experiments, pretty easily by seeing who gives the related talks at the conferences and from reference letters within the collaboration, and even just by asking around.

Regardless of where you come down on the author list debate, the fact that our author list is currently the entire collaboration puts a burden on our result approval process in that every author needs to be given the opportunity to comment on every result he/she will sign.

Before we worry about communicating our results to the world, we need to have a mechanism to communicate our work in real time to each other within the collaboration. This allows us to scrutinize the steps as they are taken so we know that we are building a solid analysis. We achieve that by giving presentations at meetings and writing emails, but we communicate probably most efficiently by writing notes to each other to document snapshots of the early stages of an analysis. This documentation can have a much smaller list of authors who are responsible for the specific set of ideas presented. Documents like this are simply labeled “COM” for “communication,” and they are not intended for public consumption. Any ATLAS member can write a COM note at any time, and people do not necessarily put the names of all of the people on which their work relies on the author list.

If you want your work to move toward official internal ATLAS approval, you can request that it be given the status “INT” for “internal”. At this point leaders of the relevant physics group appoint reviewers, and the authors have a chance to get feedback in a formal way from other collaboration members. A note that has gained INT status has undergone at least some peer review, though it stays internal to the collaboration.  The content of the INT note is often too technical for general public interest, but can be invaluable for other ATLAS collaborators who want to either reproduce a result or take the analysis to the next step with a good understanding of everything that has come before.

Some COM-notes can also become public (i.e. available to everyone on the planet). Together with published papers, these public notes report the scientific output of the experiment.  In order for the result to take the final step to become public, an editorial board is appointed, and often a new note is written (starting as a COM note) with an attempt to remove ATLAS-specific jargon and details that people outside the collaboration would not necessarily find useful. With the help of the editorial board, the note is brought to a stage where it is ready to receive feedback from the entire collaboration. If the note is approved by the collaboration it will be posted to an archive that is available to the public, submitted for publication and/or the results will be shown at conferences.

There are, of course, many details that I haven’t described, but the end result is that an analysis that has been publicly approved by ATLAS will have come under scrutiny at many stages of the process. People work very hard to make sure that the results presented to the public are worthy of being signed by the collaboration. Our goal is to work as a team as quickly as we can to get these results out to the rest of the world while at the same time ensuring that we have not made mistakes.  Our scientific reputation is on the line.

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Already Thinking About Upgrades

Monday, April 4th, 2011

It is great to be a member of the US LHC blogging team! I have followed my friends’ posts here for a while. I hope I have something to add to the conversation, but I am confident that at least one person will read this regardless of the content because I sent the link to my Mom. (Hi, Mom!)

I’m typing on the flight back to the US from the UK after a week of meetings relating to possible future upgrades of the ATLAS detector that took place at Oxford University. I can imagine you are thinking, “Upgrades?! You people just started taking data! What are you doing already thinking about upgrades?!” I feel that way myself sometimes when numbers like 2017 and 2021 are floating around the room, particularly when I know that collisions are happening that very moment in the center of the ATLAS detector. But it is difficult to imagine a physics scenario where we would not want to see data from the LHC for a few decades. To enable this to happen people had to start thinking about upgrades well before we started taking data.

So, what is the physics landscape? Let us imagine that we find something that we think is the higgs boson. It is going to take quite a bit of data to convince ourselves that what we see is the same higgs boson that is described in our standard model of particle physics, and not some other object, like a higgs described by supersymmetry. This detective work will require high statistics, which means lots of collisions, which means lots of time with the LHC running. If we do not see anything with our first few years of running we will be able to rule out the version of the higgs boson that comes from our standard model and we will have to throw ourselves into hunting for particles and processes that are more difficult to see and, again, require more statistics. We have reasons to believe that we will see something new at the energy that the LHC was designed to deliver, but some of these scenarios will require impressive experimental gymnastics, to say nothing of (seeing a trend here?) high statistics. In order to more efficiently deliver these high statistics, the LHC has plans for upgrades of its own, and ATLAS will need to respond by making changes to the detector that allow us to cope with more extreme running conditions from the collider.

There are a few reasons running for long periods of time require upgrades to ATLAS and the other detectors, even without an upgraded LHC. For one thing, some of the electronics in our detector date back to the late 1990s and we cannot expect them all to survive well into the 2020s. There also will be pretty high flux of particles delivered to the detector over the course of data-taking, particularly to the regions close to the proton-proton interaction point, so replacement parts will be needed. Let me try an analogy: You just bought a car. It would be odd to not get regular oil changes, to keep it running well as long as is possible. And if something happens to the muffler it makes sense to replace it, even if it means spending a bit more money, in order to get the most out of the initial investment. The world has certainly invested in the LHC. (Thank you, world!) Before we go forward with specific upgrade projects we need to convince each other, our funding agencies, and the people who set the budgets of our funding agencies that the projects are justified both scientifically and financially. The peer review process rightfully keeps us on our toes.

In addition to the presentations and discussions at Oxford there were a few free moments during which we were able to explore the area. I visited the pub where J.R.R. Tolkien and C.S. Lewis used to hang out. I also visited the impressive Museum of Natural History. To top it all off, we had our workshop dinner in the Keble College dining hall, which doesn’t sound very impressive until you see the space. Harry Potter could have rounded the corner at any minute and none of us would have blinked.

Thanks for reading!

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