Tuesday, February 23, 2010


Nearly two weeks ago the first research paper was published by the CMS (Compact Muon Solenoid) collaboration at the LHC (Large Hadron Collider). The paper has the sort of snappy, headline-grabbing title we have all come to associate with high-energy physics experiments: "Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at sqrt(s) = 0.9 and 2.36 TeV". It was submitted to the Journal of High Energy Physics and published by them here on February 10.

While the results of this paper are not earth-shaking (and still less earth-swallowing!), it's a landmark of sorts and has occasioned me a great deal of satisfaction for various reasons, which, this being my blog, I can share with you.

First a summary of the contents: the LHC scattered protons against protons (as will be its habit for many years to come) during its commissioning in December 2009. The CMS detector, a "cylindrical onion" in the eloquent words of its publicity team, measured charged particles emerging from the collisions during two 2-hour periods at this time. The beam had an energy of 0.9 TeV in the first part of the run and 2.36 TeV in the second part. The former measurements provided a useful confirmation of previous results while the latter represent the highest energy measurements at a collider to date. The paper says nothing about finding new particles, nor was this expected since the LHC will take a while to reach its planned energy of 14 TeV and more importantly its planned luminosity.

Here's one tiny reason why I'm gratified. Of the 2400 or so authors on this paper, I've taught three or four in the TIFR graduate school and elsewhere. This is perhaps no great achievement on my part but I'm entitled to feel mildly pleased. After all they might one day co-author a Nobel prize-winning paper (and the prize itself may go to the collaboration rather than just its boss?? Who knows, the world is a changing place.)

And yes, you read the number of authors right. The first 15 pages of this 35-page paper are a list of the authors' names and affiliations! So much for the days when we thought high-energy physics had gone too far by inflicting as many as 100 authors on us...

Here's a second and more serious reason to be happy. Publication of a paper indicates that the LHC is seriously back on track and working well, and so is the CMS detector. There's a long road ahead and I'm glad they finally seem to be on it.

On to the third reason. I'm delighted that they chose to publish in JHEP. I've been on the editorial board of JHEP since it started in 1997 and it's survived a number of critics: those who claimed an electronic journal was an un-refereed journal (these people were either deeply confused or lying, but they sat on major committees either way), those who said it was "just a string theory journal" and those who simply said an online journal wouldn't work. JHEP is short of perfect, and I hear complaints about it a lot, but in terms of impact factor it's become the leading journal in High Energy Physics and the decision by CMS to publish there is an affirmation of this role.

My fourth and last reason to be happy: the concluding lines of the paper are as follows: "Open Access. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited." JHEP's policy is that papers from subscribing institutions are Open Access and CERN is a subscribing institution. So from my point of view, the best things in life are still free.

Here's hoping this paper is the start of a history-making career for CMS and the LHC.


Prithwiraj said...

how does an author cite this paper in their cv? 4-page citation? ;)

Sunil Mukhi said...

Good question, but there's a simple answer. The author of this paper is "CMS collaboration". No persons are named on the title page.

The list of authors is on subsequent pages, grouped by institution. The ordering is: alphabetical by country, then by city, then by institution, then by author. For those who insist on a first author for this paper, that would be Dr V. Khachatryan from Armenia. Authors from the USA take up the last four and a half pages of the authors' list!

Prithwiraj said...

2 more interesting questions arise :-)
1. who reviews this paper, and what are the pressures on this person to critique (or even reject if necessary) the work of 2000+ of his/her colleagues? wont the appeal to pity (http://www.nizkor.org/features/fallacies/appeal-to-pity.html) fallacy weigh big-time on the reviewers? (even if its a double blind review the reviewer can probably guess it has 1000+ authors from the nature of the work)

2. who composed the paper? wont these 2-3 people be disgruntled at not getting any extra credit?

Sunil Mukhi said...

P: Not sure why pity would come in. The referee's job is to decide whether the work represented is sufficiently interesting and important to warrant publication. Reviewing at JHEP is not double-blind, the referee would see the list of authors (rather than 15 blank pages!). The paper was reviewed in three days, but honestly how much longer does anyone need to review a paper?

About your other point, it's not only about those who drafted the manuscript. The names of the Chairperson and Deputy Chair of CMS, Green and Gasparini, are located humbly on pages (v) and (xi) of the authors' list with no indication of their roles. CMS seems to have decided on total democracy in the presentation of the paper. This is fascinating given the first-author obsession in many other areas of science.

Prithwiraj said...

well, by pity, i didn't really mean "pity", but probably the fear of disappointing 2400 people and wastage of so many resources if the work isn't good enough. if not double blind, it could actually be more of appeal to popularity.

actually, it doesnt matter. i have just never seen a paper with so many authors so was curious :)

Rahul Siddharthan said...

About open access -- how about optionally making any article open-access in return for an extra author charge? Many biology journals do that now. Also, many biology journals make their closed-access publications open-access after a time frame (6 months or 1 year, typically). It seems ironic to me that, though physics pioneered open-access through arXiv, that spirit hasn't caught on at all among physics journals.

It took 2400 people to write the paper, but only three days to review it? I'm guessing the reviewers decided there has been sufficient internal review and they didn't need to do much. I do see this as a problem though: it privileges certain "star" researchers / research topics over others. Reviewing varies a lot across disciplines -- it can take months in mathematics, for example.

From my own experience, which of course doesn't include HEP: I find reviews in computational biology are (invariably, so far) thorough, detailed and extremely useful, whereas reviews in condensed-matter physics (of my own work, and of others that I got for referral) tend to be brief and extremely sloppy, often with no attempt to understand the work.

Rahul Siddharthan said...

ps - I too don't see how pity can come in here. If anything, it's appeal to authority: 2400 people drawn from top institutions around the world cannot be wrong :)

Sunil Mukhi said...

Rahul: To be fair, 2400 people weren't needed to write the paper but to set up the experiment. Also, while reviewing papers is usually a slow process, this is because the paper lies in a drawer until the last possible day and then is reviewed in an hour or two. For an undeniably important experiment a referee could surely bypass the mandatory cold-storage period.

That said, you (and Prithwiraj though he may not have said it clearly enough) are right that an experiment like this poses new challenges for the reviewing process. The concept of "peer review" is puzzling when most peers are authors rather than (supposedly) dispassionate judges.

BTW, I believe all JHEP papers are open-access after two years. Which is mostly irrelevant since almost all are on the arXiv anyway.

AK said...

I am sure it is a nice feeling to have couple of your students make it to the top!!