The attempted terror attack on a flight from Amsterdam to Detroit was basically the same flight I had taken less than two weeks prior on my way home from CERN.

Already my least favorite part of international collaboration was traveling by air. Somehow, I imagine my future flights to Genève are going to involve even more unpleasant security checks and rules.

There has been a lot said on the ridiculousness of many airline rules (xkcd: “A laptop battery contains roughly the stored energy of a hand grenade…”).

I have little to add, except to say that having spent a lot of time in aiports and on airlines myself, I agree that rules like prohibiting liquids adds little to our safety when flying.

Bruce Schneier summed it up nicely recently in Is aviation security mostly for show?:

Despite fearful rhetoric to the contrary, terrorism is not a transcendent threat. A terrorist attack cannot possibly destroy a country’s way of life; it’s only our reaction to that attack that can do that kind of damage. The more we undermine our own laws, the more we convert our buildings into fortresses, the more we reduce the freedoms and liberties at the foundation of our societies, the more we’re doing the terrorists’ job for them.

I hope airline companies and the TSA listen and someday make flying a more pleasant experience.

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[Sorry if this is a little dry compared to my usual posts, but this is more of a news report for the HEP community.]

Last time I mentioned the INSPIRE system as an exciting development in high energy physics literature databases (no, that’s not an oxymoron). There’s another big change going on in that field next year, but this will be behind-the-scenes. None-the-less, it’s raised a lot of questions about the ownership and financial support of an important resource that is free to anyone in the world: the arXiv.

The e-print arXiv (pronounced “archive”) is a central repository of research articles in physics, mathematics, computer science, and quantitative biology. Since its inception in 1991 by theoretical physicist Paul Ginsparg, it has had a huge impact on the way science is done by providing free access to “pre-prints” of research papers. This meant that scientists from anywhere in the world with any background could access the latest research even if their university libraries didn’t have a copy of the particular journal in which it was published. This is a big deal since the cost of many of these journals created a gap between those institutions which could afford to pay for many journals and those which could not. In many ways arXiv “brought science into the 21st century” by allowing scientists to draw upon the collective scientific community more efficiently. Many credit it for pioneering the open access movement in scientific publishing.

But with increasing costs and the state of university budgets, the Cornell University Library (which operates the arXiv) is looking to find more cost-effective ways to support the arXiv and the much-needed overhauls in the software architecture (“arXiteXture”?). [Earlier this year Cornell closed its Physical Sciences library to help trim operational costs.]  Currently the Cornell library pays the $400,000/year operating cost to make the arXiv available free-of-charge to the rest of the world. Here’s the official statement so far:

Cornell University Library is beginning an effort to expand funding sources for arXiv to ensure its stability and continued development. We intend to establish a collaborative business model that will engage the institutions that benefit most from arXiv — academic institutions, research centers and government labs — by asking them for voluntary contributions. We are working with library and research center directors at the institutions that are the heaviest users of arXiv to refine our plan and to enlist support. We expect to release the plan, with a call for broader engagement and contribution, in early 2010.

There’s also a very handy FAQ on the funding changes, which are still a work-in-progress. Because the arXiv is such an important resource to a range of disciplines, the proposed changes have had some in the physics community asking whether it’s time to re-evaluate whether a single private library system should have ‘ownership’ of the arXiv as researchers contemplated the ‘nightmare scenario’ of the arXiv becoming a pay-to-use site. (Fortunately this is not the case.) Indeed, the arXiv has been instrumental in supporting research institutions that are unable to afford the costs of journals from for-profit publishers. The FAQ provides some insight about the direction that the arXiv managers are heading.

Currently the plan is to ask the “heaviest user institutions” (other university library systems) to voluntarily contribute to support arXiv operational costs. The FAQ states that the library has already secured commitments from 11 of the 20 institutions that make the most use of the arXiv. (I’ve seen an unofficial list; these include many of the ‘big name research institutes’ around the world.) In return, besides academic karma, these institutions will be recognized for their support with arXiv banners and would possibly be privy to more detailed arXiv usage statistics. The target appears to have such contributions support a fraction of the operating budget.  There is no plan to charge individuals for uploading or downloading papers from the arXiv. This business model is meant to be a temporary plan for the next three years while a longer-term solution can be figured out in collaboration with the wider community. It seems like the arXiv managers envision this long term plan being some kind of mixture of Cornell and user-institution support, but they are open to external support, e.g. from the National Science Foundation (which many physicists have suggested).

Just before the winter break the arXiv managers had meetings with the Cornell physics department to discuss the future changes to the arXiv. Unfortunately I was unable to attend that meeting because I was already back in California to spend the holidays with my family (… and to have transcontinental Skype conversations with my collaborators), but you can expect an official public announcement about the new arXiv program from the Cornell Library this coming January.

- Flip

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Well, someone ought to keep feeding the beast on the holiday, so I will do it.  Lots of people are taking a well-deserved rest this week, but the world of high-energy physics does keep motoring along.  CERN is closed down for the holiday, but the Fermilab Tevatron is running this evening and the experiments are taking data, quality of life be damned.  Many authors on this blog have written about the differences between American and European culture, and this qualifies as one more example; the Americans aren’t going to get something like a major world-wide holiday get in the way of taking data.  When I was a graduate student at Cornell, working at the CESR storage ring there, we’d always be running through the holiday too, and as a Christmas non-celebrator, it was always a personal point of pride for me to take a shift that day.  In fact, it was always the time when the machine would have its smoothest running and we’d acquire the most data, largely because no one else was there to muck around with things.

Anyhow, we are closing out a great year for the LHC.  The repair work required a tremendous amount of effort, and it paid off in the machine performance that we saw in November and December.  Last Friday, just before CERN closed, there were presentations from all of the experiments on what they have done with the data so far, and I thought they were all really impressive.  So many things are working out of the box — we are seeing the phenomena we ought to see at these low energies and collision rates, and everything is matching up very well with simulations.  (One could argue that after twenty years of planning, we’d better be this ready!)  There is nothing in the way of new physics here, as there isn’t nearly enough data or collision energy for that, but getting these fundamentals right means that we’ll have an easier time making discoveries when the conditions exist to do so.

So all I can say is that we’re going to have a great 2010 ahead of us.  The LHC will turn back on in mid-February, ready for higher-energy collisions, and we’ll be recording data through much of the year.  I’ll try to write something here on Christmas 2010, and I expect that there will be a lot of good news to summarize.

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While this won’t catch the as much press as the LHC’s upcoming steps towards a physics run, but there are big changes coming up in 2010 to the way high energy physics literature is organized. This is very important: the vast databases of physics literature available at our finger tips through the Internet are what separate us from the cavemen. (Er… something like that.)

INSPIRE

Speaking of cavemen, those familiar with the history of the web at CERN will not be surprised to find out that the first webpage hosted in North America was a particle physics literature database, SPIRES, operated by the SLAC National Laboratory. The database allows anyone in the world to look up bibliographic data about a range of documents including items that aren’t journal-submitted papers: PhD theses, conference talks, technical notes, and even video recordings.

CERN has its own library management system, Invenio, whose killer application is the fantastic CERN document server. The CDS has a broad collection of materials, including a nice set of general audience videos that readers of this blog might like. The two systems have their own strengths: SPIRES is known for its ability to work with metadata while Invenio’s architecture is known for its scalability and performance. So, after a survey of high energy physicists, it’s no surprise that SLAC and CERN (along with Fermilab and the German HEP lab DESY) combined their resources to implement SPIRES “user-level functionalities” within the Invenio framework.

The resulting combined project was christened INSPIRE and the plan is to have a user release sometime next year. INSPIRE aims to produce a unified, modern HEP database that’s not based only on papers (and more recently recorded talks), but more generally information. This includes computer code, data, and figures. Instead of just searching, it also aims to tap into the potential of the Web 2.0 by implementing a rating system, following individual users, and even tracking data usage.

[Now for some shameless self promotion: these are all functions that I wrote about two years ago, likening them to link aggregation sites like Digg, e-commerce a la Amazon, and the grand-daddy of Web 2.0: Google itself.]

You can read more about INSPIRE through at the CERN Courier, interactions.org, Symmetry Breaking, a talk to the DOE High Energy Physics Advisory Panel,  and through some talks at the HEP Information Resource Summit. At that last link check out Travis Brooks’ demonstration of INSPIRE, or better yet, try out the alpha version yourself.

-Flip

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It’s that time of year again. This past Friday the CERN theory group had its annual Christmas party, featuring its unique brand of silliness: the CERN-TH Christmas play. I’ve not yet had the privilege to visit CERN, but one of my deepest physics desires is to one day be around during one of these parties. Recently the group started archiving their Christmas plays and making them available online. Here’s a summary of the 2008 play, courtesy of Jester at the Resonaances blog (curiously Jester wrote the year incorrectly).

The 2009 play can be found on the CERN Document Server. I wholeheartedly recommend it. It’s full of jokes about LHC media hype, pop culture, and yes, a lot of physics. The puns are packed in there rather densely, so those of you that can pick up most of the references in one viewing should consider trying out for Jeopardy. I prefer to make a game out of it so I eat a cookie for every time they mention a physicist whom I’ve met in person. Even if you don’t get any of the jokes, it’s still enjoyable to watch physicists having fun being silly.

My rough notes of the references in the play are below, after the break. (There are certainly a bunch that I’ve missed or misinterpreted.)

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Yesterday, the LHC collided its last particles for 2009. It has been an exciting end to the year, and the beginning of a new era in particle physics. The collider and all the experiments have proven that they work very well, and are ready for the first physics run.
This is also my last blog entry for the US LHC web site. It has been fun, and I appreciate all the interesting comments and questions to my posts over the last year and a half.
A few new bloggers are starting up, and I’ll be among the readers for an exciting 2010. Happy New Year!

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CERN is closing and turning off the heat for two weeks starting this Saturday. This is the typical annual closing – mostly done to save money. In France/Switzerland, electricity costs about three times as much in winter months compared to other months. Also, from what I hear, labor laws here might also make it hard to be open around this time of year.

Many people (including me) have or will be heading back home for the holidays. Once CERN opens again on Jan 4th, 2010, repairs will begin to take place of the next month and a half on various things. Our detector, CMS, should be ready by around Valentines Day, and then the LHC should start back up a week or so later!

Here’s a recent, and rare, sunset seen from my office building (most days are cloudy and rainy):

The days are about 8 and a half hours long this time of year, so I cherish whatever sun we get.

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The successful restart of the LHC ranks #9 on Time magazine’s list of the top 10 scientific discoveries of 2009. That’s not bad considering that the LHC only had its first collisions last week and is still some time away from having the integrated luminosity to make big discoveries. Despite this, the LHC has set new records for the highest energy particle collisions made by human kind and it was no small task to get this far.

If everything goes smoothly, we’re looking at 3.5 TeV per beam collisions in 2010, maybe going up to 5 TeV. High energies are sexy and look good for the press, but discoveries are all about finding an excess in the rate of some process (as we discussed in an earlier post, also Regina’s latest). In order to observe this excess, we need lots of data. Why is this? Suppose you wanted to know if Kobe Bryant or LeBron James has a higher shooting percentage. After just a few games, you could look at the stats but they would be difficult to trust: maybe one player had an off day, etc. But over the course of the entire season, the accumulated stats become more trustworthy.

Particle physicists measure how much data they have in “inverse picobarns.” After next year the good folks at the LHC expect to have a couple hundred inverse picobarns of data. By comparison, the Tevatron at Fermilab has recorded something on the order of inverse femtobarns, i.e. thousands of invese picobarns of data. That’s around the ballpark (conservatively) where physicists can really start looking for the subtle hints that exotic particles have been created.

What does this all mean? Well, it means that unless nature is very kind 2010 might still be a bit early for “paradigm shifting” discoveries. I should mention two things: (1) people are keeping their eyes out in case nature is this kind and (2) there’s still a lot of very important science to be done in this period (e.g. top quark mass measurements).

After 2010 the LHC will have a “long” shut down to prepare to ramp up to 7 TeV per beam collisions. That’s when the machine will really ramp up its search for things like supersymmetry, extra dimensions, dark matter, and the Higgs (if we don’t discover it sooner). Then the LHC can aim for #1 on Time magazine’s list of scientific discoveries.

[If any of my fellow US/LHC bloggers have more updated information about 2010 expectations, please correct me!]

- Flip

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Seth here, I have an apartment lined up now, but I’m still living at the Guest House at Lawrence Berkeely National Laboratory while I wait to move in. That means I have been in my office a lot, even over the weekend — although it being the weekend gives me license to half work and half procrastinate. (Hey, I need something to do while waiting for my code to rerun for the eleventy-billionth time!) Some of my procrastination has been on Twitter, and I’ve found some fun new things to follow if you’re interested in the LHC:

• @lhcstatus – The current actual status message sent from the LHC control room so that the experiments’ shifters know what’s going on. Its produces a lot of messages, but if you’re on the edge of the seat waiting to see how much data we get like I am, this is pretty neat to keep track of.
• @CMSecom – Running e-commentary from CMS.
• @sethzenz – Me, the work-related stuff anyway. (I’m modest, aren’t I?)

Coming soon:

• @ATLASexperiment – With only one tweet so far, this is part of the ATLAS blogging project, which isn’t ready quite yet but will be soon.

And, in case you don’t have them already, here are some existing LHC-related accounts to follow.

• @CMSexperiment
• @ALICEexperiment
• @LHCbExperiment
• @CERN
• @USLHC – Posts and other news from this website about the LHC and U.S. contributions to it.

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Hi everyone. With lots of exciting successes with the LHC startup, I thought it would be good to teach everyone a bit about Feynman diagrams. These are the funny squiggly lines that one will often see on particle physicists’ chalkboards (or whiteboards if they do experimental physics…) that describe what’s going on when particles interact. The diagrams are very simple to draw and can actually be interpreted very straightforwardly, but like many things there’s a lot of very elegant physics going on “under the hood.” Thus, in order to build a bit of foundation for that, I’d like to discuss something even simpler: the double slit experiment.

Actually, we’ll do even more: we’ll do the triple, quadruple, and infinite-slit experiment! Take that quantum mechanics textbook!  I’ll then discuss why this is the basis for Feynman diagrams. This discussion (and the images) borrows heavily from Tony Zee’s excellent textbook, Quantum Field Theory in a Nutshell (there will be a new edition next spring).

I’m not going to discuss “wave-particle duality,” the idea for which the double split experiment is often invoked. Those who are unfamiliar with this can look it up in popular physics books or on Wikipedia, but it won’t be necessary for our purposes. In a double-slit set up, a photon travels from some point A to some point B. In between those points however, is an impenetrable barrier that has two slits (S1 and S2) cut into it, allowing the photon two paths to get to the point B.

You might ask about why the photon’s path has a kink in it at S1 and S2, since it seems strange that it takes a bent path. My answer: don’t worry about it, this is quantum mechanics: weird things happen. More precisely, the probability for the particle to go from A to S1 to B is a well defined and non-zero quantity.

The point of the set up is this: we’ve constructed a system with a well defined initial state (photon at point A), a well defined final state (photon at point B) and well defined intermediate states:

1. The photon goes from A to B via slit S1 or
2. The photon goes from A to B via slit S2.

The rules of quantum mechanics tells us that if all we can measure are the initial and final states, i.e. we can’t tell which intermediate process occurred, then the physics of the process is determined by the “sum” of both possible intermediate states. Now you might ask what I mean by “sum.” Without going into the details, quantum mechanics assigns a [complex] number to each intermediate process. By summing these numbers for unmeasured possible intermediate states we get a number associated with the  entire process. We call this number the probability amplitude. It’s not important how we determine these numbers; what is important is that the square of the amplitude is the probability for the initial state to turn into the final state, i.e. a rate that we can measure in the lab. This is the actual “result” of the double slit experiment, though the actual experiment isn’t important for us right now! All you need to understand is that these paths are summed.

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I’ve been reading a lot of the comments to the blogs and realized that it’s a little unclear what physicists mean when we say we’ll find the Higgs. All the bloggers have posted pretty event display plots which are a visual representation of what we get in the detector. You can see lines of tracks in the inner detector, energy deposition in the calorimeters and tracks in the muon system. You’ll also see particle tracks bend in the magnetic field. This is beautiful and shows exactly what the detector “sees” when an event occurs. This, however, is not what physicists will use to discover the Higgs.

So what do you do exactly?

It’s never a matter of finding “one” Higgs and declaring victory. Based on different theoretical models we’ll be looking for different signatures. Each of these signatures will have certain background events. Background events are events that  have the same or similar signature as the signal (or in this case, the Higgs).

So here’s an example:
One signature we can look for is the Higgs decaying to two Z bosons. Z’s have a nice signature because they can decay into 2 electrons each. (for example… they also can decay into muons, quarks… etc, but this is just one example).

So now we have something to look for: 4 electrons which “come from” 2 Z’s. But we can’t just look for 4 electrons because there are other processes that also decay into 4 electrons. For example we can create 2 Z bosons without coming from a Higgs. This is called diboson production. This would be a background to the Higgs->ZZ signal.

So now what do we do? We have to somehow distinguish the difference between the signal (H->ZZ->4e) from the background (ZZ->4e) because in the data there is a probability that all of them will be produced. Well there are lots of ways we try to do this. One is that there would be a peak at the mass of the Higgs if we reconstruct and combine all the decay particles. In order to get this peak we’d need lots of signal events because it’s about getting enough statistics to distinguish them from the ZZ->4e background. We’d need a signal that’s ~5 sigma above the background to claim discovery. What that means is that it has a <0.01% chance of being a fluctuation in the background.

Although this is just one example of how we’d have a discovery, it’s similar for all discoveries. Some particles are easier to discover because they have a very high signal to background ratio, so it will take fewer statistics to get to ~5 sigma. The Higgs is difficult though, for a multitude of reasons. What this means in the end is that it will take more time to get the statistics to distinguish it from the background.

Then once we’ve been able to find an event that we believe is a Higgs candidate we’ll reconstruct it with the event display software that’s been seen so often on the blogs. I hope this sheds a little light on how discoveries will be made at the LHC. Although I’ve never gone through the process myself, there are lots of physicists (and LHC blogers) that have done this before (like during the top quark and W/Z discoveries). So please feel free to ask questions if you have them.

-Regina

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Now that the LHC is really operating, the machine and the science are very much in the news again.  Most of the coverage is quite positive (including some very nice words in our local press), but I have to take issue with the tone of an article that appears in today’s New York Times.  (Perhaps some of our readers have noticed your dear correspondent’s obsession with this particular news outlet.)  It does celebrate the very first collisions at record beam energies, in rather colorful language, but it also expresses a sense of national loss over the fact that this is happening in Europe, not the United States.  “Those spinoffs now will invigorate the careers and labs of Europe, not the United States, pointed out Steven Weinberg,a  physicist at the University of Texas in Austin, who won the Nobel Prize for work that will be tested in the new collider,” the article says.

I have to take issue with Weinberg, and by extension reporter Dennis Overbye.  (Overbye I don’t worry about disagreeing with, but am I asking for it by going up against a Nobelist?)  Is this so devastating for the U.S.?  To be sure, I would rather that we have the accelerator here, mostly so that I could go to visit more easily.  But then again, I would also like to have universal health care in which everyone can get as much treatment they want without anyone having to pay for it, too.  The reality is still appealing.  Americans are full participants in these experiments — we have equal access to the data, and have as much chance of discovering things as anyone else.  People from the United State have made critical contributions both to the LHC itself and to the detectors.  I probably shouldn’t suggest that it couldn’t be done without us, but I like to think that my collaborators around the world would agree that this was done more easily with us involved.  We have played key leadership roles in the development and construction of many of components of the experiments, and that leadership will continue as we move into the data analysis phase.  Perhaps most importantly, there really is a spirit of cooperation in these experiments — it is not one country against another, but everyone working together towards a common goal of scientific understanding.  Everyone involved is going to benefit from the discoveries that we make.

As I write, the LHC status page says “FIRST HIGH INTENSITY STABLE BEAMS.”  Discoveries, coming soon.

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These past few weeks have gone by in a blur. The LHC provided us with the first collisions, then it became the highest energy accelerator, and for a few minutes last night, the LHC became highest energy collider.

Crazy.

It’s been busier than usual at CERN, with people in a rush to examine the first collision data to try and learn as much as possible. But tonight, at least some of us, took a little time to celebrate. Our detector, CMS, held a Christmas Party near Prévessin-Moëns, with food, drink, and music. 800 people showed up: physicists, engineers, post-docs, students, and their friends and family. Everyone has been working so hard, putting in extra time, they deserve it.

It is an exciting time to be here.

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I have been in the ATLAS control room on shift each of the last three weeks.  Each shift was more boring than the last.  The first collisions were on a Monday. I had shift that Tuesday.  Tonight we actually had a first while I was here.  We just had the “first time with two beams with 2 bunches per beam at 1.18 TeV.”  Okay, there are a lot of qualifiers in there.  But it was still exciting to watch the big screen in the control room that gives the status of the LHC as the beams were accelerated.

Two bunches of about 10 billion protons each were circulating in the LHC in each direction.  The energy of each beam was slowly increased starting from the injection energy of 0.45 TeV, and we oohed and aahed as it went up.  I took a photo of the big screen when both beams were up to 1.18 TeV (you can see the energy at the top in the middle, “1180 GeV”).  Hopefully some time in the next few weeks we will get collisions at this energy!

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Hi, Seth here. Amidst the fun of moving and looking for apartments, I’ve also been working more than full time looking at our first collisions and preparing for more. In this entry, I’d like to share with you the very first plot I tried to make from actual collision data.

Before I continue, though, I should apologize to all my collaborators on the ATLAS experiment if the title of this post gave them a heart attack: sorry, guys and gals. Why would the title do that? Well, being a member of the ATLAS collaboration means agreeing to present our results collectively; that means that anything I learn about our collision data will only be publicly available after everyone’s had a chance to look at it and make sure it’s work they can stand behind. That’s only fair; after all, everyone contributed to the results; the plots I make are only the final few steps in a chain of design, construction and commissioning more than half as old as I am! (I’ve written about what we can and can’t blog about before.)

So why am I saying I can show you a plot? Well, take a look:

No jets here!

See the problem? It’s empty. What it claims to show is that I looked at 500 events and saw exactly zero track jets in every single one. But actually I had something set wrong when I made it, so it doesn’t really tell you anything about ATLAS data at all.

I’ve fixed the problem now. Did I see any track jets after that? Well, I can’t tell you — not for a few months at least!

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