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Ken Bloom | USLHC | USA

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Where the wind goes sweeping ’round the ring?

Thursday, October 23rd, 2014

I travel a lot for my work in particle physics, but it’s usually the same places over and over again — Fermilab, CERN, sometimes Washington to meet with our gracious supporters from the funding agencies.  It’s much more interesting to go someplace new, and especially somewhere that has some science going on that isn’t particle physics.  I always find myself trying to make connections between other people’s work and mine.

This week I went to a meeting of the Council of the Open Science Grid that was hosted by the Oklahoma University Supercomputing Center for Education and Research in Norman, OK.  It was already interesting that I got to visit Oklahoma, where I had never been before.  (I think I’m up to 37 states now.)  But we held our meeting in the building that hosts the National Weather Center, which gave me an opportunity to take a tour of the center and learn a bit more about how research in meteorology and weather forecasting is done.

OU is the home of the largest meteorology department in the country, and the center hosts a forecast office of the National Weather Service (which produces forecasts for central and western Oklahoma and northern Texas, at the granularity of one hour and one kilometer) and the National Severe Storms Laboratory (which generates storm watches and warnings for the entire country — I saw the actual desk where the decisions get made!).  So how is the science of the weather like and not like the science that we do at the LHC?

(In what follows, I offer my sincere apologies to meteorologists in case I misinterpreted what I learned on my tour!)

Both are fields that can generate significant amounts of data that need to be interpreted to obtain a scientific result.  As has been discussed many times on the blog, each LHC experiment records petabytes of data each year.  Meteorology research is performed by much smaller teams of observers, which makes it hard to estimate their total data volume, but the graduate student who led our tour told us that he is studying a mere three weather events, but he has more than a terabyte of data to contend with — small compared to what a student on the LHC might have to handle, but still significant.

But where the two fields differ is what limits the rate at which the data can be understood.  At the LHC, it’s all about the processing power needed to reconstruct the raw data by performing the algorithms that turn the voltages read out from millions of amplifiers into the energies and momenta of individual elementary particles.  We know what the algorithms for this are, we know how to code them; we just have to run them a lot.  In meteorology, the challenge is getting to the point where you can even make the data interpretable in a scientific sense.  Things like radar readings still need to be massaged by humans to become sensible.  It is a very labor-intensive process, akin to the work done by the “scanner girls” of the particle physics days of yore, who carefully studied film emulsions by eye to identify particle tracks.  I do wonder what the prospects are in meteorology for automating this process so that it can be handed off to humans instead.  (Clearly this has to apply more towards forefront research in the field about how tornadoes form and the like, rather than to the daily weather predictions that just tell you the likelihood of tornado-forming conditions.)

Weather forecasting data is generally public information, accessible by anyone.  The National Weather Service publishes it in a form that has already had some processing done on it so that it can be straightforwardly ingested by others.  Indeed, there is a significant private weather-forecasting industry that makes use of this, and sells products with value added to the NWS data.  (For instance, you could buy a forecast much more granular than that provided by the NWS, e.g. for the weather at your house in ten-minute intervals.)  Many of these companies rent space in buildings within a block of the National Weather Center.  The field of particle physics is still struggling with how to make our data publicly available (which puts us well behind many astronomy projects which make all of their data public within a few years of the original observations).  There are concerns about how to provide the data in a form that will allow people who are not experts to learn something from the data without making mistakes.  But there has been quite a lot of progress in this in recent years, especially as it has been recognized that each particle physics experiment creates a unique dataset that will probably never be replicated in the future.  We can expect an increasing number of public data releases in the next few years.  (On that note, let me point out the NSF-funded Data and Software Preservation for Open Science (DASPOS) project that I am associated with on its very outer edges, which is working on some aspects of the problem.)  However, I’d be surprised if anyone starts up a company that will sell new interpretations of LHC data!

Finally, here’s one thing that the weather and the LHC has in common — they’re both always on!  Or, at least we try to run the LHC for every minute possible when the accelerator is operational.  (Remember, we are currently down for upgrades and will start up again this coming spring.)  The LHC experiments have physicists on on duty 24 hours a day, monitoring data quality and ready to make repairs to the detectors should they be needed.  Weather forecasters are also on shift at the forecasting center and the severe-storm center around the clock.  They are busy looking at data being gathered by their own instruments, but also from other sources.  For instance, when there are reports of tornadoes near Oklahoma City, the local TV news stations often send helicopters out to go take a look.  The forecasters watch the TV news to get additional perspectives on the storm.

Now, if only the weather forecasters on shift could make repairs to the weather just like our shifters can fix the detector!

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Teaming up on top and Higgs

Monday, October 6th, 2014

While the LHC experiments are surely turning their attention towards the 2015 run of the collider, at an energy nearly double that of the previous run, we’re also busy trying to finalize and publish measurements using the data that we already have in the can.  Some measurements just take longer than others, and some it took us a while to get to.  And while I don’t like tooting my own horn too much here at the US LHC blog, I wanted to discuss a new result from CMS that I have been working on with a student, Dan Knowlton, here at the University of Nebraska-Lincoln, along with collaborators from a number of other institutions.  It’s been in the works for so long that I’m thrilled to get it out to the public!

(This is one of many CMS results that were shown for the first time last week at the TOP 2014 conference.  If you look through the conference presentations, you’ll find that the top quark, which has been around for about twenty years now, has continued to be a very interesting topic of study, with implications for searches for new physics and even for the fate of the universe.  One result that’s particularly interesting is a new average of CMS top-quark mass measurements, which is now the most accurate measurement of that quantity in the world.)

The LHC experiments have studied the Higgs boson through many different Higgs decay modes, and many different production mechanisms also.  Here is a plot of the expected cross sections for different Higgs production mechanisms as a function of Higgs mass; of course we know now that the Higgs has a mass of 125 GeV:

The most common production mechanism has a Higgs being produced with nothing else, but it can also be produced in association with other particles.  In our new result, we search for a Higgs production mechanism that is so much more rare that it doesn’t even appear on the above plot!  The mechanism is the production of a Higgs boson in association with a single top quark, and in the standard model, the cross section is expected to be 0.018 pb, about an order of magnitude below the cross section for Higgs production in association with a top-antitop pair.  Why even bother to look for such a thing, given how rare it is?

The answer lies in the reason for why this process is so rare.  There are actually two ways for this particular final state to be produced. Here are the Feynman diagrams for them:

   

In one case, the Higgs is radiated off the virtual W, while in the other it comes off the real final-state top quark.  Now, this is quantum mechanics: if you have two different ways to connect an initial and final state, you have to add the two amplitudes together before you square them to get a probability for the process.  It just so happens that these two amplitudes largely destructively interfere, and thus the production cross section is quite small.  There isn’t anything deep at work (e.g. no symmetries that suppress this process), it’s just how it comes out.

At least, that’s how it comes out in the standard model.  We assume certain values for the coupling factors of the Higgs to the top and W particles that appear in the diagrams above.  Other measurements of Higgs properties certainly suggest that the coupling factors do have the expected values, but there is room within the constraints for deviations.  It’s even possible that one of the two coupling values has the exact opposite sign from what we expect.  In that case, the destructive interference between the two amplitudes would become constructive, and the cross section would be almost a factor of 13 larger than expected!

The new result from CMS is a search for this anomalous production of the Higgs in association with a single top quark.  CMS already has a result for a search in which the Higgs decays to pair of photons; this new result describes a search in which the Higgs decays to bottom quarks.  That is a much more common Higgs decay mode, so there ought to be more events to see, but at the same time the backgrounds are much higher.  The production of a top-antitop pair along with an extra jet of hadrons that is mis-identified as arising from a bottom quark looks very much like the targeted Higgs production mechanism.  The top-antitop cross section is about 1000 times bigger than that of the anomalous production mechanism that we are looking for, and thus even a tiny bottom mis-identification rate leads to a huge number of background events.  A lot of the work in the data analysis goes into figuring out how to distinguish the (putative) signal events from the dominant background, and then verifying that the estimations of the background rates are correct.

The analysis is so challenging that we predicted that even by throwing everything we had at it, the best we could expect to do was to exclude the anomalous Higgs production process at a level of about five times the predicted rate for it.  When we looked at the data, we found that we could exclude it at about seven times the anomalous rate, roughly in line with what we expected.  In short, we do not see an anomalous rate for anomalous Higgs production!  But we are able to set a fairly tight limit, at around 1.8 pb.

What do I like about this measurement?  First, it’s a very different way to try to measure the properties of the Higgs boson.  The measurements we have are very impressive given the amount of data that we have so far, but they are not very constraining, and there is enough wiggle room for some strange stuff to be going on.  This is one of the few ways to probe the Higgs couplings through the interference of two processes, rather than just through the rate for one dominant process.  All of these Higgs properties measurements are going to be much more accurate in next year’s data run, when we expect to integrate more data and all of the production rates will be larger due to the increase in beam energy.  (For this anomalous production process, the cross section will increase by about a factor of four.)  In this particular case, we should be able to exclude anomalous Higgs couplings through this measurement…or, if nature surprises us, we will actually observe them!  There is a lot of fun ahead for Higgs physics (and top physics) at the LHC.

I’ve also really enjoyed working with my CMS colleagues on this project.  Any measurement coming out of the experiment is truly the work of thousands of people who have built and operated the detector, gotten the data recorded and processed, developed and refined the reconstruction algorithms, and defined the baselines for how we identify all kinds of particles that are produced in the proton collisions.  But the final stages of any measurement are carried out by smaller groups of people, and in this case we worked with colleagues from the Catholic University of Louvain in Belgium, the Karlsruhe Institute of Technology in Germany, the University of Malaya in Malaysia, and the University of Kansas (in Kansas).  We relied on the efforts of a strong group of graduate students with the assistance of harried senior physicists like myself, and the whole team did a great job of supporting each other and stepping up to solve problems as they arose.  These team efforts are one of the things that I’m proud of in particle physics, and that make our scientists so successful in the wider world.

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ICHEP at a distance

Friday, July 11th, 2014

I didn’t go to ICHEP this year.  In principle I could have, especially given that I have been resident at CERN for the past year, but we’re coming down to the end of our stay here and I didn’t want to squeeze in one more work trip during a week that turned out to be a pretty good opportunity for one last family vacation in Europe.  So this time I just kept track of it from my office, where I plowed through the huge volume of slides shown in the plenary sessions earlier this week.  It was a rather different experience for me from ICHEP 2012, which I attended in person in Melbourne and where we had the first look at the Higgs boson.  (I’d have to say it was also probably the pinnacle of my career as a blogger!)

Seth’s expectations turned out to be correct — there were no earth-shattering announcements at this year’s ICHEP, but still a lot to chew on.  The Standard Model of particle physics stands stronger than ever.  As Pauline wrote earlier today, the particle thought to be the Higgs boson two years ago still seems to be the Higgs boson, to the best of our abilities to characterize it.  The LHC experiments are starting to move beyond measurements of the “expected” properties — the dominant production and decay modes — into searches for unexpected, low-rate behavior.  While there are anomalous results here and there, there’s nothing that looks like more than a fluctuation.  Beyond the Higgs, all sectors of particle physics look much as predicted, and some fluctuations, such as the infamous forward-backward asymmetry of top-antitop production at the Tevatron, appear to have subsided.  Perhaps the only ambiguous result out there is that of the BICEP2 experiment which might have observed gravitational waves, or maybe not.  We’re all hoping that further data from that experiment and others will resolve the question by the end of the year.  (See the nice talk on the subject of particle physics and cosmology by Alan Guth, one of the parents of that field.)

This success of the Standard Model is both good and bad news.  It’s good that we do have a model that has stood up so well to every experimental test that we have thrown at it, in some cases to startling precision.  You want models to have predictive power.  But at the same time, we know that the model is almost surely incomplete.  Even if it can continue to work at higher energy scales than we have yet explored, at the very least we seem to be missing some particles (those that make up the dark matter we know exists from astrophysical measurements) and it also fails to explain some basic observations (the clear dominance of matter over antimatter in the universe).  We have high hopes for the next run of the LHC, which will start in Spring 2015, in which we will have higher beam energies and collision rates, and a greater chance of observing new particles (should they exist).

It was also nice to see the conference focus on the longer-term future of the field.  Since the last ICHEP, every region of the world has completed long-range strategic planning exercises, driven by recent discoveries (including that of the Higgs boson, but also of various neutrino properties) and anchored by realistic funding scenarios for the field.  There were several presentations about these plans during the conference, and a panel discussion featuring leaders of the field from around the world.  It appears that we are having a nice sorting out of which region wants to host which future facility, and when, in such a way that we can carry on our international efforts in a straightforward way.  Time will tell if we can bring all of these plans to fruition.

I’ll admit that I felt a little left out by not attending ICHEP this year.  But here’s the good news: ICHEP 2016 is in Chicago, one of the few places in the world that I can reach on a single plane flight from Lincoln.  I have marked my calendar!

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P5 and the fifth dimension that Einstein missed

Tuesday, May 27th, 2014

Among the rain
and lights
I saw the figure 5
in gold
on a red
firetruck
moving
tense
unheeded
to gong clangs
siren howls
and wheels rumbling
through the dark city.

William Carlos Williams, “The Great Figure”, 1921

Ever since the Particle Physics Project Prioritization Panel (P5) report was released on Thursday, May 22, I have been thinking very hard about the number five. Five is in the name of the panel, it is embedded in the science that the report describes, and in my opinion, the panel has figured out how to manipulate a fifth dimension. Please give me a chance to explain.

Having had a chance to read the report, let me say that I personally am very impressed by it and very supportive of the conclusions drawn and the recommendations made. The charge to P5 was to develop “an updated strategic plan for the U.S. that can be executed over a ten-year timescale, in the context of a twenty-year global vision for the field.” Perhaps the key phrase here is “can be executed”: this must be a plan that is workable under funding scenarios that are more limited than we might wish. It requires making some hard decisions about priorities, and these priorities must be set by the scientific questions that we are trying to address through the techniques of particle physics.

Using input from the Snowmass workshop studies that engaged a broad swath of the particle-physics community, P5 has done a nice job of distilling the intellectual breadth of our field into a small number of “science drivers”. How many? Well, five of course:

• Use the Higgs boson as a new tool for discovery
• Pursue the physics associated with neutrino mass
• Identify the new physics of dark matter
• Understand cosmic acceleration: dark energy and inflation
• Explore the unknown: new particles, interactions, and physical principles

I would claim that four of the drivers represent imperatives that are driven by recent and mostly unexpected discoveries — exactly how science should work. (The fifth and last listed is really the eternal question of particle physics.) While the discovery of the Higgs boson two years ago was dramatic and received a tremendous amount of publicity, it was not totally unexpected. The Higgs is part of the standard model, and all indirect evidence was pointing to its existence; now we can use it to look for things that actually are unexpected. The observation of the Higgs was not the end of an era, but the start of a new one. Meanwhile, neutrino masses, dark matter and dark energy are all outside our current theories, and they demand explanation that can only come through further experimentation. We now have the technical abilities to do these experiments. These science drivers are asking exciting, fundamental questions about how the universe came to be, what it is made of and how it all interacts, and they are questions that, finally, can be addressed in our time.

But, how to explore these questions in a realistic funding environment? Is it even possible? The answer from P5 is yes, if we are clever about how we do things. I will focus here on the largest projects that the P5 report addresses, the ones that cost at least $200M to construct; the report also discusses many medium-size and small efforts, and recommends hard choices on which we should continue to pursue and which, despite having merit, simply cannot fit into realistic funding scenarios. The three biggest projects are the LHC and its high-luminosity upgrade that should be completed about about ten years from now; a long-baseline neutrino experiment that would create neutrinos at Fermilab and observe them in South Dakota, and a high-energy electron-positron collider, the International Linear Collider (ILC) that could do precision studies of the Higgs boson but is at least ten years away from realization. They are all interesting projects that each address at least two of the science drivers, but is it possible for the U.S. to take a meaningful role in all three? The answer is yes…if you understand how to use the fifth dimension.

The high-luminosity LHC emerged as “the first high-priority large-category project” in the program recommended by P5, and it is to be executed regardless of budget scenario. (See below about the use of the word “first” here.)  As an LHC experimenter who write for the U.S. LHC blog, I am of course a bit biased, but I think this is a good choice. The LHC is an accelerator that we have in hand; there is nothing else that could be built in the next ten years that can do anything like it, and we must fully exploit its potential. It can address three of the science drivers — the Higgs, dark matter, and the unknown. U.S. physicists form the largest national contingent in each of the two big multi-purpose experiments, ATLAS and CMS, and the projects depend on U.S. participation and expertise for their success. While we can never make any guarantees of discovery, I personally think that the LHC gives us as good a chance as anything, and that it will be an exciting environment to work in over the coming years.

P5 handled the long-baseline neutrino experiment by presenting some interesting challenges to the U.S. and global particle physics communities. While there is already a plan to build this project, in the form of a proposed experiment called LBNE, it was considered to be inadequate for the importance of the science. The currently proposed LBNE detector in South Dakota would be too small to collect enough data on a timescale that would give interesting and conclusive results. Even the proponents of LBNE recognized these limitations.  So, P5 recommends that the entire project “should be reformulated under the auspices of a new international collaboration, as as an internationally coordinated and internationally funded program, with Fermilab as the host,” that will truly meet the scientific demands. It wouldn’t just be a single experiment, but a facility — the Long-Baseline Neutrino Facility (LBNF).

This is a remarkable strategic step. First, it makes the statement that if we are going to do the science, we must do it well. LBNF would be bigger then LBNE, and also much better in terms of its capabilities. It also fully integrates the U.S. program into the international community of particle physics — it would commit the U.S. to hosting a major facility that would draw world-wide collaboration and participation. The U.S. will hold up its end of the efforts to build particle-physics facilities that scientists from all over the world can take part in, just as CERN has successfully done with the LHC. To organize this new facility will take some time, such that peak costs of building LBNE will be pushed to a time later than the peak costs of upgrading the LHC.

One of the important ideas of special relativity is that the three dimensions of space and one dimension of time are placed on an equal footing. Two events in space-time that have given spatial and time separations in one frame of reference will have different spatial and time separations in a different frame. With LBNF, P5 has postulated a fifth dimension that must be considered: cost. If we were to try to upgrade the LHC and build LBNF at the same time, the cost would be more than we could afford, even with international participation. But by spacing out these two events in time, doing the HL-LHC first and LBNF second, the cost per year of these projects has become smaller; time and cost have been put on a more equal footing. Why didn’t Einstein think of that?

Thus, it is straightforward to set the international LBNF as “the highest-priority large project in its timeframe.” The title of the P5 report is “Building for Discovery”; LBNF will be the major project that the U.S. will build for discoveries in the areas of neutrino masses and exploration of the unknown.

As for the ILC, which Japan has expressed an interest in building, the scientific case for it is strong enough that “the U.S. should engage in modest and appropriate levels of ILC accelerator and detector design” no matter what the funding scenario. How much involvement there will be will depend on the funds available, and on whether the project actually goes forward. We will understand this better within the next few years. If the ILC is built, it will be a complement to the LHC and let us explore the properties of the Higgs and other particles in precise detail. With that, P5 has found a way for the U.S. to participate in all three major projects on the horizon, if we are careful about the timing of the projects and accept reasonable bounds on what we do with each.

These are the headlines from the report, but there is much more to it. The panel emphasizes the importance of maintaining a balance between the funds spent to build new facilities, to operate those facilities, and to do the actual research that leads to scientific discovery at the facilities. In recent years, there have been few building projects in the pipeline, and the fraction of the U.S. particle-physics budget devoted to new projects has languished at around 15%. P5 proposes that this be raised to the 20-25% level and maintained there, so that there will always be a push to create facilities that can address the scientific drivers — building for discovery. The research program is what funds graduate students and postdoctoral researchers, the future leaders of the field, and is where many exciting new physics ideas come from. Research has also been under financial pressure lately, and P5 proposes that it should not receive less than 40% of the budget. In addition, long-standing calls to invest in research and development that could lead to cheaper particle accelerators, more sensitive instrumentation, and revolutionary computational techniques are repeated.

This strategic vision is laid out in the context of three different funding scenarios. The most constrained scenario imagines flat budgets through 2018, and then annual increases of 2%, which is likely below the rate of inflation and thus would represent effectively shrinking budgets. The program described could be carried out, but it would be very challenging. LBNF could still be built, but it would be delayed. Various other projects would be cancelled, reduced or delayed. The research program would lose some of its capabilities. It would make it difficult for the U.S. to be a full international partner in particle physics, one that would be capable of hosting a large project and thus being a global leader in the field. Can we do better than that? Can we instead have a budget that grows at 3% per year, closer to the rate of inflation? The answer is ultimately up to our elected leaders. But I hope that we will be able to convince them, and you, that the scientific opportunities are exciting, and that the broad-based particle-physics community’s response to them is visionary while also being realistic.

Finally, I would like to offer some words on the use of logos. Since the last P5 report, in 2008, the U.S. particle physics program has relied on a logo that represented three “frontiers” of scientific exploration:

three_frontiers

It is a fine way to classify the kinds of experiments and projects that we pursue, but I have to say that the community has chafed a bit under this scheme. These frontiers represent different experimental approaches, but a single physics question can be addressed through multiple approaches. (Only the lack of time has kept me from writing a blog post titled “The tyranny of Venn diagrams.”) Indeed, in his summary presentation about the Energy Frontier for the Snowmass workshop, Chip Brock of Michigan State University suggested a logo that represented the interconnectedness of these approaches:

chip_rings

“Building for Discovery” brings us a new logo, one that represents the five science drivers as five interlocked crescents:

P5-swirl

I hope that this logo does an even better job of emphasizing the interconnectedness not just of experimental approaches to particle physics, but also of the five (!) scientific questions that will drive research in our field over the next ten to twenty years.

Of course, I’m also sufficiently old that this logo reminded me of something else entirely:

American_revolution_bicentennial

Maybe we can celebrate the P5 report as the start of an American revolution in particle physics? But I must admit that with P5, 5 science drivers and 5 dimensions, I still see the figure 5 in gold:

"I Saw the Figure 5 in Gold", Charles Demuth, 1928

“I Saw the Figure 5 in Gold”, Charles Demuth, 1928

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Building for Discovery

Thursday, May 22nd, 2014

After years in the making — from the earliest plans in 2011 for an extended Snowmass workshop that started in October 2012 and culminated in August 2013, to the appointment of a HEPAP subpanel in September, to today — we have now received the report of the Particle Physics Project Prioritization Panel, or P5. As has been discussed elsewhere, this is a major report outlining the strategic plan for United States participation in the global enterprise of particle physics for the next two decades.

As I writing this, Steve Ritz of UC Santa Cruz, the chair of the panel, is making his presentation on the report, which has the title “Building for Discovery: Strategic Plan for U.S. Particle Physics in the Global Context.” While at CERN, I am watching remotely (or trying to do, the system must be heavily loaded, and it sounds like there are technical difficulties in the meeting room). I am restraining myself from live-blogging the presentation, as I want to take the time to read the report carefully before discussing it. (The report will be available in a couple of hours, but the executive summary is ready now.) Anything this important takes some time for proper digestion! If you are reading this, you are already a fan of particle physics, so I invite you to read it also and see what you think. I hope to discuss the matter further in a post next week.

But in any case, a huge thank-you to the hard-working members of P5 who developed this report!

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Can 2130 physicists pounding on keyboards turn out Shakespeare plays?

Tuesday, April 22nd, 2014

The CMS Collaboration, of which I am a member, has submitted 335 papers to refereed journals since 2009, including 109 such papers in 2013. Each of these papers had about 2130 authors. That means that the author list alone runs 15 printed pages. In some cases, the author list takes up more space than the actual content of the paper!

One might wonder: How do 2130 people write a scientific paper for a journal? Through a confluence of circumstances, I’ve been directly involved in the preparation of several papers over the last few months, so I have been thinking a lot about how this gets done, and thought I might use this opportunity to shed some light on the publication process. What I will not discuss here is why a paper should have 2130 authors and not more (or fewer)—this is a very interesting topic, but for now we will work from the premise that there are 2130 authors who, by signing the paper, take scientific responsibility for the correctness of its contents. How can such a big group organize itself to submit a scientific paper at all, and how can it turn out 109 papers in a year?

Certainly, with this many authors and this many papers, some set of uniform procedures are needed, and some number of people must put in substantial effort to maintain and operate the procedures. Each collaboration does things a bit differently, but all have the same goal in mind: to submit papers that are first correct (in the scientific sense of “correct” as in “not wrong with a high level of confidence”), and that are also timely. Correct takes precedence over timely; it would be quite an embarrassment to produce a paper that was incorrect because the work was done quickly and not carefully. Fortunately, in my many years in particle physics, I can think of very few cases when a correction to a published paper had to be issued, and never have I seen a paper from an experiment I have worked be retracted. This suggests that the publication procedures are indeed meeting their goals.

But even though being correct trumps everything, having an efficient publication process is still important. It would also be a shame to be scooped by a competitor on an interesting result because your paper was stuck inside your collaboration’s review process. So there is an important balance to be struck between being careful and being efficient.

One thing that would not be efficient would be for every one of the 2130 authors to scrutinize every publishable result in detail. If we were to try to do this, everyone would soon become consumed by reviewing data analyses, rather than working on the other necessary tasks of the experiment, from running the detector to processing the data to designing upgrades of the experiment. And it’s hard to imagine that, say, once 1000 people have examined a result carefully, another thousand would uncover a problem. That being said, everyone needs to understand that even if they decline to take part in the review of a particular paper, they are still responsible for it, in accordance with generally accepted guidelines for scientific authorship.

Instead, the review of each measurement or set of measurements destined for publication in a single paper is delegated by the collaboration to a smaller group of people. Different collaborations have different ways of forming these review committees—some create a new committee for a particular paper that dissolves when that paper is published, while others have standing panels that review multiple analyses within a certain topic area. These committees usually include several people with expertise in that particular area of particle physics or data analysis techniques, but one or two who serve as interested outsiders who might look at the work in a different way and come up with new questions about it. The reviewers tend to be more senior physicists, but some collaborations have allowed graduate students to be reviewers too. (One good way to learn how to analyze data is to carefully study how other people are doing it!)

The scientists who are performing a particular measurement with the data are typically also responsible for producing a draft of the scientific paper that will be submitted to the journal. The review committee is then responsible for making sure that the paper accurately describes the work and will be understandable to physicists who are not experts on this particular topic. There can also be a fair amount of work at this stage to shape the message of the paper; measurements produce results in the form of numerical values of physical quantities, but scientific papers have to tell stories about the values and how they are measured, and expressing the meaning of a measurement in words can be a challenge.

Once the review committee members think that a paper is of sufficient quality to be submitted to a journal, it is circulated to the entire collaboration for comment. Many collaborations insert a “style review” step at this stage, in which a physicist who has a lot of experience in the matter checks that the paper conforms to the collaboration’s style guidelines. This ensures some level of uniformity in terminology across the all of the collaboration’s papers, and it is also a good chance to check that the figures and tables are working as intended.

The circulation of a paper draft to the collaboration is a formal process that has potential scaling issues, given how many people might submit comments and suggestions. On relatively small collaborations such as those at the Tevatron (my Tevatron-era colleagues will find the use of the word “small” here ironic!), it was easy enough to take the comments by email, but the LHC collaborations have a more structured system for collecting and archiving comments. Collaborators are usually given about two weeks to read the draft paper and make comments. How many people send feedback can vary greatly with each paper; hotter topics might attract more attention. Some conscientious collaborators do in fact read every paper draft (as far as I can tell). To encourage participation, some collaborations do make explicit requests to a randomly-chosen set of institutes to scrutinize the paper, while some institutes have their own traditions of paper review. Comments on all aspects of the paper are typically welcome, from questions about the physics or the veracity of the analysis techniques, to suggestions on the organization of the paper and descriptions of data analysis, to matters like the placement of commas.

In any case, given the number of people who read the paper, the length of the comments can often exceed the length of the paper itself. The scientists who wrote the paper draft then have to address all of the comments. Some comments lead to changes in the paper to explain things better, or to additional cross-checks of the analysis to address a point that was raised. Many textual suggestions are implemented, while others are turned down with an explanation of why they are not necessary or harmful to the paper. The analysis review committee then verifies that all significant comments have been properly considered, and checks that the resulting revised paper draft is in good shape for submission.

Different collaborations have different final steps before the paper is actually submitted to a journal. Some have certain leaders of the collaboration, such as the spokespersons and/or physics coordinators, read the draft and make a final set of recommendations that are to be implemented before submission. Others have “publication committees” that organize public final readings of a paper that can lead to changes. At this stage the authors of the original draft very much hope that things go smoothly and that paper submission will be imminent.

And this whole process comes before the scientific tradition of independent, blind peer review! Journals have their own procedures for appointing referees who read the paper and give the journal editors advice on whether a paper should be published, and what changes or checks they might require before recommending publication. The interaction with the journal and its referees can also take quite some time, but almost always it ends with a positive result. The paper has gone through so many levels of scrutiny already that the output is really a high-quality scientific product that describes reproducible results, and that will ultimately stand the test of time.

A paper that describes a measurement in particle physics is the last step of a long journey, from the conception of the experiment, the design and subsequent construction of the apparatus, its operation over the course of years to collect the data sample, the processing of the data, and the subsequent analysis that leads to numerical values of physical quantities and their associated uncertainties. The actual writing of the papers, and process of validating them and bringing 2130 physicists to agree that the paper has told the right story about the whole journey is an important step in the creation of scientific knowledge.

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A quick ski through history

Sunday, March 23rd, 2014

This past week about 175 lucky particle physicists gathered in La Thuile, a mountain town in the Italian Alps, for one of the annual Rencontres de Moriond conferences. This is one of the highlights of the particle-physics calendar, perhaps the most important gathering of particle physicists between the summer-time Lepton-Photon and ICHEP conferences for the presentation of new results. The major experimental collaborations of the world have been wrapping up a flurry of activity in preparation for the high-profile meetings taking place over the next few weeks. The atmosphere on the LHC experiments has been a bit less intense this year than last year, as the flashiest results from the 2010-12 data sample have already been released, but there was still a push to complete as many measurements as possible for presentation at this conference in particular.

I’ve only been to a Moriond conference once, but it was quite an experience. The conference is held at a ski resort to encourage cameraderie and scientific exchanges outside the conference room, and that leads to an action-packed week. Each morning of the week opens with about three hours of scientific presentations. The mid-morning finish allows for an almost-full day of skiing for those who chose to go (and as you might imagine, many do). This is a great opportunity to spend leisure time with colleagues, meet new people and discuss what had been learned that morning. After the lifts have closed, everyone returns to the hotel for another three hours of presentations. This is followed by a group dinner to continue the conversation. Everyone who has the chance to go realizes that they are very lucky to be there, but at the same time it is a rather exhausting experience! Or, as Henry Frisch, my undergraduate mentor and a regular Moriond attendee, once told me, “There are three things going on at Moriond — the physics, the skiing, and the food — and you can only do two out of the three.” (I skipped lunch on most days.)

As friends were getting ready to head south from CERN through the Mont Blanc tunnel to Italy (and as I was getting ready for my first visit to the United States in more than seven months, for the annual external review of the US LHC operations programs), I realized that it has in fact been ten years since the Moriond conference I went to. Thankfully, the conference organizers have maintained the conference website from 2004, allowing me to relive my presentation from that time. It is a relief to observe that our understanding of particle physics has advanced quite a bit since then! At that Moriond, the Tevatron was just starting to kick into gear for its “Run 2,” and during the previous year we had re-established the signal for the top quark that had first been observed in the mid-1990s. We were just starting to explore the properties of the top quark, but we were hampered by the size of the data sample at that point. It is amusing to look back and see that we were trying to measure the mass of the top quark with a mere six dilepton decay events! Over the coming years, the Tevatron would produce hundreds more such events, and the CDF and D0 experiments would complete the first thorough explorations of the top quark, demonstrating that its properties are totally in line with the predictions of the standard model. And since then, the LHC has done the Tevatron one better, thanks to both an increase in the top-quark production rate at the higher LHC energy and the larger LHC collision rate. The CMS top-quark sample now boasts about 70,000 dilepton candidate events, and the CMS measurement of the top-quark mass is now the best in the world.

Top-quark physics is one of the topics I’m most familiar with, so it is easy for me to mark progress there, but of course it has been a remarkable decade of advances for particle physics, with the discovery of the Higgs boson, a more thorough understanding of neutrino masses and mixing, and constraints on the properties of dark matter. Next year, the LHC will resume operations in its own “Run 2″, with an even higher collision energy and higher collision rates than we had in 2012. It is a change almost as great as that we experienced in moving from the Tevatron to the first run of the LHC. I cannot wait to see how the LHC will be advancing our knowledge of particle physics, possibly through the discovery of new particles that will help explain the puzzles presented by the Higgs boson. You can be sure that there will be a lot of excited chatter on the chair lifts around the dinner table at the 2016 Moriond conferences!

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Dear Google: Hire us!

Monday, March 3rd, 2014

In case you haven’t figured it out already from reading the US LHC blog or any of the others at Quantum Diaries, people who do research in particle physics feel passionate about their work. There is so much to be passionate about! There are challenging intellectual issues, tricky technical problems, and cutting-edge instrumentation to work with — all in pursuit of understanding the nature of the universe at its most fundamental level. Your work can lead to global attention and support Nobel Prizes. It’s a lot of effort put in over long days and nights, but there is also a lot of satisfaction to be gained from our accomplishments.

That being said, a fundamental truth about our field is that not everyone doing particle-physics research will be doing that for their entire career. There are fewer permanent jobs in the field than there are people who are qualified to hold them. It is certainly easy to do the math about university jobs in particular — each professor may supervise a large number of PhD students in his or her career, but only one could possibly inherit that job position in the end. Most of our researchers will end up working in other fields, quite likely in the for-profit sector, and as a field we do need to make sure that they are well-prepared for jobs in that part of the world.

I’ve always believed that we do a good job of this, but my belief was reinforced by a recent column by Tom Friedman in The New York Times. It was based around an interview with the Google staff member who oversees hiring for the company. The essay describes the attributes that Google looks for in new employees, and I couldn’t help but to think that people who work in the large experimental particle physics projects such as those at the LHC have all of those attributes. Google is not just looking for technical skills — it goes without saying that they are, and that particle physicists have those skills and great experience with digesting large amounts of computerized data. Google is also looking for social and personality traits that are also important for success in particle physics.

(Side note: I don’t support all of what Friedman writes in his essay; he is somewhat dismissive of the utility of a college education, and as a university professor I think that we are doing better than he suggests. But I will focus on some of his other points here. I also recognize that it is perhaps too easy for me to write about careers outside the field when I personally hold a permanent job in particle physics, but believe me that it just as easily could have wound up differently for me.)

For example, just reading from the Friedman column, one thing Google looks for is what is referred to as “emergent leadership”. This is not leadership in the form of holding a position with a particular title, but seeing when a group needs you to step forward to lead on something when the time is right, but also to step back and let someone else lead when needed. While the big particle-physics collaborations appear to be massive organizations, much of the day to day work, such as the development of a physics measurement, is done in smaller groups that function very organically. When they function well, people do step up to take on the most critical tasks, especially when they see that they are particularly positioned to do them. Everyone figures out how to interact in such a way that the job gets done. Another facet of this is ownership: everyone who is working together on a project feels personally responsible for it and will do what is right for the group, if not the entire experiment — even if it means putting aside your own ideas and efforts when someone else clearly has the better thing.

And related to that in turn is what is referred to in the column as “intellectual humility.” We are all very aggressive in making our arguments based on the facts that we have in hand. We look at the data and we draw conclusions, and we develop and promote research techniques that appear to be effective. But when presented with new information that demonstrates that the previous arguments are invalid, we happily drop what we had been pursuing and move on to the next thing. That’s how all of science works, really; all of your theories are only as good as the evidence that supports them, and are worthless in the face of contradictory evidence. Google wants people who take this kind of approach to their work.

I don’t think you have to be Google to be looking for the same qualities in your co-workers. If you are an employer who wants to have staff members who are smart, technically skilled, passionate about what they do, able to incorporate disparate pieces of information and generate new ideas, ready to take charge when they need to, feel responsible for the entire enterprise, and able to say they are wrong when they are wrong — you should be hiring particle physicists.

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No cream, no sugar

Monday, January 6th, 2014

My first visit to CERN was in 1997, when I was wrapping up my thesis work. I had applied for, and then was offered, a CERN fellowship, and I was weighing whether to accept it. So I took a trip to Geneva to get a look at the place and make a decision. I stayed on the outskirts of Sergy with my friend David Saltzberg (yes, that David Saltzberg) who was himself a CERN fellow, and he and other colleagues helped set up appointments for me with various CERN physicists.

Several times each day, I would use my map to find the building with the right number on it, and arrive for my next appointment. Invariably, I would show up and be greeted with, “Oh good, you’re here. Let’s go get a coffee!”

I don’t drink coffee. At this point, I can’t remember why I never got started; I guess I just wasn’t so interested, and may also have had concerns about addictive stimulants. So I spent that week watching other people drink coffee. I learned that CERN depends on large volumes of coffee for its operation. It plays the same role as liquid helium does for the LHC, allowing the physicists to operate at high energies and accelerate the science. (I don’t drink liquid helium either, but that’s a story for another time.)

Coffee is everywhere. In Restaurant 1, there are three fancy coffee machines that can make a variety of brews. (Which ones? You’re asking the wrong person.) At breakfast time, the line for the machines stretches across the width of the cafeteria, blocking the cooler that has the orange juice, much to my consternation. Outside the serving area, there are three more machines where one can buy a coffee with a jeton (token) that can be purchased at a small vending machine. (I don’t know how much they cost.) After lunch, the lines for these machines clogs the walkway to the place where you deposit your used trays.

Coffee goes beyond the restuarants. Many buildings (including out-of-the-way Building 8, where my office is) have small coffee areas that are staffed by baristas (I suppose) at peak times when people who aren’t me want coffee. Building 40, the large headquarters for the CMS and ATLAS experiments, has a big coffee kiosk, where one can also get sandwiches and small pizzas, good when you want to avoid crazy Restaurant 1 lunchtimes and coffee runs. People line up for coffee here during meeting breaks, which usually puts us even further behind schedule.

Being a non-drinker of coffee can lead to some social discomfort. When two CERN people want to discuss something, they often do it over coffee. When someone invites me for a chat over coffee, I gamely say yes. But when we meet up I have to explain that I don’t actually drink coffee, and then sit patiently while they go to get a cup. I do worry that the other person feels uncomfortable about me watching them drink coffee. I could get a bottle of water for myself — even carbonated water, when I feel like living on the edge — but I rarely do. My wife (who does drink coffee, but tolerates me) gave me a few jetons to carry around with me, so I can at least make the friendly gesture of buying the other person’s coffee, but usually my offer is declined, perhaps because the person knows that he or she can’t really repay the favor.

So, if you see a person in conversation in the Restaurant 1 coffee area, not drinking anything but nervously twiddling his thumbs instead, come over and say hello. I can give you a jeton if you need one.

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Will the car start?

Saturday, November 9th, 2013

While my family and I are spending a year at CERN, our Subaru Outback is sitting in the garage in Lincoln, under a plastic cover and hooked up to a trickle charger. We think that we hooked it all up right before going, but it’s hard to know for sure. Will the car start again when we get home? We don’t know.

CMS is in a similar situation. The detector was operating just fine when the LHC run ended at the start of 2013, but now we aren’t using it like we did for the previous three years. It’s basically under a tarp in the garage. When proton collisions resume in 2015, the detector will have to be in perfect working order again. So will this car start after not being driven for two years?

Fortunately, we can actually take this car out for a drive. This past week, CMS performed an exercise known as the Global Run in November, or GRIN. (I know, the acronym. You are wondering, if it didn’t go well, would we call it FROWN instead? That too has an N for November.) The main goal of GRIN was to make sure that all of the components of CMS could still operate in concert. In fact, many pieces of CMS have been run during the past nine months, but independently of one another. Actually making everything run together is a huge integration task; it doesn’t just happen automatically. All of the readouts have to be properly synchronized so that the data from the entire detector makes sense. In addition, GRIN was a chance to test out some operational changes that the experiment wants to make for the 2015 run. It may sound like it is a while away, but anything new should really be tested out as soon as possible.

On Friday afternoon, I ran into some of the leaders of the detector run coordination team, and they told me that GRIN had gone very well. At the start, not every CMS subsystem was ready to join in, but by the end of the week, the entire detector was running together, for the first time since the end of collisions. Various problems were overcome along the way — including several detector experts getting trapped in a stuck elevator. But they believe that CMS is in a good position to be ready to go in 2015.

As a member of CMS, that was really encouraging news. Now, if only the run coordinators could tell me where I left the Subaru keys!

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