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Seth Zenz | USLHC | USA

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Hangout with CERN, anyone?

Tuesday, February 12th, 2013

I’m helping organize the ongoing Hangout with CERN series of events, and this Thursday I get to host. To make the event a success, I need your help! Interested? Read on…

Hangout with CERN happens each week at 17:00 CET, 11 AM EST, or whatever you want to call that time. It’s an informal Google+ hangout in which physicists, engineers, IT experts, and other folks from CERN connect to tell you about what we do here. In our latest format, we devote two weeks to each topic. The first week introduces the topic and lets you hear experts describe their work, along with a quiz and a few questions from the public. (We monitor comments on Twitter and YouTube the whole time.) The second week – which is the part I work on – is even more informal: we try to have a few guest members of the public, get to more questions, and so on.

Here’s last week’s video, entitled “LHC and the Grid – The world is our calculator,” which discusses the worldwide computing system we use to analyze all the data from the LHC:

Next week’s event on Google+ is here. We’ll be discussing the same topic, and we want to hear your questions about it. Do you have a question? Might you want to participate live in the hangout and ask your question directly? Let me know in the comments!

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A Change of Pace

Monday, February 4th, 2013

Some physicists and engineers from Purdue and DESY, and me, at the beamline we used to test new pixel designs

Every so often, a physicist needs a vacation from doing data analysis for the Higgs boson search. A working vacation, something that gets you a little closer to the actual detector you work on. So last week, I was at the DESY laboratory in Hamburg, Germany, helping a group of physicists and engineers study possible changes to the design of individual pixels in the CMS Pixel Detector. (I’ve written before about how a pixel detector works.) We were at DESY because they had an electron beam we could use, and we wanted to study how the new designs performed with actual particles passing through them. Of course, the new designs can’t be produced in large scale for a few years — but we do plan to run CMS for many, many years to come, and eventually we will need to upgrade and replace its pixel detector.

What do you actually do at a testbeam? You sit there as close to 24 hours a day as you can — in shifts, of course. You take data. You change which new design is in the beam, or you change the angle, or you change the conditions under which it’s running. Then you take more data. And you repeat for the entire week.

So do any of the new designs work better? We don’t know yet. It’s my job to install the software to analyze the data we took, and to help study the results, and I haven’t finished yet. And yes, even “working on the detector” involves analyzing data — so maybe it wasn’t so much of a vacation after all!

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What Went on My Research Page

Sunday, December 30th, 2012

Remember when I was wondering, “What Goes on My Research Page?” Well, I finally decided what to put on it and got it posted:

Seth Zenz – Princeton University Department of Physics

Let me know what you think!

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Particles of the Day

Tuesday, November 20th, 2012
My copy of the 2012 PDG booklet

My copy of the 2012 PDG booklet

Last week, I got my copy of the 2012 Particle Data Group Review of Particle Physics booklet — which, along with its heavy, 1000-page full-length counterpart, we simply call “the PDG.” My very first copy, during my first months at CERN in the summer of 2003, is a vivid memory for me. Here was a book with almost everything you want to know, about every particle ever discovered! It was like the book of dinosaurs I had when I was a kid, and I read it in exactly the same way: flipping to a random page and reading a few facts about, say, the charged kaon.

My new copy of the PDG has inspired me to adapt this fun for non-experts. So each day, I’ll feature a new particle on Twitter; I’m @sethzenz, and the hashtag will be #ParticleOfTheDay. Since starting last week, I’ve featured the B0s meson, the pion, the kaon, the electron, and the Higgs.

How long can I keep this up? That is, how many particles are there? Well, that depends on how you count. The Standard Model has 3 charged leptons, 3 neutrinos, 6 quarks, the photon, and the W, Z, and Higgs bosons. But then there’s all the antiparticles. Dark matter candidates. The graviton. I could even argue for taking 8 days covering all the gluon colors! (Don’t worry, I won’t.) But most of all, there’s all the composite particles — those that are made from a combination of quarks. There are a very large number of those, and there will always be more to find too, because you can always add more energy to the same combination of quarks.

The point isn’t to be systematic. I might go back and be more specific. I might repeat. What I really want to do is find a particle each day that’s in the news or I can say something interesting about.

Flipping at random through a book of particles turns out not to be the best way to learn particle physics; ultimately, I needed to learn the principles by which those particles are organized. But it is an interesting way to tell the story of particle physics: its history and how it’s done today. After all, the particles do come out of accelerators in a random jumble; it’s our job to organize them.

Have an idea for the Particle of the Day, and what to say about it? Let me know!

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Zombies at CERN!

Tuesday, October 30th, 2012

Some friends of colleagues of mine made a zombie movie here at CERN. It looks pretty neat, and will be available for free soon online, so here’s the trailer:

Now, then. There are some things I should probably clarify:

1. This film has not been authorized or endorsed by CERN.

2. The Higgs boson obviously cannot turn people into zombies. Never mind the biology, it’s enough to know that the Higgs decays instantaneously into more ordinary particles, and never leaves the detector. If any LHC collisions could make zombies, the earth would already be filled with zombies created when ultra high-energy cosmic rays hit the atmosphere.

3. Zombies do not really exist, and they will not eat your brains. Really. I promise.

4. The LHC cannot be operated when anyone is in one its tunnels or experimental caverns. The safety systems that prevent this are quite a bit more sophisticated than the trailer seems to imply.

5. The tunnels in the film aren’t the LHC tunnels — which are continuously being used for science rather than cinematography — but they do appear to be real steam tunnels from some of the buildings here at CERN. Rather interesting and spooky, but maybe not as polished and high-tech as you were expecting.

In conclusion: it’s always fun to see zombies in cool places, especially in your own back yard. I look forward to the movie coming out. For more information, you can look at decayfilm.com, facebook.com/decayfilm, or twitter.com/decayfilm

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Are the Higgs Rumors True?

Monday, October 22nd, 2012

What Higgs rumors, you may ask? Well, there aren’t any that I know of, yet. But there might be soon…

There might be rumors soon because we are about to do another round of updates, for the 2012 Hadron Collider Physics Symposium (HCP). There aren’t any yet because our results (at least on CMS) are still “blinded,” which means that we haven’t actually looked at the “places” in the data where we see signs of our new boson. What we’re doing instead is looking at simulated data to see how much our results might improve when we add in the collisions we’ve recorded since ICHEP. We’re also putting in a few new analysis techniques, and checking them in the same way. And of course we are looking at data in other “places,” and we’re comparing it to simulations to make sure they’re doing a good job.

There will be several weeks between the moment we “unblind” — that is, look for the first time at what our signal looks like with the new data — and when results are shown at HCP. This is just as things were at ICHEP, and during those few weeks there were a lot of rumors around. It’s not possible to confirm or deny rumors when you know the status of ongoing work but haven’t yet agreed with your colleagues that it’s finished and ready to talk about publicly. So this time, I’m going to get in some general comments about rumors before I know anything at all about actual results. These comments will apply just as well to future updates.

What are we doing during the gap between unblinding and the conference? We’re checking our results, and putting them in a final presentable form. This is already compressed into a very short, hectic time, as I’ve written about before.

Are the rumors true? They are definitely not our official results, but they might turn out to be close. Or they might not. Specifically, the possibilities are:

  • A rumor is pretty much right. It’s no secret that particle physicists are bad at keeping secrets, and we really don’t want to be good at it. If one in 3,000 physicists decides to tell the Internet what our first-pass internal results look like, we can’t really stop them. Of course they’re breaking the rules, and we wish they wouldn’t, because it’s a collaborative effort and we’d prefer to agree together that we’re finished before announcing our results — because we want to make sure we did everything as well as we can. But still, our first-pass results are usually pretty close to final.
  • A rumor isn’t quite right. This could happen if we do find small mistakes or make refinements in the last few weeks of analyzing the data. This changes the answer by a bit, so the rumor is out of date. You could also make up a “not-quite-right” rumor just by making an educated guess based on our last results and how much new data we’ve taken!
  • A rumor is just plain wrong. Nobody says rumors have to be based on anything. Or they could be based on a misunderstanding of far-from-complete internal results.

We physicists working on this stuff don’t find it easy to wait for the answers either, and as Jon Butterworth has pointed out, rumors of other experiments’ results are actually dangerous for our work! For everybody else who’s tempted to indulge in rumors, just remember: you might be getting part of the picture early, or you might not. The only way to be sure is to wait for the next real update.

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For the Higgs, No Theological Assistance Required

Tuesday, October 16th, 2012

I like talking about science. I like talking about religion. I even like talking about the relationship and boundaries between the two. These are all fascinating subjects, with many questions that are very much up for debate, so I am very pleased to see that CERN is participating in an event in which scientists, philosophers, and theologians talk together about the Big Bang and other questions.

But this quote, at least as reported by the BBC, simply doesn’t make any sense:

Co-organiser Canon Dr Gary Wilton, the Archbishop of Canterbury’s representative in Brussels, said that the Higgs particle “raised lots of questions [about the origins of the Universe] that scientists alone can’t answer”.

“They need to explore them with theologians and philosophers,” he added.

The Higgs particle does no such thing; it is one aspect of a model that describes the matter we see around us. If there is a God, CERN’s recent observations tell us that God created a universe in which the symmetry between the photon and the weak bosons is probably broken via the Higgs Mechanism. If there is not, they tell us that a universe exists anyway in which the symmetry between the photon and the weak bosons is probably broken via the Higgs Mechanism. It doesn’t raise any special questions about the origins of the universe, any more than the existence of the electron does.

There are many interesting philosophical questions to ask about the relationships between models of scientific observations on the one hand, and notions of absolute Truth on the other. You can also talk about what happened before the times we can make scientific observations about, whether there are “other universes” with different particles and symmetries, and so on. Theologians and philosophers have much to say about these issues.

But in regard to searches for the Higgs boson in particular, the people we need to explore questions with are mostly theoretical physicists and statisticians.

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VERTEX 2012

Friday, October 5th, 2012

Seth talking at the VERTEX2012 conferenceNever mind my complaints about travel, VERTEX 2012 was a very nice conference. There were a lot of interesting people there, mostly much more expert than me on the subject of vertex detectors. (I’ve written before about how tracking works and how a pixel detector works. In general, a vertex detector is a high-precision tracker designed to measure exactly where tracks come from; a pixel detector is one type of vertex detector.) My talk was about the current operations of the CMS pixel detector; you can see me giving the talk at right, and the (very technical) slides are here. Other talks were about future development in on-detector chip and sensor technology; this work is likely to affect the next detectors we build, and the upgrades of our current detectors as well.

VERTEX 2012 Conference attendees at Sunrise Peak, JejuThe location of the conference — Jeju, Korea — was also very nice, and we got an afternoon off to see some of the island. The whole island is volcanic. The central mountain dominates the landscape, and there are lots of grass-covered craters. Sunrise peak, at left, erupted as recently as 5,000 years ago, but it seemed pretty quiet when we were there.

Overall, the conference was a great opportunity to meet people from all over the world and learn from them. And that’s really why we have to travel so far for these things, because good people work everywhere.

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I don’t really like flying, but…

Saturday, September 15th, 2012

An airplane wing over Jeju, Korea You wouldn’t think so, given how much time I spend on airplanes, but I don’t like flying at all. I like seeing new places, but I think I’d be just as happy exploring every stop on the New York Subway as flying to new countries and exotic locales. But then it turned out that the science I wanted to do, and also the love of my life, happened to be on another continent. (Luckily, the same one!) Being a physicist is a travel-intensive business. So here I am, on my first trip to Asia, about to be run over by a typhoon.

Look forward to an entry from me sometime this week on the VERTEX 2012 conference. The conference doesn’t have a hash tag, but I might tweet about it anyway, if you’re terribly curious how it’s going.

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What Goes on My Research Page?

Thursday, August 30th, 2012

It is time, it seems, for me to put up my first real departmental research page. This is a place to put up a picture, describe my research interests, and maybe link to some papers. It shouldn’t really be too difficult to write something up, as I have seem to have acquired a disturbing amount of practice in rambling about my research and putting up web pages about myself. But looking at others’ research pages has left me with a nagging question: what, really, are my research interests?

“CMS and ATLAS are two of a kind: they’re both looking for whatever new particles they can find.” — Kate McAlpine, Large Hadron Rap

In most fields, I would talk about a very specific set of problems I was interested in, and say what sort of experiments I was doing to figure things out. But the big detectors at the LHC try to look for everything, and I work on them because I’m interested in finding anything new that’s there. Am I especially interested in electroweak symmetry breaking because I work on the Higgs boson? Am I a precision tracking enthusiast because I’ve worked on pixel detectors? Well, yes, to some degree both those things are true — but the fundamental motivation for my research is to contribute to the overall program of understanding what the universe is made of, by whatever means my skills and the available opportunities allow.

Still, I suppose I had better be a bit more specific. Anyone have any suggestions?

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